Operating a floatplane/seaplane on water through a drawspan? Lets say that you were in a floatplane (whether it be Terry's floating Cub or a big ol' Martin Mars) and the only otherwise-reasonably-suitable landing spot in the waterway where you are trying to go, or the taxi route from your landing site to your destination dock for that matter, is crossed by a movable bridge (aka drawbridge) that will not clear your aircraft when the drawspan is closed.  How would you, the floatplane pilot, signal the bridgekeeper to open the bridge so you can land/taxi through the navigable channel provided, especially considering you don't have a foghorn to signal the keeper with, and the keeper only has a marine VHF radio, which you may not have?

Assume that the drawspan can clear your plane when open (always true for bascule and swing spans; landing under a liftspan would be rather challenging though), and that the bridge is operated by a local bridgetender 24/7 (lesser-used drawspans often require prior notice, and there are also remote-control drawbridges out there that use sensors and/or CCTV to indicate the presence of marine traffic to a bridge operator sitting far away).

When I sail we use simple air horns to signal the local drawbridges. Something like this one is usually kept on the boat. I see no reason not to keep one in your float plane if you anticipate need to hail a draw bridge or just for general marine hailing. If memory serves, it's one long blast (4-6 seconds) followed by a quick one. Similarly you could opt to carry a hand held marine radio in your plane.

Now all of that is assuming you knew you were going to encounter a bridge. If you did not plan for it then you have a few options. If memory serves some (if not all) of the bridges have land lines and if you have a cell phone you may be able to call them (provided you can find the number). If you are flying a float plane you may (should?) have a PFD on board. Many PFDs have whistles attached. This, in theory should suffice to hail the bridge. The bridge attendant may see you floating there and open the bridge as well.

You can always try, um, yelling at the guy...

Now what if the bridge is broken, there is a long train stuck on it and the attendant stepped out for a cigar break and has no intention of returning for a while? You are in the end of the day in a float plane and you have a unique ability that most ships don't have, you can go over the bridge...


How is Maximum Take Off Weight determined? How would a test pilot determine the MTOW of an aircraft. Does the manufacturer predict this value?

Pilots do not determine the official MTOW of an aircraft. MTOW will be estimated by the manufacturer during the design of the aircraft based on the required payload of the aircraft and the design configuration. It will be adjusted based on the detail design of the aircraft to comply with regulation requirements.

  §25.1533   Additional operating limitations.

  (a) Additional operating limitations must be established as follows:

  (1) The maximum takeoff weights must be established as the weights at
  which compliance is shown with the applicable provisions of this part
  (including the takeoff climb provisions of §25.121(a) through (c), for
  altitudes and ambient temperatures).

MTOW affects many other aspects of an aircraft's performance. It will affect stopping distance after a rejected takeoff, takeoff performance (including engine failure), climb performance, taxi weights, and many structural aspects. MTOW will be chosen so that the requirements for all of these conditions are met. This is why new engines or winglets which improve performance will allow a higher MTOW.

Of course, as always, the pilot has the authority to set their own personal MTOW more conservatively, if they feel it is necessary for safer operation of the aircraft.


How should a loss of communications in VFR be dealt with? Let's say I'm flying a cross country flight and I wanted to land in a Class D or enter Class C towered airport, but I lost my two-way communications radio but have my transponder squawking 7600. Should I blindly continue in and receive light gun signals to land or should I steer out the Class C and D and divert to a non-towered airport? In worst case scenario, what if my transponder is also out?

should I blindly continue in

First, never do anything "blindly".

The FAR and the AIM address the Class D question, so this part is the most easily answerable:

  FAR 91.129 (d) Communications failure. Each person who operates an aircraft in a Class D airspace area must maintain two-way radio communications with the ATC facility having jurisdiction over that area.

  (1) If the aircraft radio fails in flight under IFR, the pilot must comply with §91.185 of the part.

  (2) If the aircraft radio fails in flight under VFR, the pilot in command may operate that aircraft and land if—

  (i) Weather conditions are at or above basic VFR weather minimums;

  (ii) Visual contact with the tower is maintained; and

  (iii) A clearance to land is received.

  AIM 4-2-13 (3). Transmitter and receiver inoperative. Remain outside or above the Class D surface area until the direction and flow of traffic has been determined; then, join the airport traffic pattern and maintain visual  contact with the tower to receive light signals. Acknowledge light signals as noted above.

After that, 6−4−1 addresses more two-way comms failure actions:

  a. It is virtually impossible to provide regulations and procedures
  applicable to all possible situations associated with two-way radio
  communications failure. During two-way radio communications failure,
  when confronted by a situation not covered in the regulation, pilots
  are expected to exercise good judgment in whatever action they elect
  to take. Should the situation so dictate they should not be reluctant
  to use the emergency action contained in 14 CFR Section 91.3(b).

Since "best judgement" is very situational dependent, the rest of this is subjective:  I would not enter Class C, if there was another alternative. If you're already in Class C, and there are Class D/E/G airports available, divert. If you're already in Class C,and there are no other options, continue with the utmost caution (following the advice of the Class D procedures if able), using your own light signals to attempt to alert the tower.

Some "armchair lawyers" might even say that lost-comms (VFR) operations in Class C and even Class B could be conducted in the same manner as Class D, because each section starts with: "each aircraft operation in Class B/C airspace must be conducted in compliance with this section and 91.129."

I'd personally avoid B and C like the plague if I was VFR lost comms.


Why do semitailless swept-winged aircraft, but not delta-winged aircraft, suffer from (primarily) pitch oscillations at high mach? Semitailless1 swept-wing aircraft without active stability enhancement2 generally3 have extremely poor handling characteristics, most notably a tendency towards violent pitch oscillations at high subsonic mach numbers, and yaw and roll oscillations at mach numbers slightly beyond this.  As a result, while the swept-wing semitailless layout was briefly quite popular for transonic and supersonic aircraft in the late 1940s and early 1950s (witness, among others, the DH 108, X-4, and F7U), it was quickly abandoned, only making a comeback much (much) later, with the advent of computerised active-stability-enhancement systems.
In the meantime, supersonic aircraft near-universally switched over to delta-winged layouts, which worked just as well for supersonic flight and had none of the nasty quirks of semitailless-swept-winged layouts.  This despite the two layouts being extremely similar; indeed, a semitailless swept-wing aircraft can be seen as a delta-winged aircraft with part of the inboard trailing edge cropped out:

Why do two such similar layouts have such different handling characteristics?

1: Aircraft that do not have a separate horizontal tail, but do have a vertical tail.
2: A system where a computer constantly monitors what the aircraft is doing and continually makes tiny flight-control inputs to keep it doing what it's supposed to.
3: Although not always.

The function of a "tail" in this case is pitch stability.  Therefore, all stable aircraft must have "tails".  Aerodynamically, the rear portion of the delta is its tail.  Removing it should have predictable consequences, even in the subsonic realm.
Transonically, with shock waves dancing on the wings and a moving center of pressure, pitch stability is critical.  This is also true in slow flight, where a shifting center of pressure can overwhelm weaker pitch stability.
Subsonically, the swept tailless design can be helped by "washing out" (lowering the AOA of) the wing tips or by adding slats, which helps control movement of the center of pressure at higher angles of attack.  As Dunne ingeniously realized over a century ago, this design made for a stable aircraft.  Indeed, a swept wing aircraft with insufficient tail area could be helped with stronger slats!  (If the wing tips can handle the extra load).
Transonic and supersonic flight is another issue.  The notion of "taillessness" was a blind alley in aviation design, a mistake not to be repeated.


Why are biofuels usually blended with standard jet fuel when used? When biofuels are used in both demonstration and commercial flights, it is common for them to be mixed with standard Jet A fuel. Is this due to safety reasons, cost or due to specific properties (e.g. freezing point of biofuels) that may not enable them to be used solely all the time?

The issue with the biofuels is the low aromatic content, which changes the behavior of the fuel tank sealants. That's why blends are needed for the time being.

  (...) very low aromatic contents may cause seals and sealants to shrink and
  harden leading to acute or chronic failure. Unfortunately, most of the material qualification tests are more concerned
  with excessive swelling than shrinkage and there is little guidance offered as to an acceptable level of shrinkage or
  other changes in physical properties related to low aromatic content (NASA).

  At this stage,
  approval has been given for airlines to operate flights
  using the BtL and HEFA processes up to a limit of 50%
  biofuel and 50% conventional fuel. This is a precautionary
  measure enabling the industry to start using biofuels
  while additional assessments are undertaken on the
  need to maintain required levels of aromatic content
  in fuels. Aromatics are hydrocarbons found naturally in
  fossil-based fuels and are a necessary component for
  conventional jet fuels, forming up to 25% of the volume.
  They are not found in biomass-sourced fuels and this
  restricts the use of jet biofuels to 50% blends in order
  to guarantee aromatic content. The restriction allows
  time for an assessment of whether a synthetic aromatic
  source needs to be developed (Air Transport Action Group).

  Biofuels and FT fuels are very poor in aromatic content. This causes problems with
  seal shrinking and thus aromatics must be added to drop-in fuels in flight tests such
  that a concentration of 8% is achieved (European Commission).

  (...) aromatic hydrocarbons are
  more aggressive and cause more swell in seal materials than do paraffinic hydrocarbons

  (...)

  After the second cycle [of a jet fuel analog], the volume swell dropped
  from +22% to +13% as would be expected from the
  lower aromatic content in the fuel. However, this second cycle also caused the compression set to increase dramatically from 3% to 43%. Upon drying, the
  material again returned to its original volume, and
  compression set improved slightly. The reason for this
  significant increase in compression set is not obvious,
  but it is concerning (SAE International).

Trivia: there's been at least one demonstration flight on a jet that used 100% biofuel.


Why is the autopilot of the DHC-6 Twin Otter powered by bleed air? I was just reading through the POH of a DHC-6-100 Twin Otter and was surprised to read the following:

  3.8.2 LOW PRESSURE - OTHER SYSTEMS. The airframe deicing system and
  the autopilot are operated by bleed pressure. In the event of a low pressure
  condition, a caution light on the caution lights panel will illuminate. Under these
  conditions, the pressure may be restored as outlined in paragraph 3.8.1. However,
  if increasing engine speed does not rectify the condition, the use of the
  autopilot and de-icer system should be discontinued.

