How much thrust is needed by an aircraft to have vertical takeoff? In some airshows, I have seen some big aircraft (like 737) takeoff almost vertical.

Generally, fully-loaded passenger/cargo planes don't do that, I guess due to safety issues but I think there needs a lot of extra thrust to have an almost vertical takeoff.

So is a vertical takeoff possible in every kind of airplane (without excessive weight and giving full thrust) or only some specific ones can do it?

First, let's agree on terminology: What you saw in airshows is a vertical flight path. Flying horizontally first, the airplane pitched up until the nose was pointing straight into the sky.

Surprisingly, no thrust is needed to perform this maneuver. Even gliders can do it. What happens is that kinetic energy is converted to potential energy, the rate of potential energy increase being proportional to flight speed and aircraft mass. If you start fast enough, this vertical flying can be maintained for several seconds, until the aircraft runs out of speed and stops in midair, followed by an uncontrolled drop. Skilled pilots orient the aircraft in the right direction by starting a rotation around the vertical axis at the top of the climb, so the following drop lets them pick up speed again with the correct nose-down attitude. Now potential energy is converted back into kinetic energy until speed is sufficient for a pullout. In aerobatics, this maneuver is called a stall turn or a hammerhead stall.

A few conditions apply, however. The airplane must be able to fly fast enough to have the needed potential energy to sustain the maneuver through the pitch-up phase. This is helped if its engines add energy, so the kinetic energy bleeds off more slowly. Also, at the top of the maneuver it is flying at zero g, and this requires at least that all items on board are securely fastened. Lastly, the pitch-up needs a load factor bigger than 1 g, and the higher the maximum load factor is, the tighter this pitch-up can be flown.

Now the question has been changed: The vertical flight path is flown right after take-off. This limits the entry speed for the maneuver, and gliders will not be able to do this. If we take the 737 from the question and fly it with no payload and little fuel, the flight mass $m$ of a 737-700 is 40 tons, and the installed thrust is about 200 kN (sea level static). Let's assume that the pilot accelerates after takeoff to a horizontal speed $v$ = 100 m/s (194 KTAS) while retracting the flaps, the kinetic energy ($0.5\cdot m\cdot v^2$) is equivalent to a potential energy ($m \cdot g \cdot h$) of an altitude gain h of $$h = \frac{v^2}{2\cdot g} = 510 m$$
The engines deliver less thrust with increasing speed; maybe 40% of the weight, so the airplane will still accelerate for the first 18° - 20° of the 90° flight path change. This will delay the point when speed has been bled off and add maybe 150 m to h. At 100 m/s a pull-up with a radius of 500 m will add a load factor of 2 g. The pilot needs to pull less first and harder at the end of the maneuver in order to stay within the maximum load factor of 2.5. When speed bleeds off, so will wing lift, and in the second half of the pull-up the wing will not create enough lift to change the flight path enough in order to reach the desired vertical attitude. Also, the aircraft will be very low for a safe recovery.

This makes it rather doubtful that an airliner can be pulled up to a vertical climb after takeoff. If the maneuver is started at a higher speed and with a little more distance from the ground, I see no reason why it should not safely be possible.


Are we on the "wrong boat" with eliptical spanload all these years? In this video AL Bowers (former NASA chief scientis) talk how bell spanload solution  can reduce OVERALL DRAG by 60%(11% reduction in total aircraft drag due to spanload, elimination of the tail results in another 20-30% efficiency gain, and then 15.4% improvement in propulsive efficiency, the total efficiency increase is on the order of 60%) and  how today aeronauticals engineers dont understand at all "bell spanload concept".

So are we using "wrong" spanload solution(eliptical or all versions of eliptical) all these years?

sources :
NASA link

on bell spanload(right wing) resultant force is tilted forward, that cause thrust at wingtip. Eliptical spanload(left wing) has drag at wingtip.

often people think,that wingtip produce download(negative lift),this is not true, wingtip produce lift all the time you can see from graph lift dont go below zero line.

The elliptical and bell curves give optimal solutions to different problems. Obtaining the most efficient wing for a given span leads to the elliptical distribution, whereas the most efficient wing for a given load is given by the bell distribution. For a given central load, the bell or Prandtl wing will have longer span but a lighter structure and reduced tip losses.

For a swept wing the Prandtl type is inherently stable, so there is no immediate need for a tail stabilizer. However practical considerations include CG range, and this is the tailless type's big weakness: unless it is sharply swept, as in a typical supersonic delta, it will need a separate elevator, fore or aft, to apply the large trim changes necessary. For a straight wing an airfoil with reflex camber to give a static center of pressure will also  make it stable. But such airfoils are relatively inefficient and wing area must be increased. All this reduces the practical advantage of the Prandtl wing well below its theoretical value.

Roll inertia will also be affected by the increased span, which can impact highly manoeuvrable or very large aircraft.

One way of looking at the Prandtl wing is to see the tip section as a vortex-reducing winglet, which just happens to be blended in. I recall the Airbus A380 chief designer saying that it makes little difference in practice whether the winglet section is horizontal or vertical.

Having said all that, I am a fan of the Prandtl wing (which is really the Dunne-Prandtl wing, as J W Dunne discovered it empirically and flew it as the D.7 twenty years before Prandtl did the maths). Now that NASA have rediscovered it, I would expect it and its design principles to find some modest wider application in the future, with or without a tail. For example in long-endurance electric drones with fixed CG and minimal maneuvring needs.


What triggers a CVR to start recording? Until recently, I was under the impression that CVRs will start recording as soon as the engines are started and turn off when the engines are stopped.

However, this is not the case given there are only 2 hours of recording time.

In one airplane disaster documentary, the CVR started recording at the gate and when the plane was getting de-iced.

So when does a CVR start recording, is this something that is started manually?

The CVR (and FDR) are continuously recording while the aircraft is in operation. In the days of magnetic tape, this was done with a continuous loop. In digital systems, the same is emulated by automatically returning to the start of the storage area whenever the end is reached. In both cases, the new data always overwrites the oldest data, so the last N hours is always available. When there is a crash, investigators locate where along the loop the accident occurred, and then read all the way around the loop (physical or virtual) until they reach the accident again.


What is the difference between GVI and DVI? In any maintenance program I found some terms like General Visual Inspection (GVI) or Detail Visual Inspection (DVI) or Detailed Inspection (DTI). I want to know the difference between these types of inspection.

And which type of inspection is required in which cases.

GVI is general visual inspection and when you make a GVI, you have to be maximum an arm's length distance to the area and/or component you are searching any defects.

DVI is detailed visual inspection, it depends to the situation but usually you use a tool like a magnifier to inspect the area/component.


Could a runway include a safety device to destroy a plane's landing gear? The NTSB recently released its final report of a crash at Hanscom field (KBED) in Bedford, MA. The short of it is that the pilot tried to rotate with the gust lock engaged, preventing the plane from lifting off. It rolled past the runway and finally crashed into a ditch, where it burst into flame, killing everyone on board. (I should say that although I've flown in a small 4-seater a few times, I'm not a pilot — so please forgive me if I misused some terminology.)

One thought I had is that if the landing gear had been destroyed at the end of the runway, the crash could have been a lot less severe. In particular, I was thinking that a small wall could have been designed to knock the gear out, making the plane start skidding on its belly and presumably coming to a stop much sooner. It wouldn't be exactly safe, but it seems like it would be safer than relying on just the gear's braking power.

Does such a device exist at any airports? And if not, has it been considered and rejected for some reason?

There is indeed such a system installed at some airports. It is called an engineered materials arrestor system (EMAS). Incidents such as Southwest 1248 have shown the potential safety issues of runway overruns, as you have pointed out. The EMAS solution uses a pad of special material at the end of the runway, designed to allow landing gear to sink into the material. The landing gear is not ripped off, but as the gear travels through the material, the plane is slowed down.

Destroying the gear is not a desirable option. Although the gear on airliners is designed to safely separate from the aircraft, there is still the potential for damaging fuel tanks or other structure. The aircraft will also be even less controllable after the loss of landing gear. If a small aircraft is not going very fast, a small wall could cause it to flip over, worsening the situation.

In the crash you referenced, the aircraft was traveling very fast at the end of the runway, and an EMAS may not have been sufficient to stop the plane. An EMAS typically has a max entry speed of 70 knots, so in incidents like the one linked from the question, this kind of system may not completely prevent a fatal incident. Since the aircraft's gear must break through the material, lighter aircraft may not be stopped as effectively. However, small aircraft have been stopped with such a system.

