Can a mistake of a single air-traffic controller cause a collision between planes? I am watching season 2 episode 13 of Breaking Bad and in the episode it shows that:

  an air traffic controller, distraught from his daughter's death,
  causes a mid-air collision, resulting in debris and human remains
  raining down onto the Whites' residence, as well as the rest of
  Albuquerque

It is at the very end of the episode and it looks like he has done nothing malicious just forgot to tell something. To me this sounds really surprising that a single human error can cause such damage.

As a programmer, I know that most of the scenes about computers depicted in the movies are complete nonsense. Is this a similar nonsense about aviation or is this really possible?

I haven't seen the Breaking Bad episode, but in my experience any aviation related scenes in films and series are usually stretching reality beyond the breaking point.

But it is possible that a single mistake can cause an accident. The probability of that happening is extremely remote, though.

Typically there are a number of safety barriers (also called defensive layers) in the system(1) that prevent any single mistake from developing into a collision. However, every barrier has a small probability of not catching the problem (e.g. due to it not being perfect or being in state of maintenance / failure) so eventually a crash could result from a single mistake.

This is often called the Swiss Cheese Model (originally from Reason, J. (1990) Human Error. Cambridge: University Press, Cambridge.)

When an accident happens, sometimes the phrase "all the holes in the Swiss cheese lined up" is heard, and you now know why.

While the first hole might be the mistake of a controller, the other holes may not be mistakes but are certainly rare circumstances and flaws in the system.  Accident investigation focuses on identifying these contributing factors.

In the Überlingen accident mentioned by Portree Kid, two immediate causes have been identified(2):

  The imminent separation infringement was not noticed by ATC in time. The instruction for the TU154M to descend was given at a time when the prescribed separation to the B757-200 could not be ensured any more.
  The TU154M crew followed the ATC instruction to descend and continued to do so even after TCAS advised them to climb. This manoeuvre was performed contrary to the generated TCAS RA.

The first cause can be seen as a mistake by the controller, however that mistake could only happen because of a number of contributing factors (systemic causes):

  Management and quality assurance of the air navigation service company did not ensure that during the night all open workstations
  were continuously staffed by controllers.
  Management and quality assurance of the air navigation service company tolerated for years that during times of low traffic flow at night only one controller worked and the other one retired to rest.

In addition to the above, the Short Term Conflict Alerting (STCA) system did not display conflicts to the air traffic controller because of maintenance (not listed as a cause in the report, but discussed in the text).

The second cause is not a mistake by the crew of the TU154M, but a latent failure in the way ACAS/TCAS II was introduced. Never did anyone give guidance on what to do if the controller and the TCAS gave conflicting instructions.

In the report this is identified as a systemic cause:

  The integration of ACAS/TCAS II into the system aviation was insufficient and did not correspond in all points with the system philosophy. The regulations concerning ACAS/TCAS published by ICAO and as a result the regulations of national aviation authorities, operational and procedural instructions of the TCAS manufacturer and the operators were not standardised, incomplete and partially contradictory.

So while the accident was caused by a single mistake from the controller, there were also many flaws in the system, which all together allowed the mistake to develop into an accident.

(1) By system I mean the aviation system as a whole, not only the air traffic control (computer) systems.

(2) Überlingen accident report


Why the excessive wait after shutdown before using the manual starter valve on the PW1000G? Why must there be a long period (measured in hours) between shutdown and startup, before using the manual engine start valve? Nine hours seems excessively long.

The FCOM page reports MSN 7172 which corresponds to an A320neo with PW1127G engines. Why is this important? Because this engine family is prone to bowing, so much that it requires a dedicated cooling procedure on start performed by FADEC:

However, the ENGINE START VALVE MANUAL OPERATION procedure requires you to perform the MAN START of the engine, which disables many safety feature of the FADEC and does not permit the FADEC to close the start valve in case of the detection of an abnormal situation (this is actually the reason why you want a MAN START). So, I suspect it also disables bowed rotor protections, and this is why that procedure requires the engine to be completely cooled down.
If you are wondering how is possible that 9 hours are necessary for the engine to cool down, consider that such engine requires about 2 minutes of forced cooling even after 1 hour since shutdown (source). The most critical point for is around 2 hours since shutdown (source). In some forum you can find pilots reporting ~6 hours the needed time for residual EGT to go to ambient temperature for LEAP engine, which is even less problematic for thermal characteristics compared to PW.
So it's reasonable to think that the engine core with its massive thermal capacity may require many hours to reach ambient temperature, and the need of MAN START probably disable safety features that would avoid bowing, which does not allow you to start the engine if it's still hot.


What is the diameter of a Trent 900 engine? What is the diameter of a Trent 900 engine, i.e the diameter of the fans, from one fan tip to the one that is directly opposite it? What is the radius of the fan or the the length of each fan blade?


What is the meaning of segment in MTRs? Military Training Routes (MTRs) with no segment above 1,500' AGL shall be identified by four number characters (IR1206/VR1207)

MTRs that include one or more segments above 1,500' AGL shall be identified  with three number characters (IR206/VR207).

What is the meaning of segment in MTRs?

What is the difference between three and four?

A route is how you go from place to place.  A segment is a portion of your route which is characterized by a consistent course/altitude.

A route may have one segment, or many.  An MTR is a Military Training Route.  If no portions of the route exceed 1,500 AGL, then it is given a four-digit identifier.

I'm pretty sure that the three-digit / four-digit decision was arbitrary, but I'm ready to be educated.


Could winds of up to 150 km/h impact the structural loads on a Boeing 777? From 15 October 2016, AI 173 from Delhi to San Francisco started flying over Pacific. Jet streams over Pacific helped Air India in reducing the flight time by 2 hours, despite increasing the travel distance by 1100 km. This also made AI 173 the world's longest flight, with total distance of over 9300 miles (15,000 kilometres). It completes the journey in 14.5 hours, with average speed of 1040 km/h; 560 knots.
(Adapted from here.)
As many people are wondering, could winds of up to 150 km/h impact the structural loads on the B777-200LR? Is it ever likely to be dangerous?

Could winds of up to 150 km/h impact the structural loads on the B777-200LR?

Not at all.

The dynamic pressures on the plane depend on the plane's velocity with respect to the air, not the ground speed.

Flying in 150 km/h tailwind is the same as flying with no wind, the plane's indicated and true airspeeds won't be affected. True airspeed is the plane's velocity inside the fast moving wind tube.

Since the jet stream itself is moving, it just moves the plane with it. With the added bonus of extra ground speed, or if you're the pilot, a dreaded return flight—unless you can avoid the now headwind, usually they are avoided for the Pacific and Atlantic routes, not as often for elsewhere.

Here's a 1200 km/h subsonic flight: Jet Stream Blasts BA Plane Across Atlantic in Record Time


What is the difference between an Airbus A330-200 and an A330-243? I am just curious to know the difference between Airbus A330-200 and A330-243.
Sri Lankan Airline A330-243

Sri Lankan Airline A330-200

Airbus has a dash numbering system that specified the engine manufacturer and the engine variant in addition to the aircraft's series number. The system details can be found here:
http://www.aerospaceweb.org/question/planes/q0276a.shtml

The general format of the Airbus numbering system is Ammm-sevZ where the individual components are described below.

Ammm = model number
s = series number
e = number defining the engine manufacturer
v = number defining the version of the engine model
Z =  optional letter describing a variation of the series number

The series number refers to the different variants of a particular model that have been developed. Standard series numbers used by Airbus include 1 for 100, 2 for 200, etc. The primary exception to this system is the A300. The original series number designations used for variants of this model included the B1, B2, and B4 for passenger models as well as the C4 for a convertible freighter version. Later production variants of the A300 were designated as the A300-600 to become consistent with the rest of the Airbus product line.
The engine manufacturer codes that have been assigned to date include the following.

0 = General Electric (GE)
1 = SNECMA
2 = Pratt & Whitney (PW)
3 = International Aero Engines (IAE)
4 = Rolls-Royce (RR)
5 = Engine Alliance (joint venture of GE and PW)

The final number denotes newer
versions of the basic engine model. These numbers appear to start at 1
for the original engine and increase sequentially for updated engines.
An optional letter sometimes follows the series of numbers to
designate a variation on the series number. Common examples include
the following.

C = convertible passenger/freighter model
F = freighter model
R = long range model
X = enhanced model (?)


Do you need to have a raft if you're in a seaplane? One of the basic rules of flying over water is that you need some kind of raft if you're out of power-off glide range from land. Does that also apply to seaplanes or amphibious planes?

Here is an answer I found after a few minutes of looking up regulations online.

Federal Aviation regulations require carriage of FAA approved floatation gear when operating under Part 91 for hire (FAR 91.205(b)(12)), but Part 91 flights not conducted for hire are not required by the FAA to carry floatation equipment.
It is worth noting that local authorities, including state, county and municipal authorities, may require that all vessels, including seaplanes, carry U.S. Coast Guard approved floatation gear on board.

Found on the https://www.seaplanepilotsassociation.org/resources/faq/operations/ website.


Turbo-fan idle at high speeds, will air speed up fan speed? If N1 idle is 30%, will flying idle at very high speeds force the fan to go higher than 30%? (for example idle while descending fast)

And if no, why not?

Yes, N1 should increase as the plane reaches higher speeds. This means that the blade speed will increase, therefore, increasing N1. Now because the engine setting is constant (throttle), this means that only a slight increase in the amount of thrust will happen.


Why does the A320 IR2 MEL OPS procedure suggest to switch to ADR3? The A320 34-10-05B IR2 MEL OPS procedure additionally calls for Air Data switching to FO3.
When ADR 2 is working fine why replace its data on the FO PFD when only IR data is lost?

Even if ADR and IR perform two independent and separate functions, they are the same hardware object (example). A IR2 malfunction is a malfunction: you do not know, in general, what is causing the problem of IR2 and it can possibly be a common problem (maybe undetected on ground by the ADR2).
For example, in the ADIRS Honeywell manual you can find in the IR FAULT chapter:

The ADR function of the affected ADIRU may possibly still work, even
if the IR function is not working. Cross comparing air data
information gives the pilot some idea of the validity of the ADR data
for that ADIRU.

