Why don't airlines load their passengers like freight? Apparently, the time for boarding and deboarding an airplane is a large cost factor and something airlines try to minimize but have trouble controlling because the passengers do it themselves.
A solution would be to have passengers board a passenger cabin outside of the airplane and then slide that cabin into the plane via a nose-hatch, much like large volume freight. Has this been considered? If yes, why was it not pursued?

Boarding takes a long time, true. There are more efficient strategies (.pdf) which have been proven to speed up boarding by between 20% and 50%, still they are not adopted. Why?

You need to load the baggage, too. Also the catering. And fuel. You need to inspect the aircraft, run through checklists and brief the new crew. This all takes up time, too. Airlines do not see a big saving by loading passengers faster, and then waiting for all other jobs to be completed.

Your radical idea of containerizing passenger transport would certainly speed up things, but it would cost a lot of payload.

The most efficient pressure vessel is a sphere, and the next efficient is a cylinder with spherical ends. Pressurizing a boxy container is structurally very inefficient.
Loading passengers on palettes first and sliding those palettes through a narrow opening takes time in itself. And the palettes have their own weight, their own floor, their own support structure for the baggage racks, their own cabeling for the entertainment system. They would, however, not need their independent pressurization, so their weight impact would be moderate.
A possible "flatbed" airliner which could attain the shortest boarding times has only half as much fuselage height (or less) to transmit bending loads along its length. See here for an example of buckling in a fuselage skin due to bending loads. Now consider that reducing height by 50% will need four times more cross section in the longerons to keep stiffness constant. That will make the fuselage much heavier.

In the end, airlines go with the solution which maximizes their profits. By using a hollow cylinder and let their "cargo" self-load, they can maximize their payload and get tolerable boarding times. Tolerable for them, that is. That better loading procedures could allow you to come to the airport later is of no interest to them. If they would see an advantage in shorter boarding times, there would be ample of opportunity by improving strategies, even with existing airplane designs.


Altimeter setting and pressure altitude Student pilot here.  I thought I was smarter than this, I’m struggling with this concept.  I got the ASA test prep book and there’s a question asking what happens to the indicated altitude when the altimeter setting is changed from 29.15 to 29.85.  Answer is indicated altitude increases by 700 feet.  Ok, makes sense.
But then I’m reading the aircraft performance chapter in the Aeronautical Knowledge book.  It has a chart about finding pressure altitude, and when the altimeter setting decreases on this chart the altitude increases.  So, the converse of the concept in the question.  I can make either make sense on its own but they seem to contradict each other.  What am I missing?

Here's the difference in a nutshell:
When you change the number in Kollsman window to
bigger number and the atmosphere stays the same, the reading on your altimeter increases.
When you leave the number in the Kollsman window the same (let's say you have it set to 29.92 to see the pressure altitude) and the atmospheric conditions change so that the correct altimeter setting increases--i.e. the air pressure has increased-- then the reading on your altimeter decreases.
You increasing the setting in the Kollsman window is not the same thing as an increase in the prevailing correct altimeter setting.  They have the opposite effect on what you see on your altimeter dial.  The first thing makes the reading get higher, and the second thing makes the reading get lower.  When they both happen at the same time, the reading stays the same.
Clear as mud now?


Is there a general radio frequency in Class G for broadcasting intentions? Let’s say you’re in class G and doing some aerobatics. Is there any standard frequency you might use (perhaps MULTICOM on 122.9?) to communicate your intentions?

Assume you’re not using flight following and that you’re VFR.

I'm not aware of any regulation or AIM entry that specifies what frequency to be on.

I use the UNICOM frequency of the nearest airport when I'm out looping because I consider it to be the frequency most likely to be used by traffic near me.

It also has a mild safety benefit -- if something on my plane were to break, I'd already be on the right frequency for the airport I'm about to inhabit.


Is there a backup to fuel inerting systems? I've heard it said many times that "everything has a backup" in commercial planes.

What about the fuel inerting system (injecting nitrogen in the fuel tank). Does it have a backup? Is it somehow failsafe all by itself?

Short Answer

No, it does not have a back-up, there are some fail-safe components in the system(see below), but in general the system itself is not duplicated. The system, together with a design that avoid ignition sources within the tanks, is just a part that contributes to prevent fuel tanks to ignite. An Inerting System for commercial planes have been considered since 1996 TWA accident and first regulation arrived in may 2006.

Longe Answer

The certification CS25.981 Fuel tank ignition prevention states:

  (a) No ignition source may be present at each point
  in the fuel tank or fuel tank system where
  catastrophic failure could occur due to ignition of
  fuel or vapors.

  (c) Design precautions must be taken to achieve
  conditions within the fuel tanks which reduce the
  likelihood of flammable vapors.

So the function that should be achieved is prevent tank ignition and there are two fronts two work on, avoid ignition source, and reduce fuel vapors (similar to the two slices of cheese that rbp was mentioning in the comments).

So the fuel ignition system is a system designed to avoid fuel vapors. As can be seen in the image below, within the systems there are some redundancies (e.g.: Dual Flow Shut Off Valve), but the system itself is not duplicated.

Moreover the system is not on the Minimum Equipment List (MEL), so the aircraft can still be dispatched with the system inoperative for 10 days.


What ground-based, airline job in the 1940s could have involved radio communications? My mom worked for United Airlines in the mid 1940s in some communications capacity: she communicated by radio with United aircraft only, and she wasn't an air traffic controller.  She went to school in Kansas City in 1942 for communications.

Could anyone help me figure out what her job would have been?

Perhaps she was a flight dispatcher?

A flight dispatcher (also known as an aircraft dispatcher, airline
dispatcher, flight follower or flight operations officer) assists in
planning flight paths, taking into account aircraft performance and
loading, enroute winds, thunderstorm and turbulence forecasts,
airspace restrictions, and airport conditions. Dispatchers also
provide a flight following service and advise pilots if conditions
change. They usually work in the operations center of the airline.

-Wikipedia


What are some specific benefits of cryogenic wind tunnels? What are some benefits to using a cryogenic wind tunnel over a more traditional one? Are there certain aerodynamic properties or principles that are better studied at low temperatures?

Short answer:
A cryogenic tunnel works by taking advantage of the different properties of nitrogen gas at cryogenic temperatures as compared to the properties of air at normal ambient conditions (speed of sound, density and viscosity). This allows testing at an order of magnitude higher Reynolds numbers over non-cryogenic tunnels. Being able to achieve full-scale values of Reynolds numbers removes a significant source of error in the wind-tunnel test results.
Long citation from https://cryogenicsociety.org/resources/cryo_central/wind_tunnels/:

Dr. Robert Kilgore

The development of the cryogenic wind tunnel is one of many significant breakthroughs in both cryogenics and wind-tunnel technology made during the past millennium. Interest in the development of high-speed commercial and military aircraft resulted in a review of problems of flow simulation in transonic wind tunnels during the 1950s and 60s. One of the more serious problems was the inability to test sub-scale models at Reynolds numbers sufficiently near flight values to ensure the usefulness of the wind-tunnel data. Typically, values of test Reynolds number were too low by a factor of 10 or more.

The search for a way to test at full-scale Reynolds number began soon after Wenham built the first wind tunnel in 1870. Margoulis proposed using a heavy gas or cooling the test gas as early as 1920. Margoulis reasoned that a heavy gas, such as carbon dioxide, when cooled to 253 K would increase Reynolds number and reduce drive power requirements for fan-driven wind tunnels. Margoulis and others of his time concluded the moderate benefits resulting from cooling only to 253 K were not worth the effort.

The idea of cooling the test gas lay dormant until 1945 when Smelt studied ways of reducing the size and power requirements of high Reynolds number high-speed tunnels. Smelt’s theoretical study again noted the advantages of using heavy gases and reducing temperatures. The study by Smelt was presumably a case of independent re-invention of a good idea since Smelt did not cite Margoulis.

Cooling of the test gas was again rejected in the 1940s. This time it was rejected because there did not appear to be a practical way to cool a reasonable size wind tunnel and there were some concerns about finding suitable materials for the tunnel structure.

The concept again lay essentially dormant until 1971. We needed a way to increase the Reynolds number capability of the small wind tunnels equipped with magnetic suspension and balance systems. Dr. M. J. Goodyer was working at the NASA Langley Research Center at the time. Goodyer studied the problem and, again independently, suggested the use of either air or nitrogen at cryogenic temperatures. Goodyer and a small group of researchers at NASA Langley quickly recognized several additional advantages of the cryogenic wind tunnel concept. We immediately set out to develop a practical approach to its application. We quickly built and successfully used a small low-speed atmospheric cryogenic tunnel. It first operated at cryogenic temperatures in January of 1972. We used this tunnel, which had a test section of 18 x 28 cm (7 x 11 in.), to prove the validity of the concept as well as to develop the method of cooling the tunnel by the direct injection of liquid nitrogen into the stream.

We then decided to build a relatively small fan-driven transonic cryogenic pressure tunnel. In its original configuration (since changed), the Pilot Transonic Cryogenic Tunnel had a test section of 34 x 34 cm (13.5 x 13.5 in.) and could operate at pressures up to 500 kPa (5 atm). This extended our cryogenic tunnel experience to the pressure and speeds needed for a large high Reynolds number tunnel. The design of the Pilot Transonic Cryogenic Tunnel began in December of 1973. Initial operation was in August 1993. Again, success led to greater things; this time to the decision to build a large cryogenic wind tunnel to meet the testing needs of the United States. The tunnel would be known as the US National Transonic Facility (NTF) and would be built at the NASA Langley Research Center in Hampton VA. Construction of the NTF began in 1975. It became operational in 1982. It has a test section of 2.5 x 2.5 m (8.2 x 8.2 ft) and operates from ambient to cryogenic temperatures at pressures up to 890 kPa (8.8 atm) at Mach numbers up to about 1.2. Cooling of the test gas is by the direct injection of liquid nitrogen into the tunnel circuit at rates up to 1000 pounds per second.

