How can landing in zero visibility be safe? I recognise that autoland and ILS can enable landings in zero visibility, which I presuppose in this question (e.g. in this video where touchdown happens around 5:22). Further, suppose that the fog is so thick that runway lights are only visible after touchdown.

Then how would landing be safe or reasonable?
Would such landings recklessly over-rely on and over-trust technology?
Instead, why not wait for increased visibility or divert to another airport?
Or does this sort of landing (video linked above) only occur as the last resort, where the aircraft must land, before depleting fuel?

Such landing is safe, reasonable and completely standard business.

The ILS transmitter is rather simple, so there is not that much that can go wrong. But to qualify as category III, only which can be used with no decision height, it additionally needs monitoring circuits that check whether the correct signal is being transmitted and shut it down if it transmits incorrect signal. There is a strict limit how fast the monitoring circuit must react and the whole system is regularly tested. The monitoring system is already needed for category II, but with weaker limits for reaction time. Additionally the tower ensures no other aircraft and vehicles move in area around the transmitters where they could affect the signal propagation.

On the aircraft side for auto-land dual channel autopilot is required. So there are two systems that decode the signal and calculate the control input. If the systems disagree or if the signal fails, alarm is sounded and the pilot flying will initiate a go-around.

The controller on tower sees the aircraft on radar, so can verify that the aircraft is indeed approaching the intended runway. If the signal fails in the very last moment and there is not enough time to go around until wheels touch the ground, the aircraft won't have time to divert from course significantly, so the wheels still touch down on the paved surface. If the lateral signal fails during roll out, there is some risk of runway excursion, but that's what the safety areas are for. Runway excursions (to the sides; overruns are another matter, but they are not significant risk here) rarely result in injuries.

This is really the same level of safety as for any other system you rely on like engines or hydraulic flight controls and many other systems in the aircraft.

Note that since there is no taxi guidance, landing in zero visibility is not really possible anywhere (except, as raportech97 correctly noted below, in emergency). Some visibility is always needed (50 m should be the lowest, airport and aircraft equipment permitting) that also gives pilots chance to manually control the roll out in case of localizer failure in that phase.


Why does the ACS forbid activation of the stall warning during slow flight? In section VII. Slow Flight and Stalls, page 54 of the Private Airplane ACS, the Skills section contains in part

  $$\begin{array}{l|l}
\bf{Skills} & \text{The applicant demonstrates the ability to:} \\ \hline
\textit{PA.VII.A.S2} &
\begin{align}
\text{2. } & \text{Establish and maintain an airspeed, approximately} \\
& \text{5-10 knots above the 1G stall speed, at which the airplane} \\
& \text{is capable of maintaining controlled flight without activating} \\
& \text{a stall warning.}
\end{align}
\end{array}$$

During my primary training and when I took the practical test under the old Practical Test Standards, slow flight was conducted at minimum controllable airspeed with the stall horn blaring.

What are the motivation and supporting data behind this change to slow flight strictly above $V_{MC}$?

I attended the ACS webinar on June 25th.  This is the response from Christopher Morris at the FAA.  You can also read the FAQ on the FAA website.

If the pilot recognizes the stall warning and promptly makes an appropriate correction or airspeed adjustment, a momentary activation of the stall warning horn does not constitute unsatisfactory performance on the maneuver. As with other standards, the problem would arise from continual deviation from the standard, lack of correction, and/or lack of acknowledgment. The goal is to ensure that the applicant does not perform the maneuver with the stall warning activated.
The certification standard in 23.207 states for airplane certification testing, the stall warning must “begin at a speed exceeding the stalling speed by a margin of not less than 5 knots and must continue until the stall occurs.” This is the primary reason the suggested range above stall speed has moved from “3-5 knots” to “5-10 knots without stall warning activation.” The certification standard for the stall warning does play a role in the airspeed selection for the maneuver, and stall warning activation will vary from one airplane to the next, so it is important for the applicant to select an airspeed where the stall warning should not activate except on a momentary basis (e.g., due to turbulence).
The PTS standard for maneuvering during slow flight was for the applicant to establish and maintain “an airspeed at which any further increase in angle of attack, increase in load factor, or reduction in power, would result in an immediate stall.”
The current version of the Airplane Flying Handbook says slow flight should be performed at “the slowest airspeed at which the airplane is capable of maintaining controlled flight without indications of a stall—usually 3 to 5 knots above stalling speed.” The guidance has always intended for there not to be a stall warning, and that is consistent with slow flight guidance published in AC 120-111. However, the 3-5 knot range given does not pair well with the part 23 requirement for a stall warning (§23.207). It is not practical to maneuver in that airspeed range and not have the stall warning, which is an indication of a stall.  The standard in the PTS also implies being right above the critical AOA, which means the stall warning would be activated. This result does not align with the guidance, or with what the FAA advocates. Specifically, the FAA does not advocate intentional disregard for a stall warning while maneuvering.
The purpose of teaching slow flight is to ensure that the pilot understands how the airplane responds with less airflow over the flight control surfaces. Since airplanes are operated at low airspeeds and high angles of attack during the takeoff/departure and approach/landing phases of flight, it is essential for pilots to learn the airplane cues and how to operate the airplane in this state. Regardless of airplane type, a pilot does not need to be just below the critical AOA to experience the desired characteristics and achieve the slow flight objectives. These objectives can be accomplished without deliberately activing the stall warning through flight just below the critical AOA. We want to influence the behavior and practices the pilot will follow outside the training environment. Therefore, with the exception of performing a full stall maneuver, a pilot should always perform the stall recovery procedure when the stall warning is activated.
With respect to guidance, the change to AC 61-67 published just prior to the final decision on the AFH wording change, which drove the FAA’s decision to modify this ACS Task element. We are working on another change to ensure the AC will align with the AFH and the ACS and be consistent with AC 120-111. To further explain these changes, we intend to publish a SAFO that is now in formal coordination.
Teaching what an airplane will do at the critical AOA is part of stall training and should be addressed in that context. You allow someone to ‘ignore’ the warning in one narrow instance – as part of stall training. The pilot can still learn what happens at that point – but as part of stall training and learning the proper recoveries – not as part of slow flight.


Does it make sense to say an aircraft has an attitude of 3° or that it has a flight position of 3°? I am trying to translate an aircraft manual, and there is a diagram showing what the HUD would look like given a "posición de vuelo de 3°".

The diagram is captioned in Spanish as "vuelo horizontal a 3° de posición de vuelo".

I'm thinking  of two ways to translate this, but I think both do not completely make sense, and I think they don't make sense because the original is using terminology in an imprecise way.

If I translate it as "Level flight at 3° flight attitude", it seems off because attitude is a combination of both pitch and roll, so how could you have an attitude of 3°?

If I translate it as "Level flight at a flight position of 3°", then it seems even more off because flight position, as I understand it, is combination of all 3 angles of orientation, yaw, pitch and roll. So you can't just say "my flight position is 3°"

So I am basically writing to confirm my suspicion that this doesn't really make sense and that the diagram is more likely referring to an elevation/pitch of 3° (with respect to the fuselage reference line). If anyone knows Spanish and is familiar with the term "posición de vuelo", then that's a bonus :)

Actually most of the time when referring to "attitude" we are talking only about pitch attitude.  You can call bank angle "roll attitude" but it's more typically called "bank angle" in common usage.   If I have an airplane in a turn and I'm descending, you can just say my attitude is too low and I need to raise it, and I won't be confused as to whether you're referring to pitch or roll and will know I need to increase pitch attitude.

So 3 degrees of flight attitude would clearly, to me at least, refer to flight with the airplane's pitch attitude 3 degrees above the horizon while in level flight (or turning for that matter), not climbing or descending, which sounds like a pretty typical number.


What prevents miltiary jets and turbo-props from being refitted with a turbofan? What prevents military jets and turbo-props (such as P-3 Orion) from being refitted with a high bypass turbofan?

Anti-submarine and maritime surveillance aircraft (such as the turboprop P-3 Orion) typically fly slower and lower than the 100+ passenger jetliners.

For those speeds and altitudes, a turboprop is more economical. So there is no need that would push such a massive undertaking to retrofit an airplane.

See: Which engine is more efficient between turboprop vs jet?

That aside, let's say you have bought a P-3 Orion and you wish to retrofit it with turbofans.

High-bypass turbofans are wide, ideal position would be under the wings where the current engines are. Since they are big and the current engines are mounted mid-wing, there will be no engine—ground clearance.
Raise the landing gear, this is extremely difficult to accomplish. It's easier to build an entirely new aircraft. If it was easy, Boeing would have done it for the 737 Classic, 737NG, and 737 MAX (three opportunities).
The current engine cowls are an integral part of the wings, so new wings will be needed.
Loss of efficiency with same fuel carrying capacity means degraded range and endurance.
New cockpit instruments and controls will be needed. Almost a complete overhaul for the avionics. Which for the flying equipment (non-military equipment), costs in the neighborhood of 30% of the total aircraft cost (not taking into account the required R&D).
New electrical system, new pneumatic system, etc. Basically any system the current engines power, needs to be re-engineered.

For turbojets (and low-bypass turbofans) it's not easy, but much easier than turboprops. It has been done for the Boeing KC-135 Stratotanker for example (and to the DC-8 on the civilian side). And it's been discussed numerous times for the B-52.

Here since the speeds and altitudes are almost the same, there is now a gain in fuel efficiency (as long as we are not talking about supersonic aircraft).

Before the advent of the commercial jet age, converting a piston airplane to a jet airplane for the purposes of engineering validation was done. Such example from 1950 is the Avro Tudor 8:

(Source: Flight)


Why does the B-2 Spirit have a pattern of thin white lines? Northrop Grumman's B-2 Spirit bomber is mostly black or dark grey, but has a symmetric pattern of distinctive, thin white lines painted on its wings and fuselage. I have not been able to find anything similar on other airplanes, so why does the B-2 have these lines and what is their purpose?

