Why does the airport plate list a VASI that does not exist? I have a small but quite busy GA (General Aviation) airport I operate out of that gets over 140,000 of operations per year.  It's a popular GA destination, has an active school, and the area schools use it as a great short, narrow, practice runway. The AFD (Airport/Facility Directory) entry for the airport lists the runway as having a Tri Color VASI (Visual Approach Slope Indicator) at each end.  It doesn't exist.  As far as I've gathered it might have existed 20 years ago.

How does an oversight like this exist for such an extended period of time?

Is this something that should be reported?

The instrument approach plate lists the VASI as well, but it's never been NOTAM'd out of service.  Does this create a hazard to potential IFR traffic?

How does an oversight like this exist for such an extended period of time?

Because it doesn't get reported.

  Is this something that should be reported?

Yes, it should be reported, otherwise this oversight will exist for an extended period of time.

This dAFD website contains a link that should be followed to [r]eport any A/FD errors or changes. Somewhere down those links you'll find plethora of forms and rather confusing texts which seem not really helpful when you want to report a missing VASI. That brings us back to the answer on your first question.

Update:

In the comments, Kevin Cathcart pointed out the Aeronautical Data Inquiries form which is the appropriate form to flag the problem. Alternatively you can contact the NFDC (National Flight Data Center) via phone at 1-(866) 295-8236.

  Does this create a hazard to potential IFR traffic?

Whether it is a potential hazard depends mainly on the presence of other source of vertical guidance. Is there an ILS / gideslope active? No vertical guidance at all is a safety risk in low visibility conditions.


Where do I find the Weight Variants of an Airbus aircraft? Where do I find the Weight Variants (WV) of an Airbus aircraft?

The weight variants for each model are listed in the aircraft's type certificate which describes the type's compliance with airworthiness regulations. You can look up the type certificates from regulators such as EASA and FAA.

As an example you can look at the document for the A330. Each of the minor models (-300, -200, and -200 freighter) has its own section, and the weights are listed in the "Technical Characteristics and Operational Limitations" subsection. Below is the table showing some of the A330-200 weight variants. The maximum takeoff (MTOW), landing (MLW), and zero-fuel (MZFW) weights are defined for each variant.


Does the velocity of air in an engine increase in the compressor section or turbine section? I think it increases in the turbine section because the pressure and temperature decrease so the velocity increases but I'm not sure.

Air velocity increases in the turbine section.

In order to compress air, we need to apply work on it, like running a car engine harder to drive it up the hill. Part of the work required comes from decelerating the air that flows into the engine.

The work done can be released by accelerating the gas and letting it escape, creating thrust. The expanding gas also applies work on the turbine blades, which absorb part of the accumulated energy. Each turbine stage slows down the gas, but from a higher velocity base due to the expansion. In the turbine section as a whole, gas velocity is increased.

The faster the gas flows out of the engine, the higher the thrust that is created.


What is boundary layer, exactly? I read a lot about boundary layer but I don't know exactly what boundary layer is yet.

Airflow (or any fluid flow) will be zero at the surface of the object it's passing over. Imagine the airflow as layers (or "streamlines"), and remember the surface layer velocity is zero. As you move away from the surface, each layer will be going a little faster than the one beneath it until you finally reach "free stream" velocity. All of these low-energy (lower velocity) layers of air between the aircraft surface and the free-stream air make up the boundary layer.

Here is an illustration from NASA:

(NASA)


Is it possible to get into a spin situation while coordinated? Is there any possibility of spinning while coordinated?  Of course, any CFI would tell you no, but I wonder if the the following situation could result in a spin while coordinated:

Slow level flight in a turn
Outside aileron needed to counter over-banking-tendency; rudder as needed to keep coordinated
One wing has a higher AOA due to aileron deflection
Pull back on elevators, stalling one wing first

Yes, what you describe is perfectly possible. A stall in banked flight can result in a spin, given you fly the "right" plane.

My first flight in an ASW-20C was late in the afternoon, when most thermals had died down. I got a winch launch to maybe 350 m (the ASW-20 is rather poor in winch launches) and tried to find an updraft. In maybe 270 m I found one, but it was weak and narrow. So I slowed down to tighten the circle. Having flown a Discus all day before, I was not really alerted to watch out for a departure on stall. At some point the lateral stick force faded markedly, and out of the Discus habit I threw the stick into the circle so the inner aileron would deflect downwards to support the stalling wing. Bad choice! This aggravated the incipient stall, the aircraft rolled into the circle and pitched down. While the view from the cockpit before was blue above and green below, it got now all green. I was entering a spin.

The weakening stick force was the result of flow separation over the aileron, and while the Discus airfoil would still provide more lift with more deflection, the ASW-20 airfoil simply went into full stall.

I immediately pushed down and levelled the plane, and went on to land straight away, having lost maybe 100 m. It all took only seconds, and only long after the flight I could piece all details together. My next flight in the ASW-20 was when the thermals were much stronger. I went up to 1000 m and did stall training until I knew how it felt when stall starts and what my options are. I should had done this on the first flight, and do so on all subsequent new types I fly.


What units should use for velocity prediction equations? I'm not an expert aviation but I'm designing my own RC Plane and I wanted to estimate the maximum velocity using equations (15-20) from this paper. Honestly, I am not quite sure on the units to use for the Clmin equation and the Vmax equation, because when I try to apply the equations I end up with unreasonably high velocities.
The units I've been using for the parameters are:
$[W]=\text{lb}$
$[\rho]=\text{lb}/\text{ft}^3$
$[S]=\text{ft}^2$
$[V]=\text{ft}/s$
$[P_\text{max}]=\text{Watts}$

In principle it does not matter which system of units you choose to use as long as you are consistent. It is however always easier to do everything in SI units and then convert the result of your calculation into whatever unit system you prefer. Using inconsistent units has resulted in many accidents including the crash of the Mars Climate Orbiter. That is why NASA is using SI units now:

Public Law 94-168, §2 requires use of the International System of Units for measurement in U.S. Government programs, "except where impractical." That requirement is reflected in NASA policy, NPD 7120.4. That measurement system, formally known as the "SI" system," after its name in French, Systeme Internationale, is almost universally used by all countries except the United States. Use of SI measurement is growing in importance for international trade.

In your case, the mistake is using Watts for power, which is inconsistent with the remaining units you chose:
$$ 1 \, \text{W} = 1 \, \text{kg} \, \text{m}^2 \, \text{s}^{-3} \neq 1 \, \text{lbm} \; \text{ft}^2 \, \text{s}^{-3} $$
If you want to use imperial units, you need to convert your power to $ \text{lbm} \; \text{ft}^2 \, \text{s}^{-3} $, which can also be expressed in units $ \text{lbf} \; \text{ft} \, \text{s}^{-1} $ where lbf is the pound-force (lbm is the pound-mass)1. Horsepower is different again and I would advise against using it because there are many different definitions, the most common one being that 1 horsepower is equal to $ 550 \, \text{lbf} \; \text{ft} \, \text{s}^{-1} $.
If you stick to SI units (kilogram, meter and second), you can use Watts for power and you will get your velocity in meters per second, which is easy to convert to any unit for speed you want.

1 $ 1 \, \text{lbf} \approx 32 \, \text{lbm} \; \text{ft} \, \text{s}^{-1} $ (Thanks to Michael Seifert for the clarification), see also this question on engineering.SE.


Can this design provide more lift force than thrust from engine? The problem is depicted in the picture:

Generally, why we don't use engine blow wings to fly? Can we use wind-tunnel-like wing to generate lift force?

Can it generate more lift than thrust? If it can, how many times?

Because there is no free lunch.  A single wing behind a propeller or a fan can see some amount of performance gain from being in the propeller's slipstream, but, when you start stacking multiple wings together...it gets a little trickier.

A single wing can get an advantage from the swirl induced by the propeller, in addition to the increased speed you've remarked upon.  In a thesis written by LLM Veldhuis on wing propeller interactions, he notes that, when you have a propeller operating in front of a wing and rotating such that the inboard blade is always moving up, it changes the local angle of attack on the wing behind the propeller.  This modifies the lift distribution (notionally shown in the figure below) and ultimately decreases the induced drag of the wing for a given operating lift coefficient.  A set of experiments by Witkowski et. al. (Propeller/wing interaction) in the 1980s recorded a wing seeing up to 40% savings in induced drag based on the adjustment of a tractor propeller's rotation rate!

This is what I've, at least, seen cited at the most prominent effect of having a tractor propeller in front to of a wing.  If you have a small enough wing, though, say on the scale of UAV, there's a good chance you could have a significant portion of your wing in the propwash, which can keep the flow attached to the wing at higher angles of attack, letting you, potentially, keep a control surface or two unstalled and able to maneuver the aircraft when they normally wouldn't.

However, that's not lift, and it doesn't quite answer the question about the multiplane setup.  The problem with stacking wings so closely to each other goes back to investigations in the 1920s and can be most easily explained, I think, with the venturi effect.  When air is accelerated by the curvature of a wing, the static pressure decreases and you can a suction force, which, on the upper surface of a wing, translates into lift.  However, stack two wings (or other objects) closer together (as in the picture below), and you get something...not so good.  The image below is from a conceptual rotorcraft design submitted by the University of Maryland for the 2016 American Helicopter Society Graduate Design Contest and is a kinda strange thing called a quadrotor-biplane-tailsitter (we named it Halcyon).  However, the upshot of the image (which is colored by local pressure -- the more negative the Cp, the lower the pressure) is that, due to the wings and fuselage (the bit in the middle), you are playing a game of diminishing returns.

While the bottom wing sees very high velocity air going over it, leading to very high lift, that same low pressure zone also generates a strong downforce on the fuselage, effectively mitigating a lot of your lift (the design team estimated that it killed almost all of it, actually) from the lower wing.  The upper wing, since there's a little extra space, isn't as effected by that same phenomenon, so, in the end, the aircraft had enough lift, in theory, to fly...but it's not an efficient configuration at all.  The same would be true for a stack of wings.  In a 1923 paper by Max Munk entitled General Biplane Theory, he estimates that, in order to minimize interference effects between wings, they should be spaced apart by at least 3 chord lengths.  That would easily move your wings so far apart that not even two wings could easily stay in the propeller wake...at least for full size aircraft.