The FAA is looking at places where these systems could be useful, with a focus on runways that cannot have the recommended 1,000 foot safety area at the end. The runway safety area (RSA) is the best option for a safety buffer at the end of a runway, providing extra distance for an aircraft to stop. The article above notes that the EMAS at Burbank airport took $4 million to install, and that is a fairly small airport that doesn't usually see anything larger than a 737. Any overrun will incur certain recovery costs, but an EMAS will need to be repaired after any overrun or accidental damage, possibly closing the runway, and will be less effective until repairs are completed. Airports must weigh all of their options for providing a safe facility.


How low can a helicopter legally fly over the water with boats below? My friend was paddling in a big race in Dana Point, California and she said the helicopter was directly over her taking pictures to sell. It looks to be at no more than fifty feet above sea level (if that!); this flight behavior seems insanely dangerous and/or illegal, but maybe I'm wrong. Anyone have hard facts on this type of flying for photos?

There's no minimum altitude over open water but the pilot must stay at least 500ft away from the boats, per 14 CFR 91.119:

  (c) Over other than congested areas. An altitude of 500 feet above
  the surface, except over open water or sparsely populated areas. In
  those cases, the aircraft may not be operated closer than 500 feet to
  any person, vessel, vehicle, or structure.

There's also a catch-all regulation that prohibits endangering other people, 91.13:

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

It's very hard to tell from the photo how far the helicopter is from the boats but if your friend believes it was closer than 500ft, she can report it to the FAA.


Who operates delivery flights for commercial airlines? Seeing an A220 flying to Atlanta for delivery to Delta made me wonder: Which crew operates a delivery flight? The manufacturer’s pilots? Or the airline’s crew?

When I worked for Boeing as an intern in 2000, I got to see Boeing’s wide body delivery center in Everett, WA.  Back in those days at least, the airlines brought out a crew of lawyers, aircraft brokers and test pilots.   Typically what happened was the airline’s test pilots would take the new aircraft up for a check flight with Boeing’s factory test pilots.  This consisted of flying the aircraft from KPAE east to Moses Lake (KMWH) where they would shoot a couple of approaches and test the avionics and systems on the new airplane, then fly west out past KPAE over international waters where they, at least technically, “bought” the airplane.  Doing this outside the boundaries of the US allows the airlines to avoid paying 8% Washington State sales tax on a $200 million airplane.  The test flight concluded, they returned and landed at KPAE.  After that the airline’s lawyers and broker met with Boeing’s lawyers and a purchase price was agreed upon.  A phone call was made and the funds were electronically transferred from The airline’s bank accounts to an account belonging to Boeing.  After that, the airline’s test pilots flew the airplane out and put it into immediate service.  Typically if the airline had scheduled service from KSEA the airplane was flown on a short VFR hop down to SeaTac and parked at a gate, where it was immediately prepped and began passenger service.  When I was there, Aeroflot took delivery of a 777 which was flying from Seattle to Moscow the very night the airline took delivery.  Other strange things are negotiated in the purchases.  Cathay Pacific once made a deal with a WA state cherry co op along with the purchase of an 747-400F; the airplane flew back to China brand new with 20,000 lbs of bing cherries aboard!


At which speed is a plane traveling at hypersonic? What is the measurement used when a plane is said to travel at hypersonic? How does the air act at the nose of the plane? Would the nose and wing have to be razor sharp to cut the air? because the nose of the space shuttle seems blunt.

Hypersonic flight is generally any speeds between Mach 5 to Mach 10.  Although we set a speed delineation for the boundary between supersonic and hypersonic flows, the real boundary is where simple compressible flow aerodynamics using Mach and Reynolds numbers are no longer adequate to models the flow and multiple relationships between fluid mechanics, thermodynamics and heat transfer come into play.


How long it takes for Pilots to prepare for landing? I'm wondering how many minutes prior to Final approach do pilots decide what type of approach they will carry on with at the arrival airport like (VISUAL/CATI,II,IIIA,IIIB) ?
Like how many minutes before they get the latest METAR or weather reports and decide accordingly how to carry on with their final landing and how long all this preparation takes before the actual touchdown ?

This varies a bit based on company or personal standard operating procedures (SOP's).  However, typically a pilot/crew will receive arrival airport information either via D-ATIS (Data Link-Automatic Terminal Information Service) sent directly to an aircraft's on board equipment (e.g., ACARS - Aircraft Communications Addressing and Reporting System), or the same information converted to speech for those aircraft not equipped with an ACARS (or similar receiving system).
The information received generally includes the latest airport weather information, runway(s) in use, type of approach to expect (ILS, Visual, etc.), and any additional relevant information a pilot/crew would need to know before arrival for planning purposes.
For air carrier/high altitude type arrivals the crew generally will access the ATIS prior to the planned "Top of Descent" (TOD) point where the descent from cruise altitude will begin. It would not be uncommon to access the ATIS information 10 minutes (or more) prior to the TOD point (in a relatively lower workload environment) in order for the crew to properly prepare for arrival.  This preparation would include accessing the appropriate charts, perhaps inputting information into the onboard navigation/performance computer systems, briefing the approach procedures to be used, missed approach procedures, runway exit procedures, any special instructions noted from the ATIS.
Once the descent began (past the TOD point) and the landing preparations all completed and briefed, it could take 20 - 30 minutes before actual touchdown (or more).  This would vary based on ATC requirements, traffic conditions, vectoring, weather, etc.
For light aircraft/low altitude arrivals, the procedure the pilot/crew would take would be fundamentally similar.  ATIS information and arrival preparation would (should) be done early enough to allow for the least distraction and done in a relatively low workload environment (prior to a higher -  close to the airport - workload environment).
Again, different pilots and company SOP's may call for different procedures, but the above is common in my experience.


Is there a particular reason that EasyJet uses U2 as their code? Does anyone know why EasyJet uses U2 as the prefix for flight numbers? Other airlines have more logical prefixes. Eg. KL -> KLM, AZ -> Alitalia, BA-> British Airways, etc. Even though they do not always match the airline name exactly, they do mimic the name.

Easyjet got their IATA code fairly late on, and as such could not use EZ (which was in use by Sun Air), so they were randomly issued their IATA code of U2.

They do have the three letter code of EZY, just as British Airways has BAW as well as BA.


Is there a relation between material choice and produced lift at rotation? I'm currently learning about Rotary Winged Aircraft, and I have a question regarding lift and fluid flow.

Given two wings of different material but same shape, will there be a difference in the amount of lift, and the amount of air that is pushed down? Is the lift created related to the material choice in any way?

Yes.

Some materials are easier to shape (think composites versus metal) or stay in shape better over time or under stress (think metal versus wood). This difference between the intended and the actual shape will have the biggest material-related impact on lift.

If you slightly change the question and ask for useful lift (lift minus weight of the structure), the stiffness and relative strength of the specific material must be added to the comparison. Useful parameters are the ultimate strength relative to density (breaking length) or stiffness relative to density (strain length). A stiff structure deforms less under load, so its shape will change less. Ideally, the structure is shaped such that only under load it assumes the aerodynamically most advantageous shape while its elasticity helps it to avoid being overloaded (aeroelastic tailoring).

The surface finish is also material-related, but is more affected by the manufacturing method. A rough surface is better at very low flow speeds while a smooth surface is better at moderate to high flow speeds.


What term is the EASA equivalent of the DER in the FAA safety assurance process? When the FAA approves a hardware or software (or mixed) system for use in an aircraft requiring Type Certification, A Designated Engineering Representative (DER) is selected to work with the developers and apply the safety assurance guidelines (or other alternative means of compliance) needed for approval. Although the DER is not the final authority granting approval, de facto if you fail to satisfy the DER you won't get approval, and if the DER finds that all needed guidelines have been met and all evidence is in order, you probably will.

The EASA process in Europe is very similar, but many of the acronyms and terms they use are different, which brings me to the question:

What is the European (EASA) equivalent of what in America we call the Design Engineering Representative (DER)?

The closest EASA equivalent would be the Design Organisation Approval (DOA). According to EASA:

A Design Organisation Approval is the recognition that a Design Organisation complies with the requirements of Part 21 Subpart J.
Privileges: A DOA holder can

Perform design activities within the scope of approval

Have compliance documents accepted by the Agency without further verification

Perform activities independently from the Agency


Does the reference for AGL include obstacles? Let's say a plane flies 10m above some trees, that themselves are 10m above the underlying ground. Would that be 10m or 20m AGL?

Or, in more abstract terms: What exactly is the reference point for AGL? The actual ground that you would stand on as a pedestrian? The point where you would first impact something (even if it's just a very lightweight sprig)? something else?

How does it work with objects like high bridges, that you could fly below but could still impact on a higher altitude?