@RAC and @Hobbes are right. I found a high res photo on defense.gov.

The crop below shows WALKWAY and NO STEP instructions indeed. Similar to what you'd find on a jetliner's wing.

It makes me wonder though why the person below did not abide.

Source: https://tucson.com/news/national/costly-b--bombers-both-tech-marvels-hangar-queens/article_273b0f50-71f6-56ca-a399-401e342658c1.html


Is turbulence behind an airliner less severe during cruise? The turbulence and tip vortices behind an airliner are a familiar hazard for smaller aircraft when near an airport.  But a lightweight glider seems to have not suffered from this, when its tail was actually struck by an Airbus A 320 at altitude.  Page 8 of the accident report mentions only the choc brutal felt by the glider's occupants, and nothing about being blown around like a leaf.
At the time of collision, the airliner was descending through 8600 feet at a true airspeed of 280 knots, if my French can be trusted.  The glider was flying at 53 knots, almost perpendicular to the airliner's path.  So the glider would have encountered the airliner's wake for a good fraction of a second.  Its long wings would be quite sensitive to turbulence.
Compared to the Airbus's high thrust at takeoff, or slow speed and high drag at landing, would its turbulence be less hazardous here, at low thrust and high speed?
https://www.skybrary.aero/index.php/Wake_Vortex_Turbulence#Accidents_and_Incidents mentions some "en-route" turbulence, but only from one aircraft trailing another.  So maybe a cross-track incident is much milder.

The glider in question was "in touch" with the tip vortex of the A320 only with it's tail, and very briefly:

Picture from section 1.16.2 on page 24 of the
Accident investigation report.
The glider was flying at 53kts at almost a perpendicular angle to the path of the A320, and the tail of it struck the outer third of the leading edge of the Airbus. The G103 is about 8 meters long, a wing of an A320 is about 15 meters long, so the wings and most of the gliders fuselage were never superimposed by the wing of the A320:

Picture from section 2.4 on page 39 of the report.
As the glider was traveling across the path of the A320 at almost 27 meters per second, even its tail was out of the tip vortex in a blink of an eye, and in any case, only its tail ever was in the effect of the tip vortex. As the tip vortex forms at the tip of the wing, it's diameter is initially very small, growing larger as the distance to the plane grows.
Although the small tip vortex has high energy (high velocity), as the tail of the glider was very briefly traveling through the tip vortex, it was actually traveling in pretty much the same direction as the flow of the tip vortex was. So no great forces were exerted on the tail (except for the collision with the wing, of course...).
As such this incident can not be used as an example of the turbulence or tip vortex strength during cruise (or descent, to be precise), but the the said phenomena are less prominent at higher speed and lower angles of attack (normal cruise / cruise descent). They are at their strongest during slow flight when a high angle of attack is required to maintain a desired flight path (this would also apply for situations of high turn rate).


I just saw a plane drop off online radar; should I do anything about it? I was watching Flight Radar 24, positioned near my house, to see what planes I could spot, and noticed a Cessna 550's transponder just dropped off @ 5,325 ft in a high-speed descent!

Is there something I should do about it? Or do I assume somebody in ATC has seen it?

Is there anything anyone should do in similar circumstances?

Really there's nothing you should do in cases like these.

Flightradar24, FlightAware, and similar services should not be used for flight safety purposes, and most of them specifically state so in their terms of service (such as sections 12 and 14 of Flightradar24's terms and conditions). Their sources may go down for whatever reason -- that does not mean that the plane has crashed.

These services can only track what ATC controllers can (for the most part), so it's more likely that if there is a real issue, that they'd notice without the general public making a fuss.

In this specific case the flight was being tracked using MLAT (designated by the radar type T-MLAT, which is shown in your animated image file). MLAT flight track accuracy relies on the accuracy and number of the receivers in the area, and according to Flightradar24's website, MLAT generally only works above 10000 feet:

  MLAT

  In some regions with coverage from several FR24-receivers we also
  calculate positions of aircraft with the help of Multilateration
  (MLAT), by using a method known as Time Difference of Arrival (TDOA).
  By measuring the difference in time to receive the signal from
  aircraft with an older ModeS-transponder, it's possible to calculate
  the position of these aircraft. Four FR24-receivers or more, receiving
  signals from the same aircraft, are needed to make MLAT work. That
  means that MLAT coverage can only be achieved above about 10000-20000
  feet as the probability that signal can be received by four or more
  receivers increases with increased altitude.

  MLAT coverage is today limited to some parts of Europe and North
  America, but expanding fast.

So as the aircraft descends below 10,000 feet there is an increasing chance that you will lose it on Flightradar24's tracking system.


What is the correct crew procedure for an unreliable airspeed alert? When the crew receives "airspeed disagree" message on the primary flight displays, they may face some hazardous situation.
Is there any procedure, using a table containing pitch, power, altitude and weight, to avoid stall, for example?

As you probably know this is the situation that occurred for AF-447 (Rio-Paris) on June 2009. From the BEA report:

The accident resulted from the following succession of events:

Temporary inconsistency between the measured airspeeds, likely following the obstruction of the Pitot probes by ice crystals that led
in particular to autopilot disconnection and a reconfiguration to
alternate law, [...]
The crew not making the connection between the loss of indicated airspeeds and the appropriate procedure,

This mistake happened previously. From the same report:

Four crews did not identify the unreliable airspeed  situation: in two
cases, the crews concluded that there was an inconsistency between the
angles of attack; in the two other cases, the crew considered that the
speeds were erroneous rather than unreliable.

Then the procedure that should be used in case of unreliable airspeed:

The philosophy for processing the anomaly is described in the
“UNRELIABLE AIRSPEED INDICATION / ADR CHECK PROCEDURE” that is in
Flight Manual (AFM) and transcribed in the Airbus FCOM and the Air
France Operations Manual.

This procedure which is to be known without the support of the documentation gives time to retrieve data from the documentation (this is what you wanted to know):

See also:

Unreliable Airspeed Indications on SKYbrary.


How to determine Center of Gravity of the airplane parts? I am building a small-medium sized airplane.
Is it possible to calculate "C.G" of each part of the airplane? If yes, How?
Parts: Wings, Tail, Fuselage, Propeller(?)

Let’s start with a definition from Airplane Flying Handbook:

  Center of gravity (CG).

  The point at which an airplane would balance if it were possible to
  suspend it at that point. It is the mass center of the airplane, or
  the theoretical point at which the entire weight of the airplane is
  assumed to be concentrated. It may be expressed in inches from the
  reference datum, or in percent of mean aerodynamic chord (MAC). The
  location depends on the distribution of weight in the airplane.

Your center of gravity calculations will start out by deciding where you want to place the datum. Typically it is placed at the firewall, but sometimes it is at the tip of the spinner.

For every piece on the airplane you measure the distance from the datum. That is called the arm. For my Cherokee the front seats are at 37 inches from the firewall. Let’s say that the seats weigh 20 lbs. The moment is 20*37=740. There are two of them, so total moment is 1480. Do this for every item on the airplane and then add them up.

Divide the total moment by the total weight to get the center of gravity.

Lots of things are fairly easy to estimate: engine, prop, battery, seats, cowl, tail have easy to calculate centers of mass.

Where it gets complicated in your case is that some of the parts of the airplane can’t be treated as residing at a point. You would need to balance them to find their individual center of gravity. Or you could break them down into parts and add up the parts. For example, you could calculate the weight the last two feet of the fuselage and use the middle of that as its ARM. Then the next two feet, etc. Same with the wings.

If you are using standard parts there may already be CG information from other builders or the supplier.

This will give you an idea as to where the CG is but when you are done you need to weight the airplane and calculate the true CG. This article goes into detail on the method and calculations.


How do contemporary Russian jet engines compare to Western ones? How do contemporary Russian aircraft engines like the PS-90A1 and PD-14 compare
to similar engines from GE, PW, Rolls Royce and CFM International? How many years/generations they are behind their Western counterparts from aforementioned companies? In what ways exactly they are behind?

200 kN range

They should not be necessarily behind. To compare apples to apples, the nearest similar thrust to the Aviadvigatel PS-90A1 (171 kN) is the General Electric CF6-6 (185 kN), but the CF6-6 is 20 years older, so it's not fair.

Comparing those two, the PA-90 has better specific fuel consumption in cruise, 0.595 vs. 0.646 lb/hr/lbf. Also the bypass ratios (BPR) are 4.4 and 5.76 respectively. So even with the lower BPR, which generally would imply a higher SFC, that's not the case.

                       PS-90A1     CF6-6       PW2040

Year                   1992        1971        1981
Thrust                 171 kN      185 kN      178 kN
SFC (cruise)           0.595       0.646       0.582
BPR                    4.4         5.76        5.9
Power-to-weight        5.9:1       5.08:1      5.57:1
OPR                    35.50       25.2        27.6

The low BPR but also low SFC, high overall pressure ratio (OPR), and high power-to-weight ratio, all hint at an advanced engine.

The A2 variant for instance was developed "in co-operation with Pratt & Whitney." If I had to guess, it's because the PS-90 fills a gap in the thrust range, gone since ETOPS put the tris and quads in decline. Nowadays the most common thrusts are 100-120 kN for the narrow-bodies, and the latest big jets are 350+ kN.

Big ones

We haven't seen a twin-jet wide-body from Russia, say like the 777 or A330. If that day comes, and they decide to build an engine and not out-source it, then we can have a better comparison with what's available from the big three—GE, P&W, and RR—in the high thrust range.

100 kN range

The smaller Aviadvigatel PD-14 is still in development, and it's in the 120 kN range. Wikipedia says its SFC is 0.526, which is comparable to the CFM56 (not the new LEAP model), I'm not sure how reliable that figure is, because the references linked don't show that figure, instead they say:

  10-15% [improvement] relative to other contemporary engines of the similar thrust range and application.