(emphasis mine)

I understand why the deicing system is using bleed air, but why is the autopilot powered by bleed air? How does this autopilot work?

The following question is somewhat related:

How did old autopilots work?

but it never mentions anything powered by bleed air.

The reason (back in the day) was an envisioned low-cost autopilot ownership in smaller planes,$^1$ but it was a troublesome system as it aged.

  The first production [Twin Otter] aircraft left the Downsview factory with an option for the Honeywell H-14 autopilot. This system used large pneumatic servos to control the aircraft. This was a popular option at the time however as the aircraft and autopilot aged the maintenance involved in keeping the system serviceable resulted in many operators disabling or removing the system (rockymountainaircraft.ca).

It works via pneumatic servos; pistons that are actuated by pressurized air.

  Source: NASA

$^1$: NASA contractor report (prepared by Honeywell) on "fluidic" flight control systems (also covers the aforementioned Honeywell H-14 autopilot).


what is the difference between max nose wheel steering angle and effective steering angle? I am looking at a diagram. The max nose wheel steering angle is 72 deg and effective steering angle is 66.1. My question is now why do we not have just one nose wheel steering angle? what is the difference between max nose wheel steering angle and effective steering angle ? And what angle is used for which cases?

When the two sides of the main landing gear move, each one tends to force a circle with its own radius and center, and is at the same time influenced by the nose landing gear own radius of turn.

Source: A350-900 Aircraft characteristics, airport and maintenance planning

Some tire sliding must occur due to the difference in circles, the actual center is between the three individual centers mentioned and the radius R3 is therefore a bit impacted.

Depending on the differential action on the brakes, and the use of engine thrust asymmetry, the result varies by a few percents (between types of turn 1 and 2 above).


Why don't small planes use turbine (turboprop) engines? Turboprop engines are more fuel efficient1, lighter for the same power, mechanically simpler and consequently more reliable.  They are also slightly easier to operate (no need to fiddle with mixture) and burn cheaper fuel. As a result they replaced piston engines in all transport aircraft long ago. So why didn't they find their way into small GA planes (basically everything above 8-10 seats uses turboprops, but in the 4-seat category, nothing does)?

1Actually looks like I was mistaken. Reciprocating engines seem to be more efficient.

First, piston engines are more efficient than turboprops, so their operational cost are lower. This also means that the system mass (engine plus fuel) for a trip is lower once you go beyond small ranges. In a helicopter, the engine mass is more important, because average flight times are much shorter, so you find many helicopters with turbo engines and only few with pistons.

Next, there is a well developed infrastructure for maintenance on those pistons, and new turboprops would need new, expensive infrastructure (trained people, tools, spare parts ...)

And then there is simply no incentive to develop a new GA engine. The expense to get it certified is too large for the rather small market. This is the same as for Diesel engines.


What prevents BFS from becoming unstable when pitching from horizontal to vertical? In this video from (SpaceX's BFS landing) there is a point where the ship tilts from horizontal « belly first » terminal velocity freefall, to vertical « engine first » landing position.

The graph on the right shows that this leads to a vertical acceleration roughly from mach 0.26 to mach 0.31
induced by drag reduction due to tilting manoever itself.

Gimbaled engines are only fired when the ship is vertical, which could mean this whole tilting manoever is meant to be aerodynamically achieved.

Actuated fins and canard fins are designed to increase or decrease drag about center of gravity of the ship, like a skydiver does by moving its limbs.

But as soon as the ship starts tilting from horizontal to vertical, its body and actuated fins will generate lift. (instead of only drag)

The ship will start gliding backwards. Lift will increase to a maximum point when fins aren't stalled anymore.

Question is :

At this point (gliding backwards, almost vertical, mach 0.3, short before suicide burn) the whole ship should become unstable if center of lift is between center of gravity and aft part of the ship (engines) It's a bit like imagining one backward flying VariEze, or the aerobatic figure called "tailslide"  : It will flip over, the same way a  badminton shuttlecock does when it changes direction.

When lift becomes significant, what prevents the ship from naturally tilting back to horizontal or abruptly yaw or roll to some unpreditable new attitude (shuttlecock like)?

I agree if cg is very far back, inward folded aft fins and canard fins could create the correct pitching moment for the BFS to tilt vertical. But where should the cg be for it not to tilt about yaw axis, (or induced roll due to the massive fixed vertical fin) Some airliner trading a vertical stabilizer on its tail for one above its cockpit wont be very stable about yaw axis either.

Note that when looking at animations provided by spaceX, aft fins seem to have only one degree of freedom : The huge hinges allow changes in dihedral.

Canard fins seem to act the same but may have one more (invisible in animation) degree of freedom: variable incidence, which could add control to pitch and roll, but still is useless for yaw control.

Edit: please focus on yaw axis, consider seconds 1105 to 1107 in animation.
Canard fins don't play any role in stabilizing yaw. How can the aircraft not tumble because of yaw instability and induced roll?

The answer here is to review the history of how Space X "does it" with the Falcon 9.  To solve aerodynamicly, they extend speed brakes from TOP of booster to get it to fall tail first.  CG buffs take note, this is how it works in gravity and atmosphere. Just like a parachute or a hang glider.

Very close observation of the video shows the lower "tail fins" folding inwards, raising the aerodynamic pressure point (in this case drag) above the CG.  The rocket now behaves as an aircraft with its CG way too far back(relative to Clift), pitching up and falling "backwards" towards the ground. Rocket thrust then slows the descent for landing.

The rocket is rotating during this maneuver to its new weight down and drag/lift up configuration, with predictable increase in velocity due to lower net drag towards the direction of "flight".

It may be helpful to draw the "lift" vertical and horizontal components here to understand the forces.
The maneuver is not unlike a 1/4 loop.  It is controlled, because CG is below the Center of drag.

In response to edit regarding yaw axis, great observation!  This is a technique considered for airliners recovering from deep stall!!!  Rock back and forth to bring V stab into play to yaw out of deep stall.

But with the rocket, the gimballed motor will stop this, and before, rudder will now not be used to break the stall, but to preserve it!  This is an aerobatic maneuver, pure and simple.

What Space X does so well is transition the "deep stall" into a controlled landing.

The concern about the V stab is justified.  The Falcon 9 speed brakes are more fool proof.  Let's hope they do not "engineer themselves into a corner" with a potentially flawed design.

POST EDIT - RESPONSE TO COMMENTS

We need to keep in mind here that the animation is what may be wrong, not the actual flight plan. @qq jkztd correctly pointed out that, if the BFR was falling vertically, with no horizontal motion, the pitch up would cause horizontal motion towards the tail (beginning to glide backwards). Although the pitch up would not induce yaw, the backwards gliding BFR WOULD be unstable in yaw. Folding in horizontal fins would make it stable in pitch. A better solution may be to initiate pitch up with some forward motion, or to simply pitch up by adding more drag to "top" with speed brakes as the Falcon 9 does, or igniting gimballed rocket motor sooner.  However, sometimes, simpler is better,


What did they do before on-board toilets? I was researching Jimmy Doolittle this morning, and I found this on History.com:

  To aid his record-breaking 1922 coast-to-coast flight, U.S. military
  strategist Jimmy Doolittle invented a funnel-and-tube-based "pilot
  dehydrator"—possibly the earliest airplane toilet.

That led me to the question: What did they do before 1922 when they felt like they had to go?

Go to the toilet before departure, and hope you can find somewhere to land if nature calls suddenly :)

Same really as before a long car journey today...

Of course aircraft of that time didn't have very long endurance, so the situation wasn't likely to arise that you'd need to make a pit stop to let nature take its course. You'd have a scheduled stop anyway well before that.


What are service letters and service bulletins? How do a service letter and service bulletin differ.

In the United States and presumably in other countries, there is no Government oversight on how a manufacture communicates to aircraft owner/operators except that they must issue some form of mandatory compliance "Service Bulletin" for Part 135/121 commercial operators. There is no industry guideline for what a document is called, or the information it conveys.

Manufactures often use an assortment of documents and the type of information in each document is left up to the company. For example, Continental Motors uses almost every kind of document I have ever seen...

"Service Bulletin" i.e. SB "used by most manufactures..."
"Critical Service Bulletin" i.e CSB 01-1 "Fuel Pump Inspection..."
"Service Bulletin Mandatory" i.e M64-18 "Field Conversion to
    Turbocharging..."
"Service Information" i.e. SIL99-2A "Current Listing of Sealents..."
"Service Information Directive" i.e. SID97-4C "Cylinder Bore And Piston Fit..."
"Service Letter" i.e 556c "Shouldered magneto drive shaft bushing..."

There are others I don't have copies of such as information sent to marketing, promotions, or financial departments. Additionally, the FAA will require specific forms to be used as part of the approval for Part 135, 119, and 121 operating rules. For example some type of "trace-ability" paperwork is required to be attached to all materials and parts. A "trace-ability" document provides manufacture, model, mil-spec, fire resistance, etc.

It is interesting to note that despite the universal use of the Red, Yellow, and Green parts tagging system, their is no FAR regulation requiring it's use.


Purpose of CHT drop in piston engine shutdown procedures? One of the items in the helicopter Robinson R22 (and possibly other piston engined aircraft) shutdown procedure is to wait for the Cylinder Head Temperature to drop to a lower temperature. What is the purpose of this?

According to this document, this is to allow the engine to cool and level the oil temperature:

  CHT Drop- Wait two minutes or until you can clearly see the H on Cyl Hd
  Temp. This is to allow the engine to cool and level the oil
  temperature. Closing down too early may damage the engine.

This is most probably to prevent damage to the engine due to shock cooling. Any rapid decrease in temperature during shutdown can cause damage to cylinder heads However, note that this theory is quite controversial. This is discussed in detail here and here. Especially, as @Lnafziger points out in his answer,

  ... in fact the engine cools much more quickly when you shut it down at the end of a flight.