AGL is "Above Ground Level".  Ground is the reference.  Trees, buildings, towers, and such are obstacles.  Pilots need to be aware that obstacles exist.  Most of the smaller ones can be addressed by just flying at a safe altitude.  This is covered (in the US) by the following Part 91 rule:

  §91.119   Minimum safe altitudes: General.
  Except when necessary for takeoff or landing, no person may operate an
  aircraft below the following altitudes:

  (a) Anywhere. An altitude allowing, if a power unit fails, an
  emergency landing without undue hazard to persons or property on the
  surface.

  (b) Over congested areas. Over any congested area of a city, town, or
  settlement, or over any open air assembly of persons, an altitude of
  1,000 feet above the highest obstacle within a horizontal radius of
  2,000 feet of the aircraft.

  (c) Over other than congested areas. An altitude of 500 feet above the
  surface, except over open water or sparsely populated areas. In those
  cases, the aircraft may not be operated closer than 500 feet to any
  person, vessel, vehicle, or structure.

  (d) Helicopters, powered parachutes, and weight-shift-control
  aircraft. If the operation is conducted without hazard to persons or
  property on the surface—

  (1) A helicopter may be operated at less than the minimums prescribed
  in paragraph (b) or (c) of this section, provided each person
  operating the helicopter complies with any routes or altitudes
  specifically prescribed for helicopters by the FAA; and

  (2) A powered parachute or weight-shift-control aircraft may be
  operated at less than the minimums prescribed in paragraph (c) of this
  section.

Following (a) and (b) is the safest course. Para (c) provides a great deal of latitude to fly low but has significant risks.  Agricultural pilots fly very low all the time.  But ask any one of them and they'll be glad to discuss all the stuff they've hit.

These rules are primarily directed at VFR flight. Under IFR, ATC clearances are designed to ensure operating at safe altitudes, clear of both terrain and obstacles.

For larger obstacles such as towers and bridges, they are charted.  As you can see on the clip below:

There are a number of towers in a relatively small area.  In this case there is the underscored BITHLO TOWERS label to bring attention to them. Adjacent to the tower icons are two numbers. The number not in parentheses is the height in MSL.  In parentheses is the height AGL.


Is yelling "clear prop" required by FAA regulations? In general aviation, it's almost ubiquitous that pilots yell "clear" or "clear prop" before engaging the starter. Are there any regulatory requirements to take this action either in the form of 14 CFR or maybe in the Airman Certification Standards?

Like @mongo, I am not aware of a regulation and don’t recall seeing anything about it in the AIM. However, the Airplane Flying Handbook (FAA-H-8083-3B) says this about engine start:

  Prior to engine start, the pilot must ensure that the ramp area
  surrounding the airplane is clear of persons, equipment, and other
  hazards from coming into contact with the airplane or the propeller.
  Also, an awareness of what is behind the airplane prior to engine
  start is standard practice. A propeller or other engine thrust can
  produce substantial velocities, result in damage to property, and
  injure those on the ground. The hazard of debris being blown into
  persons or property must be mitigated by the pilot. At all times
  before engine start, the anti-collision lights should be turned on.
  For night operations, the position (navigation) lights should also be
  on. Finally, just prior to starter engagement, the pilot should always
  call “CLEAR” out of the side window and wait for a response from
  anyone who may be nearby before engaging the starter.


Is there a career path to fly fast, military jets without being in the military? I would like to pilot or fly in fighter jets however as I have mild asthma I cannot join the Royal Air Force. So is it possible to fly in or pilot these kinds of aircraft as a career without being in a branch of the military?

There's no likely career path, if you have serious enough medical problems they will probably prevent you from getting a job in aviation flying anything commercially. However, that's a separate question, you'd want to talk to an aviation medical examiner to find out what avenues are open to you.
There is a path to flying military style jets as a civilian test pilot, which is open to anyone, however you need a lot of experience and most are retired military.
However, with enough money you can fly just about anything, former military jets do go on the market, often they aren't that expensive to buy, the big costs are maintenance and fuel. If they are to be flown non-commercially the medical requirements are usually lower too. You need to be prepared to spend between \$800-\$6000 per flying hour, depending on the type.


What aerodynamic data (drag/lift curves) exists for the L-159 Alca? This is one of 3 question in "series" - one question split up in 3 to better reward those responding about each aircraft. Other questions: A-10 Yak-131

L-159 Alca is one 3 planes that are used in the ArmA 3 combat sumilator, but its aerodynamics modelling currently lacks significantly. I'm planning on writing a short "essay" to developers regarding what and how can be specifically fixed in the flight model, but I'd like to back my research with some hard data. Specifically, I'm interested in any of the following:

L/AoA
D/AoA
Side lift/SA (Slide angle)
Max G/velocity
Flight envelopes (like one below for F-15):

Torques can well be left out - it's not a full fledged simulator, but the above data can give quite a good estimation of high level characteristics already

Are there any good sources on any of the above data? Low-mach data is good enough for me.

I understand this is a tall order, but, well, SE is for expert answers - maybe a wonder happens and someone here has it? :)

From Wikipedia, the aerofoil for the wings is NACA 64A-012. If you would like a full airplane, you would need to plot it in DATCOM. DATCOM is a program that is designed to calculate drag, lift, moment coefficient, etc. on an airplane based on coordinates.

So, here is a link to the polar data I got.

If you want more accurate alpha increase, you need to download X-FOIL and learn to use it (quite a tricky program for certain people).

I am afraid the other data is almost impossible to obtain.


Why, during a magneto check, does manifold pressure increase as RPM decreases? When performing a magneto check or exercising the propeller prior to take off (constant speed propeller), you notice that as the rpm drops the manifold pressure rises slightly. Why does the manifold pressure rise?

On the intake side, the engine is effectively a vacuum pump; it's sucking in air past a restriction in a duct - the venturi and throttle plate, creating a partial vacuum in the intake passage, and measured as total pressure in inches of mercury (In cars, the MP gauge is labelled "vacuum"; similar, but expressed as a differential between ambient and duct pressure instead.  The problem with car style vacuum gauges is you can't use it to measure horsepower because you don't know the absolute pressure in the intake duct, only the differential, and you'd have to know the actual ambient pressure to work out what is the actual intake duct pressure).
With the restriction being fixed (not moving the throttle), anything that changes the pumping rate (directly tied to piston speed, therefore RPM) affects the amount of suction created between throttle plate and cylinder.  Decrease the pumping rate (or sucking rate you might say), and the vacuum goes down/MP goes up.  And vice versa.
So anything that raises RPM without moving the throttle plate moves MP down a bit because the piston is sucking harder because it's going faster, and anything the reduces RPM without moving the throttle plate moves MP up a bit, because the piston's moving slower.  As you get familiar with this, you learn to drop MP about half an inch below target when following up with an RPM reduction, knowing it will come up as you reduce RPM. And vice versa on power increases.


How do modern turboprops avoid slow spool up of early jets? I was reading about modern crop dusters that are blessed with 600 or more horsepower
turboprops and have seen them do amazingly effortless high angle of bank turns near the ground.

It seems that a slow rate of power increase would make this type of flying much more dangerous. I had imagined using air bleed gates to close and raise combustion chamber pressure instantaneously, along with more fuel.  This would involve an overdesigned compressor.

Is this how it is done?

Two ways:

As Dave pointed out above turbopropeller engine cores, like all aviation gas turbines, do have a spool up lag.  This is mitigated a couple of ways.

In a free turbine turbopropeller engine, the gas core spool is independent of the power turbine, allowing it to spin up much faster, and subsequently increase the amount of power delivered to the power turbine much faster.

In direct drive turbopropeller or turboshaft engines, the engine - and the propeller - operate at a near constant speed with increase or decrease in power provided by altering fuel flow and adjusting propeller pitch for the load.  Direct drive engines like the Garrett TPE-331 have a near instantaneous power response to power lever commands.  The downside to these designs are that they can be extremely treacherous in the event of an engine failure without an autofeather system linked to a negative torque sensor.  They are also very noisy on the ground.


Is it a standard procedure to use emergency slides without imminent danger? On 11 Jun 2017 Easyjet U23246 from Ljubljana to London Stansted diverted to Cologne-Bonn over a "suspicious conversation". All passengers were evacuated using the emergency slides, see BBC Video.

This made me wonder why this is appropriate at all:

There was no imminent danger. It's an international airport, so surely they have at least one set of mobile stairs that could have been used in a safer manner?
Apparently nine people (of 151) needed medical attention after using the emergency slides. That's 5%!
If it had been an incident and police needed to enter the aircraft, wouldn't they arrive on mobile stairs anyway?
Apparently the airplane sat for 30min before evacuation anyway, so it wasn't even faster to use the slides.