And a geared-turbofan offshoot is planned, so they want to compete with the PW1000G.

Military (trivia)

To this day the Kuznetsov NK-32 remains the "largest and most powerful engine ever fitted on a combat aircraft."

RE comment for TBO:

PS-90A:

  In 1997 the Supplement to the engine Type Certificate was received to approve the aircraft engine field operation based on technical condition without fixed mean time between overhauls (MTBO) rates.

  The PS-90A became the first Russian aircraft engine that accumulated over 9,000 hours without any removal - the engine installed on Aeroflot's Il-96-300 accumulated 9,936 hours (source).

CF6-80 (what I could find):

  ... many CF6-80s make it to two or more shop visits, with overhaul intervals ranging from 10,000 hr. for those in short-haul operations to 40,000 hr. for those in long-haul (source).

Again, comparable.

RE comment for Wikipedia SFC figures:

That's an issue with Wikipedia, they mix and match sea level and cruise SFC. The links/figures I already included in the answer are both for cruise SFC, which you can compare. There's a question here about how the SFC changes with altitude and speed. So, to compare, you need to compare figures from the same situation.

Related: Why don't Russian aircraft sell as much as their European/American counterparts?


How is hypothetical max altitude of a helicopter calculated? How do engineers calculate the hypothetical max altitude of a helicopter if the mass, altitude and length/curvature of blades are known?

From the Source:

 It shows how to calculate theoretical maximum altitude a Helicopter can achieve


How should a helicopter pilot react after V-belt breaking? I have a question concerning the V-belts of the Robinson R22 (or R44) breaking in-flight. When they break, the rotor RPM will drop and the engine will tend to overspeed. (Is this actually correct?) What are the appropriate actions? I know that I need to flare to get rotor RPM back, but do I also need to close the throttle a bit to reduce engine RPM?

A number of R22 accident reports indicate that the rotor RPM drops and the engine will tend to overspeed in case of 'V' belt failure. From the Australian Transport Safety Bureau report Reliability of the Robinson R22 helicopter belt drive system:

NTSB occurrence report: LAX92LA034
... pilot reported that the engine RPM indicator suddenly pegged at the top of the gauge and the rotor RPM began rapidly decreasing. ... Examination ... revealed that the forward v-belt was split longitudinally and displaced from the transmission pulleys. The rear belt was found off the engine and transmission pulleys.
CAA occurrence report: 99/23
... there was a bang and the engine ‘revved up’, but power to the main rotor was lost. The power loss to the main rotors was due to broken v-belts.
NTSB occurrence report: NYC08LA043
... , the engine’s RPM sharply  increased and the main rotor RPM alarm sounded. Post-accident examination of the helicopter drive system revealed that the v-belts had rolled off the sheaves
NTSB occurrence report: N993KC
The pilot ... heard a loud ‘bang’. The pilot ... observed the engine RPM was excessively high, the rotor RPM was below 80 percent and the low rotor
RPM warning horn was sounding. The on-scene investigation noted that one of the v-belts to the main rotor drive system had separated,  which caused the other belt to slip off the upper spindle.

In case of suspected belt failure, the pilot is expected to try and make a power on landing while prepared for an autorotative one. From the R-22 Flight Manual:

... if the clutch light flickers or stays on for a longer time than usual,  it can indicate a belt or bearing failure in the vee-belt  drive. If that occurs, immediately pull the  CLUTCH  circuit breaker. Select the closest  safe landing  site and make  a normal power-on landing. Be prepared  to  enter autorotation should failure of the drive system occur. The smell of burning rubber may also indicate an impending belt failure.

Note that there is no talk about the throttle. Though the R22 has two V belts, it is not designed to fly with a single one (though there seems to be some instances of that). My guess is that it is better for the pilot not to tinker with the throttle for two reasons- if the problem is somewhere else, reducing the rpm would have adverse effects and if the belt is indeed gone, it would be better for the pilot to concentrate on saving the people first and the engine later.


Does lift equal weight in level flight? Does lift equal weight in level flight? Or does it equal weight + down pressure on the tail?

Added) Let's say the total weight of the aircraft on the ground was 100,000 lbs, and when it took off and leveled off, the down force from the tail was 10,000 lbs. Then what's the total lift required to support the level flight?

When you consider the aircraft as a whole, lift equals weight in level flight. This must be true following the laws of physics.

However, if you break down the forces, the lift produced by the wings does not necessary equal to the weight of the aircraft. Lift is also generated by the body (albeit very inefficient) and by the tail. Most horizontal stabilizers generate negative lift, but some (e.g. the A380) generate positive lift.

If we ignore the fact that fuselage produces lift, and assume a configuration where the tail produces downward force, then you are correct. But the fuselage does produces lift. Modern aircraft designs use software to take that into account.


What conditions cause the gear-up warning to sound on a Bombardier DASH-8? As the title says, what conditions cause the gear-up warning to sound on a Bombardier DASH-8?

According to smartcockpit.com, warning is given when the gear has not been extended and the aircraft is in the landing configuration. Specifically,

• All landing gear not down and locked, flaps selected to 15 or 35$^{\circ}$, and both power levers at any position less than 50% torque.
• Landing gear not down and locked, one or both power levers at or near FLT IDLE and airspeed below 130 kts.

The warning also sounds when the aircraft landing gear is up and terrain clearance is inadequate during the cruise and approach phase
of flight.

Image from Dash8-200/300 - Warning Systems from smartcockpit.com


FAA Knowledge Test Question Bank - What is the source of the actual test questions? According to various online search results, the FAA test questions are not made  available to the public (page 6), but used to be.  Yet, question books claim to have the exact real questions.

How are the latest questions obtained?  I am aware of the sample questions the FAA provides, yet publications and online study sites claim to have "the most up to date" actual questions.

Are the questions available by FOI request?  Does the FAA provide the questions to publishers on some limited basis?

Years ago (35?), I taught ground school for pilots.  The question pool was not published then (it was later published, and then withdrawn), the company would send college students to take the FAA test, with the idea that they would capture certain questions, so that they could be edited and put into study guides.

As I recall the goal was about 5 questions per student taking a test.  Most of the students were not pilot candidates, but rather engineering and even humanities students at colleges.

Attendees would also report on small differences after they had taken the written, and the company question pool would be revised.

I cannot tell you what process is used today.


What time do NOS IFR Charts expire? My charts have 13 September 2018 on them.  What time do they expire?

I thought at Midnight that night local time, but have been unable to find any corroborating evidence.

In FAA-land the AIRAC cycle effective time is 0901Z. Your old charts were valid until 13 September 2018, 0900Z, the new ones are valid since 13 September 2018 0901Z.

I can't find the regulation that says it's always the case, but Google FAA 0901Z and you see that will give a ton of new charts / publications.

Here is a Jeppesen publication that explains the interpretation of the effective date.


Why are some ATC call signs different than the flight number? When listening to air control traffic, or watching flights on flightradar24.com, some flights show up with ATC call signs (as transmitted on ADS-B) that do not match the flight number as they usually do, some examples:

TK1880 / THY9QT
TOM6347 / TOM1FT
LH1660 / DLH5KK

It seems to be more frequent on flight codes that have 4 digits, but this isn't exclusive. Who assigns these call signs, and what is the pattern for the naming?

It's a solution to the Call-sign Confusion.

  Many large airlines operate call sign de-confliction programmes. These involve reviewing company call signs to ensure that aircraft with similar call signs are not likely to be routinely in the same airspace at the same time, and a process to systematically resolve ongoing issues arising from reports of similar call signs from their flight crew, ANSPs or other operators.

In busy airports, it's very common to have many flights with similar [sounding] call-signs (ATC perspective). You'd often hear the ATC stress the intended target.

Potential effects are:

  Loss of communication, loss of separation, level bust, AIRPROX, or midair collision.

However, passengers expect their bookings to be numbers, hence the split between ICAO call-sign (air traffic control) and IATA flight code (booking). From a marketing perspective, a changing IATA flight number isn't good for the customers and booking systems.

Taking TK656 (THY3YE) as an example, we also find TK65 and TK56. If one of those three were to return (emergency) or be delayed, it will add unnecessary confusion if it meets one of the others. There could very well be other operators with similar numbers in and out of Istanbul as well.

  Solution:

  Large operators should routinely consider using a combination of numeric and alphanumeric call sign formats.

  Guidelines:

  Avoid the use of similar call signs within the company
  Where practicable, proactively co-ordinate with other operators to minimize similar numeric and alphanumeric elements of call signs
  Avoid call signs with a four-number sequence; all-numeric call signs should be limited to a maximum of three digits
  Do not use the same digit repeated more than once (e.g. RUSHAIR 555)
  If letter suffixes are to be used with a preceding number sequence, limit the full string to a maximum of four alphanumeric components and, to the extent possible, coordinate letter combinations with other airspace and airport users
  Do not use alphanumeric call signs which have their last two letters as the destination’s ICAO location indicator (e.g. RUSHAIR 25LL for a flight inbound to London Heathrow)
  Where the total number of flights operated is large, it is likely to be best to use a combination of wholly some numeric and some alphanumeric call signs rather than all numeric or all alphanumeric
  If similarly-numbered call signs are unavoidable within a company, allow a significant time (at least 3 hours at any shared-use vicinity) and/or geographical split between aircraft using them
  If it is considered that useful capacity in the allocation of call signs has been reached, then consider applying for and using a second company call sign designator
  Do not use similar/reversed digits/letters in alphanumeric call-signs (e.g. RUSHAIR 87MB and RUSHAIR 78BM)
  For short haul flights, avoid using number sequences for particular routes which begin the day with ..01 and then continue sequentially through the day.

  —skybrary.aero [edited for proofreading]

Note: unlike the US, in Europe and elsewhere pronouncing numbers in a call sign requires saying each number individually, e.g. four-three-one-one, and not forty-three-eleven.


