What would be a suitable aircraft for a short haul freight forwarding business?

You would have to provide more answers to the comment I made above.

But for a relatively small payload (<4000lbs), I'd say you can't go wrong with a Cessna C208 Caravan.  You can buy a good used C208B Super CargoMaster for just shy of $1 million.

Another recommendation for that route would be the DeHavilland DHC-6 Twin Otter.  Payload is increased by 1000 lbs or so over the Caravan and you have the additional safety of two engines for over water operations.  The downside is that these aircraft are fairly prized and will set you back about $ 3-4 million.

Another heavy lifter with an excellent reputation behind it, even after 80 years of service, is the venerable Douglas DC-3/C-47.  You call, we haul 6,000lbs to just about anywhere within fuel range.

All of these aircraft are extremely rugged and have a good reputation after decades of hard use in bush flying.  They are capable of operating on short, rough airstrips - a good benefit in case you decide to expand to more remote destinations within Cuba and can carry tremendous loads.  They're also turbine powered using PT6 engines (except for the DC-3) so fuel is readily available anywhere in the world as is maintenance and spare parts.


How to find coordinates of the geometric center of a NACA 4-digit airfoil?

I guess you wish to create a halo.

You can use Airfoil Tools' NACA 4 digit generator ( http://airfoiltools.com/airfoil/naca4digit ) to generate your NACA shape. It also features a plotter were you can set chord and halo thickness.
Positive values for internal halo and negative for external.
Internal halos are interesting to build wing ribbons.

Airfoil Tools generated NACA 6415

NACA 6415 600mm chord with 15mm halo (JPG)

Airfoil Tool's NACA 4 Digit generator


Is a horizontal stabilizer necessary on an aircraft with a tandem wing?

Is horizontal stabilizer necessary for tandem wing aircraft? not if the main wings are capable of carrying out the functions of the tailplane.

The main reasons for horizontal stabilizer are twofold:

To provide stability for the aircraft, as the wing alone configuration is unstable.
To provide pitching moment as the long moment arm enables enough moment to be produced by small changes in the lift (via the elevators).

It provides other benefits too (like damping), but these are the main ones.

For aircraft having tandem wings (i.e. having two wings one behind the another), horizontal stabilizer may or may not be present depending on various factors.

If the two wings are able to provide stability and provide pitch moment by differential control of the control surfaces (elevators) on them, the tandem wing has no horizontal stabilizer, like the Scaled Composites Proteus.

"Scaled Composites Proteus in flight 1". Licensed under Public Domain via Commons.

In some cases, the above objectives may not be met with the wings alone and a horizontal tail may be required, like the Scaled Composites Advanced Technology Tactical Transport. Interestingly, the aircraft was flown in two configurations. The initial configuration had a cruciform tail.

Image Courtesy of Scaled Composites, LLC

According to DARPA report AD-A227- 498,

  Analysis of the flight test results of the "Cruciform Tail" configuration disclosed a significant deficiency in the directional stability and engine-out minimum control speed of the airplane as well as some perceived loading difficulties due to low clearance of the aft cargo door.

As a result, the configuration was changed into a twin boom 'bronco' tail and flown.

Image Courtesy of Scaled Composites, LLC

There are some advantages with the tandem wing configuration, like:

For same weight, the tandem wings are more compact (i.e. have less wingspan) as both the wings produce lift (This was one of the reasons given by Burt Rutan). They have less frontal area and less parasite drag.
In case of tandem wings, both the wings produce lift, on either side of the center of gravity and produce moments about the c.g. in opposite directions. So, for stability, the c.g. is shifted forwards (for e.g. by having the power-plant forward). As the Angle of attack (aoa) increases, the lift force shift towards the rear and as the center of pressure shifts to the rear of c.g., the tail has to produce higher downward force to produce the required counteracting moment. As higher aoa is used mostly in landings, where more lift is required at lower speeds, this is not ideal. However, in case of tandem wings, at higher aoa, lift force of both the wings move to the rear, resulting in the rear wing having longer moment arm, and by extension, larger moment. So to compensate, the lift produced by the front wing has to be larger, which produces more lift, not less. For this reason, the front wing is set at a higher incidence (so as to produce higher lift) compared to the rear one.

Source: nurflugel.com

In general, the c.g. of a tandem wing aircraft is towards the main forward wing with the rear wing at a smaller incidence compared to the forward one. This means that the forward wing will have higher wing loading and stall first. However, as the rear wing is still producing lift, the nose drops and the front wing starts to produce lift again, giving the pilot some time to react and control the aircraft, unlike the conventional configuration.

As the wingspan is less, the induced drag is more though.


What is the difference between a "compass swing" and "check swing" procedure?

Based upon the terminology I have heard over the years, a compass swing is the alignment of the compass, normally using a compass rose painted on a surface. The compass is adjusted and a deviation card is created for cardinal points on the compass.

A check swing, as I have heard it referred to, is the checking of the compass, and done with the aircraft running, and electrical loads on, similar to a compass swing, but without the adjustment.  The deviation card is verified, but there is no intent of adjusting anything.  This was typically done before we ferried aircraft over the ocean, where there would be extended dead-reckoning (before GPS and LORAN), and where flights were close to the polar regions, and compass operation needed to be verified prior to the flight.

Not that a compass is worth much near the poles (grin).

My guess is that check swing is merely a slang term, whereas compass swing is well understood and extensively documented.


What problems would the early F-16 have if they were to fight during night?

When the LWF program began, its founders envisioned an aircraft purebred to engage the Soviet threat with machines which more closely matched the majority of Soviet fighters at that time ie lightweight, very maneuverable day fighters ie equipped with minimal avionics, a cannon(s) and short range IR guided missiles.  Pierre Sprey had envisioned an even smaller fighter when he didn’t even have a fire control radar in it, but it was not developed past his proposal.

The prototype and development F-16s were a far cry from a modern Block 60+ F-16 is today in terms of avionics and capabilities, but the first service F-16, the Block 15 F-16A/B, had good day and night air-to-air capabilities with the APG-66 radars.  They were however limited to good weather air-to-ground operations as they were limited in their precision munitions delivery capability.

Upgrades over the next three decades of service led to the current incarnations of the Viper equipped with helmet mounted cueing systems, advanced fire control AESA radar sets, IR night and precision weapons targeting systems, BVR TARH capable air to air missiles, advanced glass cockpit displays, etc.  It must also be noted that, while these system offer addition capabilities, the added weight and complexity diminishes aircraft performance in traditional fighter metrics as well.  Nevertheless the F-16 still remains a fine fighter regardless.

The capability vs cost vs performance debate is always controversial and does not show any signs of ending soon, though the military seems to prefer the most advanced and capable hardware it can buy at the expense of operating costs and reliability.  This has been made painfully clear with the F-35 program.


Why is there a pitching moment at aerodynamic center?

The definition of the aerodynamic center is the following:
"the aerodynamic center is the point along the wing chord where the coefficient of aerodynamic moment is constant with respect to the AOA." It doesn't mean that it is equal to 0.
To make it simple, imagine taking a cambered wing, if you look at the center-line of the profile, it will have a changing AOA along the chord of the profile. Setting the wing at a 0° AOA will result for a positively cambered profile into a negative AOA and a negative lift near the leading edge and a positive AOA and lift near trailing edge. Thus creating an absolute torque pitching down the wing profile. The aerodynamic center is the point where the coefficient related to this torque is not impacted by the AOA.

The point you are referring to is the center of lift ($P$). It's the point where the aerodynamic torque is equal to 0. But this point location is changing with respect to the AOA. You have the following relation:
$$C_{m_F} = C_{m_P}-(x_P-x_F)\cdot C_Z \rightarrow  x_P = x_F - \frac{C_{m_F}}{C_Z}$$
Which means that for a classic wing with positive camber and thus negative torque, the center of lift is located after the aerodynamic center in cruise condition with $C_z > 0$.

It is more practical to always express the aerodynamic load at a given fixed point, the aerodynamic center with the couple (lift, torque) than expressing just the lift at the lift center which is moving with respect to flight conditions.


How do single engine airplanes handle changes in torque?

Single engine airplanes experience torque proportional to the amount of engine power used. Pilots mitigate this torque by applying engine power smoothly and gradually. Since the torque on most planes will be applied to the airframe in the counter-clockwise direction from the point of view of the pilot, the pilot further mitigates this torque by applying Some right rudder when applying engine power. Aircraft manufacturers mitigate torque by offsetting engine placement and control surface neutral positions slightly. Quick applications or reductions in engine power will still cause the torque to be noticeable enough to create a left turning tendency.


If an aircraft is not IFR-equipped nor the pilot IFR rated, is it possible to get a border country to grant access from their CAA authority?

Note: A flight plan (FP) is needed for crossing a border, even for VFR.

For US-Canada, the answer is yes to VFR-only planes/flights/pilots. Note: for crossing the ADIZ, that would require DVFR (Defense VFR).

For UK-France, also yes. Note: even a mixed FP is possible (VFR-IFR-VFR). Below are excerpts from UK AIP:

  1.11.1 Pilots undertaking Cross-Channel flights are reminded that a flight plan MUST be filed for all flights to or from the United Kingdom which will cross the United Kingdom/France FIR Boundary.

  1.11.2 Specific FPL addressing requirements are detailed in paragraph 2 VFR Flight Planning.

  2 VFR Flight Plans

  2.7.1.1 The CAA have received reports that some VFR flight plans, filed for flights between France and the United Kingdom, have not been received at the UK destination aerodrome. Although these reports are infrequent, they nevertheless identify a significant safety aspect of cross-channel flight planning. The ability of the Air Traffic Service Unit at the destination aerodrome to be aware of an inbound flight is a key factor to alert search and rescue services, when appropriate.

  2.7.3.1 Additionally, for flights to/from France, the French Authorities require the frontier crossing point (the UK/France FIR boundary position) to be included in Item 15 (Route) of the FPL. To assist pilots, the UK now includes the ATS route reporting points on the Southern England and Wales 1:500 000 chart. These can be used as a frontier crossing point. A position may also be shown as LAT/LONG, or as a bearing and distance from a route reporting point or navigation aid.