By taking full advantage of the cryogenic concept, the NTF can test at Reynolds numbers of 120 million. This is an order of magnitude increase in Reynolds number capability over non-cryogenic tunnels. Being able to achieve full-scale values of Reynolds number removes a significant source of error in the wind-tunnel test results. The net result is that commercial airplanes are more efficient and combat aircraft are more maneuverable.

We routinely use cryogenic wind tunnels to test at full-scale conditions (including some scaling parameters other than Reynolds number) for such diverse things as solar towers and submarines. Around the world we now have three large Cryogenic Wind Tunnels used for a variety of aerodynamic testing and fundamental research. These include the US NTF, the European Transonic Windtunnel (ETW) and the Kryo Kanal Köln, both located in Köln, Germany. In addition, there are another 20 or so smaller cryogenic wind tunnels used for a wide variety of purposes in nine countries.

The use of cryogenics in wind tunnels may be unique among the various uses of cryogenics. Most people use cryogenic temperatures because they want to take advantage in the change of some property of a material. For example, they want to turn an ordinary conductor into a superconductor. However, a cryogenic tunnel works by taking advantage of the different properties of the nitrogen gas itself at cryogenic temperatures as compared to the properties at normal ambient conditions (speed of sound, density and viscosity).

As used in cryogenic wind tunnels, cryogenic technology is making a major contribution to experimental aerodynamics.

“It is easy to invent a flying machine; more difficult to build one; to make it fly is everything.” — Otto Lilienthal, Pioneer Glider Pilot


How is the term "Coast" defined for FAA regulatory purposes? 14 CFR 91.1 defines the applicability of part 91. This paragraph defines two areas of jurisdiction where certain parts of part 91 apply:

within the United States, including the waters within 3 nautical miles of the U.S. coast
the airspace overlying the waters between 3 and 12 nautical miles from the coast of the United States

By exclusion the third area is the airspace overlying waters beyond 12 nautical miles from the coast of the Unites States. Part 91 therefore does not apply in this area. The FAA explicitly states this in letters of interpretation, for example, in Di Marco (2008).
The term "coast" appears to be undefined in any readily available FAA resources.
How are we to understand this term as applied to the scope of applicability of §91? For example, would a shore of one of the Great Lakes—Lake Huron for example—be considered a "coast" for this purpose? To apply the question more specifically, would a pilot be required to comply with the 250 knot rule of §91.117 if below 10,000 ft while 15 miles off the US shore over Lake Huron.

Coastline means the territorial sea baseline. In the language of international treaties like UNCLOS, the territorial sea doesn't include internal waters, regardless of their size. NOAA confirms this, notes however also, that not all US court decisions follow that view. NOAA also provides a map to view the US territorial waters & exclusive economical zone, which shows that the great lakes are neither.


Why wasn't a scramjet used for the Concorde? Why didn't Concorde use a scramjet engine for supersonic flight, but it is used in the Airbus and Skreemr hypersonic flight concepts to achieve supersonic speeds?

A supersonic ram jet (scramjet) requires a fuel with a very high flame speed, so the combustion doesn't take place after the fuel-air mixture has left the engine. Aviation fuel would be completely unsuitable, and only hydrogen gives acceptable results. The low density of gaseous hydrogen, the storage problems associated with cryogenic hydrogen and the creation of a hydrogen infrastructure would had created tremendous problems for the Concorde development.

A scramjet is like wing sweep: It is best avoided if possible, but necessary if you want to go really fast. For the scramjet the speed above which it makes sense is Mach 4 or 5, and Concorde was designed for Mach 2.


What is stall speed exactly? I used to simply think It was the speed where any attempt to pitch up to maintain an equilibrium between lift and weight would result in flow separation, But Wikipedia says;

But I noticed in a Sim I play, The stall buzzer plays whenever the airspeed gets under a certain point, No matter what angle of attack?
I first thought this was a bug or flaw in my simulator, But why on earth would there be a stall? As said before, stalling is not dependent on speed, so what exactly is "Stall speed"?

Stall speed is whatever airspeed you have when the wing reaches the stall angle-of-attack.  When we say  "stall speed", we often mean the 1-G stall speed, but under the right conditions we can place the wing at the stall angle-of-attack at a higher or lower airspeed.

The simulator may have a flaw.  Also, you may not have a good understanding of what angle-of-attack is, and how it relates to pitch attitude.  What exactly makes you think that the wing is not near the stall angle-of-attack whenever the stall buzzer is on?  Just because the nose is below the horizon?  That would be a misconception.  In  a high-drag, low-thrust descent, the flight path can be so steep that the nose can still be below the horizon even when the angle-of-attack is quite high.

In straight-line (unaccelerated) flight, angle-of-attack is much more closely related to airspeed than to climb rate or sink rate.  In wings-level straight-line flight, for shallow to moderate climb or descent angles, the relationship between angle-of-attack and airspeed has essentially nothing to do with whether the aircraft is climbing, descending, or flying level.  In these parts of the flight envelope, to a first approximation, any given airspeed is associated with with one particular angle-of-attack, regardless of the climb rate, sink rate, or pitch attitude.  It sounds like this is what you are seeing on the simulator.  This is normal!

Your question suggests that you may think that a descending flight path is evidence that the wing is producing less lift than in level flight, and therefore should be harder to stall, or should stall at a lower airspeed.  Actually, inadequate lift is not the fundamental cause of a descent, and for shallow to moderate descent angles, the wing is only creating very slightly less lift than it would in level flight, creating an imperceptible change in the unaccelerated stall speed.

To check the functioning of the simulator, try pitching up into a very steep climb that forces the airspeed to decrease.  When the stall buzzer comes on, can you make it go off immediately with a very aggressive forward push on the stick or yoke?  If not, something is probably wrong with the simulator.

If everything is working right, with some practise, you should be able to fly a semi-ballistic arc with the G-load near zero as you go over the top, and with the airspeed dropping well below the normal stall speed as you go over the top, without the stall warning buzzer coming on.  This will be easier to investigate if the simulator includes a G-meter.

If some parts of this answer don't make sense to you and you want to better understand the balance of forces in level, climbing, and descending flight, some of the links given at the end of this answer may help: How does an aircraft descend without its nose pointing down?

For more, see the "See How It Flies" website, especially chapter 2.


How are electronic instruments and other equipment powered in a glider? Radios and other electronic devices must be battery-powered. What sort of battery - and does its capacity impose a limit on flight duration, or can they be recharged in flight with a turbine?

Gliders generally use "Gel Cell" or Sealed Lead Acid rechargeable batteries, a little bigger than a block of butter, that will run designed-for-glider low wattage radios, and sometimes transponders, and FLARM systems (a kind of TCAS) and various other gadgets, and are good for several hours of operation (the total current draw of all the services might be under 1A when not transmitting on the radio, so a 5 AmpH Gel Cell 12v battery might be plenty unless you are talking all the time). Enough for normal glider flights and tasks, and if necessary you can hook up a second one if expect to be out for more than 4-5 hours.

Some newer batteries of the more exotic Lithium chemistry are starting to come on the scene, but the thing is the gel cells are light enough and are effective and trouble free, and don't require an STC (Supplemental Type Certificate; basically a 3rd party field modification), so the switch away from gel cells will be slow.

Recharging in flight with a turbine would be a real L/D killer so it's out of the question.  Much better just to install provision for a second battery for long flights.


Are commercial VFR flights legal? I live in Southern California and was surprised to learn today that a local company is operating very short-haul VFR flights as an alternative to car commuting.

https://www.floatshuttle.com/

I can understand operating out of small airports to keep costs down, but flying VFR for a service like this seems unusual to me. Is this legal?

It depends on the operator's "opspecs" which are negotiated between them and the FAA. Generally in the US the vast majority of part 121 scheduled airline operations are required to be IFR, but plenty of part 135 charters are permitted to fly VFR. They may be subject to weather minimums higher than the general VFR limits.


Left hand seat, is it so important? With reference to this article on aviation herald at Accident: Shanghai B738 at Shanghai on Jan 3rd 2020, tail strike on landing, captain and first officer swapped seats in flight where the report discusses swapping seats between captain and first officer. I'm trying to figure out why so much weight was given to swapping the seats - except may be bad timing.

As a person who is not affiliated with aviation, I am curious to know apart from responsibilities and prestige that goes with the position, are there any differences between flying from right hand side vs left hand side. Does captain side has more controls available?

If someone gets incapacitated for whatever reasons, how is it managed?

Additional question - as pilots move up the career, do they have to learn few skills again like controls they used to perform with left hand vs right hand as they swap the seat.

There should not be any great differentiator between left and right seats. The American Airlines Training Center FFS (simulator) for the B737 has the nose wheel tiller only on the left side. The actual aircraft should be set up identically to the simulator. Other than that, most pilots at the ATP and airline levels should be comfortable in either seat.

In larger and/or turbine powered aircraft (as well as the majority of glass cockpit aircraft), the instrumentation is duplicated on both sides of the aircraft. You both have the same information. But, there is only one set of controls for some things like the throttle quadrant, autopilot, and radios located in the center of the panel, overhead, or on the central pedestal between the pilots. It’s like an American (me) driving a fifteen passenger, stick-shift van around London for the first time. Driving and even shifting are simple procedures. It is even simple to remember in which lane to stay when turning corners. But, your entire ingrained site picture is off. And which hand does what is reversed. Simple to overcome with experience and practice.

With low time pilots, on the other hand, there is quite a difference. Most pilots get most of their first 200-500 hours flying left seat only. Most six-pack steam gauge training aircraft have their instruments oriented toward the left-seat pilot. Making the transition to right seat can be a challenge at first. But, this challenge can be easily overcome with practice. Think of it this way, try playing a musical instrument or a sport with opposite hand orientation from the way you first learned it. Try even to tie a tie or your shoe laces opposite your normal routine. It is not impossible. It becomes a non-issue with some practice. I still find it daunting to land from the right seat even though I can perform most other maneuvers somewhat fine although with more thought.