Dead reckoning navigation: gyromagnetic compass, how it is stabilized? I am studying aircraft navigation systems, as what concern autonomous navigation a compass is obviously essential, but magnetic compass is not reliable in short term maneuvers due to accelerations so it has to be stabilized by a directional gyro. What i don't understand is how the gyro is connected to the compass and stabilizes it.

In modern airliners is this device still used ? Is there an electronic substitute with no mechanical gyro (a part from GPS system) ?

Gyromagnetic compasses do indeed exist even in smaller aircraft, and need not be overly complex. The basic principle for an analog system is as follows:

Heading is measured against a gyro rotating in the vertical plane (just like a normal heading indicator). The gyro may be in the instrument case, or electronically repeated from elsewhere in the aircraft.

The earth's magnetic field is sensed by a sensing unit, a "Flux valve" usually located in the wing, or otherwise in a good position to minimize electromagnetic interference from the aircraft.

The gyro position and the magnetic reference are compared electronically and the resulting difference becomes an error signal. This error signal is sent to electric motors on the gyro frame, which will move to very slowly (a few degrees per minute) correct the gyro to align with the magnetic reference, combining the short term accuracy of the gyro with the long term accuracy of the earth magnetic field. To further enhance accuracy, cut-out switches cuts the error signal out when the aircraft is banking/accelerating, as this tends to give a less precise magnetic signal from the flux valve, while a gyro is unaffected by it. See the Bendix King KCS55A for a real life example.

On older, larger aircraft, you'll find similar installations. On modern aircraft, with inertial navigation platforms (IRS) heading is often taken from the inertial platform as true heading, with magnetic variation applied from a database to provide magnetic heading.

The IRU will in that case (among other things) act as a kind of gyrocompass, finding true north by leveling and rotating 3 nowadays usually mathematically modelled gyro planes (solid state Ring Laser Gyros, no moving parts), to align with true north, by sensing gravitation and angular movement around gyro axes from the rotation of the earth. The planes are then kept level by integrating gyro data, and filtering/fusing it with accelerometer data, movement over earth curvature, Schuler tuning, other sensor data etc.)


Can an airliner fly out of a downburst? Many aircraft accidents have been caused by downbursts. A downburst is basically a strong downward wind that forces the aircraft toward the ground and causes it to crash. Is it possible for an airliner to escape the downburst and land safely with this much force pushing down on an aircraft?

Here is a downburst illustration: Source:(www.mikesmithenterprisesblog.com)

First take a look http://www.erh.noaa.gov/cae/svrwx/downburst.htm for info on downbursts.

An aircraft encountering a microburst (the more localized form of a downburst and that which airline crews train for) can counter it in two basic ways:

establish, if possible, a climb rate through the descending air that is greater than the downward vertical speed of the air.
fly through the column of descending air to air that is not descending or is at least descending at a lesser rate

And, of course, do this without stalling the airplane, especially as you come out of the burst. A practical scenario is that your max climb rate through the descending air can at least reduce your descent rate toward the ground enough that you will be able to transit the burst before hitting the ground.

I was never in a full blown microburst for real, but I practiced recovering from them many times in simulators. For 747-100/200 aircraft in the 1990s the procedure was:

thrust levers all the way forward
raise the nose until you get the stick shaker
fly the aircraft straight ahead while keeping the speed solidly in the stick shaker range.
do not change the aircraft configuration, in other words don't mess with the flaps or the gear.

In simulators it's a wild ride. You can tell how far into the stick shaker range you are by the frequency of the shaker by feel and by its noise. The closer you get to an actual stall, the faster the stick shaker will go, so the idea was to keep the shaker on but not too fast. Since the airspeed will be varying rapidly, you have to do that with large pitch changes.

There was controversy back in the 1990s as to whether what we were trained to do was actually the best way, especially as to not changing the aircraft configuration and how deep to go into the stick shaker. Perhaps now the thinking is different.


What material is the B737 wing skin made out of? What material is the B737 wing skin made out of?
I actually couldn't find much information on the wing skin upper and lower panel materials for the B737, the general guess is of course aluminium, but I'm hoping to know specifically what series of aluminium?
The 2000 or the 7000 series? even within these, specifically which one like, Al 7068 or Al 2124?

Aluminum alloy 7178 on the upper skin
Aluminum alloy 7055 on the lower skin
Here is some technical information


Can aileron differential eliminate adverse yaw? Can aileron differential completely eliminate adverse yaw?

That depends on flight speed.
Adverse yaw is strongest at low speed. A high-aspect ratio configuration will not be able to avoid adverse yaw, regardless of the degree of aileron differential.
At high speed the same airplane might roll fine without rudder corrections, because then aileron differential will be able to compensate for the then low adverse yaw if enough differential is provided.
Depending on airfoil rear camber, adverse yaw is also good for reducing aileron control forces. Again, the effect varies with speed and will result in a high degree of force reduction at low speed while forces are still high at high speed. The need to keep aileron forces growing with deflection angle is normally the limit for aileron differential, so it is impossible to tailor differential to overcome adverse yaw at low speed even for wings of moderate aspect ratio.


Do airports charge airlines for extra time spent on ground due to weather conditions? I heard somewhere that airlines pay the airport depending on the time spent at the gate. Suppose there are weather conditions that cause the aircraft to be delayed at the gate, such as heavy rain lasting few minutes, snow requiring half the runway to be closed to remove the snow, and so on.

What happen in those exceptional conditions? Does the airport still charge the airline for all the time spent at the gate? Is there special tariff for exceptional weather conditions?

The correct answer may differ for each pair (airline, airport) and can be found in the contract that they mutually agreed upon. Such contracts are mostly seen as a business secret, and most of their contents are not known to the general public.

As far as I know, both parties agree to do their best to keep everything working during every weather. Which means that there has to be enough equipment to clear a runway really quick, such that these "penalties" are "background noise" in the overall bill, even compared to the penalties caused by other reasons. The airport may decide not to bill the airline most of these penalties, as long as the airline won't try to bill every loss caused by the airport's fault. As a rule of thumb, you don't upset your business partners like that over peanuts, more so if claims go both ways. They may even have agreed on how many minutes delay won't be billed.

Yet, this partnership may be put to the test when one of the partners is seen as cutting cost at the expense of the other, or when one really unexpected condition occurs (like that volcano on Iceland, which disrupted air traffic in central Europe for two weeks or more).


Why does flying inverted in a jet trainer starve the engine of fuel when there's a pump? Such planes have an engine-driven fuel pump. If the pump isn't strong enough, wouldn't suction feeding assist?

How does a modern fighter jet / aerobatic plane overcome this?

Also, any general information on inverted flight and its effects on fuel/oil/hydraulics is welcome.

I find it hard to make a general answer since the fuel systems could be different between various aircraft, but, according to Jan Roskam's Aircraft Design series (I just had to return the book, but I think it's Part IV in the series) some model of the F/A-18 utilizes the following system which, in sustained inverted flight (or any sustained flight condition wherein the aircraft does not experience a positive load factor), would eventually starve the engine of fuel.  Keep in mind too that fuel isn't the only factor for sustaining this flight condition: oil flow through the engine is typically gravity fed (reference for that is an engineer from Bell Helicopter who worked on the V-22 powerplant).  Suction is used to scavenge the oil out of the engine/gearboxes/etc, but the flow of the oil up to a point where suction will pull it out is via gravity (or whatever acceleration the aircraft is experiencing).  Hence, not only do we need to provide fuel, but we also need to provide for proper oil flow as well.

Anyhow, the F/A-18 fuel system.  Again, I wish I had the image from the text to show you, but the basic idea is this: if you had a flop tube capable of scavenging from the entire fuel tank, it would engender more problems than it solved.  Hence, inside of the primary fuel tank there's a second, smaller tank.  This tank has a series of poppet valves that allow fuel to flow into the inset tank during coordinated (i.e., positive load factor) flight.  When the aircraft is not experiencing a positive load factor, the pressure of the fuel on these valves holds them closed and the fuel stays within the inset tank.  A short flop tube within this space provides fuel to the engines for the duration of the maneuver.  However, as noted, this inset tank is only a portion of the larger main tank, so its capacity would be some fraction of the main tank, limiting the duration of the maneuver.

So, to answer your question (how does fuel starvation happen and why isn't it solved via a pump) it's a design problem that, per the printing of that text, could not be solved by adding capacity to the pump.  There just simply wasn't fuel present at the fuel sump to be scavenged.  The real design problem would lie in the design of flop tubes capable of scavenging from the entire tank without creating more design problems (an assumed point on my part).  Examples, I think, would crop up if you decided to make a multiplicity of flop tubes (larger pumps required, more parts, more complex plumbing, etc.), or longer flop tubes (potential risk for damage to the tube head/tank with increased "flopping" inertia, larger pump required for greater head losses, etc.)...but I also don't know what the current standard is.


Aircraft pilot's seats: what is the notch for? If you do a Google or Bing search for "Aircraft Pilot Seat" then choose images, you might notice a large number, perhaps majority of them, have a notch cut out of the front of the seat. What is this notch for?

Notches are circled here:

Original Source

(Please, no potty humor or scatological jokers need apply here)

It's either for clearance of the column of the yoke or moving the crotch strap of the harness closer to the body of the pilot.

Alternative yoke designs remove the need for the notch:

(source: airliners.net)

Alternative control methods like the Airbus sidestick also remove the need. As Henning Makholm noted, the seat strap just goes through the cushion.


What is so special about new Russian jet engine called PD-14? I think PD-14 engine is being promoted by Russians as something extraordinary.

What is so special about PD-14 that the West doesn't have?

Can you explain this in layman's terms?

Well, development of any large high bypass turbofan is something extraordinary. It probably took thousands of engineers and specialists working for many years to develop this engine, with a development cost measured in billions of dollars.  Only a handful of companies in the entire world are able to achieve this.

