How are the hours that count toward fatigue limits calculated by the FAA?

Flight prep and other non-flying duties are accounted for, but not under “flight time.” There are seperate regulations for time “on-duty” and time actually flying.

Flight Duty Period

The flight duty period begins when a flightcrew member is required to report for duty with the intention of conducting a flight and ends when the aircraft is parked after the last flight. It includes the period of time before a flight or between flights that a pilot is working without an intervening rest period. Flight duty includes deadhead transportation, training in an aircraft or flight simulator, and airport standby or reserve duty if these tasks occur before a flight or between flights without an intervening required rest period.

Flight Time

The regulations define flight time as: when the plane is moving under its own power before, during or after flight.

Rest period

Rest periods are “measured from the time the flightcrew member is released from duty.”

Cumulative hours

Cumulative hours are limited for both flight duty period and flight time. There are 7 day and 28 day limits on FDP; there are 28 day and 365 day limits on block time. The 7-day and 28-day limits are expressed as hours, so a rolling 168 hour limit (7 days) and rolling 672 hour limit (28 days). [thanks Ralph J]

This info was taken from the FAA Fact Sheet – Pilot Fatigue Rule Comparison


What limits high altitude powered paragliders other than the engine?

Stalling speed increases with altitude. Maximum altitude is the point at which stalling speed rises to meet maximum airspeed. To get higher, the options are to; increase thrust, increase wing area, reduce weight, or improve aerodynamic efficiency. These principles apply to all aircraft using aerodynamic lift.
In the case of the paraglider, its aerodynamic efficiency is not very good. So maximum airspeed is low and the stall speed will soon catch up with it as it climbs. It is worth sacrificing a little weight to greatly improve the wing profile and enclose the pilot and engine - but the plane is then no longer a paraglider.
The other main problem with a simple paraglider is pilot support systems. Time to altitude is measured in hours, during which time the pilot lives inside a pressure suit; the kind of thing worn by Lockheed U-2 pilots on an intercontinental reconnaissance flight. Refreshments, especially drinks, will be necessary. If you put all the support equipment in a great big backpack, like an Apollo astronaut but with longer EVA endurance, where are you going to put the engine? Something a step up from a paraglider again becomes a necessity.


Are the guns on a fighter jet fixed or can they be aimed?

They are fixed, and many attempts were made over the years to have an aiming capability - and all failed. That should tell you something.

The earliest aereal combats used indeed handguns which were pointed at the adversary by the pilot. But it soon became obvious that only the rapid fire of a machine-gun will give the pilot a realistic chance of hitting a fast-moving target.

During the Italo-Turkish war of 1911 and 1912, the Italians used aircraft in war for the first time. Since the Ottoman Empire had no air force yet, the Turks engaged European aviators who flew their own aircraft, taking a handgun along to shoot at the Italians.

The same was tried in the opening months of WW I, but it soon became obvious that only a machine gun was effective. Before gun synchronisation was invented, pusher designs were fielded, some of which carried a dedicated gunner in a seat ahead of the cockpit.

Vickers F.B.5 "Gun Bus" (picture source)

Of course, the much smaller and nimbler Fokker single-seaters with gun synchronisation made such designs soon obsolete.

When Great Britain prepared for WW II, the firing power of bomber turrets impressed the Generals so much that they ordered several dedicated fighters with a gun turret mounted right aft of the cockpit. The resulting Bouton-Paul Defiant was again too slow and easily outmanoeuvred by the single-seaters, and the Blackburn Roc and the Hawker Hotspur were even worse. The Defiant's only successful role was as an early night fighter; when attacked by day it could only join others in a Lufbery circle to defend against being shot down itself.

Bouton-Paul Defiant F. Mk.I (picture source). Note the retractable belly-mounted antenna masts which gave the gunner a free field of fire in the upper hemisphere.

Another attempt was made by the MiG design bureau in the 1950s. In a dogfight the pursuer needs to get inside the circle of its opponent in order to score a hit with a fixed machine gun. The Russians thought: Why not pivot the gun into the circle, so the pursuer can fly the same circle as its opponent and still shoot at it? A MiG-17 was modified accordingly, but flight testing soon revealed that the recoil from the machine gun would push the nose of the fighter down and outside of the circle when the gun was not aligned with the longitudinal axis of the fighter, so this idea was dropped very soon.

Now I need to mention that rarely are the guns completely aligned with the longitudinal axis; instead, they point slightly up to compensate for the ballistic bullet drop at the expected distance of the target. Also, wing-mounted guns point slightly inward, again to ensure the bullet path is straight ahead when it catches up with the target, a procedure called gun harmonisation. This also means that interceptors will have their guns pointing up slightly more than those of air-supremacy fighters. One particular case involved the MiG-15: Being designed to fight large B-29 formations, the guns were badly aligned for fighting the F-86 Sabre during the Korea War. The MiG-15 armament consisted of two 23mm guns and one 37mm gun with very different ballistics. In order to ensure that the path of all bullets would meet at the right distance for fighting bombers, the 23mm guns pointed more up, and when used against the much smaller F-86, the Russian and Chinese pilots opened fire at a shorter distance so that the 23mm bullets would fly over the target while the 37mm bullets went below it. This was a major reason for the poor kill ratio of the MiG-15 vs. the F-86 despite the MiG's better performance.

Gun harmonisation on a jacked-up P-47 (picture source)

Modern high-off-boresight missiles with helmet-mounted cueing (or sight-controlled missile targeting) have turned that longtime dream of shooting at what the pilot is looking into reality, and the gun is carried largely as a low-priority weapon of last resort.


What's the exact moment were the spoilers are supposed to be deployed on a A320?

PL at idle is one of several conditions (weight on wheels, N1, wheel speed etc) that have to be satisfied to get ground lift dumpers to come out on airliners.  Reverse isn't required.  Once on the ground, just moving the PL levers back toward TO thrust makes them come back down.


Can anyone identify this 1910s era biplane?

It isn't German or even European, not with an OX-5 engine on the front - unfortunately there were hundreds of similar designs in the post-ww1 period, however the fact that it has a two bay wing and the struts are wire braced instead of having a diagonal narrows it down, and lo and behold, the Pitcairn PA-3 Orowing appears to be a match.


What does the acronym PDA stand for in the aviation domain

Pull-down apex. It's an additional attachment point in the center of the parachute. Putting force on it makes the parachute open up more like a half-donut, rather than a half-sphere. That provides more effective area for an annular parachute. That hole in the middle is needed for stability.

Link: one product of this type with a bit of explanation.


Why don't combat aircraft have rear-facing weapons?

If your opponent is directly behind you, you have lost the fight. The point of basic fighter maneuvering, or BFM, is to keep your opponent off your tail and hopefully get on his. Everything you would learn as a fighter pilot centers around ensuring you would never have to use a rear-firing weapon.

In addition, visibility directly behind the pilot is typically poor; humans can't turn our heads 180 degrees, and if we could we'd be staring at the headrest behind us. A few fighters have had rear-view mirrors, typically ones with a two-piece canopy including the Eurofighter, F-15C and F-14 among others, but the one-piece bubble canopy on fighters like the F-16 and F-22 give no good place to put a mirror that wouldn't further interfere with the pilot's forward vision. Rear-view cameras would be laughed at by pilots as a waste of an MFD.

A cannon firing backward would also be a pretty single-purpose weapon; in a multirole fighter you might get a chance to use it to add insult to injury when pulling out of a ground run, but in all likelihood you'll either have peeled off to one side as soon as you pickled your bombs, or you'll be toss-bombing and not even overfly the target. The only real reason you'd ever fire it would be to keep someone directly behind you on their toes.


What instruments or avionics do balloons usually have?

The magic regulation for minimum equipment on a balloon (in the USA) is 14CFR31.85 ("Required Basic Equipment" for manned free-air balloons).

The FAA requires that balloons be equipped with:

For all balloons

  [Reserved]
  An altimeter.
  A rate of climb indicator.

For hot air balloons (additional equipment):

  A fuel quantity gauge.
  An envelope temperature indicator.

For captive gas balloons (additional equipment):

  A compass.

Beyond what's required by regulation, in most free balloon operations I've seen they also carry an aviation radio and/or a CB radio (to communicate with their ground crew) - this is usually a handheld transceiver.

The FAA Balloon Flying Handbook also makes for interesting reading. They talk about required and optional instruments and equipment found on various types of balloons in Chapter 2.


That's one of the two ice detectors manufactured by Collins. Below is not precisely the model used by A220, but serves to illustrate the general layout of the unit:

Image ref: Collins

From this Collins fact sheet, ice detectors

  use a magnetostrictive technology to drive the sensing probe to resonate at its natural frequency. As ice accretes on the probe, a shift in resonance frequency occurs. When the resonance frequency reaches the set point, an ice signal is activated...


What sources of weather are approved by the U.S. National Weather Service?

There is an ongoing issue with this, as far as I am aware. First off, this does not apply to part 91, and nothing does as far as I am aware: you can get your weather from anywhere, but having it on record with FSS or DUATs gives you a little more padding if something goes wrong.

If you're going to get weather online, which most large operations do, the FAA requires air carriers to get weather information only from Qualified Internet Communications Providers (QICP). This is outlined under AC 00-62. Or rather, it was outlined there. 00-62 was quietly cancelled in mid 2013. In addition, the only list of QICPs (which would have answered your question) I know/knew about was removed from the FAA website.

A few weeks after it was cancelled I found out about it and called the FSDO to ask (Memphis or Louisville, I don't remember which). The man who should know told me that I knew about as much as he did. Their regional offices hadn't told them anything, and he was telling everyone to continue using the qualified service they were previously using until they learned more.

I have not called them back since, but after a quick search, I only found this OpSpec document and one that it supersedes from a few months before (8900.199). There is also a newer one in the series (8900.242) but it seems to have no information relevant to the question. I must adimit that this document is a bit over my head, but it seems that they did an overhaul of the weather regulations regarding 135 and 121, and that use of a QICP is no longer required. So I take it that unless your carrier is only certified to use a certain system, you're now allowed to use whatever you want to get the weather.