I'm just wondering what prompted them to deploy the slides in the first place. I'm under the impression that they need to be replaced upon use and hurried evacuation didn't seem to be necessary in the first place.

As a passenger, I think a lot of people might get argumentative over not having stairs. Especially when small kids and disabled people (e.g. dependent on a wheelchair) are on-board. Not to speak of the economic and public relations impact...

If an evacuation is called for the quickest method must be used, in this case slides. No exceptions no questions. Passengers can complain after they are out but they are not given a chance to argue during the evacuation, force can be used to clear an argumentative passenger so that the other passengers can get out. The 30 minute delay was before the decision to evacuate, it has nothing to do with the actual evacuation. Full scale evacuations require no more than 90 seconds for the aircraft to be certified.

What the police need is completely irrelevant to the evacuation.

Slides can be inspected, repacked, and reused, they are test deployed at regular D maintenance inspections.(maybe C as well. D is every 6 years C is every 2 years) Emergency doors are also routinely opened for testing.

A passenger needing medical attention could very well be nothing more than a stubbed toe, light scrape, or being out of breath.


How are take-off segments defined? From take-off performance calculations I remember that the take-off and initial climb was expressed in a number of segments. Each segment had its own performance requirements. I presume they are described in some FAR / JAR but I don't know whether to look under certification or operational requirements.

What are the segments and how are they demarcated?

Do they differ for aircraft types (propeller vs. turbofan, number of engines?)

Are these segments used for certification, operationally or both?

You can find the 4 segment climb profile described for transport category airplanes in the (old) Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25A) Ch 10 and codified in 14 CFR 25.111.  The full 4 segment profile described below assumes an engine failure at $V_1$ and stipulates a climb and speed profile to clear obstacles.  During normal all-engine ops this profile is still technically in place but you'll hit your speed and altitude targets in such a way that you'll takeoff into a climb with increasing airspeed and no intermediate level off (you will still likely use parts of the profile for your flap retraction schedule).
The segments of the climb are:

Liftoff to 35' and $V_2$
At liftoff you are assumed to be in takeoff configuration with at least one engine not operating.  After liftoff you will retract the gear and accelerate to $V_2$ while climbing.  The goal here is the reach 35' height before the end of your takeoff distance.  Note that for propeller aircraft, this height is 50' instead of 35'.

35' to acceleration height flown at $V_2$
During this segment you climb at $V_2$ until you reach a height at which it is safe to level off and accelerate.  This height is called the acceleration height and is normally 400' AGL.  However, this value can vary per runway and will be available to you in your performance data for a particular runway.

Level flight at acceleration height to $V_{FS}$
You are clear of all obstacles, and now your goal shifts from altitude to airspeed.  Level the airplane and accelerate.

Continue climbing at $V_{FS}$ to 1500' (typical)
Once $V_{FS}$ is reached you will continue to climb at that airspeed.  This will also mark your transition from takeoff flaps to a clean configuration.  The height of 1500' is a typical value but may be different based on obstacles for a specific runway.

Enroute climb
Upon reaching 1500' (or whatever altitude is used in the previous segment) at $V_{FS}$ you transition into your enroute climb.  At this altitude you will begin to perform checklists for the engine failure you experienced between $V_1$ and liftoff and your after takeoff flows and checklists.

Fig 10-36 FAA-H-8083-25A pp 10-30
A transport category airplane with an engine inoperative must be able to meet the climb gradients stipulated in the image above.  The climb gradients vary by number of engines,


Why increase or decrease rudder when using elevator in turns? In normal 30 degree bank level turns, instructors teach students that if you are to correct your altitude you also need to change your rudder input.
Why is that?

For example if you are descending in your turn you are to pull the elevator and also lessen your rudder input. And if you are climbing in your turn you are to push the elevator and push more rudder.

Is this because of you are tightening your turn when pulling elevator and therefore you are starting to skid and therefore you need to lessen your rudder to compensate. And if you are pushing the elevator you are doint the opposite starting to slip and therefore you need more rudder.

Or is there some other explaination to why you need to do this?

EDIT:

Hi,

no I think you have misunderstood the question.
They do not teach to use the rudder to compensate for pitch/altitude.

They teach properly to use the elevator. But they say that when you make a change with elevator to a higher nose you don't need that much of rudder than before. And when you use the elevator to push nose down there is more need of rudder.

The rudder change is just to compensate the need due to change in configuration. Not to use it to change the altitude.

Instructors that teach that to students are fools.  You should be using rudder only as required to keep the ball centered - period.  If you are applying rudder to influence the pitch attitude, to "help hold the nose up", this is very very bad, and leads to stall/spin accidents.

Rudder is mostly being used to counteract adverse yaw from the aileron inputs, and to some degree to correct for yawing motions caused by power changes.  But in any case it is strictly used to keep the tail lined up behind the nose in the airstream.  Anything else and you are skidding or slipping in the turn.

If you are in a 30 deg banked turn, and are descending, the total lift from the wings is insufficient; you need more elevator input, NOT top rudder, which creates a slipping turn, which will make the airplane flick over the top into a spin if you stall while doing it.

Don't overthink it. Ailerons to keep the bank angle, elevator/power to control the pitch and altitude/speed, rudder to center the ball; just do whatever it takes.


Won't sonic booms prevent Space X's BFR intercity transport plan from being acceptable? Considering that Space X have just announced that their BFR can take anyone anywhere in the world in under 1 hour, that would be enormous speed, does this rocket not produce sonic boom?  If not is it because of its shape and that it does not have wings? Will it ever be allowed to fly across the US above the oceans and anywhere at those speeds considering again sonic boom?

The only way to get anything that far that quickly is to send it into space, and that's exactly what Musk is suggesting. The BFR will launch a passenger carrying spacecraft out of the atmosphere and into a sub-orbital path, it will re-enter the atmosphere close to its destination. Rockets launch pretty much straight up and a sonic boom would have to compete with the rocket itself on noise. Once above the atmosphere there is no sonic boom because there is no air.

On re-entry all spacecraft create a sonic boom, for most of the re-entry this is  inaudible from the ground because the air is extremely thin, once in the lower atmosphere it gets louder. By the time the spacecraft gets low enough to create a really big sonic boom it's usually at a subsonic speed and would not make any boom at all. The shuttle and Apollo spacecraft both created sonic booms on re-entry, that's covered in this Space SE Question.

So, are sonic booms a problem in this idea? It depends, the space shuttle re-entered over the continental US many times and it never bothered anyone, but if it was happening a few times a day it might be a problem. You could get around that for the most part by re-entering over sparsely populated areas or the ocean.

More likely it's not the sonic booms that people won't want from a noise perspective, but the launches.


Does the FAA dictate that bridges are closed for the Thunder Over Louisville airshow event? A big tradition here in Louisville is "Thunder Over Louisville". This starts the celebration for the Kentucky Derby. 'Thunder' is an airshow, fireworks, fair, concerts, and a nice day out along the river. This event leads to the closure of bridges over the Ohio River. Some closures are brief, such as I-65. Others are days long because fireworks and other aspects of the theatrics are positioned there.

We have a new pedestrian bridge called "The Big Four Bridge" which was opened very recently. This bridge is closed despite being a very obvious attraction to attendees and it can ease car traffic by allowing foot traffic across the river. There are many notices that this bridge is closed, but none of them cite the authority that closed the bridge.

Does the FAA hold sufficient authority to close bridges, roadways, or other locations for an airshow?

If so, what resources should I use to locate these closure notices?

This question is simply a curiosity. There are many logical reasons for the 'Thunder' organizers, local police, state police, and the FAA to close the pedestrian bridge. I want to learn more about what authority the FAA specifically would have in this matter just for the sake of learning.

The FAA has no authority over roads, bridges or any other public roads. Usually, it's the the event organizer who's responsible for requesting and coordinating road closures; think of triathlons, parades etc. And even without the FAA, there are very good reasons for the local police to close the bridges: rubbernecking and accidents caused by distracted drivers; keeping people safe when fireworks are set off from the bridges and so on.

But, at least in theory the FAA could indirectly require road closures as part of an airshow waiver.

Most airshows require a waiver, i.e. permission from the FAA to 'ignore' certain regulations. The list of regulations that can be waived is in 14 CFR 91.905 and you can immediately see why some of them would be waived for an airshow. These ones in particular seem very relevant:

  91.111   Operating near other aircraft.
  91.117   Aircraft speed.
  91.119   Minimum safe altitudes: General.
  91.303   Aerobatic flights.

The full instructions for issuing a waiver are long and detailed but there are lots of requirements to ensure minimum distance between aircraft and spectators, and to ensure that the energy vectors of aerobatic maneuvers are not directed towards crowds.