How often does an autopilot update control surfaces' positions? How often does an autopilot update the position of the ailerons (or any other control surface) during cruise? Per second, per minute, or something else?

So often that to any observer (visual or tactile) it appears continuous.

I say this as someone who has 2500 hours operating a transport category airplane. The flight director provides continuous guidance that the autopilot continuously follows. When holding the control column with autopilot on (below 10k feet you hold the controls even with autopilot engaged) you would interpret it as continuous input (the autopilot moves the controls just as if the other pilot were flying).


How do planes search for submarines? I am interested in the process of using maritime patrol aircraft in an antisubmarine role. I hope there is some general answer, because I have no idea what such missions look like.

How long can such a mission be and how big an area can it cover?
What techniques are used during such missions?

Update. Added: much more informative P-8 diagram, sonobuoy diagram, ASW training film (see bottom), ESM, minor formatting fixes. Removed: consolidated two sonobuoy loading pics (linked but not shown inline).

This principle method of airborne sub-hunting is using sonar to search a wide area around your ships in the direction of advance. The intent is less tracking subs as it is to deter them from getting into a good position to shoot and/or obtaining a firing solution on your ships.

ASW is a long, complex topic (see bottom for USN training film). This answer will be brief unless someone has more questions.

Airborne sensors include:

Sonobuoys

Passive - (omnidirectional or directional) - subs are very quiet today. Detection ranges is extremely short. <100 m by some accounts.
Active - all subs are coated with anechoic tiles to absorb acoustic energy
A P-3 would go through about 10-30 buoys over a 6-10 hour mission
A P-8 can apparently cary 120 sonobuoys.
Some vendor specs are available.
GREAT video of sonobuoy deployment. (This is one type. Not all are this complex.)

Source. Illustrator.

Alternate view #1. Alternate view #2. Credit.

Dipping sonar

Unique to ASW helos

Credit: USN

MAD - magnetic anomaly detector

The large boom extending behind the tail:

Credit: DoD

looks for large metallic masses
limitations: short range (100s of meters), which requires aircraft to fly very low over the surface (increasing airframe fatigue and fuel consumption). Descending from cruising altitude also takes time.
upside: good localization (spatial accuracy), relatively few false positives.
downsides: Equipment is large and heavy. For these reasons, a MAD boom is not included on the current USN P-8, the navy's newest long range maritime patrol aircraft.
Counter-measures:

Sub can dive deeper to reduce their chances of being detected. Typical SSN operating depths are 400 m. The Type 214 claims a 700 m test depth.
Some modern subs are made from non-magnetic steels (eg, German Type 212, Type 214) or titanium (Soviet Sierra, Alfa, and Papa class SSNs, portions of the Typhoon's 5 pressure hulls).
Subs also undergo degaussing

LA-class USS Toledo (SSN-769) prepares to get underway after four days at the Magnetic Silencing Facility. 5 Feb 2010. Credit: USN

Radar

Historically, more useful for detecting subs on the surface, forcing them to spend more time underwater, where they were less effective (slower, limited endurance, limited sensor range). For much of WWII, German U-boats were essentially submersible torpedo boats. Most of their attacks were actually made on the surface.
Today, our improved radars can detect submarine periscopes (and their wakes) at significant distances, forcing subs to take only very short glimpses. The periscope is actually quite useful for ID-ing targets and obtaining ranges and headings much more quickly than stalking with sonar alone.

Signal intercept, ESM

You may detect a sub communicating over radio. You may also detect a sub if it uses its radar (very seldomly).

Visual

If you're directly above a sub at shallow depth, you can see it. Needless to say, this is extremely rare, but is one reason operating in shallow, littoral waters is dangerous. If you're lucky, you might spot a periscope wake. It's also unlikely you'll see a surface wake. At periscope depth, subs move very slowly. And at operating depths, surface wakes are extremely minute, likely undetectable even by radar and advanced processing, although attempts have been made.

Credit

EO/IR

General SA but may occasionally detect exhaust fumes (eg SSK snorkeling) or periscopes/wakes.

Other non-acoustic methods

Chemical (eg hydrocarbon sensor) - to detect snorkeling subs recharging their batteries
LIDAR - potentially faster than MAD. Limited depth and search band. Less effective in turbid coastal waters. Not used operationally.
Radar to detect the minute thermals from warm water heated by reactors. (Claimed by Russians, not demonstrated by US.)

Examples

Land-based maritime patrol aircraft examples: P-3 Orion (modded L-188 Electra), P-8 Poseidon, ,

P-8 Poseidon (modded 737-800ERX).

The Boeing 737 Technical Site. Source page with lots more info.

BAE Nimrod (based on the de Havilland Comet)

Source

Carrier based platforms include: S-3 Viking, SH-60 Seahawk

SH-60 Seahawk - sensors includes a variable-depth active/passive sonar, sonobuoys, and MAD.

MAD bird (orange/red). Credit: DoD

Anti-submarine warfare intro

COORDINATED ASW PART 1 - Coordinated Anti-Submarine Warfare 2089 (HD version below)


How does a Machmeter behave if the static port is blocked during a constant CAS climb? Question: How will the machmeter behave in a constant CAS climb if  the static source becomes blocked?
Answer: The machmeter reading will decrease.

Why? I couldn't find any logical reason for the machmeter reading to decrease. My understanding is that when CAS is constant during a climb, the TAS should increase. If the static source is blocked, this will only increase the TAS further to maintain same CAS because the static pressure outside is less than the pressure in the blocked static source.

I fail to understand how the local speed of sound (LSS) is related to a blocked static source. Because LSS is related to temperature only, so it decreases during a climb.

That means that Mach speed = TAS (increasing) / LSS (decreasing) = overall increase in Mach speed

What am I missing?

A Machmeter doesn't use the true airspeed (TAS) or the local speed of sound for its readings since the TAS measurement can't be obtained without getting the Mach number first.
The calibrated airspeed (CAS) shown to the pilot is also used by the Machmeter, it measures the speed based on the pressure differential between the pitot tube and the static port.

If $P(pitot)$ $>$ $P(static)$, then the speed reading will be positive.

The bigger the difference, the faster the speed.

If $P(pitot)$ $<$ $P(static)$, then the speed will read zero since the speed indicator doesn't allow negative speeds.

A blocked static in a climb will cause (2.), and it would require an extremely fast flying to get the gauge to show any speed reading above zero, probably even faster than the plane can handle.
The blocked static will also freeze the altimeter and show zero vertical speed. Glossing over how such a climb can be maintained, let's assume there are different pitot-static sources, one for flying and one for the Machmeter.
Answer:
After the static-port is blocked in a climb, the Machmeter will within minutes (or seconds if it's a fast climb) drop to zero, just like its CAS reading.
Do note:

Aircraft flight instruments use pressure differential, not temperature, to compute the Mach number.
— Wikipedia

and

The true airspeed is calculated by the Air Data Computer from the Mach number and the outside air temperature.
— Is the Mach number shown by an Air Data Computer considered a "true" Mach number?

As you can see, it is the Mach number that is used to know the TAS, not the other way around.

Pre climb and blocking.

Blocked, then climbed at same speed.

(Source)


What is the correct traffic pattern at a towered airport? When flying into a towered airport in VFR, is the pilot expected to enter a standard traffic pattern, or should the plane be flown in the most direct route to final as practical?

For example, if westbound into a class D airport with a north-south runway landing on runway 18, should the pilot enter the pattern at a 45 midfield, fly parallel on downwind as usual, then start the descent normally when abeam the threshold, turning left base and final? Or should the pilot simply fly to the north of the field and start the descent and turn a left final approach?

The AIM 4-3-13 doesn't really explain towered airport operations, as far as how to enter the pattern. This is the most relevant explanation I can find:

  When necessary, the tower controller will issue clearances or other
  information for aircraft to generally follow the desired flight path
  (traffic patterns) when flying in Class B, Class C, and Class D
  surface areas and the proper taxi routes when operating on the ground.
  If not otherwise authorized or directed by the tower, pilots of
  fixed-wing aircraft approaching to land must circle the airport to the
  left. However, in all instances, an appropriate clearance must be
  received from the tower before landing.

I've only flown into a few class D airports (only 3 months since I got my license), and wasn't sure about how to approach the field in certain situations. Some were straight in approaches, but a couple were generally as I described above. The tower usually says to report at 3 miles, or when turning to final. "When necessary" ATC will issue clearances for traffic patterns, but what to do if they just tell you are clear to land? Does "circle the airport to the left" mean do the full pattern procedure?

During flight training I never experienced anything other than pretty much a straight in approach to class D.

Edit: I found this explanation on a flight instruction website: "Pilots do not fly a standard traffic pattern at a towered airport, with a 45-degree entry to the downwind leg. Instead, aircraft enter the airport vicinity as instructed by ATC, reporting arrival on an assigned pattern leg and then accepting further instructions or a clearance to land."

This seems to contradict the AIM explanation. And again, what if ATC doesn't instruct anything, what are they expecting the pilot to do? A standard pattern or a straight in approach as direct as possible?

When flying into a towered airport, you will be given specific instructions, as per the ATC Handbook, Section 10, Arrival Procedures and Separation such as:

"make left traffic for runway 15"
"enter a right base for runway 15"
"make straight-in runway 15"

You can also request whatever you want, like: "Tower, Cessna 3-3-Lima, information bravo, requesting left base for 15"," and the controller will then evaluate your request and issue you instructions.

These instructions refer to the following diagram form the Pilots Handbook of Aeronautical Knowledge (PHAK, p. 13-12):

Traffic patterns are also covered in the Pilots Flying Handbook, Chapter 7, and states that:

  When operating at an airport with an operating control tower, the
  pilot receives, by radio, a clearance to approach or depart, as well
  as pertinent information about the traffic pattern.