You can read those documents here, the three I mention were published under AFS-200. Search for that and you'll find them and more.

So I did some more research:

Check out 8900.1 Ch 26 Section 2. Regulatory Sources of Aviation Weather Information and Aviation Weather Information Systems – Parts 91K, 121, and 135. The first bit has a good overview of all the weather products and their intended purposes. Relevance to the question starts at 3-2073(A) Weather Reports Prepared by the NWS or a Source Approved by the NWS. (page 6 in the PDF version).

Much further down it says (in reference to part 135, 121, 125, etc certificate holders only):

  B. Accessing Weather Information via the Public Internet. Certificate holders and
  program managers often access weather information via the public Internet. When accessing
  weather information this way, certificate holders and program managers are required to use
  weather information that is provided by a weather source authorized by regulation, or approved
  by the Administrator, and is listed in the certificate holders’/program managers’
  OpSpecs/MSpecs. In the past, the FAA maintained a list of approved QICP. However, the FAA
  no longer approves QICPs. The FAA has canceled AC 00-62, Internet Communications of
  Aviation Weather and NOTAMS, and no longer maintains a list of approved QICPs. Certificate
  holders and program managers using the public Internet to access weather information are
  responsible for ensuring accurate and timely delivery of information without data corruption
  during the transmission.

That's all pretty cut and dry, I think, but keep in mind that those OpSpec papers mention that everything in 8900.1 Ch. 26 is under review and has been edited recently and will be further edited in the near future.


Why is a procedure turn required if you are more or less on the final approach course?

Read that other question again.  He was approaching from the SSW and made an assumption based on the approach segment from AUGIE.  He wasn't actually on the AUGIE-BEJCY leg as it would be impossible to be there if he were approaching from the SSW.

His clearance was "Direct BEJCY cleared for the GPS 01 approach".  That clearance, in lieu of any specific instructions about the procedure turn, requires that the procedure turn be flown.  He assumed that because he was roughly on the extended centerline of the runway SSW of the airport that he was exempt.  However, there is no charted course there labelled "NoPT", so his assumption was incorrect.

Back to your question of why someone flying from that location would have to fly the PT, and the answer generally boils down to "TERPS".  The leg from AUGIE can be flown at 3000 ft while the area minimum safe altitude is 3100 ft.  It is very likely the minimum enroute altitude over that area is higher than 3100 feet.  This means a pilot that is using BEJCY as the IAF may be considerably higher altitude than 3000 ft.  On this approach you ideally want to be at 2500 ft by the FAF at CUCTO.  If you are approaching BEJCY from any direction other than AUGIE this means you cannot start your descent from whatever altitude you are at down to 2500' until passing BEJCY.  The procedure turn is not only for course alignment but also to descend to the procedure altitude from the enroute environment.


What is "Takeoff Minimum: NA" for US Airports as depicted in Terminal Procedures?

On page D1 of the TPP-Abbreviations

NA.......Not Authorized

Sometimes they give the reason why it is not authorized like in your examples. Other times they don’t. In these cases, you can’t use the runway for IFR departures. (non-Part 91)

N/A.......Not Applicable

I don’t recall seeing this terminology in the departure minimums section, so if you could show me where you found it, maybe I could explain it.


Why do the F/A-18 and the F-22 Raptor have horizontal stabilizer as well as canted rudders for pitch control?

The rudders on modern fighters are canted mostly to reduce their radar cross section. A straight vertical tail would produce a corner reflector in combination with the fuselage or the wing and would send radar waves straight back to their source. To reduce the detection radius, such a behavior must be avoided. The first aircraft to use this trick was the SR-71.

On the F-18 an additional reason was to move the tips of the vertical tails into the lateral position of the chine vortex: The wing's big leading edge extension produces a strong vortex at high angle of attack which improves the effectiveness of the tails and gives better yaw control. However, the bursting of the vortex would cause heavy buffeting, and an additional fix was needed to improve the fatigue life of the tails.

The horizontal tail is a necessity for pitch control and to trim the flap moments in the landing configuration. Just look at Boeing's entry to the JSF competition: The X-32 was initially planned as a delta with only vertical tails, but when the Navy refined their carrier operation requirements, Boeing had to add a conventional horizontal tail to achieve the required angle of attack and minimum speed.

Boeing X-32 (left, source) and the planned production version (right, source) with the added horizontal tail. The F-117 was an Air Force plane with very limited agility, so it could get away with a tailless design. Real fighters and carrier airplanes cannot.

Giving the horizontal tail dihedral reduces its effectiveness in two ways:

Angle of attack changes from pitch variations are reduced by the cosine of the dihedral angle, and
the vertical component of the aerodynamic force is also reduced by the cosine of the dihedral angle.

Note that the drag of a V-tail depends on the total lift created, regardless of its direction. Only the horizontal component is effective for pitch control, so a steeply angled V-tail is very ineffective for pitch control. In air combat the high drag will reduce performance when it is needed most.


Can I log multi-engine time abroad, when I'm not rated for multi in that country?

FAR 61.3 stipulates what is required to fly N-registered aircraft outside the united States.  There is nothing about flying non N-registered aircraft outside the U.S.  Rightfully so, the FAA does not have jurisdiction in that case.

To answer your question, you will need to reference that country's rule.  If they are an ICAO country, the rules are probably very similar.


In the ARINC specification, why is baro altitude (label 204) measured in Knots?

It's an error. Attachment 2B does show that label 204 from the GNLU (Equip ID 056) and GLU (Equip ID 060) as being in knots (highlighted below). That is not correct, it is a BNR in feet as shown for Air Data System (ID 006) and ADIRU (ID 038). Knots only applies to Label 204 from the FMS (ID 002).

It's still incorrect in A429 P1-18, March 2012.

ARINC 429 contact at ARINC Industry Activities, ARINC 429 Maintenance is Jose Godoy. email:jose.godoy@sae-itc.org


An aircraft engine is a thermodynamic device, that converts heat to mechanical power. A 'virtual' air parcel entering the engine goes through a thermodynamic cycle, which determines the bulk of the power plant efficiency, which include quite a big chuck of irreversibele air friction, with a minor role for bearing losses.
The engineering optimisation process however includes a lot more than just power plant efficiency. At the bottom line, the optimisation is tailored towards generating the most dollars of profit per unit of time, but a more optimistic view is that the engineer will optimise the aircraft fuel efficiency as a whole. In practice, this results in finding a balance between power-to-weight ratio and fuel efficiency, as additional weight increases the power required.
A recuperator is a heat exchanger between the compressor discharge air and the engine exhaust air*. Its goal is to replace part of the energy required from combustion of fuel by energy extracted from the exhaust, and does not modify the thermodynamic cycle in any way. I looked up some (approximated) data from a PT-6 turboprop at 850shp: [source, copied from training manual]

Ambient: 300K
Compressor discharge: 600K
Turbine inlet: 1200K
Exhaust: 800K

A recuperator could in theory cool the exhaust to 600K and heat the compressed air to 800K (ideal infinitely long counterflow heat exchanger) for a delta of 200K. The total desired temperature increase from compressor discharge to turbine inlet is 600K (1200K-600K), so we can reduce the fuel flow required by 1/3rd (only 400K delta still required). That seems excellent!
In practice, heat exchangers are bulky (air is a terrible fluid to transport heat). Furthermore, it's only operating on a 200K difference. The real question then is whether a real-world air-to-air heat exchanger (likely of cross-flow type, like an automotive intercooler, so less efficient than a counter flow heat exchanger) can be made so efficient that it does not introduce more losses than gains. Historic evidence suggest this is unlikely, especially if cost is considered (the material must be able to withstand 800K).
Furthermore, if we're going down the road of heat exchangers, different options are available. For example, an intercooler (cooling between compressor stages, which actually improves the thermodynamic cycle) could work on a higher temperature differential as well as lower absolute temperature, and would only present a single flow obstruction when the air is still nicely compact (power required is volume flow times pressure drop!) inside the engine. However, historic evidence again suggests that this is not cost-efficient, and instead seems to favour increasing the combustion chamber temperature and pressure.
*You may wonder, why not heat the intake air with exhaust air? We would work on a much larger temperature difference! In fact, this would be counterproductive, as the thermodynamic cycle operates on the difference between high and low temperature. Increasing the temperature at the inlet disproportionately increases the power required to compress the air, and does not result in an increase in turbine power (which in the end operates on a pressure differential, and cannot extract work from hot air at ambient pressure). There's a reason we use intercoolers, not inter-heaters in compressors.


Not storms, but there is a concept called "Pressure Pattern Flying" where you plan routing to stay in favourable circulation around Highs and Lows, to the extent that deviations to follow the circulation flow and stay in tailwinds can get you there sooner than going straight.  To take advantage of this you need to be going fast enough and with the range to span pressure regions. Although Lindbergh talked up this sort of thing in the 30s in his own flying, it's generally something exploited by airliners on transoceanic flying.
And in fact the North Atlantic Track system adjusts the tracks northerly or southerly daily to maximize or minimize the effects of winds around pressure systems, especially focused on jetstreams, which form at frontal boundaries at the tropopause. It might be worth a significant deviation from straight line point-to-point flight to ride downstream in a 100kt 10 mile wide jet that's going your way at 31000 ft (or whatever level the tropopause is at for a given region and time of year).
As far as storm systems go, nothing good happens near one.  You stay away from them regardless of the size of the aircraft, 20 miles being the convention, and ideally on the upwind side.  One hazard of passing by a thunderstorm cell on the downwind side, even if well clear of it, is running into hail falling in the clear air after it shot out the top of the cell.


Take a look at https://www.sciencedirect.com/topics/engineering/angle-of-attack  and  https://www.grc.nasa.gov/WWW/K-12/WindTunnel/Activities/lift_formula.html.
Lift graphs have a linear portion for small angle of attacks (and in 2D scenarios), but drag and airflow (laminar (non-shedding) vs. turbulent (shedding)) are both are non-linear, and both affect pressure and thus lift, and are important in real-life and 3D calculations.