Where can I find details of the holding models for JFK, Schiphol, Heathrow and Dubai? Does anyone know the stack (holding) models for the JFK, Schiphol, Heathrow and Dubai airports? I mean, not where the aircraft hold but rather how is it planned and what concepts are used? Or how I can find that data?

Most chars can be found in the local AIP. Most charts containing such data are the 'Standard Arrival' charts, such as location, heading and holding time.

For the  Netherlands (Because you asked for Schiphol) it would be http://www.ais-netherlands.nl/aim/index.html


Aborted take off due to not closed cargo doors. How this will be signalled? A hypothetical situation (I know that it is very unlikely to happen in real). When closing cargo doors, a piece of fabric from the luggage carrier's uniform stick in between. The cargo door is actually closed (no real danger), but the latching sensors are sending a misleading signals.

How this will be communicated in the cockpit? What visual or audio signal will be used / emitted in the cockpit to inform the crew about the reason? Is there any specific light or button as an endpoint for cargo doors sensor? Is there any specific sound?

How will the crew communicate to the tower the reason for an aborted take off (what kind of message, who will do this -- flying pilot, non-flying pilot)?

Clarification: This question is for the sake of the story that I am writing. It (both story and the question) involves Boeing 777 taking off from LHR in August 2014.

Aborted take of is due to a misleading information coming from cargo doors' sensors that reveal a possible problem only during take-off, not before (i.e. during taxi). The doors are actually closed (no real danger posed after check). But there's a tiny piece of fabrics from cargo loader's uniform stick in between doors. This question is a follow-up or alternate version of this question. Here I'd like to know what happens, if such situation will be detected before V1. In linked question I am asking about the same situation detected after V1 or shortly after take-off and thus after such aircraft returns safely to the airport and clears the runway.

I am aware that most airline experts will say that such situation is not possible at all. I am, on the other hand, a system designer and I know that such "ghost" situations of "neither 0 nor 1" sometimes do happen. But, for the sake of this question, if you feel uncomfortable with such reason -- let's assume that take-off was aborted due to any other reason, i.e. engine failure. I belive that such reason has similar severity as the need of checking whether cargo doors are really closed due to fact that on-board computer provides misleading data.

I'd lilke to underline that this is purely hypothetical question. I am aware that while such questions are sometimes hard to answer, they're in general quite welcomed in this site and are not off-topic.

You will typically get a DOOR OPEN alert displayed on the EICAS system.  A competent crew would have spotted such a discrepancy before pushback.


Why do some pilots call a go-around an 'overshoot'? A couple of months ago I was watching some Ice Pilots NWT re-runs, and I noticed they kept saying 'overshoot' when talking about a go-around. Is this standard Canadian phraseology? Or is it perhaps old phraseology? Or is it simply reworded for the benefit of the TV audience?

I'm not asking about the meaning of the word 'overshoot' which is quite clear, but it was being used were every pilot I know would use the word 'go-around', i.e. calling "overshoot, overshoot, overshoot" when shoving the throttles forward.

Looking at the Glossary for Pilots and Air Traffic Services Personnel (TP 11958E) at the Government of Canada web site, the definitions of overshoot and go-around are

  overshoot

  (1) To pass beyond the limit of the runway or landing field when
  trying to land.

  Fr: dépasser

  (2) Other expression for: go-around

and

  “Go around”

  An expression used in radiocommunications to instruct a pilot to
  abandon an approach or landing.

  Fr: « Remettez les gaz »

  go-around

  The procedure followed by a pilot who decides to abandon an approach
  or landing.

  Fr: remise des gaz

Plus, looking at various Flight Test Guides listed at the Canadian Government Air Transportation site it appears that pilots in Canadian flight schools are taught "overshoot" procedures for missed approaches (vice go-around).

Seeing as you were watching a reality TV show dealing with Canadian pilots, it is not surprising they use the terminology they were most likely taught in flight school (in Canada).


How do the actuator loads (e.g. for the ailerons) vary between different flight phases? Assume the hinge moment is given as

$HM = 0.5\rho v^2*C_{h\delta} \delta*S*c$

$\rho$ = air density

$v$ = air speed

$C_{h\delta}$ = Hinge moment coefficient

$S$ = Control surface area

$c$ = average surface chord

the resulting moments / actuator loads are mainly influenced by the aircraft's altitude (air density $\rho$), speed $v$ and the control surface deflections $\delta$. (AoA is neglected to keep it simple)

Can there be anything said about the actuator loads regarding different mission types or flight phases? E.g. does cruise (high altitude and speeds, small surface defelctions) cause higher actuator loads than approach (low altitude, low speed, larger surface delections).

I was planning to use X-Plane to investigate this, but as far as I know it will only output the rudder's deflections, not the hinge moment itself.

Any ideas about this?

Indeed the hinge moment equation is (with index $_s$ for surface)
$$H_s = C_{h_s} \cdot ½  \rho V^2 \cdot  \delta_s \cdot S_s \cdot \bar{c_s}$$

The moment coefficient $C_{h_s}$ depends on aircraft angle of attack, surface deflection (!) and trim tab deflection, as depicted in the figure below (from this answer). It is not a simple constant linear function due to shading of horizontal tail in the flow of other bits of aircraft structure.

So of course, hinge moment calculation depends on aeroplane configuration and geometry. But as @JanHudec mentions in a comment, the two main variables here are dynamic pressure and surface deflection.

Full surface deflection at cruise speed results in the largest hinge moment. It may also result in structural forces higher than the limit design forces, for instance load factors > 2.5g. It would be safest if the actuator force can never exceed the hinge moment required to reach maximum load factor, which would require making plots of (hinge moment for max. load factor) vs. airspeed, at different c.g. at maximum weight.


What does this METAR remark mean? 'RMK RWY 7 ATIS G LL' I understand the long form:
"Remarks: runway 7 Automated Terminal Information Service (ATIS) G landline"

But what I don't understand is what runway 7 has to do with the ATIS information (this particular airport has one runway, RWY 7-25). What does the 'G' mean? What does the 'landline' mean?

I have a suspicion that you're looking at KLZU's METAR. Basically, they're inputting their manually written METAR into the system, and when they send it out they're adding the Runway in Use(RWY 7) and ATIS code(ATIS G) to their METAR, which they're really not supposed to do. I suspect that LL is the person who recorded it's operating initials at the facility, also not supposed to be transmitted as a part of the METAR.


Could the cargo hold of an aircraft be re-designed to carry passengers? This image had me intrigued:

It looks like two semi-circles, the upper part for passengers and the lower part for cargo.
I was wondering, for short haul flights, could the lower part be converted like the upper part, so the plane could carry more passengers, like a basement stuff, no windows and lower fares. We could do away with cabin luggage and stuff to take care of maximum takeoff weight, and anyways my thought was towards short haul flights.

In principle, yes. The cargo hold is pressurised and (depending on the aircraft and the installed options) reasonably temperature-controlled. However, it's probably not feasible; there are three major issues to be worked out that I can think of off the top of my head:

Cargo hold height and windows. It's a bit hard to tell from your picture, but even on a large widebody plane the cargohold is not that high (the cabin floor is lower than halfway). The A330 (as an example) carries LD3 containers in its cargohold, which are about 160cm tall; the cargohold is not much taller than that. Most passengers cannot walk upright inside it; the cargo hold on smaller aircraft is even lower (the one on the A320 is designed to carry LD3-46 containers, which have a height of about 115cm). Also, the lack of windows would bother passengers in the lower deck.
Emergency exits. In an emergency, passengers must be able to get out of the plane within 90 seconds. At best you would need to install additional doors in the cargo hold; at worst, you will not be able to meet this requirement (because of the low ceiling, people can't move as quickly)
In a crash landing, the lower fuselage may buckle, which serves to cushion the impact for the people in the passenger cabin. You would need to show that the passengers in the lower deck can survive a crash landing.

Note that some airlines use part of their lower deck for galleys, crew rests and even lavatories.


What should a Pilot do if they encounter foreign military jets? Say you're flying an amateur-built plane just out over the waters of, say, Alaska. And then you encounter a fleet of maybe 5 foreign military jets directly above you, and then you get radio transmissions from the group in Russian. Well, what should a pilot do? The pilot doesn't understand Russian and is clearly not over any foreign airspace as the pilot is flying less than 20 miles south from the shores of Alaska, which shouldn't be somewhere that foreign military jets should be scaring pilots.
Would heading back to shore really be a good idea? The jets could potentially be hostile. So, what would be the wisest decision in this sort of scenario?

According to ICAO conventions the offical international language of aviation is English therefore it is unlikely that Russian fighter pilots will speak in Russian to a foreign pilot. If the pilot overlfying American waters, it's unlikely that Russian fighters are free to intercept planes in American airspace.
If such scenario happens, the pilot can report the situation to the ATC, then the situation will quickly escalate. If the private pilot is in American airspace and Russian fighters are not authorised, the private pilot should be safe following ATC directions and/or continue the route as planned. USAF will take care of the rest.


Can a pilot use legal psychoactive cannabinoids? How do the FAA and airline companies treat pilots using substances like Delta-8-Tetrahydrocannabinol on their down time? Like CBD, Delta-8-THC is a legal derivative from marijuana.

Delta-8-Tetrahydrocannabinol (Delta-8-THC, Δ8-THC) is a cannabinoid found in the cannabis plant. It has psychoactive properties; the effects are less potent but comparable.
Delta 8 THC metabolites trigger many drug tests looking for Delta 9 THC metabolites. These compounds are chemically similar.
Whoever needs to pass a drug test (pilots included) should not take them.


Is there a database of airport ceilometer raw data? I am interested in obtaining raw ceilometer data, to test some cloud/aerosol layer identification algorithms.

Is this type of data freely available or will I need to ask for it directly from the airport?
Do airports keep an archive of raw data or simply of cloud heights as determined by manufacturers algorithm and provided in METAR reports?

OGIMET looks like it goes back to 2005.

My favorite weather site Weather Underground has historical data.

It seems like you need to plug in dates one at a time but there are plenty of ways to skim a page and im sure you can ask them for a data dump if you know what you need.


