Yes, that is correct procedure, except that if you're flying an instrument approach, switching to destination altimeter should be part of your approach setup "chart briefing" (which likely happens before you get handed off to the tower).

From AIM 7-2-2(a)(1) (emphasis mine):

  [Set the altimeter] to the current reported altimeter setting of a station along the route and within 100 NM of the aircraft, or if there is no station within this area, the current reported altimeter setting of an appropriate available station. When an aircraft is en route on an instrument flight plan, air traffic controllers will furnish this information to the pilot at least once while the aircraft is in the controllers area of jurisdiction. In the case of an aircraft not equipped with a radio, set to the elevation of the departure airport or use an appropriate altimeter setting available prior to departure.

Unfortunately the AIM text doesn't directly address destination altimeter settings, but section 4-1-8 alludes to the fact that controllers must verify you have the best destination altimeter setting, either by telling you or by having you report that you have the current ATIS or the AWOS/ASOS broadcast ("the numbers" for the latter):

  a. Numerous approach control facilities have established programs for arriving VFR aircraft to contact approach control for landing information. This information includes: wind, runway, and altimeter setting at the airport of intended landing. This information may be omitted if contained in the Automatic Terminal Information Service (ATIS) broadcast and the pilot states the appropriate ATIS code.

  b. Such information will be furnished upon initial contact with concerned approach control facility. The pilot will be requested to change to the tower frequency at a predetermined time or point, to receive further landing information.

For instrument approaches under IFR, setting and checking the altimeter to the destination's setting should be part of your approach briefing checklist. My personal "checklist" includes the altimeter setting as part of the weather information when I get to the bottom of the chart and check ATIS/ASOS/AWOS numbers against the approach minimums.

Interestly enough, the FAA's Instrument Flying Handbook doesn't have much to say on altimeter settings at all (except for mentioning that keeping the setting up to date is important and that bad things can happen if you don't).


Is it possible to drive a prop directly from a jet engine without a gearbox?

As a side comment, there is a type of engine researched in the 80's/90's, but never marketed, where an unducted fan is driven directly by the turbine shaft without a gearbox: The propfan. It's close to your idea, albeit the unducted fan is not exactly a propeller. Safran has restarted researching on this design, end of 2017, for an operational use after 2030.

Two counter-rotating unducted fans on a free turbine engine (source)

Having discarded the propfan, let's go to the actual answer!

Short answer

A propeller rotational speed doesn't exceed 1,000 or 1,500 RPM (it depends on its size too). The slowest shaft of a jet engine spins in the range of 5,000 to 15,000 RPM, sometimes more. A reduction gear is used to compensate for the difference.

A fan may spin at 5,000 RPM, however the use of a reduction gear is also desirable, though it is often avoided by limiting the speed of the core, at the expense of a loss of efficiency. New aircraft like the A320 NEO can be fitted with geared turbofan engines, for better performance.

The reason the turbine cannot spin at a lower speed is that a low speed means low torque, a problem common to many air-breathing engines (maybe except the free turbine).

Dotted line: Theoretical torque at low speed. Plain: Actual torque. You may compare with trying to pull away in a hill in fourth gear.

Low torque also means increased spool up time, a drawbacks that is often a no-go factor.

Details

Jet engines must rotate at high speeds by principle, as a lot of air must be compressed to burn a lot of fuel in a small amount of time. On the other hand the fan or the propeller are more efficient at low RPM.

Let's see how engineers have dealt with these two opposite needs in different engine types.

Single-spool turbofan

The simplest design is the single spool engine (all discs rotating at the same speed). While this is possible, the output shaft is at a high rotational speed. This is usable for a fan which also rotates at high speed. The core compressor is not as efficient as it could if it rotated faster.

The Snecma M53-P2, used on the military jet Mirage 2000, has a rotational speed of 10,600 RPM.

Better efficiency can be achieved by increasing the compressor speed and reducing the speed of the fan. It requires the use of a distinct second spool.

Two-spool turbofan

Such configuration is used in many turbofans (Rolls-Royce being a notable exception with a third spool). A low-speed / low-pressure turbine drives the fan and usually the first stages of the compressor.

From this EASA certificate, the CFM56-7B used on all B737 NG has a maximum HP shaft speed of about 15,000 RPM and a LP shaft speed of about 5,400 RPM.

Increased efficiency needs to further increase the fan diameter but also to slow down the fan to keep the linear speed of the tips at a reasonable value. A slower fan will not be directly driven by the turbine.

Geared turbofan

Slowing the LP turbine adds complexity and also creates a problem: The output torque also decreases (which is a phenomena in all mechanical engines). This leads to increased reaction times after thrust requests, with also means less safe engines. A gearbox is used to prevent sacrificing the precious torque. This unusual configuration is an option on the A320 NEO.

PW1000G (formerly known as project GTF) has a HP shaft at 20,000 RPM, a LP shaft at 15,000 RPM, and the fan connected by a 3:1 reduction gearbox rotates at 5,000 RPM.

planetary reduction gearbox 3:1 (source)

If the altitude is sacrificed for other benefits and the engine is used in denser air, then a turbofan is not anymore an efficient solution.

Turboprop

When the fan is replaced by a plain old propeller working at a much slower rotational speed, the use of a speed reduction gearbox with a larger ratio is a required all the more for the same reasons.

The Dash 8 / Q400 which has STOL performances, is equipped with two PW150A turboprops. The PW150A is a two-spool core with a free power turbine (two discs not linked to the gas generation section). The free turbine allows for better propeller speed management, allowing an engine start with the propeller stopped.

From its EASA certificate, the HP shaft runs at 31,150 RPM, the LP shaft at 27,000 and the maximum output shaft speed doesn't exceed 1,020 RPM.

PW150A (source)
Note: this schematic is not accurate, but it illustrates the principle. Look with an accurate (but less readable) schematic of the engine sections.

Additional experimentation: Propfan

Interestingly there is an intermediate solution between the fan and the propeller: The unducted fan. It combines the advantages of a high rotational speed and the lack of duct, the drawback being the noise generated by unducted blades close to Mach 1 airflow at the tip.

Testing was conducted by several engine manufacturers but no engine was launched on the commercial market for reasons that appear to be non-technical. An example studied by GE and Nasa combined a double unducted fan (UDF) and a free turbine in a new type of engine known as propfan, in a pusher configuration.

(Source)

The two counter-rotating fans were mounted directly on the free turbine output shaft without a gearbox.


Does an instrument rating bridge category and class?

The Airman Certification Standards for the Airplane Instrument Rating shed light on this question. There are four classes of instrument rating for airplanes and that the tasks required for each class differ:

The abbreviation(s) within parentheses immediately following a Task
refer to the category and/or class airplane appropriate to that Task.
The meaning of each abbreviation is as follows:
ASEL: Airplane – Single-Engine Land
ASES: Airplane – Single-Engine Sea
AMEL: Airplane – Multiengine Land
AMES: Airplane – Multiengine Sea
Note: When administering a test based on this ACS, the Tasks
appropriate to the class airplane (ASEL, ASES, AMEL, or AMES) used for
the test must be included in the plan of action. The absence of a
class indicates the Task is for all classes.

So your assumption is correct. You need an instrument rating in each class of airplane you wish to fly IFR. However, per §61.57 (c) (1) your   currency can be accomplished in different classes in the same category but you can’t mix and match categories e.g. 5 approaches in a SEL and 1 in a MEL is OK. 5 approaches in a SEL and 1 in a helicopter is not OK.


Where did the standard pressure 29.92" come from?

It is called "standard pressure" because 29.92 In-Hg (or 1013.25 hPa) is the standard atmospheric pressure at sea level according to both the ISA (International Standard Atmosphere) and the US 1976 Standard Atmosphere.

Below 18,000ft, local altimeter settings are used because you need to know how high you are above terrain, or whether or not you're at the proper altitude for an instrument approach, or at pattern altitude, etc. In cruising flight above 18,000ft, except for a few places in the world, you are well above any terrain, so errors in actual altitude of even a couple thousand feet is unlikely to cause a problem. In this case, having all airplanes use a common altimeter setting is useful because it 1. doesn't require you to change it frequently as you pass through changes in pressure, and 2. it helps ATC ensure separation without having to inform flights every 10 minutes of a new setting. It makes sense to use standard pressure in this case because it represents a good baseline average, and you may have noticed that reported altimeter settings tend to average around 29.92 anyway.

That being said, there are instances where you may still need to know the en-route altimeter settings for flight planning purposes. Suppose the minimum safe altitude along your route is 19,000 ft MSL and current pressure is 29.42. If you decided to cruise at FL190, you would actually be flying at about 18,500ft MSL, and would be below your minimum safe altitude. Colder than standard temperature can have similar effect as low pressure, and will result in the airplane being lower than the indicated altitude.


How to calculate the variation of Z force with elevator deflection (Zδe) in Nelson for pitching dynamics?

There are a couple ways you can estimate control derivatives ($C_{L_{\delta e}}$ is a control derivative). You can then transform the coefficient from stability-axis to body-axis for use in the state space equations of motion.

Elevator is basically a full-span or part-span plain flap. Knowing that, you have several tools at your disposal:

USAF DATCOM: It contains semi-analytical equations to estimate 2D flap lift increment, and corrections to 3D with aspect ratio and taper ratio. Not the easiest to read resource, but it is free and forms the backbone of many conceptual design software and books.
ESDU: Items 70011 and 74011 contains semi-empirical relationships for estimating full-span 3D flap control derivative. ESDU contains step-by-step examples and is the authoritative source for all things aerospace in conceptual design and validation. Unfortunately, it isn't free.

Before going further, I should mention that tail experiences downwash from the wing. So converting from the tail stability-axis to aircraft body-axis requires converting the total tail incidence angle ($\alpha_t = \alpha+i_t-\epsilon$). Of course, you'll need to find downwash itself, which would be the topic of another question.

Vortex-Lattice Method: AVL is a reliable and free VLM, and is the go-to tool for conceptual low subsonic aerodynamics. Good thing about it is you don't necessarily need to estimate downwash; it directly outputs the control derivatives in aircraft stability-axis.