  Example:

  Cap Gris Nez - RINTI
  Cap Gris Nez - 51N00130E
  Cap Gris Nez - RINTI23005
  Cap Gris Nez - DVR16010

As for how that would work, by checking the AIP (1.6  Mechanisms for Filing a FPL), it will be done via 'flightplanningonline' (a fax option is available too).

Also worth submitting, even if not required for a flight to France, is the general aviation report (GAR).

As for the minimum navigation equipment, it is found in GEN 1.5 of each country's AIP. As an example for the UK:

  All aircraft (except gliders and SLMGs) under IFR within Controlled Airspace below FL 245.

  VOR receiver, DME and automatic DF (except aircraft with Special VFR clearance).

Assuming a single-engine plane flying VFR and not for the purpose of public transport and below FL 245, there doesn't seem to be any special requirement for navigational equipment, except for ILS if flying into "certain aerodromes within Control Zones".

In short, you can fly a bare-bones plane across the Channel if you wish, but since weather can and does quickly change, you need to have an exit strategy if faced with visibility below 5 km and/or lots of unanticipated clouds.


Which are the requirements for the water supply on board?

The IATA standards as per the IATA Drinking Water Quality Pool are based on

  ISO 17775, WHO requirements or EU/98/83/EC or those set by the civil aviation authorities of the participating airlines

Source

Airlines and operators will periodically test their water in aircraft, ground service vehicles, and filling stations for bacteria contamination (E-coli, coliform, etc).

Some aircraft may not actually have potable water tanks or may have removed them. Horizon Air operates their Q400 Dash 8 aircraft without potable water.


Why don't cockpit windows suffer pressure leaks?

The Comet did not have pressure leaks.

The original structure of the Comet, which had a pressurised cabin (a new technology in airliners at the time), featured rectangular windows with sharp 90-degree corners. This concentrated the stresses in the aircraft skin at these points resulting in accelerated fatigue, cracking and finally catastrophic failure of the fuselage starting at a window corner. This first happened to BOAC Flight 781

The first prototype de Havilland DH106 Comet at Hatfield. Note the square windows.

(From the Imperial War Museum collection, public domain)

A later Comet 4 which now has rounded windows.

(By Ian Dunster (Own work) [CC BY-SA 2.0 uk (http://creativecommons.org/licenses/by-sa/2.0/uk/deed.en)], via Wikimedia Commons)

The photograph you have posted is not a 737. It's a wooden cockpit mock-up intended for a flight simulator. It will never be pressurised, and the builders are more concerned with the overall shape than detail around the windows.

Take a look at a real 777 cockpit:

(Source: Chris Sloan, AirwaysNews.com)

Notice that the corners at the ends of the widows are rounded, as are all the other corners around the window frame. There is one panel (second from left) that appears not to have this treatment. This panel can be opened (although not when the cabin is pressurised) and is built into its own frame that is fitted into the cockpit window structure. A failure in this frame will not propagate to the rest of the aircraft.


Where can I find the active time of a MOA on the VFR chart?

It's in a table on the border of the sectional.  Looking at the Chicago sectional, this is along the top....


What is the significance of hover performance in helicopters (HIGE, HOGE)?

Ground effect is a condition where the performance of the aircraft increases while operating near a firm surface. In general, a helicopter is considered to be in ground effect when it is hovering less than one-half of its rotor diameter from the ground and the effects become negligible when the helicopter is more than a rotor diameter above the ground.

While hovering near the ground, the induced velocity at the rotor is reduced, which reduces the power requirement for a given rotor thrust (lift); equivalently, the rotor thrust is increased for given power due to ground proximity. Also, near ground, the rotor tip vortex is reduced.

Due to this, the helicopter can hover at higher gross weight (equivalently, at higher altitude for given weight) in ground effect (HIGE) compared to out of ground effect (HOGE).

Image from copters.com

Usually, the altitude at which a helicopter can hover at a given weight (and atmospheric conditions) is given for both HIGE and HOGE conditions. HOGE is much more restrictive compared to the HIGE. For example, the following image compares the hoer performance of R44 helicopter in and out of ground effect.

Data from helicopterforum.verticalreference.com and aneclecticmind.com

In a sense, HOGE represents the absolute limit of the helicopter performance and it should be considered for operational calculations where there is no availability of rigid surfaces for vertical takeoff and landing or their presence is not confirmed.


The aircraft you are mentioning are completely different from each other and some of them are not even named according to the US Tri service Naming System.

In general, the aircraft retain their original designation given even though the later versions have little in common with their predecessors.

The F 15 was a direct result of the studies that followed the Vietnam war and the a response to new generation Soviet aircraft like the Mig-25.

"McDonnell Douglas F-15A USAF". Licensed under Public Domain via Wikimedia Commons.

The F-15 was designed purely as a air superiority fighter, with full emphasis on maneuverability and agility with "Not a pound for air-to ground!". The first to variants of the F-15 were called F-15 (single seat) and TF-15 (two seat), which were retrospectively named F-15A nd F-15B after the introduction of F-15C. The F-15E was a strike variant; however, it could defend itself against enemy aircraft and thus retained the 'F' title.

"F-15E Strike Eagle" by Gerry Metzler - IMG_214. Licensed under CC BY-SA 2.0 via Commons.

The case of F/A-18 is different. The initial plan was to purchase three different version of the aircraft, F-18A (Fighter), A-18A (Attack) and TF-18A (Trainer). However developments in avionics and some design changes led to the
first two versions joined together as F/A-18A and the trainer version being named F/A-18B.

"US Navy 050803-N-0295M-148 An F-A-18B Hornet, assigned to the U.S. Naval Test Pilot School, folds-up its landing gear after taking off for a training flight from Naval Air Station Patuxent River, Md" by U.S. Navy photo by Photographer’s Mate 2nd Class Daniel J. McLain

Most of the aircraft in service today are multirole and their names mostly reflect what their intended purpose is rather than their actual purpose. With modern avionics and high precision weapon systems, almost any aircraft could be made a strike aircraft

It is to be noted that the naming convention is followed only loosely in some cases. A good example is the F-117 Nighthawk, which is not a fighter aircraft in any sense of the word.


Is there a solution to radio interference?

Firstly, it is worth noting that the blocked radio transmission is only one point on a very long list of factors that caused the horrible accident on Tenerife. There is enough redundancy in aviation systems and procedures that a single fault somewhere in the system will [almost] never be enough to cause an accident. Weather, stress, a terrorist attack, company policy, poor CRM and many other things were also contributing factors.

Communication between air traffic control (ATC) and pilots is mostly based on simplex radio. Simplex radio only allows one station per channel to transmit at the same time; if two stations transmit at the same time, the signal will be blocked. Sometimes, if one signal is stronger, it will be possible to hear that signal but not the other. The main problem is that the two stations transmitting will have no way of knowing that they are blocking eachother. This limitation regularily results in various incidents - for example, when there are two aircraft with similar sounding radio callsigns on an ATC channel, one crew might mistake an instruction for the other flight, thinking it is actually meant for them. If both flights read back the instruction at the same time, neither of them will hear the readback from the other aircraft and realise the mistake, and ATC might hear just one of the readbacks, and not realise that both flights are following the instruction meant for just one of them.

So why isn't there work being done to phase out simplex radio in aviation?

There is. It's called CPDLC, or Controller-Pilot Datalink Communications. (Other, similar systems exist as well, with different names. In the following I will just discuss CPDLC).

CPDLC is a digital system that allows ATC and pilots to communicate via text. It is already widely deployed in many areas, one example being Maastricht UAC, one of the busiest area control centres in Europe. Multiple stations can transmit at the same time, without the risk of blocking other transmissions.

So why do we still have simplex radio?

So far, CPDLC is only used for area control. In areas where ATC instructions are time critical, such as an approach or aerodrome environment, we still rely on simplex radio, because it is guarenteed to be instantaneous - and pilots are used to acting immediately to a voice instruction. However, it should only be a matter of change of procedures and appropriate training before CPDLC can be used in all phases of flight.

More importantly, aircraft equipment is expensive. Replacing a simplex radio with CPDLC equipment involves a significant cost per aircraft. While this may be feasible for large airlines, remember that they only make up a part of flights. There are thousands and thousands of private planes, balloons, gliders and whatnot, and private pilots or flying clubs may simply not have the funds to implement CPDLC. And obviously, ATC can't turn off their simplex radio until everyone has equipment to replace it.

Another disadvantage of CPDLC, or other communication equipment that allows direct communication between cockpit and controller working position, is that it reduces situational awareness. A big advantage with simplex radio is that everyone has to listen to what everyone else is saying, since you can't talk when someone else is talking. This gives pilots the possibility to establish a mental picture of the traffic around them, which ultimately increases safety. As we saw with Tenerife, the lack of such a mental picture can result in tragic outcomes. However, simplex radio has probably prevented many other accidents, because everyone on the frequency knew what was going on around them. The Providence incident of December 1999 comes to mind as one example among many.

So, is there a solution to radio interference? Yes, there is. Is it easy to implement? No, it is both technically and financially difficult. Will it necessarily prevent accidents such as the one on Tenerife? No; a thorough safety and risk analysis must be carried out before deploying it everywhere.


Which parts of an airplane are made of buoyant material?

Passengers are reminded of #1 & 2 above on every safety brief.
Beyond that, you aren't going to get up out of your seat before the crash and attempt to latch on to some buoyant part of the structure, so it isn't an actionable question in the context it is asked.  (Which is a polite way of saying who cares...)
Stay in your seat until the violent motion stops, then follow the instructions of the surviving crew to evacuate the aircraft in an orderly manner.
Allow women and children to go first if able.  Whatever might be floating after the crash is over is buoyant, and may be used.


What happens when an airplane is retired?

There are a few things that can happen:

They are sold to another airline - In some cases the plane may still have life (cycles) left and may find it's later days flying for another outfit. Sometimes airlines for countries with emerging economies can only afford older aircraft and they may end up far from their original homes.
They are sold to cargo airlines - cargo airlines may buy old passenger planes as they may not always be looking to fly the fanciest new airliners since the customer rarely talks back ;)
They end up in the bone yard - aircraft with life left on some parts hold at least some value and may be relegated to a bone yard to be picked over for years to come.
Ultimately, scrap metal always has value...