By the time a pilot reaches the CFI level, they should be more than comfortable in the right seat. Most of their flying from the start of their CFI training on will be from the right seat including the checkride. Some CFIs will even fly solo from the right seat out of habit. Especially in aircraft that only have a right door.

As far as pilot incapacitation, with only limited experience in the B737 sim, I can’t think of much you can do from one seat that you can not do from the other. Operation of the nose wheel tiller and certain circuit breakers come to mind. I think the cabin pressure controls would be a stretch from the captain’s left seat position depending on their reach. It would still be a good idea to remove the incapacitated pilot from their seat if able. Just to make sure that they do not accidentally get in the way of the controls. It would also be of great aid to have someone coherent in the vacated seat to help with the radios. Even if they are not a pilot.


Can you identify this fighter aircraft? If someone can identify this aircraft, please tell me which aircraft this is?

It's a Russian YAK-141

This was the VTOL prototype meant to compete with the Harrier and perform carrier-based work (note: edited for clarity)

  Designers from the Yakovlev bureau found out, that the double engine scheme of the Yak-38 and Harrier was not suitable for the new plane. Instead they created a layout with a single engine, that could turn 95° down, located in the middle of the fuselage, just behind the center of gravity. [Two additional vertical thrust engines] would turn on only during vertical take-off, vertical landing and hovering. Engineers had to stretch body of the aircraft for aerodynamic stability. This is why the Yak-141 is larger than its predecessor, the Yak-38.

The plane was never mass produced

  The Yak-141 multi-role fighter did not enter production. The funding for this program ceased in 1991 after a landing accident on the aircraft carrier, when one prototype landed during excessive side wind and was badly damaged. After collapse of the Soviet Union military funding was limited. In 1992 the Yak-141 program was canceled as it happened with many other promising weapon systems. Also by 1995 Russia decommissioned all Kiev class aircraft carriers, this plane was intended for.


Why do some Turbofan engines have multi-stage fans? I was wondering why some turbofan engine have multi-stage fans.
e.g. F-119 engine:

F100

Saturn AL-31

All three engines you show are for fighter jets flying at supersonic speeds. These engines need a low bypass ratio: Why do military turbofan engines use a low bypass ratio?
To achieve more thrust at lower bypass ratios, the bypass air needs to be accelerated more, which requires more than one fan stage because axial compressors can only add a limited pressure difference per stage:

Low bypass engines often have a multistage fan which generates a low volume but relatively high speed air stream whereas high bypass engines usually have a single stage fan which generates a high volume but relatively low speed air stream.

(SKYbrary - Turbofan Engine)
In principle, high bypass ratio engines where more air is accelerated less are more efficient and therefore used on modern airliners, but they are not suited for supersonic flight.


What model is this strange airplane-helicopter combination? I'm a local historian in Fort Collins, CO and I'm trying to find out anything I can about the helicopter/plane image in the attached picture. The only thing I know is that it was parked in a early Fort Collins airport.

It is a Pitcairn PCA-2 autogiro. From the linked article:

  This aircraft is a Pitcairn PCA-2 autogiro, S/N B-12 (ATC #410), manufactured in April 1931 by Pitcairn Aircraft, Inc., Willow Grove, PA. It came from the factory with a Wright J-6 engine (S/N 12528) of 300HP. It had a Hartzell steel propeller.  It was a three-place craft, weighing 3,000 pounds.

Apparently, the aircraft was owned by Amelia Earhart and sponsored by Beech-Nut packing company.

  NC10780 was sold to George Palmer Putnam, husband of Amelia Earhart, of New York, NY on May 7, 1931.  This autogiro is the “older” (by a week) sister ship of NC10781 flown through Tucson by John M. Miller.


What is the 'arm' at the rear of the X-29? In this image of the Grumman X-29, there is an 'arm' just above the exhaust nozzle leading forward and, apparently, attached to the right side of the fuselage. What is this and what is it for?

Source: Wikipedia X-29 Article

I realize this is an experimental aircraft, but it doesn't look like sensors (like the probe off the nose), it looks more like a structure for lifting the plane.

Two X-29's were built, and the only difference between the two is that #2 has an externally mounted spin recovery chute attached to the tail. That is what you are seeing in this picture. The chute is packed in the tube structure and the "arms" are structural to distribute load.

Source

  The only significant difference between the two aircraft was an emergency spin chute deployment system mounted at the base of the rudder on aircraft No. 2.

Here is a video of the chute deployed

And here are more details from NASA on the chute system

The reason that #2 needed this and #1 did not is that #2 was going to be conducting experiments at up to 67° angle of attack, where entering a spin was much more likely. #1's AOA was limited to about 21° and was considered the "phase-1" flight dynamics platform, while #2 was the "phase-2" platform.


Why does Boeing use two different door-types (B757 hinge vs. B767 slide)? Why did Boeing use a sliding door for the B767?

And why wasn't it used in later Boeing planes?

Edit:
Looking up other airframe manufacturers I realised that the B767 was introduced prior to the B757. And that other airplanes featured slide-up doors as well but the B767 was the last one featuring them. Could it mean it was some kind of fashion of the airplane design until the late 70s?

Outward swinging doors require a great deal of effort to open and close, and can require the operator to potentially lean outside of the aircraft and risk a fall to close.  The 757 door originally had an issue where shorter operators could not get enough leverage to open (see: Making It Fly in the Seattle Times.  Upward doors were used for a while but they are finicky to operate and maintain and if the opening mechanism fails can be very difficult to open in an emergency.

The translating "gooseneck" door was originally designed by Airbus.  The design is simple, reliable and easy to operate.  It has more or less become standard on all new aircraft designs.


Do airplanes have vapor recovery systems for refuelling? Related to the question regarding pressure refuelling and this one regarding fuel vapors at large airports.

Refuelling an airplane involves putting fuel into tanks which are "empty" but are in fact full of dangerous air-fuel vapors. I do not believe many airplanes use "bladder" type flexible tanks which would avoid the creation of these airspaces.

When fuel goes in, the vapor has to go somewhere else. In contemporary cars, there is a vapor recovery both in the fuel system (activated carbon cylinder) as well as in the fuel nozzles.

If I understand both pressure refuelling as well as regular refuelling systems for airplanes and airliners, neither seem to have any sort of vapor recovery system. Wouldn't this be a considerable source of greenhouse gas emissions, let alone a tremendous fire hazard? Or is there a vapor recovery system being designed or implemented to mitigate this.

You are correct on both your assumptions about the fuel vapour. It does have a greenhouse effect, though I would suspect that the amount of fuel required to make the air saturated in the fuel tank is not likely to be more than some tens of grams. It also presents a fire hazard.
However we again face the same issue as with many other systems that would be environment-friendly and safe: the cost.
Companies, both airlines and airport operators, carefully evaluate all cost to benefits. In this particular case the environmental effect is likely to be considered neglible, and the fire risk is tackled with other measures, such as grounding, clear-areas, ventilation etc. Those were covered nicely in the previous questions.


What does the flashing green-light signal (return for landing) actually mean to NORDO aircraft? Studying for the PSTAR I see that a flashing green signal while in the circuit means "return for landing" but this is not actually defined anywhere. What does that mean?

NORDO = "is an aircraft flying without a radio"

What I was taught that this meant was ...

... because they could not communicate with you, but they wanted you to not land on this pass (interval a mess, crossing traffic, winds maybe wrong, a dozen other things that might crop up) it was more or less "the runway will be ready for you if you take another lap in the pattern." This also gives them a bit of time to get all of the other aircraft in the pattern out of the way of the aircraft in distress. (And the steady green ought to confirm that on the next pass, if all things go well).

Tower operators would rather get that aircraft who can't talk to them onto the ground.  What they want to avoid in this case (again, this is what I was taught by a salty old Navy controller when I was in flight school) is that they wanted to avoid the aircraft attempting to land being "spooked" by a red light and thinking they can't land at this field.  And then waving off and flying off in search of another field while still NORDO.

The green light is the 'friendly' light between choices of red and green. Put in the chief's colloquial jargon: "Flashing green lets the pilot know "the runway will be there for you when you come back for your next approach."

The Canadian Aeronautical Information Manual, which has all of the signals to include the two that are relevant to this question, can be found here.

The teaching that I got may no longer be current, but the lights shown to a NORDO airborne aircraft still mean the same thing as they did when I was taught.

  Steady Green:  cleared to land
  Flashing Green: return to land (to be followed at the proper time by steady green)


Why are digital autopilots better than analog? I've heard many people say that a digital autopilot is better than its analog equivalent. How do the two differ in design and the way they control the plane?

Early autopilots would only control one degree of freedom. Starting with the yaw damper of the Me-262, they were a simple feedback loop involving a gyro, a single control surface and some damping circuitry. Example: A roll gyro was coupled to the ailerons and kept the wings level. Commanding a bank angle would simply shift the zero point of the gyro to a different angle, and some damping made sure that the movement was slow and did not overshoot.

This, however, would neglect any cross coupling. Banking flight needs more thrust to keep altitude, but the roll autopilot would not "know" of engines or throttles, just ailerons. The same was true for analogue pitch and altitude hold systems which had a simple feedback loop with the throttle and the elevator, but no other controls.

Modern digital autopilots, starting with the one in the X-31, control all axes in parallel and use a multitude of sensors and feedback loops to control the whole aircraft in one go. This is much easier to achieve with digital control, and gives smoother responses since cross-coupling effects can be anticipated and corrected before they manifest themselves.


Where can I find the best site to learn aircraft design on a small scale? I am undergraduate student still trying to figure out a lot about Aerodynamics and aircraft design. I am learning how to design rc planes.

So the thing I know the weight of my plane which is between 700 gm to 1000 gm and velocity which is 13 m/s.

I just know the basics that is the lift formula and other fundamentals. I want to know how to design a nice fuselage for my plane and also how to keep balance in my plane. I seriously need help and also there are courses where you learn all this, but they ask for heavy cash.