Does the Prandtl flying wing have a lower maximum speed than other designs? Does the design of the wing with its "twist" near the wingtips necessarily limit the maximum speed of an aircraft utilising that technology?

Also, with the leading edge profile/attack angle varying along the length of the wing, does this generate any unusual strain requiring complex engineering to accommodate?

( I am a novice here-as I am sure you can guess but a very determined one and I am going to build a Micro Turbine-powered(hopefully!) Prandtl-type wing for myself this year, I may need to consult the many experts here on a regular basis.)

Please try to minimise any mathematical equations in your answers since I’m a bit rusty on my math.

Short answer: Yes.
Maximum speed is correlated with wing loading. A high wing loading shifts all speeds up. A flying wing will always have a lower wing loading in comparison to a conventional design when payload, range and landing speed of both are identical. So you will start at a disadvantage.
Due to the high lever arm of the conventional tail, the conventional configuration can use high-lift devices (or highly cambered airfoils) for a much higher maximum lift coefficient than what is possible in regular low-pitching-moment airfoils. This allows to keep the wing small for the same landing speed. Unfortunately, the flying wing is restricted to those low camber or even reflex airfoils because its surfaces for creating a pitch balance have a small lever arm and, consequently, a poor moment-to-lift ratio.
The design of the Prandtl wing leads to a bit of downforce at the tips when in normal flight in order to lower the wing's root bending moment. But only a bit. Sweep places this downforce in the aft region of the wing so the inner, more forward region has to create all the lift for carrying its own weight, the payload and, of course, compensate for that downforce, too. Since the low wing bending moment will allow for a light wing, the total lift requirement is rather low, too, but still encumbered by the aforementioned loads.
Now to the maximum speed: A flying wing will allow for very low drag coefficients. There are no intersections between parts and no tailboom which adds friction drag, so for a given wing loading a flying wing will allow to reach high speeds with limited power. However, the lower wing area of the conventional design with the same landing speed has less wetted area and so can easily accommodate that tailboom drag. Once the details like part intersections are well designed, the conventional design should come out ahead.
What you need to watch out at high speed is flutter: That wide, light, swept wing will start to flutter much earlier (at lower speeds) than the rigid, strong, small, straight conventional wing. With sweepback you will encounter a speciality of flying wings, a coupling between the short period mode and the wing bending eigenfrequency. Since the short period mode frequency goes up with speed and the bending eigenfrequency is constant over speed, flying fast will bring both together and require a stiff wing in order to shift that point up. Don't forget that pitch damping of flying wings is an order of magnitude lower than that of conventional designs, so the short period mode will show up in a Prandtl wing if you go fast enough.


What is the regular stall speed of an F-16 flying in a straight-and-level path? I want to know what is the minimum speed that an F-16 can fly at without stalling.
I have searched the web, but found no exact information answering my question.
Most of them say that it depends on many factors, like payload and maneuvering. But, for simplicity, I want to know the stall speed of that plane flying in a straight path at a constant altitude.

If there is no exact answer, I want to know the regular stall speed, just an average value of that speed, for a clean F-16A weighing 18,000 kg flying in a straight & level path.

I don't have exact data either, but we can easily make an estimate with data from Wikipedia. Note that I explicitly neglect high-lift devices which are present on the F-16 (notably the strakes which generate significant vortex lift), the variable angle of incidence (washout), as well as body lift which probably plays a significant role as well.

I estimate the aircraft weight to be around $150\,\mathrm{kN}$. The wing area is approximately $28\,\mathrm{m}^2$, and the NACA 64A204 airfoil used has a max $C_L$ of 0.8. Fill that in the lift equation $$L=\frac{1}{2}C_L\rho v^2$$

we get a speed of about $100\,\mathrm{m/s}$ which is about 200kts.

At the angle of attack of max $C_L$, the L/D is about 10, so the engine has to deliver $15\,\mathrm{kN}$ of thrust to maintain level flight. This angle of attack is approximately 6 degrees, and due to the probably positive angle of incidence between the fuselage and wings, the thrust angle is likely less than 6 degrees w.r.t. the horizon. This means that the vertical component of thrust is about $\sin(6°)\approx 0.1$ times smaller, or $1.5\,kN$. Given the error bars on my estimates (especially the aircraft weight), this does not warrant a recalculation because most of the weight is indeed carried by the wings.


When did airlines start using seat belts for passengers? When did airlines start using seat belts on passenger flights?

The world's first airline used Zeppelins, and there was no need for seatbelts.

In WW I seatbelts were standard issue for pilots, at least in Germany.

After the war, the airlines used seatbelts irregularly. Below are two pictures of the cabin of the Junkers F-13, the first all-metal passenger aircraft, which was first operated in 1919.

Junkers F-13 cabin, front view (picture source)

Junkers F-13 cabin, rear view (picture source)

While the belts on the front seats are clearly visible, the rear seats seem not to have them. If the picture date (Oct. 10, 1919) is to be trusted, they were used right from the start in 1919. The way they are fixed to the wicker seats, however, looks rather flimsy and will not give much protection in a crash.


What happens if I am flying at a higher Lift/Drag ratio than required? I created for me a table from an aircraft for Mach=0.8 for alpha= 0° to 8°
Actually, I an alpha of alpha=4° should be sufficient, so that my lift coefficient is enough, to counterbalance the weight in steady horizontal flight. The corresponding lift/drag ratio is 8.
I could now choose also alpha=8° , with a lift/drag ratio of 12.
My question: regarding the range equation(breguet) it is better to have a higher lift-drag ratio for making more range.
But I am wondering: if I choose alpha=8° my lift coefficient is greater than the one I need, so in the end, my aircraft will climb ? This would not be a steady horizontal flight.
Am I right?

If your optimal lift coefficient for long range cruise flight is greater than what you need, you are flying too fast, or too low.
For cruise flight, your lift needs to equal the weight, otherwise the aircraft will accelerate upwards (in the body frame of reference).
If you know the lift coefficient that is optimal for cruise, you need to adjust the airspeed and density (altitude) to make sure that the resulting lift equals the weight.
$W = L = \frac{1}{2}\rho V^2 C_L S $
$\rho V^2 = \frac{2 W}{C_LS}$
Reduce speed and/or increase altitude until the lift and weight are equal at the optimal lift coefficient. That will give you the maximum range.


Why does the US President fly in an obsolete 747-200? The Boeing VC-25A ("Air Force One") is a heavily modified 747-200. The two current airframes (SAM 28000 and 29000) were put into duty in 1990 and are slated to be replaced in 2017, although I suspect that latter date is optimistic.

These two 747-200s are among the last remaining 747-200s in service. I suspect that they are the best-maintained 747-200s in the world and they have considerable sunk costs in their custom rigging, but even when the aircraft were put in service in 1990 their model had already been replaced by the 747-300 (1982) and 747-400 (1989).

Why hasn't the VC-25A been replaced to keep up with the times? A 747-400 airframe is lighter, faster, and bigger (let alone a 747-8). These would all seem to be suitable features for what is most probably the most important aircraft in the USAF fleet. Is there some attribute of the 747-200 that makes it particularly well-suited for this role despite its obsolescence in the market?

The 747-200 derivatives used for transporting the President of the United States are VC-25's operated and maintained by the United States Air Force. The US Air Force tends to keep planes for a long time, as they still operate 707 and B-52 aircraft twice as old as these 747's. The E-4 aircraft, also based on the 747-200, have been in service for 40 years. The reasons for keeping the VC-25 aircraft flying are similar to these other examples.

A lot of work went into the VC-25 aircraft. They have been modified to add aerial refueling capability, defensive mechanisms, and include extensive additional electronic equipment for communications. Installing the special interiors was also a major task. As with a bomber or AWACS, there is a large initial investment in development to design the systems and build the aircraft. Upgrading components and providing proper maintenance allows these aircraft to perform their missions long after their entry into service.

Another difference is the engines. The 747-200B model has GE CF6-50E2 engines producing 52,500 lbf thrust each. The VC-25 aircraft have newer CF6-80C2B1 engines producing 56,700 lbf thrust each, which is the same engine as the 747-300. Newer engines go a long way towards improved performance.

As DeltaLima notes, these aircraft do not spend nearly as much time in the air as commercial aircraft. Yet there are many commercial aircraft in service with similar or greater age, including some 747-200 aircraft.


What is the significance of a squawk code? I've been looking for a detailed explanation for how the transponder works and the importance of a squawk code.

The squawk code is assigned by Air Traffic Control to the aircraft and is used for radar identification purposes. It is a 4 digit octal number (each digit has a value in the range [0-7]).

The flight crew enters the assigned squawk code into the transponder control panel and the radar extracts the code using a Mode-A interrogation (or UF5 / UF21 interrogation in case of a Mode S radar/ transponder).

The extracted squawk code can then be used to correlate the radar reply with an aircraft's flight plan. A number of squawk codes are reserved for generic purposes and emergencies. These codes are used in emergency, or when no flight plan correlation is needed. Some generic codes are:

1000 - Conspicuity code signalling the Flight Data Processing system to use Mode-S Aircraft ID for flight plan correlation. (Primarily in Europe)
1200 - Visual Flight Rules standard squawk code (USA & Canada)
2000 - Used when entering a Secondary Surveillance Area and no code has yet been assigned.
7000 - Visual Flight Rules standard squawk code (ICAO, USA & Canada use
1200 instead)
7500 - Unlawful interference / hijack (ICAO, worldwide)
7600 - Radio communication lost (ICAO, worldwide)
7700 - General emergency (ICAO, worldwide)


Why are planes flying in a zigzag path over Long Island when approaching JFK? Every time I've flown into JFK Airport from the east I've noticed that the plane takes a weird zigzag path over Long Island. Why is this? Is it because of noise laws?

There are 3 STARs (Standard Terminal Arrival Routes) into JFK that cross over Long Island:

PARCH 3 RNAV ARR:

PAWLING 2 ARR:

ROBER 2 ARR:

(Jeppesen charts)

None of these have particularly pronounced zigzag patterns, so what you describe is probably not coming from the waypoints of the arrival procedure.