Which type of traffic pattern information ATC might give you, depends such factors as where you are relative to the airport, other traffic, noise abatement, obstructions, local procedure, etc.  For example, in the diagram below:

N or NE of the airport, you could be given "Left traffic"
NW you could be given a base entry
W you could be given a straight in.
If you're SW, S, or SE of the airport, you could be given the same pattern instructions as the north side, but with RIGHT instead of LEFT, or you could be instructed to overfly the field and enter, say, left downwind.

If you are in contact with ATC, and don't know what you're expected to do, then key the mic and ask the controller.


How do X-shaped control surfaces work? I watched this video of the Raytheon SDB II and noticed that it seems to have no control surfaces on its wings, just the four fins on the tail. How do these fins work to alter the attitude of the SDB and other missiles or aircraft using the same scheme? For example, if it were to pitch downwards, which fins would need to move and in which direction?

First, the precise terms is not fins, but control surfaces. Fins would be fixed but the four rear surfaces can rotate around a spanwise axis. By rotating, they can be positioned at an angle to the airflow, thus deflecting it and creating an opposing force.

Compare that to a V-tail on an aircraft. They work in the same way by creating a force normal to their plane. While this force has a vertical and horizontal component, the horizontal components of the single surfaces cancel each other when all surfaces are rotated by the same angle. Their vertical components will add up, creating a pitching moment.

When the left and right surfaces are rotated by the opposite angle, their vertical force component will cancel while the horizontal component will add up, thus creating a yawing moment which swings the tail around.

  If it were to pitch downwards, which fins would need to move and in
  which direction?

All four surfaces will move trailing edge down, so the resulting force will point up and pitch the whole craft nose down.


Why are aircraft tyres not grooved horizontally? Why are aircraft tyres not grooved horizontally like vehicle tyres? If the tyres are grooved horizontally won't it help in achieving more friction and reduce the chances of veering off?

Almost all the aircraft operating from prepared surfaces have circumferential grooves in order to remove water between the tyre and runway surface.
From Dunlop site:

Most Dunlop aircraft tyre designs feature circumferential grooves moulded into the tread to disperse water from beneath the tread in wet runway conditions.
The tread helps to reduce the risk of aqua planing and improves traction and grip between the tread and runway surface.

In 1960s, NASA carried out a number of studies to determine the effect of tread design (among other things) for operating on wet runways and settled on the circumferential groove shape.
In case of aircraft operated from unpaved surfaces, the tyres may have some type of cross-tread pattern.


Why does the cabin pressurisation switch have a manual mode? Reading about Helios Flight 552 it is clear that the pressurization switch on a B737 has two modes: AUTOMATIC and MANUAL

Since it appears that one of the causes of the accident was an incorrect setting of the switch to MANUAL and due to hypoxia the first officer didn't spot the problem, why is it that a MANUAL setting is offered if it can lead to such disasters?

What is the use of the MANUAL position of the switch if the setting has to be set to AUTO for the flight?

The B737 Next Generation models (737-600, -700, -800, and -900) all use a digital cabin pressure controller, which has AUTO, ALTN, and Manual modes.  Older 737's may use this digital controller or an analog controller with Auto, Standby, Manual AC and Manual DC modes.

From MyAirlineFlight.com, which also has a depiction of the older, analog panel.

In the digital panel, the Auto mode selects between two digital controllers which swap every flight so that if #1 is primary (in control in the Auto mode) this flight, #2 will be primary next flight.  The ALTN mode makes the "other" controller primary, so that if the primary controller fails, the other one can be selected.  With both the digital and the analog controllers, the Manual mode gives the pilots direct control over the outflow valve.

There are several reasons that this control is sometimes desirable; none of them are particularly common.  First, if you need to perform a ground pressurization check, the pilot or mechanic uses the manual mode to close the outflow valve and allow the aircraft to pressurize on the ground.  It isn't common, but there are some checks that require it.  Second, the manual mode is used to verify that the outflow valve DOES open and close.  This used to be a check performed by the pilots, but (in large part due to the Helios accident mentioned), it is now a maintenance-only function for many operators.

Third, if the flight must be conducted unpressurized, the manual mode allows this -- open the outflow valve fully, and there is no pressure differential -- say if you had a damaged window that needs to not be pressurized while the aircraft is ferried to where the window can be replaced.

Fourth, in the case of an emergency evacuation, it may be necessary to quickly depressurize the aircraft, and the manual mode allows the crew to open the outflow valve with only DC (i.e. only battery) power available.  (The automatic modes need AC power to operate.)

Finally, if both digital controllers fail in flight, then the crew needs a way to control the pressurization, and the manual mode is used for this.  Getting to this point is quite rare, but it can happen.  Controlling the pressurization manually takes a lot of time & attention by the First Officer, so it isn't something that's practiced in the aircraft, and because the really big cues that you're doing it well or poorly come from what your ears feel, it isn't something that's done in the simulator either.  But there has to be a way to manually control the pressurization, so the Manual mode is it.  (Loss of all generators in flight could also put you in this position -- with no AC power the Automatic mode is unavailable.  Again, an extremely rare event.)

With the removal of the outflow valve check from the pilots' preflight, the switch is typically left in the AUTO position always, unless maintenance is doing their checks.  More than a few times, crews got distracted in the middle of the outflow valve check, left the switch in manual, and never got back to it.  The usual result was a Cabin Altitude Warning shortly after climbing above 10,000'; if the crew recognized their error, they could simply switch back to Auto and continue.  If they didn't realize that they'd done, they'd shortly get a call from the back asking why the masks had dropped, and that was usually the big clue that things had gone wrong & they needed to go back & land.

One might wonder why the Manual mode is annunciated by a green light rather than an amber one -- the amber light would show up when checking the Master Caution.  That was a design decision by Boeing a few decades ago, and I don't have insight into their thinking there.  (Much like, why did they use the same horn for Takeoff Configuration Warning as for Cabin Altitude Warning... it evidently seemed like a reasonable idea at the time.)


Do seaplane have designated landing areas? Do seaplanes have to land in particular places or are they allowed to land pretty much anywhere there is room to land safely?

Taken from seaplanes.org:

While most pilots assume the FAA has jurisdiction over landing areas, including water-based landing areas, the truth is much more complex. Jurisdiction rests with the person or organization that "owns" the waterway. This may be a Federal or state agency, a local government, a private corporation, or an individual. Determining who controls a waterway is the first step in determining whether it is legal to land on that body of water.
A second complication enters in the picture with overriding jurisdictions, most commonly state-imposed seaplane base licensing requirements. In several states, notably Ohio, New Jersey and Indiana, seaplanes may not land unless the proposed landing area is certified as a seaplane base, regardless of whether the waterway owner provides permission or not. To determine whether this is an issue in your area, call your state aeronautics office (often a division of the state department of transportation), check the Water Landing Directory, or call SPA Headquarters (863/701-7979).


What are the strategies for getting familiar with a GA aircraft before considering a purchase? Looking over the comments and answers in this question got me to thinking: How does a new pilot get familiar with the large variety of GA aircraft when contemplating a purchase?

Initially there's a vast number of aircraft to even be aware of—for example, I'd never heard of a Citabria before today. So I suspect it would be easy to overlook the perfect aircraft by virtue of simply never having a chance encounter with it. I suppose the answer to this is to attend airshows and fly-ins.

Then obviously some considerations can be satisfied with light research, such as seating and performance characteristics. But outside of that, once you have a short list, how does a pilot go about getting a "test drive"..?

Like so many before, I'm presently learning in a 172. Afterwards, though, I'd be interested in getting endorsed for a low-wing. A nearby FBO offers training in Piper Arrows—but what if I was curious about flying a Mooney, or a V-tailed Bonanza ..or a ..Citabria?? :) How do the Mooney pilots get their first flight in one??

I'm mostly interested in light, single-engine models, and I realize this question is rather conversational, but I'll appreciate any insights.

There are lots of ways to go about this.

Rent: as you have mentioned nearby FBO's have various planes although they are almost always Pipers (Warriors, Arrows, occasionally a Saratoga or Lance) or Cessnas since those are common trainers. You may also find a light twin here and there as well as a Grumman or something like that. In this case you can rent what you want to try and go up with an instructor.

Friends: As you fly more you will meet people at the airport. Often times these are plane owners and they have a whole variety of stuff. Eventually people may offer to take you out for a flight in their plane (which will be way better maintained than a lot of trainers). If you tell someone you are interested in purchasing the same make and model they have, they may be more inclined to take you up. You may also meet other people who are training in a different plane than you. For example, I fly the Warrior and Archer at my school and another student who I have become friendly with flies the 172. Since we are not check out in the other planes respectively and we are about at the same point (close to our check rides) Im sure we will fly with each other in the respective planes in the future.

Flight Clubs: A lot of local airports have flight clubs that sometimes own a nice variety of stuff and you may be able to meet a member and have them take you up to show you around what ever it is they have, you may even be able to join the club and get checked out in their planes.

Internet: The internet is abuzz with forums for just about every big maker out there. Some are free and others are super cheap to join if they cost anything at all. You can often times find local owners on these forums who may be willing to take you up or at least show you their plane. You would be surprised how hard it can be to find people to fly with sometimes.

Dealers: Much like cars new planes come from dealers. You can always try your local dealer (although Im not sure if they will take you up) I would think they would at least let you sit in the plane. There are dealers spread across the country but if you can rent a plane now you can always fly to them (Piper, Cessna, Mooney)

When You Buy: When (if) you buy a plane you will need to insure it. Generally insurance companies will require time in type to get the insurance. You can sometimes agree upon mandatory instructor time in the plane you just bought before you fly it solo. This allows you to be able to buy just about any plane and not have a ton (if any) time in it.

Finding Strange Planes: When (if) you go to buy a plane you will define your mission. After doing so you will begin to talk to people about what you want and you will get plenty of suggestions on what to buy that fits your mission.

Strange Planes Are Strange For A Reason: I can only assume you are training (or have your PPL) and are thinking about getting a plane. To this I will offer some advice I have been given. Planes are no small item to own, fiscally, legally, and simply physically, they require a lot of space. There is a reason the common models are common. They fit a lot of missions, are generally reliable, easy to fix and get parts for as well as easy to fly. While I lust for a Mooney M20 Acclaim Type S the truth is (money aside) I am no where near ready for a 200+ knot plane that is nothing but slippery. Remember to respect the machine.