It's not a website, but it's totally worth buying: Dan Raymer's Simplified Aircraft Design for Homebuilders (ISBN 10: 0972239707  ISBN 13: 9780972239707) is applicable to RC aircraft and has the best ratio of comprehensive coverage to beginner-friendliness of any resource I know.


Is there an instrument departure procedure or minimum performance gradient in the absence of a published standard instrument departure? Is there an instrument departure procedure or minimum performance gradient in the absence of a published standard instrument departure (SID)?

Departing under instrument flight rules (IFR) in the United States airports sometimes have a SID procedure or alternate take-off minimums which must be observed in order to provide terrain and obstacle clearance.

If there is no SID or alternate take-off minimum published, is there a standard departure procedure to be used in the absence of other procedures? Is there a climb performance gradient which is assumed that provides clearance under such a departure?

Yes, the required obstacle clearance is based on this minimum performance:

Cross the departure end of the runway (DER) at at least 35ft AGL (that's above the DER, not above the airport reference elevation)
Climb to 400ft above the DER before turning
Maintain a climb of at least 200ft per nautical mile (FPNM) until reaching minimum IFR altitude

The minimum IFR altitude is 1000ft above obstacles, or 2000ft in mountainous areas.

This is explained in detail in Chapter 1 of the FAA Instrument Procedures Handbook (starting on page 1-14). The FAA carries out an assessment to see if the airport needs a specific procedure (ODP or SID) and if it doesn't then the standard clearance performance above applies:

  If an aircraft may  turn in any direction from a runway within the
  limits of the  assessment area and remain clear of obstacles that
  runway  passes what is called a diverse departure assessment, and  no
  ODP is published.


Are there any Boeing 747 still flying for commercial use? No American airline flies it anymore, but the Jumbo has been mythic for decades:

ANA B747-400. Wikimedia, photo by Kentaro Iemoto

Is it still possible for a passenger to board a Jumbo Jet?
Which airlines are still operating the B747 in 2018?

Quite a few, actually.

British Airways is the largest operator of B747-400 and flies a number of routes:

  Where does the Boeing 747-400 fly?

  The aircraft operates on a variety of routes, including:

  Beijing  Boston Cape Town Dubai Lagos

  Las Vegas Mexico Miami New York (JFK)

  Phoenix San Francisco Toronto

Air China operates both 747-400s and 747-8s

KLM does so but is phasing the 747-400 out

Korean Air, Lufthansa, Thai Airways, Virgin, El Al, Saudia operate 747s, among others.

Wikipedia lists 489 747s in service as of July 2017 though around half of them are cargo and the numbers would have reduced still further by now.

The latest data that I could lay my hands on lists the following airlines (less than twenty, sadly):

  Air China
  Air India
  Asiana Airlines
  Atlas Air
  British Airways
  China Airlines
  Corsair
  El Al
  Iraqi Airways
  KLM Royal Dutch Airlines
  Korean Air
  Lufthansa
  Mahan Air
  Qantas
  Rossiya Airlines
  Thai Airways
  Virgin Atlantic
  Wamos Air


Why would one wing stall before the other? Reading about the Douglas C-133, I see this:

  The second issue discovered was stall characteristics gave very little
  warning to the crew. The left wing was found to stall before the right
  wing. The fix was simple, a small strip of metal was attached to the
  right wing causing it to stall at the same time the left wing would
  stall.

The issue affects the whole type. What would cause one wing to reliably stall before the other?

In general, aircraft aerodynamics can be affected from manufacturing tolerances or consistent asymmetries.

The reason can be due to any asymmetry in the wings or fuselage shapes, or wing-to-fuselage fixtures.


Does a glider pilot need to file an IFR flight plan to legally fly in cloud in class E airspace in the US? Does a glider pilot need to file an IFR flight plan to legally fly in cloud in class E (controlled) airspace in the US? Or could he or she contact ATC and receive a clearance to enter cloud without actually filing an IFR flight plan?

Assume that the glider pilot has an instrument rating in airplanes (as required by FAR 61.e.3), and the glider has all the equipment required to legally operate in Instrument Meteorological Conditions under Instrument Flight Rules.

Background information-- I know of a case several decades ago where a glider pilot legally thermalled high into a towering cumulus cloud to set a state altitude record under conditions similar to those described above.  The state record would not have been granted if the flight had been conducted in violation of any FARs.  I don't know whether or not an IFR flight plan was actually filed.  Note that FARs 91.619 and 91.153 do contain the phrase "Unless otherwise authorized by ATC" when describing what information must be included on in IFR flight plan, so if an IFR flight plan was filed in this case, it may have looked quite different from a typical one.

Related--

Does a request for a Pop-Up IFR clearance constitute filing a flight plan?

Can you file an open-ended IFR flight plan?

What IFR clearances may a pilot obtain from ATC directly without a pre-filed flight plan with FSS?

What IFR clearances may a pilot obtain from ATC directly without a pre-filed flight plan with FSS?

As answered here, requesting a pop-up IFR from ATC counts as "filing" a flight plan.

It should be noted, as explained here, that airfiling with ATC is a "workload permitting" activity, meaning ATC is not obligated to grant it. They can always refer you to FSS.

Climbing or descending through a cloud layer is one of the generally accepted use cases for pop-up IFR requests, so while ATC might be surprised by a glider asking for it, I can't see why they wouldn't treat it the same as an airplane requesting the same.

The main challenge I see, at least for non-motor gliders wanting to climb, would be phrasing the request correctly to get a clearance they can physically comply with. Maybe "circling within Xnm of present position" to allow for thermaling? It's also possible to request a 3D box if you want to do more complicated maneuvers/work; I'm pretty sure I've seen a question here on that.


Can you help me identifying this circa 1910 airplane with tail number 72? Circa 1910 airplane with tail number seventy two

(Click for larger image)

It is a Wright, allright, but more probably an EX. The EX was a modified Model R, which in turn was a modification of the Model B. The R and the EX were single seaters, whereas the B would seat two.

Picture of a Model B replica, as taken from its Wikipedia article:

Picture of a Model EX, taken from this site.

The EX was the model used by Cal Rodgers for his epic transcontinental flight. Note the lengthened tail and the closer wings, which allowed to reduce rigging wire and, thus, drag. The "72" shows the same features, so I think it is a Wright Model EX.


Where is RC aircraft flying allowed in the US? In the US, where are you allowed to fly RC aircraft? AMA says you should stay away from airports and below 400 feet. Is there any actual law about this?

I'm guessing you are free to fly on your own property. How about other places? Does it have to be an actual RC field? Can it be a park, as long as you don't endanger anyone?

If this varies with local rules, is there some reference for finding more information about which areas allow/disallow it?

Update

Everything in the second section (my original answer) used to be true (well, except for the first statement), but doesn't consider that the FAA Modernization and Reform Act of 2012 made this regulatory.

The FAA has a webpage that discuss it in more detail , but here is an image that covers the basics:

There is also a much more detailed letter of interpretation from the FAA which discusses their ability to enforce the regulation and many other parts of 14 CFR 91 if a model aircraft endangers another aircraft, flies within 5 miles of an airport without receiving a clearance, flies into a restricted area, etc.

The short version is that it isn't regulated (yet).  For more details, read on.

FAA has an Unmanned Aircraft (UAS) Questions and Answers page on their website which addresses this:

  Do I need permission from the FAA to fly a UAS for recreation or as a hobby?

  There are two ways for recreational or hobby UAS fliers to operate in the National Airspace System in accordance with the law and/or FAA regulations.

  ...

  Option #1. Fly in accordance with the Special Rule for Model Aircraft (Public Law 112-95 Section 336). Under this rule, operators must:

  Fly for hobby or recreational purposes only

  Follow a community-based set of safety guidelines

  Fly the UAS within visual line-of-sight

  Give way to manned aircraft

  Provide prior notification to the airport and air traffic control tower, if one is present, when flying within 5 miles of an airport

  Fly UAS that weigh no more than 55 lbs. unless certified by a community-based organization

  Register the aircraft (UAS over 0.55 lbs. and less than 55 lbs. can be registered online at registermyuas.faa.gov; UAS 55 lbs. or greater must be registered through the FAA's paper-based process)

The other option is to obtain a pilot certificate and comply with part 107 UAS regulations.

The FAA has also published an Advisory Circular Model Aircraft Operating Standards, which states:

  1 - PURPOSE. This advisory circular (AC) provides guidance to persons operating Unmanned Aircraft (UA) for hobby or recreation purposes meeting the statutory definition of “model aircraft” contained in Section 336 of Public Law 112-95, the FAA Modernization and Reform Act of 2012. This AC describes means by which model aircraft may be operated safely in the National Airspace System (NAS). Nothing in this AC changes the requirement to comply with the statute or any applicable regulations.

  ...

  6 - MODEL AIRCRAFT OPERATIONS.

  ...

  b. Model Aircraft Hazards in the NAS. While aero-modelers generally are concerned about safety and exercise good judgment when flying model aircraft for the hobby and recreational purposes for which they are intended, they may share the airspace in which manned aircraft are operating. Unmanned aircraft, including model aircraft, may pose a hazard to manned aircraft in flight and to persons and property on the surface if not operated safely. Model aircraft operations that endanger the safety of the National Airspace System, particularly careless or reckless operations or those that interfere with or fail to give way to any manned aircraft may be subject to FAA enforcement action.

  c. Determination of “Model Aircraft” Status. Whether a given unmanned aircraft operation may be considered a “model aircraft operation” is determined with reference to section 336 of Public Law 112-95:

  (1) The aircraft is flown strictly for hobby or recreational use;

  (2) The aircraft operates in accordance with a community-based set of safety guidelines and within the programming of a nationwide community-based organization (CBO);

  (3) The aircraft is limited to not more than 55 pounds, unless otherwise certified through a design, construction, inspection, flight test, and operational safety program administered by a CBO;

  (4) The aircraft operates in a manner that does not interfere with, and gives way to, any manned aircraft; and

  (5) When flown within 5 miles of an airport, the operator of the model aircraft provides the airport operator and the airport air traffic control tower (when an air traffic facility is located at the airport) with prior notice of the operation. Model aircraft operators flying from a permanent location within 5 miles of an airport should establish a mutually agreed upon operating procedure with the airport operator and the airport air traffic control tower (when an air traffic facility is located at the
  airport).

  d. Public Law 112-95 recognizes the authority of the Administrator to pursue enforcement action against persons operating model aircraft who endanger the safety of the National Airspace System. Accordingly, model aircraft operators must comply with any Temporary Flight Restrictions (TFR).