For conventional layout, all three tools should give you similar answers. Otherwise, you may not know the true value until you have access to wind-tunnel.


How can I build the 40 hours instrument time required for an instrument rating?

The remainder of the 25 hours can be completed with a Safety Pilot, a CFI, or a CFII.

A safety pilot must be able to act as PIC of the aircraft you are flying. Also, if the safety pilot is acting/desinated as PIC, both you and the safety pilot can log PIC time for when you are flying under the hood. If you are acting as PIC, the safety pilot can log SIC time for being a required flight crew member (FAR61.51(f)).

You cannot file an IFR flight plan or fly in IMC unless a current Instrumented Rated pilot is on board and acts as PIC.


Is the aircraft neutral point a function of the tail incidence angle?

I have done some homework and I will explain why the Neutral point does not vary with the tail incidence angle.

The above equation is the fundamental equation defining the location of the neutral point.

We can see that the Neutral point is a function of the following factors only,

Aerodynamic centre
Tail volume (Horizontal tail sizing and Arm length)
Tail efficiency factor (Ratio of dynamic pressure at the tail and at the wing),
Lift curve slope for the wing and HT (CLalpha - which is fixed and not dependent on the tail incidence),
Downwash effect
Fuselage moment contribution

So none of these factors are dependent on the tail incidence angle and hence there musnt be a change at all. What shocked me the most is the fact that errors in variable quantites can be accounted for but errors in quantities that shouldnt vary is very confusing. It is a very standard statement that '' Static margin or ultimately the Cmalpha shouldnt get affected by the change in tail incidence''
This is the information I could get about it.


What are the recent developments in the satellite-based tracking of aircraft?

The German Space Agency (DLR) worked with ESA to track flights from space using ADS-B, the same technology behind flightaware etc.
Some info about it is here

A commercial entity, called Aireon, is planning a global constellation to monitor aircraft that will piggy-back upon the next generation of Iridium satellites. But, unfortunately, the recent setbacks to SpaceX launch capabilities have delayed Aireon's schedule. The first launch of the Iridium-NEXT satellites occurred on Jan 14th 2017 and the entire constellation - providing near global ADS-B coverage - is planned to be complete by mid-2018.

Aside from ADS-B, there is also research going on to track aircraft through their exhaust emissions (something I'm working on right now). Nothing is published about that yet, though.


How to identify an aircraft from its NC- N-number?

Single wing prop driven multi seat aircraft? Not sure what you mean by this. A quick search on the FAA registry indicates it's a Cessna 414A.

Also, the style of tail number with NC is older, Wikipedia has an explanation of the various styles of aircraft identifications.

  An older aircraft (registered before 31 December 1948) may have a second letter in its identifier, identifying the category of aircraft. This additional letter is not actually part of the aircraft identification (e.g. NC12345 is the same registration as N12345).

An older aircraft with the same N-number on the FAA registry is the BT-13.


How do cross-wind correction controls help while on the ground with wings level?

Your assumption is that the wings are level when both main wheels are on the ground. But this is not necessarily true. Even when both wheels are on the ground, the wings can still have a small tilt. The suspension of each gear works independent of the other, and the weight on the wheel determines how much the suspension compresses or the gear strut will bend. By deflecting the ailerons, you re-distribute the lift between the wings, and control gear compression.

Please note that with the ailerons level, your wing will create a sizable rolling moment in a crosswind, which means that the load distribution between the two main wheels is uneven without aileron correction. Also, the fuselage will create a side force of its own, and this force increases with speed as more of the flow around the fuselage will be attached.

The slight tilt angle of the wing also slightly tilts the lift vector, and this, together with the side force of the fuselage, creates the side force which causes the skidding when this side force is large in comparison with the low load on the wheels shortly before takeoff. You need to tilt the wing into the crosswind to create a counter-force which can compensate the side force of the fuselage, only then the whole aircraft will not experience a side force.

I know, the picture below shows a glider and not a Citabria, but the principle is the same. The high wing arrangement creates a sizable rolling moment even without dihedral.


Why does spoiler extension during touchdown cause a pitch up moment?

Pitch-up upon spoiler deployment would occur if the spoilers are positioned aft of the center of lift of the wing when in its landing configuration. In this case, the spoiler kills off lift on the aft portion of the wing while the leading side of the wing (in front of the spoilers) is still generating lift. The lift generated by the portion of the wing in front of the spoilers is then not balanced by lift generated by that portion of the wing behind the spoilers, producing a net upwards pitching moment.


Is high speed buffet possible at supersonic speed?

All pilots who transited into supersonic speed on older designs which were not perfected for transsonic flight reported that suddenly all that shaking and vibrating stopped and flight became smooth again as soon as they went over Mach 1.

So the answer is no. With supersonic speed the buffeting stops.


What is the lift-to-weight ratio during takeoff for an ultralight?

Your (lift to weight ratio) load factor is less then 1 during climb.

In a climb or descend only some of the weight is counterbalanced by lift, another part is counterbalanced by thrust. So lift is less then weight in a steady climb. (But Thrust is greater then drag) To calculate the exact Lift to weight ratio we will need more information.


What are the differences between direct law and mechanical back-up?

The key piece of knowledge to understand a FBW system is that you need to differentiate between signalling and actuation.
signalling is what tells the control surface to move and to what position. In old airplanes, this was by steel wires. In FBW airplanes it's by copper wires carrying an electrical signal.
actuation is what actually moves the controls surfaces to the commanded position, the muscles. Traditionally this is hydraulics, but you can also find electric actuators these days.
For the Airbus, Normal, Alternate & Direct all use electrical signalling (whether produced by computers or not). But what to do if there's no electrics? That's Mechanical backup, where you have steel-wire signalling of specific surfaces.


Which American twin tilt-rotor aircraft is this a scale-model of?

Looks like the Bell XV-3, "an American tiltrotor aircraft developed by Bell Helicopter for a joint research program between the United States Air Force and the United States Army in order to explore convertiplane technologies."


What are the issues involved in converting a quadjet into a twinjet?

Yes, you'll get a wing redesign to allow for the higher weight and thrust of the engines: the inboard engine mounts now need to be twice as strong.

You can also run into ground clearance issues. An engine twice as powerful is often also larger. Here's a GE 9X engine being tested on a Boeing 747. You can see it's pretty close to the ground, and needs a really short pylon.

Going from 4 to 2 engines also means replacing half the instruments in the cockpit. You could save a lot of weight by removing the wiring for the outer engines, but that'd be a major operation.

Historically, the advent of high-bypass engines coincided with the introduction of widebody aircraft for a huge increase in passenger capacity and efficiency. So e.g. Boeing could make more money by offering a new design instead of selling 2-engined 707s.

For the remaining 4-engined airliners (B747 and A380) no engine is powerful enough to allow a 2-engine conversion. An engine powerful enough would be even bigger than the GE 9x shown above, and would scrape the ground when installed on a 747.

Finally, I'll leave you with a response to footnote 1: The VC-10 was used to trial the RB.211 engine, which was 2x as powerful as the original Conways:


Why do children need to leave the plane during a refueling operation?

You can find interesting lectures about the refueling in a Airbus Flight Operation Briefing Note or in the CAP 748.

When they have children leave the plane, it is probably a company thing! There are no such rules that all passengers have to deboard a plane during refuel (with JetA and similar). But, as you can see in the Airbus FOPN, there are some requirements that need to be met. Each manufacturer as well as each company probably has its on way of interpreting  of the rules and regulations issued by the CAP and the FAA.

Summing up, it is basically by the pilots and therefore the company's discretion what to do with the passengers (or children) on board during refueling as long as saftey requirements are met!


How do you know the maximum load a control surface can withstand?

Elevator loads are the function of the design and flight envelope. Looks like a small plane, so look up for example CS-VA 391 (or the correct national code for your category) how to calculate the loads. Base air force distribution on the horizontal tail can usually be assumed to be triangular, and increment from control surface deflection need to be added, also usually approximated as a triangular distribution acting from the hinge line.


How can a Boeing 747 take off from Princess Juliana 7,546 ft runway?

(Source: Boeing)

The approx. 10,700 feet Wikipedia figure is for a fully loaded 747 at sea-level. The lighter the plane, the less runway it needs. The 7,500-foot runway at TNCM allows a takeoff at 84% of the maximum takeoff weight. (Not taking into account any climb restrictions, such as the big hill over there.)

And as Terry pointed out, "ambient temperature also enters in. The cooler the air is, the more you can lift." And vice versa for a hot day.


They're presently not in use.

The accident investigators don't generally clamor for them, since there are very few questions that they can't answer with FDR and CVR readouts, where a CIR would provide useful information.  The voices proposing them as a great idea tend to come from elsewhere -- from those who think they'd be a cool idea, but who don't fully understand the capabilities investigators already have.

Pilots are, understandably, averse to the idea -- working where your every word is recorded every minute of every day isn't thrilling, but the protections for CVR recordings are pretty strong, since only transcripts (not the actual audio itself), and transcripts edited down to relevant portions only, are all that can be released, and those only in case of accidents (at least in the USA).

Video isn't nearly so easily transcribed as audio, and any such description of moving images opens up far more possibility of subjective or dramatic interpretation of what's shown, and ample opportunity for YouTube "experts" to craft alternate - if wildly implausible - narratives. The idea of a public outcry, or an aggressive lawyer, demanding the release of the full video of a crew's last minutes, or hours, opens up the unsettling possibility that families may see a loved one's final moments in far more detail than simply transcribed words on a page.

And let's be honest, in a full day at work, who doesn't have moments that, edited down to a few out-of-context three-second clips, wouldn't paint a poor - if utterly inaccurate - picture of who you are and how you work?

Until and unless actual accident investigators build a persuasive case for the need for such technology in our cockpits, such devices are likely to remain in the realm of the hypothetical.  There is simply no evidence that they would do anything to make aviation any safer.


It comes from Q codes for morse communication. They where set up without a clear rhyme or reason that I can see besides being ordered alphabetically.