I haven't been to Thunder yet so I don't know to what extent the aircraft actually maneuver vs. flying in stable formation down the river. But, it's at least very plausible that the FAA has issued an airshow waiver requiring a minimum distance from spectators that can only be guaranteed if some of the bridges are closed. And, if the park area around River Road is the main spectator area, then any aerobatic maneuvers would have to direct their energy vectors along the river, i.e. towards the bridges. That could require the airshow organizers to request that the bridges be closed.

Unfortunately I couldn't find out if airshow waivers are public or not (a quick search on faa.gov didn't find any) so I don't know if it's possible to check which FAA regulations have been waived for Thunder, or what conditions they placed on the organizers.


How can I become a pilot in Tanzania? I am a student in Tanzania and it's required to take PGM (physics, geography and math) to qualify for studying as a pilot. After qualifying, what am I supposed to do to study for a CPL, and what help can I get if my financial status is limited? Are there any scholarships for people in this situation?

I don't really know how civilian or military pilot training takes place in Tanzania, but I might recommend that you make a visit to a fixed base operator at a local airport there in Tanzania and talk with the staff about flight training.  They may be able to assist your further on that path.

A basic Google Search for Flight Training in Tanzania turned up this place.  I don't know how close you are to Dar es Salaam, but they do have a private flight school out there and could better assist you.

As for scholarships for flight training, check these guys out.

Oh, and these guys as well.

Good Luck with your training.


What is this RAF biplane, and where was the photo taken (possibly in the 1920s)? My grandfather is in the middle row. He joined the RAF as a boy entrant in 1920. He served in Iraq 1924-27 and India 1927-29 so I suspect by the uniforms this is from one of those postings.

I believe the plane is an Airco DH-9A.

https://en.wikipedia.org/wiki/Airco_DH.9A#Interwar_RAF_service

The location may be Iraq. It looks like the RAF 55(B) Squadron: https://en.wikipedia.org/wiki/No._55_Squadron_RAF#Between_the_Wars.

On another picture I think I recognise the dog on the right in your picture (but now a bit older): https://55bomber.wordpress.com/2010/12/02/raf-55b-squadron-hinaidi-iraq/

Blotto:


Why is the fuel pump in the startup procedure for a Cessna 172? I thought fuel pumps were reserved for fuel injected planes in startups and during critical flight phases for all planes?

However. There are some X-Plane flight tutorials that tells us to use fuel pump in startup of C172 aircraft as if we are flying a fuel injected plane. I don't think its necessary for an gravity fed engine but why would someone use fuel pump in a high wing carburetor plane start up? Isn't it a waste of battery?

Many 172s are fuel injected.

I've flown both carbureted and injected 172s.

On a carbureted model, you prime by pumping the primer between 2 and 5 times.

On a fuel injected model, you prime by running the fuel pump for about 3 to 5 seconds with the mixture open.

As for why you do that, the short answer is because the POH says so.
The more precise answer is that gravity feed alone is not enough to push fuel through the fuel injectors (which are very tiny little holes in the cylinders)


What is the purpose of the pressure relief door fitted on the PW1127G-JM engines of the A320NEO? Hey guys many times during my exterior walkaround I noticed on the A320NEOs that they have this pressure relief door and our SOP for the exterior walkaround states to check that this door is closed. However I would like to know what is the purpose of this door? As it's not mentioned in the FCOM.

Inside the nacelle cavity of a turbofan engine and in the casing of the engine core, there are different zones or closed compartments used for ventilation/cooling and in the case of the nacelle lip, also for anti-icing (see the first two images below). If a highly-pressurised duct (such as the anti-ice inlet duct shown in the 3rd image) bursts, the pressure builds up to a dangerous level, despite the ventilation exits. To prevent structural damage to these closed compartments, pressure relief doors are installed which are triggered automatically.

Edit: my first answer lacked some details, so I rewrote it.


Is it possible to take PPL lessons in different locations and countries? I have been wondering if it is possible to do flight lessons in different locations? For example, I am currently taking my PPL lessons (VRF) in Manchester, UK. I usually travel between countries in Europe and America.

I was wondering if my travels take longer than 2 weeks if it was also possible to take the opportunity to do a lesson in one of them? Or if regulations would made it impossible to do so?

As a practical matter, it will probably be too much hassle to get signed up with new flight schools in each city/country you visit for only one or two lessons, especially in the US where you need certain classes of visa (no VWP), permission from DHS, etc.

Also, FAA and ICAO/EASA rules can be pretty different. If you know one well, you can fairly easily learn the other (or just muddle along without anyone noticing), but I wouldn't want to mix the two during primary training. Learning one set of rules is hard enough.

The only case where this might make sense is if you'll be visiting the same city repeatedly and can get the same instructor every time, which eliminates most of the overhead. I did this (both cities in US), and my home instructor would give me a specific list of things to work on for each trip, and when I came back, I'd show what I'd learned and we'd move on to the next thing. After I soloed at home, I did a mock checkride for my other instructor and he soloed me too. Having two instructors did cost me more in total flight time, but it minimized calendar time because instead of losing proficiency by having long gaps between lessons, I was gaining proficiency by flying regularly. It also helped that the two had different teaching styles, so if one wasn't getting through to me, the other would. Still, I wouldn't recommend it if there's any other option


Like transponders, can flight recorders be turned off? I never knew much about airplanes before the tragic incident of Malaysia 370. I have been spending a lot of time on Twitter reading various articles and investigations; in one of the articles I read, they stated that unlike transponders, "black boxes" cannot be turned off.

  However, each ELT is specifically designed for each aircraft, so it
  cannot be tampered with. You also cannot turn off the black box, as it
  runs throughout the flight, recording every 30 to 60 seconds.

Is it really impossible to turn off the black boxes from within the plane?

There is no switch for the FDR, but there is a circuit breaker and by pulling this you are removing aircraft power from the FDR.  However, this does not mean you are necessarily turning it off, as some FDR can be equipped with an internal power supply as a backup to aircraft power.

The quote in the question (bolded emphasis mine):

  You also cannot turn off the black box, as it runs throughout the flight, recording every 30 to 60 seconds.

is a case of an "expert" or journalist confusing the lack of an on/off switch as an inability to turn something off.  As you'll find many examples of in the media, they don't always get it right.  The circuit breaker may not be a true on/off switch, but pulling it does accomplish de-powering (assuming no internal power supply) and thus turning off the FDR.


Did the First Officer of Ethiopian Flight 302 trim in the wrong direction? Looking at the accident report of Ethiopian Airlines Flight 302, it says the cut out switches were used. But the manual trim moved from 2.3-2.1? My reasoning for asking this is because the timeframe on this specific input is 5:40:42-5:43:11 which goes up to the point the crew re engaged the electric trim motors. It sounds like they’re being vague for a reason. Did the First Officer trim in the wrong direction and then tell his Captain “It’s not working”?

On the Boeing 737 the trim wheels are directly connected to the stabilizer jackscrew with cables. The force required to move the trim wheels depends on the load on the stabilizer. The more you are out of trim, the more force is required to move the stabilizer.

From the 737 NG FCOM (9.20.8 Flight Controls - System Description - Stabilizer Trim, emphasis mine):

  Manual stabilizer control is accomplished through cables which allow the pilot to
  position the stabilizer by rotating the stabilizer trim wheels. The stabilizer is held
  in position by two independent brake systems. Manual rotation of the trim wheels
  can be used to override autopilot or main electric trim. The effort required to
  manually rotate the stabilizer trim wheels may be higher under certain flight
  conditions. Grasping the stabilizer trim wheel will stop stabilizer motion.

left: trim wheel with handle stowed (source), right: jackscrew in the tail (source)

The FCTM (8.17 Non-Normal Operations) explains the correct procedure for manual stabilizer trim (emphasis mine):

  Runaway Stabilizer

  Hold the control column firmly to maintain the desired pitch attitude. If
  uncommanded trim motion continues, the stabilizer trim commands are
  interrupted when the control column is displaced in the opposite direction.

  Manual Stabilizer Trim

  If manual stabilizer trim is necessary, ensure both stabilizer trim cutout switches
  are in CUTOUT prior to extending the manual trim wheel handles.

  Excessive airloads on the stabilizer may require effort by both pilots to correct the
  mis-trim. In extreme cases it may be necessary to aerodynamically relieve the
  airloads to allow manual trimming. Accelerate or decelerate towards the in-trim
  speed while attempting to trim manually.

  Anticipate the trim changes required for the approach. Configure the airplane
  early in the approach. When reaching the landing configuration, maintain as
  constant a trim setting as possible. If a go-around is required, anticipate the trim
  changes as airspeed increases.