What hardware and software is needed to put together a basic flight simulator?

(first off, I need to post a new picture of my sim rig soon.  It's improved since then)

1. Yoke vs. Stick

Try to model it after a plane you're actually going to fly.

If it's a yoke-controlled model (like a Cessna), then you should have a Yoke.
If you're working towards a stick controlled plane (like a Piper Cub), then you should get a simple joystick (not a fighter-pilot-styled super fancy one).

I have this model:
But I want to upgrade to:

2. Throttle

After that, I think a throttle is important.
Making the throttle precisely mirror your chosen airplane is not as important.
(pushing a lever is pretty similar to pushing a control rod).

The three-lever model comes with the Pro Flight Yoke.
Or you can get a a Push-rod version like this:

(more updates when I have time)


If the APU is switched off but the APU bleed is on, will the engine bleed valve close automatically?

The answer is in the FCOM:

So, the ENG bleed valve closes if:

Reverse flow detected
ENG 1 starter valve not closed
APU bleed valve open
Bad things (Overpressure / Overheat / Leak)
ENG BLEED switch is off or FIRE pb pushed

So, if APU is not ON, the APU BLEED valve is closed, and then the condition 3 is false. If all the others conditions are also false, then the ENG valve would open.


Is it possible to use a split rudder as an air brake?

It is possible but there are side effects.

If both rudders would be deflected to opposite sides to cancel out each others yaw moments, their drag will act as an air brake. But since the top rudder is further from the center of gravity than the bottom rudder, the resulting roll moments of the rudders don't cancel each other out. As a result the aircraft will start to roll. This can then be counteracted with the ailerons.

Since the rudders don't deflect as far as air brakes would, they would be less effective. If they would be designed to deflect more, the increased forces upon them and on the control system would require a heavier construction and thus add weight to the aircraft.


Is an eclipse considered 'night' for regulatory purposes?

No: that does not count as night flying.

The CAA defines "Night" (Air Navigation Order, Article 129) as:

‘Night’ means the time from half an hour after sunset until half an hour before sunrise (both times inclusive), sunset and sunrise being determined at surface level;

Similarly, the FAA's definition (FAR 1.1) is:

The time between the end of evening civil twilight and the beginning of morning civil twilight, as published in the American Air Almanac, converted to local time.

Since an eclipse is neither a sunset or sunrise, nor does it happen between evenings and mornings, it does not fit the definition of "Night" for legal purposes.


What things do you consider when choosing a fixed base operator (FBO)?

I'll throw in my 2 cents here but I am by no means super experienced in this realm.

Amenities is not a huge deal for me. Generally I fly to go somewhere, while a nice interior is always a bonus, I'm fine as long as there is a bathroom and a receptionist to pay. Generally I'm at the airport to tie up and then leave and go about my business. Some place to sit to wait for weather to improve is nice but I by no means care if the couch is leather or 1970's velour as long as I can sit on it for a while.
I flight plan with ForeFlight.com so I won't comment on what you should have but in today's day and age I would consider a WiFi connection in the FBO a must have since lots of people use tablet based planning now.
Fuel cost is always a consideration and you should try and remain competitive to your local areas as much as possible.
The key for me is a well laid out and clear website that lists prices for what ever you offer and other important information. Maybe an airport map with the location of the FBO clearly marked. A phone number to call for questions is also important.
A solid relationship with a local taxi service is a bonus and a courtesy or rental car would be even better, but I understand how this could be a runaway cost on some level.
Local knowledge is good if there are specific things that may be odd about the airspace and major airport issues that may arise.


What are the Ikarus C42 wing loading limits?

My club has a C42B that is used both as a trainer and a recreational aircraft, so I stopped by and looked in the Pilot's Operating Handbook for that one.

Now, before I say anything else: obviously, if the exact values matter, then always consult the POH for the specific airframe in question!

With the above preliminaries thus out of the way:

The structural limits are stated as maximum positive wing loading +4 G, and maximum negative wing loading -2 G.
The wings can be removed, and the POH lays out the procedure for this (as well as, obviously, that for reattaching them).

At least while quickly glancing through the text, I didn't spot anything obvious which would indicate that this differs between variants in the C42 series.


What pilot safety features and equipment are on an A380?

I think Saftey guy asks about features like the escape hatch from the 747. Probably there is something similiar on the A380:

I think that I can read the label Escape Rope on the cover of at the top right. You can look around inside the cockpit here.


What is the difference between Level Change and ALT INTV during VNAV descent?

Altitude Intervention will start a descent only if VNAV is the active mode (and the MCP altitude is below the current cruise altitude). If you're in Altitude Hold, then VNAV isn't active, and the Altitude Intervention button won't start a descent.
On the other hand, Level Change is its own mode, and selecting it (with a different altitude set in the MCP than what you're at) will always produce a change - either climbing at climb thrust, or descending at idle.  In both cases, flying at the speed set in the speed window.
VNAV is complicated, because while modes like Level Change, Vertical Speed, Altitude Hold, and GS Capture do "this," where "this" is a single easily understood thing, engaging VNAV means that we've given control to the computer logic, which can do lots of things. And we have to have an understanding of that logic to understand what VNAV will do. The Speed Intervention button and the Altitude Intervention button are inputs to the VNAV system only; VNAV also considers the altitude window and, when it's open, the speed selection. And of course VNAV uses what we've entered into the FMC as well.
For all its complexity, VNAV is one mode; Level Change is another.  To start the descent, Level Change will always do it, but then you aren't in VNAV with its various features (such as meeting the speed & altitude constraints in the LEGS page). If you're level in Altitude Hold and wish to start a descent in VNAV, then you should select VNAV & observe that the FMA changes to show VNAV as the active mode. Now, Altitude Intervention will work, as well as "Descend Now" on the CDU's Descent page.
The key is knowing what mode is active - and that's on the FMA. If Altitude Hold is active, you'll have to change the mode to start descending. You might change to Vertical Speed or Level Change to start down right now.  If VNAV is active, you have the tools which that mode gives you to control your path, and you can also select a different mode too (useful if VNAV isn't doing what you need the airplane to be doing right now).
In line flying, we'll generally prefer to stay in VNAV as much as possible, so if I'm at cruise altitude in Altitude Hold, I'll generally engage VNAV. Thus, I can control our cruise speed via the FMC, and when I'm given "descend at pilot discretion..." I can set the MCP altitude to the new clearance, and let VNAV manage the descent - starting it right at the calculated Top of Descent, managing the speed thru the transition from Mach to IAS, meeting step-down constraints on an arrival, etc.
There are times that the other modes are useful; for a 1,000' climb or descent, Vertical Speed at 1,000 FPM is a more gentle ride than going to full climb or all the way back to idle, and for "descend now to FL xxx and give me a good rate" then Level Change fits the bill.
Mostly, though, VNAV is what's active.


What is the maximum temperature of engine bleed air for de-icing the wings?

This is based on aircraft type and manufacturer approved limitations.  Typically it’s limited by temperature or duration of use.  Compressor bleed air is tapped at around 450° F, hotter than a typical household oven.  These high temperatures can begin to significantly affect the yield strength of aluminum alloys typically used in aircraft construction, approaching the design factor said of safety and potentially resulting in a local structural compromise during high load factors, etc.


Can someone identify if this is a Boeing or an Airbus?

There's no need to be an aviation wizard - Easyjet only fly Airbus A319 and A320 aircraft.

Even if you didn't give the airline, I would guess that it is an A320. Comparing the size of the engine to the person suggests it is a narrow-body aircraft, and 737 engines have a distinctive, flattened lower surface, whereas the A320 series are more cylindrical.


What RNP level is required for an RNP approach if the chart does not specify a value?

RNP approaches require a minimum value of 0.30, be it LNAV only, LNAV/ VNAV or RNP AR. Most of the approaches around the globe are RNP approaches. So, they do not put in the value because it remains the same at 0.30.
In RNP AR approaches they put in the value because these are approaches that require specially trained pilots and specially equipped aircraft. That is where the AR comes from. It stands for Authorization required. The RNP AR approaches have RNP values starting from 0.30 down to 0.10. The biggest difference between a typical RNP approach and an RNP AR approach is the lateral obstacle clearance. In an RNP approach, you have a clearance of two times the RNP value (0.30 x 2 = 0.6 miles) and also a buffer of 0.2 miles either side. In an RNP AR approach, the buffer is taken out of the picture and it only offers two times the RNP number left or right. If the RNP value is 0.10, then the lateral obstacle clearance will be 0.20 miles either side. This allows tighter approaches in areas with high obstacles such as mountains (such as Innsbruck). But because such approaches are a bit demanding you need better equipment. So, airplanes that are not designed for it need extra modifications. These modifications will depend on the manufacturer and it will also depend on the actual procedure. The pilots who fly these approaches need extra training as well, so that they are more accustomed to flying it and to teach them the required contingency procedures. Depending on the operator and the aircraft configuration, an RNP AR approach maybe approved with an RNP value between 0.30 and down to 0.10. For example, Airbus offers A320 and A330 with modifications and approvals for either RNP AR approaches with 0.30 or 0.10. In case of the A350, the aircraft comes with RNP AR 0.10 approval as a basic setting.

For LPV approaches, there is not an RNP value as it is basically an ILS type approach flown to category I minima using the GPS and a ground based GPS signal augmentation system such as WAAS (Wide area augmentation system).


How do I get an FAA okay for a private runway?

You're probably already aware that the FAA itself does not require the operator of a private airfield to receive any kind of approval from the FAA. However, there is a process in place to register a private airfield, and indeed the notice (not approval) is mandatory. The result of that process might satisfy your local authority.

The three FAQs starting here are pertinent. You need to file FAA Form 7480-1, either by mail or via the OE / AAA system.


Does the Piper PA-28 Cherokee wing have laminar flow behavior?

Short answer: Yes. You would see laminar flow.

Longer answer: It depends. In case of the wind tunnel it depends on the laminarity of the wind tunnel: Older designs had too much turbulence to allow for much laminarity. It was precisely for that reason that laminar flow was not well understood in the first decades of aviation.