But, if you compare the publicly available specs for PD-14 to a similar size modern engine such as LEAP, you'll find that while the PD-14 engine is competitive, it's not anything that will have P&W, GE, or RR too worried.

Thrust to weight ratio is comparable to LEAP
Bypass ratio is a little lower than LEAP, which would be expected to translate to slightly worse fuel efficiency.
Overall engine pressure ratio is comparable to LEAP
Thrust specific fuel consumption looks a little worse.

There are also several key parameters that are not publicly available, such as the manufacturing cost, purchase price, the lifetime of the major components (i.e. how many flights before you have to replace the turbine blades), the cost to repair the major components, and the reliability (how often to you have to cancel a flight because something broke just as you were loading passengers). Because this data is not easily available to the public, I'm sure they will claim it's great, but there is no easy way to verify.  Probably they are comparable in all regards and it's just marketing spin.


Is there an additive that can lower the freezing point of jet fuel? Does an additive exist to decrease the freezing point of jet fuel? I have found an additive that decrease the freezing point generated by drops of water (appears between 0 and -10°C), but I'm needing to reduce the freezing of the fuel (-45°C).

There is an additive known as a Fuel System Icing Inhibitor (FSII), it is designed to be mixed with the fuel of non-fuel heated aircraft i.e military. Mixed in at about 0.10-0.15% is optimal to reduce the formation of ice crystals, which will stop it freezing.

Source: http://www.advancepetro.com/fsii.htm

Alternatively, Jet A-1 fuel has a freezing point of -47°C, which is below your threshold and could be useful. Or if Jet A-1 is unavailable you could try Jet B which has a lower freezing point of -60°C, but is more dangerous to handle, and is less prevalent and hence unavailable at many locations.

Sources: http://webarchive.nationalarchives.gov.uk/20100814170713/http%3A//www.dstan.mod.uk/standards/defstans/91/091/00000600.pdf

http://www.csgnetwork.com/jetfuel.html


Why do No Tail Rotor (NOTAR) helicopters use an enclosed variable pitch fan? Aerotécnica AC-14 was an early no tail rotor prototype which used the ducted exhaust from the turboshaft to counter the torque of the main rotor. The concept seems simple with few moving parts.

It didn't use a (seemingly complicated) enclosed variable pitch fan driven by the main rotor transmission, neither did it use Coandă effect (even if it may have), like modern NOTAR does.

Why has a much more complicated solution been adopted for modern no tail rotor systems, and why was AC-14 concept abandoned?

(Autorotation yaw behavior may be one safety issue, even if autogyro autorotation procedures are quite safe.)

They use a shrouded fan because these use less power than a jet for generating the same thrust. I could find a reference in Principles of Helicopter Aerodynamics by J. Gordon Leishman: he states that using jet exhaust for anti-torque required high power and that directional sensitivity was poor.

Hiller Aircraft made a tailless prototype.
The Nord Norelfe was constructed in 1954 and was used for the Aerotecnica AC-14 mentioned in the OP.
The design was tested in the Cierva-Weir W-9

The reference to high power would refer to the generic issue with jets providing thrust: it costs less power to accelerate a higher volume of air to a lowish velocity (like a propeller does) than to accelerate a lowish volume of air to a higher velocity (like a jet exhaust does).


Do aviation intercoms have a standardized compatibility with radio stacks? I have been seeking an intercom unit for a Cessna 172N that has four seats but only two headset jacks, and I would like my rear passengers to be able to communicate without yelling.

Aviation intercoms have external radio transmit switches, but the airplane also has its own built-in radio transmit system.  How does the transmit function trigger in this type of system?  Do they send a certain audio signal frequency or tone to the COM stack that tells it to transmit?

Are most intercoms universally compatible with all com stacks if they use the same plug types?

This is a good question - the comments above answer most of it, but here are some more details:

Short answer: yes, they are pretty much standardised. Any modern GA intercom will work with any modern GA radio.

Part of the job of the intercom is to tell the radio when to transmit, and to route the correct microphone signal through to it. This is almost always done using a single wire which signals "transmit now", and a pair of wires for the microphone signal from the headset corresponding to the PTT button that was pushed.

On more advanced integrated setups, the signals might be transmitted over a digital bus, but outside of fully integrated setups like the G1000 (and even then on some models), there are always ways to connect standard aircraft radios to the intercom.


How do you calculate indicated airspeed on a flight plan? I'm planning my cross country journey for my flight test and it seems I forgot how to calculate my indicated airspeed.

The indicated airspeed must be from the POH, right?
The the true airspeed is from the IAS and TAS correction table in the POH?
Then the ground speed is based on TAS, with the wind factored in?

I'm flying a mid-late 70s Cessna 172 skyhawk.

You do not calculate indicated airspeed: It is an indicated value, you read it from the airspeed indicator. (I suppose you can calculate it if you really want to, but I've got no idea why you would want to do so in the context of flight planning.)

You determine what airspeed to use for flight planning purposes using your aircraft's performance data (from the POH or other manufacturer documents): There will usually be either a chart or a table giving true airspeed as a function of power setting and density altitude.
(True Airspeed is a more useful number for planning purposes as it saves you a calculation.)

When in flight you can calculate your true airspeed based on the indicated airspeed and density altitude. You can then compare this to your planned figures from the performance charts to determine if adjustments are necessary to your flight plan (ETA, Fuel use, etc.)


Would random sitting arrangement be the best way of boarding for passengers? This is more in relation to flights which have a single class of passengers with a short haul flight duration. Why don't airlines adopt random seating arrangement i.e. first come first serve basis. We already see business class passengers of having the flexibility of boarding at their own convenience.

This might solve the problem of boarding, and might also encourage people to board quickly.

To solve the issue of cabin baggage, we could have dedicated space for each passenger, by dividing the existing baggage space by the number of seats below. This would take care of 'greedy' passengers. Also, passengers can check beforehand if they are carrying excess luggage.

The Mythbusters tested various boarding patterns in their previous season (see the digest here, full episode here) and came to the conclusion that "random-random" (close to Southwest-style) was the fastest way to board (though the least liked), and that the current most common method among traditional airlines (back to front) was the slowest. Alternate styles including two forms of "WILMA" boarding (Window-Middle-Aisle, United does this) and "Reverse Pyramid" style (which U.S. Airways used to use) were both fast and very well-liked by the volunteers. I have some issues with their testing methods though:

They only allowed for a single test of each boarding plan, using the same group of volunteers each time. That means two things:

Order of testing matters, because your group will generally become accustomed to getting on and off a plane, which will speed things up as the day progresses.
Any "noise" inherent in a variable of the test that you are neither controlling nor testing cannot be cancelled out and can skew the results.

They tested the control (back to front) first, meaning their volunteers were totally unfamiliar with the "plane" and thus would be expected to be slowed by inefficiencies born of this unfamiliarity. If no other test were repeated, it should have been this one (at the beginning and end of the day) to compensate for this.
First/business class were always boarded first (this is common but not universal among airlines), while every other ticketed passenger regardless of age was boarded according to their individual seat, with only "lap children" boarding with their parent (airlines nowadays require a ticket and seat for anyone over 2yo, so boarding families with pre-adolescents was not really tested). This is opposed to other variables such as overloaded passengers, guys heading "upstream" to the lavatory etc which they sprinkled in to spice up each boarding experience.

One final thing; boarding faster only means you're sitting in a cramped airliner seat longer. Getting passengers aboard an airplane is usually the easiest and quickest part of turning an airliner around. Unloading/loading baggage, refueling, preflight checks etc all take longer in the aggregate than anything going on inside the cabin.


What is this fighter-like plane with huge wings? Can anyone identify this strange plane? It looks like they took wings from a bomber and put them on a fighter body...
What was its purpose?

The Martin/General Dynamics RB-57F Canberra is a reconnaissance aircraft.

The RB-57F was derived from the Martin B-57 Canberra, a tactical bomber and reconnaissance aircraft built on license from the British English Electric company. With its enlarged wings and more powerful engines, the RB-57F gained extreme altitude capabilities. It can climb up to 24,000 m (80,000 ft). It was developed and built for the US Air Force. The first flight was in June 1963.

900 British and 49 Australian Canberras were built. 403 American B-57s have been produced, of which 21 have been converted to RB-57F. Some aircraft were operated by the air forces of Pakistan and Taiwan. Two RB-57F crashed on USA territory, and one aircraft was lost over the Baltic Sea. Only a few aircraft have been salvaged. Most of the RB-57Fs ended up at the AMARC bone yard (source).

The particular aircraft on the question's picture with serial number 63-13291, was converted from a B-57 in 1964 and served the US Air Force till 1974, when it was put into storage at the AMARC bone yard.

picture source: NASA (https://acd-ext.gsfc.nasa.gov/People/Newman/wb57_pics.html)

picture source: NASA (https://airbornescience.nasa.gov/gallery/aircraft/WB-57_-_JSC)

Today there are still 3 planes (now called WB-57) in service for the NASA Airborne Science Program.

There is a Wikipedia article about this type.


How unusual were MH370's final ATC exchanges? There are 2 noteworthy occurrences in the ATC radio transcript within just minutes of a 3rd noteworthy, quite unprecedented occurrence in aviation history:

At 01:07:55 MH370 unnecessarily reported maintaining FL350 a second time
At 01:19:29 MH370 famously only replied "Good Night, Malaysian 370" without reading back the frequency for the handover, although this is an ATC instruction that should be repeated (see below)
At 01:20:33 MH370 "goes dark" (losing XPNDR, ACARS and SDU).