What are heat detection sensors and how can they cause a speed error?

It seems that the pilots didn't activate pitot tube heaters but the investigation is not completed yet.

"Pitot tube, also known as Pitot probe, is a flow measurement device used to measure fluid flow velocity."

So detection sensors in your question refer to pitot tubes and failure to turn on their heaters in icing conditions can cause incorrect airspeed indication. This in turn may lead to incorrect decisions from pilots or autopilot.


Does diving after a take-off help gaining altitude?

When an aircraft can barely climb after take-off, it may be flying on what is called 'the backside' of the power curve.

Flying at very low speed:

costs a lot of power because of high induced drag
means that the engines are inefficient because they are optimised for higher speeds.

As a result, the excess power available, that is the difference between the required power and the maximum available power, is very low when the aircraft flies close to the minimum flight speed. And the excess power is what is needed to climb the aircraft.

When the aircraft is flying below the speed at which the best angle of climb is achieved (Vx), it will be able to improve its climb angle by accelerating. To do so, the aircraft needs to use available power to accelerate, instead of using the power to climb.

Stopping the climb or even descending a bit will convert the available excess power and optionally height (potential energy) into speed. While this initially does not give extra clearance above the obstacle, the available excess power increases drastically. This in turn gives the ability to climb at a much steeper angle, allowing the aircraft to clear the obstacle.


Is "excess thrust" possible in a steady state vector diagram?

First, we must be clear on what exactly is "excess thrust". I will list two possible definitions, although many more may be possible.

Excess thrust is the component of the resultant force in the direction of the flight path. Using this definition, excess thrust and steady state flight are directly at odds (because any net force results in an acceleration). So in that case, no, excess thrust is not possible in steady state flight.
Excess thrust is thrust minus drag. It splits the big lumpy thing called 'thrust' in two numbers: one that is used to counter drag (which is always there), and another that can be used for useful things.

Since we already answered the first option, I will now produce the free-body diagrams for the second option.

On the left, we have level flight. We recognize the four fundamental forces of flight: lift (blue), weight (green), drag (red), thrust (orange). It is immediately clear that all forces cancel each other, and we will happily coast along.
In the middle, we have a steady state climb. All vectors, except the weight vector, are 'tilted' back and change magnitude. Lift has decreased slightly, and as a consequence, drag has also decreased minutely (although this doesn't really matter). The biggest change can be seen in thrust, which has almost doubled in magnitude!
On the right image, I have proven that despite all these changes, the net force is still zero. I have replaced the lift- and drag vector in purple by subtracting drag from thrust. But wait a second! That purple vector is exactly what I called 'excess thrust': thrust minus drag! So this purple vector gives us a nice indication of how much 'extra' thrust we are using to make sure the resultant force on the airplane is still zero.
The sometimes heard term, "max excess thrust available" is then an indication of how far we can 'tilt back' the blue lift vector. On the diagram on the right, it should be obvious that this 'stretches' the purple 'excess thrust' vector. Steepest climb is thus achieved when the excess thrust equals the max excess thrust available.
Glossary

Resultant force: also called net force. The sum of all forces that act on the aircraft.
Steady state flight: all acceleration (in Earth's reference frame) is zero. I.e., level flight, steady climb, steady descent. Due to $\vec{F}=m\vec{a}$, zero acceleration means zero resultant force.

Addendum I: From the comments, "A Piper Cub cannot take part of its thrust and apply it for lift." We see in the image above that sadly, that is exactly what a Piper Cub must be doing to climb at all. The excess thrust $T_e$ requirement $T_e = W \sin \beta$ with $W$ lift and $\beta$ the climb angle. If very little excess thrust is available, we had better keep $\beta$ small - exactly what you would expect for a little cub!
Addendum II: below, the same image but with excess thrust according to definition 1. The vectors are no longer a 'closed triangle', and the net force is not zero. The aircraft is now accelerating.

Images created using IPE.


What G forces does a pilot perceive in a "1 G" barrel roll?

You can't do a barrel roll at 1G.  It's a loop pulled out into a coil, and you have to pull pitch to get it started so you are going to be 1.5 to 2 starting out, declining to 1G to .5 at the top, and pulling 1.5 to 2 on the pullout.

So the sensation at the start is like a hard climbing turn (which is what you're doing), pressed into your seat with about the force of a steep turn at the start, declining to normal gravity or bit less (giving a bit of that giddy becoming weightless sensation, but not coming out of your seat) as you ease off the pitch coming around the top, and about the same pressed into the seat force as at the start, or a little more, on the pullout.

A good barrel roll should be no more than 2Gs peak, but how much is a function of pilot skill and of the airplane's ability to keep up the energy through the first half.  A jet with oodles of power to keep the speed up in the steep rolling climb can get away with a very gentle pull and will see only about 1.5 or less on the pull up and pull out.

But it's always going to be more than 1 starting out and finishing off and when Tex Johnston said in an interview it was a "1G maneuver", he really meant "not much more than" as in less than 2 (and no worse than a steep turn, unless you screw it up and fall out).  Watch the film of the barrel roll and you see a firm pull up at the start with a fairly steep nose down attitude on the exit, which would have required a pull of at least 1.5 G in returning to level flight without over speeding.


Is there any application where the crescent wing would be the best wing planform?

You are right, it helps to de-sweep the outer wing. The main advantages are (read this Flight article from 1965 here for a much more detailed explanation):

An identical critical Mach number over the whole span as sweep is reduced together with relative thickness.
A smooth cross-section distribution in the direction of flow which helps to reduce transsonic drag.
A tendency to pitch up in ground effect such that the wing will essentially land itself, especially when combined with a T-tail.

However, as long as wings are made of aluminum, the manufacturing effort is significantly higher.

The basic problem is the needed two-dimensional bending of the skin panels. Using a straight spar line and a straight leading edge requires bending only in one dimension, but when sweep changes, the skin panels would need to stretch in some corners while being bent. This requires much more expensive tooling, or a break in the structure which increases structural mass.

Even one composite wing I know of has a straight leading edge, even though the aircraft would have benefited from de-sweeping. Both the TKF-90 and the X-31, which were designed by the same people before, had reduced sweep on the outer wing, and for good reason. When the multinational project started and they talked to the BAe engineers, the British side insisted on a straight leading edge for easier manufacture, ignorant of the fact that using composites made their point moot. Yes, that was practically the same company that had built the Victor before.

Another disadvantage is the fact that any sweep change will convert bending moment into torsion. Normally, this reduces the incidence of the outer wing when a swept-back wing is bending under lift loads. De-sweeping the outer wing will introduce an uptwisting torsion which can cancel the torsion from sweep-back, and Handley Page claimed that the Victor wing was close to aero-isoclinic. However, this reduces flutter damping, resulting in a lower wing flutter speed (PDF!). If the wing's aspect ratio is low, this is manageable, but with higher aspect ratios the wing needs to be stiffened.

To answer your question directly: In the majority of cases it is aerodynamically advantageous to vary sweep with relative thickness, but it is not structurally and economically efficient. In the delta wings of combat aircraft which need to operate over a wide range of angles of attack, de-sweeping the outer wing produces indeed the best wing planform, even when economics is included.


Could adding a gearbox to the Trent 900 improve the efficiency of the A380?

It would not be a simple task to add a gearbox to an existing engine like the Trent 900. The whole engine is designed to operate as a whole, with each of the three shafts rotating at an optimal RPM. The gearbox would have to be designed to work with the existing engine hardware, which would mean compromises on efficiency. The engine would also have to be modified to find room to fit the gearbox in.

A gearbox also does not automatically mean an engine will be more efficient. The geared PW1000G achieves similar efficiency to the CFM LEAP which does not have a gearbox.

It's much more likely that a new engine would be designed for the A380. Airbus has previously said that this was planned for some point in the future. However, a new engine is not cheap for either the engine company to develop or for Airbus to integrate. The A330 and A320 programs have gone this route but they are also designs with high demand.

A new engine would have to generate enough demand to justify the cost, and it does not seem that Airbus sees this demand yet. Airbus has been struggling to find new orders for the A380 and has been slowing down production. It's not clear that better efficiency is enough to make the plane sell. Four engine planes are inherently limited in their efficiency versus twin engine planes. The four engines add more drag and weight versus two engines, and increase maintenance costs.

The A380 also requires special accommodation in the air and on the ground for its large size. The 747 has been around for much longer and does not need as many special accommodations. Boeing went to the expense of redesigning the wing and adding new engines for improved efficiency, yet is still struggling to find orders.

More recently Airbus has announced that they are considering "A380 plus" which will include new winglets, wing changes, and other design tweaks to improve efficiency. This will be a much cheaper way to add efficiency than a new engine, if that efficiency will mean more orders.


Where to find information on ILS categories at European airports?

The information you are after is, unfortunately, rather distributed.

Eurocontrol maintains a useful list of websites ordered by state, found here:

European AIS

Or by registering for an EAD Basic account you can access the European AIS Database in a more centralised and user friendly way, found here:

European AIS Database


Will Thrust on Rotor (Main) increase with altitude?

I presume that OP means torque on the rotor, since thrust must always compensate weight to maintain altitude. Thrust T, torque Q and power P equations for momentum theory in the hover:

$$T = C_T \cdot \rho A (\Omega R)^2$$

$$Q = C_Q \cdot \rho A (\Omega R)^2  R$$

$$P = C_P \cdot \rho A (\Omega R)^3$$

with $C_Q$ being identical to $C_P$.

At any altitude, thrust must equal weight. Air density $\rho$ decreases with increasing altitude, so $C_T$ must increase with increasing altitude which it does linearly.

Above graph from Leishman shows the relationship between $C_P$ and $C_T$, which can be approximated as:

$$C_P = \frac{\kappa \cdot {C_T}^{3/2}}{\sqrt{2}} + \frac{\sigma \cdot {C_D}_0}{8}$$

with $\kappa$ = loss factor and $\sigma$ = blade solidity.