So you have no guarantee that if IR2 is faulty, then ADR2 works. This is why, for precaution, you switch F/O on ADR3.


Where does the term “throttle quadrant” come from? The area of many flight decks that contains throttles or thrust levers is often referred to as the “throttle quadrant” or “thrust lever quadrant” even if it’s not one of four parts of the panels.

Where does the term come from?

The term quadrant refers to the panel containing the levers and is derived the circular arc in which the throttles are placed:

  throttle quadrant

  The recess in which the throttle is located and moves. ... It derives its name from the circular arc in which the throttle is placed.

Looks like the term entered aviation from the rudder controls in a ship:

  quadrant

  A frame fixed to the head of a ship's rudder, to which the steering mechanism is attached.

  3.1 A panel with slots through which a lever is moved to orient or otherwise control a mechanism.

Here's a rudder quadrant

Rudder quadrant; image from titanic-model.com


What kind of flight-control redundancy does the Tu-204 have? The Russian Tupolev Tu-204 and variants are reported to be digital fly-by-wire. Are they quadruplex redundant? Do they have manual or analog back-up systems?

The Tu-204 does not have mechanical back-up, but it does have analog back-up. Its FBW is three-channel (same hardware, but different software).

(...) being the only Soviet airliner to have flown with a fly-by-wire control system, lacking any mechanical backup (...)
The Tu-204's digital fly-by-wire control system is probably the most advanced feature of any Soviet airliner. It works on all three axes—pitch, roll, and yaw—and is broadly similar in function to that found in the A320.
(...)
The same hardware, but dissimilar software, is used in the three channels of the digital fly-by-wire system, says Lanovski. A "quorum filter" monitors their outputs, and if two channels fail a three-channel analogue system automatically takes over, giving a catastrophic failure probability for the complete system of less than 10-9 per flight-hour, says the Soviet official. Pilots have felt no difference when the analogue system has been switched in during flight tests, says Lanovski.

Source: Tupolev's new twin, Flight International, 20 May 1989


How is the same takeoff performance achieved by a specific engine type on aircraft of different sizes? The entire B737Max family (B737Max7,8,9,10) uses CFM International LEAP-1B (Source) engines, despite the B737Max10 carrying up to 60 more people than Max8.

My question is how do all of the aircraft in the family achieve the same takeoff performance, despite such a remarkable difference in their size, with the same engines?

There are several model variations of that type engine.

Refer to the Type Certificate Data Sheet (TCDS) for the Boeing 737.  You will find listed the specific model number numbers and thrust for each approved engine.

For example, here are the CFM engine models approved for specific model/serial numbers of the 737.  You will have to get the latest revision of the TCDS for new models, like the 737 MAX.  This excerpt from the 737 TCDS shows the model variety of one type engine (the CFM56-7B) as approved for certain 737s:


What is this old biplane on a float? I'm hoping for some help in identifying the plane in these two photographs I found in my father's collection.

It looks a lot like a variant or a copy of the Curtiss Model E (aka Curtiss A1) from 1912:

There is a youtube video of it flying in 2011.


What is that missing instrument on a Beechcraft 1900C? (Full image) Beechcraft 1900C.

I cannot find the name of the missing instrument even in the manuals.

Originally there was no instrument at this place, except for UE series with an electrically driven artificial horizon, where there was a fast erect pushbutton/indicator for the copilot gyro.

According to Wikipedia, UD series is for the military model and UE series is for 1900D, so I assume UC series is for 1900C model. Instrument panel for series UA/UB/UC:

Instrument panel from training manual, models UA/UB/UC (source)

Anything visible here has been added after the aircraft left the plant, when the panel was retrofitted. When browsing pictures of this cockpit online, we can see various additions:

Sources: Left, center, right

Looking at details of your image, we can see there was likely a sticker and a button associated with the instrument. This could fit with a battery temperature indicator and its test button:

Source: Right

This configuration was actually found on F-GPYY. Comparison:

Source: Right

Full cockpit of F-GPYY when it was an aircraft of the now defunct French Air Littoral operator:

Photo by Thierry Izzi, source


What are the typical lift, lift coefficient and drag coefficient for a A320 in cruise? What would you expect the typical lift force and coefficient of lift and drag to be for a A320 at cruise?

Considering flight at 36,000 ft, mass approximately 72 tons, velocity 230 m/s with a surface area of 122.6 m² and density 0.366 kg/m³.

The results I've calculated seem a little high, CL=0.666 and L=724 kN

In s/l flight, weight and lift are practically equal, so  –if those are metric tons– the lift will be 72000 x 9,8 = 705600 N. Now, concerning the CL, we may solve for CL the expression for lift:

$C_L = \frac{2 · L}{\rho V^2  S } $

$C_L = \frac{2\cdot9.8\cdot72000} { 0.366 · 230^2 · 122.6 }$

$C_L = 0.595$

Now, assuming a L/D of 15, the CD = 0,594/15 = 0,039


Was it ever considered to optimise a jet to normally operate with one engine shut off? As I understand it, the current trend to reduce all commercial aircraft to no more than two turbofans has long-relevant reasons – the more engines, the higher the fuel consumption – and earlier jets mostly had to come with more to ensure reliability.
Now, the naïve solution to design an aircraft with 3 or 4 engines but needing only two has obvious economic flaws and a normally mounted engine introduces so much drag that it's certainly always better to run it than not. However it is not unheard that existing aircraft designs were upgraded with better engines (particularly for economic reasons: stern look at 737MAX). I'm thinking particularly of trijets here: the 727 for instance did have its outboard engines upgraded to higher-bypass ones in its career. I could well imagine that they thought about whether the center engine could be made obsolete altogether – just make the new engines 50% more powerful each, and thus degrade the center one to a mere emergency backup. (And do something aerodynamic about the S-duct so it wouldn't be too detrimental for drag anymore.)
Was any such redesign seriously pursued by one of the major manufacturers?

I can think of one example: the Hawker Siddeley Trident 3B.
This had a fourth, small engine buried in the tail, which was only used during takeoff. They did this because it was cheaper than redesigning the aircraft for different engines.

Since the Spey 512 was the last of the Spey line, extra thrust would be difficult to obtain. Instead of attempting to replace the three engines with a completely different type, which would have been difficult with one engine buried in the tail, Hawker Siddeley's engineers decided to add a fourth engine in the tail, the tiny Rolls-Royce RB162 turbojet, fed from its own intake behind a pair of movable doors. The engine added 15% more thrust for takeoff, while adding only 5% more weight, and it would only be used when needed. BEA accepted this design as the Trident 3B, and ordered 26.


Why do older students take longer to learn to fly? I have heard or read many CFI’s say that older students take more time to learn to fly. I know that as we age our brains in general have more difficulty learning new things, but what part of flying is it that usually takes longer for older students? Do they have more trouble learning things like procedure, regulations and aerodynamics or is it the physical coordination of controlling the plane, judging distances, etc. that takes longer? Maybe it’s the multitasking involved?

This question is more related to human aging and learning than it is to aviation. When people age, there is a toll on several parts of body and the acquired skills may not stay as sharp as they used to be.

As we age, learning new things become harder, not because we are getting stupid, but because learning new things is intrinsically hard. Almost all people get into a profession in their early 20s, but it becomes harder to change their career later in life. The reason is that they have more things on their mind to worry about as opposed to the early phases of life.

One does not stay young forever. And you cannot point out one or two or ten things which makes learning new things hard. It is a combination of many factors. That being said, becoming a pilot in your 50s or 60s is harder than in your 20s or 30s, but there are many old pilots who can do and have done things which younger ones cannot do. Example: Captain Sully

You can ask why most athletes are in their 20s, not in their 60s, and will get a similar answer.


What is the effect of sudden extreme temperature change on brake disks of large aircraft? What is the temperature of brake disks at maximum altitude of a jumbo like a 747 and airbus A380 for say a 10 hour flight.  Does the temperature drop below zero and what is the effect on the metal material used on the disk from the sudden change in temperature from one extreme, below zero degrees celcius to over 700 degrees celcius when braking?

The temperature changes from altitude to ground are not (usually) rapid. Therefore the possible sub-zero to red-hot case is not as severe as may be thought. If carbon discs are the example, they require temps that are almost beyond steel discs braking capability.


How can I log simulated instrument time and approaches in a single-place aircraft? Is there a way to log instrument approaches in VMC when all you own is single-place aircraft? (or aircraft with only one pilot station - I own a Long EZ). The regs seem to indicate that I have to rent another aircraft, which seems to defeat the entire purpose of maintaining currency, as I would be logging my approaches in an aircraft of a different type, with potentially different avionics.

Unfortunately, the only way for you to get simulated instrument time will be to rent a dual-control aircraft, or to use an approved simulator. Since you can do back-to-back approaches in a simulator, you may be able to find one that charges almost as little as the equivalent amount of fuel in your Long EZ. Especially since you can forego, startup, run-up, taxi, takeoff, landing, and shutdown.
The alternative to the above is to plan on dropping everything whenever you have a suitable IFR day, and go flying. Surely, there are a couple of IFR days in which the weather is not too severe every six months.
If you can deal with the fact that your flight time will not be within your control, you could partner with another aircraft owner of a two pilot place aircraft. That pilot will need a safety pilot as well. Then, you can just alternate who is under the hood.
Another, less convenient and effective, but more productive option is to schedule and budget a regular flight and ground lesson with a CFII once a year. If you make this a recurring lesson with the same career instructor, you can coordinate with them to make this a combination IPC/BFR. This and the random IFR day you may get in a years time should keep you current. It also has the additional advantage of possibly learning something new or relearning something forgotten.
All of the above options address the issue of staying current. None of them address the issue of staying proficient in your aircraft with your avionics. For this I suggest making half of our VMC approaches as actual or practice IFR approaches. You may not get the visceral experience of being in IMC. But, it will allow you to practice your proficiency.