This temporal proximity caught my attention and left me wondering if the 2 ATC transmissions cited above are out of the ordinary (and thus a possible precursor of what was to come).

background information:

  What are some important things controllers usually expect you to read back?
  • Clearances: headings, vectors, altitudes, transponder codes, and radio
  frequencies. (a288)

  « The last radio transmission “Good Night Malaysian Three Seven Zero”
  was spoken by the PIC. However, he did not readback the assigned
  frequency, which was inconsistent with radio-telephony procedures. »
  (safety investigation report, p.431)

questions

Please cite what (if any) ATC rules have not been followed.
From your experience as flight controllers or pilots, how unusual is that ? Is this rather unheard of or occurring fairly regularly ?
Is the handoff procedure described below by the 767 Captain technically correct and does the missing step 3 permit the conclusion that step 2 was not executed either ?

  @Edward_767, a 767 captain, has closely studied the audio recordings
  of the MH370 radio transmissions. He is convinced that the second
  altitude call at 01:07:55 was NOT made by the Captain, but by the
  First Officer, possibly because the captain was not in the cockpit at
  that time. His theory is that the first officer made the call because
  he was not sure whether the captain had made the previous altitude
  call at 01:01:14.

  He makes another interesting observation regarding the final exchange
  where MH370 is handed off to HCM. He states that the typical radio
  procedure would be to

  receive the new frequency (in this case, 120.9 MHz)
  dial it into the radio as the standby frequency
  read back what frequency was dialed in as part of the confirmation of the handoff
  listen for the final transmission
  hit the radio switch which swaps the active and standby frequencies
  and call ATC on the new frequency.

  In the transmission that acknowledged the handoff to HCM, the captain
  did not read back the frequency. Ed believes this is because the new
  frequency was never dialed into the radio, as the captain never
  anticipated making a call to HCM ATC. Ed believes the missing
  frequency during the acknowledgement of the handoff is yet another red
  flag.

  The time between the 2 transmissions would be less than 15 seconds. It
  was 13 seconds at MH370’s previous controller handoff, where the new
  frequency was read back. At the handoff between Kuala Lumpur and Ho Chi
  Minh, the pilot acknowledged the handoff, but never read back the new
  frequency, and the call to Ho Chi Minh was not made. That leaves a window
  of only about 15 seconds for the abnormal event that caused the turn back.

ATC transmission log (full transcript incl. taxiing here)

I have not heard the actual audio in context; I've only read the transcripts.

However, from the transcripts, I see the timing between some of their calls as a bit confusing and unusual.

01:01:14 | MH370 | Malaysian 3 7 0 maintaining level 3 5 0
This is slightly odd, because 11 minutes earlier they were told to climb to 350.   I do not think it is common to report when you have finished your climb.  ATC can see you leveling off at your assigned altitude.

Because of this unexpected, slightly odd call, ATC responds with:01:01:19 |  ATC  | Malaysian 3 7 0
("You called me.  ATC is here; I hear you loud-and-clear; Go ahead: What is your request?")

There is no response for 6 and a half minutes. This could reasonably be because MH370 has no request, and doesn't need anything from ATC, or perhaps they are having radio difficulty and did not hear ATC's call?  The most extreme interpretation would be that there is currently something happening in the cockpit that is distracting them.  Perhaps a lack of oxygen? Or some other distraction?

After 6 and half minutes, MH370 makes the same call again:
01:07:55 | MH370 | Malaysian...3 7 0 maintaining level 3 5 0

Again, this reads like the preface to a request.  Perhaps they didn't hear ATC last time, and are calling in again with a request? Perhaps they're suffering from hypoxia, and don't even remember that they already reported in?

ATC quickly responds the same way again:
01:08:00 |  ATC  | Malaysian 3 7 0
(I'm still here, I still hear you.  Go ahead with your request.)

Silence again for 11 minutes, before ATC gives them a normal instruction to change to the next frequency.  MH370 responds normally by acknowledging the instruction. At this point, we have confidence that their radio is working, and can probably rule out technical problems for the earlier lack of a request.

Technically, they should read back the frequency, but it is not at all unusual for a pilot to just acknowledge when he is confident he copied it right, such as a crystal clear transmission, or a route he's flown many times and a frequency he knows well.  Or, the lack of confirmation could indicate hypoxia or another mental impairment. Or that he has no intention of copying the frequency or changing to it.

My biggest point of concern and confusion is that MH370 twice reports their altitude, which sounds like they're calling ATC to make a request, and then says nothing more for 6 and 11 minutes.  The significance of this is not at all clear.  Either hypoxia or radio/electrical problems would explain this.  A cockpit struggle does not seem apparent, but some sort of distraction in the cockpit could cause them to start a conversation but never complete it.

My personal opinion, without much supporting evidence, is mental impairment, potentially due to failed pressurization, carbon monoxide, or other contamination like engine-oil in bleed air, which has been known to cause neurological damage.


How much force does a 747 land with? I've been told before that the runways for large commercial aircraft have to be built to withstand a large amount of force.  But I'm wondering exactly how much it is?  When a 747 touches down, how much force is being imparted from the wheels to the tarmac?  And, further, how much force is imparted into the runway while the plan is braking right after touchdown?

Bonus Points:

How much weight does the gear + the wheels absorb and dissipate?
I'm sure there's a range from a "greaser" landing with light braking all the way to whatever the highest the main gear is rated for, it would be nice to know both extremes and the mean.

I do not know the exact numbers for oleo stroke and so on, but this is how you would calculate this. A 747-400 weighs 400 tons on take-off and 296 tons on landing, maximum. See here for the source of those figures.

Next is the landing speed, this is approx. 160 knots = 82 m/s. Now let's assume the pilot has misjudged the height and does not flare, but slams the aircraft with the 3° approach angle into the runway. It is supposed to survive this, so let's just continue. This gives you a vertical speed of 4.3 m/s, and at 296 tons this is an energy of 2,750 kWs = 0.76 kWh, which needs to be dissipated by the landing gear. Now I make the assumption that the gear stroke is 0.5 m (those who know please put it in the comments, and I will correct the calculation). We have 0.5 m to decelerate a mass of 296 tons from 4.3 m/s to zero. If we assume a constant deceleration, the force will also be constant and the sink speed will decrease linearly.

The average sink speed during this process is 2.15 m/s, so it will take 0.23 s and an acceleration of 18.5 m/s$^2$. Force is mass times acceleration, so the force is 5,473 kN or 1.23 million pounds. This is just the inertial force to stop the descent. While taxiing to the take-off position, the aircraft will press with 400 tons = 878,000 lbs on the runway, since the wings do not yet produce any lift. This shows that even a hard landing does not stress the landing gear so much - after all, the acceleration is just shy of 2 g, acting on a much lighter plane.

In reality, the landing gear of a 747 is staggered, so the inner main gears will touch the ground first. Also, I expect that the force will not be constant along the whole gear stroke. This will change the details of this approximation, but the general magnitude should not be different.

This answer goes into more details on how to calculate the damage an airplane will do to a given runway or apron.

Now for the braking stresses. The landing field length of a 747-400 is 2175 m, and let's just assume that the pilot forgot to use thrust reversers, aerodynamic drag was switched off that day, and all the braking power had to be supplied by the 16 main wheels. Let's also assume that the pilot uses 1200 m of that field length for braking (I'm just making this up to get to an upper limit of what force will act on the tarmac). Now we need to decelerate from 82 m/s to zero within 1200 m. Linear deceleration means an average speed of 41 m/s, so the whole process takes 29.27 s. Dividing speed by time yields a deceleration of 2.8 m/s$^2$.

To bring the aircraft to a full stop, we have an energy of 995,152 kWs = 276.4 kWh to dissipate along a distance of 1200 m. Using again Newton's second law, we see that this requires a horizontal force of 829 kN = 186,322 lbs, which translates into 51,8 kN = 11,645 lbs per wheel. This is certainly more than what happens in reality, but to put it into proportion: The static load per main wheel at the maximum landing mass is 174 kN = 39,150 lbs (assuming that 4% of the mass is carried by the nose gear). This extreme (horizontal) braking force is still less than 30% of the (vertical) static load, which is well below of the maximum braking coefficient of an aircraft wheel on a dry runway.

EDIT:
CGCampell correctly remarked that emergency procedures at take-off weight will produce the biggest braking loads. Now I will calculate the highest possible braking loads, and for this I need this plot of a polynominal for the braking coefficient, which is the ratio between vertical and horizontal forces before the tire skids. I do not know the source; I collected it somewhere in the past and never found a reason to doubt its validity.

Shortly before the aircraft comes to a stop, the highest friction coefficient is reached, and then little lift is produced by the wings, so the vertical tire loads are those of the static case. At 96% of 400 tons acting on 16 wheels, this is 24 tons = 235,344 N = 52,907 lbs of downward force per wheel. Since the friction coefficient is 1 at low speed, the same load is transferred horizontally from each wheel to the ground, almost five times more than what I approximated for the landing above. Clearly, going to the limits produces much higher loads.

Formulas used in the calculation:

How to calculate the deceleration of a mass $m$ from a speed $v_0$ to $v_1$

Energy has no absolute value, we just add or subtract energy. The amount of energy change $∆E$ between the aircraft at a speed $v_0$ and at a speed $v_1$ is:
$$∆E = \frac{m}{2}\cdot (v_0^2 - v_1^2)$$

The unit of energy is the Joule, which equals the Watt-second or the Newton-meter. Thus 1 J = 1 Ws = 1 Nm = 1 $\frac{\text{kg}\cdot \text{m}^2}{\text{s}^2}$. Metric units are neat, right?

In physics, energy $E$ equals work $W$, and work is performed when a force $F$ travels along a distance $s$. As does the braking force, acting on the moving aircraft:
$$E = W = F_{brake}\cdot s$$

How do we get the rollout distance $s$?

We use the fact that the energy change due to deceleration equals the brake energy:
$$\frac{m}{2}\cdot (v_0^2 - v_1^2) = F_{brake}\cdot s \Leftrightarrow s =  \frac{m}{2\cdot F_{brake}}\cdot (v_0^2 - v_1^2)$$

How can we find the time $t$ it takes to slow the aircraft down?