So power required increases with $T^{3/2}$, and therefore increases with increasing altitude. Since $C_P$ = $C_Q$, torque does as well. Note that the weight at altitude has decreased due to the fuel burn required to reach higher altitude, which will compensate some of the additional torque required.


Why does carburetor icing require manual attention by the pilot?

Not every motorized engine is the same: For example, you would be hard-pressed to find a carbureted car these days.

The most similar kind of land-vehicle engine you'll find would be a motorcycle engine, and those do in fact suffer from carburetor ice:
- A discussion of carb icing on the Ninja 250
- A thread about carb ice on Bike Talk Forums

Older cars with carburetors were also susceptible to carburetor ice, and eventually included measures to avoid or mitigate it.
This could include passive changes such as mounting the carburetor in a warm part of the engine compartment (usually above the block, in a downdraft configuration), semi-active changes like "heat risers" which would feed warm air into the intake (usually behind the throttle plate, but occasionally in front of it), or fully-active systems like automatic "heat flaps" and "Time/Temperature switches" which do the same thing as the carburetor heat control in an airplane but without the driver's input or control.

These systems aren't usually fitted to aircraft as they add both weight and complexity, and can come with their own disadvantages (such as reduced power if the carburetor heat flap is in the "on" (heating) position during takeoff or on a go-around).

So why don't we hear about ground vehicles suffering from carburetor ice as much? Three main reasons:

Carburetor ice is most likely to form at low power settings.
Your car or motorcycle probably doesn't spend much time at or near idle power unless you're stuck in traffic: A few seconds coasting to a stop and then you accelerate away again.
Carburetor ice is less dangerous when you're on the ground.
One of the most common times you'll have a carburetor ice problem is during an approach/landing, with the engine at or near idle power for an extended period of time (this is why many aircraft call for carb heat during landing). Having your engine die at this point is a pretty serious problem, especially if you need to execute a go-around.
The analog in a car or motorcycle is having your engine stall after spending an extended period idling (standing or stopped in traffic). Having your engine die when you try to accelerate away is inconvenient and will probably make other drivers honk their horns at you and say unkind things, but it's unlikely to kill you.
There's nothing the driver can do about it.
A driver doesn't usually have a "carburetor heat" handle to pull (except possibly in very old cars), so you can't turn around and say "Your engine stalled because you didn't do this." On top of that because the problem is usually more inconvenient than dangerous on the ground it's not likely to make news: "Driver had to sit on shoulder for 30 minutes while their carburetor thawed out. Hundreds inconvenienced by rubbernecking traffic." is simply not as newsworthy as "Airplane crashed!"


What is the lowest RNP approach requirement without being RNP AR?

In ICAO DOC 9905 (Required Navigation Performance Authorization Required Procedure Design Manual) you can find the following definition in Chapter 2.1

  RNP APCH versus RNP AR APCH

  2.1.1 RNP APCH is defined as an RNP approach procedure that requires a lateral TSE of +/-1 NM in the initial,
  intermediate and missed approach segments (MAS) and a lateral TSE of ±0.3 NM in the FAS. Guidance on
  implementing RNP APCH operations can be found in the PBN Manual, Volume II, Chapter 5, Implementing RNP APCH.

  2.1.2 RNP AR APCH is defined as an RNP approach procedure that requires a lateral TSE as low as ±0.1 NM
  on any segment of the approach procedure. RNP AR APCH procedures also require that a specific vertical accuracy be
  maintained as detailed in the PBN Manual, Volume II, Part B, Chapter 6. The datum crossing point (DCP) for RNP AR
  procedures is the point located above the landing threshold point (LTP) or the fictitious threshold point (FTP). The RNP
  AR APCH criteria apply only to those aircraft and operators complying with specified additional certification, approval
  and training requirements. RNP AR APCH procedures are only published where significant operational advantages can
  be achieved while preserving or improving safety of operation. The RNP AR certification and approval requirements are
  contained in the PBN Manual. For the purposes of applying the criteria contained in this manual, RNP AR procedure
  obstacle protection is associated with RNP navigation accuracy requirements. The RNP navigation accuracy
  requirement is used to determine the area semi-width value (in NM) of a protection area associated with a segment of an
  instrument procedure.

So, yes, any procedure below the 1.0/0.3 NM standard is defined as RNP AR.

You will not normally find curved segments (RF turns) on an RNP APCH chart, as these segments require a recent FMS as noted in ICAO DOC 8168 Vol. II Part III Appendix to Chapter 5.

  Note 5.— RF may only be used for RNP procedures flown by aircraft equipped with systems that are compatible with ARINC 424-17, or later.

In those cases the chart will be promulgated with RF required.


Does a type rating give a person the privileges of an instrument rating in any category or class of aircraft which he/she is certificated in?

61.63(d)(1) requires that if you don't have an ATP that you hold an instrument rating to obtain a type rating. The type rating itself does not grant instrument privileges.

(d) Additional aircraft type rating. Except as provided under paragraph (d)(6) of this section, a person who applies for an aircraft type rating or an aircraft type rating to be completed concurrently with an aircraft category or class rating—
(1) Must hold or concurrently obtain an appropriate instrument rating, except as provided in paragraph (e) of this section.

Paragraph (e) exempts aircraft incapable of instrument maneuvers and instrument flight from this requirement.
This does mean that you can do the instrument checkride concurrent with the type rating. If your hypothetical PP-ASEL gets typed in a citation, he will end up with a PP-ASEL with instrument airplane rating and the citation type.


Propeller Characteristics at Different Altitudes

Your lift and drag polar is Reynolds number dependent. You need to check if you are happy with what XFoil generates for you. Airfoil characteristics are fairly constant over a wide range of Re, so it might not effect you at all.

Also, if you are running high tip speeds, there is another pote increasing altitude drops the temperature as well, so you are increasing the tip Mach number, which you need to make sure stays within the validity limits of your calculation method.


Does flow separation starts earlier at higher airflow speeds?

It is generally assumed in incompressible aerodynamics that the Reynolds number over a wing is so high that the effect of the Reynolds number (same air viscosity, same wing chord, only variable in Re is speed) on the lift coefficient is negligibly small. I can think of two areas where this assumption breaks down:

Very small (for example RC model scale) wings, where the Reynolds number is appreciably reduced. As the air in this case is less turbulent, flow separation occurs earlier.
Compressibility effects such as shockwaves occuring on top of the wing at transonic speeds, where we have to include not Reynolds but Mach number in our lift coefficient estimation. The effect of Mach number on max. lift coefficient depends on the wing design, some fighters are optimized for it, while most aircraft have their max lift coefficient and max angle of attack reduced at transonic speeds.


If you're selecting increasing cabin altitude, you are lowering cabin pressure.  To do that you have to let some air out of the balloon (the pressure hull).  So the valve has to be opened more (they usually never fully close because there is always more inflow than needed to maintain cabin pressure with both engines running - how much open depending on how leaky the pressure hull is).


How the aircraft sense the sink rate during autoland?

The radar altimeter doesn't calculate the rate of descent. A radar altimeter only gives height information, but it can take many readings very quickly and feed that data to a computer which will calculate the rate of descent.


What were those multiple flights leaving London night of 29th Aug 2019?

Nothing stands out on Flightradar24 for that time period by using the playback function. So most likely they're not civilian.

What I found was a military-related NOTAM via notaminfo.com/ukmap:

  MIL EXER. MIL PARACHUTING AND HELICOPTER HOIST OPERATIONS WI 5NM
  RADIUS 515900N 0012500E (BAWDSEY, SUFFOLK). FOR INFO 01638 545012.
  2019-08-0649/AS3

  FROM: 29 Aug 2019 18:30 GMT (19:30 BST) TO: 30 Aug 2019 00:30 GMT (01:30 BST)

The time matches if we account for padding, and the drop area would make them fly west to east to arrive at Bawdsey, depending on their base and your location.

If too concerned, you can trying calling the number quoted above.


Can a large passenger aircraft recover from a stall?

The main thing that is required for a stall recovery is just the ability to drop the nose to decrease angle-of-attack and regain airspeed (and, of course, adding power helps, too.) Except in the case of deep stall, there is still sufficient air flowing over the horizontal stabilizers (and, thus, the elevators) in an airliner to push the nose down during a stall. Furthermore, most airplanes (including nearly all, if not all, airliners) are designed with a center of gravity forward of the center of lift. In normal flight, the air flow over the horizontal stabilizers actually pushes the back of the plane down, which holds up the nose. During a stall, this airflow is reduced (still present, but to a lesser degree,) which will cause the nose to tend to drop by default during a stall condition, even if the pilot (or autopilot) gives no additional control inputs at all. As such, normal (e.g. not fighters or aerobatic planes) will recover from a stall on their own with no additional control inputs, given enough altitude.

As already mentioned, some altitude is also usually required for successful stall recovery. This is because the recovery procedures involve dropping the nose which will briefly result in some descent. The lack of sufficient altitude to recover was the main problem in Asiana 214, which crashed just short of the runway in San Francisco. The aircraft was already too low and too slow to recover before the pilots acted. If I remember correctly, they started attempting a go-around only about 7 seconds before the aircraft impacted the seawall. At that point, there was nothing they could do. A small, piston-engine aircraft probably still could have recovered from that situation because piston engines spin up much, much faster than jet engines and could provide the power needed to recover much faster. Pushing the nose down alone would still technically have recovered the plane from the stall condition in this case, but that wouldn't have been very helpful, since it would have meant a nose-first impact into either San Francisco Bay or the seawall, which would obviously have been a much worse outcome.

Another problem that can happen (though is very, very unlikely on an actual airline flight, but much more likely on cargo flights in airliners) is for the cargo to shift to the point that the center of gravity is too far from where it's designed to be for stall recovery to be possible. This is what happened on National Airlines Flight 102, a 747 cargo flight departing from Bagram Air Force Base in Afghanistan. Very shortly after takeoff, the cargo shifted to the back of the aircraft, preventing the pilots from being able to lower the nose enough to keep the plane from stalling. It stalled and crashed before ever leaving the property of the airfield.