Where is the landing distance for seaplanes specified? I need to know, is there a specified distance for the landing areas of seaplanes? In airports, we have generally distances are defined according to the flight requirements. I need to know whether there are certain distances defined or just making the landing area by guessing?

is there a specified distance for the landing areas of seaplanes?

A cautionary note: As @MikeSowsun said, the required distance to land a seaplane is MUCH shorter than that required to takeoff. For operational planning purposes, what you should be interested in is takeoff distances. My offhand guess is that landing distances are less than half that of takeoff runs. At least that was I think true of the old J3 floatplane I used to fly.

Now I assume you're including floatplanes as seaplanes. There are relatively few hulled seaplanes these days as compared to floatplanes, and compared to the numbers of the wheeled configuration of a given aircraft for which floats are available, the number of floatplanes is relatively small, which may account in part for the POH (pilots' operating handbook) for aircraft usually not providing performance data for float configurations. There are also differences in performance depending on the make and model of the floats being used.

All that said, you can often find performance details for current production floats on a given aircraft on the float manufacturer's website. For example, http://www.wipaire.com/aircraft_page/cessna-caravan-series/ gives that information for the Cessna 208 on Wipaire amphibious floats. In this instance, the takeoff run on water with the Caravan's small engine is 2341 feet, takeoff over a 50 foot obstacle 3660 feet. The same manufacturer's figures for a Cessna 206 on their amphibious floats is 1770 feet takeoff run, 2850 feet over a 50 foot obstacle.

  just making the landing area by guessing?

Not by guessing, but looking at the intended area of operation in the light of past experience and judging whether they can takeoff from that area.


Why isn't the Presidential 747 "Air Force One Heavy"? Aircraft with a maximum takeoff weight of at least 300,000 pounds add the word "Heavy" to their callsign.  (Example: Lufthansa 415 Heavy in this video.) The current Presidential 747's have a maximum takeoff weight of 833,000 pounds.  Yet, it flies (when the President is on board) with the callsign "Air Force One", not "Air Force One Heavy."

Why not?

Practically speaking, the 'heavy' designator ('super' for A380 and An225) is to help enforce separation requirements due to wake turbulence. In case of AF1, it is not as if other aircraft are going to be allowed near it, so the designator is redundant.

Regulation wise, FAA JO 7110.65T Section 4. Radio and Interphone Communications, specifically states that the 'heavy' designator should not be used:

  When in radio communications with “Air Force One” or “Air Force Two,” do not add the heavy designator to the call sign. State only the call sign “Air Force One/Two” regardless of the type aircraft.


Why bits are mixed up (interleaved) during ATC transponder mode A and mode C reply format? In the image above from radartutorial.eu, we can see that the sequence of bits are c1 a1 c2 a2 c4 a4 during the reply of ATC transponder mode A.
Why are the bits not transmitted like c1 c2 c4 then a1 a2 a4. Why this mixing up or interleaving?

Mode 1 transponders only had six bits: A1, A2, A4, B1, B2 and B4, which clearly wasn’t sufficient to identify specific aircraft.  Each day, all pilots would be given a common code to squawk when returning so the air defense folks would know they were friendly, whereas a foe would only have a 1/26 chance of guessing correctly.
Mode 3/A upped this to twelve bits, adding C1, C2, C4, D1, D2 and D4. However, the C bits were cleverly interleaved with the A bits, and the D bits with the B bits, at twice the transmission rate. The result was that (for instance) Mode 1 code “12” and Mode 3/A code “1200” looked the same, at least to the primitive equipment of the era. This was specifically intended so that Mode 1 aircraft could work with Mode 3/A radar sites and vice versa, allowing a gradual upgrade. Where the new equipment was in use by everyone, individual (“discrete”) codes could be assigned to each aircraft.
This is also why, to this day, xx00 codes are mostly “non-discrete”, i.e. they have a general meaning rather than identifying a specific aircraft.


Is this plane safe to fly on? The turbine blades look damaged While waiting for a recent flight, I observed this aircraft with what appear to be rather worn turbine blades.  Is this close to being a safety issue or is it purely cosmetic?

Yes, it is safe. Prior to every flight, ground technicians and one of the pilots will complete a pre-flight walk around of the aircraft, which includes checking the engines thoroughly. Any issues with the turbine blades would be noticed at this point and the flight would not depart.


Why is the thrust-specific fuel consumption much worse for high bypass turbofans at cruise? General Electric GE90
Takeoff: 0.278 lb/lbf/h (28.3 kg/kN/h)
Cruise: 0.545 lb/lbf/h (55.6 kg/kN/h)
Source: https://en.wikipedia.org/wiki/General_Electric_GE90#Specifications

I assume this is typical for a modern HBPR turbofan.

But why?

Of course, as altitude rises, the reduced air density means the fan has less airflow, causing less thrust to be created. But then again, the bypass ratio does not change, so the core airflow also decreases by the same amount as fan airflow. So fuel flow should be decreasing too! So why is the TSFC TWICE as bad for cruise as takeoff? Is it because of losses in the fan duct increasing rapidly with speed?

(By the way, I know the higher speed helps reduce the seat-mile consumption, but still.)

EDIT: Wait what the? RB211, another HBPR turbofan, has almost no difference between cruise and "sea level" https://en.wikipedia.org/wiki/Thrust-specific_fuel_consumption

Yes, that is typical for high bypass ratio (HBPR) turbofans.

  But why?

Because the entry impulse goes up while the exit impulse stays roughly constant. Thrust is the difference between both, derived over time.
The moving engine needs to slow down the airflow for combustion to take place, and then needs to accelerate the air by more than it has been slowed down to have positive thrust. Hence, SFC goes up in parallel with speed.

While the internal process inside the engine in flight is very similar to that at rest (only the pressure levels are increased by the ram effect of the moving engine and density drops with increasing altitude), thrust is reduced due to the smaller impulse difference in flight. Since a HBPR engine accelerates most of the air volume streaming through it by only a little, the average exit speed is relatively low compared to a jet engine with no bypass flow. This is similar (but less severe) to a propeller where thrust drops with the inverse of speed.

SFC gets even worse in supersonic flight. For a meaningful SFC comparison speed needs to be the same.

Thrust-specific fuel consumption in g/kN·s of a turbofan engine with bypass ratio 3. Y axis shows altitude in Meters. Isolines wer made with R contour function and should be more rounded in reality.


How does the dihedral angle work? I've been looking for this topic on the internet but I don't have enough concrete answers. Suppose we have a plane with dihedral and it has a suddenly swinging to the right (watching from the nose of the plane), so the right wing goes down. I'm trying to understand why the right wing generates more lift than the left wing when it has a sideslip. I have seen in some sites that the sideslip induces a flow from the tip to the root and this makes the right wing increase locally the angle of attack, hence the lift of this wing increases too.

But, why the right wing increases the angle of attack? I think it couldn't be possible because the sideslip flow is in a different plane respect the mainstream.

Basically, dihedral effect is that during banking, the 'lower' wing will experience a higher angle of attack compared to the 'higher' wing, and a result, a greater lift. The resulting net force and moment reduces the banking angle, reducing stability.
Consider a wing with a dihedral angle $\Gamma$ with a forward airspeed of $u$. If the sideslip angle is $\beta$, the wind due to sideslip is $u \cdot \sin\beta$. From geometry, the normal velocity induced due to dihedral, $v_{n}$ becomes $u \cdot \sin\beta \cdot \sin\Gamma$.

Image from Stability and Control of Aerospace Vehicles
Note: The notations are different in the figure; but the principle is the same.
For our purposes, we can take the sideslip velocity ($u \cdot \sin\beta$) as $v_{y}$. Now, consider two sections from the wing - one each from the 'lower' and 'higher' sides. The induced velocity is of the same magnitude in both the sides, while the direction differs, as can be seen from the above figure.

Image from people.rit.edu

Image from Stability and Control of Aerospace Vehicles
For small angles, $v_{y}$ is nearly equal to $u \beta$. The induced angle can be given as,
$\Delta \alpha = \frac{v_{n}}{u}$.
From the earlier relations, we have,
$\Delta \alpha_{1} = \beta \cdot \sin\Gamma$, and $\Delta \alpha_{2} = -\beta \cdot \sin\Gamma$.
Because of these induced angles, the lift on the downgoing wing increases by $\Delta L$, while of the other one decreases by $\Delta L$. The net result is that the 'lower' wing experiences an increases lift, causing a rolling moment, which causes the banking angle to reduce.

Image from Stability and Control of Aerospace Vehicles


What does a 10nm/20nm circle on instrument approach charts mean? A lot of instrument aproach charts (VOR or ILS) have a circle around the navaid. It can be 10/20 NM or in km, like the 20km circle in the image. What does this circle mean?

It can be 20 km, or 10 NM.

Since you've shown an ICAO-style plate, ICAO Annex 4 Aeronautical Charts says:

  11.3.3.1 Except where this is not practicable, a distance
  circle with a radius of 20 km (10 NM) centred on a DME
  located on or close to the aerodrome, or on the aerodrome
  reference point where no suitable DME is available, shall be
  shown; its radius shall be indicated on the circumference.

So whenever possible, this circle must be shown.


Where do airports use 3-bar VASI for the visual glideslope? What are some airports that have a 3-bar VASI system?  I am trying to find some locations to compare what the chart supplements say to the supplements for those with 2-bar VASI systems.

Runway 8 at Albuquerque International Sunport Airport (KABQ) has a 3-bar VASI.

KABQ's current Chart Supplement page1 lists the VASI for Runway 8 as a VASI(V6L): a 3 bar, 6 box VASI located on the left side of the runway. The airport diagram also depicts the VASI as a V3: a three-bar VASI.

The VASI bars are also visible in aerial images, such as here on Google Maps:

1The current Chart Supplement page will expire and this link will be broken. For future reference, the updated Chart Supplement page can be found elsewhere, such as on this SkyVector page.


Does an increase in lift always cause an increase in lift-induced drag? An increase in lift causes an increase in drag. Is it always true? I am confused with two points.