Looking at flightradar24.com, we can currently see BAW1 approaching JFK:

This already looks a bit more like a zigzag. It would seem they are arriving on the PARCH3 or ROBER2 until ROBER and then received radar vectors onto final approach for runway 31L/R. These vectors are typically given by ATC (Air Traffic Control) for spacing reasons.

When going back to yesterday evening using flightradar24's Playback feature, one finds much more pronounced turns over Long Island (thanks to ymb1 for suggesting this):

Here, aircraft are approaching runways 22L/R. You can see that there are also aircraft from the South and West joining the queue to land and ATC needs to make sure there is enough separation between the aircraft. The easiest way to achieve this is by instructing them to fly in a certain direction ("radar vectors") until there is enough space to fit them into the queue, which results in such a zigzag pattern.

Such turns can also be more localized than shown here. See e.g. Why did my LGA-ORD flight make an S-shaped turn round the time it was passing a storm?, where a flight into Chicago made an S-shaped turn during the descent, which would also feel like a zigzag. Such instructions can also be given to aircraft while they are still flying on the STAR over Long Island, especially when there is a lot of traffic during peak hours.


Why aren't grid fins used as wings for low speed aircraft? Grid fins are used "commonly" in aerospace - usually for things like control of guided bombs or spacecraft. The most obvious example is SpaceX's use on the Falcon 9, but the US and Russian militaries have been using them for decades.
My understanding is that there's a tradeoff with grid fins. They offer greater control authority (and/or lift) in a more compact space, and require less torque to turn/reposition than the equivalent wing would. The downside is that they have a lot more drag, and are almost useless at trans-sonic speeds.
My question is: Why aren't they used as wings (to produce lift) on low-speed aircraft and RC drones? I was unable to find any examples of grid fins being used as wings or lifting surfaces. It seems like if it were possible to create more lift in less space someone would have used it in a design. Am I missing something obvious here? I'm guessing yes. :)

No, not as/on aircraft, and there are good reasons.  They're useful elsewhere, and should make good kites.
Prototype multiplanes flew, quadruplanes reached production, triplanes served operationally in WWI, and biplanes were retired from almost all uses (military and civilian) by early WWII. The biplanes that still fly for purposes other than display are used for low-speed work.
As speeds increase - and we almost always want to get people and goods somewhere quickly - the power lost to drag increases dramatically, in proportion to the cube of the airspeed.  Any construction that increases drag is going to limit speed, payload, range or probably all of them for a given engine power. Biplanes (and to an even greater extent multiplanes) are inefficient at lifting because of the interference between the airflow over the lower wing and under the upper - now squeeze the wings closer together so you can fit more, and this gets worse.
The surfaces (or struts/wires) perpendicular to the lifting surfaces, making up the grid fin or the bracing of a multiplane don't contribute lift but do contribute drag.
Grid fins are sometimes useful: they're compact, more so if the aspect ratio means they can be stowed as by SpaceX and on missiles/glide bombs.  SpaceX use the grid fins in landing, where drag isn't a downside so long as it doesn't cause too much heating.


Wind tunnel- test section design question? 1)Why test section room is so so big,is this because to reduce interfrence  between test object and walls?
2)Is test section room open to outside atmopsheric pressure or must be  100% air proof?
3)How they achieve clean airflow where test object stay if test section room is much wider than nozzle and collector,isnt air mixing with air jet?

An open jet wind tunnel has the advantage of giving a smaller effective blockage ratio than a closed jet wind tunnel. Because the jet is not constrained by walls around the jet in the test section, the airflow can distort more than a closed jet wind tunnel - giving the same flow results as a larger closed jet tunnel.
There are however disadvantages with the open jet tunnel, such as the effect of the collector on the flow (this creates a longitudinal pressure differential referred to as "buoyancy"), and the effect of the shear layer that forms at the jet nozzle (the Kelvin Helmholtz instability can create transient flow effects and can be a noise source). When standing in the test section of a running tunnel, there is a lot of secondary airflow outside of the jet because of the open section.
The test section does not need to have a pressure different to atmospheric pressure, and does not need to be sealed. There can be vents in the test or return section of the tunnel, but they may create flow disturbances as well as allowing noise into the test section.
The free shear flow around the edge of the jet can be a source of disturbance for flow in the test section, however tunnels are designed so the disturbance is still far away from the model. Of course there are pressure fluctuations that interact with flow over the model, which are difficult to control. Some wind tunnels are designed with adaptive and slotted walls, which combine the benefits of open/closed sections, however they need much more setup than just putting a model in and turning on the fans.


Do any aircraft carry spare parts for making repairs? I was curious to know, are there (or were there) any aircraft that regularly carry spare parts to be used for replacement or repairing the aircraft itself? If so, what are those spare parts?

I'm not talking about built-in redundant systems like a second radio, but rather actual physical spare parts. For example, a car carries a spare tyre.

South African Airways flights to 'less developed' locations in Africa often carry a mechanic and some spares on board. If there are no suitable repair facilities, supplies or maintenance personnel available at the destination, then their own guy can fix any minor mechanical issues. If there's a major problem then they would have to fly in additional repair supplies and staff (and fly out the stranded passengers).

I found this out on a flight from Johannesberg to Lilongwe (Malawi). A seat was broken in the passenger cabin and SAA's on-board mechanic was able to fix it after a short delay. The captain explained briefly why he was on board.

I assume that other airlines or operators who operate in undeveloped areas would do the same. It's a lot cheaper to carry a mechanic and a few spares than it is to have an aircraft, crew and passengers stranded. If anything on the MEL is broken then an airliner isn't airworthy so even a 'minor' issue can ground it.

I guess that the military might do the same for similar reasons, but I have no idea at all about that.


What changes do narrow-body airliners undergo to serve (relatively) long routes? I will try to pose a well-structured question here on the longest routes ever or currently served by small, narrow-body airliners - specifically, the Boeing 737 and the Airbus A319 and A320.

Set aside special versions in the likes of the Boeing 737-700BBJ, what makes a small, narrow-body airliner serve routes that are longer than those on which it is usually deployed?

Which is to say, what is added or changed, on the design side of things, to the structure or operability of planes that are not specifically designed for long distances, to make them capable of flying longer distances? I guess the answer is ETOPS, but I am not sure of what this implies from the operational standpoint.

For my moderate understanding it is quite impressive that narrow-body birds can fly from, say, Tokyo Narita to Mumbai - a distance of approximately 6,800 km or 4,220 mi (All Nippon Airways Boeing 737-700ER, flight NH829). Another example is Sunwing Airlines flight WG481 from Vancouver to Punta Cana (a Boeing 737-800 which flew for 5,930 km or 3,690 mi).

A list of such unusual performances can be seen here.

The 737 ER (Extended Range) differs from the rest of its family by having an extra fuel tank extending its effective range.

Legally speaking (for US registered aircraft) you don't need to carry life preservers for each passenger, if you are only flying over land routes. So if a plane is being used for say a JFK $\rightarrow$ Nashville route, they would not be required to carry life preservers; but if they decided to use the plane on an over water route, they would have to outfit it as such.

Inter-Country travel may also effect the outfitting of a plane, as various countries have different equipment requirements (although most are the same now). Long haul routes may very well translate to non domestic routes, which means the plane may need to be outfitted with extra equipment that is capable of working on foreign systems.

There may be some paperwork involved around certifications as well. For example the FCC does not require domestically operated aircraft (commercial and GA) to have radio station licenses; however, it's often required by many foreign entities. A domestic only plane may need to obtain one of these licenses before heading to is destination.

On a bit of a side note the pilot must also be familiar with the destinations' regulations and methods of operation. For example here is a nice briefing from the FAA on flying into China.


Why are the 737's variable-speed generator drives so unreliable? The 737 Classic has two different possible styles of engine-driven generators, distinguished by the generator's drive mechanism: the constant-speed drive (CSD) and the variable-speed constant-frequency drive (VSCF).
The original VSCF drives were very unreliable, failing roughly three times as often as the constant-speed drives.  A 2001 modification programme by Boeing and the generator manufacturer improved this somewhat, but the generator drives remained unreliable enough for VSCF-equipped 737s, even those with modified drive units, to be subject to stricter limitations than other 737s (the United Kingdom's CAA requires them to remain within 45 minutes' flight time of a suitable airport, even if only one of the generators is VSCF-driven and the other has the reliable constant-speed drive; I don't have information on whether other regulatory authorities have similar limitations for VSCF-equipped 737s).
Why are the 737's variable-speed constant-frequency generator drives so much less reliable than the same aircraft's constant-speed drives?

@Jpe61 is correct in his comment that it's likely an electronics issue, since indeed a VSCF is mechanically simpler.
VSCF is also used on the MD-90, with poor initial reliability[1] – MDC went back to IDGs for the MD-95 (717).[1] It's also used on the 777 (only for backup, also with poor initial reliability[2]), and on the F/A-18.[3]
Capacitors
The F/A-18 utilizes cycloconverters, while the aforementioned civilian applications utilize DC-links (possibly the voltage-source inverter type based on this patent by Sundstrand, the makers of the 737 unit).[3]

... when electrolytic capacitors are used, in the case of a voltage DC-link, there is potentially a reduced system lifetime (Wikipedia: AC-to-AC converter § DC link converters).

More here: Wikipedia: Electrolytic capacitor § Operational characteristics
Your link says "the failure rate was just over 1 every 2,000 hrs". The 2,000 hours match the lifetime graphs in the article linked above (shown below). This being the culprit is supported by a paper on aircraft power generation:

The VSCF systems, apart for some noteworthy exception previously mentioned [referring to the F/A-18 and F-117A], did not get the same level of diffusion of IDG systems. This can be safely attributed to the role played by the PEC [Power Electronics Converter] (either ac/dc or ac/ac), which processes all the generated power and represents a single point of failure. Therefore, the PEC needs to be designed for the full-power rating and with high reliability requirements.[4] [emphasis added]

High load and cooling
Once you lose a generator, say running at 0.35 load, the other needs to pick up the slack and run at 0.7 load. The CAA's imposed limitation despite the redundancy tells us they don't trust the VSCF at high loads.