Note: this FCTM is from a 737 NG, not a MAX. The part about "trim commands are interrupted when the control column is displaced in the opposite direction" is no longer true when MCAS is active on the MAX, the rest is still valid though.

You can also see this procedure applied in this YouTube video by Mentour Pilot.

Regarding the Ethiopian crash: I don't want to speculate on what the crew did, but if

  the stabilizer position gradually moved in the AND direction from 2.3 units to 2.1 units

then it did indeed move in the wrong (AND - Aircraft Nose Down) direction.


Why don't airport have heated runways to deal with winter conditions? It is for years that I ask myself as a frequent flyer why there is no Airport using a system, like built-in electrical resistances on Runways to avoid Delays/Cancellations and even closing Airfields during winter? The costs of such a system would be for sure less than closing an Airfield for one day.

Removing snow from runways is not the biggest problem. Snow can be ploughed from the runways pretty quickly. The problems occur:

When it is snowing, especially in snow storms with strong winds and poor visibility. The wind and visibility are bigger problem than the snow laying on the runway and when the snow fall rate is such that the snow becomes a problem itself, the heating system would not be able to keep up melting it anyway.
Due to snow and ice accumulating on aircraft preparing for take-off. Obviously heating runways would not help in this regard.
Due to fog, which is much more common in winter. Again, heating runways would not help in this regard.

So runway heating would probably not help very often.

Also the runway has to be extremely strong, because aircraft have much higher weight on each tire than cars. A heating system with adequate durability would therefore be really expensive.


When to switch from ground to tower frequencies at controlled airports in the US? I have heard that you can switch to the tower frequency once you are at the runway hold line and are ready for takeoff without getting permission from ground control to switch frequencies.  Is this always true or does the procedure vary for different airports?

While I acknowledge the answer by GdD to not change frequencies until instructed, that is at odds with my experience.

When I call Ground, then request and receive taxi-instructions, I stay with Ground to the runway hold short line.   I've never had Ground give me an explicit instruction to switch to Tower.

When I start my run-up checks, I switch to Tower (unprompted) to start hearing what is happening in the airspace.  When my run-up is complete, I call Tower with a "ready for takeoff".

I've never had Ground, Tower, or any Instructor tell me differently.  I've never observed another pilot wait for an explicit frequency change instruction from Ground, and I believe that is the way I was taught.

Note: this only applies when you've taxied to the hold-short with Ground.  If Ground tells you to switch earlier, do it.  If you want to switch earlier, request it.


Why are some pitot tubes more prone to icing than others? I understand that there were several cases pitot tube failure in a certain way.

The pitot tubes were clogged by ice when the airplane was in cold and wet conditions.
The remedy was to exchange the pitot tubes by a different model from a different manufacturer.

As an example, there was an Airworthiness Directive (DGAC 2001-354) applying to the A330 and possibly others, explicitly requiring to replace the model installed when delivered by a specific other model.

The A330 originally came with pitot tubes from Goodrich Sensors and Integrated Systems,  part number 0851GR. The Airworthiness Directive of 2001 required to replace these by pitot tubes made by Thales, part number C16195AA, or a specific, more recent model from Goodrich.

I assume all models from all manufacturers have the same basic construction, like all can be heated, for example.

What is it in the construction of the pitot tubes that makes the difference?

Is it just a design flaw in the Goodrich series that was fixed later? Somehow I expect it to be something more general. Are there other manufacturers building pitot tubes with a similar flaw? (That would be a good reason to require replacement with a specific model.)

Actually the answer is quite complex, but essentially depends on the local aerodynamics, shape of the probe and the anti-icing power (heating).

Imagine an airplane flying around a cloud, it essentially approaches air with small drops of water floating around, those drops of water impact the pitot tube and some of them keep over the pitot tube surface.

Now, the key question is if that water will or will not become ice. That essentially depends how long the water keeps over the surface and the local temperature.

Keeping on the surface depends on the shape of probe and the local pressure. The water temperature will depend on a balance between the external temperature (also dependent on the local pressure) and the balance of power applied to the probe to avoid freezing.

So, the phenomena is quite complex and depends on all of these factors, and the potential case of pitot tubes prone to icing will likely being a condition unexpected and outside margins as all these factors are taken usually into account.


Are new airliners less safe than older the two first years after they are marketed? Looking at the 2014 Allianz Global Aviation Safety Study for airliners:

The last generation of aircraft (1974 and forward, including A320 and B737) have a very low rate of accidents: less than 2 accidents per million of departures. This rate is better than all previous generations.

However this rate is lower only one to 2 years after the model has been on the market. Prior to this milestone, the rate is higher than previous generations, except the very first one.

Why is the first year rate of accidents so relatively high? It seems we have almost the same number of accidents before two years, than during the rest of the aircraft life.
Is there an obvious reason for having aircraft of the last generation apparently less safe at their life beginning than the two previous generations?

Just a thought - when a new aircraft is introduced, if there is an accident/incident early on there are very few aircraft of that model flying and the million hour mark is hard to reach.

This may skew the accident rate wildly.  Earlier generations were simpler and were turned out of the factory at a higher rate than newer, more complex aircraft.


How are Landing Fees Collected? Some airports (mostly busy Class B airports from what I gather) have a landing fee. For example, in the Airport Facility Directory for San Francisco, there is a section under "AIRPORT REMARKS" that says "Ldg fee." In a Summary of Airport Charges for San Francisco airport, this fee is listed as at least $190 for Fixed-wing GA aircraft! There is no mention in this document about how the fee is collected, however.

How is this fee collected?

This depends on the airport but at KPNE where I used to fly there was a $5 landing fee (paid to the city of Philadelphia) that was collected at the FBO (where I rented the plane from) when I paid for the rental. I think if you do not pass through an FBO they will hunt the tail number down and send a bill to the party that has the aircraft registered. Its tough to fly into an airport and not pass through the FBO (unless you are just doing touch and goes). I would assume that for commercial traffic the airline/owning body pays and may even be billed by the airport monthly but I don't know the specifics I only know what I have seen for GA traffic.
If you are curious you can check out the Philadelphia Airport (KPHL and KPNE) legislation here which outlines the various fess and collection mechanisms the city imparts. Keep in mind these are city owned airports, see section V for details on collection but in short,

Section V Part d
Non-tenant Air Carriers and Operators not providing adequate surety or security in form and amount satisfactory to the Department of Commerce, to ensure payment of fees and charges, shall be required to pay all incurred fees and charges prior to aircraft departure.

For the point of contrast lets take a small privately owned airport here in the US, Solberg Airport in NJ has "ramp fees" for parking and the such, but like most small airports like this, these fees are waved with the purchase of fuel (usually at least some minimum amount). There would be no way to avoid paying (well Im sure there is) since usually the only way off the tarmac is through the FBO.


What is physics explanation for minimum sink rate airspeed? I did some research on Minimum Sink Rate, and saw much information defining it, (such as it is the speed at which the aircraft will remain in the air for the longest time, etc.) and how it is generally lower than Best Glide speed, and is generally a few knots above stall speed. There was also some information about what is used for (when you are trying to remain airborne for as long as possible after engine failure in order to deal with an emergency, or for gliders to maximize the climb effect from a thermal),

…. But I could not find, anywhere, an analysis/explanation for how this works, from a Physics perspective, as you can easily find to explain Vx, (best angle of Climb airspeed), and Vy (best rate of climb airspeed), that explain/analyze them from a Physics perspective (Vx is speed at which you have the highest Excess Thrust, whereas Vy is the speed at which you have Maximum Excess Power).

Also, from my limited understanding, what I did read seems to violate my basic understanding of what Min Sink Rate means, from a Physics Perspective. As I would understand it, Min Sink Rate Speed is the speed at which your rate of descent is the lowest, (you will remain airborne for the greatest amount of time). This is equivalent to the airspeed at which the aircraft is losing altitude, (Potential Energy), at the slowest possible rate. With no power on the aircraft, loss of energy (altitude) is directly related to total drag, (energy must be conserved!), and this occurs at L/Dmax.  All the complexities involved with determining Maximum Excess Power, or Maximum Excess Thrust, as are required to analyze Vx and Vy, become moot.  So although it appears to be accepted wisdom that Minimum sink is different from Best Glide, this seems to violate basic physics. They should both occur at the airspeed (AOA actually) where total Drag is minimized, i.e., at L/Dmax. Where am I going wrong?

From first principle, assuming the airplane is a point mass, no wind, small angle of attack, and thrust acts in-line with drag:

$$T-D-W\sin \gamma=m\dot{V}$$

where $T$ is thrust, $D$ is drag, $\gamma$ is angle of climb, $m$ is mass of the airplane, $W=mg$ is weight, $V$ is airspeed/forward speed (assuming no wind).