Why is the empennage design of this Lockheed 1049E so complicated?

Complicated is a matter of opinion and I wont address that specifically since its somewhat subjective. But the core of the question is "why did the L-1049E have 3 tails" which is a legitimate question for this site.

The design was to allow the aircraft to fit in hangars of the time

  A sleek fuselage, something like an elongated fish with smooth curves,
  featuring a circular cross-section, a snub nose, and a triple-fin
  tail. Triple tailfins were selected because a single tailfin would
  have been too tall to fit into typical hangars.

The L-1049E had tricycle style gear that was quite tall (for the time) and a standard single tail would have made the aircraft too large to fit into the hangars that most fields had.

The above link also discusses that for a particular Military version ("WV-1") of the aircraft the lower section of the tails were extended to compensate for a radome being mounted on the top. This came along only a year into the design and the subsequent builds may have been a hold over.

Weight as a result of the added rudders would not have been as much as you may expect since they were traditional fabric covered style surfaces


If I am pushing my aircraft into the hangar with a tow bar, at night, with the engine off, am I required to activate my rotating beacon?

The AIM gives good advice, but that is really all it is. It is acceptable methods of complying with the regulations, but you are not required to comply with what the AIM says. In questions of what you are required to do, especially in questions of whether you might be at risk for a violation, we want to look at the regulations in 14 CFR.

14 CFR 91.209 states, in pertinent part:

  No person may:

  (a) During the period from sunset to sunrise [...]—

  (1) Operate an aircraft unless it has lighted position lights;

  (2) Park or move an aircraft in, or in dangerous proximity to, a night flight operations area of an airport unless the aircraft—

  (i) Is clearly illuminated;

  (ii) Has lighted position lights; or

  (iii) is in an area that is marked by obstruction lights;

  (b) Operate an aircraft that is equipped with an anticollision light system, unless it has lighted anticollision lights. However, the anticollision lights need not be lighted when the pilot-in-command determines that, because of operating conditions, it would be in the interest of safety to turn the lights off.

Note:
Position Lights are commonly called Nav Lights
Anticollision Lights can include what are more commonly called Strobe Lights and Beacon Lights (See AIM 4-3-23)

Lets first look at what the above regulation says about operating requirements. Is your given scenario (engine off, etc.) an example of operating the aircraft? 14 CFR 1.1 gives the following definition of operate:

  Operate, with respect to aircraft, means use, cause to use or authorize to use aircraft, for the purpose (except as provided in §91.13 of this chapter) of air navigation including the piloting of aircraft, with or without the right of legal control (as owner, lessee, or otherwise).

By that definition I would argue that towing, pushing, or otherwise moving an unoccupied aircraft with engine(s) shut off would not be operating that aircraft anymore than leaving the aircraft parked overnight would be operating it, since you are not using the aircraft for the purpose of air navigation. Thus I would say that you are not required to follow any rules that pertain to operating the aircraft, such as that any installed anticollision light be lighted.

(This is in contrast to an airliner pushing back with a load of passengers, flight crewmembers at their stations, electrical power on, APU running, etc., which would be operating, since the aircraft is being used.)

This leaves us with the Park or move paragraph. This paragraph specifically pertains to "in, or in dangerous proximity to, a night flight operations area of an airport".

What is a night flight operations area? Absent any proffered definition, the plain reading of the phrase—as I read it—would be an area used, or subject to use, for flight operations at night. In other words, any public use airport with an apron or taxiway that is open to flight operations at night could and should be considered—by my reading—a night flight operations area. Whether the area is a movement or non-movement area shouldn't matter. Could someone else reasonably taxi past you (or into you!) at night? That's probably a night flight operations area.

Thus, for your given scenario, if you are pushing your aircraft back into a tie-down spot on an apron that is open to night flight operations, by regulation it must be either:

a) clearly illuminated;
b) have lighted position lights; or
c) be in an area that is marked by obstruction lights.

I typically see airport ramps clearly illuminated by large overhead lights. This clearly meets the first requirement. Another means of compliance would be to turn on an internal hanger light to clearly illuminate the airplane when you push an airplane in off a taxiway into a hanger.

You are also good to go if you are in an area that is marked by obstruction lights. I don't think I have ever seen these demarcating an area where you would be pushing or towing an airplane (I'm thinking of those lighted construction barriers), but if you saw them I suppose you would know.

In the absence of clear illumination or an area marked by obstruction lights, if you are going to park or move the airplane at night, you had better turn on the position lights. And this, I think, is where you could be at risk for a violation.

Note that, even in that case, the requirement is for position lights, not the beacon. Unless the aircraft is being operated, there is no requirement that any installed anticollision light be lighted.


Since you mention 'frontal passage' it is assumed that the term "air mass" is understood and also the reasons for the movement of air masses. The movement of an air mass relative to the earth's surface is what we, standing on the surface, physically feel and experience as wind.
There are things that affect the smooth flow of the air mass, such as terrain, pressure gradients, other air masses, man made obstacles etc. and these can occur at different scales. By this we mean at the continental/oceanic scale, down to the scale of human made buildings or small but significant natural outcroppings.
Localised and somewhat unpredictable short term disturbances to the smooth flow of the air mass are what we perceive as 'gusts'. Visualize it in a similar manner to the way flowing water is churned by an obstacle in its flow path and the factors that cause the churning. Try listing these factors for yourself, both for water, and for the atmospheric air.


How does a towed banner maintain a steady tilt?

Banners have a lead pole to keep the leading edge straight. This pole is weighted at the bottom, which ensures that the top and bottom of the banner remain in the correct place.
By itself, this would ensure the banner remain perfectly vertical. To achieve the proper angle for viewing on the ground, a tab is attached to the top of the lead pole, adjusted to the required angle to push the top of the pole in the desired direction to achieve the right viewing angle.
Here's a quick sketch to try to illustrate the setup, with the banner, pole, weight, trim tab, and harness:

Here, we're looking at about a 45 degree angle from ahead of the banner, with the trim tab adjusted to the left of the banner's direction of flight, causing the top of the banner to tilt to its right:

In other words, the tab at the top of the pole acts similarly to an airplane's rudder, where deflection to one side results in a force applied in the opposite direction.
More reading here:
Aviation Stack Exchange: How are banners kept upright?
Pilots of America: Banner aerodynamics
Quora: How are flying banners stabilized?


What a fix is has been answered here but for now let's just say it's a known location that a pilot can navigate to if he has the right equipment. Fixes are shown on various charts and approach plates.

As for using those fixes on an instrument approach, there are lots of variations and details but again, let's ignore most of that for now. The basic concept is very simple:

Fly to an Initial Approach Fix (IAF)
Fly to other fixes as needed to execute the approach
Land (or go missed)

For example, here's the RNAV (GPS) 36R approach at KHSV:

You can see at the bottom of the map portion of the plate that both MASHA and FEWER are IAFs, so that's where the approach starts. Let's say you're approaching from the south-west and you've already descended to a reasonable altitude for starting an approach, following a STAR or vectors from ATC.

ATC says something like "N12345 proceed direct MASHA, cleared for the RNAV 36R approach". That means that you are now cleared to execute the approach as shown on the chart, with no further instruction from ATC (although they might have vectored you towards the IAF initially).

The chart tells you that at MASHA you need to be at at least 3000ft MSL so you simply fly there at or above that altitude. Since it's a GPS approach, you load it and activate it in your GPS unit, and you can follow the GPS track to MASHA.

After MASHA, the next fix is ENIKY and the GPS track will lead you east to that fix (which is a heading of 091° from MASHA). The profile view at the bottom of the plate shows that you must still be at or above 3000ft at ENIKY. Then you turn left to 002° and fly to UJOTY, where you must be at or above 2700ft. Then you continue to GEPDE at or above 1180ft. Then you land :-)

Of course, I'm ignoring a huge amount of detail here - like everything else printed on the approach plate! - but since this question is about fixes the main point is that they're simply a series of waypoints that you fly over (or past) to get to the runway. And obviously you also have to control your altitude as you descend, but the altitude is defined by the approach procedure, it isn't part of the definition of the fix itself. The same fix can be used in multiple approaches: MASHA and FEWER are also the IAFs for the RNAV (GPS) 36L approach).

Even though different approaches define and use fixes in different ways, the basic idea is always the same: just fly from one fix to the next until you get where you're going.


What do aircraft accident investigators do in between incidents?

NTSB investigators handle General Aviation incidents that you never hear about, as well as the Commercial incidents that make the nightly news.

There are new incidents every single day.
Try reading AVHerald for a sense of what happens, or searching the NTSB Aviation Database.

They have plenty of work.


Some aircraft have a "taxi speed indicator". Here's one I found on ebay for an Airbus:


Is there a planned ADS-B update that would allow ATC to view an aircraft's traffic coverage?

No, this is not being planned as a future update. The current ADS-B mandates of USA and Europe foresee ADS-B version 2 (EUROCAE ED-102A / RTCA DO-260B for 1090ES) to be implemented in 2020. Work on the development of version 3 of the standard has started but the retransmission of received data is not foreseen currently. Because of 1090 MHz spectrum overload, integrity, security and latency issues I don't think it is a particular good idea either.

For oceanic areas ADS-B coverage will be provided by satellites equipped with ADS-B receivers. Aireon is a company that will use the next generation of Iridium satellites to provide oceanic ADS-B coverage for ADS-B.


Why did my transatlantic flight meander off the great circle?

Most flights across the Atlantic don't fly direct great circle routes; they use the North Atlantic Track system, which is an array of "lanes" you might say, usually 60Nm apart, like one of those slot car racing places with 6 or 8 lanes of cars.  Just about everybody that can make the trip non-stop will be in the tracks at various altitudes. Off each coast are an array of fixed entry point fixes called Oceanic Entry Points as jumping on or jumping off points.

The north/south position and the precise routing of the tracks is set up each day, with the focus on eastbound traffic in the morning and westbound in the evening, and are moved up and down the take advantage of winds or weather, especially jet streams.