The airfoil on the Cherokee is the NACA $65_2415$, and its Reynolds number in normal operation is in the single digit millions. The laminar bucket is ideally between the lift coefficients from 0.2 to 0.6, and the Reynolds number is low enough to allow for laminar flow. When you approach stall, however, the upper side has a pronounced suction peak near the nose which lets the flow rapidly transition to turbulent flow right after the peak. Laminar flow can only be found on the lower side (if surface roughness is low enough).

The pressure distribution over the rear 50% of the airfoil shows a constant pressure rise, so the onset of stall is marked by flow separation which starts at the trailing edge and slowly marches forward with increasing angle of attack. This leaves the suction area in the forward part unperturbed and keeps lift nearly constant around stall.

Contrast this with the stall behavior of the 5-digit NACA series, which can only be described as nasty. Stall is marked by flow separation right past the suction peak at the nose, and the lift coefficient suddenly drops by at least 0.2 counts when the airfoil stalls. Only some laminar airfoils have a similarly harsh stall behavior; this happens mostly when their designers were too ambitious and achieved the pressure rise with a Stratford pressure distribution. This is a distribution which keeps the separation margin constant along its length, and at stall it is exceeded everywhere at once, creating a sudden, large separation.

A well-designed laminar airfoil has a gentle stall behavior. Its lift coefficients with laminar flow are normally quite a bit away from stall, and its stall characteristics can be tailored independently from the region with laminar flow. Using a NACA $65_2415$ instead of a NACA 23015 is not a marketing gimmick, but a sound choice.

Regarding the performance: As long as the plane has a fixed landing gear, the laminarity of the wing will have little effect on top speed - the parasitic drag of all those things sticking out from the airframe will dominate drag. In addition, the higher the Reynolds number in flight is, the shorter the laminar flow will be before it transitions to turbulent flow, so the effect is much reduced at higher speed. Also, the way the wing is built makes a lot of difference, because every rivet head and every gap will create a wedge of turbulent flow behind it.


Can the CG move out of bounds as fuel is used?

With a straight wing aircraft with all the fuel in the wings, the fuel is close enough to the C of G across the span of the tanks that the C of G shift as fuel is consumed is insignificant.  When this is the case, the weight and balance chart won't have any special requirements to show C of G shift, relative to the fore/aft limits, from fuel burn.

If there is an aux tank that is forward or aft, the effects of its fuel level on C of G will be included in the airplane's weight and balance, and there may be limits on loading of cabin or cargo incorporated into the weight and balance data, and special instructions for C of G calculations when it's being used along with curve added to the wight and balance graph.

On swept wing airplanes, sweep and dihedral in wing tanks causes C of G to move forward as fuel is burned (level drops in the tips first, which are aft).  On swept wing airplanes with a center tank, the center tank is almost always burned first and it causes an aft shift of C of G as its fuel is burned, followed by a forward shift as the wings are consumed.

The C of G charts of swept wing airplanes will include a fuel burn curve to show the C of G location variation with fuel burn. If no center tank, the curve will slant or curve to represent the forward shift, and if there is a center tank it will have a kind of sideways V shape as the C of G moves aft and then forward as the pounds of fuel load declines.

Bottom line is, do whatever the weight and balance chart for the airplane says to do.  If it's something like a 172, there isn't going to be any major shift. If it's something like a Taylorcraft with a nose tank, C of G will shift aft as fuel is burned.  To keep things simple, there may be a baggage restriction that is intended to prevent exceeding the aft limit when the tank is empty at the end of a trip.


Why weren't the Airbus A330 engines designed with a system to stop their fans?

Complexity and weight, what airlines hate most.

Has it been done before? Yup. A variant of the Convair B-36 Peacemaker was able to stop the windmilling when the jet engines were not needed (that variant had 6 piston engines and 4 jet engines).

(Source)

  The metal petals filling the inlet prevented the jets from turning in the wind as the B-36 cruised for long periods of time with them turned off. The petals retracted to allow the jet engines to be ignited for extra thrust during take-off and high speed dashes. A strut braces the nacelle against swinging from side-to-side.

Scaling this up for the big diameter engines for that very rare engine failure is not cost effective. Instead planes can survive, and are extensively tested for, vibration and flutter.

How rare is very rare?

  By the 1970s, advancing technology had set the stage for two-engine, turbine-powered airplanes to safely exceed the 60-min operating restriction [away from the nearest airport]. The result was ETOPS, which began in 1985 with 120-min diversion authority and the requirement for an average engine in-flight shutdown (IFSD) rate of just 0.05 per 1,000 engine-hours. With 180-min ETOPS authority, which followed in 1988, an even more stringent reliability target of just 0.02 IFSDs per 1,000 engine-hours was specified (Boeing, 2003).


What would be the stall speed of Solar Impulse?

Solar Impulse has no flaps and a high aspect ratio wing. Therefore, the c$_{l_{max}}$ of the wing should be no higher than 1.8, most likely 1.6. While a rigid airfoil can be designed with a higher c$_{l_{max}}$, it will not have an attractive L/D and a shorter wing would have a c$_{l_{max}}$ below that of the airfoil. Since no fuel is consumed, mass is constant, which makes it very easy to give a lower bound for the minimum speed.

Solar Impulse 2 has 269.5 m² wing area to carry its 2.3 tons of mass. This is a wing loading of just 8.53 kg/m². If we assume standard day conditions at sea level (density $\rho$ = 1.225 kg/m³), we find vor v$_{min}$:

$$v_{min} = \sqrt{\frac{2\cdot m\cdot g}{c_{l_{max}}\cdot S\cdot \rho}} = 9.24 \;\small{\frac{m}{s}} \;\text{or}\; 33.27\; \small{\frac{km}{h}}$$

For those of you from metrically challenged cultures: This is 18 knots or 20.67 mph.


Who decides when landing gear requires an overhaul?

The aircraft manufacturer in consultation with the regulatory authority will publish a maintenance schedule that details what maintenance is required and at what interval.

For simple types the maintenance my be no more that a visual inspection and a tyre pressure check.


What is the absolute velocity change through compressor+burner?

The flow enters the compressor at approximately Mach 0.4 to 0.6 in order to ensure a high mass flow with still subsonic compressor blade speeds. Compressing the air allows to reduce flow speed, and between compressor exit and combustion chamber is a diffusor to reduce flow speed even more. Why? To ensure a high degree of combustion! The longer the reactants remain in the combustor, the better. And large combustors are heavy, so they are kept as short as possible.

As soon as the air heats up, it picks up speed. In that respect your graph is not quite correct (or it assumes a rapidly widening cross section through the combustor). But the general relation between pressure and speed is right: While no energy is added or removed, the sum of pressure energy and kinetic energy of the flow is constant. While both the compressor and the combustor add energy and the turbine removes it again, the nozzle is such a region of constant energy. Here the remaining pressure of the flow is converted into speed.


Means of protection against hunter-killer UAVs

By far the cheapest method for protecting a limited area would be to use an aerostat to carry aloft a jammer. Vehicles like the Reaper rely on a satellite uplink to maintain their command and control. As long as the aerostat is well above the altitude of the Reaper it can easily jam it. The cost of this option might be around \$1 million with an annual operating cost of \$200,000 and an effective diameter of about 10-20 miles.

A more expensive, but more flexible response would be to just shoot it down. To do this you would need an air surveillance radar, a high performance turboprop with machine guns like a Texan or Super Tucano, a pilot and a crew to operate the radar. With this method you could deny a pretty large area, maybe 100 miles in diameter easily, possibly more. The cost of this would be about \$3 to \$5 million plus annual operating costs of about $500,000. If you want to spend a bit a more a Yak-130 would be an excellent light attack jet to consider for anti-drone work. You might be able to find a used Yak for under \$10 million and it is a bitchin aircraft that can go double the speed of a Predator plus it has its own radar.

Missile systems would not really work because the types you would need to reach the altitude a Reaper operates at, are very expensive and complex (which is exactly why the Reaper flies at those altitudes). However if you could catch the Reaper while it was taking off or landing, a small missile like an RBS 70 would be even cheaper, assuming you could obtain that weapon.


What is the difference between SSR and ADS-B?

The biggest difference between SSR and ADS-B is how the aircraft position is determined. Secondary Surveillance Radar uses a radar antenna on the ground to send an interrogation signal and then determines the position based on the reply from the aircraft transponder:

The radar antenna rotates (usually at 5-12 rpm) and transmits a pulse which is received by the onboard equipment (transponder). The transponder sends back a reply containing at least a code (if operating in Mode A) but more often this is combined with level (mode C) or other information, e.g. aircraft identification, selected level, etc. (Mode S). The information received depends on the interrogation mode (A, C or S) and the transponder capability. [...]

When the reply is received, aircraft position (range and bearing) is determined. The range is calculated by knowing the time difference between the interrogation and the reply (the speed of propagation is the speed of light). The azimut is taken from the antenna position.

(SKYbrary - Secondary Surveillance Radar (SSR))
An aircraft equipped with ADS-B Out will regularly send signals without an interrogation. The aircraft position can therefore not be determined based on receiving such a signal. It must therefore be encoded in the signal itself, which requires that the aircraft knows its own position from a GNSS source:

ADS-B is a Surveillance technique that relies on aircraft or airport vehicles broadcasting their identity, position and other information derived from on board systems (GNSS etc.). This signal (ADS-B Out) can be captured for surveillance purposes on the ground (ADS-B Out) or on board other aircraft in order to facilitate airborne traffic situational awareness, spacing, separation and self-separation (ADS-B In).

(SKYbrary - Automatic Dependent Surveillance Broadcast (ADS-B))
ADS-B usually uses the same frequency of 1090 MHz to transmit, but it may also use other frequencies (see this answer for details).
Not only ADS-B signals can be received by other aircraft (ADS-B In). The ACAS (Airborne Collision Avoidance System) can also receive replies from SSR:

ACAS II is an aircraft system based on Secondary Surveillance Radar (SSR) transponder signals. ACAS II interrogates the Mode C and Mode S transponders of nearby aircraft (‘intruders’) and from the replies tracks their altitude and range and issues alerts to the pilots, as appropriate. ACAS II will not detect non-transponder-equipped aircraft and will not issue any resolution advice for traffic without altitude reporting transponder.