Source: airliners.net

One feature on the MD-90 is the air scoop for cooling the VSCF components. The more electronics are used, the more intricate cooling is needed (you can't just dip them in engine oil).
Maintenance practices
There's an official Honeywell video on installing the MD-90's VSCF with hints at improper maintenance practices, which would be a headache for an airline since the system is very niche with different tolerances.
Summary
So whether it's a 737 or an MD-90, the issues seem to be:

Cooling
Capacitors
Maintenance practices

Note that the technology hasn't become obsolete, at least academically: a 2017 paper proposes a "novel DC-Link VSCF AC-DC-AC" for the Embraer 190/195, from which:

Problems existed with the older VSCF systems in the past; however, the switched power electronics and digital controllers have matured and can be now, in our opinion, safely integrated and replace existing constant-speed hydraulic transmissions powering CSCF AC generators.

1: Douglas Jetliners, Guy Norris and Mark Wagner, page 85
2: Boeing tackles 777 power problems, 18 August 1999, flightglobal.com
3: Control of Power Electronic Converters and Systems, Volume 2, page 341
4: Madonna, Vincenzo, Paolo Giangrande, and Michael Galea. "Electrical power generation in aircraft: Review, challenges, and opportunities." IEEE Transactions on Transportation Electrification 4.3 (2018): 646-659.


What does it cost to get a hot air balloon to 30,000ft? I'm interested to know what it would take to get a hot air balloon, with a 600lb load, to 30,000 feet. Is this cheaper than flying a plane with a similar load to the same altitude?

If a special balloon is needed, what is the cost of that balloon compared to the typical recreational hot air balloon? What is the quantity and cost of fuel necessary to make it to that altitude, and hover for a few minutes prior to descending?

A Hot Air Balloon should be able to reach 30,000 ft just fine as according to Wikipedia the world record altitude for Hot Air Balloons is 69,852 ft.  Besides the necessary survival gear for the occupants (Pressurized oxygen and environment suits) a special propane tank would be needed as according to wikipedia:

  However, if the liquid propane in the fuel tanks is too cold (0 °C/32 °F or less) it does not generate sufficient vapor pressure to adequately feed the burner(s). This can be overcome by charging the fuel tanks with inert gas such as nitrogen or by warming them, with electric heat tapes for example, and insulating them against the cold.

Another thing to consider is that you would need special permission from the FAA to go into Class A airspace which goes from 18,000 to 60,000 feet MSL. Usually only IFR rated aircraft can fly in this airspace.  The FAA may require you to fly with a radio and/or transponder if you do get the permission to fly in this airspace.

I do not know how much propane would be required as I don't fly Hot Air Ballons but it would probably depend on the outside air temperature (less fuel in colder air).


How a customer could choose "A330-Neo" or "A350 Regional" on shorter routes? According to Wikipedia, Airbus is studying a new A350 Regional that effectively is a think that I suggested some time ago when I asked "Why is the A330neo more efficient than the A350 on shorter routes".

In that question I said:

  why for shorter routes A330neo is more efficient than A350? Could not
  be enough to have an 350 with lower fuel capacity (in case shorter
  length) and maybe reduced engine power (the opposite of higher power
  in A350-1000) thanks to reduced weight?

Now, it seems that with this model Airbus is creating a more evident overlap in its proposal to market for shorter routes because, as written in A330neo Wikipedia page, is written:

  A330neo enables profitability on shorter ranges where the longer-range A350 and Boeing 787 aren't optimized.

So what reasons could push a customer to choose to A330-Neo or A350 Regional on shorter routes?

This probably just boils down to the economics of the route. An aircraft for a route is chosen based on more factors than just fuel efficiency. Airlines have to weigh in other factors like:

Number of landing/take-off slots available at the airport

This is because an airport can only support so much traffic. It may be more economic to fly a larger aircraft with more seats than multiple flights.

Cost of gates/landing fees, etc

Airports make money by charging per-passenger and per-aircraft fees. If an aircraft is parked at a gate, it is costing the operator to be there, so the more aircraft the more expensive it gets. Airports may charge depending on the size of the aircraft as well.

If the airport is equipped to handle an aircraft of that size. Some regional airports can't handle larger aircraft (either from a gate/facility perspective or a runway/taxiway surface one).
How many passengers need to travel that route on a daily/weekly basis
Regional fuel costs
Training/currency requirements for pilots and how easy it is to move between them

If going from the A320 to the A330 is a simple course vs the A350 being a whole new endorsement, they may choose the A330 to be able to have higher utilization of the existing pilots vs having specialized crew.

Same as above except substitute mechanics, spare parts, etc. This is a major reason that Southwest only fly's 737's, short or long-haul.
Ability for the aircraft to service other routes.

All said and done they need to pick the aircraft that is the most economic for the intended mission and fits into the business model of the company more. Airbus isn't going to take a customer that wants the A330 and push them into an A350, it isn't like buying a car where the salesman upsells you, the customer by the time they approach Airbus for a purchase contract already knows exactly what they need. Think of it more like buying tools (where you need exactly the right tool for the job) than it is about buying a car (the Corvette is nice, but have you looked at the Prius?)...


FIS-B Product Registry Location I'm a software engineer that's interested in decoding raw FIS-B data. DO-267A (E.1) points me at http://fpr.tc.faa.gov/default.asp as the location of the FIS-B Product Registry. However, I have been unable to connect to this website the last 2 days. Does anyone know if this is still the correct site? Is the data hosted anywhere else?

I have been unable to determine if the Product Registry has been formally relocated or replaced. However, I was able to find all of the relevant information in DO-358A. It wouldn't surprise me if this has become the de facto Product Registry, replacing the FAA website.


Could some one explain me with the mathematical relations on how the double bubble fuselage cross section (example A380) is designed. Could some one explain me with the mathematical relations on how the double bubble fuselage cross section (example A380) is designed.

A380 actually has an elliptical cross section, not double bubble. 'Double bubble' fuselage cross sections (also called double lobe) are usually used in case of aircraft which require specific arrangements for carrying passengers/cargo and in which case using a circular or elliptical fuselage would result in a large wastage of space or because this type of arrangement is cheaper to make. Another reason for this appearance is that some aircraft were extensively modified (for reasons other than the original intentions) resulting in this shape.

The double lobe fuselage aims to reduce the wasted space by having fuselage in two intersecting circles, joined together at the floor. The (relative) size of the circles is determined by the requirements. A good example is the Boeing C-97 Stratofreighter, which was a military transport based on B-29 Superfortress.

Boeing notes:

  ... it had a double-lobe fuselage consisting of two intersecting circular sections, so that the 74-foot-long (23-meter-long) upper deck had a larger diameter.

Image from Boeing.com

The civilian counterpart of the C-97, the Boeing 377 Stratocruiser inherited this shape having a double lobed structure, with 100 passengers on the main deck plus 14 in the lower deck lounge.

Boeing 377 Stratocruiser fuselage cross section; image from tdpri.com

These aircraft were later modified to carry oversized aircraft parts as the Pregnant Guppy, Super Guppy and Mini Guppy, all having the distinctive double lobed design.

Note that most of the double bubble aircraft are for carrying cargo. Contemporary aircraft with a similar arrangement include the Airbus Beluga which again are used for transporting oversized aircraft parts.

Airbus beluga, image from australianaviation.com.au

The Beluga is an example of how specialized requirements required this design. This aircraft was designed because none of the available large transports had enough space to transport the required sub-assemblies. Designing and building a new aircraft for carrying these sub-assemblies (including fuselage sections) would have been prohibitive (only five were made); so Airbus modified an existing aircraft according to requirements.

Another aircraft that acquired this shape as a result of modifications was the Hawker Siddeley Nimrod, which had this shape due the addition of a bottom section to the De Havilland Comet. The lower section had the radar, bomb bay etc, while the upper section had the crew.

Quite a few airliners have utilized this shape in the past, though the shape is not as pronounced. Airline manufacturers, from Boeing to Douglas used them as they are efficient in using space. For example, the Boeing 707 fuselage cross section below shows this design.

707 fuselage cross section; image from forum.justflight.com

Also, as I noted before, the A380 has an elliptical cross section, not double bubble.


Light Plane: Transition to Right-Seat Flying: How to Prepare, What are Common Errors? I'm preparing to start my CFI training and have almost exclusively logged all my time from the left seat of a Cessna 172 or 182. Is there a standard training program to transition to flying from the right seat? If not, how do people generally prepare, in an effort to make this less opinion-based, what are some common errors that pilots might make when learning to fly from the right seat?

Related: Is an approval required to fly from the right seat?

First, congratulations!  Earning a CFI certificate is a real undertaking.

For a literal textbook answer to your question I suggest opening this PTS pdf (assuming FAA CFI) and searching for "common errors" until you find yourself in relevant (to you) sections.  There are many examples.

On a personal note, I found that talking through every action made maneuvers go smoothly and let the instructor/examiner know that what I was doing is intentional.  It also forced me to follow my own directions so, since I knew what was supposed to happen, I just said it aloud and then did it.  It sounds silly but it worked well.

The transition to right seat flying is simple.  You'll have it down in an hour or two.  Nothing to it.  It's actually kind of anticlimactic.  Which plane are you using?


What is the reference plane for the ILS glideslope angle? Is a 3-degree glideslope based from the runway surface slope at the point where the antenna is installed or is it referenced to a zero-degree plane?

If you know of a design document or FAR/AIM reference, please include that as well.

It is referenced to the zero-degree plane, and depending on obstacle clearance it may be a little steeper (3.5° or 4°). There is no reason to refer it to the runway slope as it defines a sink rate to speed ratio during final approach.


On a modern Aircraft like the A320 or B737, is it possible to disable computer interference with the control inputs of the pilots? One more question due to the recent and unfortunate events in the case of the second ever B737 Max 8 crash.

As far as I know, the first of the two crashes was caused by the MCAS System, that overwrite the inputs of the pilots as a faulty reading of an angle of attack sensor indicated a stall (that was not actually happening).

Knowing (rather, having an idea of) what a difficult time pilots have in such situations I wonder if it is at all possible to stop the aircraft from executing such maneuvers.