If the force is constant, the acceleration $a = \frac{m}{F}$ is constant, too. So the speed over time $v(t)$ is:
$$v(t) = v_0 + a\cdot t$$

We decelerate, so $a$ is a negative number. But the same works for a positive acceleration, too. To find the time $∆t = t_1 - t_0$ we make use of the fact that v varies linearly over time, such that the average speed is the arithmetic mean between $v_0$ and $v_1$. And time is just distance divided by speed:
$$∆t = \frac{2\cdot s}{v_0 + v_1} = \frac{m\cdot s}{F_{brake}\cdot(v_0 + v_1)}\cdot (v_0^2 - v_1^2)$$

With such formulas it is always a good idea to compare the units on both sides. Yup, seconds, so the result is really a time.


What happens when a temporary pilot certificate expires? What can I do if my not-so-newly issued temporary pilot certificate is about to expire and I haven't gotten my permanent certificate yet?  Is there any way that I can keep flying while waiting for it, and is there a way to check on the status of the permanent certificate?

According to this AOPA article, you can request an extension online through the FAA's Airmen On-Line Services.

You also can look up your current status here:

http://www.faa.gov/licenses_certificates/airmen_certification/new_verification_info/

In my case, this was updated about a week before my card arrived in the mail.

You can also see what date's submissions they have processed here:

http://www.faa.gov/licenses_certificates/airmen_certification


Do airways with multiple numbers (e.g., J89-101) imply combined segments? On SkyVector, I see many airways with 'multiple' names such as J16-36 or even J89-94-100-128. I can't find any information on how to interpret these names.

I'm guessing it's a convention to say that for some portion of the airways, J89 and J94 overlap - but presumably it's still valid to simply route along J94 including those shared segments?

Example near KORD

Yes, from your example J34-68-538 are jet routes that share a segment and aircraft on different routes may travel the same segments between waypoints. A complete explanation is in the FAA's Aeronautical Chart User Guide.


What are the consequences of pumping the throttle in an carburetor piston engine airplane during start? I have seen an expert commercial pilot pumping the throttle during start for a Cessna 152 and ever since I thought that was ok to do so, but recently studying for ATPL I read about that these technique can produce a risk of engine fire during start. What are the consequences of such a start on short or long term on the engine?

Pumping the carb during a cold start, in an updraft engine such as the 152 has, is the #1 cause of engine fires, and can be eliminated by the proper and factory recommended starting procedure.

The correct procedure is to prime, then open the throtte about 1/4" and then crank the engine.  All planes vary, especially if the primers are varnished up to one degree or another, but here is some guidance for a 152 and 172:

10C  - 1 full pump of primer

0C   - 2 pumps of primer

-10C - 3 pumps of primer

-20C - 4 pumps of primer, however the engine should be preheated prior to starting at this and colder temperatures.

Using the primer, puts a charge in either one or all cylinders, which is adequate to compensate for carb fuel/air mix being condensed on the cylinder walls at the ambient temperature.

Using the throttle pump to enrichen the mixture sprays a little squirt of fuel into the carburetor. If the engine is not running, much of that fuel drips downward out of the "bottom" or inlet side of the carburetor.  Too much (easy to do) will drip out, and load the inlet box, and can also drip to the ground.  If the engine has even a small backfire, it may ignite the additional fuel there, which will rapidly heat up the carb which has an ample supply of more fuel.

If you can't start with the primer, it is likely that the primers are varnished up and need to be cleaned by a mechanic.  They come out, similar to spark plugs.

Also in the 152, you may have a primer on #1 or on all four cylinders. It largly depends on where the plane was initially delivered.  If a colder climate, the plane would likely have come with four primers.


What are the differences between Bearing vs Course vs Direction vs Heading vs Track? This answer from English.SE does not focus on aviation, and does not explain 'Track'.

In basic, simple English, would you please compare and contrast all 5 terms in my question's title? The differences between 'course' vs 'heading' was generously explained in this answer.

This is how I explain it, hopefully it helps more than hinders!

Heading:
This is where my nose points - and seeing as my nose is attached to my head, this is where my head (and thus my machine) is pointing relative to North.

Course:
This is my INTENDED path of travel that I have calculated taking into consideration winds, variation and declination.

Track:
This is my ACTUAL path traveled over ground - just like a set of tracks I would leave behind in the snow or sand, relative to North

Bearing:
This is the angle between the location of an object, machine or destination and either:
- my heading. This is called 'Relative Bearing'.
- or magnetic  north (direction toward the magnetic north pole). This is called 'Magnetic Bearing'.

So from the picture, if I take off from Springfield enroute to Shelbyville. My course (the intended path) is due East, or 090 degrees. I notice my winds are Southerly (from 183 degrees / to 003 degrees), so I make my heading 095 degrees to compensate for wind drift (or 5 degrees crab into the wind).

If my calculations are bang on, my track should be the same as my course, however I misjudged the winds, finding out my resulting track over the ground is 081 degrees - I must correct (by increasing) my heading to get back on course.

Now with some airports, the navaids (NDB or VOR) are not directly at the airfield but some distance away, so if I wanted to either fly directly to the NDB or figure out my position in space during enroute nav checks, I would take the bearing to the NDB/VOR either relative to my heading or relative to magnetic north to find its position.

Hope this helps.


Why is fuel quantity expressed in flight hours Going through a few aircraft documentaries online, I've noticed the thing that they usually express the fuel quantity in flight hours.
Ex - A 747 burns 4 litres of fuel every second. So with a ton of fuel, it'll stay in air for roughly 3-4 minutes.
Why are flight hours a necessary term while consider fuel quantity? I mean shouldn't they be worried about how much distance they can cover in an emergency to reach an airport, instead of how long they can stay in the air?
Seems a question related to endurance but couldn't find any proper explanation

It’s primarily due to wind.
Aircraft move through the air at a certain speed, which makes it tempting to give range in miles (or kilometers), but the air itself is moving as well, and often at a large enough fraction of the aircraft’s airspeed that it materially affects range across the ground.
For instance, say you have a Cessna 172 with four hours of fuel (plus reserves) and a cruise speed of 110kt. With a 30kt tailwind (140kt ground speed), your range is 560nm. But going the opposite direction with a 30kt headwind (80kt ground speed), your range is only 320nm—just over half as far!
To make it even more complicated, the winds will have different directions and speeds at different altitudes and locations, and all of that changes over time too, which is one of the reasons pilots (or dispatchers) have to carefully plan each flight’s route and fuel load, even for a “fixed” daily route between the same two airports.


What limits high altitude powered paragliders other than the engine? Due to their extremely low wing loading, powered paragliders stall at very low indicated airspeeds compared to other airplanes.  A typical paraglider can continue flying all the way down to 10-15 knots.
That suggests the idea of using a fabric wing for flight at very high altitudes.  At 100,000 feet, for example, an IAS of 10 knots corresponds to a TAS of 85 knots, well below the speed of sound.  Suppose that we take a power source that works at low air density – say, a solar-powered electric motor or an engine with an onboard oxidizer tank – and attach it to a paraglider.  Would anything prevent such an aircraft from flying stably at 100,000 ft?  For example, would flutter be an issue?

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


Where Can I Find the Master Minimum Equipment List for the A320 Series (UK / EUR)? I'm currently trying to locate the Master Minimum equipment list for an Airbus 321.

I have the FAA (US) version of this document, but I'd like a copy of the UK or EUR version if possible.

The Master Minimum Equipment List page on CAA doesn't contain a link to the any airbus series

http://www.caa.co.uk/application.aspx?catid=33&pagetype=65&appid=11&mode=list&type=sercat&id=16

I found a page on the flight safety committee that contains 5 historical links to lists for the A320 series aircraft. But all of these links are dead.

http://www.ukfsc.co.uk/information/caa-notifications/275-caa-master-minimum-equipment-list-amendements-mmel

Can anyone point me in the right direction as to where I can find this document? I would prefer the revision that was current in September 2013 for UK and Europe.

The latest revision of the MMEL for the A320 family was approved a month ago by EASA. The EASA website only contains a PDF document with the MMEL approval signature for Airbus aircraft.  For some manufacturers (e.g. Cessna) the full MMEL is included on the EASA website.

The information page on MMELs says:

  Each MMEL document is the property of the (S)TC holder, and only made
  available here in full if requested by the (S)TC holder. If a full
  copy is not available here then please contact the (S)TC Holder to get
  a copy of the document in question.

So you have to contact Airbus in this case.


How much money can be saved by removing seats? If have an airbus A380, and I remove 500 of the seats entirely from the airplane (Along with their overhead compartments), and the remaining 300 or so seats I fill up normally with people, is the MPG of Kerosene used by the plane substantially different?
Basically, assuming airlines could do it quickly (which right now they can't) would removing seats and overhead compartments from the plane be a substantial way to reduce costs on empty planes?
The limit of this question is also something I'm curious about. If I have an Airbus A380 completely stripped of seats and overhead compartments, how much better is its MPG compared to a normal one filled with people and baggage?

The amount of time and manpower required to remove empty seats before a flight, transport them to the plane's next destination (presumably on another aircraft), then reinstall necessary seats for the next flight with 450 passengers (instead of this flight's 300 pax) would far exceed any potential cost savings of removing them for the flight. (Oh, don't forget, the remaining 350 seats would have to follow the plane to its 3rd destination because that flight is booked full.)
The biggest issue would be getting the seats themselves moved around so they could be reinstalled at the next destination. Not every aircraft uses the same seats, the mix of seats (cattle class, business class, first class) will be different on different versions of the same model of aircraft, even those owned by the same airline, so having a stock of seats at each airport that could be installed when the outgoing pax count is higher than the incoming pax count would be impractical.