Jet streams flow along air mass boundaries at the top of the troposphere and change constantly as air masses move.  The tracks are set up to try to exploit or avoid them depending on whether they are favourable or not (as well as other weather systems).


Why isn´t TOGA thrust always 100% N1 or N2?

TOGA thrust is not always 100% N1 (or N2), because TOGA thrust is actually not about delivering the absolute maximum thrust that can be provided. Rather, it's about delivering a guaranteed large amount of thrust, to ensure the performance of the aircraft is what the pilot expects, and what the flight manual states will occur. The level of thrust needs to be predictable. So it's got to be the same with a new aircraft, as one 5 years old (for example), and the engines are about to be overhauled.

To achieve this, engines are "flat rated". See What is a Flat Rated Engine?

To repeat that answer a bit, a flat rated engine, produces a constant, or the same amount of thrust, up to a certain ambient temperature. This is achieved by having a margin (gap) between the maximum thrust the engine provides, and what it can really produce. This also results in a temperature margin between the engines actual turbine temperature, and the red line temperature. This means as the engine degrades, it can increase its operating temperature without hitting the red line (until it has degraded a lot), and so still provide the same level of thrust.

When a gas turbine's engine control is designed to produce the same thrust at different ambient temperatures, it means N1 speed will be higher on a hot day, than a cold day. See how in the figure, for a constant thrust, N1 is increasing as ambient temperature goes up? N1 has to go up as ambient temperature increases, because hotter air at the intake is less dense than colder air, so the engine needs to run at a faster RPM to make up for the lower density.


When filing an ICAO flight plan with LPV, is marking GNSS equipment necessary or redundant?

You should fill both G and B.
If I understand the last row of the official ICAO guidance correctly, field 10 (equipment code) of the flight plan must contain at least B and G if you want to fly LPV approaches:

(cropped from ICAO Guidance for the provision of NAV/COMSUR information in the New ICAO 2012 Flight Plan)
You will also have to enter "NAV/ SBAS" in field 18.
This is also confirmed by the following information on the ForeFlight support page:

When specifying a PBN code, be sure to also specify R (Code for Performance-Based Navigation (PBN) Approved) and the associated sensors that the PBN code requires. For example, PBN Code D2 is RNAV 1 using GPS, therefore Equipment Code G (GNSS) must also be specified.
[...]
These tables are a general aid for entering filing codes in ForeFlight and are not an authoritative or comprehensive equipment specification. Consult the AFM or AFM supplements for your aircraft to determine which codes are actually appropriate before attempting to file using ForeFlight. The codes listed below are in addition to the other ICAO Equipment code that may be appropriate for your aircraft.
WAAS

GNS 430W - R, B, and PBN B2, C2, D2
GNS 530W - R, B, and PBN B2, C2, D2
GNS 480 - R, B, and PBN B2, C2, D2
GTN 6XX/7XX - R, B, and PBN B2, C2, D2
GPS 175 - R, B, and PBN B2, C2, D2
GNX 375 - R, B, and PBN B2, C2, D2
G1000, 2000, 3000, 5000 WAAS - R, B, and PBN B2, C2, D2

(foreflight.com, emphasis mine)


FAR 91.215-- may an aircraft with no electrical system and no transponder overfly Wheeler AAF at 9500' MSL?

Yes, the following statement indicates that aircraft without electrical systems may penetrate the mode C veil at any altitude (presumably excluding cases where the penetration would immediately bring them into Class B or C airspace, or would immediately place them above underlying Class B or C airspace):

  "The practical effect of paragraph (b)(3) with respect to your
  question is that it allows non-equipped aircraft to enter the
  30-nautical mile circles surrounding Appendix D, Section 1 airports
  between the surface and 10,000' MSL and to operate beneath the floors
  of the associated Class B airspace..."

From this page 2 of this 2006 interpretation from the FAA Office of the Chief Counsel.


Is a Control Law Degradation in Airbus Planes displayed on the ECAM?

Since you are trying to understand how the crew is aware of law reconfiguration, it's important to look at this event in its context, why it does happen and what are the consequences for the control of the aircraft. You may skip this overview and go to the direct answer to your question which is in the last section of this post.

Flight control system and computers

The crew and the FMGS (autopilot) send commands to redundant computers:

2x ELAC (elevator aileron computer) for elevators/THS and ailerons,
3x SEC (spoilers elevator computer) for elevators/THS and spoilers,
2x FAC (flight augmentation computer) for rudder,

and computers send commands to actuators.

Source.

When the system is fully functional, all computers work using a normal law and it provides protection against:

excessive pitch and roll attitude,
high-angle-of-attack,
high-speed and low energy,
excessive load factor.

This can be done by receiving aircraft dynamic data from multiple sensors visible in the diagram.

If a flight control computer fails (or stop receiving required data), the crew receives an indication on the overhead panel:

Source.

When one or several of those computers fails, the role of the remaining ones are redistributed.

Reconfiguration of the computers

The failure of an element of the flight control system needs that other available elements compensate for the missing computer or peripheral. This reconfiguration allows available computers to control an additional axis using other laws. However departing from the normal law for an axis means losing one or more of the protections available under the normal law.

Degraded laws are:

alternate law (two levels: With and without reduced protections),
direct law (no protection),
mechanical (mechanical linkage between controls and control surfaces).

The mechanical mode is a backup mode to control the tail surfaces from the pedals and the pitch trim wheels in case something prevent actuators to work (e.g. loss of all electric power sources before the RAT is deployed).

Source: Airbus A320 FCOM

Alternate and direct control laws modify the relation between the stick movement and the flight control movement (linearity and amplitude).

Effect of pitch axis alternate law in different phases of flight

After the flight control system has transitioned to an alternate law, some protection may be available, but law may also transition again according to events representative of the different phases of the flight. Here is what happens around alternate law on pitch axis, which a change to direct law as the landing gear is extended:

Source: Airbus A320 FCOM

A very degraded flight control system: Direct law

While alternate law on a given axis still maintains (under some conditions) some level of flight envelope protection, this protection is lost when degrading to direct law. According to the axis, the direct law impacts are:

Pitch: The stick commands linearly elevators movement, automatic pitch trim is unavailable, all pitch protections are lost as well as alpha-floor.
Roll: The stick commands linearly surface movement, but overall amplitude is different according to slats/flaps status, only ailerons and spoilers 4/5 are used (all spoilers if ailerons fail).
Yaw: Mechanical control using the pedals, yaw dumping and turn coordination unavailable.

Permanent indications on PFD

Green $\sf \scriptstyle \color {green} {\text {=}}$ indicate active protections: Bank angle ± 67°, pitch angle at 15° nose down and 30° nose up. On the speed scale, speed limits for alpha protection.

Loss of protections after the degradation from normal law is indicated by amber $\sf \color {orange} {\text {x}}$.

Source: Airbus A320 FCOM

When the direct law is in effect for pitch the amber warning $\sf \scriptstyle \color {orange} {\text {USE MAN PITCH TRIM}}$ is displayed below the lines of the flight mode annunciator.

In addition if the law transitions to mechanical backup (which is supposed to be a transitory state), a red $\sf \scriptstyle \color {red} {\text {MAN PITCH TRIM ONLY}}$ replaces the amber indication.

General alerts

Audio chimes are triggered at the time of a component failure, when the mode changes. Alerts also activate either of the overall alerting lights (master warning and/or master caution).

ECAM messages

Failures and law activation trigger messages on the ECAM, with suggestions for crew actions.

Source.

However, and this was noted by investigators on AF447 accident, ECAM messages can be shown or hidden in the scrollable list according to messages priorities, due to the high number of messages that may appear in a short period of time during such sequences of events:

Source.


What are design or functional differences between sticks and yokes?

There is some link between the type of control and the design maneuverability of the aircraft.

Consider a yoke.  Imagine twisting it to bank.  You are moving it with a twisting motion of one or both arms and in general, aircraft fitted with such yokes are capable of low to moderate roll rates.  Big displacements are uncommon but small, rapid, alternating changes are common.  Watch a wide body PF making control movements during a landing with any kind of xwind or turbulence.  They are less sensitive and give more visual feedback as to the control positions.

Now consider a stick, central to the pilot flying.  This is moved with a movement of the arm, generally only one, and can be rapidly displaced easily.  This is normally associated with aircraft with high rates of roll, especially in an aircraft designed to rapidly null out or reverse the roll.   It is also physically easier to move a stick than a yoke under high-G as the arm movement gives a longer lever.

A great example of this was the Vulcan which, despite its size, enormous wing area and large fin, was so rollable that it could out-maneuver the interceptors of its day.  It has a control column rather than a yoke and the PF would throw it around at altitude as if it were a fighter.  This would not be easy to do with a yoke.

I'm a bit long in the tooth and haven't flown fixed wing for many years.  I am not familiar with the rationale behind side sticks which are fitted to both low and high performance aircraft.  I am guessing they are fitted more for reasons of ergonomics than for performance.


What is the relationship between drag and sink rate?

total drag (mostly induced drag at high AOA) exceeds thrust available and the airplane develops a sink to try to regain equilibrium.

That is exactly right. At best L/D, induced drag is half of total drag and at lower speeds it becomes dominant, growing with the inverse of airspeed squared.

  Some people have said that weight exceeds lift, but I'm pretty sure this isn't the case.

You did well not to listen to those people. If the aircraft doesn't accelerate downwards, lift still equals weight. At a constant sink rate the aircraft does not accelerate.

As you say, the aircraft is in an equilibrium. Because you choose to add less power than what was necessary for level flight, the aircraft behaved similar to a glider. Allow me to use a glider for my explanation. Below is one with the dominant forces added as arrows in level flight. Clearly, there is nothing to compensate drag (red):

This airplane is not in equilibrium and does what you did in order to slow down: It flies level while drag is exceeding thrust (which is per definition zero in a glider).