In a total power off scenario, $T=0$, and assuming steady-state, $\dot{V}=0$:

$$\sin \gamma = -\frac{D}{W}$$

The rate of climb ($\dot{z}$), which is the negative of sink rate, is related to angle of climb by: $\dot{z}=V\sin \gamma$. Therefore, we have:

$$\dot{z}=-\frac{DV}{W}=-\frac{P_R}{W}$$

Therefore, for minimum rate of descent, we would like the minimum power required ($P_R$).

Note: for minimum glide slope, it corresponds to $L/D_{max}$, but not for minimum rate of descent.


What accuracy is required in todays ADS-B position reporting? I would like to know what accuracy is required for ADS-B position reporting.

For example, mobile phones A-GPS capable have 10 meter position error with perfect conditions.

Is this similar with ADS-B GPS receivers?

You can report any accuracy you want over ADS-B, as long as the position source is compliant with TSO-C129 (or later revision), TSO-C145a/C146a (or later revision), or TSO-C196 (or later revision).

ADS-B gives amongst others:

a position,
an associated Navigation Integrity Category (NIC) based on the GPS Horizontal Protection Limit; and
an associated Navigation Accuracy Category for position (NACp) based on the Estimated Position Uncertainty / Horizontal Figure of Merit.

If the positioning system cannot provide integrity or accuracy, the ADS-B transmitter will encode the NIC/NAC as 0 (unknown). This warns users of the ADS-B data that the position source is not to be trusted.

In day-to-day operation, ADS-B is required to provide:

an integrity limit less than 0.2 nautical miles;
a reported accuracy of less than 0.05 nautical miles;

Practically, GPS will occasionally give lower accuracies / integrity, but it will be reflected in the NACp / NIC so that users of the data can decide how to handle this lower quality data for their purposes.

Mobile phone A-GPS chips are typically not certified under the TSO's mentioned above and they don't provide integrity information. These chips are thus not suitable for ADS-B.


Why do VFR-flights need a clearance in class D airspace? I ask myself why VFR-traffic has to get ATC-clearances in class D airspace, because as far as I know, ATC doesn’t provide separation for VFR-traffic in this airspace class...
So why for example is a VFR pilot given the clearance (or is that an instruction) to maintain 4000 ft in class D airspace, if he is responsible for the separation, and not the controller?

Because class D is controlled airspace.
While you are correct that VFR-IFR separation is not provided in class D airspace, the major advantage compared to class E airspace is that, because VFR is subject to a clearance, ATC knows exactly where all VFR aircraft are, enabling ATC to provide very accurate traffic information and/or collision avoidance.

So why for example is a VFR pilot given the clearance (or is that an instruction) to maintain 4000 ft in class D airspace, if he is resposible for the separation, and not the controller?

ATC can certainly limit you to a specific altitude, but as a VFR flight ATC can never lock you on a specific heading (since you must also be able to turn to stay clear of clouds). All rules regarding right-of-way in the air are based on turning - not climbing or descending - so being instructed to maintain a specific altitude should not limit your abilities to follow the normal rules of right-of-way.
Although not technically required, ATC will often provide some sort of separation between VFR and IFR in class D, at least in cases where there is an obvious risk of collision. But the normal separation minima do not apply, and ultimatively it is pilot responsibility to practise see-and-avoid (which is made significantly easier compared to class E or below because ATC can provide accurate traffic information).
If we go one step "up" the ladder, to class C - where VFR-IFR separation is provided - a major difference for VFR is the requirement for a mode A/C transponder. A transponder is normally not required in class D for VFR traffic, which is another reason ATC is not necessarily able to provide IFR-VFR separation in class D.
There are different use cases for the different airspace classes, and different countries and ANSP's will make use of them as they see fit in their local environment. The existance of the different airspace classes makes it possible to graduate the service provided to suit most situations:

Class G: No separation
Class F: No separation, but advisory service
Class E: IFR-IFR separation, no radio/transponder for VFR
Class D: IFR-IFR separation, radio+transponder required for VFR
Class C: IFR-IFR and IFR-VFR separation
Class B: IFR-IFR, IFR-VFR and VFR-VFR separation
Class A: IFR-IFR separation, VFR not allowed


What's the idea behind leaving control of slats and flaps to pilots in autopilot? When you watch airliners' flight videos on Youtube, you see pilots still control the slats, flaps and landing gear during the climb and landing phases even after autopilot is engaged. Why doesn't autopilot simply control them when it is capable of it with help of the FMS? Why is
their control still left to pilots, who anyway depend on the FMS (if they have one) to figure out the "right" configurations?

The key thing is that not every flight is the same. Sometimes the landing gear is left up for longer for noise abatement, sometimes it goes out earlier if more drag is required. On a non-straight in approach it's sometimes a good idea to extend the gear earlier. If the brakes heat up too much on the taxi before takeoff, the gear may need to be left down for a bit for extra cooling.

Flaps are a bit different as they are typically set for a certain speed, but the principle still applies. For example if turbulence is encountered which effects the airspeed, having the autopilot moving the flaps the second the flap movement speed is triggered is unhelpful.

Basically, these are things that require the active judgement of the pilots considering the individual factors of that specific flight. It's impossible to automate all of this satisfactorily even with pre-planning. Even if you could it would further introduce an overreliance on automation for very little gain.


What preparations should I have to fly from the US to Mexico? I am holding a US private pilot certificate with instrument rating, and planning to fly a single-engine aircraft from US to Mexico.

Regarding legal, visa, airspace/ATC knowledge requirements, flight plan filing, what do I need to prepare and how may I find the materials (in English).

AOPA has a guide here. I think it should cover most of your points apart from visa/immigration, because that isn't really an aviation issue (unless perhaps you're commercial air crew using a flight crew visa). Don't forget to plan ahead for re-entering the US, there are a bunch of requirements for that too, including using eAPIS.

Some points from the guide are:

Documentation: you need a radio license for the pilot and the aircraft
Insurance: add Mexico to your insurance policy if it isn't already covered
Flight plan: you must be on an IFR or defense VFR flight plan to cross the ADIZ
Night VFR isn't allowed in Mexico (with a few exceptions for flights to the US)
It looks like the more paperwork you have with you, the better
FBO services are likely to be more limited than in the US, and fees are often higher

Also check out the Caribbean Sky Tours Pilots Association, they publish a pilots' guide to Mexico and Central America.


Why is JetBlue's IATA code B6? I understand why JetBlue's IATA code isn't JB since that belongs to a pre-existing helijet service in Canada, but why is it B6?

Is there some history behind the B6 moniker?

I don't know, but ...

If you look at the IATA application form you will see there is nowhere for the airline to indicate the code it would like to receive.

I imagine many new airlines might indicate a preference in an accompanying letter (e.g. they would like a code starting with a specific letter)

If you look at the allocated codes you can see that, initially, some attempt was made by IATA to make the two-character codes mnemonic

AA = American Airlines
BA = British Airways
etc

However if JB was already allocated, it is reasonable that the IATA
staff would look for an available code starting with either J or B.
Since the Blue of JetBlue is more distinguishing than the Jet part of the name, the IATA employee may have started with B and noticed that the following were already allocated

B1 Bravo Passenger Solution Pte., Ltd.
B2 Belavia
B3 Bhutan Airlines dba Tashi Air Pvt L
B4 ZanAir Limited
B5 East African Safari Air Express Ltd.

(note I have not checked dates these codes were allocated but the hypothesis seems plausible to me)

The last two are puzzling but perhaps they changed their names (perhaps as part of a takeover, merger or split). Airline codes do get reused. For example, B5 was used by FlightLine before it went out of business.

Then B6 would be the next available code.


What radio equipment do pilots use to communicate with ATC? I know of the transponders used for communication by Air Traffic Control, but apart from that, what radio equipment do pilots use to talk to ATC? What modulation method is used?

https://en.wikipedia.org/wiki/Airband
emphasis added

As of 2012, most countries divide the upper 19 MHz into 760 channels for amplitude modulation voice transmissions, on frequencies from 118–136.975 MHz, in steps of 25 kHz.

A typical plane often has two communication radios, referred to as COM1 and COM2.
Each radio has an active and standby frequency. The pilot can listen to either radio, or both radios at the same time, but can only broadcast on a single radio.
There are often 2 navigation radios as well, NAV1 and NAV2, which can be tuned to VORs or other radio beacons, and the pilot can listen on those radios (typically for Morse Code IDs, Recorded Voice broadcasts, and occasionally, Voice-over-VOR ATC)


What are these antenna-like protrusions for on an airliner? This is a JetBlue A320:

I've always wondered what these are for, but could never find the answer. I'm guessing a few of them are for receiving information from satellites.