In general, pitch stability (more precisely known as longitudinal static stability) is what makes an aircraft capable of stall recovery, not maneuverability. While it may seem counter-intuitive to those not familiar with aerodynamics, it's likely actually easier to recover from a stall in an airliner than it is in a fighter (and almost certainly easier to recover in, say, a Piper or Cessna than a jet fighter.) This is because more maneuverable aircraft (such as fighters and aerobatics aircraft) are usually less stable than less maneuverable aircraft like airliners and normal GA aircraft.

The answers to this question give a thorough explanation of stall recovery which I would recommend reading. Its answers apply to how stall recovery is performed in any normal airplane, not just airliners. That question isn't specifically about whether airliners can recover from a stall, though, which is why I didn't mark this one as a duplicate.


Why can't pilots manually fly a low visibility approach instead of using auto land?

Pilots are required to operate by two separate sets of regulations, protocols, and procedures when flying an aircraft. They are Visual Flight Rules (VFR) and Instrument Flight Rules (IFR). The rules are dependent upon what type of airspace you are flying in as well as cloud ceilings and visibilities outside the aircraft. Most commercial flights, including virtually all scheduled airline services are conducted under IFR.

Landings conducted under VFR must be done by flight under visual references and are subject to specific limitations on cloud ceiling and visibility minimums for the specific airspace surrounding an airport. If the local weather drops below these minimums, you cannot takeoff or land under VFR and the airport can only accommodate IFR traffic in this weather.

IFR operations require pilots to fly specific procedures during departure and approach to an airport. These procedures themselves set weather limitations on the flight depending on aircraft and airport equipment, NavAid availability and GPS reception and the specific regulations in which the flight operation is being conducted under eg. Part 91, 121, 135, etc. If the weather does not meet these minimum requirements, the flight is not permitted under IFR either, which is why airline flights get cancelled in bad weather such as snowstorms, etc.

IFR Instrument Approaches into airports are broadly divided into 2 categories: Non-precision approaches, which provide lateral guidance to either the runway threshold for a straight in approach or to the airport itself for a visual circling approach and landing.  Precision approaches provide the pilot with both lateral guidance to the runway center line and a glide path to the runway touchdown zone. Both types of approaches have minimum ceiling and visibility requirements along with specific minimum altitudes and decision points based on your aircrafts’s approach speed. If you do not have the runway environment in sight when flying these approaches at these points and altitudes you cannot continue the approach to landing under visual conditions and must fly the missed approach procedures specific to this instrument approach.

The most common type of Precision Instrument Approach is the Instrument Landing System or ILS which uses terrestrial radio signals to guide the pilot along an approach path and identify specific points in the approach. ILS approaches fall under 3 different categories, or CATs.  CAT I approaches are standard ILS approaches and can be flown by most IFR Certified aircraft. CATs II and III approaches require specific additional flight crew training, and aircraft equipment.

CAT III approaches are the most precise ILS approaches and have 3 three additional subcategories: IIIa is the most precise approach that still allows the pilot to hand fly an aircraft equipped with an approved HUD. IIIb, and IIIc require the use of a coupled autopilot and allow for even lower weather minimums. CAT IIIc approaches are “zero-zero” meaning they can be flown with ceilings of 0 ft AGL and visibilities less that 1/16 of a mile, though they do require the visibility be great enough to adequately allow the crew to taxi the airplane off the runway environment to parking. Again these are limited to specifically trained flight crews, specifically equipped aircraft and specific airport infrastructure.

While CAT IIIb and IIIc ILS approaches do require a coupled autopilot to perform them, all other Non-precision and Precision Instrument approaches can be flown by hand - and all aircrews should be able to do this in the event of an autopilot failure.


Is there any way I can check the status of my medical?

The standard way to check the status of your medical application is to call the Aerospace Medical Certification Division at (405) 954-4821.

When you call, it's very likely that you will hear a recorded message saying that due to high call volumes, they are unable to assist you. If you do, call again later. When I was checking on the status of my own application, I had to call quite a few times before my call was finally answered.


Why did Concorde not have horizontal stabilizers?

(Source: concordesst.com)

It does have elevators in the form of elevons at the trailing edge.  A delta is effectively a tailless flying wing with a really long chord.  Like any flying wing, pitch stability is achieved by down force generated at the local trailing edge by a control surface that does the same job as a regular elevator/stab, by applying down force to balance the forward pitching moment of the CG ahead of the centre of pressure (an airplane is really just a teeter totter with the C of G at one end and the elevator at the other).

Fuel transfer is used to keep the C of G in a sweet spot range to minimize trim drag, which is the penalty taken in generating the down force at the rear, so that the down force can be no more than necessary for adequate pitch stability.

As for why they didn't use a horizontal stabilizer, the reason is that the delta plan form with elevons provides the required stability and control in pitch and allowed the designers to dispense with a separate tail surface, greatly reducing the drag of a separate tail (not eliminating, because there is still a drag penalty from the elevons generating down force).  Same reason anybody goes with a flying wing.  Plus, you need lots of sweep for low supersonic drag and lots of wing area for high altitude efficiency, so a tailless delta fits the bill.

A limitation of this is a narrower CG range (a more limited forward CG than with a regular tail that is farther aft and has more leverage) because the elevons have a short moment arm, a limitation of all flying wings.  The ability to transfer fuel to adjust CG would help with this and I think Concorde's modest passenger loading didn't cause the CG range issues that a normal airliner would have to deal with.


Why do cargo aircraft still have floors?

Because the overwhelming amount of cargo is fairly small and floors allow easy loading of both decks at the same time which is more important than the ability to load big cargo on occasion. By having floors you can load standard cargo containers quickly and efficiently. It also gives you the ability to standardize the containers with a reasonable degree of reuse most importantly they can fit into the lower deck of a passenger aircraft with out modification. Passenger airlines make a lot of money moving commercial cargo.

When it comes to flying around big, cumbersome cargo there are simply aircraft designed and built for such a task like the Airbus Beluga

(source)


What is preferred in an emergency landing: a road or a cornfield?

Really depends on what you are flying, what's growing, what season and what the roads are like. Our Cessnas have used gravel roads a couple of times, either due to problems aloft or at the airport (bad weather). In the Alberta prairies finding a side road to land on is no problem whatsoever. 100 and 200-series Cessnas have fairly narrow fixed gear that can take an amazing amount of abuse, don't know about other types.

A real cornfield, with the corn fully grown, will destroy a light aircraft. The plants are 2-3m high with a hard, heavy log of corn at the top. Hit a couple of thousand of them at 100km/h..... (Skydiving centers in corn country have firm advice for landing in the corn: keep your legs crossed.)

Ripe canola is also nearly 2m high and is a bushy plant interwoven with it's neighbors. You'll probably flip over forward. Wheat is the best choice.


A rainbow is created by refraction of sunlight so you have to be in the right position to see it. The effect is only created at some distance. A rainbow that you see from the ground may appear to be in a particular place in the sky. An airplane could fly through that space and it might appear to you that it is passing through it The occupants of the airplane, however, would not see a rainbow there.


Yes. Gulfstream G500 and G600 are the first civilian transport category aircraft to have active sidestick. However, instead of mechanical linkages between the two sticks, the side sticks are coupled electrically. It's much more prevalent in military aircraft.

Source: Aviation Week

So why isn't it being adopted by aircraft manufacturers with side stick controls (e.g. Airbus, Bombardier)? It pretty much all has to do with costs.

Active side sticks introduce more failure modes, such as jam and runaway, which would involve more software and mechanisms to detect and mitigate. These add complexity and introduce failure modes in their own rights, and they all add up to costs.
There is very little certification mandate to make side sticks active. All the objectives, such as stick force/G, stick force/V, have been met by passive side sticks. Airbus introduced envelope protection, most likely not because it was a nice-to-have, but because certifying the combination of lack of aerodynamic feedback on the inceptors and the choice of a pure C* control laws without speed stability demands it.
Certifying the first civilian active side stick is costly (but now it's been done by Gulfstream). There needs to be clear market reasons to do so. For Gulfstream, it may be (personal hypothesis) that the aircraft is being catered to the ultra-rich clientale and a novelty factor. For commercial aviation, the only reason I can think of is safety, which brings us to...
Would active side stick actually increase safety by leaps and bounds? This is a topic under research so the discussion has personal bias. On the A320 and A220, if both PF and CP side stick commands are detected, an aural "Dual Input" warning would sound. Obviously, AF447 crew ignored it. The final BEA accident report didn't mention the lack of tactile feedback as a reason for the crash; rather, crew confusion on stall recovery and lack of airspeed disagreement warning were highlighted.


Why can't the flex temperature be lower than Tref? Also why can't we perform a flex takeoff on a contaminated runway?

The engine is flat rated below Tref, and the thrust decreases above this temperature. The point of using a flex takeoff is to run the engine at a lower power setting, where its limit would be at a higher temperature. Using a temperature below Tref would result in the same thrust as Tref. The graph from Airbus below helps to illustrate the relationship between the variables.

Source


Why are some non-towered airports charted with an empty circle?

Your first stop for questions like this should be the FAA Aeronautical Chart User's Guide. In the VFR Sectional & TAC section it says:

  Runway patterns will be depicted at airports with at least one hard surfaced runway 1500´ or greater in length.

If you look up the details for 62C in the Chart Supplement or whatever other source you like, you can see it has two grass runways, i.e. no hard surfaced runways.

As for the hash marks, they do mean that fuel is available.


What’s the grey altitude depicted in the profile view on Jeppesen charts?

The grey areas are the minimum descent altitude (MDA) for each approach segment. Below those altitudes there are hazards in those segments. When you conduct the approach you should be aware of those altitudes and take action if you get too close to them.


Can a dual-engine aircraft take off with only one engine?

It is a regulatory requirement (EASA CS 25) that commercial aircraft can safely fly should one of the two engines fail at any point of the flight, including takeoff at speeds beyond $V1$. (the maximum speed at which it can still stop before the end of the runway).