So what to do? Just like when flying a turn, the pilot will now tilt the lift vector. That is the biggest force at his command, and he does so by pitching down. Now the airplane is in a glide, the direction of flight is slightly down and the lift vector (which is per definition perpendicular to the direction of the airspeed, which again is equal to the direction of flight if there is no wind) is equally tilted forward. This is what the next sketch shows:

Now we have a component of lift pointing forward, and that component is equal and opposite to drag. The rest of the lift is needed to compensate the weight, so the lift force is a tiny amount larger than weight. The sink rate is speed times the tilt angle, which in turn is what is needed to have the sine of lift $L$ equal drag $D$. Mathematically speaking, this is:
$$D = L\cdot sin(\gamma)\;\;\;\text{and}\;\;\;\gamma = arcsin\left(\frac{D}{L}\right)$$
with $\gamma$ as the angle of the direction of flight relative to the horizon.
The sink rate $v_z$ is $$v_z = v\cdot sin(\gamma) = v\cdot\frac{D}{L}$$
That is the direct answer to your question: The sink rate is the product of speed and the inverse of the lift-to-drag ratio. At small angles the ratio is approximately equal to its sine when expressed in radians, so I left the trigonometry out of the last equation.


What do these explanations for propellor RPM increases mean?

The troubleshooting section from the Hartzell Propeller Owner's Manual No.411 states:

B. Engine Speed Varies with Flight Attitude (or Airspeed)
   (1) Small variances in engine speed are normal and are no
       cause for concern.
   (2) Increase in engine speed while descending or increasing
       airspeed:
       (a) Non-feathering ( )(A,B)1 series propeller:
           1 Governor is not increasing oil volume in the
             propeller.
           2 Engine transfer bearing leaking excessively
           3 Excessive friction in the blade bearings or pitch
             changing mechanism

Reasons 1-3 relate to the propellers inability to adjust its blade angle to maintain a constant RPM when descending and airspeed is increased on non-feathering propellers.

The transfer bearing allows governor controlled oil into the crankshaft interior then to the propeller hub. If the bearing is leaking excessively the oil may be leaking back into the crankcase and there may not be enough oil pressure going into the hub to increase the propeller blade pitch and slow the engine down.

If there is excessive friction in the blade bearings the propeller blades may not move freely within the hub even when adequate oil pressure is supplied by governor and oil system.


Where is the fire suppression material injected into a jet engine?

I’m wondering where exactly does the suppression material go into the engine? Does it all flow into the core or is it distributed to different places.

It is distributed with some nozzles. But the exact position of them depends on the specific engine. In this slides you can get an idea of the positions for a turboprop engine. They usually cover at least the core, and some other zones that should be separated by firewalls. This image (from Boeing) gives you an idea of the different zones, which I expect they are covered by different nozzles:

and this image (from the same link) contains the position of the fire detectors, which I expect to be covered by at least one nozzle:

Does the loss of the cowl render it ineffective? I expect that halon would only work in an enclosed space. It

Probably yes. Engines are not designed to have catastrophic failures like the Flight UA-328 (they are supposed to contain any failure). So, probably not even the fire protection system is designed to handle such case. A large destruction like that may have potentially cut some of the fire protection tubes and damaged the firewall protections.


As pressurized aircraft's windows exist of several layers (usually three) there's this little hole to compensate differences in the pressure between inside and outside the aircraft.
Inside the aircraft the pressure is much higher than outside so without this little hole the windowd layers would be pushed together and break.


Could a private pilot violate 'commercial' rules if there is no compensation or expense sharing at all?

Yes.  Without compensation, a private pilot can violate 'commercial' rules.

For starters, the FAA considers the ability to log flight time as compensation.  A legal interpretation to John Harrington issued October 1997 clarifies that point.  The regulation that you are asking about is quoted below.

  § 61.113   Private pilot privileges and limitations: Pilot in command.

  (a) Except as provided in paragraphs (b) through (h) of this section, no person who holds a private pilot certificate may act as pilot in command of an aircraft that is carrying passengers or property for compensation or hire; nor may that person, for compensation or hire, act as pilot in command of an aircraft.

An interpretation to Mike Sommer in part says

  The FAA construes the terms “compensation for hire” very broadly. It does not require a profit, profit motive, or the actual payment of funds. Instead, the FAA views compensation as the receipt of anything of value. In an interpretation letter to John W. Harrington, from Donald Byrne, Assistant Chief Counsel, October 23, 1997, it is stated that, “any reimbursement of expenses (fuel, oil, transportation, lodging, meals, etc.), if conditioned upon the pilot operating the aircraft,’ would constitute compensation.”

In 1985 the FAA chief counsel determined that there had to be a bona-fide common purpose in conducting the flight.  See the Chero Interpretation from December 1985.

  Section 61.118(b) allows a private pilot to share the operating expenses of a flight with his or her passengers. Additionally, the FAA has interpreted 61.118(b) so that the only allowable share-the-costs operations are those which are bona fide, that is, joint ventures for a common purpose with the expenses being defrayed by all passengers and the pilot. Nor does Section 61.118 permit pilots who want to build up time toward their commercial pilot certificates to carry expense sharing passengers to a destination at which they have no particular business. (emphasis added)

To answer your question.

The pilot flies the passenger somewhere they weren't planning on
going, but nonetheless enjoy. I'm assuming this is not a problem,
and happens most days.

There is no problem here.  The pilot would pay for the expenses of the flight anyway so taking a passenger is OK.
The pilot flies the passenger to visit a family member, one they wouldn't have visited otherwise.

This is only legal if the pilot pays for all expenses.  Since the FAA has determined compensation quite broadly I would expect they would also consider food and lodging as compensation as stated previously in a legal interpretation.  The pilot would, for all practical purposes, pretend the passenger was not there and make their own arrangements.
The pilot flies the passenger to a specific recreational event, which they are attending.

This is legal and the pilot can share the costs with the passenger.
The pilot flies the passenger to a specific recreational event, which only the passenger is attending.

This goes back to #2 above.  The pilot does not have a bona-fide common purpose for making the flight.  They cannot accept any compensation in any form for the flight to be legal.


Airplanes have a long history of evolution, and so do computers.

But some latest developments seems to suggest that, yes, people are working on it to use a single computer system to display and control everything, but right now the innovation front is in the automotive industry where regulatory complexity is lower.


Do crosswind takeoffs increase the chance of a compressor stall?

The general FAA regulation on turbine engines on airliners is § 25.939

§ 25.939 Turbine engine operating characteristics.
(a) Turbine engine operating characteristics must be investigated in flight to determine that no adverse characteristics (such as stall, surge, or flameout) are present, to a hazardous degree, during normal and emergency operation within the range of operating limitations of the airplane and of the engine.
(b) [Reserved]
(c) The turbine engine air inlet system may not, as a result of air flow distortion during normal operation, cause vibration harmful to the engine.

The FAA has published Advisory Circular 25.939-1 which provides more detail as to how this regulation should be met. The takeoff phase is critical for safety, so the FAA requires testing to show that:

No adverse engine operating characteristics (mild, moderate, or severe) should exist after the power setting phase (normally completed by 60 to 80 knots) of the takeoff procedure through attainment of the enroute configuration and climb to 1,500 ft. above the airport.

The "adverse operating characteristics" are defined in more detail earlier in the AC. So to answer the question, no, it is required by law that jet engines have no issue with takeoffs in crosswinds. The faster an aircraft is moving, the less the crosswind airspeed component is. Once the aircraft is flying, aside from control inputs or changes in the atmosphere, the air stream comes from straight ahead.
The highest amount of relative crosswind will actually occur while the aircraft is sitting on the ground. Note that unlike the takeoff phase:

Taxiing: No adverse engine operating characteristics (mild, moderate, or severe) should exist during taxiing except for operation in crosswinds and tailwinds where mild adverse operating characteristics are acceptable.


In a fighter jet, what is the average weight of the ejection system?

The F-14 manual describes the ejection system as:

  The aircraft is equipped with an automatic electronically sequenced command escape system incorporating two Navy aircrew common ejection seat (SJU-17(V) 3/A (pilot) and SJU-17(V) 4/A (RIO)) rocket-assisted ejection seats.

That means the seats are an integral part of the system.

According to this page, the weight is 228 pounds (103 kg) and it has a "maximum thrust [of] 4,800 pounds for 0.25 seconds".

A cockpit seat on a Boeing 737 weighs around 40 kg if we are to trust this replica vendor, so we can say the addition of the ejection elements adds 63 kg. Of course a 737 cockpit seat is much heavier than a WWII non-existent seat (the pilots brought their own cushions). This might be useful however if you want to compare a B-52 with and without ejection seats.

Below is an image for that ejection system, and as I gather, that's a very common (average) model found on many US aircraft.

(Click for larger size.)


Why has the European Union banned several airlines?

I think the policy is completely justified. An analogy: You wouldn't allow an unsafe and unapproved car onto a highway in Europe where it presents a unjust danger to everybody else.

You have to remember that the European Union is a fairly compact bunch of nations: To get to Paris from Southeast Asia or Africa, you're probably looking at overflying at least two or three other countries. Thus, a single flight will have wider implications and involve multiple nations. The policy keeps everybody somewhat happy that they have safe airlines in their airspace. It also keeps their own citizens off the airline in question.

I do not think that it is a question of 'caring'. If they do not feel that the airline can safely fly, they ban it. Note that a fair number of the EU blacklist are automatically banned by country if they have insufficient oversight. It's also not a permanent 'thing' or sentence. Garuda Indonesia was on the EASA blacklist for two years until they brushed up, and are now back flying into the EU. Perhaps it might even have been good, since it pushed the company to improve their standards?

Here is a recent quote on the Iraqi Airlines ban:

  ATW understands from unidentified sources that 600 non-EU airlines had applied for TCO authorization. Most had been granted with few problems, but a small number of airlines were subject to greater scrutiny because of their perceived high-risk status. Source

While perhaps less prominent, I think the United States will quickly block any unsafe airline from coming in, although perhaps on a more case-by-case basis. I believe there are other hurdles, such as airport security requirements, that have to be settled to fly into the United States and can act as barriers. I believe the same applies for any other nation.