Lift increases with an increase in airspeed but induced drag reduces with an increase in airspeed.
Higher aspect ratio wings generate greater lift but create less induced drag.

When looking at statements like these, it's important to consider which parameters are varied and which parameters remain fixed.

Let's get this out of the way first by correcting your statements:

Lift increases with increase in airspeed with constant angle of attack but induced drag reduces with increase in airspeed with lift force remaining constant
Higher Aspect ratio wings generates greater lift with constant wing surface area but creates less induced drag with lift force remaining constant.

As you can see, each half of your statement refers to a different scenario. The bottom line is that for lift generation, it's more efficient to give a small change of velocity to a large air mass, than a large change of velocity to a small air mass (because force is generated by momentum change which is linear in velocity, and induced drag is due to the kinetic energy imparted on the air mass which is quadratic in velocity).

When flying fast or with slender (high aspect ratio) wings, you affect a larger air mass every second. You can do two things: either keep your angle of attack constant and get a lot of lift out of the air mass, or in case you don't want to do aerobatic maneuvers, you decrease the angle of attack until lift once more equals weight, and get less induced drag.


Why and how do flaps increase the curvature of the wing? Why or how do flaps increase the curvature of the wing? Do they alter the curvature of the upper surface of the wing?

Flaps change both the camber of a wing as well as its chord line and angle of attack. All the following images were taken from this article.

You can see the camber line here in a retracted scenario:

And here in an extended scenario:

As for the why, flaps are generally used to allow you to slow an aircraft down at a give pitch angle. This allows the pilot to pitch the aircraft down without an increase in speed. Generally a pitch down (given no other things are changed) will result in an increase in speed.

Flaps also change the angle of attack of the wing as well as the chord line:

All of this is a bit of an over generalization as there are many types of flaps and it's worth looking into the different types and how they operate.


What's the relation between speed of an aircraft and takeoff distance? I'm making a tool that when given : weight of aircraft , takeoff speed , runway length and some other parameters , it analysis the takeoff performance and states whether using the brakes now is safe or not . So I'm looking for a mathematical relation between the takeoff speed and the takeoff distance to use it in my code . Based on the given speed I want to determine whether the runway length will be enough or there will be a hazard . Is there any mathematical formula for calculating the takeoff distance using takeoff speed and weight ?? or how do people calculate that ? I need any method .
Any help is appreciated . Thanks

I think your question is regarding new aircraft under design and not for existing planes?

The dynamics of ground roll/stopping is governed by one equation:

$$m\ddot{x}=T-D-\mu(L-mg)$$

where $T$ is thrust, $D$ is drag, $\mu$ is friction coefficient, $L$ is lift, $m$ is mass and $g$ is gravitational accel. Since thrust, drag and lift are a function of airspeed (and spoilers + brakes + thrust reverser should abort occur), the most naive way is just to numerically integrate the equation twice to get the distance at time.

That being said, don't forget that takeoff distance and accelerate-stop distance must be considered with all engines operating and with the critical engine failed. $V_1$, assuming not limited by controllability, should be selected such that the two distances balance. Also keep in mind that a good portion of takeoff distance is rotating and accelerating to $V_2$ before 35ft with the critical engine failed. The previous equation does not account for that portion.


DC Generator on hotel mode ATR 72-600 Does the time an ATR 72-600 is running in hotel mode contribute to the flight hour (FH) limit of the DC Generator?
Does running an ATR 72-600 in hotel mode degrade the DC Generator brush differently than running the engine in normal operation?

To start, the FH timer starts when the aircraft takes off (weight-off-wheels) and stops when the aircraft lands (weight-on-wheels).  This means that whether the engine is in hotel mode or running for taxi, the aircraft (and the DC Gen) are not accumulating FHs.  One thing to consider is the difference between an engine hour (EH) and a flight hour.  Engines have hard time limits based on how many hours the engine was run, not on how many hours it is in flight.  One might think that since the DC Gen is directly driven by the engine, that the wear rate should be based on EH, and I might agree with them. However, since the DC Gen is an accessory component (isn't a PWC part, doesn't come with the PW127 engine), the component is lumped in with the rest of the airframe systems, FHs are accumulated just like any other system outside the engine.

You would be right in saying that some aircraft components have hard time limits, that at a certain number of FHs, they need to be replaced. Good examples would be the engine (for overhaul), landing gear and some structure.  The components and the aircraft as a whole lose its certification if the hard time limits are exceeded.  The DC Gen however, more than likely has a soft time limit.  This means that the DC Gen is certified to be on the aircraft until it malfunctions.  The manufacturer of the DC Gen would likely impose a soft time limit, meaning that if the soft time limit is exceeded, it is out of warranty.

When the engine is in hotel mode, the only difference is that the prop and the turbine powering the prop are arrested.  The LP and HP sections of the engine are running as they normally would during taxi.  This post has some helpful images on what the internals of a turboprop look like (reference the second image, the first one is a PT6 I believe).  Hot exhaust air is still rushing past the arrested turbine that would normally power the prop.  This may cause some back pressure that the Full Authority Digital Engine Controller (FADEC) would need to account for, but in terms of the speeds and torque seen by the HP section, accessory drive and DC Gen, the wear seen on the brushes of the DC Gen would be no more than the wear seen during an engine taxi.


What is the authority in the UK? Is the United Kingdom subject to the EASA's authority or the CAA's (Civil Aviation Authority) authority?

EASA: this is a European Union body, so yes, the UK is a member state.

CAA: There are many Civil Aviation Authorities worldwide, basically each is a national entity within the corresponding state. So, specifically for the UK, yes, there exists a body known as CAA that is a state entity, formally independent but in practice dependent on the UK Government (Dept. of Transport). Their web page is: http://www.caa.co.uk/

Due to the complex configuration of EU law, both EASA and the UK CAA can have their word to say on operations within UK territory. Though, as CAA say themselves:

  The CAA works closely with the European Aviation Safety Agency (EASA) to promote the highest common standards of safety and environmental protection in civil aviation.


What is the smallest manned jet aircraft? In the movie Spy Kids (2001), there is a scene where the characters board a small jet aircraft "built for one passenger". The aircraft is about 2 meters tall with a 3 meters wingspan, and features a single jet engine, air intake located below the canopy, and tricycle landing gear.

Which got me wondering: what is the smallest fixed-wing jet-powered aircraft to date?

Some clarifications:

The aircraft must be able to takeoff and land under its own power (i.e. aircraft launched mid-air does not count).
The aircraft is propelled by one or more turbojet or turbofan engine(s) (i.e. no propellers, no rockets).
"Smallest" is measured by wing span.
The aircraft must be pilot operated (i.e. RC aircraft does not count).
This is not a question about whether an aircraft that small is possible, since there is already another very similar question. Rather, this question is about the smallest aircraft successfully flown in history to date.

The BD-5J is what guinness world records claims to be the smallest but it is larger than the Cri-Cri in its jet implementation (the BD-5A is smaller than the Cri-Cri but prop powered)

If you want to count really experimental stuff the Martin Marietta X-24A lifting body has a wingspan of only 11 ft 6in. making it the smallest. Although I will admit it is predicated on a lose definition of "wing" and is rocket (not jet) powered.

Although if you broaden your definition of "aircraft" Yves Rossy's jet wing backpack is the smallest coming in at a wingspan of 7.9 ft. It is still piloted, jet powered although I do not think it can take off under its own power.


What type of computers are in a flight system? I know there are many types of flight computer systems, with varying names and capabilities.

I'm more interested in knowing what the computers, themselves, are made of?

They certainly are not "off the shelf" computer components - and are more likely specifically built single-board computer systems running some sort of Real-Time OS. Where can I find out more information about one (and/or purchase one) if I were inclined to test software on one at home?

Historically, avionics manufacturers have used off-the-shelf processors on custom circuit cards.  Processor selection has been based on getting a reliable processor (established history) at a reasonable price and an expectation that it will be available for a long time.  The high turnover (obsolescence) in processor design along with a lack of design integrity in commercial products is causing avionics companies to move towards custom chips.  Though some products meet the integrity by using two dissimilar processors (though it doesn't address the obsolescence issue).  I am aware of a number of older designs using 486 and PowerPC processors.

Operating systems (just like all the a/c software) have to comply with the appropriate level of DO-178 (currently rev C).  In practical terms, that means the OS has to meet DO-178 Level A.  There are a number of commercial solutions available.  LynxOS-178 is one.  Integrity-178 is available from Green Hills.  Wind River also has a product available.


Do airlines have an ATC schedule they have to adhere to? Do airlines have to include a departure window when they file their flight plan, or communicate it otherwise?

As many people know, airlines operate on schedules, but I think we all have seen delayed flights, sometimes for 10 mins, sometimes for a couple of hours. However, that is the airline and the customer's problem. Do ATC or the Management at the airport have a departure window though, so if the plane does not depart in between these times; and it is not the airport's fault, they will not let the plane depart, or fine them?

The estimated off block time, EOBT, which is the time at which the flight is planned to leave the gate at the departure airport, has a validity of +/-15 minutes. If the plane is not able to depart within this window, the company must send a new ATC flightplan with an updated EOBT.

In some cases a calculated takeoff time, CTOT, is issued to a flight. This is the exact time the plane must begin its takeoff roll. It is given based on airspace or airport congestion along the planned route of the flight, to prevent overload in individual ATC sectors. The flight must begin its takeoff roll within -5/+10 minutes of the CTOT. If unable to comply, a new CTOT must be requested.


What is allowed with the new EASA SPL license? Are you allowed to fly for profit with SPL? If I have understood correctly, SPL is to LAPL(S) as CPL is to PPL, but with no extra requirements over LAPL(S), but I have problems believing this.

Assuming I have understood the rules correctly, I can upgrade my MGPL to LAPL(S)+TMG and therefore to SPL+TMG with no extra effort. After doing the conversion and flying PIC for 75 hours, I would legally be allowed to ask the passengers to pay for my flights. This seems to be too far from the current rulings that I have trouble believing this.