I know that on an Airbus A320, there is different flight laws. While during "Normal Law" all the various protections the A320 has are active (Stall protection, overspeed protection, bank protection with all their proper names and so on), they are not active in "Direct Law". There are two more levels between "Normal" and "Direct" (namely "Alternate" and "Abnormal Alternate"), but let's ignore them for this question.

I have never flown an A320 in real life and lack the training any A320 pilot goes through, but in the Simulators I have flown (not talking FSX here!) you could "exit" out of "Normal Law" by turning off the flight computers on the overhead, like the ELAC, FAC and SEC, and go into alternate or even "Direct Law".

So the question is: is this actually possible on a real A320 as well? And is there a similar method on a B737 (Max 8)?

For A320 it is possible also in the real aircraft. The problem with disabling flight control computers is that it also disables associated control surfaces. If you disable all five computers, you disable all surfaces and the aircraft goes in to "Mechanical backup" mode, which leaves pilot only the control of the trimmable horizontal stabilizer (ie. pitch trim) and rudder. Wide bodies are similar, although they have more redundant flight control computer architecture.

The correct procedure to override normal law in Airbuses is to switch two ADRs off, which forces controls to alternate law. This disables most of the protections leaving only load factor protection. All control surfaces would still be operating with automatic pitch trim. This would be used only in undue protection activation.


What does Airbus means by long product cycles? I was reading this article. The article was about issues that Airbus may face if the UK does a 'Hard Brexit'.  At the very end of the Article though, Airbus says

  Airbus makes wings for all its jetliners in the UK. The France-based
  company campaigned against Britain leaving the EU ahead of the UK
  vote, but has said it would not make abrupt changes to its operations
  there due to long product cycles. - foxbusiness.com

Can anybody elaborate what the company means by long product cycles?

A long product cycle means that the lifecycle of a product spans a long time. Aircraft models are often produced for more than 30 years (the 737 and 747 are now approximately 50 years in production).

At the same time, the capital expenses to build a production line are enormous. And in starting up a production line there are always teething troubles which take time and money to iron out. Therefore it would be a waste of capital to move a production line from the UK to mainland EU.

That only is viable when a new aircraft model is introduced and an old model is phased out. New models don't appear every year and it seems that most of the current models are still selling well so unless there will be a huge cost associated with keeping the production line in the UK (e.g. taxes, increasing labour cost, unfavourable exchange rate) no changes are to be expected soon.


How to replace two propellers on the same aircraft reaching the time limit? When both propellers of the aircraft reach the time limit (60 month) and need to be replaced, can both propellers be replaced at the same time and perform only one flight test to reduce time on ground or should they be replaced one at a time just for safety or to investigate any discrepancy that may arise?

Since replacing a propeller with the same propeller that is in the Type Certificate is not a major repair, the FAR(s) (CFR Title 14) that most apply are 43.7 and (assuming the airplane is under Part 91) 91.407.

43.7 states:

  (a) Each person performing maintenance, alteration, or preventive maintenance on an aircraft, engine, propeller, or appliance shall use the methods, techniques, and practices prescribed in the current manufacturer's maintenance manual or Instructions for Continued Airworthiness prepared by its manufacturer, or other methods, techniques, and practices acceptable to the Administrator, except as noted in §43.16. He shall use the tools, equipment, and test apparatus necessary to assure completion of the work in accordance with accepted industry practices. If special equipment or test apparatus is recommended by the manufacturer involved, he must use that equipment or apparatus or its equivalent acceptable to the Administrator.

  (b) Each person maintaining or altering, or performing preventive maintenance, shall do that work in such a manner and use materials of such a quality, that the condition of the aircraft, airframe, aircraft engine, propeller, or appliance worked on will be at least equal to its original or properly altered condition (with regard to aerodynamic function, structural strength, resistance to vibration and deterioration, and other qualities affecting airworthiness).

So you must follow the maintenance manual and put the airplane back in a state at least as good as original. If you think that putting them both on does not qualify to satisfy this requirement, then you should do them one at a time. If it does satisfy this, then in that case, 91.407 comes into play, which states:

  (a) No person may operate any aircraft that has undergone maintenance, preventive maintenance, rebuilding, or alteration unless—

    (1) It has been approved for return to service by a person authorized under §43.7 of this chapter; and

    (2) The maintenance record entry required by §43.9 or §43.11, as applicable, of this chapter has been made.

  (b) No person may carry any person (other than crewmembers) in an aircraft that has been maintained, rebuilt, or altered in a manner that may have appreciably changed its flight characteristics or substantially affected its operation in flight until an appropriately rated pilot with at least a private pilot certificate flies the aircraft, makes an operational check of the maintenance performed or alteration made, and logs the flight in the aircraft records.

  (c) The aircraft does not have to be flown as required by paragraph (b) of this section if, prior to flight, ground tests, inspection, or both show conclusively that the maintenance, preventive maintenance, rebuilding, or alteration has not appreciably changed the flight characteristics or substantially affected the flight operation of the aircraft.

I would argue that a propeller change cannot be satisfied by (c) above and does require a flight test. However, there is nothing that requires separate flight tests UNLESS the maintenance manual requires it, in which case part 43.7(a) from above comes into play. But as a "fail safe" a good run-up on the ground at high throttle with the brakes applied, followed by an inspection of the work can give good confidence in the work prior to the flight test.


How to navigate onto VOR RWY 18 approach at KDEC? Maybe a dumb question.  I've seen a few places where a VOR approach doesn't have an obvious (to me) way to get lined up inbound without radar vectors.
Say you don't have GPS and you're navigating with VORs.  You'd like to do the VOR RWY 18 approach to KDEC, and you're coming from somewhere north of the AXC VOR the approach is based on, like the BMI VOR for example.  How would you get yourself established on this approach without radar help?
It seems reasonable to me to fly (off-airway) R-180 outbound from BMI and intercept the approach course of R-349 inbound to AXC.  However I'd heard (though don't have any regs to back it up yet) you can only transition from enroute to an approach based on a fix that appears on both charts.  So I suppose you can't essentially vector yourself this way with the off-airway R-180.  Is this true?  If so, I'd be super grateful for a FAR/AIM reference if you know it!
So then what fix appears on both the enroute chart and the approach plate?  Only AXC is on both.  But if you fly directly to AXC from BMI then you're facing the wrong direction.  You'd be incoming on roughly R-352 and then need to turn around and fly outbound on R-349.  A HILPT would be just the thing on an approach, but here we wouldn't be on an actual approach yet and I haven't heard of them being used outside approaches.  Would you do a HILPT at that depicted hold, or just hang a uey here, or is neither really right?
As I said, maybe a dumb question, but it's stumping me.  Thanks for the help!

I would expect to receive radar vectors to final if I was coming from the north into Decatur, IL.   However, we do not plan on radar vectors when we flight plan because we could lose our ability to communicate with ATC.
I would fly the victor airways to AXC.  I might plan on coming in on the 029 radial (V191) to AXC.  I am hoping for a clearance for the approach by the time I get to AXC.  When I hit AXC, I would them make a right turn and proceed outbound on the 349 radial on the approach plate.
With a proper clearance, I would maintain my cleared altitude till TRACS and then descend to 3100 FT and finish the approach using the procedure turn to line up with the runway.
You are more than welcome to fly off routes provided you remain within the service volume of the navaid you are using.  For AXC the service volume is from 1000' AGL to 40NM (for low altitude flight).  There are no restrictions to the service volume in the Chart Supplements.  If you are going to do this (and ATC clears you), you will fly the OROCA as a minimum altitude.  The off-route obstacle clearance altitude (OROCA) for this quadrangle is 3200 FT MSL.  You could file BLM direct AXC and only be one degree off the final approach course.  (See AIM 5-4-7(f))
However, you are still required to cross an IAF before you start the approach.  You will fly over AXC and then turn around to fly the procedure turn... you cannot just cross TRACS and descend for the landing.
A procedure turn is always required if it is depicted on the chart with four exceptions (AIM 5-4-9)

Receiving radar vectors to final approach course
On a route marked "NoPT" on the approach plate
Received a clearance for a straight-in apporach from ATC
Performing a timed apporach


How can true altitude be calculated from pressure altitude, temperature and altimeter setting? The manual that came with my Jeppensen E6B has the following sample...

  If an aircraft is flying at 12,500 feet with an outside air
  temperature of -20C and the altimeter is set on 30.42 inches of
  mercury, what is the true altitude?

The explanation goes on to find a pressure altitude of 12,000 feet.  After placing -20C over 12,000 we find 12,500 (12.5) on the B scale and read the true altitude of 12,000 (12.0) on the outer ring.

Looking closely at the outer ring, I see that the true altitude is actually just slightly below 12,000.  Now for practical purposes I realize we don't worry about differences like this and round the result.  But I'm working on a project in which I need to calculate the true altitude precisely.  I'm having a difficult time finding the formula.  The closest thing I have found says the correction is 4 feet per thousand feet indicated per degree off of ISA.

When I attempt to apply that formula to our sample problem I get 4 * 12.5 * -35 = -1750.   Applying that correction gives a value far below expected so obviously I'm doing something wrong.  Can someone straighten me out here?  References to documentation with educational value are especially welcome.

I would think the OAT in the example is what your on-board thermometer is showing, so at 12,500 ft, not at sea level. ISA is +15°C at sea level, but at 12,500 ft it is -9.8°C, so you are just -10 off ISA. Let's see. 4 ⋅ 12.5 ⋅ (−10) = −500, so the formulas match.

Note though, that this is still just an approximation. The temperature lapse rate might also differ and that would have to be taken into account as well. The more precise equation is also nonlinear.


Why does idling RPM increase with altitude in a jet engine? The Snecma-Larzac 04-C6 idling RPM ranges from approximately 53% on the ground to 85% at high altitude. Why is that?

For one there is less resistance to the fan and compressor due to the decreased air density -> more rpm out of the given power. On the other hand, the mass flow needs to be high enough to sustain the operation of the engine -> both lead to a higher rpm...