(SKYbrary - Airborne Collision Avoidance System (ACAS))


What is the difference between a flow and a checklist?

Generally speaking a checklist is an actual list of items to check, and a flow is a pattern of movement across the aircraft controls (switches, dials, etc.) which will accomplish some subset of the items on a checklist.

A flow should be essentially "muscle memory" for a pilot and performed by rote, where a checklist may be more detailed and include more specific guidance.

As you can probably tell flows and checklists are closely related (with flows usually being derived from checklists). The two are complimentary tools that are used together: A pilot will follow a flow, and then verify that the required items have been completed using the checklist.
In larger/more complicated aircraft it's not possible to fully memorize some of the checklists, so flows are used to accomplish the "red box" immediate action items before proceeding to the full checklist.

As a simple example, consider the engine power loss flow & checklist for a Piper Cherokee.

Engine Power Loss Flow (Red Arrow & Numbers)

Mixture (Set appropriately - usually "Rich")
Throttle (Set appropriately)
Carb Heat / Alternate Air (On)
Magnetos (Both)
Electric Fuel Pump (On)
Primer (In & Locked)
Fuel Selector (On a tank that has fuel)

Manufacturer's Engine Power Loss Checklist (Blue Numbers)

Fuel Selector - Switch to a tank containing fuel.
Electric Fuel Pump - On
Mixture - Rich
Carb Heat - On
Engine Gauges - Check for an indication of the cause of power loss
Primer - Check Locked.
If no fuel pressure is indicated  check tank selector position to be sure it is on a tank containing fuel.
Ignition Switch - "Left" then "Right" then back to "BOTH."
Throttle and Mixture - Different settings.
(This may restore power if problem is too rich or too lean a mixture, or a partial fuel system restriction.)
Try another fuel tank.
(Water in the fuel could take some time to be used up, and allowing the engine to windmill may restore power. If power loss is due to water, fuel pressure indications will be normal.)

In this example the flow accomplishes nearly all the checklist items, but it does so moving over the panel in one direction. As a practical matter the flow is accomplished by just moving your hand along the bottom of the panel: "Push the mixture. Push the throttle. Pull the carb heat. Twist the mag key. Flip all the switches UP (on). Pull the primer and make sure it doesn't move. Move the fuel selector lever to the other tank."
Completing the flow takes less than 10 seconds and can be done with one hand while your other hand is pitching for best glide speed.

The manufacturer's checklist for an engine power loss moves around the panel in a more haphazard way, but it also adds a few items (checking the engine gauges & fuel pressure indication), and provides more specific guidance on possible causes like fuel contamination (water in the fuel) & how to deal with them. These items could be important if the memory items from the flow don't restore engine power, assuming you have time (altitude) to spend troubleshooting them.


What is the difference between a nacelle and a cowling?

The definition of a nacelle refers to the housing of anything on the outside of an aircraft. Engines are the most common thing in these housings.

  a streamlined housing or tank for something on the outside of an aircraft or motor vehicle.

The definition of a cowling is specifically a removable cover of the engine.

  the removable cover of a vehicle or aircraft engine.

So a nacelle refers to the whole covering of an engine that is outside the plane, typically on the wing. The cowling would just be the removable part of this cover. As Jan Hudec commented, engines mounted in the nose, as is typical in smaller aircraft, would have a cowling to allow access and cooling to the engine, but technically not a nacelle, since the covering would be part of the fuselage.


How can I calculate takeoff distance in a generic way?

For air carrier type aircraft, the chart you show in your question (sometimes called a "run-around-chart") is generally digitized in some form (performance data printed out on dispatch release, or in a Flight Management Computer on board the aircraft or handheld device provided to crews).

For light aircraft, likely there are many software apps available for the most popular types.

Here is a picture of an Apple APP I noted online for a Cessna 172.


Is the A330F main deck cargo compartment pressurized? If not, what is the purpose of the structural cargo access door?

You're correct- for cargo aircraft derived from passenger planes, the cabin is pressurized. This reduces the complexity and certification requirements. Also, this allows for easy conversion too. The thick door may be due to two reasons:

To improve load carrying/transferring capacity- airbus talks about

  ... the aircraft’s reinforced fuselage and doors, which increase shear and bending/running loads..

also, the thick door will help protecting the crew should the cargo move forward in flight.
To act like an airtight seal between the cabin and cockpit, so that it prevents smoke ingress into cockpit and to enable the crew to extinguish fire. FAA Class E (for cargo aircraft) requires isoaltion between the cargo compartment and cockpit.

Another thing to note is that even a number of military 'cargo' aircraft have pressurized cabins (An-124, I think is among  exceptions), as they are also used in Medivac and causality evacuation roles- these require the cabin pressure to be set higher than normal.


Is an Aileron Roll Easier Done Opposite The Rotation Of The Plane's Propeller?

Yes: Rolling one direction easier than the other, as you mentioned, newton's laws are at work here.

Special Tricks? Also Yes.  There are several design strategies to deal with asymmetries of thrust from propellers.  Bear in mind that these thrust asymmetries are not always at work, so any design feature is a trade off.  The propeller must be running, angle of attack is a factor, etc.  I have heard of asymmetrical wing incidence used, but more often a slight offset of a tail-plane, such as the vertical stabilizer is used.


What lights are used on top of a building or structure near an airport?

The general guidelines are:

  4.3 Lighting Systems. Obstruction lighting may be displayed on structures as follows:

  Aviation Red Obstruction Lights. Use flashing lights and/or steady-burning lights during nighttime. Tower structures are typically
  marked with flashing red lights. Buildings and smaller obstructions
  located near airports should be marked with steady-burning red lights.
  (See Chapter 5).
  Medium-Intensity Flashing White Obstruction Lights. Medium-intensity flashing white obstruction lights may be used during
  daytime and twilight with automatically selected reduced intensity for
  nighttime operation. When this system is used on structures 700 feet
  (213 m) AGL or less, other methods of marking and lighting the
  structure may be omitted. Aviation orange and white paint is always
  required for daytime marking on structures exceeding 700 feet (213 m)
  AGL. This system is not normally recommended on structures 200 feet
  (61 m) AGL or less.
  High-Intensity Flashing White Obstruction Lights. High-intensity flashing white obstruction lights may be used during daytime with
  automatically selected reduced intensities for twilight and nighttime
  operations. When this system is used, other methods of marking and
  lighting the structure may be omitted. This system should not be used
  on structures 700 feet (213 m) AGL or less, unless an FAA aeronautical
  study shows otherwise.
  Note: All flashing lights on a structure
  should flash simultaneously except for catenary support structures,
  which have a distinct flashing sequence between the levels of lights
  (see paragraph 4.4).
  Dual Lighting. This system consists of red lights for nighttime and high- or medium-intensity flashing white obstruction lights for
  daytime and twilight. When a dual lighting system incorporates
  medium-intensity flashing white lights on structures 700 feet (213 m)
  AGL or less or high-intensity flashing white lights on structures
  greater than 700 feet (213 m) AGL, other methods of marking the
  structure may be omitted.

Specific details are spelled out in AC 70/7460-1L CHG1 Obstruction Marking and Lighting.


Why aren't passengers sorted before embarking?

Many airlines do, to a degree.
That's why airliners are often boarded in sections (for example row 1-10, then 11-15, etc.).
Problem is many of the passengers don't listen to instructions, and rush the boarding agent the moment the lights go on indicating boarding has started, in part because they're afraid there won't be space for their 4 bags in the cabin, each of them oversized, if they're not the first on board.

And THAT's the real problem, many airlines not being rigorous about enforcing cabin luggage allowances and pushing people with excess to the back of the line and having them gate check (at additional fees) those bags consistently.


What is a plausible scenario for aircraft sabotage for a science fiction novel?

If the alien has to see it to fix it, that rules out anything not visible from the windows (i.e., tail, landing gear, etc.)

If the alien is a passenger, the only moving parts that come to mind are the ailerons.

Have your saboteurs cause a complete failure of the aileron controls (In a Gulfstream 3 I think it's cables with a hydraulic boost, but I could be wrong).  A semi-cut cable won't be caught on a preflight (who takes apart a wing?), but could break over the ocean.

Your alien could save the day by directly manipulating one of the ailerons to keep the plane level.

I don't know the forces involved - I hope your alien is really strong.


To keep the wings straight.

If you remove them there is very little to prevent the wing from rotating around the vertical axis.

All the other cables are attached to the king post or the seat. This cannot provide the leverage needed to counteract the wing yawing relative to the seat.


Is it feasible to replace a C152's engine with multiple small turbine engines?

Have a look at the Cri-Cri propeller and jet versions.  Yes, jets can be mounted near the nose, but the plane must still balance at within its specified CG range.  This is why removing the engine in front and placing jets in back is out (unless you want to really go crazy and mount a Gatling in the front). Remember, it must balance.
However, at Cessna (152) speeds, props are vastly more efficient, so a $turboprop$ is not out of the question and, indeed, these are found on crop dusters.
"Pocket jets" are also found on motor gliders, and I have often thought of putting 4 of these on a sailplane.
However, another key consideration is how much stress an airframe can take.  With jets come higher speeds.  These planes are built to flying within a certain speed "envelope" regardless of propulsion source.
The "Screamin' Sasquatch" may interest you.  Here a jet is mounted on a sturdy bi-plane, and yes, it works.


We all know the saying "From High to Low, Look out below"  Some were taught that this only applied to pressure differences and thus were instructed to get a new altimeter setting every 100NM or so.  This is a good recommendation.

Temperature differences from standard also causes errors with the altimeter.  The same saying above holds true with temperature variations.

An altimeter setting is defined as: (ref. Pilot/Controller Glossary)

  The barometric pressure reading used to adjust a pressure altimeter for variations in existing atmospheric pressure or to the standard altimeter setting (29.92).