Do airliners like Boeing and Airbus use airfoil variation along the span for their wings? Airfoil variation will make a significant difference in airflow over the wing, thus proper variation according to the lift profile should improve the overall aerodynamic performance. But by how much? Are major aviation manufacturers using it? I can't find any reliable information on this.

Every good design varies at least the thickness: While the root needs to be thicker to enclose an efficient spar, the tip can be optimised for aerodynamics, which usually results in a root thickness of 16% to 21% and a tip thickness between 9% and 13%. Look at Dave Lednicer's incomplete guide to airfoil usage for an exhaustive collection of aircraft and their respective root and tip airfoils. Generally, larger aircraft tend to use thicker airfoils because scaling laws dictate that their structure has to carry higher loads.

Transsonic designs like airliners need to pay special attention to thickness because a thicker airfoil will encounter local supersonic flow at lower flight Mach numbers. Also, a thicker wing will store more fuel and will be lighter, so the compromise is around 13% thickness on average. With supercritical airfoils, a root thickness of 15% and a tip thickness of 11% has become widely used. Unfortunately, the exact airfoils of modern airliners are not published.

Another reason for varying airfoils is wing sweep. Left with the same airfoil over span, the isobars on the surface would show less sweep, creating a steep pressure recovery at the center wing (with potential for early stall) and suction peaks near the leading edge at the tips. Such an isobar pattern will use the available wing area less efficiently, so designers strive to make the isobars parallel to the local sweep angle by adjusting the local airfoils. At the root the maximum thickness must be shifted forward while tip airfoils need a more backward maximum thickness. Also, camber near the root is reduced up to the point where negative camber along the mid section of the airfoil chord is used.

Here are a few older ones:

Type                        Root airfoil           Tip airfoil
Boeing 377 Stratocruiser    Boeing 117 (22%)       Boeing 117 (9%)
Douglas DC-7                NACA 23016 (16%)       NACA 23012 (12%)
Lockheed 749 Constellation  NACA 23018 (18%)       NACA 4412 (12%)
Lockheed 385 L-1011 TriStar  ? 12.4%                ? 9%
Saab 340                    NASA MS(1)-0316 (16%)  NASA MS(1)-0312 (12%)
Tupolev Tu-104              PR-1-10S-9 (15.7%)     PR-1-10S-9 (12%)
Vickers VC-10               Pearcey 13%            Pearcey 9.75%
VFW 614                     NACA 63A015 (15%)      NACA 65A012 (12%)

Modern CFD techniques and composite structures allow to optimise the local contour at the wing-fuselage intersection such that no single root airfoil is used but a continuous variation which delays local flow separation and shock strength as much as possible. This also means that no stock airfoil is used, and most modern designs have their custom-made airfoils.


What changes were made to the 777 as a result of British Airways 38? Regarding the crash of British Airways Flight 38, a 777 inbound to Heathrow, the AAIB final report, section 2.8 states that frozen fuel deprived the engines of fuel pressure resulting in the crash.

What changes were made to the 777 as a result of this event? Additionally, a bonus question... are there any other cases of this issue causing problems on the 777?

The aircraft accident was caused by ice accumulating in the Fuel Oil Heat Exchanger (FOHE) of the Rolls-Royce Trent 800 engines which subsequently blocked fuel flow to the engines. The official accident investigation concluded:

  The investigation identified the following probable causal factors that led to the fuel flow restrictions:

  Accreted ice from within the fuel system released, causing a restriction to the engine fuel flow at the face of the FOHE, on both of the engines.
  Ice had formed within the fuel system, from water that occurred naturally in the fuel, whilst the aircraft operated with low fuel flows over a long period and the localised fuel temperatures were in an area described as the ‘sticky range’.
  The FOHE, although compliant with the applicable certification requirements, was shown to be susceptible to restriction when presented with soft ice in a high concentration, with a fuel temperature that is below -10°C and a fuel flow above flight idle.
  Certification requirements, with which the aircraft and engine fuel systems had to comply, did not take account of this phenomenon as the risk was unrecognised at that time.

(official accident report summary)

(image source: official accident report)

The FAA issued an amendment to an older Airworthiness Directive (AD) in March 2009:

  Boeing Model 777-200 and -300 Series Airplanes Equipped With
  Rolls-Royce Model RB211-TRENT 800 Series Engines

  [...]

  SUMMARY: The FAA is superseding an existing airworthiness directive (AD) that applies to
  certain Boeing Model 777-200 and -300 series airplanes. The existing AD currently requires revising
  the airplane flight manual (AFM) to include in-flight procedures for pilots to follow in certain cold
  weather conditions and requires fuel circulation procedures on the ground when certain conditions
  exist. This new AD retains the fuel circulation procedures. This new AD also revises the AFM
  procedures required by the existing AD. This AD results from a report of a single-engine rollback as
  a result of ice blocking the fuel oil heat exchanger. We are issuing this AD to prevent ice from
  accumulating in the main tank fuel feed system, which, when released, could result in a restriction in
  the engine fuel system. Such a restriction could result in failure to achieve a commanded thrust, and
  consequent forced landing of the airplane.

(AD 2009-05-11)

The NTSB then requested a redesign of the FOHE from Rolls-Royce:

  The US National Transportation Safety Board (NTSB) on 11 March released urgent safety recommendations for the redesign by Rolls-Royce of the fuel-oil heat exchanger on Trent 800 engines powering Boeing 777s.

  NTSB says Rolls-Royce is already working on a redesign that could be available in twelve months, but still felt compelled outline the need for the heat exchanger overhaul.

(flightglobal.com)

In Europe, EASA required the new FOHE to be installed since January 2011 at the latest:

  Reason:

  This Airworthiness Directive has been raised following an incident involving dual
  loss of engine response in the final stages of approach leading to touchdown
  short of the runway. The phenomenon involved in the loss of engine response
  has also been seen in flight affecting just one engine.

  Post incident analysis and investigation has established that, under certain
  ambient conditions, ice can accumulate on the walls of the fuel pipes within the
  aircraft fuel system, which can then be released downstream when fuel flow
  demand is increased. This released ice can then collect on the FOHE front face
  and limit fuel flow through the FOHE. This type of icing event was previously
  unknown and creates ice concentrations in the fuel system beyond those
  specified in the certification requirements.

  To mitigate the risk of dual engine FOHE blockage within the Trent 800 engine
  powered Boeing 777 fleet, which constitutes a potential unsafe condition, this
  Airworthiness Directive instructs replacement of the FOHE with a modified
  standard incorporating enhanced anti-icing and de-icing performance.

  Required Action(s) and Compliance Time(s):

  Within 6 000 flight hours from 10 July 2009 or before 01 January 2011,
  whichever occurs first:

  Replace the FOHE with an FOHE modified in accordance with RollsRoyce Alert Service Bulletin RB211-79-AG257, dated 24 June 2009
  (published 10 July 2009).

(EASA AD 2009-0142)

Regarding your bonus question: Yes, there was another incident (Delta Air Lines Flight 18, 26 November 2008) where ice accumulation in the FOHE resulted in an engine rollback (luckily only one engine this time):

  Since we issued AD 2008-19-04, we received a report of a single-engine rollback as a result of
  ice blocking the fuel oil heat exchanger (FOHE) on a Model 777 airplane equipped with Rolls-Royce
  Model RB211-TRENT 800 series engines. The data confirm that ice accumulates in the fuel feed
  system and releases after a high thrust command, creating blockage at the FOHE and resulting in the
  inability of the engine to achieve the commanded thrust. Examination of the data from the rollback
  shows that the second of two maximum thrust step climbs was performed approximately 40 minutes
  prior to the thrust rollback. Ice was released within the fuel system during the step climbs and formed
  a restriction at the FOHE of the affected engine, as evidenced by an increase in engine oil
  temperature.

(AD 2009-05-11)


What's the relationship between AOA and airspeed? We know that any aircraft will stall at its stall speed (for a specific weight, CG position, etc.) but also, that the same airplane will always stall at the same angle of attack.
I´ve read that IAS is just the easy way to control AOA, because in reality it's all about AOA and nothing to do with airspeed. That when changing IAS we are changing the relative wind and thence AOA. On the other hand, I know that the critical AOA doesn´t change with weight (it will always be the same for a given airfoil) but the stall speed will.
There are also high speed stalls... I'm confused. Can we get into a stall without reaching the critical AOA? What's exactly the relationship between AOA and IAS?

"Can we get into a stall without reaching the critical AOA?" -- no.
"We know that any aircraft will stall at its stall speed (for a specific weight, CG position, etc.)"-- we need to add "G-loading" to this list of parameters.  The "stall speed" we usually talk about is the 1-G stall speed.  Change the weight or the G-loading, and the airspeed correlating to the stall angle-of-attack changes.
"On the other hand, I know that the critical AOA doesn't change with weight"-- correct, but for a given G-loading, such as 1 G, the airspeed correlating to that critical AOA scales according to the square root of the weight.
"What's exactly the relationship between AOA and IAS?" -- if we know the IAS where the wing reaches the stall AOA at some given weight and G-loading, then we can adjust that IAS for some other condition by multiplying by the square root of the change in weight times the square root of the change in G-loading.  "Change in" meaning the ratio, i.e. new divided by initial.
The fundamental relationship between AOA and IAS is that net lift force at any given AOA is proportional to airspeed (IAS) squared.
Here's an extra complication that you may not want to worry about right now -- the "dynamic stall" -- What is the immediate cause of stall? -- scroll down to last paragraph.


What's the advantage of using short wings rather than long wings? To clarify the question, I mean the type of wing used on a Concorde or a fighter jet, vs a glider's long and thin ones. What is the aerodynamic reason for using a short wing when the plane is faster?