  Control Following Engine Failure  1 An acceptable means of showing
  compliance with CS 25.143(b)(1) is to demonstrate that it is possible
  to regain full control of the aeroplane without attaining a dangerous
  flight condition in the event of a sudden and complete failure of the
  critical engine in the following conditions:

  a. At each take-off flap setting at the lowest speed recommended for
  initial steady climb with all engines operating after take-off, with –
  i. All engines, prior to the critical engine becoming inoperative, at
  maximum take-off power or thrust;  ii. All propeller controls in the
  take-off position;  iii. The landing gear retracted;  iv. The
  aeroplane in trim in the prescribed initial conditions; and

  b. With wing-flaps retracted at a speed of 1.23 VSR1 with – i. All
  engines, prior to the critical engine becoming inoperative, at maximum
  continuous power or thrust;  ii. All propeller controls in the
  en-route position;  iii. The landing gear retracted;  iv. The
  aeroplane in trim in the prescribed initial conditions.

Source

For a clip of this happening just as the aircraft is rotating, take a look at this video:

A simulator video of the procedure is also available:


Why do some airlines operate fleets so diversified?

There are two philosophies for fleet selection:

One type / model or one manufacturer approach
Multi manufacturer divide and conquer approach

First of all, a single model fleet is only possible for airlines that operate on sectors of comparable length. You can't do intercontinental and regional flights with the same aircraft model efficiently.

As you observe, there are obviously costs associated with flying different types of aircraft. A single type fleet like for example Ryanair (B738), Southwest (B73*) and Easyjet (A320 family) operate, means the cost of maintenance, training, etc can be kept low. Adding a few aircraft of another type to the fleet would mean additional tools in stock, diversified training and a separate flight crew group and lots of other cost factors.

Aircraft manufacturers know that too. So if you need another 10 - 20 aircraft, your standard supplier will ask a high price for this fleet extension, knowing that the competition is never able to put in a compelling offer when all additional cost are taken into account. Only if the batch size is large enough the competitor might be able to offset the additional costs with a unit discount.

That is where the mixed fleet operator has an advantage. Since the additional overhead costs of a couple extra aircraft from type A or B are minimal, they have a better position while negotiating with the manufacturers.

Single manufacturer airlines usually order aircraft in large numbers, otherwise they would not get a proper deal; multi type airlines can order aircraft in lower numbers.

And then there are politics. Sometimes a national airline will be subjected to political pressure to buy from a certain manufacturer. This is especially the case for airlines operating in the international / intercontinental market. The extra fleet cost incurred will be (partially) offset by deals in another field.


When may commercial pilots release their shoulder harness?

You essentially have two questions, which I will answer in turn:

When may commerical pilots release their shoulder harnesses when operating under commercial operations rules such as §121
When do such pilots actually release their harnesses in practice

Regarding your first question:

14 CFR 91.105 does generally apply to commercial operators and air carriers. However, §121, §135, and §137 each provide equivalent regulations which duplicate or exceed the language found in §91.105.

14 CFR 91.105 states, in pertinent part:

  (b) Each required flight crewmember of a U.S.-registered civil
  aircraft shall, during takeoff and landing, keep his or her shoulder
  harness fastened while at his or her assigned duty station. This
  paragraph does not apply if—

  (1) The seat at the crewmember's station is not equipped with a
  shoulder harness; or

  (2) The crewmember would be unable to perform required duties with the
  shoulder harness fastened.

14 CFR 121.311 states, in pertinent part:

  (h) Each occupant of a seat equipped with a shoulder harness or with a combined safety belt and shoulder harness must have the shoulder harness or combined safety belt and shoulder harness properly secured about that occupant during takeoff and landing, except that a shoulder harness that is not combined with a safety belt may be unfastened if the occupant cannot perform the required duties with the shoulder harness fastened.

14 CFR 135.171 states, in pertinent part:

  (b) Each flight crewmember occupying a station equipped with a shoulder harness must fasten the shoulder harness during takeoff and landing, except that the shoulder harness may be unfastened if the crewmember cannot perform the required duties with the shoulder harness fastened.

14 CFR 137.42 states, in pertinent part:

  No person may operate an aircraft in operations required to be conducted under part 137 without a safety belt and shoulder harness properly secured about that person except that the shoulder harness need not be fastened if that person would be unable to perform required duties with the shoulder harness fastened.

Under each regulation, the flight crewmember may generally unfasten his or her shoulder harness at any times other than during takeoff and landing, or if the shoulder harness would interfere with performing required duties. The one exception to these allowances is found under §121 in instances where the shoulder harness and safety belt are combined1.

These allowances notwithstanding, a certificate holder may include in its General Operating Manual provisions that flight crewmembers must adhere to requirements that exceed those given by regulation.

Regarding your second question:

In practice I never release my shoulder harnesses from the time I seat myself and fasten my safety belt and shoulder harness until the aircraft has come to a stop and I am ready to leave my seat at the end of the flight. I have also never seen a fellow pilot at my air carrier release his or her shoulder harnesses while in flight. Others will doubtless have different experiences.

Prior to my time with my present employer I have witnessed pilots who make a practice of not wearing the installed shoulder harness at all (given the circumstances I don't think they would have had a very good argument that it would otherwise interfere with performing their duties). I have also witnessed pilots who unfasten both the shoulder harness and safety belt after landing while still taxing at the end of a flight. This later practice is not against regulation2 but may be of questionable judgment in some cases.

1 §121 requirements for combined safety belt and shoulder harness:

14 CFR 121.311 also gives the following, in regards to the requirements for aircraft to be equipped with combined safety belts and shoulder harnesses:

  (f) No person may operate a transport category airplane that was type certificated after January 1, 1958, or a nontransport category airplane manufactured after March 20, 1997, unless it is equipped at each flight deck station with a combined safety belt and shoulder harness that meets the applicable requirements specified in §25.785 of this chapter, effective March 6, 1980, except that—

  (1) Shoulder harnesses and combined safety belt and shoulder harnesses that were approved and installed before March 6, 1980, may continue to be used; and

  (2) Safety belt and shoulder harness restraint systems may be designed to the inertia load factors established under the certification basis of the airplane.

I read this to mean that, for aircraft specified under §121.311(f) above, unless a shoulder harness was approved and installed before 6 March 1980, then the aircraft must be equipped at each flight deck station with a combined safety belt and shoulder harness. Furthermore, under the requirements of §121.311(h), when the flight deck stations is so equipped with the combined safety belt and shoulder harness, no provision of §121 allows for that shoulder harness to be unfastened during takeoff and landing, even if the shoulder harness would interfere with performing required duties. Presumably the approval process for those harness systems would ensure that no interference would be possible.

2 14 CFR 91.107 does generally require that each person on board a U.S.-registered civil aircraft must have a safety belt and any installed shoulder harness properly secured about him or her during movement on the surface. However, this requirement does not apply to required flight crewmembers or to any operations conducted under §121, §125, or §135. See §91.107(b).


Why did some aircraft use hand-crank instead of gravity for alternate gear extension?

They had to manually crank down the gear because the electric system was damaged.

"As the B-17 limps closer to base, Dearborn orders the landing gear dropped. Only one wheel descends due to electrical failure caused by battle damage, but the crew are able to manually lower the malfunctioning wheel just before landing."

Free fall only works for hydraulic powered landing gear systems. The B-17 uses an electrically driven motor to raise and lower the gear.

Not all hydraulic landing gear can free fall. PBY-5A's have hydraulic gear and emergency gear extension used a backup hydraulic pump. Additionally you could manually break the up locks and then manually push the gear to the locked position.

I bet many other WWII era aircraft with hydraulic gear were similar. Free falling hydraulic gear probably came much later.


Where to find information about number of seats knowing the aircraft Registration ID?

The usual way would be to find out which airline operates that aircraft. Usually Google will give the answer. Otherwise planespotters.net will help. In this case it is Norwegian.

Then seatguru will show you what the interior configuration is.

I don't know whether these website have public API's that could help you and I think that is a bit off topic for Aviation.SE.


How "over-engineered" were old planes and how "over-engineered" are they now that we have more advanced testing and research options?

You are right that older designs used (and needed!) higher safety margins. I would, however, not call this over engineering. But that is besides the point.

The biggest advances have been made in materials! Not just new alloys, but much better quality control in manufacturing. The aluminium sheets and slabs you would get from a factory 50 or 80 years ago had much greater variations in local strength, and in strength between different production batches. The same goes for fasteners, forgings, whatever. Computer-controlled manufacturing and the relentless effort to improve quality and consistency have made this possible. Only wood is still the same as it was then, but Basil Bourque is right: Processing the wood has also improved by leaps and bounds.

But now consider what we do when we stress a wing: We use the maximum static lift coefficient, add aileron deflection and use that bending moment at v$_A$ to size our wing spar. We do this by applying a safety factor of 1.5 (§25.303). For parts with a more error-prone production process additional factors need to be added (see §25.619).

And now consider what happens in the real world: The dynamic maximum lift coefficient, which does not obey the rules and regulations imposed by the FAA, will easily be 1.3 times bigger than the static lift coefficient used for stressing the wing spar. In tests up to 150% have been achieved. Makes you think how sensible that safety factor really is. While we understand the static loads very well (because they are easy to study), dynamic and fatigue loads still happen to surprise the engineers from time to time. A little extra margin sometimes can be quite useful.

On the Eurofighter the structural safety factor was indeed reduced to 1.4 with the reasoning that more precise modeling and simulation would allow to use a smaller margin.


Why are the top speeds for jet engines higher than for propellers?

The thrust of a propeller is proportional to the inverse of airspeed, while the thrust of a pure turbojet is roughly constant over airspeed in the subsonic region. This means that two airplanes with the same static thrust, one propeller-powered and the other jet-powered, will reach very different top speeds.

And, no, piston engines are more efficient.