SPL = Sailplane Pilot License
LAPL(S) = Lightweight Aircraft Pilot License (Sailplane)
CPL = Commercial Pilot License
PPL = Private Pilot License
TMG = Touring Motor Glider

I know very little about this, but it looks like you can fly commercially with an SPL if you pass an additional checkride. This is from the UK CAA, and the same wording is quoted on a bunch of European gliding organization sites:

  You cannot operate commercially, or receive any kind of payment, until
  you:

  Are 18 years of age or over
  Have completed 75 hours of flight time or 200 launches, after your licence has been issued
  Have passed a proficiency check with an examiner

EASA's Part-FCL guidance defines what the additional checkride includes:

  AMC1 FCL.205.S(b) SPL — Privileges and conditions

  CONTENTS OF THE PROFICIENCY CHECK FOR THE EXTENSION OF SPL PRIVILEGES TO EXERCISE COMMERCIAL PRIVILEGES ON A SAILPLANE

Note that it calls it an "extension" of SPL privileges, which strongly implies that an SPL by itself doesn't allow commercial privileges. There is one exception, which is that an instructor can be paid to instruct with just an SPL. The CAA site says:

  The exception to this is for holders of a SPL with instructor or
  examiner privileges, who can be paid for the following:

  Flight instruction
  Conducting skill tests and proficiency checks

  for the LAPL (S) or SPL and any associated ratings and endorsements.


Can small RC aircraft utilize a steel sheet monocoque construction? I have seen small RC aircraft built from just about everything: cardboard, sytrofoam, fiberglass, aluminum, coroplast, etc.

Most these designs are at least partial monocoque designs. Is there any reason why sheet steel cannot be used? In comparison to aluminum, thin sheet steel is very cheap or even free. Most appliances in the US are built from approx. 1/32 inch sheet steel. It can be worked using standard tools available in a hardware store.

Are there any requirements that sheet steel would not be able to meet? I am aware that the weight-to-lift ratio of the aircraft is likely to suffer, but as long as it is capable of flight I don't consider this as much of a problem.

Yes, it can be done, but to do it well is a lot of work. You will also need to use a thinner gauge than 1/32" to get the weight down.

Note that one of the very first all-metal aircraft was made of 0.2 mm (1/128") sheet steel and flew well. However, building it required a corrugated substructure and a welded steel tube frame for strength. Still, it was heavier than necessary so its builder switched to aluminium for later designs.

Generally, the tension length of steel (strength relative to density) is roughly equal with that of aluminium or titanium; however, you will need to use high-grade steel to be comparable with aircraft-grade aluminium, so some of the price advantage will be lost.

But there is a distinct disadvantage with higher-density materials. While their strength scales linearly with wall thickness, their buckling strength scales with the square of their thickness. You will end up with a very delicate structure which will require careful handling to avoid local dimples and a stiff substructure to avoid early failure in compression. Also, introducing loads locally (say, for a landing gear or an engine mount) will require local reinforcements which should ideally be multi-layered and taper out in several steps.

If you want to scale an existing structure down, make sure you place the stiffeners closer than what a scale construction would require. But I am sure you will prefer to bond the sheet steel to a styrofoam core. Use a higher-density styrofoam with better compression strength and be generous with local reinforcements, and the model should turn out fine.


Does the size of control surfaces affect maneuverability, and if they are smaller, is it easier to stall? Does the size of control surfaces effect maneuverability and make it easier to stall?

There are at least 3 possible cases and unfortunately your question doesn't tell which one you would consider valid.

The maneuverability (the maximum rate of rotation?) can be measured by the moment of the force exerted by the surface at the CG.

Let's consider the area of the control surface is smaller, and...

All other parameters are unchanged, in particular surface airfoil, center of pressure, and angle of attack:

As the currently selected answer tells, the maximum lift available from the control surface is lower, hence the maximum moment is lower, and the maneuverability is reduced.

As the airfoil and the angle of attack are unchanged, the stall characteristics are unaffected.

This theoretical case is unlikely to be seen as the designer would certainly compensate the reduction of the area by some other change.

The surface is moved to a location further from the CG to maintain the moment with the smaller lift force:

Neither maneuverability nor stall characteristics are affected.

The angle of attack is increased to generate more lift and compensate for the smaller area:

Maneuverability is decreased as the maximum lift obtained with the maximum angle of attack is decreased.
Stall is easier to trigger as the angle of attack (for an equal moment) is closer to the stall angle.


Does the Autopilot switch to ALT ACQ mode at a fixed altitude difference from target altitude? For example, if climbing (or descending for that matter) at 3500 fpm, will the AP switch to ALT ACQ mode at the same point it will as when climbing or descending with 1000 fpm? Or does the point of the switch is variable and depends on the ROC or ROD?
I am specifically interested in the B737NG.

The simple answer is that autopilots are designed to fly the aircraft in the same way that a human pilot would.....only more accurately!
If you were climbing/ descending at 3500fpm you’d anticipate the level off earlier than if climbing/descending at 1000fpm or you’d risk exceeding g limits and it wouldn’t be a very smooth transition.
Autopilots, including the 737NG, take into account the ROC/ROD to ensure a smooth transition to level flight so yes ALT ACQ engagement will vary.


Could the Mars helicopter Ingenuity have been test-flown outdoors at JPL just for the heck of it? (not that they would) The Ingenuity helicopter that has flown on Mars is designed for roughly 0.01 bar pressure and a colder atmosphere made of mostly CO2. See links (including video) in this answer to What JPL laboratory is this exactly, and what are the functions of these amazing-looking control panels? in Space SE and sources linked within. For more about Mars' atmosphere see this answer to What could Perseverance listening to Ingenuity reveal? there as well, and sources within.
The counter-propagating rotors (driven by separate motors but synchronized) spin at about 2500 RMP. The propellors are huge by Earth standards compared to the tiny weight that they carry. But we also have to remember that it will weigh more on Earth. See answers to Does Ingenuity rotate via differential rotor speeds or differential angles of attack? and sources within for more on that.
Question: Hypothetically, could the Mars helicopter Ingenuity have been test-flown outdoors at JPL just for the heck of it? Not that they would ever do such a thing (it will have been kept very clean and very very safe at all times) but from a technical stand point would it have flown? What rotor speeds and torques would have been necessary, and would these have been possible with the light-weight motors optimized for Mars flight?

No, Ingenuity was too heavy and underpowered to fly while on Earth.
From 27:30 to 29:00 in the video of a 2021 May 13 press event, one of its designers, Matt Keennon, manually pilots what he called a "terrestrial version of Ingenuity,"  officially named Earth Copter, nicknamed Teri or Terry.  (Reporters have had to guess at the spelling.  The transcript of a 60 minutes segment has Terry, but that neglects I for Ingenuity.)
At 24:45 Matt explains that its only significant hardware differences compared to Ingenuity are that it is lighter (he doesn't say how much), and that its motors are taller, with twice the torque.  Aerovironment hasn't published any hard numbers about Terry, or possibly even any text at all since even its name remains disputed.
But it's clear that they designed Terry to closely mimic how Ingenuity would fly on Mars (see the section "Iterations" in Inside Ingenuity With AeroVironment), so they wouldn't have lightened it and used much more powerful motors for capricious reasons.  It had to actually fly.  A direct quote from Matt at 24:45:

We also reduced the weight of Terry compared to Ingenuity because it's flying in Earth's gravity.

Co-designer Ben Pipenberg also says:

Terry is designed to fly here on Earth, so the motors were redesigned and are more powerful and have a higher torque to handle the denser atmosphere and the higher gravity.


How long did the SR-71 take to get to cruising altitude? How long did it take for the SR-71 to go from taking off to 80,000 ft, including refueling?

According to the performance data in the manual it takes 19.9 minutes to get to 70,600 feet.

Refueling time will depend on how much fuel is needed for the mission as well as how long it takes to hook up to the tanker. The manual covers the operations for that but  I dont see a flow rate of fuel in there. A lot of that stuff is covered in this podcast.


What if there are no volunteers to sit in the emergency exit row? I'm currently seated in the emergency exit row, and had an interesting thought. If I was unable or unwilling to assist the crew in an emergency and operate the emergency exit, then I am supposed to contact a flight attendant to be reseated.

But the emergency exit row sucks. The seats don't recline, there's no under-seat storage, there's not even tray tables. What if nobody volunteers to switch seats with me? Will I be rebooked onto a different flight? Or maybe will someone be forced to switch seats with me?

(Let's assume for the purposes of this question that I am physically unable to operate the emergency exit, say because of a broken arm. Let's also assume that the flight is fully booked and there's no empty seat that I could be moved to.)

The government requires any passengers seated in an exit row to be 15 years of age or older, be willing to assist in an evacuation and have no limitations that would prohibit their assistance.

Source: United

I.e. you won't be given that seat if you can't assist or unwilling.

Personally I always request an aisle emergency [exit] seat near the window. This way the bulky slide is out of my way and I get plenty of legroom. I'm very tall, legroom matters. You'll always find someone willing to switch if they're tall. What I'm saying is, this seat that you hate, others love.

But in your very specific hypothetical scenario of a full flight and wrong seat and unwilling passengers, the government says someone must switch. If the issue causes too much trouble, then someone (who is causing the trouble) will be escorted off the plane more likely, freeing up a space...

... to be immediately filled by someone from the standby list who doesn't mind sitting in the exit row. voretaq7

Have a nice flight.


Why do T- tail airplanes have a shorter vertical stabilizer? Airplanes with a T-tail design have a shorter vertical stabilizer than the conventional design , what is the reason?

Two reasons:

T-tail design is often imposed on designs with twin engines mounted at the aft fuselage. This means they have a small moment arm in the yaw direction, the vertical tail is dimensioned to compensate for engine failure. The further away form centreline the engine is mounted, the higher the yawing moment that the remaining engine exerts upon engine failure.
The horizontal stabiliser at the top of the vertical stab functions as an aerodynamic barrier, like a winglet does. This prevents a vortex from streaming off of the top of the vertical tail when yawing, and thereby increases the effectivity of the vertical tail surface. This effect was researched in NACA TN 2907, at five different locations and three different spans:

The graph below shows calculated effective increase of aerodynamic aspect ratio, as function of where on the fin the horizontal tail is located. If completely at the top or at the bottom, the aerodynamic aspect ratio is about 50% higher than when at the centre, resulting in increase of the lift curve slope of the fin of roughly 15%.