Other countries say no as well, just perhaps not being as 'vocal':

  Some Thai-registered airlines earlier faced flight restrictions by Japan, South Korea and Indonesia, following an audit of Thailand's air operations by the UN-based International Civil Aviation Organisation. In June the agency raised a red flag over aviation safety standards and gave the country until November to tackle the issue. Meanwhile, the US Federal Aviation Administration (FAA) last Friday gave Thailand 65 days to address shortcomings it had found. Source


Many cruise missiles have wings of some sort, although these can be very small like on the P-700 (barely larger than their control surfaces) or foldable in such a way that makes them not obvious when the missile is in a stowed configuration, like on the Tomahawk or Kh-55.

Additionally, the narrow body of the missile provides lift. Though it is much less effective at it than a wing would be, this is a design trade-off that can be worth it in some scenarios. For supersonic cruise missiles the narrow-body lift is usually enough and the lack of wings is a plus, as they would generate a disproportionate amount of drag at $M_{\infty} \geq 1.0$.

One of the main traits of slender wings (and bodies) is that their effect on the surrounding airflow grows with speed at a much  slower rate than that of a high-aspect-ratio wings, making them suitable for high speed applications.


Is it easier to land planes on an aircraft carrier with a high flight deck?

Then

It used to matter, because aircraft would sometimes approach the carrier at a lower altitude than even the flight deck before pulling up briefly and practically stalling onto the deck, allowing for a lower speed landing. Similarly, the higher flight deck would give an extra couple of metres of acceleration if over-shooting the flight deck and having to go around. As such a high-decked carrier gave a little more margin for error.

Now

It makes virtually no difference - modern aircraft approach at the same angle and airspeed regardless of the height of the deck (within reason). They also perform approaches significantly more accurately. If anything, the higher deck could be considered a (very) slight disadvantage, as it may display a higher rolling moment than a low deck carrier. This is unlikely to cause any issues, however.


What is "established" on an RNAV approach?

NOTE: This answer is specific to the United States as the question uses an example approach procedure from an airport in the United States. Procedures may vary for other nations. Consult the respective Aeronautical Information Publication for specific guidance.

As long as you hear the magic words "cleared  approach," you can begin your descent as soon as you cross the IAF the first time (while beginning your teardrop maneuver) and continue to descend to the minimum altitude while in the circuit, which is at or above 2000 for this particular procedure.

Note that you MUST be on a published segment of the approach before making your descent, otherwise terrain clearance is not assured.

The controller will expect you to proceed from the IF to the FAF after the first circuit is complete (a course reversal maneuver, if executed counts as the first circuit). You must advise the controller if additional circuits are required in order to lose altitude. Also, if the controller clears you for a "straight-in" approach and doing so would result in an excessive descent rate, it is incumbent upon you as the pilot to advise the controller that you are unable.

Reference: FAA JO 7110-615, Approach Clearance


Can civilian aircraft fly through or land in restricted airspace in an emergency?

FAR 91.3 states that any pilot in command may deviate from any regulation or rules to the extent needed to deal with the emergency.  That includes entering restricted or prohibited airspace.

In the example that you suggested, yes you could do so and land at the Groom Lake flight test facility at KXTA, provided you could reach their controllers or contact Nellis Approach Control declaring an emergency.  I will say that if you do enter R-4808 N and land there, don't expect them to roll out the welcome mat.  You will be immediately met by USAF Military Police who will arrest you, most likely at gunpoint, and spend several hours, if not days, there or outside the compound being extensively questioned by Air Force Security personnel, the FBI and Homeland Security.  Your aircraft will be impounded and inspected, possible indefinitely, and search warrants issued for your property.  If they find out that you faked an emergency to enter that compound, you are in very serious trouble and face a variety of federal charges including trespass upon a classified installation and whatever else the DoJ can throw at you.

In addition, you would need a very, very good reason to even be anywhere near Area 51, as it is in the middle of a military reservation geographically the size of the nation of Switzerland in the middle of south central Nevada.  There are no published routes over the airspace and all commercial and civilian traffic is kept far, far away.  Details about the airfield are not published on government aeronautical charts or regional A/FDs.  See the VFR sectionals and enroute charts below.

While Area 51 is a pretty extreme example, people have had emergencies and landed in military or other restricted facilities.  The usual response from the authorities is to detain and question you to determine what happened and inspect the aircraft to verify your story.  If it's a legitimate emergency, no harm is done and they will release you and the aircraft; the NTSB will file and incident report and that's it.


Critical altitude is the maximum altitude where the engine turbochargers (or turbonormalizers) can maintain sea level standard pressure to the engines. Above the critical altitude the engines will produce less power, although still delivering more power than an normally aspirated engine at the same air density.


What additional functionality is provided by the F-14 nose pitot, absent in early models?

The probe on the nose isn't a pitot tube (although it might looks like one).

That's an AoA sensor as explained here: Home of M.A.T.S. - Sensor Probes

Reported from the link above:

  Angle-of-Attack Nose Probe: The Angle-of-Attack (AOA) is an essential dimension since it measures the angle between the aircraft's vertical flight direction and the vertical wind direction. A too high AOA means that at a given speed the wings will fail to produce lift which will result in a loss of controllability and stability. This is especially important during the landing phase where the aircraft is fairly slow approaching the carrier and also during air combat maneuvering where a loss of controllability can be deadly.
   Each AOA probe measures the pressure at several points and then the AOA is calculated. Usually, several AOA probes are installed to measure a correct AOA.
   Note that this probe was not installed on very early F-14As

The same site, on a related page, report what you've alredy found:

  The first fleet Tomcats were not equipped with any nose probe, but todays F-14s carry a small nose probe to gather air pressure data to calculate the angle-of-attack


Why weren't the rotor tips of the Djinn directly fed from the turbine's exhaust?

The soot in the burned exhaust will eventually clog the ducting. The higher temperature will deform the rotor, or tougher heavier materials will be needed.

The stream of a  high BPR turbofan (ignoring the size) when channeled into narrow ducts will raise the stream velocity, but lower its pressure, which will be an overkill in terms of thrust needed.

Therefore "slightly warm" clean air is best.


How does the rotor blade material affect aircraft performance?

The Hot and High conditions refer to the worst atmospherical conditions for the performance of an aero-engine in general. This is due to two phenomena:

HOT: When the outside temperature is high, on one hand, the pressure decreases (due to the decrease of density of the air) and thus the mass flow rate and thus the power decreases (the power is proportional to the mass flow rate). On the other hand, the ratio TIT/Ta (Turbine Inlet Temperature of the atmospheric temperature) will also decrease. This will lead to a reduction of P and to a reduction of the effective efficiency (the power and the effective efficiency are proportional to this ratio), the result is also an increase off the specific fuel consumption (SFC).
HIGH: At high altitude, the pressure decreases and thus the density and the mass flow rate. The power will then decrease (as above for the HIGH condition) and the SFC will increase.

What are your options then ? Well, you can put a more powerful engine to compensate for these conditions but you will most probably increase the weight and the fuel consumption a lot (and the cost for sure). You can use the same engine but at a higher regime, but again, you will consume a lot which is not ideal. But there is another solution: you can make your helicopter or aircraft lighter. This whey, you need less power. And that's what brings composites in general; an important gain of weight.

Hope it helps !


Are Transponder Mode A and C still in use?

Yes. According to Title 14 CFR §91.215   ATC transponder and altitude reporting equipment and use.

Specifically:

  (a) All airspace: U.S.-registered civil aircraft. For operations not
  conducted under part  121 or 135 of this chapter, ATC transponder
  equipment installed must meet the performance and environmental
  requirements of any class of TSO-C74b (Mode A) or any class of
  TSO-C74c (Mode A with altitude reporting capability) as appropriate,
  or the appropriate class of TSO-C112 (Mode S).

the use of Mode A or Mode C (e.g.: Mode A with altitude reporting capability) is acceptable for flight under Part 91. That covers all of general aviation (GA), of which a large percentage use Mode A/C transponders.

With the upcoming ADS-B mandate, many GA operators are switching to Mode S to get the 1090 MHz ES ADS-B.  But others are keeping the Mode A/C and adding a 978 MHz UAT to meet the ADS-B requirement. In any case, there are still a large number of Mode A/C transponders in use and likely will be the case for quite a while.

Mode S is optional and only required for operations under Parts 121 (Air Carriers) and 135 (Air Taxi).

For Part 121, a Mode S transponder is required by §121.356   Collision avoidance system.

For Part 135, Mode S is required by §135.143   General requirements.


What is the ambient temperature used in RTCA/DO 160?

Ambient is the conditions in the test lab.  DO-160 defines it in sec 3.5:

  3.5 Ambient Conditions

  Unless otherwise specified, all tests shall be made within the
  following ambient conditions:

  a. Temperature: +15 to +35 degrees Celsius.

  b. Relative Humidity: Not greater than 85 percent.

  c. Ambient Pressure: 84 to 107 kPa (equivalent to +5,000 to -1,500 fi)
  (+1525 to -460 m).

  When tests are conducted at ambient conditions that differ from the
  above values, the actual conditions shall be recorded.

So anything within this range is acceptable and if it isn't within the range, just document what it is.

You'll also note that in each of the temperature profiles, the test starts at ambient at T0 and shifts to the first controlled test temp at T1. DO-160 includes the following Note as the time to transition from ambient to the test temp will vary:

  1) Temperature rate from T0 to T1 is not specified.

You have to remember that DO-160 is about testing extremes. If the equipment can't operate at any point in the ambient range, it's unlikely to operate at the extremes.

BTW, the latest version of DO-160 is rev G.  You should use it for new products.  Using rev D would only be appropriate for re-testing of a product originally developed to DO-160D.


How many staff are needed to support aviation on an aircraft carrier?

The ship's complement for a Nimitz class carrier is 3200. That is the crew required to maintain ship operations.

A further 2480 crew comprise the Air Wing - everyone needed to perform duties directly associated with flying activities, including maintenance, ordnance handling, emergencies, etc. It's treated as a separate entity because any one of ten Air Wings could be embarked on a carrier at any given time.

That is a total crew of 5680.

I couldn't find a breakdown of specific trades or ranks for either entity.

Source: Wikipedia

Note that the newer Gerald R. Ford class carriers make extensive use of automation, and so have several hundred fewer crew members in the ship's complement.