  ...

  Model aircraft must not operate in Prohibited Areas, Special Flight Rule Areas or, the Washington National Capital Region Flight Restricted Zone, without specific authorization.

  e. Model aircraft operators should follow best practices including limiting operations to 400 feet above ground level (AGL).

  f. All other operators and for additional information on Unmanned Aircraft Systems please visit: http://www.faa.gov/uas/ .

Note that this is "guidance" and recommended procedures that the FAA "encourages voluntary compliance with" in order to "reduce the potential for hazards and create a good neighbor environment with affected communities and airspace users."

That being said, any city/county/state could have rules on their books, but there is not national guidance for this.


What is the probability that passengers can survive a ditching in a 747 at MTOW? Let's suppose a catastrophic EFATO has occurred while climbing out of JFK from Runway 31L, the aircraft is at its MTOW and the best option is to set it down in Jamaica Bay. How long would the aeroplane float and what are the chances of surviving?

Aircraft are designed with ditching in mind, but the outcome depends on many circumstances, most importantly on how calm the water is and how well the aircraft can be controlled.

The Wikipedia article on Ditching lists emergency water landings and other accidents where aircraft ended in water.

There is no ditching by 747, so we don't have any specific reference. However:

B747 is not that different from other types of aircraft. Controlled ditchings on calm water were successful in different types; it is likely that one would be possible with B747 too.
How long the aircraft would remain afloat depends on the damage. But if it did not break up, it would likely manage to keep afloat for the 90 seconds needed for evacuation. And the slides can be used as life rafts.
There was one case where B747 ended up in water after overrunning runway (so at lower speed than landing), China Airlines flight 605, and the aircraft did remain afloat long enough to evacuate it.
Also any aircraft that will be used for flying across large bodies of water, which obviously includes all variants of B747, must be certified for ditching. This involves designing it so that, at least according to model, a controlled ditching will be smooth enough not to cause serious injuries to occupants and will leave it afloat long enough for successful evacuation.


Do multiple go-arounds on the same flight happen in commercial aviation? I know that go-arounds are pretty rare: somewhere around 2 per 1000 approaches. In large commercial aircraft the rate is probably even lower due to crew quality, instrumentation, conservative decisions etc.

But are there instances of multiple go-arounds having to be initiated by a flight crew on one flight? I'm just curious to hear of any such stories. Two GAs? Three GAs?

I suppose if the reason is Weather related or equipment related the chance of a multiple go around might exist?

A related question is after how many weather related go-arounds would the crew decide to divert to the alternate. Either by rule, company procedure or plain heuristics.

P.S. Let's restrict this to non-training flights by scheduled airlines.

None of four airlines I worked for (two commuters, two Part 121) had specific guidance as to the max number of go-arounds. However, as mentioned in the other answers, 2 or 3 was believed to be a good rule.

The only time I did multiple go-arounds, all missed approaches, was trying to get into Pullman, WA during a snowstorm in the late 1980s in an SA-227 Metroliner. I tried the VOR approach 3 times. Each time when we got down to the MDA, we did not have the forward visibility to descend further. Each of the 3 times the station personnel saw us pass over, and each time passengers looking out the windows saw the runway below us when we were overhead. That, of course, resulted in our being criticized when we arrived at our alternate by some passengers for not having landed at Pullman. I had explained en route to the alternate the problem with forward visibility, but when you've disrupted people's travel plans, they don't want to listen.

I briefly considered the feasibility, when we were over the runway, of entering a tight left turn to see if I could keep the runway in sight, but I rejected that. And, yes, I considered descending below the MDA before catching sight of the runway. That would have been doable as I was very familiar with the airport and knew that the gently rolling fields around the airport topped out well below the MDA.

The problem was that with all the snow on the ground and the snow in the air, we couldn't determine our altitude above the ground visually until we were actually over the runway. The fields around the airport had no trees, they were wheat fields in season. Even if I had chosen to bust the MDA, I still would have been too high for any kind of a normal landing when I caught sight of the runway end. If getting down was an emergency, we could have done it. It wasn't technically legal, but you could go into beta with the props and really drop out of the sky, then as you flared come out of beta. But it wasn't an emergency, so we went to our alternate, which was actually our next stop anyway, so all of the passengers weren't unhappy.

The advantage of multiple approaches is that conditions might get better while you're doing them, and you can get in. The disadvantage is that the nervous energy you're expending is telling.

Our SA-227s had no-autopilots, no radar altimeters, and, of course, no GPS. I imagine that these days that airport has one or more GPS approaches that would make landing in those conditions a piece of cake.


What was the first aircraft equipped with a RAT? RAT are common in airliners today to provide  emergency electrical and hydraulic power. Yet, firsts airliners (prior to WWII) may not require the same amount of power than today's airliners (which are bigger and require electrical and hydraulic power to keep all electric-assist requirements, computers, hydraulic actuators,...).

The historic section of the wikipedia article speak about windmilling on the FW-189's engine as a precursor to RAT, but I fail to see anything related to first device whose only role is provide power.

My question is: What was the first aircraft equipped with a RAT? Was it military or civilian (it may not be a airliner)?

EDIT: given the comment by Peter Kämpf, I edited the question to include all aircrafts. Thus having an answer mentioning both airplanes and other aircrafts.

So far, the oldest I have found is LZ-127 Graf Zeppelin, first flight in 1928. It used a propeller-driven generator to power its radios and a second one (with buffer battery) to keep the ship illuminated. In the drawing below (source) they are indicated as "Wind-Dynamo", being on both sides of the main gondola.

I am rather sure that the wartime Zeppelins used those generators as well, but have yet to find proof for it.

LZ-127 on August 26, 1929, in Los Angeles (source). The right generator is circled in red.

EDIT: Now I have found a source that attributes a RAT to the Zeppelin Staaken Riesenflugzeuge of WW I. The source is Tom Morrison's book "Quest for All-Weather Flight" and it says on page 28:

  In November 1917 the Drexler bank indicator was introduced instead [of the Anschütz gyro]. Much simpler than the Anschütz instrument, it weighed only 5 kg (11 pounds). It was powered by electricity from a generator driven by a small propeller in the slipstream and took less than a minute to run up to speed.

So this dates the first RAT back to November 1917. Sorry, no online sources.


How do I calculate the normal component of the velocity at the midpoint of a source straight panel? I am reading "Fundamental of Aerodynamics " by J.D.Anderson Fifth edition. Now I am at the chapter 3. If you got the book, please go to the page 286, the part that says: "when j = i, the contribution to the derivative is simply $\lambda/2$ ". How could it be $\lambda/2$ ? I thought it would be zero.

I will summarize the problem for those who don't have the book:

We have a uniform flow and a source sheet cover the the surface of a known body. We have to find out the $\lambda=\lambda(s)$ along the source sheet that when we superimpose the uniform flow with this source sheet, we obtain the streamline over surface of the body.

A source sheet is an infinite number of line sources side by side,
where the strength of each line source is infinitesimally small

We approximate the source sheet by a series of straight panel over the body surface (if we take n panels, then we have to find n values of $\lambda$)  and calculate the velocity at each panel and set the normal component of it equal zero.

Take a point $P$ at the middle of $i$th panel and calculate the velocity at $P$ induced by the panels, or just calculate the normal component of the velocity at P. The book said that the normal component of the velocity contributed by only $i$th panel at the mid point $P$ of this panel is $\lambda_i/2$. I don't know how to calculate this, I have tried and thought it would be zero.

@Peter: Look at the image, you can see the velocity induced at P by the panel i is in the ab-line direction (I mean the horizontal direction). Then, the normal component (vertical direction) of it will be zero

You can find a mathematical derivation of the $\lambda_i/2$ result in Katz and Plotkin, chapter 10. In this PDF, the result you are looking for is on page 234 (250 of the file itself). Anderson approaches things a bit differently, but you should be able to see at a high level how the approaches are analogous. The math gets a bit complicated and it's really not necessary to comprehend every step in detail to understand the application to aerodynamics. However, a good exercise if you really want to dive into the math is to translate Katz and Plotkin's approach into Anderson's notation, or vice versa. For me, though, it's good enough to see that it can be done and move on with the more interesting applications.


What is the source of emergency power for a 727? I've found a couple of sources that state the 727's APU cannot be started while flying, as it draws air from the wheel well.

  It drew air from inside the wheel well, so it was only for use on the ground.

https://aviation.stackexchange.com/a/37715/34744

  The APU on the Boeing 727 can be used for ground operation only.

https://www.boeing-727.com/Data/systems/infoapu.html

Additionally, the battery on the 727 doesn't power all of the systems on the "essential bus", and presumably cannot start the engines.

http://cyberpilot.tripod.com/electrical_system.html

So what happens if you lose all engine power in a 727? How can the engines be restarted?

According this rather detailed page on the 727's engines:

  To restart in flight, an "air start" may be attempted. The start
  switch should be placed in the FLIGHT START position which will arm
  high energy ignition. The starter valve will not open. Ram air
  entering the engine is sufficient for start if the aircraft's speed is
  above 150 knots. When the start lever is moved to IDLE, fuel is
  introduced and the igniters are activated.


How can a stowaway hide in the undercarriage? I'm curious about how and where a stowaway could hide in the undercarriage of a plane.

According to this news report:

  The man, believed aged 24, was found in the undercarriage of the
  plane and was taken to hospital.

Wheel wells are deceptively large spaces when the gear is down. It is fully possible to climb up and hide inside one. It's a very different story when the gear is retracted. On many aircraft, the gear doors are  closed when the gear is not in motion, making the space look bigger.