Another reason to have shorter wings on high-speed or maneuverable aircraft deals with the aircraft's aspect ratio, which is the ratio between its length to is breadth/chord. Longer wings (high aspect) bend more under load, and may twist, which causes structural issues. Additionally, aircraft with shorter wings (low aspect) can roll much quicker. This means that a fighter jet with short wings may roll at rates up to 720 degrees/second while a large airliner or cargo plane may roll at 15-60 degrees per second.

A third reason is parasitic drag. From the linked wikipedia article above:

  While high aspect wings create less induced drag, they have greater parasitic drag, (drag due to shape, frontal area, and surface friction). This is because, for an equal wing area, the average chord (length in the direction of wind travel over the wing) is smaller. Due to the effects of Reynolds number, the value of the section drag coefficient is an inverse logarithmic function of the characteristic length of the surface, which means that, even if two wings of the same area are flying at equal speeds and equal angles of attack, the section drag coefficient is slightly higher on the wing with the smaller chord. However, this variation is very small when compared to the variation in induced drag with changing wingspan.
  For example, the section drag coefficient $c_d$; of a NACA 23012 airfoil (at typical lift coefficients) is inversely proportional to chord length to the power 0.129:
   $$ c_d \varpropto \frac{1}{(\text{chord})^{0.129}}.$$

Since parasite drag increases with airspeed, and high aspect wings have higher parasite drag, it makes sense for high-speed aircraft to have the wing that creates less drag at high speeds, and the slower aircraft to have the wing that creates less induced drag. You can see this in a simple graphic of the drag curves:

(Since the induced drag is lower at high speeds anyway, there is little point in minimizing that, rather minimize the type of drag that is a much larger factor at high speeds)


How to find polar curves of airliners? The pilots operating manual of our Cessna 182 contains the lift-versus-alpha and lift-versus-drag data of the airplane, so I assume this is data that should be publicly available.

Is there a trustworthy resource where I can get the polar curves of different aircraft, especially airliners? I'm looking for that of the Airbus A350 XWB in particular.

Polar curves for older airliners can be found in lecture notes or technical publications. The drag polars of the most recent ones, where no independent measurement is yet possible, are a closely guarded secret. If you see something, it will be restricted such that an important part of the puzzle is missing. For the polars to be meaningful, you need aircraft mass and flight conditions, air temperature and density and sometimes also engine thrust information to make any meaningful comparisons. Also be aware that the Airbus method to determine the reference area is different from Boeing's, but at least those methods are published. Full disclosure is only available to potential customers on the basis of an Non-Disclosure Agreement (NDA).


What is a "Land And Hold Short Of" light? A runway inspection found a "Land And Hold Short Of" (LAHSO) embedded light had become dislodged and had caused damage to a tyre.

http://avherald.com/h?article=4bb1964c&opt=0

What is such a light, and what does it look like?

See also How are runway lights constructed?

It's an in-pavement (flush) light bar that indicates the hold-short for the LAHSO operations. See: What is a land and hold short clearance (LAHSO)? For the FAA they are:

  FLASHING L-850A OR L-850F LIGHT FIXTURE (Source: AC No: 150/5345-54B)

A single L-850F unit in the light bar looks like this:

(adbsafegate.com)

(FAA AIM) The light bars are located as indicated by the blue arrows.

I tried to find a video to show the pulsating white light at night when in use, but I couldn't find any. By checking Boston Logan (KBOS) on Google Earth, and zooming in at where the LAHSO hold-short lines are, the flush light fixtures can be barely seen:


Can the mass flow rate for different power settings be determined? Is it possible to determine the mass flow rate for different power settings? Unfortunately I was unsuccessful in finding the engine specification for the PW2037 so I used the data from this source, which states that the mass flow rate at take-off for the PW2037 engine is 1210 lb/s. Given this flow rate, would it be possible to calculate the mass flow rate at idle setting? And therefore also the mass flow rate for 50% engine setting (or 25%, 75%, etc.)?

An answer in this question suggests using thermodynamic equations to approach this. However, I am not too sure on how to use these equations.

Yes, it can be done but you need a complicated model with information only the producer has access to. The data in your source are not enough.

You can play around with this a bit https://www.grc.nasa.gov/www/k-12/airplane/ngnsim.html but don't expect overly realistic answers. You have to use the Tunnel Test Mode for off-design performance after entering all the data you have available. And you should pick the "turbofan" engine type.


Which airport is the busiest general aviation airport in the world? Which airport in the world has the highest amount of flight training and general aviation traffic? I am wondering for year-long traffic totals rather than temporary spikes in traffic due to airshows or similar events.

US
According to General Aviation News in Feb 2020 that would be Van Nuys in California.

Van Nuys Airport (KVNY), Van Nuys, California: 155,420 local GA operations + 332,117 itinerant GA operations = 487,537.
Phoenix Deer Valley (DVT), Phoenix, Arizona: 130,886 local operations + 243,075 itinerant = 373,961.
Centennial Airport (KAPA), Denver, Colorado: 153,744 local operations + 133,098 itinerant = 286,842.
Ernest A. Love Field (KPRC), Prescott, Arizona: 177,233 local operations + 85,290 itinerant = 262,523.
Long Beach Airport-Daugherty Field (KLGB), Long Beach, California: 151,912 local operations + 101,734 itinerant = 253,646.
Portland-Hillsboro Airport (KHIO), Portland, Oregon: 160,261 local GA operations + 83,381 itinerant = 243,642.
Phoenix-Mesa Gateway Airport (KIWA), Phoenix, Arizona: 166,519 local operations + 66,727 itinerant = 233,246.
Falcon Field (KFFZ), Mesa, Arizona: 175,051 local + 53,307 itinerant = 228,358.
Grand Forks International Airport (KGFK), Grand Forks, N.D.: 212,325 local + 12,634 itinerant = 224,959.
Gillespie Field (KSEE), San Diego/El Cajon, California: 140,189 local + 68,061 itinerant = 208,250.

Source: https://generalaviationnews.com/2020/02/03/top-10-busiest-general-aviation-airports/
Anecdotally; although not American, I just realised I learned to fly at the 5th busiest GA airfield in the US. Mind blown!
UK
Contrast this to the UK, which has a fairly busy GA scene:

Official Civil Aviation Authority statistics have revealed that Gloucestershire Airport at Staverton was amongst the busiest in the UK during 2011, with the majority of the traffic being GA aircraft  [...] Gloucestershire appears at number 13 in the list of 64 UK commercial airports, handling 66,715 flights during the year -- just pipping Bristol and beating other major regional airports such as Newcastle and Belfast.

As you can see the UK's busiest GA airfield doesn't even come close to the US' 10th busiest.
Australia
Not so easy to find a list, and there is more than one contender for busiest
Jandakot deems itself to be busiest by movements:

Jandakot Airport is "the busiest general aviation airport in Australia in terms of aircraft movements". The airport recorded 208,778 aircraft movements in the fiscal year ending 30 June 2018

Moorabbin seems to be the busier by aircraft movements, and is clearly a strong contender.

With over 295,000 aircraft movements each year, Moorabbin Airport is the second busiest airport in Australia. [...] Moorabbin Airport is Australia’s leading general aviation flight training airport located in the south-east of Melbourne.


Are there any real life instances of aircraft aborting a takeoff or landing to avoid a vehicle? I came across a fake video of an A380 closely avoiding a fuel truck. More details at Snopes including a link to the YouTube video.

While this video is not real, I'm interested in finding out if it's a realistic situation and if there are any real instances where accidents have been avoided because crew decided to abort takeoff or landing as a result of an unexpected runway intrusion as seen in the video.

Not only is it possible but it happens. This is formally called a "runway incursion" and it does happen like 2005 Logan Airport runway incursion or the B733 / vehicle, Amsterdam Netherlands, 2010. Skybrary has a full list you can find here which is quite lengthy and includes a full section for Vehicle Incursion.


Does the Enroute Phase begin at a 30NM distance from the departure airport? ICAO's Doc 8168 Volume II ("Aircraft Operations") states:

Part III "Performance-Based Navigation Procedures"
Section 1 "Underlying Principles"
Chapter 1 "RNAV Concepts"
1.2 "Flight Technical Error"
Table III-1-1-2. Phase of flight [...] En route (greater than or equal to 56 km (30 NM) from departure
or destination ARP. [...] Terminal (SIDs, STARs, initial and
intermediate approaches less than 56 km (30 NM) of the ARP).

A similar categorization can also be found in FAA's Order 8260.58A ("PBN Instrument Procedure Design"), which states:

1-2-5 "Obstacle Evaluation Area (OEA) and Flight Path construction"
b (2). Width. [...] For the en route transition, legs that cross a point 30 NM from ARP, the OEA primary area width expands or tapers at a rate of 30 degrees relative to course to the appropriate width [...] A departure or missed approach segment designed to cross a point 30 NM from the ARP more than once changes to RNAV 2/RNP 2/A-RNP (en route mode) and remains expanded when it crosses the boundary the first time.

They way I interpret the above instructions is that a departure procedure should end (either explicitly or via vectoring) at a 30 NM distance from the departure airport, where optionally the enroute transitions of the SID will guide the aircraft and prepare it for the cruise flight phase.
On the other hand, take FINZZ TWO where the distance between LGA airport and FINZZ is less than 15 NM, something that contradicts the aforementioned convention of 30 NM between the airport reference point and the start of the enroute mode.
Could somebody help me realize what I'm getting wrong?

You are not getting anything wrong, I think you are simply overthinking something that isn’t actually important.  The 30nm distinction is somewhat arbitrary, and presumably captures most arrival and departure procedures.  There is nothing magical or binding in this number, and there is nothing pilots will do differently when flying a published route or procedure based on distance or phase of flight.

For example, let’s say the last point on a published departure procedure is less than 30nm from your departure airfield, and the next point on your filed route of flight is outside of 30nm.  Your question implies that there would be confusion as to whether you would be in the terminal phase or the enroute phase of flight as you flew between these two waypoints, is that basically correct?  My point is that this distinction does not matter.  You will not fly the aircraft any differently if it is one or the other, you will simply navigate to the next point on your route while climbing or maintain assigned altitude.