Is co-flow jet wing technology workable?

Amazing! British pioneer JW Dunne proposed this as a propulsion system around 1901 but Sir Hiram Maxim told him it would not work. (ref. unpublished documents in the Science Museum Archive's Dunne collection). Nine years later Henri Coanda built a ducted "jet" plane on broadly similar principles, which failed miserably (The Wikipedia article is not very good, but I know of none better online). But they all failed to understand the opportunities for suction lift, instead trying to exploit it to entrain a greater volume of air and create thrust.
More modern blown-wing systems have tried to improve on suction lift using similar methods, but have always foundered on the power requirements for the blower and structural weight penalties of all that wing ducting.
Here is a PDF from their web site. It appears to achieve high lift/STOL performance through high AoA and the Coanda effect, basically turning itself into a giant blown flap. Alternatively it provides modest forward thrust by stimulating circulation and thus maintaining lift at a slight negative AoA.
Well, it probably does work - see wind tunnel images - but I would also want to see those wing weights, blower power figures and cost-benefit analyses before believing it is any more practicable than yesterday's approach.


Can a lightning strike lead to structural damages of the fuselage and eventually cause decompression?

Decompression is a tricky thing.  The aircraft is already quite "leaky" and without a steady flow of pressurized air from the engine bleed air (or compressors, in the case of the 787) the altitude in the cabin will rise slowly. There is a pressure controlled outflow valve in the back of the aircraft that is usually about 10-20cm square. The pressurization system stuffs air in constantly, and the outflow valve opens and closes to keep the interior pressure at the correct altitude.  Any hole smaller than the amount of air the pressurization system can pump in will just be handled by the outflow valve closing somewhat.  Depressurization due to structural failure is fairly rare.  Most recent would be Southwest 1380, where an uncontained engine failure broke a window.

I have not heard of a lightning strike even piercing the aircraft fuselage in modern civilian aircraft, much less in the cabin area.  There are a few cases I have heard of it happening to military aircraft, and in those the hole was fairly small (about 2-5cm in diameter).  Aircraft are regularly hit by lightning, and extensive testing is done to simulate lightning strikes before an aircraft can be certified.


Why is this missile positioned in this odd position? How can it be launched correctly?

You're seeing the Sidewinder on the folded up wingtip of the F-18 that is in the foreground out of frame except for its wing tip and missile sticking up at the bottom.  The airplane is between the camera and the adjacent F-18 who's canopy is visible.  The long lens being used foreshortens and compresses everything distance wise so it looks like the missile is 6 inches from the canopy when it's actually probably 20-30 ft closer to the camera.


Did the Douglas SBD Dauntless have a second set of controls?

The Dauntless did have controls for the rear gunner- a pair of permanently attached rudder pedals and a control stick that was stowed away on the port side until needed. See:

https://www.tapatalk.com/groups/warships1discussionboards/sbd-dauntless-flyable-from-rear-cockpit-t2435.html

Juan Jimenez is correct that it would be very difficult to operate, what with the armour plate for the pilot and the radios right in front of the gunner. See here for a story of flying a veteran Dauntless where the pilot gets a brief familiarisation flight from the gunner's seat (it's mentioned in the fourth paragraph after "SBD Glider: Engine Out"):

https://www.aopa.org/news-and-media/all-news/2011/january/pilot/flying-a-national-treasure-the-sbd-dauntless

You can see the gunner's control view at the Smithsonian's walk-around view of the Dauntless, it's images four and seven in the collection (six shows the pilot's view and eight the gunner's real place of business):

https://airandspace.si.edu/collection-objects/douglas-sbd-6-dauntless

Photo seven


How do Flight Test Engineers plan and execute sortie profiles?

Three main factors influence the flow of a flight test sortie: data requirements, test point priority and flight efficiency.  For example, consider a test sortie that requires evaluation of stall handling qualities.

Data requirements specify which altitude, weight and cg, and configuration are required for each stall test point, for example.
Test point priority comes from the test team or test plan. One test point may be more important than others.
Flight efficiency refers to the need to minimize time between test points, minimize wasted fuel, and consider geographic position or airspace boundaries that may affect the test.

Balancing all of these things requires experience and judgment.  At the beginning of the flight, the aircraft is heaviest, so it makes sense to do test points that require heavy weight.  The second most important thing is to consider high priority test points. What points of high priority combined with heavy weight should be considered.  Finally, deciding the flight path that accommodates these two characteristics is the last factor.

This combination of judgment and knowledge and skill is difficult to describe accurately, and often two experienced professionals will come up with different, and equally acceptable, answers.


How do small unmanned fixed wing aircraft protect themselves against lightning strikes?

You design your structure, as in larger aircraft, considering where the strike could potentially hit first, and where it would leave.

The rest is electrically bonding everything together, and creating a continuous electrical route from each entry point throughout the structure to the potential exit zones.

Calculating or measuring the electrical resistance throughout the paths is the way to quantify the effectiveness of the design. If it’s zero, the lightning would not hit this aircraft (or would pass through it without causing any harm). However, this conflicts with the scenario of triggering lightning strikes.

To attract lightning, you can simply put a sharp, massive metallic pole, in electrically isolated from the rest of the fuselage.


What airfoil design does the MQ-9 Reaper UAV use?

The wing root of the General Atomics RQ-9 is the Drela GW-19/GW-25.

The wing tip airfoil is the Drela GW-27.

Because of their application, you will likely have difficulty finding study results of vortex generators used on that blended airfoil. There are papers, but I have only seen them in the DTIC library, and I do not recall the classification of them. However, the aircraft has been exported, so you may find some open literature on the airfoil, and the adaptations and optimization of it.


What factors are considered when a runway is planned?

First, wind rose data, unless you built the airport in the early 20th century without weather data.

By BREEZE Software (http://www.breeze-software.com/) [GFDL or CC-BY-SA-3.0], via Wikimedia Commons

It's nice to check old airports and see how they evolved over time. In the past they usually built three runways, each separated by 60 degrees in direction, to cover the compass. Over time some are lengthened, others demolished, more are added in the favorable direction, and so on. Nice example is KORD if you want to hunt the history on your own.

Example of runway closure: Why did the north / south runways close at Daugherty Field (KLGB)?

For a commercial airport expecting long haul jets, you need a long runway, to bring down civil works cost you need to find a place with a relatively flat terrain that would house said long runway.

Airport's elevation also plays a factor to runway length. The higher the airport, the longer the runways need to be. Surrounding terrain also is important. Unless you can build an island: VHHH.

For sun direction, engineers recommend Ray Bans, since the Earth spins.


It didn't directly lead to the tail separating. What separated wasn't just the de-ice boot, it was the whole leading edge on the left stabilizer. That caused a stall of the left horizontal stabilizer and an increase in drag on the left side. The wings of an aircraft have a tendency to pitch the aircraft down (as they're behind the center of gravity and provide a force upwards), while the stabilizer produces a force downwards to keep the plane's pitch stable. With the loss of lift on the left stabilizer, there was less downforce (leading to a pitch down), more downforce on the right than on the left (leading to a right roll), and more drag on the left than the right (leading to left yaw).

These rather violent motions led to massive aerodynamic loads on the plane, resulting in the next failure: the left wing. When this failed, the plane violently rolled right, for reasons I'm not quite sure of (I get violently rolling, but am unsure why it was to the right). This roll stressed the plane even more, and that is when the tail ripped off the plane. The direct cause was extreme aerodynamic forces caused by the flight path, not the leading edge separation itself.


Is it possible to convert a passenger A380 to carry cargo?

Airbus originally planned on a freighter version and UPS and FedEx both ordered some of them. Production delays with the passenger version resulted in the freighter version being delayed and both of them canceling their orders.

The main issue why there is no freighter version is that the internal volume of the aircraft is too large to make it economical for cargo operations. I.e. the density of the cargo generally is too high to take advantage of the full internal volume before hitting the aircraft's maximum take-off weight. As a result, you end up hauling a whole lot of "extra airplane" around. The only time that extra volume is useful is for really low-density cargo loads.

That extra internal volume is useful if you have to move a large number of passengers into slot-constrained hub airport like London Heathrow or JFK but packages don't care much about personal space...

In words other than mine:

  An A380-F would be too fat to fly at a profit: The plane would hit the maximum payload (a constraint of weight) before its maximum cubic space (a constraint of volume). Its design can’t support the maximum payload required to generate a profit.

Here are some good other more in-depth analyses.

Something that was surprising to me initially was the amount of modifications that are necessary to convert a passenger aircraft to a cargo aircraft. This paper from a Bedeck Aviation Group (Boeing affiliated passenger to cargo conversion house) provides a good breakdown of the steps required for a 767 conversion. This video from Boeing provides a good visual summary as well (music and hair styles are an added bonus).


The ARTCC Controller is telling a flight crew currently descending to descend to FL150 at their current rate of descent e.g. 2000 fpm, etc. either to expedite their current descent or the controller is satisfied with the current rate of descent to traffic separation and flow into the terminal area where the flight will be landing.


What is the minimum speed a glider can thermal at?

I do a lot of soaring and you thermal at min sink +/-, which is normally just few knots above stall, around 1.1 Vs.  The slower you can go the better (smaller circle) and sometimes going below min sink is worthwhile if it lets you core the thermal better, but your ability to do this can be limited by the glider's particular stall characteristics and your own flying skills.

On gliders with docile stall behaviour you can pretty much circle on the edge of the stall buffet.  A glider that breaks sharply with not a lot of warning, and wants to roll off, you need to leave more margin lest you enter a spin while above someone else and you might thermal at min sink or a little above.

The Schweizer 1-26 has very docile stall behaviour with a very strong pre-stall buffet that starts well before the stall break, and you can thermal a 1-26 right in the buffet range, shuddering and shaking as you go around.

BTW the best thermals come from lighter brown fields, that are dry.  Moisture in the ground makes it store heat and this tends to move the thermal activity to later in the day, and makes it milder.  Spring time after a very dry winter with little residual snow cover to moisten the earth when it melts will yield boomer conditions on good soaring days.


Can a person with unilateral anosmia in the right nostril become a commercial pilot with a class I medical?