With a T-tail, the horizontal stabiliser at the top functions as an aerodynamic barrier, while the fuselage at the bottom end provides some barrier function as well. Depending on the local fuselage circumference and shape of course.


How does an aircraft maintain level flight while accelerating? Let's assume a plane is initially moving at constant speed, level flight with a certain angle of attack. If the plane's thrust is increased, the plane's horizontal speed increases (at one point the drag force catches up and becomes again equal to thrust. The speed becomes constant at that point).

But while the speed is increasing, the lift would increase and would the plane start climbing. How can we keep the plane in horizontal level flight while the speed is increasing? Does increasing the thrust need to be simultaneously complemented with controlling some of the rear lift surfaces to oppose the natural lift increase due to the wing?

Simply put, in the scenario stated, to maintain level flight the appropriate amount of nose down input would be applied.

As the op points out, the increase in speed through the air increases lift, and the AOA (angle of attack) needs to be reduced.  This is normally done with stick (or yoke) input, followed by trim.

On most aircraft the lowering of the nose would be accomplished by lowering the elevator (and/or raising the trim tab) on the rear horizontal surfaces.


Does a 1lb crow expend only 7.68 Watts to fly at 37 km/h? The Wright brothers and the 1 pound crow that flies at 37 km/h expending just 7.68 W

In an 1905 letter to Octave Chanute, Wilbur Wright evaluated the power, used by a 1 lb bird to fly at 34 ft/s, utilizing a relation that can be rewritten as:

eff x Power = Thrust X Speed = Drag x Speed,

where: eff (the efficiency of the crow) = 75%, Drag/Lift = Drag/(mg) = 1/8 and mg = 1 lbf.

In consequence, Power = (1 lbf x (1/8) x 34 ft/s ) / 75% = 7.68 W.

  "The power consumed by any bird or flying machine may be figured from the formula wv/ac, in which w = weight, v = velocity, 1/a = ratio of drift to lift, and 1/c = efficiency of the screws or wings as propellers. In the case of the crow flying at 34 ft. per second, or 2,100 ft. per minute, I would fix the value of l/a at 1/8, and 1/c at 1/.75; when we have (1 x 2100)/(8 x .75) = 350 ft. lbs. per pound of weight.1 The minimum value of l/a may be rendered independent of velocity by regulating the size of the wings. The value of 1/c is about the practical limit of the efficiency of screws under usual conditions, and I see no reason for believing that wings are more efficient than screws, as propellers. It is quite incredible that, when flapping, the wing can be kept at the optimum angle at every point, as in soaring; and there are losses due to the fact that the pressure is not vertical throughout the stroke. Although I think 25 percent a fair estimate of the probable loss from both sources.
  Birds unquestionably develop power many times greater than is consumed by our Flyer, per pound weight. if you will fix in your mind the distance within which a small bird acquires full speed, say 30 miles an hour, and then figure the power necessary to accelerate its weight to this velocity, I think you will be astonished. I know I was almost dumbfounded, especially in view of the fact that the power available for acceleration is over and above that used in flying. I shall be curious to know what distance you fix upon as that within which a sparrow acquires full speed.",
  Letter of Wilbur Wright to Octave Chanute, Dayton, March 11, 1905

7.68 W/lb seems a quite low figure as long as, it's generally accepted that any model plane with less than 50W/lb is going to struggle (see The Watts Per Pound rule)

Does a crow only expend 7.68 W/lb or at least it is possible to build a model plane able to fly at 37.3 km/h (34 ft/s) developing just 7.68 W/lb shaft power?

The number cited by Orville looks quite reasonable. The crow is just cruising along, not banking, accelerating or climbing.

Now add a climb speed of just 1 meter (3.3 feet) per second, and the additional power is 5,93 W. Let it circle with 60° bank angle, which would double the required lift, and the power for staying aloft increases to 15.36 W.

Next comes the flight speed, which goes up with the root of the wing loading. The American crow has a wing chord between 25 and 33 cm and a wing span between 85 and 100 cm. Taking the average puts their wing area at maybe 0.25 m² (it is almost rectangular, after all), and their wing loading at 1.8 kg/m². I would expect that a battery-powered model would have a higher wing loading, maybe 5 kg/m². The required power goes up with the third power of speed, and the speed itself increases with the square root of the wing loading. This makes the model of the crow fly at 62 km/h and consume a power of 35.5 W - just for straight and level flight. Add some margin for acceleration, banking flight and climbing, and the 50W/lb rule looks quite reasonable.


Can I act as SIC with these specific type ratings? Can I act as SIC on a part 91 ferry flight, if I hold...

a DC-9 type rating and the flight is in an MD-80?
a B-737 type rating, can I act as SIC on a B-737NG?

The single B-737 type rating includes all variants of it, from the -100 through the Max; if you were typed in a -200, you have the type, so there is nothing else required in that regard to be Second In Command (SIC) on a 737 NG. (Source... my experience, having flown the -200, classics, NG's, and the Max, all with the one "B-737" type on my certificate.)
The DC-9 family is similar; I don't think there is a separate type for the MD-80.
That all said, there are other requirements pertaining to recency of experience and training. The other answer by @wbeard52 covered these. The pilot would also need a current medical. But as far as required ratings, those mentioned in the original question are sufficient.


Does the Airfoil Tools Cd/Alpha Curve include both induced and parasite drag? I'm looking at Cd / Alpha for the SD7062 Profile:

http://airfoiltools.com/airfoil/details?airfoil=sd7062-il

Wondering if it includes both induced and parasite drag. How does one tell?

To answer the question you have to look at the source:

Induced drag is a drag type which appears on wings with finite span. The polars given are for a 2D profile section and therefore without induced drag.

What about the parasitic drag? Using Wikipedia's definition only skin friction and form drag are taken into account. Interference drag, which is a 3D drag type dependent on the position of other bodies, can't be included either.


If both propellers and wings are airfoils, then why do propellers deflect air perpendicularly to the rotor, but wings not? Here is my dilemma.  I have seen a lot of videos of airfoils in wind tunnels, and I've noticed how the airflow always moves away from the trailing edge parallel to the wing, or at a very small angle away from the wing as in this video:

I've also heard that propellers are nothing more than rotating wings (airfoils), producing lift sideways as opposed to upwards.  What confuses me is that in the case of the propeller, the airflow leaves the propeller at a much higher angle, and not straight as is with the wing.  In other words, the airflow is deflected backwards from the prop.  I just can't understand how the wing and propeller, which are two very similar shapes (maybe not that similar, but they operate by the same principle), deflect air in two radically different directions.
I have a few thoughts on why this happens, but I think it's better if someone tells my first.

Don't let wind tunnels fool with your perception of reality. In the real world, it's the wing that moves while the air remains stationary.

Consider a video just like the one you posted, but filmed with a stationary camera. (The one in your video is attached to the wing and moves along with it.) You'd see the folowing scenes:

The field of view is filled with stationary air.
A wing quickly passes through the video from right to left.
The air now moves downward more or less vertically.


To use the equipment suffix "G", does the GPS have to be certified for IFR? To use the equipment suffix "G", does the GPS have to be certified for IFR flight?

Yes, using GPS for IFR requires a certified unit. The AIM 1-1-17(b)(2) says (emphasis mine):

  Authorization to conduct any GPS operation under IFR requires:

  (1) GPS navigation equipment used for IFR operations must be approved in
  accordance with the requirements specified in Technical Standard Order
  (TSO) TSO-C129(), TSO-C196(), TSO-C145(), or TSO-C146(), and the
  installation must be done in accordance with Advisory Circular AC
  20-138, Airworthiness Approval of Positioning and Navigation Systems.
  Equipment approved in accordance with TSO-C115a does not meet the
  requirements of TSO-C129. Visual flight rules (VFR) and hand-held
  GPS systems are not authorized for IFR navigation, instrument
  approaches, or as a principal instrument flight reference.


Why are emergency vehicles needed for a runway excursion? When passenger jets have a runway excursion incident such as this one in Birmingham it is apparently common practice to send emergency services vehicles to the aircraft.

Why are emergency services vehicles necessary?
I would think the plane is more than capable of getting back onto the Tarmac, so why doesn't it?

Why are emergency service vehicles necessary?

Something might have been damaged. What if something was and there is a fuel leak somewhere? Hydraulic leaks are also dangerous, and more likely as hydraulic lines run to the brakes and nose wheel steering. Better safe than sorry, so emergency services go check.

Sometimes, they also disembark passengers via the ladder if it looks like towing the aircraft to terminal will take too long and the aircraft is on unpaved surface where the mobile stairs have trouble going.

They can also help with moving the plane, especially on smaller airports that only have one runway and so have to close until the plane is moved away anyway.

  I would think the plane is more than capable of getting back onto the Tarmac, so why doesn't it?

No, it isn't. Aircraft not designed for unpaved surface will usually sink in somewhat, especially if the ground is wet, and require a lot of power to pull out. Sometimes, the tow truck is enough to get it out, sometimes they have to put planks under the wheels and sometimes they have to get out hydraulic jacks or inflatable support bags.

Even if the plane did not dig in and is easy to move, providing the power with the engines is not a smart thing to do, because the engines will throw up dirt and stones that could damage them, other parts of the aircraft, or something else around. Tow truck is much better for that job.


What would an all-flying aileron look like, and would it be a good idea? The only info I could find about someone doing this IRL was the British Army Aerorplane No. 1, but I don't think it ever flew with them. I don't know much about how this would affect the aerodynamics, but maybe it would give more roll? I'm not that experienced in aviation, could someone tell me the implications of this?

The word aileron specifically refers to a part of the airplane, usually, but not always, connected to the back edge of the wing, that is used to control roll and to turn the aircraft when used in conjunction with the rudder.