We also know there is a direct correlation between pressure and temperature and thus an altimeter setting is corrected for both pressure and temperature.  This means one thing, the altimeter error is zero at the field elevation.  As the aircraft gets climbs higher above the field, the altimeter error will increase.

There is a table in the Aeronautical Information Manual (7-2-8) that lists altimeter error due to temperature as a function of altitude (AGL) and temperature.

Here is the formula that will give you this table.  The formula can be found in Canadian Aeronautical Information Manual (RAC section).

The United States Air Force has a PowerPoint that discusses this topic.

The FAA has recently come out with Info 15002 which requires pilots (after 9/17/2015) who fly into "Cold Temperature Restricted Airports" to correct their altitudes for colder than standard temperatures.  To determine if your airport is part of this program you must go to the Aeronav FAA website and search for Cold Temperature Restricted Airports.  There should be a link at the bottom of the page.

Here is a graphic showing all the airports in the United States that were part of the program in February 2015.

Because Lnafziger wanted Alaska.

Not only is the pilot required to correct for the segment but they are also required to inform ATC of the new altitudes they will fly.  This is to ensure traffic separation with other airplanes who are not temperature correcting their altimeters.

Pictures taken with permission from All About Airplanes blog.  All rights reserved.


Electrically heated windshields are mostly transparent, but their colors vary from light blue, yellow or light pink. Please explain

The heating element in cockpit windows is typically a thin film comprised of a transparent conducting oxide - indium tin oxide is common. In thin layers, it is transparent to the visible light spectrum but acts as a mirror in the infrared. As with all transparent conductive films, there will be some  tradeoff between transparency and conductivity.
Thin-film interference is a natural phenomenon in which light waves reflected by the upper and lower boundaries of a thin film interfere with one another, either enhancing or reducing the reflected light. When the thickness of the film is an odd multiple of one quarter-wavelength of the light on it, the reflected waves from both surfaces interfere to cancel each other. Since the wave cannot be reflected, it is completely transmitted instead. Thus when white light, which consists of a range of wavelengths, is incident on the film, certain colors are intensified while others are attenuated. Thin-film interference explains the multiple colors seen in light reflected from soap bubbles and oil films on water. It is also the mechanism behind the action of antireflection coatings used on glasses and camera lenses.
For any certain thickness, the color will shift from a shorter to a longer wavelength as the angle changes from normal to oblique. This interference produces narrow reflection/transmission bandwidths, so the observed colors are rarely separate wavelengths, such as produced by a diffraction grating or prism, but a mixture of various wavelengths absent of others in the spectrum. Therefore, the colors observed are rarely those of the rainbow, but browns, golds, turquoises, teals, bright blues, purples, and magentas.
Additionally, keep in mind that in its thicker, bulk state, indium tin oxide is naturally yellowish-grey. Therefore, the thicker the film, the more it's natural color will influence the light passing through it. I don't know the natural colors for every transparent conductive film material, but it stands to reason that there will be some variation in natural coloration there as well, owing to the different elements included in the composite.


Why is the speedbrakes rate of retraction 25 seconds when used at speeds greater than 315 knots/.75 Mach on the A320?

Please read the entire answer to understand the matter even if the answer goes a bit beyond the question.

On the A320 wings you have panels that may open upward and that could be used to fulfill 3 different functions: ground spoilers, speed brakes, roll spoilers.

The outer panels are used in addition to the ailerons for roll function, that is helping the ailerons only on one of the wing according to the turn direction.

The central panels are used in flight for the speed brake function as follows: when the pilot order is beyond a limit the Fly By Wire will provide protections because an excessive drag might damage the wing structure, so the higher the speed the lower will be their maximum angle of deployment and their speed of deployment even if the pilot gives a full order of deployment.

The drag produced by the air brakes causes a mechanical torque on the wings roots, a sudden removal of the drag would be similar to a stress cycle, therefore deployment and retraction are managed to protect the wing structure.  Any pitching effect of these surfaces in flight is automatically compensated by the FBW through the elevators.

At landing the ground spoilers function is as follows; all the surfaces are deployed fully if the function is armed.


Is it possible to make an analogy between a lever and an airplane wing in terms of force applied over distance?

Well, they call them air PLANES for some reason.  Maybe not a lever, how about a ramp?

How does 1/4th the thrust lift a given weight?  One consideration that is very important for aviators is to realize the best way to use thrust is to create speed.  Speed creates lift.

It is indeed a minor miracle that the airflow over a wing at flying speed creates so much upward force.  One way to see how this works is to look at the back of a boat while it is travelling slowly.  See the swirls and eddies of the water in the wake.  Now speed up and the water separates from the stern and forms a wave behind the boat. The lack of water at the stern is the same as air being deflected away from the top of the wing at sufficient speed.
This area of lower pressure near the wing is lift.  How much to lift a one ton Cessna? The wing is roughly 5 x 40 = 200 square feet.  200 square feet x 144 square inches/square feet = 28800 square inches.  2000 pounds/28800 square inches = 0.07 psi.  Not much, but it works!

Slow down and the wave collapses back to the boat.  This is a stall on a wing.  So lift is INDIRECTLY produced from thrust by forward motion (and angle of attack).


Would a tumbleweed sucked into a jet engine on takeoff cause a serious problem?

Luckily tumbleweed rolls and doesn't fly [like some geese].

I tried to check how much an average one weighs, I couldn't find out. But it will cause some degree of damage. The engine can fail, but if it's just one tumbleweed then it's just one engine, it'll be serious but not dangerous. Airliners can fly with one engine inoperative, they are designed for it.

If it happens before the airplane reaches what's called a V1 speed, the flight crew can just abort the takeoff.

I didn't find any occurrence/report of it happening before. And it hasn't been tested before (they test using chicken guns).

Airport tower controllers and ground staff are vigilant in spotting such things, as this story shows:

  Escorted back for questioning!


What's the difference between FAA Part 61 and Part 141 training?

There's no singular right answer, it's up to the individual and how he or she learns best. The biggest difference between the two you'll find is that part 141 schools are always very structured in their training regiment. That is not to say part 61 isn't (nor does it imply that it's better for everyone), it's just that part 61 does things according to what they wish with less FAA oversight.

You might know that under part 141, the earliest you can get your ticket is 35 hours, while part 61 requires a minimum of 40 hours. Don't let that red herring influence you; almost everyone takes more than 40 hours regardless of the school type.


Is there a rule concerning the offloading of a missing passenger's baggage?

This question was covered over on travel.stackexchange and seems like there is a European reg on it.

  In Europe, the question is covered by Regulation EC 300/2008. Annex I,
  section 5.3 reads

  Baggage reconciliation

    Each item of hold baggage shall be identified as accompanied or
    unaccompanied. Unaccompanied hold baggage shall not be transported,
    unless that baggage has been either separated due to factors beyond
    the passenger’s control or subjected to appropriate security controls.

I cant find any hard regulations but there seems to be some discussions floating around that would imply a domestic US flight may depart with your bags and without you here in the states.

I can speak from experience while on a flight departing CDG for DUB the plane was held to remove a bag that belonged to a passenger that decided to take a different flight.


Why are some Tomahawk missiles' nose duck-nose shaped?

I developed the shape for Convair back in the late 90's.  It was called a chined nose and Carlo is right, there were no aero considerations for this shape.  It was purely RCS.


What is the difference between CAN and ARINC?

the communication between the cockpit and the controllers is done by using Arinc protocols. And the data transmitted by probes to the controllers is done by CAN.

That depends very much on the aircraft type.

  And when can we use each one of them (Arinc and CAN)

When you design your own aircraft you get to choose.

CAN stands for Controller Area Network. CAN is a bus standard designed to allow microcontrollers and devices to communicate with each other in applications without a host computer. It has its origins in the automotive industry.

ARINC stands for Aeronautical Radio, Incorporated. ARINC is an organisation that amongst other activities produces technical standards for avionics and provides services to aircraft operators.

Amongst the ARINC standards there are a number addressing data communications between avionics components. Most widely used is the ARINC 429 standard which describes an avionics data bus. ARINC 429 allows a single transmitter to communicate data to up to 20 receivers over a single bus.

Comparing CAN bus to ARINC 429:

Cable

CAN: STP or UPT, possible to implement on fiberoptic cable
ARINC 429: STP

Speed

CAN: 1 Mbit/s (high speed) / 125 Kbit/s (low speed)
ARINC 429 100Kbit/s (high speed) / 10-14 Kbit/s (low speed)

Directionality

CAN: bi-directional, connected units can send and receive on the same cable.
ARINC 429: uni-directional, a unit either transmits or receives from a cable.

Number of units on a single bus

CAN: unlimited, although in practice no more than about 32 units will be sharing a bus to avoid data collisions.
ARINC 429: one transmitter can serve at most 20 receiving units on a single cable.

Since ARINC 429 has only a single transmitter, timely data arrival is guaranteed, while CAN has to incorporate transmission collision detection & correction which incurs non deterministic time overhead.

On the other hand, ARINC 429 only uses a parity bit for bit level error detection whilst CAN allows for various methods including CRC checks

Some of this data is obtained from an article on CAN bus in avionics magazine.

Newer ARINC busses like 629 or 664 (AFDX) allow for higher speeds and bi-directional communication. These may eventually replace ARINC 429 (but never underestimate how slow progress in aviation is)


So there's a lot going on in your question to address. First, and most importantly, the info you linked is for ATC, not pilots. you won't get any usable info of how to fly IFR in this airspace. You won't need to know any of this to fly IFR. You won't need any of this to fly VFR either, for what it's worth.