Now there are some things that are accomplished during arrival and departure phases that may be worth discussing to clarify things and satisfy your curiosity on the subject.  However, most of them are done as a result of passing a certain altitude.  For example, at a certain altitude during climb out power may be adjusted for noise abatement and efficiency.  Passing through 18,000 feet altimeters will be adjusted to 29.92 and perhaps switched into a different mode.  This will be captured as part of a climb checklist.  Reaching cruise altitude another checklist will be accomplish that will include things like adjusting cruise power, checking cabin pressurization, etc.

Preparing for arrival similar descent and approach checklists are executed that will include obtaining weather and local altimeter setting, approach briefing, etc.  Passing 18,000 on the descent altimeters will be set to local setting, passing 10,000 speed will need to be slowed to 250KIAS.  Checklists can be triggered by either altitude or distance from the destination, but again the distinction between exiting the enroute phase and entering the terminal phase is not really that important.  The thing that matters is understanding when you are established on the published procedure you have been cleared for.  The actual distance from the airport where this actually occurs is of no real concern as long as you fly what you are cleared for.

If IFR there will also be a hand off at some point between the Air Route Traffic Control Center and the local approach controller, but this will likely be tied to altitude as well.  Also, you may be handed from one approach controller to another, but this will occur as you cross sector boundaries and is based more in geographic radar coverage and not a concentric range ring from the airport.

Finally, most modern GPS navigation systems will automatically change the sensitivity of the course deviation indicator in different phases of flight with the least sensitivity in enroute phase, more in terminal, and greater yet in approach phase.  (This is basically what the section you quoted above is referring to)  However, they will cycle as the aircraft passes the first or last waypoint of a procedure that is loaded into the system and not at some distance in between.  In other words, if you are navigating to the first point of a STAR or instrument approach the system ought to retain enroute CDI sensitivity until this point is reached.  The upon passing the waypoint it will cycle to the greater sensitivity of the terminal or approach phase.  For this reason is it important to understand what phase of flight your GPS considers you to be in, but know that it will not cycle at 30nm or any other arbitrary distance in between, but at the waypoint where the transition occurs.

To reiterate, there isn’t a specific checklist or different way of flying related to the transition between terminal and enroute phase of flight, nor is there any such thing as a “no man’s land” in between phases if a point on a SID or STAR is within or outside of the 30nm distance referenced in your question.


Are multi-crew operations in a single-pilot aircraft counted towards ATPL requirements? I thought that you had to perform all your ATPL multi-crew time in aircraft with a certificated minimum of 2 crew, but I've heard of some pilots using time in single-pilot aircraft towards their EASA ATPL licence. Is this true? If so, could someone explain how is this possible?

According to the UK CAA you need:

  500 hours in multi-pilot operations on aeroplanes;

Notice that it does not say anything about the aircraft being multi-pilot/certified for two crew members.

An air carrier can specify in their ops manuals that, for their operations, they require a particular airplane to be operated with two crew members even if it is only type certificated for one crew member.  If their manual is approved, then it is now a "multi-pilot operation" regardless of the type-certification status of the airplane.


Why 360 degrees is in the top instead of 90 degrees in aviation? Normally on 2D map, if there is point say A(0,0) in the center and there is point B in the 2nd quadrant . The angle is always in 90<=x<=180. But in aviation, it is 270<=x<=360 . Why ?

Treat this as a basic question.

Conventionally, geographical maps are shown with the North up and North is also by convention 0 degrees (or 360), which is equal to the compass heading of North. The angle increases clockwise, with 90 degrees being East. This is not specific to aviation; in fact during flight the preferred presentation is to have the map oriented such that the direction of flight is upward.

The mathematical plane you seem to describe on the left has the primary axis as the angular datum (also by convention, more info here and here). So the positive x-axis is 0 degrees. The angle increases counterclockwise, so the positive y-axis is 90 degrees.


What forces act on an airplane's door from the outside in cruise? The inside cabin pressure from what I understand is pressurized to the values found at 6000-8000 feet high (11.34 psi at 7000 feet), at which point we can find the amount of force can be found acting against the door internally.

What about the pressures outside of the door? Is it just the pressure of the altitude of the plane acting against the door, or are there other forces involved, such as the force of the wind?

A door that is, say, 36" x 80" (0.9m x 2m), with a surface area of 2880 sq/in (1.8m2), at 8 psi (55kPa) max cabin pressure differential, which most airliners run at, will have roughly 12 tons (102kN) acting on the perimeter fittings trying to blow it out. Any other forces acting on it are microscopic in comparison.

For non plug type doors that depend on bayonet latch pins, the shear loads on the pins are such that it is impossible to move the latching mechanism.  If superman was able to move the operating lever, it may or may not just bend the linkage, but no human will be able to move it.

For a plug door of the dimensions above, it has to move inboard to start to open it, so you would have to be able to apply 12 tons of pull force to unplug it.

Just the acrylic cabin windows are holding back over half a ton each when you are cruising along at 38000 ft.

This is why you don't have to worry about a crazy person trying to open a window escape hatch in flight.


What are the advantages or disadvantages of a mid wing design? Are there advantages or disadvantages to a mid wing design for a monoplane? If so, how would this design compare to a high wing or a low wing monoplane design?

What might be the aerodynamic advantages or disadvantages?
What might be the design or structural advantages or disadvantages?
What might be the control or flight characteristic advantages or disadvantages?

The mid wing is mostly used in combat aircraft and rarely in passenger jets. The reasons are mostly structural.

Aerodynamically, the mid wing is the best option as it is much more streamlined and has less interference drag compared to the high and low wings.

The mid-wing also has neutral roll stability, which is good from the prespective of combat and aerobatic aircraft as it allows for the performance of rapid roll maneuvers with minimum yaw coupling.

The mid wing has certain disadvantages when it comes to structural design as far as passenger and cargo aircraft are concerned- the wing will have to either pass through the fuselage, eating into usable volume or the structure has to be strengthened around the fuselage to carry the loads. This is the main reason this type of wing is rarely found in commercial airliners.
There are some aircraft which do have mid mountedwings, like the Piaggio Avanti, which has the wings passing behind the cabin and canards and the Hansa jat, which solved the problem by sweeping the wings forward and thus passing it through the rear fuselage. These types are rare, however.

Image from hansajet.de
This type of wings are used by a number of combat aircraft, however, for example, the Dassault Rafale.

Image from http://indiandefence.com
For combat aircraft, the adoption of mid wings means that the landing gear have to retract into the fuselage for keeping the length under check. The mid wing allows for the carriage of weapons and fuel tanks in underwing pylons however. Also, the pilot's visibility is not affected during turns as in the case of high wing.


What liability concerns would drive an airplane homebuilder to scrap their plane? Via this post by Ron Rapp, I found this video of a plane owner and builder dismantling a GA plane and then scrapping the airframe. The video claims this is because

  after consulting with aviation attorneys and other experts regarding builder's liability, the owner concluded there was only one way out.

However, I'm completely in the dark about - and rather baffled by - what this liability risk would be, and how it relates to the Van's Aircraft lawsuit. What liability would a builder pilot be under in the event of a crash that they would be able to avoid if the plane were factory-produced?

I understand that the aircraft owner had sought for some time to donate the aircraft. I would presume that he had come to a time in life where he was, or felt he was, no longer able to fly the aircraft, and so was seeking to rid himself of what may have become a burden (hangar fees, etc.).
To quote liberally from the builder/destroyer's daughter who created and uploaded the YouTube video (this is quoted from what she wrote in the video description):

It took him two years to make this decision about his plane. He did actually try to donate it to a couple of aviation schools in the area and the schools politely refused the offer. He also tried to donate to a local museum and was also refused.
He knew when he built the plane he might face this decision one day, but he hoped some of the laws would have changed by that time.
[...]
Mr. Ron Rapp, author of the article “A Tragic Pile of Twisted Metal” and noted blogger on his website The House of Rapp., highlights many reasons my Dad made this decision among others.
A couple months before my dad made his final decision, a local fellow pilot was named in a lawsuit because he sold the plane he built to a man that later crashed and killed himself in the plane. The spouse of the buyer filed the suit and also named other companies who made parts used to build the plane.
Many have commented that he should have used a limited liability entity, such as a LLC or a corporation to sell the plane. However, because the plane was not, at the time of manufacturing, owned in a properly capitalized limited liability entity with a legitimate business purpose and was, in fact, used purely for personal reason, courts would in almost all cases “pierce the corporate veil.” Therefore, this does not offer adequate (or any) protection.

I don't think I can add a whole lot to that. Apparently, he had decided that he was unwilling to take on the liability of letting someone else fly what he had built. In the absence of a party interested in the aircraft for anything other than flight, he chose to destroy it.


Are there any rules requiring hands/feet on the controls at all times? Are there rules that require one of the pilots in a large commercial aircraft to have positive physical control of the yoke/joystick at all times?

And the same question for the rudder actuators, if any (pedals)?

There is nothing I can find in the FARs requiring that a pilot keep their hands and feet on the controls at all times.
Such a requirement would be impractical and dangerous in many situations (such as when writing down a clearance in the air: For most people if you keep your hands on the controls while writing you will have a tendency to push, pull, or twist them, resulting in unintended attitude changes).

The most relevant sections of Part 91 would be 91.3 and 91.13:

14 CFR 91.3 (FAR 91.3) says:

  §91.3   Responsibility and authority of the pilot in command.
  (a) The pilot in command of an aircraft is directly responsible for, and is the final authority as to, the operation of that aircraft.
  . . . .

and 14 CFR 91.13 (FAR 91.13) says:

  §91.13   Careless or reckless operation.
  (a) Aircraft operations for the purpose of air navigation.
   No person may operate an aircraft in a careless or reckless manner so as to endanger the life or property of another.

  (b) Aircraft operations other than for the purpose of air navigation.
  No person may operate an aircraft, other than for the purpose of air navigation, on any part of the surface of an airport used by aircraft for air commerce (including areas used by those aircraft for receiving or discharging persons or cargo), in a careless or reckless manner so as to endanger the life or property of another.