The British Army No. 1 was based on the Wright Flyer design, and while some early airplanes did incorporate wing-warping to bend the wing itself instead of using ailerons, the No. 1 actually incorporated separate ailerons, mounted above and in front of the leading edge of the lower wing.

Perhaps, instead of aileron, you meant to say wing or airfoil. In that case, several examples exist of modern flying-wing aircraft, such as this B-2 Spirit, which designs the entire aircraft as one large airfoil.

UPDATE
Wing-tip ailerons were utilized in some designs, such as this Stout Skycar.

NASA did testing on this aileron configuration to determine whether or not this design would counteract the adverse yaw effect of traditional aileron placement. When ailerons are behind a wing with a large upper camber, it can partially shield the aileron that is deflected up, reducing its effectiveness. Moving the ailerons to the wingtips proved to significantly mitigate this issue, although not entirely - this due to the interference between the outer edge of the wing and the inner edge of the tip aileron. Nevertheless, there were also significant problems. The NASA study showed a substantially reduced rate of climb compared to traditional trailing-edge aileron. Additionally, there was a near doubling of drag from each wing, largely due to vortex generation caused by the necessary gap between tip aileron and wing. Further, while a traditional aileron may utilize multiple hinges, a tip aileron was pivoted on a shaft, where torque loading and flex became an issue. Finally, when connected via direct linkage, researchers observed that control loads felt at the yoke were often up to 3 times heavier than for conventional ailerons.
Here is an article by Bob Whittier explaining more.


Question about the difficulty of a couple of airplane maneuvers I have a hypothetical scenario and I was wondering if any experts might be able to speak to it.  I will lay out the scenario, with a couple of specific questions, and maybe some honest answers will come if I leave out the dog whistle words :)

A plane is travelling at 322 Knots at 6800 feet and wants to simply
point the nose down and hit the ground somewhere within a target of
34 acres.

A plane is traveling at 336 knots at 6800 feet and begins a spiral
decent reducing speed over the next 2'40" completing a 270º turn,
coming out of the turn at 2200 feet.  The radius of the descending
circle at about 2.75 miles.

From the altitude of 2200 feet, travelling at 312 knots, said plane
increases speed over the next 40" finishing at the wall of a great
invisible barrier going 488knots, just five feet of the ground. The
descent rate increases exponentially beginning at 3200ft per minute
until getting to 5800 feet per minute travelling from 418 to 488
knots from 1200 feet to 5 feet in 12 seconds.

How easy or difficult would any of these maneuvers be to undertake, say in a Boeing 757, for a pilot who

had just been hired by a major airline?
Has several 1000 hours of flying experience
Could fly a Cessna if someone sat next to her to watch in case things went south (literally).

A sincere thank you - while this post may seem to have some snark, it is asked with 100% intellectual sincerity.

Calvin

A runway at a decent size commercial airport is ~200' wide and 10,000` long, which is about 2 million square feet or 45 acres, most of this is for roll out can pilots generally have no issue touching down in the first 1000 feet which covers an area just under 4.6 acres.
So its safe to say that a pilot can maneuver a plane from 6800 feet down to a landmass of 34 acres.
A turn of that as described could be achieved with a ~30 degree bank, that decent rate is fast but not unachievable.
Aggressive decent rates like this would likely not be possible in a 757 but low and fast is not out of the question for some planes

Any airline pilot (fresh in or about to retire) should be able to pull off the first two maneuvers with out an issue . A decent CFI would likely be able to coach someone threw these maneuvers if they were just starting out. As for the last maneuver, your gonna need a G Suit....


Who inspects commercial aircraft seats for defects (and when)? Do inspections of aircraft seats occur only after passenger complaints, or do the major carriers conduct their own inspections at regular intervals?

Apart from what ymb1 and Zach Lipton mentioned, the passenger and flight crew seats are thoroughly inspected during the scheduled maintenance of the aircraft, in which the aircraft can be grounded for several days up to some weeks. Depending on how extensive is the maintenance check, the following items can also be inspected amongst others:

Condition of seat floor attachment fittings for tightness.
Reclining function, except those before and after the emergency exits (these must not recline at all).z
Removal of the seat cushions in order to inspect the seat structure.
Periodic replacement of all seat covers (washed or new).
Seat belts for condition, operation and proper attachment to the seat.
Life vests for presence, condition and expiration date.

Sometimes, when the repair is beyond the capability or the approval of the maintenance center it can be sent to a specialized seat overhauling center.

For more information and fun you can check the British Airways B747 D-check video


Could you land a large airplane on short circular runways? Considering that building runways is expensive and that they take up a lot of space, could you land a large commercial airliner on a circular runway, braking as you go around the curves?

As a matter of physics, there's a certain amount of braking and steering force available to the aircraft after it lands.

Suppose the aircraft touches down moving due north, and continues clockwise around your circular runway. After a quarter-circle it travels due east -- but that means that enough braking force has been applied to reduce the northward component of its velocity to zero, while also giving it some eastward velocity.

If only that eastward force hadn't been applied, the aircraft would be at a halt now -- using less force than what's necessary for it to follow the circle.

So if the plane can keep itself on a circular runway, it will be even easier for it to come to a halt on a straight runway whose length is the radius of the circle.

(Also, the plan ignores that the critical factor in the length of runways is not landing but taking off -- there must be enough runway to brake down safely if the takeoff is aborted just before rotation. And taking off from a curved runway sounds even crazier than landing. If the runway is horizontal, the plane would become airborne in the middle of an uncoordinated turn...)


How do flap track guides work? I am planning to build a large-scale LEGO airlier with most parts functional. Doing a little looking at pictures and research I see that commercial airliners have an underwing body that houses the flap track guides. How do they work mechanically?

There are different ways of moving flaps. The trivial case where they rotate around a hinge point which lies within the airfoil contour does not increase wing area. Fowler-type, backward-moving flaps are possible in three general ways:

Douglas flap: Here the flap rotates around a single hinge line which lies substantially below the airfoil contour. As the name suggests, this is used on many Douglas Commercial aircraft.

Douglas flap, left: retracted (source); right: extended (source). Their long and narrow supports make them easy to recognize.

Four- or five-bar linkages: These are mechanically more complex, but enable a more compact mechanism. As their name suggests, four or five linkages are connected with bearings and enable a more complex movement. The drawing and the animated GIF below are taken from Wikipedia and show the mobility m which increases with the number of joints. This would be my recommendation for a Lego model; just make sure that the forward bar is longer than the rear bar - this will give you a realistic movement of the flap.

Above: Linkage mobility (picture source). Below: Four bar linkage (picture source)

Sliding block guide: Here you find real rails and rollers which move along them to enable the most complex and precise movement, even for multi-element flaps. While a four-bar linkage will have a continuously increasing ratio of deflection angle to backward shift, a sliding block guide makes it possible to set the deflection angle independent of the backward shift, and allows the biggest backward shift for a given size of the mechanism. See the Boeing 747 flap tracks below for an example.

Boeing 747 flap tracks (picture source). Note that the upper block is supporting the first flap segment and the lower block the second. Actuation is via a spindle; the linkage in the lower left corner is actually the mechanism for moving the flap fairing.


Is the Meredith effect utilized in the cowling design of air-cooled engines? The P-51 is famous for its advanced-for-its-time aerodynamics, the prime example of which is the radiator design under the belly which utilizes the Meredith effect to, in effect, turn it into a mini jet engine. Now, the cylinder walls and cooling fins of air-cooled radials are much hotter than whatever cooling liquid that's used in the P-51's water cooler, so is it possible to produce a similar cowling for the air-cooled radials? Is there any example of such a cowling on WWII airplanes?

The Meredith effect is to recover radiator drag by using engine heat for thrust, just like a jet engine.  It worked very well in the P-51 Mustang, actually adding a few knots of airspeed.

It also would work well with any source of heat, including a nuclear reactor, so yes it would work with aircooled engines.

The issue is drag from the radiator.  Aircooled radials have much greater frontal drag, so it worked, just not as well.  Efforts to reduce drag in the B-36 bomber resulted in roasted engines, particularly the rearward banks of the "corncob" R-4360 radial.  Overheating is a major concern, as is drag.  Engineers try to find a good balance.


How does MCAS communicate with other systems to know if the flaps are retracted or not? How exactly does MCAS communicate with the flaps setting to know if the flaps have been retracted?

I just noticed on the preliminary report for ET302, the flaps were set at 5 degrees. It doesn’t say when or if the pilots retracted them completely. So I’ll assume the flaps were at 5 degrees the entire flight. So it makes me curious about these systems communicate, if I understand correctly, MCAS and everything was perfectly fine, the only faulty part was the AoA, so there shouldn’t have been a problem with the systems determining whether or not flaps were set.

MCAS is implemented on the Flight Control Computers (FCCs). The FCCs communicate over an aviation data bus, ARINC format. The B737NG used ARINC 700 series standard for communication - sensor information is linked to the FCCs via the avionics data bus. The B737MAX may or may not use a later standard ARINC bus.

There are two FCCs on the B737MAX. From this link:

  Computer redundancy. As of 2019, the two flight control computers of Boeing 737 never cross-checked each other's operations; i.e., each was a single non-redundant channel. This lack of robustness existed since the early implementation and persisted for decades. The updated flight control system will use both flight control computers and compare their outputs. This switch to a fail-safe two-channel redundant system, with each computer using an independent set of sensors, is a radical change from the architecture used on 737s since the introduction on the older model 737-300 in the 1980s. Up to the MAX in its prior to groundings version, the system alternates between computers after each flight.[191] The two computers architecture allowed switching in flight if the operating computer failed, thus increasing availability. In the revised architecture, Boeing required the two computers to monitor each other so that each one can vet the other.

So not only do the FCCs know if the flaps are retracted, they now know if their computations correlate.


Why can military aircraft descend below the DA / MDA during an instrument approach? According to §91.175(c)

  Except as provided §91.176 of this chapter, where a DA/DH or MDA is applicable, no pilot may operate an aircraft, except a military aircraft of the United States, below the authorized MDA or continue an approach below the authorized DA/DH unless—

So why are military aircraft exempt from this restriction?