A piston engine produces a constant torque $\tau$, independent of speed. This torque drives the propeller which produces work $W$ per unit of time on the air passing through it. This work per unit of time is power $P$ and proportional to the product of torque and propeller speed $\omega$, which is again constant over airspeed $v$. The power to propel the aircraft is the product of thrust and airspeed and equals engine power times propeller efficiency $\eta_{Prop}$. When airspeed goes up, thrust must go down proportionally for power to stay constant.
$$P = \tau\cdot\omega = T\cdot v\cdot\eta_{Prop}$$
$$\Rightarrow T \varpropto \frac{1}{v}$$

Turbojets, on the other hand, profit from flight speed because the intake pre-compresses the air when it slows down ahead of and in the intake. This pre-compression lifts the pressure level of the whole engine, so it sees an increased mass flow with increasing speed, producing higher thrust. This effect by itself would increase thrust in proportion with the square of flight speed, but the same effect which reduces the thrust of a propeller acts on a turbojet as well. This effect, however, is less pronounced because the jet accelerates less air to a higher speed, and both cancel each other, roughly.

Turbofans are more similar to propeller engines, so here the thrust goes down over airspeed, and more so for higher bypass ratios. Turboprops are even closer to piston-powered propellers, so their thrust drops even more with increasing speed. This means that the speed at which drag equals thrust drops when you move from turbojets to turbofans, and further to turboprops and is lowest for piston-powered propeller aircraft.


What is the dutch roll filter? How does it work?

I assume you know what a dutch roll is, if not here is a brief summary:
At the airplane yaws to one side the wing that is moving forward has a higher speed and creates more lift which causes the aircraft to roll towards the trailing wing. There are also effects like the vertical stabilizer usually being above the center of gravity which at great side slip angles causes the aircraft to roll towards the trailing wing as well. And lastly there are effects like the fuselage causing a disturbance on the trailing wing.
All these effects depend on the aircraft type and wing configurations. But generally speaking a yaw rate creates a roll rate as a side effect. And if you move the rudder left and right constantly then you cause the wings to rock, which is called a dutch roll. This behavior is quite unpleasant for passengers in the back or front because they are accelerated left and right.

To suppress this side effect of a yaw motion creating a roll motion and a subsequent dutch roll you can add a "durch roll filter" to the yaw damper control system. All it does from my understanding is to combine the normal feedback loop for the yaw rate with a second loop for the roll rate. This causes the yaw damper to reduce rudder deflection slightly whenever the roll rate picks up and increases it again when the roll rate stagnates which can stabilize the dutch roll and causes a more uniform roll rate.
Modern fly by wire aircraft can also use the ailerons to dampen the dutch roll much more effectively. But if the yaw damper can only affect the rudder than this is obviously not an option.

I'm not 100% sure when it's used but I'm guessing that all modern airliners have this because there are people in the far back that would get motion sickness really quickly when the yaw damper allows a dutch roll and the aircraft swings side to side on every turn. For a small general aviation aircraft this may not be needed and development costs can be kept low.

As per all control systems I think the yaw damper with or without this filter has to be certified. And if the system is changed later on will also have to be tested and certified. Depending on the aircraft type you may need redundant yaw dampers


Is it allowed to scatter human cremains (ashes) from an aircraft?

AOPA has an entire article on it that's worth reading and while it's generally fine with the FAA (assuming the pilot isn't being careless or reckless), there may be other regulations or laws that apply. The article mentions:

Permission needed for scattering over federal land
Permission needed for scattering over water (federal and local regulations)
State burial requirements

But there are two specific aviation regulations that might apply to the flight. First, 14 CFR 91.15:

  §91.15   Dropping objects.

  No pilot in command of a civil aircraft may allow any object to be
  dropped from that aircraft in flight that creates a hazard to persons
  or property. However, this section does not prohibit the dropping of
  any object if reasonable precautions are taken to avoid injury or
  damage to persons or property.

Second, you said that you plan to have a "contract" with someone to scatter the ashes, which implies that you're going to pay the pilot. If that's the case, then the pilot may not use an experimental aircraft for the flight. That's because the FAA considers carrying human ashes to be carrying property (Harris interpretation, 2009) and 91.319(a) doesn't allow carrying property for compensation in experimental aircraft:

  (a) No person may operate an aircraft that has an experimental
  certificate—

  (1) For other than the purpose for which the certificate was issued;
  or

  (2) Carrying persons or property for compensation or hire.

Finally, note that accidents can and do happen and in at least one case two people died while spreading ashes (although to be fair, the toxicology data was fairly 'interesting' in that one).


It's certainly reasonable to think a business jet cabin is quiet. Several business jet makers pride themselves on having models with quiet cabins. It varies a lot depending on the business jet, and exact numbers for the cabin sound level aren't usually listed.  It varies for airliners too with the A380 being an example of a very quiet jet and the 777 being noticeably louder.

If you're on a luxurious G280 or G650, the sound level would be relatively very quiet at less than 50 db (unofficially).  Even other private jets from my limited knowledge allow you to have conversations at even a few feet of distance without much struggle.  If you were operating an old loud engine like a Learjet 24 (which actually had turbojet engines) or a GII, the sound would probably somewhat limit conversation.

Exact sound levels are hard to find, in part because measuring a consistent sound level depends on so many factors, including cabin configuration, airspeed, engine thrust, air conditioning status, and position inside the aircraft.  Engine loudness, which is only part of the picture, is well studied and published (example).

Loud jet engines are rarer these days thanks to variety of factors, including the fact that operating loud jets is just plain illegal nowadays in many countries.  They actually make hush kits for older engines to get them down to legal levels.


What is the minimum radio and navigation equipment for required for VFR and IFR certified aircraft?

In the US, this in in 14 CFR 91.205, Powered civil aircraft with standard category U.S. airworthiness certificates: Instrument and equipment requirements.

There's a lot of detail so you can check the whole thing, but looking only at communication and navigation items, the required equipment is:

VFR (including night VFR)

Magentic direction indicator
Altimeter (for airspace navigation)

IFR

Instruments and equipment as for VFR
Two-way radio communication and navigation equipment suitable for the route to be flown
Rate of turn indicator (for timed turns)
Directional gyro
A clock (this question explains why a clock is needed for IFR navigation)

That list might seem very short, but remember that under VFR there's no requirement to have radios and there are even some vintage aircraft flying around with no electrical system.

Under IFR it's fairly obvious that you need a radio for ATC communication and whatever navigation equipment is needed for your planned flight, e.g. you can't fly a GPS approach unless you have an IFR-certified GPS. But there are multiple approach types and they all have different equipment requirements so the regulations just give a general statement.

Note that commercial flights operating under parts 135 or 121 will have additional requirements; the information above is really the bare minimum that's legally possible for GA flights.


Why does setting the Legacy 600's transponder to standby mode also deactivate its TCAS?

At least under FAA regulations the TCAS system goes into standby (by design) if the transponder fails

  A Mode S transponder is required to be installed and operational for
  TCAS II to be operational. If the Mode S transponder fails, the TCAS
  Performance Monitor will detect this failure and automatically place
  TCAS into Standby. The Mode S transponder performs the normal
  functions to support the ground-based ATC system and can work with
  either an ATCRBS or a Mode S ground sensor. The Mode S transponder is
  also used to provide air-to-air data exchange between TCAS-equipped
  aircraft so that coordinated, complementary RAs can be issued when
  required.

TCAS II systems get their altitude information from the transponder, which is a vital parameter to the system working.

(source)

All modes also require a functioning Mode S transponder

  Stand-by: Power is applied to the TCAS Processor and the Mode S transponder, but TCAS does not issue any interrogations and the
  transponder will reply to only discrete interrogations. The
  transponder still transmits squitters. Note: If the aircraft is on the
  ground and transmitting extended squitters, it is not required to
  transmit short (acquisition) squitters.
  Transponder: The Mode S transponder is fully operational and will reply to all appropriate ground and TCAS interrogations. TCAS
  remains in Stand-by.
  TA Only: The Mode S transponder is fully operational. TCAS will operate normally and issue the appropriate interrogations and perform
  all tracking functions However, TCAS will only issue TAs; RAs will be
  inhibited.
  Automatic or TA/RA: The Mode S transponder is fully operational. TCAS will operate normally and issue the appropriate
  interrogations and perform all tracking functions. TCAS will issue TAs
  and RAs when appropriate.

Strictly speaking all of this is only applicable to TCAS II systems but based on the noted case and my reading of the accident report it appears TCAS II was the system in use in this case.


Is there an abnormal condition that could have caused this fatal accident involving a stall?

Your question:

  Suppose that we take the pilot at their word, however. Is there any type of abnormal condition that might have caused a "feeling in the controls that something is not right", and which could cause the nose to drop with "none of the signs of a stall" occurring beforehand?

A couple of thoughts:

In a 60 degree level bank turn, stall speed increases by about 40%.
See below for information regarding indications of an approaching stall in the G103. (from the G 103 C Twin III Acro manual)

The flight manual, section 4, indicates that with aft cg there is a stall warning 2-3 kts before reaching stall speed - (read) "There is a tail vibration which increases with continuing pull on the control stick." I think the note above (highlighted in yellow) means that with forward CoG, at max weight, there is no stall warning at all, i.e., the glider just stalls (nose drops without warning). I could be wrong, but this seems to me to be what the note means.

Here is a copy of the manual for the Grob G103 Twin III Acro: Grob G103 flight Manual

Here is a copy of the NTSB report I believe covers this accident: Grob 103 Accident - NTSB Identification: CEN09LA353


What brakes are used between line-up and takeoff?

Just toe brakes. Typically the instruction between line-up-and-wait and clearing for takeoff is very short, maybe ten seconds.
In simpler aircraft, the parking brake just "pinches" or closes off the brake fluid line to keep the wheel brakes held, but in the fly-by-wire airliners, the parking brake just clamps the normal wheel brakes as if the toe brakes were held.


Are new airliners less safe than older the two first years after they are marketed?

Just a thought - when a new aircraft is introduced, if there is an accident/incident early on there are very few aircraft of that model flying and the million hour mark is hard to reach.

This may skew the accident rate wildly.  Earlier generations were simpler and were turned out of the factory at a higher rate than newer, more complex aircraft.


How to locate the coordinates of the Center of Gravity of an airfoil?

To compute the inertial properties of your blade, you need a couple of things: a way to compute inertial and elastic properties along the blade, a blade layout, and some idea of the expected load you want this to carry.