So basically it's perfectly legal for a pilot to fly with their arms crossed and their feet flat on the floor, even without an autopilot, as long as the pilot in command remains able to exercise operational control of the aircraft as required to ensure the flight remains safe and legal, and as long as they are not acting in a "careless or reckless manner" (like letting their altitude wander all over the place while sitting with their arms crossed).


How do modern commercial aircraft handle dust storms? I live in West Texas where dust storms are an occasional fact of life. I am interested in how modern jet aircraft handle dust storms such as the one seen in the photo. From a pilot POV I can see that sand is no different than fog with high winds. However, from a mechanical standpoint, this is a high velocity abrasive being shot at the vehicle and through the engines.

How do modern airliners and their crews deal with a large sandstorm?

Would a standard weather briefing warn a pilot of the possibility of a sandstorm?

What would the appropriate action be for a pilot who suddenly finds themselves above a sandstorm in a piston or turbine aircraft?

How would a pilot judge when a dust storm is too dense to enter safely?

There is an interesting presentation on the impact of dust on aircraft here. And the Flight Safety foundation has a good article that breaks down a lot of aspects here and is worth the read.

It's not just the reduced visibility, but the associated high winds that can be a real danger for aircraft operating in a dust storm.

  Dust storms pose a significant hazard for aviation. Not only do they
  drastically reduce visibility, they also are associated with very
  strong winds that can seriously affect an aircraft in flight. Engines
  can be damaged by ingesting the dust.

But as per your questions directly

  How do modern airliners and her crews deal with a large sandstorm?

They most likely will avoid them as they would any heavy weather activity. The extremely reduced visibility might bring the airport below operational flight minimums, thus making an approach or departure impossible.

  Would a standard weather briefing warn a pilot of the possibility of a
  sandstorm?

One main issue with dust storms is how fast they come up, and this can make them harder to predict than a storm that is rolling across a region.

  It was a typical early summer evening in southern Arizona, U.S., this
  past July 5. At 1751 local time, the Phoenix Sky Harbor International
  Airport was reporting 10 mi (16 km) visibility with winds of 7 kt. But
  all that changed in a matter of minutes.

As for what to do when you find yourself over or in a dust storm check this article out of a firsthand account.


Is turboshaft fuel efficiency affected by N2 loading? When using a free power turbine turboshaft, does fuel burn get affected by N2 loading? I am asking as I want to in the future bench test a turboshaft for fuel burn, but I don't know if the loading would affect the fuel burn.

The free turbine shaft can be called $N_2$, but $N_f$ is more common.
Your fuel control for a turboshaft is not so simple. It requires a Fuel Control Unit and an engine control that needs to know how much torque is being produced at the $N_f$.

A fuel control unit [acts] as an intermediary between the operator's controls and the fuel valve. The operator has a power lever which only controls the engine's potential, not the actual fuel flow. The fuel control unit acts as a computer to determine the amount of fuel flow needed to deliver the power requested by the operator.

and

[A] turboprop or turboshaft engine control system has an additional job to do that is not shared by its turbojet and turbofan counterparts. It must control the speed of the propeller or the free turbine, and it usually governs the pitch angle of the propeller blades. (Source)

If you are not bypassing the FCU and other engine control systems, you do need a varying load to have control over the fuel flow (indirectly).
Running an unloaded turboshaft at high power is very dangerous, as the free turbine will be rotating at RPM's way above its design limits. Unloaded free turbines may also cause an auto shutdown.

By Emoscopes (Own work: drawn using XaraXtreme) [GFDL, CC-BY-SA-3.0 or CC BY 2.5], via Wikimedia Commons

Free turbine engines are now commonly fitted with a device to shut off the fuel supply at the HP cock if torque in the turbine output shaft suddenly falls to zero.
A drawback to the simple free turbine turboprop is its behaviour if the load suddenly falls to zero. In such a case, the unconstrained free turbine overspeeds and will be destroyed by centrifugal forces.

In other words, you do need a load of varying degrees, you cannot test an unloaded fully assembled free turbine engine.
As for efficiency, efficiency is a measure of fuel flow per unit thrust/torque, so a load is needed to get that measurement.


What constrains a paraglider vertically? I recently flew on a tandem paraglider for the first time. Since then I keep asking myself a question I have no clear answers to.

While flying I clearly perceived the lift generated by the airfoil, but the strongest feeling I had was as if the paraglider hung to a rail, like a suspension railway, or to a cable, like a cable-car. In other words, I perceived a very strong vertical constraint. I know the airfoil generates lift, but I understand the amount of lift is not enough to give you a stability feeling like when driving a truck! To be similar to the constraint produced by a rail, this vertical constraint should be in the order of thousands of kg, IMHO.

Any suggestions on how to estimate this amount, and its origins?

To be similar to the constraint produced by a rail, this vertical constraint should be in the order of thousands of kg, IMHO. Any suggestions on how to estimate this amount, and its origins?

The thing is that the constraint is something you "perceived":

  I perceived a very strong vertical constraint

not that was actually there.

Only gravity, lift, and drag (and thrust, if powered) are acting on the paraglider, nothing else.

And the lift is easily estimated, as it is roughly equal to the weight of the passengers and the aircraft summed up and being this a paraglider, definitely not in the range of the thousands of kg.

Having this been your first experience, the sensation can easily be explained by your lack of familiarity with the transportation method.


Carrier frequency and transmit power of a commercial aircraft I have a few questions on the radio comms. aspects of commercial aircrafts.

At what (central) frequency does an aircraft communicate with a control tower? Is the communication over one frequency only? How much is the transmit power of the antenna per channel on both uplink and downlink? Is it per hertz?

Also please correct me if I’m wrong: From my readings, aircraft-airport communications is analog only, correct?

At what (central) frequency does an aircraft communicate with a
  control tower?

This is different for every tower, although due to the limited discrete frequencies around the globe they are repeated, generally far enough apart its not an issue. Specific frequencies can be found for US airports on either charts or in the AFD.

  Is the communication over one frequency only?

Generally every tower only has a single frequency, there are some airports or enough traffic to warrant multiple frequencies. They are often segmented by approach direction or runway.

  How much is the transmit power of the antenna? Is it per hertz?

Transmit power may vary based on airport but should be constant across the frequencies.

  Also please correct me if I’m wrong: From my readings,
  aircraft-airport communications is analog only, correct?

Not analog only, digital comms are used. For the airport environment there are systems such as CPDLC for delivery clearances and D-ATIS for digital airport information.


What do airline pilots eat on a flight, and when? Do airline pilots eat while flying or do they wait until they are back on the ground?
If they do eat, do they get the same food that is served to the passengers or do they bring their own meal?

1: Do pilots eat during flight or they wait until they are back on the ground?

As pilots happen to be humans, their metabolism works in a similar fashion as yours or mine work. So they eat when they are hungry. On a long flight, they can eat during the flight, but on short flights (e.g. 30 minutes - 2 hours), they might not get enough free time to have a meal.

On busy days, pilots may not get enough time to have proper meals, so they try to eat small meals containing more nutrition. This is detailed in an article on Airline Pilot Central. They also avoid heavy meals before a flight.

2: Do they get the same food that is served to the passengers or do they bring their own meal?

Most of the time, food served to the passengers is the same which is served to the pilots, although they don't eat the exact same food. An airline pilot revealed that:

  ... the pilot gets the first class meal and the copilot the business
  class meal.


Why the Antonov AN-225 has negative dihedral wings combined with a positive dihedral horizontal stabilizer? I know the reason why it has negative dihedral wings, but I do not really know why it is combined with a positive dihedral horizontal stabilzer, which are the benefits this configuration provides?

The reason for the wing anhedral has been answered here long ago.

Tail anhedral or dihedral can have several reasons:

To avoid ground contact during rotation (when the aircraft pitches up in order to lift off the ground). This is needed with a swept tail, so tail dihedral can be found on many airliners. Clearly, the An-225 tail has ample distance to the ground, because the vertical tail surfaces extend for ⅓ of their span below the horizontal tail, so any ground contact can be ruled out even for an un-dihedraled tail.
To move the horizontal tail away from the wing wake. When you look at the tail of the An-124, you will see no dihedral and a mounting point quite similar to that of the An-225. But if the An-124 has no problem with an un-dihedraled tail, so should the An-225. This can also not be the reason.
To add some more vertical tail surface. This trick has been employed on the Handley-Page Victor or the F-4 Phantom II. On the An-225, the outer verticals would shield much of the horizontal tail and little additional side force will be created by the dihedraled horizontal tail. So this cannot be the reason, either.
For a H-tail: To move the attachment point of the vertical surfaces closer to their middle. Imagine the An-225 horizontal tail had no dihedral: Then the verticals would need to be mounted on the tips of the horizontal near their bottom (they need to be so high up in order to allow the An-225 to rotate, after all). This would mean that all side loads would act above the attachment point, producing a sizeable bending moment which has to be carried along the spar of the horizontal tail, making the outer tail structure a lot heavier. With a little dihedral, the attachment point can be moved further up, close to the middle, so the bending moments in the vertical and horizontal tails can be a lot lower.

Antonov has designed H-tails before (on the An-14, the An-22 Antei, the An-28 and the An-38), and in all cases the vertical had a sizeable part of its surface below the horizontal tail. The only design on this list which also had some tail dihedral is the An-14 from 1958, and here the attachment point is almost in the center of the vertical. So it looks like the Antonov design bureau applied a trick on the An-225 which they had known for at least 30 years before the An-225 took off for the first time.


Do nose cones work well at high angles of attack? On a lot of fighter jets, I see a heavily slanted intake, such as the F-15.

I always thought this is to help ingest air at high angles of attack. However, what about something like the MiG-21?

There's no slanted intake there. Yet on Wikipedia it does say, "Its G-limits were increased from +7Gs in initial variants to +8.5Gs in the latest variants." And it has a citation for it.
So my question is, do nose cones work well at high angles of attack? And if so, how?

No, they don't.
The slanted intake is slanted because the top part produces a compression shock wave that hits the lower intake lip so all of the compressed air is ingested and nothing is wasted. In order to do this reliably up to Mach 2.5 (where the Mach cone angle is 73.8° from the vertical), the whole intake needs to be slanted by those 73.8° (actually a bit less due to the intake wedge). In order to adjust the intake for different Mach numbers, one or both parts are adjustable, as shown in the F-14 example below.