They are fairly easy to access through the landing gear with a little bit of climbing, or if low enough (like the example below) just jump up into.

 737 Wheel Well, Petr Volek, from airliners.net

A graphic about a similar event in Hawaii a few months ago:

 From the Independent

Gear stowaways are not new and there have been plenty of occurrences over the years, unfortunately most result in fatalities.

Gear bays are unpressurized, hence normally very cold with air too thin  to sustain life.
Gear bays are very cramped when the gear is up. If you're in the wrong spot, you will be injured.

It is when the landing gear is lowered (and doors opened) for landing that the fatalities occur, assuming they have not already expired from the environment during the flight. Unable to hold onto the airframe and stay off moving parts they (very gruesomely) fall out minutes away from landing. This is also the story that media often picks up.


Was I nearly involved in an accident? This is a while ago but it has been bugging me now and then.

On September 11 2011 (yes exactly 10 years after 9/11!) I was flying Easyjet 3467 from London Stansted Airport (STN) to Copenhagen (CPH). Scheduled departure was 18:40 local time but the flight was heavily delayed (around 4 hours as I recall) due to another bizarre incident.

Anyway, as we were finally sitting in the plane and taxiing, suddenly the pilot announces that he just got info that another airplane had been heading to land just where we were and had only been some 60 seconds away! A lot of passengers seemed to gasp for air and the pilot sounded quite shocked as well. But there was no other explanation added.

Is there a database of such events so I could look up more about what happened?

I found the flight on FlightStats (sign in required) but there were no real info.

No, you were not nearly involved in an accident.

If the flight crew is ready to go, an Airbus A320 takes about 40-50 seconds from the moment take-off clearance is given until lift-off. As soon as the aircraft is off the runway, the next one can land. On some busy airports, 60 seconds between take-off clearance and the next landing is a daily occurrence.

In 60 seconds, there is a lot that can prevent an accident. For example, ATC could instruct the incoming aircraft to go around should the departing traffic not be ready to take-off. This is quite a normal event which happens every day at busy airports around the world. In such a case, the aircraft ready for take-off would have to wait for the incoming traffic to pass overhead. It sounds like you may have experienced such an event.

Here is a video of something similar happening in Birmingham.

Since it is a 'normal' event, there is no central database that tracks these issues.


How do I choose the correct params? I am very new to airplane design. I am working on this project to design a flying wing glider (no propeller) that would glide in a circular pattern with a fixed radius of 250 m after being released at a height.
Here is all that I know now:
I was reading around the internet that a choice of delta wing would be good for maneuverability of the glider, however it would be bad for operating at low speeds. I guess that this design would not fit me because it has very poor lift. But at the same time a wide plank kind of design would not be able to perform a turn that well. So I've decided to choose a swept wing for the flying wing. However, I am not able to decide properly the angle of sweep required. I know that the stall angle and the twist of the wings depend upon it, but I don't really know how to tackle the problem (as I guess I would require a high stall angle to provide me the lift).
When it comes to choice of airfoils, I am currently looking at HS522, MH60, and NACA 22112 and Eppler 186 airfoil. However, again I can't really choose between them. From my understanding, I require a reflexed airfoil with high camber and high thickness to provide me with good lift as I plan to operate at slow speeds close to ~20 m/s.
Wing loading and banking of the turn is another thing that I understand is related to each other but I don't understand how I can reach a common point between them. From my preliminary analysis of the situation, I have reached a bank angle of 9°. Is that a good angle? I read on online resources that the standard bank angle is 25°. Is that relevant in this case? Or do I approach this problem by deciding the wing loading and then move on to the bank angle?

Thanks

A flying wing needs an airfoil with an s-bend, so no regular airfoil (none of the ones you mentioned). And you need to incorporate a significant twist towards the wing tips to make it fly stable (incidence is about 10° lower at the tip).

Knowing your turn radius and your desired speed your bank angle is a given, independent of aircraft mass. You can compute it with the centrifugal force and the lift portion that points into the turn...

r = TAS * TAS / ( g * sin( bank ) ), with true airspeed (TAS) in m/s, g = 9.81 m/s/s, r in meters. (if I'm not mistaken)

When you know the mass of the aircraft (roughly) and your airfoil lift coefficient that you want to work with (e.g. 0.5 to 0.8 or so) you can work out how much wing area you'll need to fly that turn without stalling. You could also chose a wing loading and compute the lift coefficient for your turn using the basic lift equations and the force equilibrium...

25 degrees is a good bank angle for passenger aircraft, more makes the passengers scared :) Not applicable here.

I'd start with an existing design of a flying wing and then make alterations to that. A famous aircraft that comes to mind is the Horten H.IV glider. Another example could be the Marske Pioneer 3


Were there any test flying incidents during which the pilots managed to escape the plane? I am only asking about flight testing civilian jets, not military ones. I know that all test pilots have to be equipped with a parachute, so I wonder was there any incident where the test pilots and test engineers had to leave the plane during the flight, and managed to reach the earth? Alive or dead.

Do civilian space ships count?

In the VSS Enterprise crash  the captain survived. The plane broke up around him and he was able to unstrap his seat after which his parachute automatically deployed. The co-pilot died in the crash.


How do hot air balloon pilots avoid collisions? There are many places in the world where hundreds of hot air balloons are flown in close proximity to each other. How do the pilots steer them away from each other to avoid mid-air collisions?

Wind blows all of them in one direction and I'm sure there are plenty of calculations done by these expert pilots prior to taking off, but I am also sure that not all the balloons will react to wind at exactly the same rate.

What happens when they are getting too close for comfort? Do they have horizontal movement control?

Credits: NewYorkUpstate.com

Ironically this image already has one collision in it on ground.

I grew up in a family hot air ballooning business, and while I haven't been involved in a few years, I can answer your question in two words: They don't!
Taking Off
As far as collisions go, the other answers have mostly addressed this: hot air balloons only control vertical movement, so with all the balloons experiencing the same wind, they'll move at approximately the same speed.
When taking off, we always angled the balloon so that the wind would blow from basket to envelope. In a large group, such as at festivals, we would maintain the same practice as much as possible, and have a line of balloons perpendicular to the direction of the wind. Often, this would restrict the space enough that inflating balloons would roll slightly into adjacent ones, but with a competent/strong person on the crown-line (the rope attached to the top of the balloon, used to maintain stability in the event of crosswind), the small gusts which caused localized rolling could be overcome.
In large groups, when a balloon is ready to lift off, the pilot will typically ensure nobody is going to be directly overhead, then apply more heat to lift out quickly. This prevents the basket from catching any of the envelopes of the balloons still on the ground. As mentioned, once in the air, collisions are not really a problem.
EDIT: I believe you can see two balloons on the ground but vertical which are pressed up against each other in the picture you've provided. Try looking near the middle, just to the top left. You can see that the envelopes are harmlessly pushing away from each other while the baskets are still quite far apart.
In The Air
Balloons are huge and move slowly, particularly slowly relative to each other. If two balloons are exactly level and one directly blocks the wind to the other when a gust comes, it's possible for one to suddenly gain speed. I've never seen gusts strong enough or long-lasting enough to create a speed difference of more than a couple miles per hour, so when the balloons do touch, the envelopes gently 'kiss,' then bounce back. This can, at worst, create a slow rocking of the basket.
Now, the last situation, if a pilot is unaware of another balloon directly overhead and starts going up, it could be a problem. However, pilots typically have radios and can communicate with each other if it's necessary. The pilot in the unseen balloon above would start applying heat to try to get out of the way as well as radio some (likely unkind) choice words to the pilot below him.
Landing
This is more of an after-thought, but if a pilot wants to land and another balloon is already there, the pilot will simply stay in the air a little longer to find another landing site.
Competitions
A second after-thought, but I know about 10+ years back there were a couple competitions at festivals where pilots would receive a special ribbon device and a partner-balloon. The device would mark the longest the ribbon had to extend. Each of the pilots would attach one end to their basket, then the duo who stayed the closest to each other would win a prize.
Another type of competition also occurred in which the pairs of pilots would take off about 15-30 minutes apart and the second pilot would have to try to land as close to the landing site of the first one as possible. Sometimes, this meant landing at roughly the same time and in uncomfortable proximity. Safety is always the first concern of a good pilot, though! If a pilot wasn't sure it could be done safely, he or she wouldn't do it!
Summary
As longwinded as this is, the gist of the answer is that balloon-balloon collisions aren't very serious unless the basket is involved. Typically, they move slowly enough to make it easy to avoid unwanted collisions, despite their lack of horizontal control.


Can Air planes fly through rainbows? I am wondering whether or not it is possible for an air plane to fly through a rainbow, and, if so, does anyone have any pictures or experiences of what you can see?

I've always been intrigued by this.

A rainbow is created by refraction of sunlight so you have to be in the right position to see it. The effect is only created at some distance. A rainbow that you see from the ground may appear to be in a particular place in the sky. An airplane could fly through that space and it might appear to you that it is passing through it The occupants of the airplane, however, would not see a rainbow there.


How does altitude affect the speed of sound? I read once that the speed of sound decreases as altitude increases.  I wonder if that's true and, if so, are the pressure waves made at high altitude lesser than the ones at low altitude because of the difference in air pressure?  And, lastly, does that mean that lower speeds at higher altitudes will be subject to the problems one encounters when approaching mach speed?

I read once that Mach speed decreases as altitude increases.

The speed of sound is solely dependant on temperature.

$$
M = \sqrt{\gamma RT}
$$

where $\gamma$ is the ratio of specific heats, $R$ is the molar gas constant and $T$ is the temprature in Kelvin. For Earth's athmosphere at 15° Celsius,

$$
M=\sqrt{1.4\times 287\times 288.15}=340\,\text{m}/\text{s}
$$

Does temprature decrease with altitude? Well, not always as can be seen by the international standard atmosphere:

(source: cam.ac.uk)

  ....are the pressure waves made at high altitude lesser than the ones at
  low altitude because of the difference in air pressure?