Starting with elastic properties--this can be either really straightforward or VERY tricky, especially when you start throwing composites around.  That said, this is true primarily because composites can be tailored into having just about whatever material properties you want...but the analysis of composites for essentially what you're doing was the PhD dissertations of two grad students I know.  The one is developing an analysis tool for aeroelastically tailored blades (also mentioned here, in a study by Sandia National Labs: http://energy.sandia.gov/wp-content/gallery/uploads/SAND2001-1303A.pdf), which sounds like what you're trying to do.  In short, these blades take advantage of strategically tailored material properties in order to achieve variations in blade twist purely based on a blade's operating condition.  If you are going to develop your own composites design code (or have one!), I think this is a feasible goal and I'd recommend you to "Analysis and Performance of Fiber Composites" by Agarwal, Broutman, and Chandrashekhara for an intro to composite analysis.  Based on that text, you could develop an analytic design code that might get you into the ballpark, and maybe start developing some finite element models to go beyond that.  It requires a fair amount of setup, and, since I don't think it was the main thrust of your question, I'm not going to write it out.

I think it suffices to say that back-of-the-envelope estimates for composite materials are hard to come by.  That said, it can be a rough approximation to treat composites as "black aluminum", or as an isotropic material with the bulk mechanical properties of the material (though it nullifies the aeroelastic tailoring you're shooting for).  Note that this requires you to have a symmetric layup schedule, as described in this short course from the US Naval Academy (https://www.usna.edu/Users/mecheng/pjoyce/composites/Short_Course_2003/7_PAX_Short_Course_Laminate-Orientation-Code.pdf).  This isn't the main thrust of your question, however, so I'm not going to delve into it further...it's just a head's up since composites can be more trouble then they are worth, especially if you have access to more traditional machining resources that you can use to make blades out of materials that are easier to shape (plastics, etc.).  The FAA has a nice guidebook too, and, depending on how fluent you are with this stuff, it may be of interest: https://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/amt_airframe_handbook/media/ama_Ch07.pdf.

If you're not shooting for aeroelastic tailoring or your analysis, for whatever mission you're planning for doesn't show that you get a terrible performance gain, it may be worth it to just try and make a variable pitch mechanism instead.

Alright -- on to inertial properties.  If you're looking to compute the blade's dynamic stability, you'll need inertial properties around multiple axes of rotation to account for the 3 modes of blade motion: blade flapping (i.e., motion of the blade out of plane with the rotation of the propeller), pitching (or twisting), and lagging (motion of the blade in the plane of rotation that occurs in addition to rotation of the blade itself).  Blade stability is related to the coupling of these three modes.  For an application I had (wing of constant cross section, isotropic material), I assumed the following cross section, including a quarter-chord spar and skin.

To solve for the inertial properties of the section (so that I could do a simplified aeroelastic stability analysis), I moved point by point along the airfoil surface.  For example, take the picture below.  It's a zoom in on the upper surface of the previous image.

To find the signed area of a convex polygon, in this case the quadrilateral defined by P1, P2, P3, and P4, the equation is (where x is in the chordwise direction, z is in the vertical direction, and y is the spanwise direction along the blade):

$A=0.5\sum_{i=0}^{n-1}(x_iz_{i+1}-x_{i+1}z_i)= 0.5\left[((x_{P1}\cdot z_{P2})-(x_{P2}\cdot z_{P1})) + ((x_{P2}\cdot z_{P3})-(x_{P3}\cdot z_{P2})) + ...\right]$

...and so on.  Similarly, the centroid can be determined by

$x_c = \frac{1}{6A}\sum_{i=1}^{n-1}(x_i+x_{i+1})(x_iz_{i+1}-x_{i+1}z_i)$

(formulas are most legibly given at https://en.wikipedia.org/wiki/Polygon#Area_and_centroid).  Just use the parallel axis theorem (essentially just weighted average of the centroids and areas) to get all these individual pieces to yield the sectional area and centroid (which, for an isotropic material at least, is the location of your neutral axis).

Moving on the second moment of area (which you'll need for computing stability), it's a similar formula (found at https://en.wikipedia.org/wiki/Second_moment_of_area#Any_polygon):

$I_{xx}=\frac{1}{12}\sum_{i=1}^n(z_i^2+z_iz_{i+1}+z_{i+1}^2)(x_iz_{i+1}-x_{i+1}z_i)$

($I_{zz}$...is similar -- just swap x and z).  Also:

$I_{xz}=\frac{1}{24}\sum_{i=1}^n(x_iz_{i+1}+2x_iz_i+2x_{i+1}z_{i+1}+x_{i+1}z_i)(x_iz_{i+1}-x_{i+1}z_i)$

Apply the parallel axis theorem to get all these individual moments to combine into a sectional property.

Once you have those implemented, the question is just what area do you want to integrate (i.e., is the blade solid, how large is your LE weight, etc.), and what are the elastic properties of those sections.  Then just apply the above.  The out of plane moment of inertia is the sum of the in-plane moments (i.e., $J = (I_{xx}+I_{zz})$).

Finally, as to actually computing dyanamic/static stability, I have a reference text...but it's a set of course notes and I'm not sure the best way to post it as the method is quite involved.  My apologies, but I'm coming up a little short on a good reference for this and may update this question later if I do find something good, however, in the interim, I'd advise you to look at helicopter dynamics texts, which will be a source of material for performance analysis computations too.  One source I could find online is by Bramlette and seems to have the basics well covered, but doesn't venture into rotor stability analysis: http://airspot.ru/book/file/63/bramwell_helicopter_dynamics.pdf


How and where is the ILS Glide Slope DDM to dots conversion defined?

The problem you're having is that there is no standard definition of dots. There are various standards that come into play and I'll try to explain how they fit together.

As you noted +/- 0.175 DDM is specified as "full-scale deflection."  This is in Annex 10 and, as mins noted, DO-192 for glideslope. It's also in DO-195 for localizer.

But what is 0.175 DDM and why is it referenced as "full-scale"?  DDM is the Difference in Depth of Modulation of the 90 and 150 Hz audio tones that comprise the LOC and GS signals. The significance of 0.175 DDM is it defines the value at the limits of the course deviation display (full scale).

Annex 10 requires the installation of an ILS requires (for most runways) the radiation pattern of the localizer to place full scale at the threshold of the runway at +/- 350 feet. With the LOC antenna at the other end of the runway, this sets the angular deviation guidance for the approach.

This standard means that shorter runways will have a wider LOC beam than a longer runway. There are minimum and maximum angular widths, so very short runways (<~3000 ft) will all have the same maximum width and very long runways will have the minimum width.

Back to the ILS MOPS (DO-192 and DO-195). The MOPS has a standard for display of deviation in terms of centering accuracy (0.0 DDM) and linearity of the display out to "full-scale".  Even if the display isn't part of the ILS receiver it's bound by the MOPS.  In this case (which is common today), the radio is tested to comply at the "output to the display" and must have an interface spec to allow a display to be interfaced. The display - even if it's part of a glass PFD - has to meet the MOPS. And after installation they have to be tested to show they work together within the spec.

But what about the dots? The MOPS don't specify what the display looks like. The requirement is that the pilot can discern the center, the limits, and that the indication is linear within a few percent. Dots are not specified or required.

You identified a generic convention of 2 dots at full scale. I would agree this is common on air transport aircraft. But the GA aircraft I learned to fly in all had 4 dots on the CDI at full scale. And to be even more confusing, many of the new RNP deviation displays don't have any dots, just a bar with a center and end marks with the steering line on top.

In over 20 years of working in avionics, I've never found anyone who could say definitively why 2 dot displays became standard. My suspicion is that flight standards (and airline op specs) typically call for a missed approach if the deviation exceeds half scale. The 2 dot display puts a dot at that point and at full scale. It makes for good human factors. Getting the needle inside the outside dot means you've captured the signal. After getting on course, a deviation out to the first dot means it's time to go missed.


Where can I find complete aircraft blueprints for the purpose of study?

You might buy some kit builder plans, as they have generally more detail than I have seen in commercially available aircraft.

With commercially available aircraft, I have bought several aircraft new, and despite pre-purchase attempts, have been unable to shake loose a complete set of prints.  Even the limited prints I was able to receive were essentially licensed, and NDA agreements were executed, copies had to be accounted for, etc.

You might be able to find prints from one of the better plan developer, which might meet your needs.  Some might be rather inexpensive.  I have plans for the Varieze and LongEz and have seem plans for other aircraft. Some are more detailed than others.

However, I would like to set an expectation that you will learn little about aircraft design, and perhaps a tiny bit about aircraft manufacturer.  There are better materials, including textbooks.


What happens to EGT after a bird strike?

No two bird strikes are the same when it comes to engine parameters, we can look at this incident.

Bird strike in both engines, yet only one showed above-normal EGT.

In a jet engine, the bypass air assists in cooling, damage will disrupt this air flow.

The core might still be running, or flammables (oil, fuel, etc.) might leak and catch fire.

In an engine fire, EGT-rise is one of the confirming factors.

However, according to the NTSB report for Sully's plane:

  No in-flight or postaccident fire occurred.

So if it is just an engine failure, the engine will spool down.

Even if the damage prevented the windmilling, EGT should still drop. If the EGT sensors were damaged, an indication of EGT reading failure is to be expected.

Also the engine vibration indicator should show very high vibration after the bird strike.

(Source)


Do pilots need special training to land Lockheed U-2 reconnaissance aircraft?

All military pilots will receive special training when learning to fly a new aircraft, whether that is in a simulator, a 2 seater version of the same aircraft, or both. An F-16 pilot is not going to fly a F-15 without considerable training. Training is recommended even for light aircraft as well when learning a new model.

If you are asking whether the U2 is harder to land than many other airplanes then yes, the U2 is a very challenging aircraft to land because of it's shape, but also because the pilot can see very little of the runway. In fact the procedure for landing a U2 calls for a vehicle to speed down the runway behind it with another U2 pilot in it to talk the flying pilot down.