When you fly IFR you file a flight plan that includes your route, destination, and nav points, which are those funny named things like WAVEY in the chart you linked. This is done before you even step in to the plane. Generally a day ahead or early in the morning of your flight, but you can file it right before. a lot of pilots (this is for non-commercial) will take off VFR and then "pick up" their filed flight plan after they are en route. this means you don't have to wait for an IFR release on departure. You just take off, fly in the general direction you are headed, and then ATC will direct you via nav points the rest of the way (or if you're lucky tell you to proceed "as filed", which means no changes to your original plan). For commercial they don't usually have to wait for the release because they are scheduled flights. Thats kind of a different world. I bring up how it happens for non-commercial because you will do a LOT of that kind of flying before you have to be worried about how United and Delta get off the ground.

an IFR approach plate for pilots is still confusing, but there isn't nearly as much going on as what you have linked. Approaches are very very specific for the runway, type of approach (look up types of instrument approaches), and a number of other factors. specific to the point of each has a special thing you do if you can't land for any reason and have to "go missed". This is a huge portion of the IFR training, and nobody can really be self taught this or know how to do it right away. IFR is the hardest rating for a reason.

Don't get too cocky about being able to talk to ATC while VFR. Thousands of experienced pilots a year go through comms training because it's hard. In vatsim is one thing, but the real world of radio is one of the most stressful and elusive parts of the flight. get something wrong and you can lose your license or your life.

If you want to get started with reading charts go to sportys.com and buy their VFR sectional training chart. It's 3 dollars and gets you a manageable section of a navigational chart to learn how to plan and plot and read an aeronautical chart. Theres a lot going on there, you have true longitude and magnetic longitude lines, VORs, airport info, waypoints, obstructions, ground levels, airspace, MOAs. Don't think of VFR as "the easy flying".


Is it quiet in the cockpit when flying faster than the speed of sound?

No, for two reasons:

Speed of sound is always relative to the material the sound propagates in; it moves faster through denser media, such as the aluminum structure of the aircraft itself. The aircraft's structure moves with the aircraft, so the vibrations of the jet engines will be transmitted to the cockpit/cabin at the same speed as when the airplane were flying subsonic.
The air inside the cockpit is still, and so sound within this local bubble is unaffected by the speed of the bubble itself (and so sound can travel faster than sound). If this weren't true then radios and other cockpit sound sources like alarms would be inaudible at supersonic speeds, which would be a major safety hazard and tactical disadvantage to supersonic flight.

You actually don't even have any significant aural cues inside the cockpit that you've exceeded Mach 1; you have to rely on your airspeed gauge to tell you.


What is the difference between GVI and DVI?

GVI is general visual inspection and when you make a GVI, you have to be maximum an arm's length distance to the area and/or component you are searching any defects.

DVI is detailed visual inspection, it depends to the situation but usually you use a tool like a magnifier to inspect the area/component.


Why do people put $1 & OVC on aircraft bills of sale?

This practice is really more of an accounting/finance question than an aviation one, but it's common enough that it's probably worth addressing here.

When reviewing an aircraft's registration record you will frequently see the price on the FAA Aircraft Bill of Sale form given as "\$1.00 & OVC" (One dollar and Other Valuable Consideration) as shown on the example below (click to enlarge).

The "Other Valuable Consideration" can be anything of value: Personal favors, other property (a car, a different airplane), blackmail information on someone you don't like, or (most commonly) money in excess of \$1.

In a strict cash sale recording the amount on the bill of sale in this manner protects the sale price from prying eyes: Anyone with \$10 to spend can request an aircraft records dump from the FAA which will contain every bill of sale filed, but if the price is listed as some small dollar amount plus "Other Valuable Consideration" it's impossible to determine the exact price paid using only the bill of sale.
Note that in cases other than a strict cash sale other documents filed with the FAA (for example recording a lien against the aircraft to secure a loan financing the purchase) may disclose the purchase price depending on how those documents are filed: Some include the amount of the debt the aircraft is securing, others simply state "The debt identified by loan number 12345." which would still protect the confidentiality of the sale price.

As a means to avoid taxation recording the sale price as "\$1 & OVC" almost never works: The tax authority is going to ask you the value of the "Other Valuable Consideration" and base the tax due on that amount.
If you tell the tax authority the aircraft was really only worth $1, and record it as such, they're going to want to know why: Generally even an unairworthy aircraft is worth more than that for the value of its parts.

Conversely if you get a ridiculously good deal on an airplane it can be to your advantage to fill out the bill of sale accurately & present that along with other documents pertinent to the sale to your tax authority: You may be able to get the sales/use tax based on the ridiculously good deal rather than an appraised market value.


What is the typical sink rate during a well-executed carrier landing at the moment the main wheels touch the deck?

A lot. About 3-4 m/s (600-800 fpm). This is the speed at which 'normal' landing gear begin to break.

For carrier landings, there is no flare, so the touchdown speed equals to the sink rate on the final approach. The procedure in the linked question mentions 700 fpm.

We can arrive at a similar figure if we consider the standard carrier glideslope 3.5° (pdf) and the typical approach airspeed of ~120-130 kn. If we allow 20-30 kn for carrier speed and headwind, then for 100 kn (51.4 m/s) closing speed we get 51.4 m/s * sin 3.5° = 3.14 m/s ≈ 620 fpm.


What are the B737 MAX 8's OEW and max payload?

The type certificate of the Boeing 737 provides the following table for the MAX:


What prevents a propeller from detaching completely from the engine body?

Nuts. Technically nuts and bolts.

If you look at pictures of propeller hubs (google "propeller hub") you'll see that the individual prop blades are held onto the prop hub by nuts and bolts holding the hub halves together. Or for wooden props they're bolted directly onto the hub.

If you then take the hub apart, you'll see that the hub is attached to the shaft using nuts and bolts.

I sometimes see people asking why aircraft engineers specify very expensive nuts and bolts for certain parts of the aircraft when a cheaper part can handle an equivalent load. Your question is exactly the reason - it's better to over-engineer certain parts like the prop assembly than have the prop accidentally fly off during flight.


What do the abbreviations on this Jeppesen Dataplan mean?

GRS = Groundspeed

MCS = Magnetic Course

FU = Fuel burned that leg (100s)

FR = Fuel Remaining

T = OAT in degrees C, apparently without the sign.

S = Shear value (measure of turbulence) forecast

FF/E = Fuel Flow per Engine per hour

With thanks to @mins for filling in the gaps!


What are the names of the antennas which I have marked in this picture of a Boeing 737?

ATC, Altimeter Transmitters and Receivers, and DME-1


What ATC entities does a commercial airliner communicate with?

This answer details the procedures used in the US. Other countries will be similar, possibly with different names for some positions.

When preparing for a flight, after their flight plan has been filed, the pilots will first talk to the clearance delivery controller. This controller clears their planned route and altitude. At larger airports this may be done via text rather than voice. The pilots may also call their company dispatch to get the route or fix any problems.

If there are significant delays in effect at the airport, the pilots may have to talk to the metering controller. This controller is responsible for holding aircraft at their gates. Weather at departure or arrival airports may reduce the number of aircraft the airport can handle. There is no sense in sending the aircraft onto the busy taxiways if they will just have to sit there and wait for weather or traffic before they can depart.  The metering controller will eventually hand the pilots off to the next controller when the aircraft is finally cleared for departure.

Again at larger airports, the next contact will be with the ramp controller. This controller is responsible for a ramp area near the terminals. The controller will let the pilots know when it's safe to push back, and which way they should turn at the end of the push back. After starting their engines, the pilots will receive instructions for exiting the ramp.

Once pilots reach the edge of the ramp area, they will call the ground controller. This controller is responsible for managing traffic on most of the taxiways. The pilots will receive instructions for taxiing to their departure runway. If this route takes them across an active runway, the ground controller will have to clear this with the tower controller, or possibly have the pilots switch to the tower controller for permission to cross the runway. At small airports, the ground controller handles all of the previous positions as well.

Upon reaching their departure runway, the pilots will switch to the tower controller. The tower controller is responsible for the active runways. Busy airports may have multiple tower controllers managing different runways. The tower will clear the pilots for takeoff, ensuring proper separation between any other arriving/departing aircraft.

Shortly after the aircraft starts climbing, the tower will hand the pilots off to the departure controller. Depending on the location and traffic levels, this could be the same controller and frequency as the approach controller. This position is part of the TRACON (Terminal Radar Approach Control) facility. High traffic areas will have their own separate TRACON facility, while in lower traffic areas this will be combined with a tower location. In other countries this is referred to as the Terminal Control Center (TCC).

The approach controller's responsibility is routing aircraft leaving airports in the area to avoid conflicts between aircraft, but often the pilots will just fly the published departure procedure. The departure controller receives reports of weather such as precipitation or icing and passes this on to other aircraft.

Upon reaching a certain altitude, the departure will hand the pilots over to the center controller. This position is part of an ARTCC (Air Route Traffic Control Center), often abbreviated to "center". The US has 22 ARTCCs, each further divided into different sectors. Sectors are consolidated between controllers depending on traffic levels. Other countries refer to this as an Area Control Center (ACC).

The center controller is responsible for traffic at higher altitudes, primarily enroute traffic. The aircraft may pass through multiple centers, and each center may have different sectors controlled by different controllers. The pilots will be handed off between these controllers. Pilots must request altitude or course changes (for efficiency or weather reasons), and controllers may issue changes for traffic reasons. Controllers also handle pilot reports of conditions such as turbulence.

If the flight is crossing large areas of ocean, the flight may be handed over to an oceanic controller. These controllers do not always have radar coverage of the aircraft they are controlling. They rely on the aircraft following their published routes and altitudes, and providing regular position reports. The lack of radar means there are also more strict rules about deviations from flight plans.

As the pilots get closer to their destination, they will start on their arrival procedure. This usually specifies altitudes and possibly speeds, so the pilots will need to plan when to start their descent in order to meet these restrictions. The center controller will know the procedure and instruct them to follow it, and possibly issue deviations as traffic requires.

At some point before arriving, the pilots may also contact their company at the arrival airport. They may need to coordinate passenger needs such as wheelchairs or medical/security issues, or communicate maintenance needs. They will also coordinate what gate they are scheduled to use. This can also be done via text, such as through ACARS.