There is no simple answer to this. Here's NASA's opinion:

  Altitude determines the distance shock waves travel before reaching
  the ground, and this has the most significant effect on intensity. As
  the shock cone gets wider, and it moves outward and downward, its
  strength is reduced. Generally, the higher the aircraft, the greater
  the distance the shock wave must travel, reducing the intensity of the
  sonic boom. Of all the factors influencing sonic booms, increasing
  altitude is the most effective method of reducing sonic boom
  intensity.


Why would METARs and ATIS both report exactly the same wind direction? I understand that METARs report wind direction as true and ATIS reports it as magnetic. But at Camarillo (KCMA) both are reporting the same wind direction and speed even though the magnetic variation is 12.5 degrees. Why does the written versus spoken rule not apply here?

For the US
From the FAA ATC manual:

2−9−3. CONTENT

NOTE− [...] The ASOS Operator Interface Device (OID) displays the magnetic wind as “MAG WND” in the auxiliary data location in the lower left−hand portion of the screen. Other OID displayed winds are true and are not to be used for operational purposes.

Which confirms the ATIS winds are magnetic.
I just listened to KCMA ATIS, the wind reported is 10 degrees more than the METAR.
Make sure you match the ATIS and METAR times. On liveatc.net they were not the same, I had to check the METAR from aviationweather.gov to get the correct reporting time.

For Europe
It's not the same.
Both METAR and ATIS report mean wind information, for the direction, both report in true heading. ATC report is magnetic.

ATIS wind velocity is latest two minute average. The wind direction broadcast is given in degrees true.
[...]
ATC plain language ad hoc wind directions given during final approach or just prior to or during the take off roll are likely to be given in degrees magnetic.
— skybrary.aero


Which Airline don't use the Flight Number 191 anymore because of bad luck? This question came up while reading an article about mysterious plane incidents. It told that some airlines do not use the flight number 191 because of bad luck.

  In fact, there have been so many catastrophes that, much like hotel
  owners who refuse to have a 13th floor, some superstitious airlines
  have completely done away with the number “191.”

Does somebody know some Airlines who are not using this flight number
for that reason?

Well, you can be pretty sure that Delta and American no longer use that flight number, as it is pretty standard for airline to retire a flight number of an accident flight.

Beyond that, I'm sure there are a multitude of carriers still using Flight 191.

For example, Air India 191 is in-flight at the time of writing . Air Canada 191 is scheduled


In what portion a non-GPS approach, can a pilot legally fly with GPS as primary navigational resource? In IFR-GPS-equipped (/G) aircraft, a pilot flies most of the segments with GPS as primary navigational resource* even the route is along victor airways or VOR radials. However, when we start the approach, we have to switch the nav source from GPS to the nav source specified for the approach. In this context of using GPS for non-GPS approaches,

When should a pilot switch away from GPS? Is it from an IAF, FAF or upon ATC vectors to intercept the final approach course?
If the a pilot executes a missed approach, when can the pilot switch back to GPS? Is it when established on course direct to the holding fix?

*By primary navigational resource, I mean it provides the signal/data source for the CDI needle on a HSI, that a pilot, autopilot or flight director refers to make actions or action suggestions.

An appropriately installed GPS may be used until crossing the final approach fix on a non-localizer approach, and until the segment requiring navigation via the localizer on a LOC, ILS, SDF, or LDA approach. It's generally approved and legal at any other time.

During the missed approach, a pilot may switch to GPS immediately, unless the missed approach requires navigating by using the localizer, in which case the ground-based navaid must continue to be used until the procedure no longer requires navigation by reference to the localizer.

The FAA covers this in AC 90-108:

  An otherwise
  suitable RNAV system cannot be used for the following:
  a.   NOTAMed   Procedures.
  Unless otherwise specified, navigation on procedures that are
  identified as not authorized (“NA”) without
  exception by a NOTAM. For example, an operator
  may not use a RNAV system to navigate on a procedure affected by an expired or unsatisfactory
  flight inspection, or a procedure that is based upon a
  recently decommissioned NAVAID.
  b.   Substitution on a Final Approach Segment.
  Substitution for the NAVAID (for
  example, a VOR or NDB) providing lateral
  guidance for the final approach segment.
  c. Lateral Navigation on LOC-Based Courses.
   Lateral navigation on LOC-based courses
  (including LOC back-course guidance)
  without reference to raw LOC data.


What was the record for the highest man-made flight before Gagarin's spaceflight? My recent conversation with uhoh reminded me of something which stays kind of unmentioned in history of air and space flight, namely the altitude record prior to Gagarin's Vostok 1 mission. I wonder what the highest human flight had been before the first spaceflight occured. There's a Wikipedia list on (airplane, helicopter and balloon) flight altitude records: Flight altitude record, which but is quite muddled up. From the list I conclude that Iven Kincheloe's Bell X-2 flight on Sept 7, 1956 was the altitude record until Vostok 1, Kincheloe having reached an altitude of ~126,300 ft (~ 38,5 km). Am I right and why does it remain so unmentioned, somehow? I mean like it was the highest flight until Vostok 1 and the highest airplane flight until the ones of the X-15.

Joe Walker flew X-15 #2 to 169,600 ft (51.7 km) on 1961-03-30, thirteen days before Vostok-1.
Source: X-15 flight log


Does autopilot disconnect when a danger alarm like GPWS triggers? I was wondering if any of the (E)GPWS callouts would make the autopilot disconnect?
If the Alpha Protection is active (like in Bilbao, 2014) would it disconnect? That would give PF full control of the aircraft and could help to recover from the upset, correct?

This is the Quick Reference Handbook procedure from an old A320 training manual.

(The EGPWS procedure is a memory item, pilot's are not expected to look this page up when they encounter a EGPWS warning)

The first two sub items answer your questions. The autopilot needs to be switched off manually and the instruction is to pull up to full back stick and maintain. The Alpha protection will prevent the aircraft from stalling, that is why the stick can be maintained at full back deflection.

Airbus' safety magazine FAST #23(PDF) giving guidance on flying protected aircraft, specifically advices pilots to apply full backward stick deflection in GPWS situations since the alpha protection will prevent the aircraft from stalling and the resulting flight path is the most effective way away from danger.

To illustrate a possible the effects of Alpha protection in an (E)GPWS situations, let's go to Bilbao again, but now in March 2001(PDF). An A320 on final approach encountered a wind shear causing the aircraft to descent fast. This caused the GPWS to trigger a warning. The pilot applied TOGA power and back stick deflection, but the Alpha protection predicted the aircraft to stall and prevented a higher nose attitude. As a result the aircraft didn't stall but crash landed on runway threshold. This accident demonstrates that the GPWS does not affect the flight envelope protection system.


How do airplanes get stacked in a holding pattern? This question prompted me to wonder how it works at a major airport. Let's say four airliners all are scheduled to arrive within a few minutes of each other to a major airport, perhaps from the four cardinal directions. Things are already backed up at the airport, let's say landings are (temporarily) restricted due to an emergency landing.

Can you describe how ATC might direct the four flights and what they would do themselves?

ATC has many tools "in their belt" to keep traffic separated. When things back up, it can get crowded. Emergencies and weather regularly cause disruptions and ATC handles them according to the circumstances.

To illustrate some possibilities, I will use Seattle as an example here. You can find the airport information here.

Most aircraft coming into the area will be commercial flights on IFR flight plans, and they will follow a Standard Terminal Arrival (STAR) into Seattle. You can find this seciton towards the bottom of the AirNav page. There are different STARs depending on the direction from which the flight is arriving. Each STAR will include published holding patterns.

Listed here is the direction of arrival, the name of the STAR, and the holding fixes:

East - EPHRATA - FLAAK, EPHRATA, ODESS
East - GLASR - LOSTT, TEMPL, JAKSN
Southeast - CHINS - SUNED, BRUKK
South - OLYMPIA - BTG, OLYMPIA
Southwest - HAWKZ - BTG, HAWKZ
Northwest - JAWBN - JAWBN
Northwest - MARNR - MARNR

As you can see, there are 11 different holding fixes across the seven STARs. If you have one aircraft from each direction, they can each hold at the fix according to their STAR. The busiest STARs have multiple holding fixes that may be used. Aircraft may also be stacked on the same hold at different altitudes. You can read some FAA information about holds here.

Aircraft may also choose to divert. Depending on how much fuel they have and how the weather/emergency is playing out, they may not want to hold indefinitely on the GLASR arrival at LOSTT. Generally ATC will not ask for a diversion unless absolutely necessary. Among others, Portland, Vancouver, and Spokane are all fairly close to where the aircraft may be holding and could be viable alternates.


How difficult is it to avoid ground loop in practice? In my simulator (flightgear) directional control during take-off of most tail-draggers is extremely difficult. When the tail lifts off, it immediately starts to turn to the left with no crosswind, but with sufficiently strong crosswind from the right it might be to the right. It takes very swift and hard rudder application to arrest and then easing the pressure to avoid overcontrolling. Otherwise the turn rate keeps increasing and ground loop occurs.

It is worse with some models than others. Some models are almost impossible to take off at full or normal take-off power and while most are, it is very difficult to keep them on the runway, because even if I manage to arrest the initial swerve, the aircraft is then turned a bit and attempts to re-align it tend to again provoke ground loop.

Controlling propeller aircraft with tricycle landing gear is on the other hand never difficult, even for the more powerful ones.

I suppose some of the models are wrong. For example the Pitts S1C model is almost impossible to take off. But how difficult should it really be to keep the plane aligned?

And, what would likely be wrong with model that is too difficult to control? Centre of gravity too far aft of the mail landing gear? Or something with the vertical stabilizer? There does not appear to be any parameter for vorticity of the propeller slip stream; it is apparently calculated from the power.

Or is this one of the cases where simulator is much more difficult than the real thing, because in the real thing you have force feedback and get to use your built-in accelerometer (vestibular system) and in the simulator you don't?