We aren't medical professionals here, and no Aviation Medical Examiner (AME) posts on this board as far as we know.
The best answer is to schedule an appointment with an AME and have him review your case. If the answer is "yes" you can get the medical, this is a cost you'll be paying anyway (and I'd suspect that is the answer you're likely to get). If the answer is "no," better to get it from an authority, rather than an internet message board.
AOPA can help you locate an AME who specializes in "interesting" cases, some of whom may well be able to review everything over a phone call or video chat, at least to the point of recommending your best course of action.
Go with an AME's answer, rather than ours. Best of luck to you!


What is the true meaning of the word “wilco” when used on the radio? What is its origin?

"Wilco" is short for the phrase "will comply," meaning that the speaker will follow the instructions to which they are replying. Merriam-Webster places the origin at 1938, some time after the invention of radio, likely in military usage.

Although the phrase "roger wilco" is sometimes used, it is considered redundant since the "roger" (meaning "received and understood") is implied.


Are NATO fly-by-wire fighters designed to feel like F-14 Tomcats?

Most decidedly not, at least not for the first fly-by-wire fighter in the NATO arsenal, the F-16. Its stick, in initial block versions, did not move at all, instead using piezoelectric load cells to detect stick pressure. This caused some issues with novice Viper drivers overreacting to the stiffness of the controls compared to anything they had flown and overrotating the jet on takeoff, smacking the turkey feathers on the ground. Later blocks put a little play in the stick.

As far as the Tomcat being an easy plane to fly, Top Gun kind of over-romanticized it. The TF30 engine initially put into these aircraft was underpowered and terribly unreliable (one thing the movie did get right is that the engines were prone to compressor stalls when encountering disturbed air such as jetwash or even their own missile launch trails). The aircraft itself, while a big improvement in dogfighting over the F-4, was still big and heavy, the result of requirements that it be a long-range supersonic interceptor in an era without supercruise or the relatively light AMRAAM missile; the aircraft instead had to be able to haul a full load of AIM-54 Phoenix missiles intended for the ill-fated naval variant of the F-111, along with the large, complex radar system to lock on and fire them, and a boatload of fuel to get all that out to patrol range and back.

The Navy's initial mixed results with the F-14A, along with the extremely high costs of the aircraft ($32 million each at the height of production) and the lack of ground attack capabilities, were mirrored in the USAF with its F-15 program; the looming retirement of the F-4 was about to leave both branches without a fighter capable of the Phantom's multi-mission capability, and both the F-14 and F-15 were big expensive interceptor-style pure air-to-air fighters, which some Air Force brass believed was proof that nothing had been learned from Vietnam. The USAF commissioned the Light Weight Fighter competition, which produced the F-16, a light, relatively inexpensive multirole fighter that has become one of the most successful land-based fighter jets in history. The Navy preferred some traits in the USAF's losing aircraft, the YF-17, such as the twin-engine design for durability, and it would go on to develop this design into one of the most successful naval aircraft of all time, the F/A-18 Hornet and Super Hornet.

The Tomcat eventually lived up to its promises with some engine and avionics upgrades (including a hybrid-FBW system and a LANTIRN pod to add air to ground smart bomb capabilities) but the aircraft was by no means a perfect plane or a dream to fly.


Is the physical MAX8 design bad because software is required for the aircraft to stay airborne?

Just to address a misconception

alone, unpowered, the craft is not 'aerodynamically stable'.

I don't believe this is true.

Unpowered
The problem addressed by MCAS is not specifically unpowered flight but flight when the aircraft has a high angle of attack. Because of the need to mount the wider engines further forward to maintain ground clearance, there is a tendency for the engine housing to cause additional aerodynamic forces that rotate the aircraft in the pitch axis - these forces tend to push the nose up. The forces are higher than on prior 737s.

By "unpowered" you might be thinking more of electrical power than engine power. The two are usually related. However any aircraft like the 737 has multiple electric power generators, if the generators on both main engines fail, there is a Auxiliary Power Unit (APU) that can provide electrical power. If both engines and the APU fail, many aircraft have a ram air turbine (RAT) that deploys to produce hydraulic and/or electric power. If both engines, the APU and the RAT fail, there are batteries that provide enough power for minimal necessary controls for a short while, maybe of the order of 30 mins.
I don't know about the 737, but the 30-year-old A320 family of fly-by-wire aircraft has a mechanical backup mode where the pilot can control the aircraft using purely mechanical means and non-electrical instruments. In 30 years I think the closest any aircraft has come to this was a 2005 A319 incident where the cockpit went dark and I believe the pilot flew for a while without any computerised aids, they quickly restored power and continued to their destination. I know of no reason to think the 737 is more dependent on computers for stable flight.
Even without any electrical power, an aircraft like the 737 ought to be no less "aerodynamically stable" than the earliest 737.

Aerodynamically stable
It is normal for aircraft trim to be adjusted during various phases of a flight. The aircraft is still considered 'aerodynamically stable'. When commencing an unpowered glide, the pilots would likely adjust trim. This applies to almost all aircraft.
It is normal that an aircraft in flight, without manual control inputs and without automated inputs from an autopilot etc, can exhibit undesirable flight characteristics such as a phugoid cycle. An aircraft with this sort of behaviour is normally regarded as aerodynamically stable.
I have not read anything to suggest the 737 NG or MAX series are inherently unstable. Even in an unpowered glide.
So far as I know, the only aircraft that are deliberately made inherently unstable are high-agility fighter aircraft.

Maneuvering Characteristics
MCAS stands for Maneuvering Charactersitics Augmentation System. From what I've read, a large part of the motivation for it was to make the aircraft controls feel the same as an older generation 737 - hence the name. Boeing felt that a pilot getting out of an older 737 could get into a 737-MAX and use & experience the same forces on the control yoke as before when climbing out after take off etc.

Related:

How are fly-by-wire airliners controlled in case of complete electrical failure?

Can large airliners such as a 747 maneuver without electricity?

What went wrong inside Boeing's cockpit?, BBC, 17 May 2019


Does "cleared into the Bravo at 3500" mean I must wait until I hit 3500 before entering it?

On one hand, they know my heading and altitude, so I assume that I should continue straight on, entering the Class B in my climb and level out at 3500 feet, which I have done often with no consequences.

This is what the controller wants you to do.  It's slightly sloppy phraseology - "Cleared into Bravo, climb and maintain 3500" would be better.  But what she said is not really ambiguous in any practical way.  She would definitely not be expecting you to turn away, then climb, then turn back toward the B.


Why is it necessary to fly in visual conditions to certain unmanned airstrips?

Two reasons:

1) It takes time and money to create an instrument approach procedure, and possibly not enough people have requested that one has been created.

2) A certain amount of obstacle clearance is required, if for some reason the required safety cannot be guaranteed using instruments, the FAA can simply not create a IFR approach


Would titanium be a better option for aircraft skin if cost were not a factor?

even assuming price would not be an issue, formability certainly would be. Ti is much harder to bend, drill and cut than Al so building a plane out of cheap Ti would significantly increase its manufacturing costs over Al. Ti retains its strength at high temperatures far better than Al but in subsonic aircraft like passenger planes, airframe heating is not a design limiter that would drive a choice between selecting Ti or Al.


Is it possible to build a flight-capable aircraft powered by compressed gas?

In aircraft design, the main problem is energy density of the energy source. Even with the phenomenally high energy density of kerosene fuels (>42 MJ/kg), the fuel still represents a sizable chunk of the weight of an aircraft. For example, fueling an Airbus A330 will double its weight!
According to Wikipedia, compressed air has a practical energy density of about 0.1MJ/kg. There is no way you can offset the enormous amount of compressed air required by downsizing your engines. You would go from 110.000 kg of fuel to over 400 million kg of compressed air.
A more relatable example would be a Cessna 172. It can carry 212 litres of fuel, or about 150kg. On top of that, it can carry about 190kg of useful payload. If we instead use compressed gas, we would need over 60.000kg of compressed gas to get the same range.


Is it possible to hack an airplane while it's moving (in general)?

The answer to

  Is it possible to hack an airplane while it's moving?

is "theoretically yes, movement has no effect on a plane hackability".

  How can someone "touch" a moving airplane, have the time to identify it and then to hack it?

All the people inside the airplane are touching it during the whole flight, they know which airplane they are flying with, and they have a flight worth of time.

  How can someone, without having specialized machines, can hack an airplane?

Theoretically, for some components, you don't need specialized machines (see below), you need a laptop and an ethernet cable

see here (TL;DR version ), or here, and finally, from here

  First, the airplanes. The problem the GAO identifies is one computer security experts have talked about for years. Newer planes such as the Boeing 787 Dreamliner and the Airbus A350 and A380 have a single network that is used both by pilots to fly the plane and passengers for their Wi-Fi connections. The risk is that a hacker sitting in the back of the plane, or even one on the ground, could use the Wi-Fi connection to hack into the avionics and then remotely fly the plane.

  The report doesn't explain how someone could do this, and there are currently no known vulnerabilities that a hacker could exploit. But all systems are vulnerable--we simply don't have the engineering expertise to design and build perfectly secure computers and networks--so of course we believe this kind of attack is theoretically possible.

As we read here, though, safety critical components are not that easy to compromise:

  it’s essential to understand that aircraft systems can’t be updated in-flight or on the fly. This means that if an attacker is seated on the airplane, there’s no way they could modify systems. There are only three ways to update a system on a modern aircraft:
  1. Take the hardware off the aircraft and return it to the manufacturer for a factory performed update.
  2. Some larger airlines have their own maintenance organizations with the required specialized equipment to perform a bench update of a particular system using a portable data loader (PDL) or some other type of specialized data-loader.
  3. On-wing update [...] Specialized hardware (physical switch(es)) must be set, to place the IMA and relevant systems in maintenance mode. Once the aircraft systems are in maintenance mode, a maintenance engineer needs to follow a sequence of steps to push the update to the target system. The concept of an automatic update does not exist for any safety-critical system.

So, to summarize: yes, researchers have identified non-critical systems that could be hacked (as the passenger entertainment devices), but so far nobody has demonstrated the feasibility of hacking a critical system