The most simple reason is the military has its own set of flight rules (AFI 11-202, OPNAVINST 3710.7U) that for many years duplicated many of the applicable FAR/AIM regulations. In addition, the varied mission sets and training scenarios the military operates under sometimes require them to do non-standard things, so there are a number of "carve-outs" for them to perform and regulate their own maneuvers. In general, any exception to these rules are rare, unless specifically laid out in an instruction, and likely to be used only in times of national emergency or operational necessity.

One example of a reason to descend below an MDA or DA would be when shooting a self-contained approach. A self-contained approach (SCA) or IPRA (Independent Precision Radar Approach) is one where the aircraft uses its own navigational capability (INS/Radar/Radio Altimeter) to guide the aircraft to the runway without ground-based navigational aids. Referencing the old AFI 11-202v3 AFSOC Sup, it details when constructing SCAs,

  7.4.6.5 For AFSOC SCAs and IPRAs, the MDA/DA will be commensurate with aircraft equipage capabilities and mission requirements. The applicable obstacle clearance will be maintained until descent on the final approach segment.

While practice requirements for SCAs require good weather, operational weather minimums will be much lower, and specified by the MDS-specific operations procedure. This may in some cases allow an aircraft to shoot an approach to a runway and descend below any MDA/DA on an existing approach, based on on-board capabilities.


What is the benefit of spoilerons compared to ailerons? Some airplanes like the B-52 or the MU-2 use spoilerons instead of ailerons to control roll. What is the benefit of ailerons vs spoilerons and vice versa?

Two reasons often-cited for having spoilerons:

better roll control (especially during stall)
doesn't take up space for flaps

Because of their location, they don't need to take up space which could be used for flaps. For example, on the MU-2, the primary reason for using spoilerons was to allow for full-span flaps at the rear, lowering clean wing area while still having acceptable stall speeds in the takeoff/landing configurations (and therefore shorter landing distances). This is one of the reasons for it to takeoff from runways less than 3000 feet, while having a cruise speed of up to 300 knots.

However, spoilerons have the disadvantage of killing lift, which can be deadly in situations such as a one-engine-out situation in a twin. To compensate for this, usually minimal constant spoiler use is recommended, and mostly rudder is used if an engine fails. If available, aileron trim (despite the name, there aren't any "real" ailerons on such an aircraft) is used to reduce drag if long-term use is expected.

Spoilerons tend to have less of a difference in roll rates at low and high speeds, compared to ailerons -- this could either be considered an advantage or a disadvantage, depending on the situation and whether a pilot is used to one type of roll control or another. This can negatively affect the roll control feel of the aircraft though, as it might feel slightly sluggish at higher airspeeds. They also tend not to provide much (if any) feedback to the pilot, which is a disadvantage.

Note that most large airliners use both spoilerons and ailerons for roll control, to be able to still have an aileron while supplementing large control inputs with the spoilers.


Which engine manual must a pilot legally use? Many aircraft have engine/prop performance information provided by the manufacture such as Bonanza, Cessna, Mooney, etc AND the engine manufacture. The performance or recommended settings may vary between the two-- i.e. Bonanza E-series Continental engines with Hartzell props.

Additionally there may be pilot organizations or other reputable sources that diverge from these manuals. Such as operating the engine LOP (lean of peak).

As a pilot, does one manual have legal precedence or may I choose any source of data for operating the engine and prop?

FAR Part 91, in a certificated plane, private piot in a private plane, you can fly however you'd like.  Charles Lindberg taught lean of peak to pilots on WWII to save fuel for long distance ocean flights.

Check the engine manual, you will find you can fly as lean of peak as you can manage.  I find it hard to do with carburated O-360 engine. Usually I lean out until it gets rough, then enrichen some.  I just had a 4-channel engine monitor installed, so now I can start experimenting and see how well it really does LOP, maybe playing with some carb heat to help stir up the air flow better.
With fuel injection engines, you can adjust/swap out the injectors to get better fuel flow into each cylinder for better lean adjusting.

Leaning helps maintain good fuel/air mixture so you don't run too rich and waste fuel.  If you check later year Manuals, you may find better direction on leaning for your engine as well.  For the Cessna Cardinal, I have a 1977 POH that I use to supplement my plane's 1973 POH, Cessna got smarter as time went on it seems and some things are covered better.

Flying commercially may be a different manner. There the Company may specify one thing over another, you may not have a choice.


Is a new type of TSA pre-approval required before commencing flight training? A friend of mine owns a flight school in the states.  A Designated Pilot Examiner (DPE) has informed his staff that a new TSA regulation will require all new prospective flight students to meet with a DPE prior to starting any flight training.  That is, every new student will need permission from a government agent prior taking a flight lesson from any flight school (61 or 141).

I would typically dismiss this as nonsense but, considering he source of the info is a DPE, I'm curious to know if there is any truth behind this rumor.

Does the TSA plan to implement rules that require every prospective student to seek pre-approval from a government agent (not just a flight school) prior to beginning flight training?

Current regulations require the flight school, or independent CFI as the case may be, to verify citizenship and retain records.  This can be done in minutes.  The DPE indicates that appointments are required and additional fees assessed for the new layer of government approval.

Say it ain't so!

(Answer completely rewritten based on new information)

Does the TSA plan to implement rules that require every prospective student to seek pre-approval from a government agent (not just a flight school) prior to beginning flight training?

Not exactly. US citizens can still start flight training whenever they want. But from April 1, 2016 pre-approval from "a government agent" (the TSA) is required prior to soloing. Foreigners will still need TSA approval before starting flight training.

The final rule on this has now been published in the Federal Register and the TSA will indeed vet all student pilots, as of 1 April 2016 (my emphasis):

  This action requires  applicants to apply for a student pilot
  certificate through a Flight Standards  District Office, designated
  pilot  examiner, airman certification  representative associated with
  a pilot  school, or certified flight instructor.  Aviation Medical
  Examiners will no  longer issue a combination medical  certificate and
  student pilot certificate.  Student pilot certificates will be issued
  on the same medium as other pilot  certificates and will have no
  expiration  date. All student pilot certificates issued  before the
  effective date of this final rule  will expire according to their
  terms  unless they are replaced by another  pilot certificate. This
  final rule responds  to section 4012 of the Intelligence  Reform and
  Terrorism Prevention Act  and facilitates security vetting by the
  Transportation Security Administration  of student pilot applicants
  prior to  certificate issuance. This action  withdraws the proposal
  for pilot  certificates to include a photograph of  the individual
  pilot.

But note that a student pilot's license is still not required in order to start training, it's only required in order to solo. So under this new rule, a US citizen can start flight training as usual, but can't solo until he gets TSA approval for his student pilot application:

  IRTPA [the Intelligence Reform and
  Terrorism Prevention Act] required that security vetting  of all individuals, including
  pilots, must  be successfully completed by TSA  before the FAA issues
  a certificate.  Therefore, applicants for student pilot  certificates
  must be vetted to receive  their certificates and operate an aircraft
  as pilot in command.

This also means that AMEs will no longer issue student certs, only medical certificates. The FAA expects that processing will take several weeks, which may be an issue for accelerated training programs that aim to get you a full pilot's license in a month or less:

  The FAA estimates that the  turnaround time for student pilot
  certificates can be reduced to an average  of 3 weeks or less,
  provided that initial  security vetting by TSA indicates that  the
  applicant is eligible for the  certificate.

There was also some concern that it wouldn't be possible for pilots to solo on their 16th birthday any more because of the processing time, but the FAA specifically addressed that point, essentially by asking students to submit their application well in advance.

On the 'plus' side, the new regulation specifically says that pilots licenses will still not have a photograph (at least for now), which would have added more time and costs to the whole process. And the new student certificates will be plastic, not paper.


What is the oldest aircraft still in production? What is the oldest aircraft still in production? I Googled it but only got the answer to the oldest military aircraft still in production.

Longest production run (civil)
The Beechcraft Bonanza seems like a likely candidate for 'oldest design still being made'; first flight was 1945, and it's still in production today (albeit made by the same parent company that makes Cessnas!). Even during the general aviation downturn in the US of the 1980s & 90s, production continued, as Kevin Cathcart pointed out in the comments:

FAA registrations show no gap in years of manufacture of the A36 Bonaza. I was able to find a registration for one manufactured in every year from 1980-1999 in california alone. Production did drastically slow during that time frame, but it never stopped.

Longest production run (military)
The Lockheed C-130 Hercules military transport first flew in 1954 and has been in continuous production ever since. According to Wikipedia, they've even been built in the same factory (in Marietta, Georgia) the entire time.

Because only around 2,300 have been produced (only!), they don't show up on the 'most produced aircraft list' mentioned in another answer.


Why do multi-engine privileges not propagate down to single-engine? From this answer, privileges of single-engine and multi-engine are separated. A pilot who obtained his PPL on a single-engine and his CPL on a multi-engine is not permitted to exercise his commercial privilege on a single-engine airplane. To do so, he must past another CPL exam on a single-engine plane.

Why is this do? I see no reason why a pilot who can operate a multi-engine airplane safely is incapable of doing the same in a single-engine. Training in a multi-engine would include an all-engine-failure scenario, which would be similar in single-engine.

Just like having a SEL Commercial with a MEL PPL doesn't mean you can operate a MEL commercially.

The certification requirements require the demonstration of particular maneuvers like a Chandelle which includes a slow-flight phase. Slow flight on a single is significantly different than slow flight on an MEL because of p-factor and aircraft handling. Same thing with lazy-8's

Another reason is engine-outs. Engine outs have to be demonstrated, and on a Multi, an engine out means you can limp it to your closest airfield. On a single, unless you are in gliding distance, you will be putting it down off-field.

The FAA also has different test standards for SEL commercial versus MEL commercial. Because you've demonstrated satisfaction on an MEL doesn't mean you are proficient in SEL operations for the same maneuvers, so the FAA makes you demonstrate it.