Your simulator gives you a realistic experience: This is normal. What you experience is the gyro effect of the propeller and engine while you change the pitch attitude. When you lift the tail, the axis of rotation is changed and the engine-propeller combination pushed downwards, causing a precession force which acts orthogonally to the plane defined by the down movement and the axis of rotation.

Since the engine is forward of the center of gravity, this precession force is pushing the nose sideways: Left for a propeller which spins clockwise (when observed from the pilot's viewpoint), and vice versa.

The best way to avoid a change in direction is to keep the tail to the ground with the stick aft until you know you are fast enough to lift the tail, and when you lift the tail up, you apply rudder simultaneously. Don't let the tail come up by itself!

I learned this in a Dimona motorglider. Now think of flying a small, light airplane where the propeller is bolted firmly to the heavy engine crankcase, both rotating. The airplane will dive or climb when you change direction! This is what pilots had to endure in the First World War, when they flew aircraft with rotary engines. When engines became more powerful, this became so bad that some aircraft were almost unflyable. See this answer for more.

That crosswind is turning the nose into the wind after lifting the tail should also be no surprise: While the main gear is still on the ground, the plane will weathervane into the wind once the tail is lifted.


What is the optimum viewing angle to search for something on the ground from the air? Continuing my series on our upcoming search for a downed Douglas B-18 bomber in Alaska* (13 more days to go!), I've started to think about the angle we should use to "look down" at the terrain.  This is especially important because I will be mounting go-pro like cameras on the airplane to capture what we "see" on the ground as we go.  I will do this with this handy tie-down mount I came across:

This mount allows the camera's to be positioned at any downward angle.  I wouldn't think that either straight down or straight ahead would be optimum...I would assume a good angle would be somewhere in between.

Obviously this question has some relation to photography, and I may also post this question to Photography.SE.  However, I would also assume there are a great number of pilots and other aviation professionals with experience searching from airplanes/helicopters for things on the ground.

So my question is, what is the best angle (relative to straight ahead) to search for something on the ground?

Keep in mind that I will be searching over glaciers around an active volcano in partially snow covered terrain.

* Related posts:
Where can I find more information about my grandfather's crashed B-18a bomber on Mt. Redoubt Alaska? and
What navigational aid(s) would WWII bomber pilots have used while flying in instrument conditions?

Straight Down is most likely the best angle but there is of course cases to be made for other scenarios. In your case if you are looking for something on the ground that is potentially obstructed a straight down view is going to give you the most direct view and will prevent something from falling out of frame if an angled view cause an obstruction to block it.

The real problem in areal viewing/photography/imaging is the air its self. They touch upon it in this podcast nicely but when it comes to spy satellites (a similar use case) the actual resolvable resolution was limited by the air not the imaging sensor. Its important to go up on a clear day as haze, even VFR legal haze can have a big impact on this.

If you are intending on using a GoPro I might advise getting something with a longer lens (especially if you intend to be at any kind of substantial altitude). For comparison you can check out some of the stuff I have captured with a GoPro here none of that footage was shot over 5000 and most of it below 3000 and it is difficult to pick out smaller objects on the ground in the footage. At the flat mounting angle I use you can see how trees obscure things behind them.

As for mounting bigger lenses, its clearly impractical to point large lenses straight down but there is a work around. Historically spy planes used some kind of mirror set up to look straight down at the ground mounting the large lenses flat in the plane pointed at a mirror.

There are even some smaller GA planes built for this specific purpose with cameras already mounted. Some may simply have a camera trap door. It may be worth it to try and track down this kind of service for your mission.

Your lens choice will also be quite important. The GoPro has a fairly wide lens which offers a great big field of view but considerable edge distortion in actual practice at longer distances. I would advise trying to rent or borrow (unless you own) a decent DSLR with a standard to short-tele lens. On top of that I would not video tape the adventure, I would set the camera to take a series of time laps photos pointed straight down. Most modern cameras can resolve a much higher res image photo than they can video and in the end of the day at a modern frame rate you are going to end up with a log of overkill footage at your given speed. This is how planes like the SR-71 did it back in the day. In this case a decent GPS enabled camera is key, remember you are looking through this data after the fact so you need to know where the picture was actually taken to make it useful.

You also need to think about field of view a bit. The wider the lens the more land you can cover in a single pass at a given altitude but you do so at the cost of angular resolution. The longer the lens the smaller field of view with the benefit of higher angular resolution.

Note: You will find some info out on the web about the use of wide angle lenses in areal imaging. The common ones were the likes of the Zeiss Biogon and Distagon mated to either a custom platform or in the case of the moon missions a Hasselblad body these particular lenses are phenomenally sharp in the edges even wide open. They are however the exception to the rule and most modern wide lenses make trade offs to be compact and light weight. To be safe I would stay away from wide lenses (anything bigger than maybe 28mm on your standard Full Frame SLR) for your trip.

One fairly reasonable option is the variety of mirror reflexive telescope/tele-photo lenses out there. Something like this one could be useful in your endeavor. A few of these have passed through my collection and they are far from great but they do get the job done when you need a big lens in a small package. However I would take a used lens like this one which can be had for the same price any day.

For the sake of a complete answer Im going to add more details although in your specific case they may not apply.

The most successful areal imaging programs quickly adopted stereo imaging setups. In this case 2 cameras were used each mounted slightly off axis of centerline. The Corona program as well as the KH-7 Gambit satellites used such a system with great success. The images when viewed later created a somewhat 3D rendering of the ground which provided superior analysis abilities over the more traditional single camera units. This kind of effect could be achieved with 2 cameras mounted on some kind of bar and a little pre calibration.


How does a plane's weather radar ignore returns from other weather radars? In busy and congested airplane areas (around large airports, for example), there could be dozens of commercial aircraft, all with their own weather radar transmitters/receivers actively transmitting and receiving radar signals.  How are the radar receivers able to discern between their own radar's returns from those of other aircraft?  I can't imagine them to all have different TX frequencies to prevent interference, but not sure how else the receivers could be set to reject other aircraft's radar transmissions.

"Radar to radar interference" / "Mutual radar interference" is an ongoing research topic, though much of the current research (based on my cursory Googling) seems focused on interference between radars on self-driving cars.  That leads me to believe a certain degree of radar-to-radar interference is currently just tolerated.
The link shared by randomhead gives us some insight into how maritime radars mitigate mutual interference, both directly and indirectly.  The same techniques should be applicable to aircraft weather radars, which tend to also be X-Band and also be pulsing radars.
Directly

The interference rejection capability of the radar essentially relies on timing differences between the radars.  A pulse radar sends out many pulses, separated by around 1 millisecond.  Microsecond-resolution timing between the transmission of the pulse and the receipt of its echo is used to determine range to a target.
Interfering radar pulses will arrive somewhat randomly on that microsecond timescale, but actual target echoes (e.g. from weather) will be correlated across multiple pulses.  The radar can be made to only acknowledge a return as real if enough echoes arrive.  Related topics here seem like "m-out-of-n" detection, "binary integration", "coincidence detection", "dual threshold detection", and "double threshold detection".
Activating the "interference rejection" mode on a radar (or having it always on, which I suspect is the case on many aviation weather radars) will cause a radar to reject certain weak real returns (more false negatives).  Luckily, clouds full of precipitation tend to return radar fairly well.

Indirectly

A different section of the same link gives instructions for tuning radar.  This implies that there is room in the band for more than one transmitter to be operating simultaneously, though it may not be organized formally into channels.  This is reinforced later in the description of the Search and Rescue Transponder (SART) scanning the radar band for pulses to reply to, which wouldn't be necessary if they all operated on the same frequency.
So, automatically or manually, weather radars should also be able to deconflict by frequency separation.  This will, of course, run into limitations as the number of transmitters grows, but at least it reduces the amount of work the Interference Rejection mode has to do.

If the radar can change properties of its pulse, such as the pulse length or frequency modulation, it can potentially use those properties to distinguish between its pulses and pulses from other transmitters.  The link doesn't really support that being used to reduce interference in maritime navigation radar, though, and I kind of doubt it's used for such in aviation weather radar either.  I think I've heard of schemes like that being used for more warfare-oriented radars but that's even further outside my own expertise.


What is the difference between Mechanical Engineer and Aerospace Engineer? I really want to get into the Aerospace Engineer industry (I want to design the plane's airframe and basically a little bit of everything) but have no idea what to major in for any job.
I'm really thrown off by all these sites which have mechanical engineer and aerospace engineer jobs but they consist of basically the same job description.
Can you please clear this confusion for me?

If you want to work on the landing gear or passenger seats, a mechanical engineering education is the best qualification.
If, however, you want to work on control surfaces or fairings, an aerospace engineering education is better suited.
While both teach similar basics, the aerospace education is much heavier on fluid mechanics and lightweight design. Having studied aerospace engineering in Germany, I was shocked to learn that master students in Aero/Astro at MIT had no idea how to design a screw connection. Therefore, much depends on the country and its ways of teaching. In the US you will get an excellent education in one narrow field at the cost of breadth. In other countries your education might take longer and give you less expertise in one field but will cover the fundamentals much better.
In general, at university you will be taught how to learn. You will learn the basic stuff which will enable you to read special literature and you will learn where and how to locate resources that help you along. This will be the same in both branches and it depends on you to round out your knowledge yourself.
To quote from an earlier answer:
Take the example of Ed Swearingen: He never went to engineering school, but spent years working with airplanes, gradually moving from handling to repair to improving them. In the end, he was a successful self-employed consultant who helped with a number of airplane designs and created some of his own designs, too.
So here is what I propose to do:

Hang out at a local airport (ideally one with lots of hardware passing through the local repair shops).
Don't shy from getting your hands dirty and from asking questions until you are satisfied with the answer.
Try to find experienced engineers and work closely with them.

Do that for 10 years and you will be hard to beat as an aircraft designer. If you happen to attend University in Germany, be sure to become a member of one of their Akafliegs - that is the best start into an aviation engineering education.
It also helps to build and fly model airplanes. Models can give you valuable lessons in aerodynamics and flight mechanics.