When descending out of center's airspace, pilots will be handed over to the approach controller. This position is part of a TRACON and handles arriving traffic. Depending on the location and traffic levels, this could be the same controller and frequency as the departure controller. The pilots will continue to follow the arrival procedure, again with any deviations issued by the controllers. The departure controller receives reports of weather such as precipitation or icing and passes this on to other aircraft. The controller may also issue information about weather observed on radar, although each aircraft also has its own radar onboard. The approach controller will then provide vectors to the pilots as needed to get them to an approach procedure. The approach controller will then clear the aircraft to fly a certain approach to a certain runway.

Once the aircraft is established on the approach a few miles from the runway, the pilots will be handed over to the tower controller. The tower will clear the aircraft to land. If the aircraft has to go around, the pilots are sent back to approach to be sequenced back onto the approach. The tower controller also receives reports of wind shear and at what altitude pilots break out of the clouds, to pass on to the next aircraft.

After exiting the runway, the pilots will change to the ground controller. As before, the ground controller issues taxi instructions to get the aircraft to the appropriate ramp.

Before entering the ramp, the pilots will call the ramp controller. The ramp controller must see if the aircraft's scheduled gate is available. If not, the aircraft will have to wait on a taxiway somewhere. Once the aircraft's gate is free, the ramp controller allows the aircraft to enter the ramp, and park at the gate.


There are numerous unclassified papers talking about LOC, GS, MLS and other navaid jamming. There are also instances of that happening, both intentionally and unintentionally.  The issue with consumer electronics is made worse is that local consumer electronics on the plane can have local oscillators in the receivers.  They are small signals, but they are close to the antenna, hence the greater risk.

Jamming LOC (lateral ILS guidance) and VOR are similar. GS interference is a bit more difficult to provide false readings that make sense to a pilot, when the transmitter is off airport.

The reality is that even GPS can be jammed, faked with stronger signals, etc. Numerous companies make GPS-GNSS simulators, and it is not rocket science to integrate those into jamming systems.  Some of the countermeasures are documented in open literature, and other countermeasures and methods are not.  GPS jamming becomes an issue with various weapons delivery systems, and creating effective countermeasure packages with limited size-weight and power (SWAP) is a constant challenge.

I concur with @STWilson, that if faced with the possibility of interference, it would be good practice to monitor your approach with GPS, NDB, OM and other navaids.  For example, one can always start a timer crossing the OM, even if doing an ILS. Certainly in a war or terrorism situation, additional cross-checks are good investments of effort.


Have any airliners successfully landed on a runway after striking a tree?

Searching through the Aviation Herald database for incidences with the word tree, I found 3 cases:

An Eagle Air Let L410 contacted a tree during departure from Lankien in South Sudan. The right wing tip was damaged, but the aircraft continued to its destination, where the wing tip was repaired:

A China Eastern Airbus A320 contacted trees during a go-around at Wenzhou after losing visual contact with the airport during approach. The damages were only found after landing though:

A post flight inspection found scratch marks on the right main landing gear, slats and flaps of right main wing and the inlet of the right hand engine (CFM-56). An inspection of the right hand engine revaled damage (dents sized up to 0.2 mm) to all 36 fan blades, scratch marks (13cm in length) at and twigs embedded in the oil discharge.
[...]
Due to the late decision by the crew the right hand wing, right hand engine and right hand main gear impacted and clipped treetops outside the airport perimeter.

A Cebu Pacific Airbus A320 came in contact with trees, but the damage was also only found after landing:

a subsequent pilot inspection found branches and leaves embedded in the right hand main gear, the right main gear was leaking hydraulic fluid. The occurrence was rated a serious incident and is being investigated by Philippines's AIB.


How do coefficient of lift/drag variation with speed differs between swept and unswept wings?

It's not so simple.
For swept wings it is essential whether the leading edge is sub- or supersonic.
What does that mean?
If the leading edge is within the Mach cone emanating from the tip of the wing, it is called subsonic. The approaching air will "sense" what is coming and behave much like in subsonic flow. This avoids wave drag and keeps nose suction alive; an effect that can be maximized by the use of conical camber: Here, the leading edge is bent down similar to a cone surface with its apex at the wing root and the cambered part increasing towards the wing tip. This forward-facing part of the wing experiences suction which helps to pull the airplane forward.

Conical camber on the wing of the SR-71 (own work)
Of course, such a swept wing with a subsonic leading edge will also stall quite like it does at subsonic speed. However, the drag caused by a fully supersonic wing is so much higher that the small benefit of a higher lift coefficient does still not make it attractive. The drag at those high lift coefficients is so high that any airplane will quickly decelerate to subsonic speed once it tries to reach those lift coefficients.


Turbofan engine start - Why does ignition occur so early?

Traditionally the fuel is introduced by the pilot at a specified minimum RPM, but this is a function controlled by the pilot-eye-hand brain interface (only on the newer pushbutton start FADEC engines is this function fully automated) and we all know how imperfect this interface is.

With a traditional system, you need to allow some fudge factor in case the pilot adds fuel early, and also if there are system faults it gives a bit of time for the fault to be detected and displayed. So most start systems start the igniters running as soon as the starter is on (in the pre-FADEC days it wasn't too hard to ruin an engine, which is why captains traditionally handle starting).

The RPM at which fuel is to be turned on is actually bit sooner than really necessary, to let the engine help the starter bring it up to self-sustaining RPM.  The minimum RPM is there because you need a minimum mass flow going to the burner can to control the flame and therefore the temperatures (these engines are "air cooled" after all and the majority of the mass flow is not actually being burned, but being used to contain the flame boundaries - some flame does make it back toward the turbine during start, as you see when the ITT spikes, but it has to be minimized, and the more mass flow the better).

You can delay introducing fuel well past the minimum RPM, and you will actually see a lower ITT peak on a non-FADEC engine by doing so (because, as I said above, more mass flow provides more flame control), but this really adds to wear and tear on the starter.

When I was in the Regional Airline business supporting CRJs we observed that a lot of captains made it a practice to delay fuel introduction quite late (like waiting to 25-30% instead of 20% for the GE CF-34) because they noticed that the ITT peak was lower when fuel was delayed.  However this had to be balanced against shorter starter life and we advised against getting carried away with this because the marginally lower starting ITT peak didn't appear to actually improve engine life, while shortening starter life significantly.

On the other hand, it's important to know that it isn't essential to get the fuel on right now when the RPM is at the fuel introduction value and you can do it at a relaxed pace. If the nominal value is 20%, putting fuel on at 23 or 25% does no harm, so take it easy (pilots in training (including me) would fumble with the thrust lever lockout thinking they had to get the fuel on exactly at the right time).


Airborne holdings are usually handled by ACC or approach sectors, typically manned by ACS or APS rated controllers respectively. There is no separate rating for "stack controllers" as you call them.


Can you identify this plane from 1920 and prior vintage?

I'm pretty sure that this is a Lincoln PT, part of the Lincoln Page PT series, although the PT/PT-K was in the late 20's and early 30's:

Source: Wikimedia Commons

You can read about it from EAA:

  The Lincoln PT-K model was the next development of the Lincoln-Page PT, designed specifically as a flight training or low cost sport flying airplane. The “Page” had been dropped from the company name before the PT-K came out, so the “PT” stood for “Page Trainer”.

  The PT-K was considered a well designed airplane from an aerodynamic standpoint in 1929, taking into account the mannerisms of a student pilot. The fuselage had a long moment arm for the tail surfaces, meant to desensitize the pitching and bucking of a nervous student pilot as he worked his way through the curriculum. In other words, the Lincoln was not too fussy and wouldn’t get all upset due to a little pilot error.

  The PT-K was powered by a 100 hp Kinner K5, which could max out at 104 mph. It was no exceptional trick for the PT-K to perform a well rounded loop from level flight; there was really no need to dive and gain excessive speed to bring it around.

  The structure of the PT series proved to be quite rugged. The original design had a split axle landing gear configuration with a shock absorbing bungee chord. The later design featured a stiff-legged rigid gear, coupled with low pressure airwheels. The low pressure airwheels had more than enough “give” in the sidewall so that no further shock absorption was needed.

  The PT-K was available with a few options, including a metal propeller, a lightly framed fully enclosed canopy for cold weather flying, navigation lights, and engine starter. One other item available as an option was Bloxham “Safety Sticks”. This option allowed the instructor to disengage the student’s control stick if a student “froze” during the flight.

The aircraft in the picture is restored, but the strut matches especially around the cockpit.

The Lincoln PT was offered with a different V-8 engine, the Curtiss OX-5 but there is no evidence that one was ever sold. You sir may have that evidence as you don't seem to have the PT-K version, but the PT version.


When do pilots facing bad weather turn back (U-turn)?

There is no definitive, objective, commonly agreed upon set of criteria that I am aware of that provides an answer to your question.

Certainly airline dispatch departments strive to send aircraft along routes that will minimize exposure to extreme conditions if that's an option, and there may even be changes of schedules involved, but in the end, it's the aircraft captain who has to make the decision in the cockpit, in flight.

As such, and as illustrated by the answers to your previous question, individual captains will employ different criteria. In my experience in the ITCZ and given my outlook, you did your best to pick your way through avoiding the "red" if reasonably possible, and if not possible, you minimized your time in the red.

Doing a U-turn was not an option that we typically considered. This was the attitude and practice of all of my peer group save one. As I remember, he turned back once, and he subsequently left the company. By his own admission, he wasn't cut out for the type of flying we were doing.

Having to cross any of the red during en route flying was not something you had to often do. You could almost always avoid that.

And remember, what the red means is heavy precipitation, which, while potentially accompanied by severe turbulence, does not always mean that will be the case. Thunderstorms with heavy precip would sit over Victoria Harbor in Hong Kong along the IGS approach to the old Kai Tak airport, and we would shoot the approach through the red. There would be turbulence, but nothing abnormal.

Conversely, the absence of red does not ensure there will be no severe turbulence. The worst ride I ever had was going through a "clear" area the radar showed between two cells.

Concerning making a U-turn, and especially flying in the ITCZ westbound during the day, if you did a U-turn you might well find that your return route of flight has closed in and might well be worse than the forward route to your destination. If the heat of the day is building in front of you westbound, the sun's insolation has been building more behind you than in front of you.