Cross sections of the F-14 intake at subsonic, transsonic and supersonic speed. Note that the shocks of the supersonic example do not fit well with the intake geometry – the geometry is optimized for a much higher Mach number than shown. See here for a better example.
Here is (admitted a quite messy) cross section of the F-15 intake. The adjustable upper wedge is clearly visible (picture source):

In order to minimize losses, the upper intake uses adjustable ramps in order to force additional shocks so the compression happens over a sequence of weak, oblique shocks.
Regarding spike intakes: They were the lightest and simplest way to produce efficient supersonic intakes and were ill suited to large sideslip angles or angles of attack. Note that they were a characteristic of early supersonic flight when speed was the main objective and have since been replaced by ramp or even pitot intakes.


Why not use the yoke to control yaw, as well as pitch and roll? (Inspired by this question about rudder hand control on joystick-equipped aircraft.)

Most civilian fixed-wing aircraft (post-1987 Airbus airliners being the primary exceptions) use a yoke (essentially a steering wheel mounted on a vertical column that can swing back and forward) to control pitch (pushing the yoke forward pitches the nose down; pulling the yoke back pitches the nose up) and roll (rotating the yoke clockwise rolls the aircraft to the right; rotating the yoke counterclockwise rolls the aircraft to the left), but control yaw via a separate set of rudder pedals (pushing on the left-foot pedal yaws the nose to the left; pushing on the right-foot pedal yaws the nose to the right).

If the yoke were used to control yaw as well as pitch and roll, this would allow the pilot to make coordinated turns using just their hands, rather than having to remember to push with one of their feet at the same time, and would eliminate the risk of accidentally applying the brakes when steering on the ground.

A couple of possible ways for yoke-based rudder control suggest themselves; one would be to tilt the column from side to side (tilting the column left would yaw the nose to the left; tilting the column right would yaw the nose to the right), while another would be to push one of the yoke's horns forward while pulling the other back, rotating the yoke about its vertical axis (pushing the left horn forward and pulling the right horn back would yaw the nose to the right; pulling the left horn back and pushing the right horn forward would yaw the nose to the left).

Here's an illustration of what I've in mind:

Why don't any aircraft use the yoke to control all three axes, rather than just pitch and roll?

The modern control yoke is directly derived from the "joystick" control that became standard on aircraft in the days when Glenn Curtiss personally ran the company that was the main competitor to the Wright brothers.

After inventing aileron control (the Wrights were still using wing warping at the time -- this was before 1910), Curtiss needed a way to control movement of the ailerons, and subsequently of the rudder.  The original 1903 Wright Flyer had the wing warp controlled by sliding the pilot's platform (a flat surface, on which the pilot lay prone) right and left, and coupled the rudder, so that roll and yaw were inseparable.  Curtiss decoupled them, and needed to add a third control -- and since he was also sitting upright, even in his first airplane, his feet were available.

Running the elevators and ailerons on the control stick was obvious, and it was equally simple to put one's feet on a bar that directly operated the rudder -- and this layout became the standard almost instantly.  Even the Wrights adopted it before they demonstrated their Flier to the Army.

Over time, there have been a few examples of variations.  Airplanes that brought back coupled rudder and aileron, like the Ercoupe, let the pilot fly with "feet flat on the floor" -- and it seems to me there was at least one design, from the biplane era, of a transport aircraft with rudder operated much the way you describe; a control wheel mounted on a joystick, with stick movement controlling roll, and wheel rotation controlling yaw.

The fact this has only appeared in a very small number of designs suggests that, as noted in a comment, it's a bad idea to change something that's been long standardized -- yet, we have a good number of aircraft, ranging from sailplane to jet fighter and large transport, that use "sidestick" -- in which, in the transport case, the pilot in command actually flies with his left hand, while the copilot flies with his right.  Joysticks continue in wide use as well, especially in smaller or higher performance aircraft, or those with ejection systems.

The other, and I believe the main reason we don't see control schemes like what you describe is that it becomes impossible to maintain precise, separate control of roll and yaw.  When the same pair of hands are doing both jobs, the brain will mix them together, or in trying not to, will reverse mix (leading to a forward slip or a skid, the latter widely considered very hazardous at low altitude and speed).  If you have an aircraft in which it's difficult to avoid mixing either adverse or proverse rudder while applying aileron, it'll be difficult to land or take off in crosswinds, hard to maintain a precise final approach, and nearly impossible to fly high precision maneuvers (like air to air refueling or tight formations).


How does a lean die-out occur in a turbine engine? Essentially a lean die-out occurs at higher altitudes with low engine speed, and low fuel pressure, which results in a weak flame. So an overly lean mixture exists.

With these conditions, how would this exist? Typically at higher altitudes you're assuming there's less air, and with a lower engine speed, you'd get less ram air going into the compressors.

With these conditions, how would this exist?

The comment by @mins appears to answer the question for modern engines, although I'm not quite sure if I'm interpreting your question as you intended, but if your intent is to find out how this happens from an operational standpoint, here's an answer for the P&W JT9D-3 through -7 engines as used on 747-100/200 aircraft. In 10 years of flying with these engines, I only had a flameout once, so it wasn't a major problem, and the -3 engines were more susceptible than the later variants.

The scenario is that you're above 35,000 and you've reached your descent point and need to reduce power from full cruise to idle. We were taught to first lower the nose to ensure that we wouldn't lose any airspeed (a little gain was okay) and then to slowly bring the thrust levers all the way back. As I remember, we typically took at least 5 seconds to get the levers back.

In other words, if you suddenly reduced power or lost airspeed, you risked a flameout.

From the pilot's standpoint, if you had a flameout, all you did was tell the flight engineer to restart it when low enough that that was possible.


What is engine-out taxi out time? What is engine-out taxi out time?

a) The time between the first movement of the aircraft under its own power and the start of the last engine

b) The time between the first movement of the aircraft regardless if it's being pushed back without any engines running and the start of the last engine

And one additional question - how would you define the the start of the last engine?

a) The moment the fuel valve is opened

b) The first moment the engine is running (stable N1, fuel flow, oil pressure and temperature, etc.)

c) Something else

It's the time taxiing without engines on, for example when under tow or during push back. As opposed to when you're taxiing under the aircraft's own power

The second is potentially subjective, but I'd personally count it as the moment the engine is actually running, post-start up procedure: that's the moment when I could use the engine as an actual engine with useful power.


What distance can you see aircraft lights from? My parents bought a house and it's approximately 50-60 km from the nearest airport and one day when it was dark I've noticed lights on the sky and because I live in a big city close to the airport I came to the conclusion that this have to be airplane lights. Is it possible to see them from that far?

Aircraft lights can be easily spotted 50-60 km away during clear nights.

I used to live in Rotterdam and could spot aircraft at night when they turned exactly towards me at ARTIP which is an initial approach fix of Amsterdam airport Schiphol. ARTIP was exactly 100 km from my house.


Is there a good reason why modern airliners can't have conventional landing gears (vs. tricycle landing gears)? By "good reason", I mean a reason that we definitely cannot overcome with reasonable changes in aircraft design, control laws or procedures.

As possible benefits of this I see a much smaller (= lighter) tail landing-gear than the nose landing-gear. Also, an opportunity to reduce tail-strike margins (=increase incidence, reduce landing speed). And of course there is all that space at the front of the fuselage that is freed for other uses (systems, cargo, stairs,...?)

One drawback is of course passenger comfort. But passengers already experience high pitch angles during climb, and we could imagine to have the tail of the aircraft raised up (on a stand?) for boarding/deboarding. Also the APU has be moved (but I don't think this is impossible).

Short answer: Yes. Not one, but several. A taildragger configuration for modern airliners comes with several disadvantages:

Visibility during taxiing is much worse.

Visibility while taxiing is a safety-relevant issue (Picture source)

Braking hard will result in a headstand. And with today's landing speeds, braking hard is needed if you want to fly from standard length runways. Carrier-borne aircraft were the first to feel this consequence of increasing landing speeds, so they converted first to tricycle gears.

That is what is colloquially called a "headstand" (Picture source)

Loading and unloading will become more complicated. The current way of sliding containers manually on a flat deck would need to be replaced by internal winches pulling the containers up the ramp to the door.
Drag during ground roll is much higher as long as tail lift is not sufficient to get the tail up. Take-off distances would also become longer.

In short, it comes down to minimizing field lengths and increasing safety.

Who says there are no taildragger airliners? (Picture source)


Why is mid point RVR given? I cannot understand why mid point RVR is issued and what's the significance of it

It is (or was - I'm not sure) relevant because it is limiting:

The touch-down zone RVR is always controlling. If reported and relevant, the mid point and stop end RVR are also
controlling. The minimum RVR value for the mid-point is 125 m or the RVR required for the touch-down zone if less,
and 75 m for the stop-end. For aeroplanes equipped with a roll-out guidance or control system, the minimum RVR
value for the mid-point is 75 m.
Note: “Relevant”, in this context, means that part of the runway used during the high speed phase of the landing down to a speed of
approximately 60 knots.

source: JAR-OPS 1.405 - 1.0.5 (f)
The significance, I suspect, is because it's useful to be able to see where you are going when moving at high speed along the mid section of the runway and in manual control of steering.


How to keep a Garmin GTX330 turned off when powering on avionics? There seems to be an option in the GTX 330 settings that keeps to unit from powering on when receiveing power from the power system.

I flew in two different airplanes and one immediately powered on the transponder, the other one keeps the transponder turned off, until I press ON.

Looking thru the Pilot's Guide and Installation Manual didn't give me any clue.

Can someone help? Seems like an undocumented feature.

If pin number 1 on the back of the GTX330 unit is connected to power (+), the unit will turn on. If it is not, you will have to manually press the on button. If you remove power from pin 1, it will not turn it off.
See the installation manual, which is findable by a simple Google/Bing search, page D-1, figure D-1, Note 3.