Why is the Tu-144 the only commercial airplane with canard configuration? I understand the delta wing was chosen because of the supersonic cruise (like the Concorde), and canards were added to reduce the approach/landing speed. But canards may be used without delta wing (e.g. Focke Wulf F-19, Soukhoï Su-47, Rutan Voyager,...), so I don't understand why the canard wing configuration is not used among commercial aircraft.

Short answer: Canards make most sense with negative static stability and high maneuverability. Commercial aircraft don't need either, so a conventional layout works best.

For a statically stable aircraft, the conventional layout gives most efficiency with sufficient damping. Static stability requires that the forward lifting surfaces create more lift proportionally to their size than the rear surfaces. Here is an answer to a related question.

You want the airplane to return to the original flight attitude if it has been disturbed, say by a gust or a jolt on the stick. This can be done by creating proportionally more lift with the forward surfaces (= the wing in a conventional configuration) than with the rear surfaces (= the wing in a canard configuration). Say the jolt pitches the aircraft up. Now the aerodynamic forces should change in a way which increases lift proportionally more on the rear surfaces, so the aircraft pitches down and returns to it's original attitude. By distributing lift the way I mentioned above, the same change in angle of attack on both forward and rear surface will create a proportionally higher lift increase on the rear surface, making the aircraft (statically) stable.

That requires that one of the (mostly) two surfaces is not contributing as much to lift creation than it could. You want this surface to be the smaller one of both, so the whole configuration can create as much lift as possible at a given speed. A canard would be a poor choice for a commercial airplane, because the big wing would now fly at a fraction of it's potential.

Once you shift the center of gravity back to improve maneuverability, things get different: Now the rear surface is creating proportionally more lift, so the smaller surface should go in front. Voilá, a canard!

Now add forward sweep, which will make the wing tips twist to higher angles of attack when lift is increased, and you get a really responsive aircraft (but need to be careful not to overstress it!). This was done on the X-29 and the Berkut.

As jwenting pointed out, the canard on the Tu-144 was not a control surface, but should be considered a detached slat of sorts. Also, by adding some lift ahead of the wing it allows to lower the wing flaps in slow flight, increasing the lift potential of the main wing while maintaining the location of the center of gravity and stability.

And while we are at it: The Piaggio Avanti has a canard, and a conventional tail, too. Here the canard helps to put the wing spar behind the cabin area, makes it easier to fly with a wide range of c.g. locations and to increase aerodynamic damping. This is one of very few examples in commercial aircraft of canards done right!


Exceeding VLO and by how much is too much? Piper Seminole (PA-44-180) VLO (max gear retraction speed) is 109 KIAS. I've heard that manufacturer published limitations are significantly lower than actual structural and system limitations. What are the potential repercussions of retracting gear at 10, 20, 30 KIAS over VLO?

The gear itself and its attachments being pretty beefy, you can't really damage the gear legs extending them at any speed the airplane can fly at.

The limitations usually relate to the doors, which are more delicate, and having large surface area, are far more affected by air loads.  So the main effect of exceeding a gear speed limitation is the risk of bending or distorting, or in extreme cases blowing off, gear doors.

If you have a minor exceedance of 10kt, I'd just give a visual check of the doors later.  If it was a major exceedance of 20kt or more a tech should look at it. The doors may look ok at a glance, but if they are deformed they can prevent the gear from extending next time, if, say a distorted door's edge overlaps the opening and slips past on retraction but hangs up on extension.

Extension/retraction speeds, VLO, or speed you can operate the gear selector, and maximum operating speed with the gear down, VLE, or speed you can fly with the gear down and locked, are sometimes different (VLO is normally lower than VLE if they are) because there is a limit speed that affects the gear while in transit, whereas once down and locked you can speed up.  This can be from sequenced gear doors that are only open during the extension/retraction cycle, or a limitation on the ability of the hydraulic system to retract, say, a forward retracting nose gear against air loads (a speed limitation could also be related to a stability and control issue as well).

I dimly recall from my multi training days (but not totally sure) that the limitation on the Seminole was related to its rather weak hydraulic pump which had to work too hard above a certain speed, stalling the pump or popping the CB, something like that.  Some amount of safety margin would have been applied to the speed the problem was happening at, giving the published limitation of 109.


How do airlines handle communication/notification after an accident? I'm a frequent subscriber of airport messaging services where you get notified of check-in queue times, delays in takeoff, ETA + 10 minutes, landed timestamp, baggage claim time and these kinds of information, but not life-dependent messages.

However, if something bad happens I assume I won't get a "Flight X crashed and burned" message on my cell, but most likely a "Contact the airline at 555-1212 for more information" or something similar.

What's the standard operating procedure in these cases?

If an airline has an accident, the chances are you (as the next set of passengers to board that plane) will be the least of their concerns - if there's an incident then it tends to be a case of all hands to action stations to deal with the media, emergency services, families of any potential victims, provide assistance where possible etc. That said, they do have some procedures they attempt to follow. These vary a little from airline to airline.

Most will make an attempt to contact you via text/email if they have it or via the GDS to your travel agent, depending on how far away you are from your departure day/time. It also depends whether you gave contact information to the carrier or your travel agent, whether your travel agent passed it on or, indeed, whether you used a travel agent at all.

The next set of passengers rightly tends to be second priority after dealing with the incident, however. Often if you're on the next flight, therefore, the communication will be a little slow and the first you'll know about it will be when you arrive at the airport - also remember that there's a good chance you're already at the airport, or are on a connecting flight.

If you get to the airport, you'll likely be informed by the staff there who will attempt to get you onto another flight with the same company or another carrier.

As an addition from the comment below, if you're a family member etc who's signed up to flight alerts from the airline in order to hear about delays/diversions etc (some airlines provide this as a service to avoid inconvenience and avoid too much waiting traffic at the terminal), then you'll likely be one of the first priorities. The system is normally set up to send automated or manually-triggered pre-written messages, but in an emergency will usually be used to send a manual message to relevant family members etc.

Obviously this only applies if you've signed up to the service, and only usually applies to the airline's own service: if you've signed up with a third party flight tracking service, they likely have no more information than you do.


Is it possible to fly a B-24 under Bixby Bridge? If that sounds like a ludicrous question it's because I believe it is, but here is why I'm asking.

My grandfather flew B-24s in WWII and there was something of a local legend that he once flew a crew-laden Liberator under Bixby Bridge (near Big Sur along the CA coast). Here is a short video of the bridge:

I say no way. Aside from the the idea of a trained military aviator so recklessly risking crew lives (not to mention court martial, etc.) straining credibility, I think such a feat is physically impossible for an aircraft of that size. But then, I'm not a pilot - I just pretend to be one on X-Plane. I have relatives (also not pilots) who are convinced the story is true. Those of you who fly IRL, what do you think?

Unfortunately my grandfather passed before I was born so short of breaking out the Ouija board there isn't really a convenient way to ask him!

A Liberator has  wingspan of 34m, while the central span of the bridge is 110m wide, and 280ft high, so the aircraft will fit under the bridge.

Bixby creek approaches the bridge from the north-east, with a straight-ish approach of about 0.3miles. Approaching low from the north-east, and dropping down into the creek at the earliest opportunity might allow even a Liberator enough time to descend below the level of the bridge deck and recover over open sea, although the waves might be a little too close for comfort.

I wouldnt want to attempt it in a fully-laden B-24, but with a light fuel load and crew I'd say it's doable. Whether anyone ever did it is another story...


What is the purpose of those casing treatments and how were they designed? The images show a kind of casing treatment used in Russian aero-engines.
From what I have found out the first engine featuring this kind of casing treatment was the Tumansky R-13. Since then it was used in numerous Russian jet-engines (e.g. Tumansky R-29 or Klimov RD-33).

Casing treatments are usually used to increase the operating range of compressors. And there exists a wide range of different types/geometries of casing treatments:

I was not able to find any documentation or publication on the working principle of the Russian casing treatments and how they were designed. Since they were designed in the 1950s their design was likely done by correlations. The interesting thing is that the design of the 1970s looks very comparable so the advances in 1. computing power and 2. operating experience did not change them.

Does anyone have information on:

The design rules for these casing treatments (stagger angle, skew angle, axial position)?
The working principle or intent (recirculation, blowing, sucking)?

The casing treatments shown work by providing an alternative path for the rotor tip leakage flows; which otherwise collect at the rotor tip when highly loaded and block the flow resulting in a surge.

The lack of change is because there was no significant improvement in computing power between the 50s and the 70s that would help with such designs, (in fact it is only very recently that the flows can be accurately modelled.) and the cost of the experiments required to substantially iterate the design would be prohibitive.

The difference in designs is partially driven by parallel development, partially by patent avoidance, and partially the desire to minimise the impact on the compressor's components and its efficiency.


Is there any automated go-around procedure? In Wikipedia's description of one of air crashes (probably Thai Airlines, if I recall correctly), I found a remark saying something like that: "Crew decided to go around, but apparently decided to undertake this procedure manually".

I'm surprised. "Apparently"? Making go around manually is something odd? Do we have any automated (autopilot-based) go around procedures or techniques in common use? I was always more than sure, that procedures like go around or touch-and-go are always made manually by a pilots.

For go-around, several things have to be done in the moment the decision is taken:

Apply full power (obviously),
disconnect autopilot glide-slope mode,
disarm spoilers and retract them if they are extended,
disarm autobrakes and
in some aircraft reduce flaps.

Modern airliners, and some smaller aircraft, have a method for doing all of these at once via the TO/GA button. On Airbus aircraft it is done by just advancing the thrust levers to the TO/GA (full power) position, but on Boeing aircraft and many other types it is a separate button on or near the thrust levers.

So if the crew "apparently decided to undertake this procedure manually" it means they moved the thrust levers forward and started changing the other things. And probably missed one of them.

Notes:

I am not sure whether lateral mode remains under automatic control or not and it probably depends on aircraft as some can connect autopilot to only roll or only pitch and others don't. Pitch control is manual immediately after go-around in either case.
The last flap setting usually adds a lot of drag and a little lift. In some types the drag is too large and the flaps have to be retracted to the last usable position. On other aircraft they can be used in any position and have to be left were they were to avoid loosing lift.