Why was there no issue with the Tu-144 flying above land? The Concorde didn't fly supersonically above land, it only could above the ocean. The Tu-144 however flew between Moscow and Almaty, so entirely above land; why did it fly like this? Didn't it have a that loud sonic boom? If no, why not? If it had, why did it fly above land anyway while the Concorde refused to go supersonic above land?

The actual 'legal' reasons have already been mentioned. However, there was a bit more to it.

Tu-144 was meant to fly over land from the beginning; there was no way around it, unlike Concorde. So it was designed to fly higher. In particular, Tu-144 had about 20% lower wing loading and 20% higher thrust-to-weight ratio (at MTOW) than Concorde. (The reality was a bit more complicated; for example, Concorde was limited to FL600 again for 'legal' reasons, due to certification of the pressurisation system AFAIK).
Soviet citizens, apart from not being asked their opinion, were quite used to sonic booms from military aircraft. In many places of the country, they wouldn't even raise an eyebrow. In the Urals where I grew up, I heard them almost daily.


Is the Cirrus SR22T a turbo-prop? Or does in just have a turbocharger? Is the Cirrus SR22T a turbo-prop? Or does in just have a turbocharger like in a car?

It is a turbo charged piston aircraft (much like turbo charged car, the engine is somewhat similar to that found in the older air cooled Porsche 911's (think 930 turbo)).

Turboprop is generally short for Turbine-Propeller which is a propeller aircraft powered by a turbine engine.

Turbo charged piston aircraft are piston driven engines with a turbo charger, many often may carry the T or TC designation after the model number. Such as the Piper Saratoga TC or SR22T

In this case we can reference the SR22T's Specs from the website

  Airframe & Powerplant

  Continental TSIO-550-K 315 HP Turbocharged Engine


Can crews hand-fly an RNP AR approach in IMC? Required Navigation Performance (Authorization Required) approaches require multi-crew with special training and strict equipment, similar to ILS CAT II/III.

Typically, the aircraft must have at least the following equipment: dual GNSS sensors, dual flight management systems (FMS), dual air data systems (ADS), dual autopilots, and a single IRU. (Source: FAA AC No: 90-101A.)

In IMC, can such approaches—which may include radius-to-fix segments (RF)—be flown by hand following the Flight Director cues, or must the autopilot be engaged? Such approaches usually have very small tolerances for navigational errors especially in mountainous areas.

(airnav.com) KGUC RNAV (RNP) RWY 06.

Related: What is a SAAAR instrument approach?

Each operator can impose their own requirements that are at least as strict as what the FAA requires, and these tend to be more strict.  For instance, one operator I'm familiar with requires both INS's to be working, not just one.

For that operator, it's allowable to hand-fly an RNP approach using the Flight Director if the RNP is 0.3 NM, but if it's any lower then the autopilot must be used.


Can an airliner be refueled while the APU is running? Race cars can be refueled while the engine is running. I assume this is a dangerous task done by highly specialised technicians.

If ground support is not available, an airliner may keep the APU running to be able to provide power to restart the engines.

If ground support is not available and refuel is needed, can an airliner refuel while the APU is running (technically and legally)?

If the question is too broad, it can be narrowed to best sellers (B737 and A320 families).

Refueling an airliner with APU running is a perfectly normal procedure and it is done daily all around the world. The APU is located at the tail cone partially to reduce the risk of fire spreading to the fuel tanks, which are normally in the wings and center fuselage.

Some operators and authorities (not all) restrict starting and/or stopping the APU while fueling.


What action should the pilot take when a TCAS RA (Resolution Advisory) provides opposite guidance to ATC instructions? If a TCAS Resolution Advisory (RA) specifies a "Climb," but in response to the same potential traffic threat, ATC issues instructions to "Descend"
what course of action should the pilot/crew take?

In the 2002 Überlingen mid-air collision, one crew followed the ATC instruction to descend instead of the TCAS Resolution Advisary to climb. This caused the deaths of 71 people.
Equipment and procedures have improved since then. Pilots should always follow TCAS Advisory and there is a FAA rule that deals with this. 91.123   Compliance with ATC clearances and instructions.

91.123   Compliance with ATC clearances and instructions.
-
(a) When an ATC clearance has been obtained, no pilot in command may
deviate from that clearance unless an amended clearance is obtained,
an emergency exists, or the deviation is in response to a traffic
alert and collision avoidance system resolution advisory. However,
except in Class A airspace, a pilot may cancel an IFR flight plan if
the operation is being conducted in VFR weather conditions. When a
pilot is uncertain of an ATC clearance, that pilot shall immediately
request clarification from ATC.
(b) Except in an emergency, no person may operate an aircraft contrary
to an ATC instruction in an area in which air traffic control is
exercised.
(c) Each pilot in command who, in an emergency, or in response to a traffic alert and collision avoidance system resolution advisory,
deviates from an ATC clearance or instruction shall notify ATC of that
deviation as soon as possible.
(d) Each pilot in command who (though not deviating from a rule of
this subpart) is given priority by ATC in an emergency, shall submit a
detailed report of that emergency within 48 hours to the manager of
that ATC facility, if requested by ATC.
(e) Unless otherwise authorized by ATC, no person operating an
aircraft may operate that aircraft according to any clearance or
instruction that has been issued to the pilot of another aircraft for
radar air traffic control purposes.


Does a safety pilot log PIC, or SIC? I just got my private pilot license and I want to build-up time with another private pilot

lets say I am acting as a safety pilot and we make a flight of 3.7, and his time under the hood was 3.4 in C172

1-as a safety pilot, what is my total durain time?

2- as a safety pilot, am I going to log PIC, or SIC? and how much?

I keep getting different answers. It would be really appreciated if you cite your source.

Yes you can log time as safety pilot where you are taking legal responsibility for maintaining VFR separation during hood practice.  Otherwise it has to be a multi-crew situation by operating rules or due to the aircraft type.  This covers it pretty good.  https://www.aopa.org/training-and-safety/learn-to-fly/logging-cross-country-time/logbooks-and-logging-time


What trimotor is this model? What trimotor is this model?

(own work)

I believe it's the French Couzinet 71 'Arc-en-Ciel'
https://www.hydroretro.net/etudegh/arc-en-ciel_atlantique_vol1.pdf


Is there any benefit to science from the Swiss built solar plane flying across the globe? Are there any innovations that were made during the development or flight of the Solar Impulse plane that would go into any type of regularly used airplanes in the near future?

As you can see from the massive delay in its flight schedule, the Solar Impulse II has run into some problems. This is always an indication that something has been learned. Unfortunately, what has been learned is that electric flight is even harder than expected.

The value of this particular airplane is the demonstration that purely electric long-range flights are possible, and in this it ranks with the first rocket-powered airplanes in 1928 and 1929 - yes, it can be done, but for now there is no practical value in it.

As for long term developments - this is just speculation, but I doubt that in 50 or 100 years we will see the Solar Impulse II as the starting point of a new era.


How are airlines able to work out gate allocations so far in advance? When flying on a long-haul flight, you can often see gate allocations for when you land a hour or two before actually arriving at the airport, including transfer information and connecting flights. However, with so many aircraft and frequently changing situations, how do they manage to allocate these gates so far out in advance?

Route times are pretty well known. If you know when the plane should depart and how long the flight should last, it's pretty easy to calculate when it will be arriving. Give a few minutes leeway on either side, and you should be good. If the plane is not there on time, you send it somewhere else.

Most large aircraft have some sort of ACARS that allows them to talk to company dispatch and let them know if they're going to be early or late, among other things. Barring that, they almost always have a company radio frequency that they can relay messages on one way or another.


Does an airline have to pay if fighters intercept one of its aircraft? It sometimes happens that because loss of radio communication or because wrong frequency tuned in during ATC handover etc... a country has to send fighters to intercept an aircraft in its airspace. If such happens, does the airline have to pay a fine (presumably this would/should cover the expenses of the dispatched fighters)? What happens with the pilots who make this mistake?

Let's assume a European country, member of NATO and a commercial flight.

EDIT - 2018-12-17

It looks my country (Hungary) will be the first in the EU which will charge airines (actually based on the Hungarian Official Gazette they can charge anyone not just commercial flights) in this case. The amount itself is not defined, the Aviation Authority will be responsible for determining it (of course along with the military counterparty). Link for the Hungarian Official Gazette - in Hungarian

Probably not very likely. In 1978 Soviet Union asked US\$100,000 (\$375,200 today) for "caretaking passengers" after their interceptors forced to land KAL 902 on the frozen lake (has never been paid). However firing the two R-60 missiles from interceptors into the airliner was for free.


Why is there a difference between nosegear retraction directions? I've noticed that on almost all aircraft (Boeing, Airbus etc.) the nose gear rotates forwards for retraction.

However, on a some aircraft, in particular a few Russian models, the opposite is used: the nose gear is rotated towards the rear for stowage:

(this includes the Tu154, Tu134)

Is there any logic behind this decision? I imagined it was better to place it folding forwards, such that the gear was assisted into place by the air, especially for manual free fall. Looking at pictures of the TU-154 with its gear down, there seems to be plenty of space forward.

For both main and nose landing gear the main and really only consideration is where they can make space for the gear (there is no standard direction for retracting the main landing gear either; the Tu-154 retracts main gear rearwards into the anti-shock body).

The most common configuration is retracting nose gear forward, because it's easy to make space for it there leaving more space for the cargo hold. I don't think the air pressure during gravity extension plays any role in the decision.

Most older Russian planes were however originally designed with glass nose seating navigator, so they did not have the room there. It was no longer the case with Tu-154 though. So they either had other equipment there or were simply used to making it retract rearward and didn't think about the advantage of changing it.

The most common configuration for main gear is retracting it inward into the wing box, but note that the Tu-154 is exception there as well retracting the main gear into the rather large anti-shock bodies. Because they needed the anti-shock bodies they thought how to use them and there were not that many options.