They are the various communication and navigation antennas of the aircraft. This figure shows the location of antennas in A320, the type of aircraft in picture.

Source: pprune.org

Some antenna (the ones with *) are optional and the installation varies with customer. The communication antenna location in A320 can be seen in this image.

Image from airbus training course from airbus.altervista.org

And the navigation antenna location in this one:

Image from airbus training course from airbus.altervista.org

The dome (2 in the picture) is the radome for the wi-fi system introduced by Jetblue, dubbed Fly-Fi.

Source: nycaviation.com

So,

1,3,4 - VHF
2 - Wifi
6 - ELT


Why is the aviation industry taking so long to move away from the tube with wings model? The industry is spending billions on maximising fuel efficiency and reducing other costs associated with the tube-with-wings model. When will novel designs like semi-dirigible and lifting body arrive, what's the delay, surely the industry will be forced into a corner before the latest batch of airliners are due for retirement?

In aviation there are simply configurations that work the best when working out all the compromises caused by competing and contradicting objectives, and these become timeless and continue for many decades until some completely new physics paradigm comes along to upset the apple cart.

So, the tube with wings is the most efficient way to do it, not from some optimized theoretical single minded objective standpoint, but from the real world need to balance this goal against that goal.  You need to minimize frontal area, and to get the most people in the smallest frontal area, you have to arrange them lengthwise.  But not too long, so at some point you have to make the tube wider instead of longer.  A tube, low in drag, efficient structurally and easy to make, can't be beat.

The various radical approaches almost always fall short in key ways, which is the real reason you don't see them.  That doesn't mean stopping experimentation, because some day someone will come up with a radical configuration that sets a new standard while managing to meet all sorts of secondary needs, and then everybody will start to copy that configuration.

I always like to point out the ultimate engineering sweet spot as the pinnacle of this sort of thing, and really, probably the originator of the "tube with wings" concept - the Douglas DC-3, the greatest engineered conveyance of modern times.  This is a set of engineering compromises in such perfect balance, that eighty five years after it was designed, at the end of the second decade of the 21st century, they are still purchased and operated as working machines to earn a living for somebody, pretty much as they were originally built, as opposed to being operated for show or fun or as a museum piece.  That's engineering perfection, the grandfather of all modern airliners, still making money for people, the original tube with wings.


How was flutter mitigated in jets such as the F-15 and F-16? As I understand it flutter was a serious problem for early jets, like the XF-104. Flutter can affect any of the extended members of an aircraft during high-speed flight, including the wings and the vertical stabilizer. The problem seems to have solved, however, by the time that the F-16 and F-15 were designed.

How is flutter mitigated in the F-15 and F-16?

Short answer: By not  flying faster than the 104 did and adhering to the lessons learned.

Flutter first started to cause crashes in WW I when improved engine power and aerodynamics made a substantial rise in flight speed possible. Every time technological advance allowed higher speeds, flutter became an issue which was then solved both by trial and error and by analytics.

From NASA TM 4720:

  The first recorded flutter incident was on a Handley Page O/400 twin
  engine biplane bomber in 1916. The flutter mechanism consisted of a
  coupling of the fuselage torsion mode with an antisymmetric elevator
  rotation mode.

This was easily fixed by removing one degree of freedom for the elevator: Initially, both sides could be moved independently, and by connecting them with a torsion tube the flutter mode could be avoided.

From control surface flutter in WW I, which was generally solved by the practice of balancing all control surfaces (something the early aircraft designers were oblivious of), flutter problems moved to primary surfaces from 1925 on. Again NACA TM 4720:

  Air racers experienced many incidents of flutter from the mid-1920's
  until the mid-1930's as attempts were made to break speed records

The first analytical testing was performed by von Schlippe in 1935 in Germany. He vibrated the aircraft at increasing speeds and measured the resulting amplitude. An increase in amplitude indicated a reduction in damping and imminent danger of flutter.

Typical amplitude over speed plot (from NACA TM 806, which is a direct translation of von Schlippe's work which was first published in Luftfahrtforschung Vol. 13 No. 2, February 1936)

With jets and their higher speeds, new types of flutter occurred. Again NACA TM 4720:

  Supersonic speeds also produced a new type of flutter known as panel
  flutter. Panel flutter involves constant amplitude standing or
  traveling waves in aircraft skin coverings. This type of instability
  could lead to abrupt fatigue failure, so the avoidance of panel
  flutter is important.

Since maybe fifty years every new design must go through a static vibration test to check which elastic eigenfrequencies exist. Analytical methods are used to predict the (speed dependent) aerodynamic frequencies and the structure must be modified to remove any possibility of resonance. Next, the airframe is tested in flight at ever increasing speeds and with exciters at the tips of all surfaces (those can be like the vibration motor in your smartphone, only bigger, or, in the simplest of cases, the pilot moves the control surfaces). At increasing speeds, the exciters are run through a frequency sweep (typically from 5 to 60 Hz) and the resulting amplitude is measured by strain gages or accelerometers.

Below is a diagram (taken from NACA TM 4720) depicting the flutter test of the F-14. The F-14 and F-16 went through the same procedure to make sure flutter is no issue in operation. Modern fly-by-wire designs can even use their control surfaces for active flutter suppression.


Why is thrust available constant with speed for turbojet engines, when it varies with speed for turboprop engines? Similarly, why is power available (nearly) constant with speed for a propeller engine, while it varies for a jet engine?

Turboprops and turbojets - or, more broadly, jets - produce thrust in somewhat different ways.

First of all, let's address the way thrust is produced. Per Newton's 2nd and 3rd laws, force equals acceleration times mass, and an action (accelerating the air) produces an opposite reaction. After canceling out the variables (the math is easy to find), thrust is proportional to T=v*m' (m'=mass flow rate), and power transferred to the air is proportional to P=v^2*m'/2. All velocities are  in the airplane's frame of reference.

Now let's go to how engines produce this thrust. A jet engine first decelerates the incoming air to a near-zero velocity, generating drag, then accelerates it to a constant velocity, higher than the initial one, producing thrust. Both v and m' for a jet engine vary across the envelope, but they change much slower than the plane's speed. The engine spends roughly the same amount of power per unit thrust at any velocity.

A propeller doesn't decelerate the air at all. It only accelerates the incoming air by some amount. This converts power P into velocity v. Now, per above, P~v^2. If you encounter air moving at 0 m/s, you need 5 kJ/kg to accelerate it to 100 m/s. If the air is already moving at 100 m/s, you need 15 kJ/kg to get it to 200 m/s.

The result is that propellers encounter less resistance at low airspeed, so they get more thrust per horsepower the slower the plane is. This allows them to push more air or push it faster, producing more thrust. For fixed-pitch propellers, this works by producing more air delta-V and less drag. High-performance turboprops tend to have variable pitch propellers, which will be adjusted to push more air (slower) at low airspeed, or less (but faster) at high airspeed.

Turbofans, combining a fixed-pitch ducted propeller with a turbojet core, are somewhat in between. They lose some efficiency and some thrust as they gain more speed, like propellers, but their curve is much smoother and closer to turbojets in this regard.

The above is an extreme simplification (as is the jet's thrust curve in the question), just enough to get the idea across. The jet's actual thrust is also non-linear, which has been addressed in another question: How (and why) does engine thrust changes with airspeed?


Are the nearby airplanes cleared of the sky when launching Falcon Heavy? I was checking Flightradar24 when launch occurred and didn't see any difference. Also, 3 boosters landed back successfully. I assume the sky has to be clear of airplanes to avoid any potential collision?

SpaceX launches from Cape Canaveral Air Force Station (CCAFS), Vandenberg Air Force Base (VAFB), and Kennedy Space Center (KSC). All three have Restricted/Warning areas overhead and out to sea, from the surface to "unlimited" (i.e. space). It is illegal to fly through active Restricted airspace without permission. Warning areas are used over international waters and thus flying through them is not illegal, but they give fair warning you may not survive the experience, so pilots treat them the same.

These areas aren't active full time, but since activation of these areas is unpredictable (most have fixed schedules), airlines never plan flights to pass through them; it's simpler to fly around them every time, even though most of the time it isn't necessary.

GA flights, though, are quite common in those areas when they're inactive; ATC will allow flying over the launch areas, landing facilities, etc. as low as 500ft. When they're active, it's not uncommon for dozens of GA planes to be circling just outside the area to get the best view of the rockets, both going up and coming back down. However, GA flights don't show up on most flight tracking web sites by default, so you may not be seeing them.


Can ADS-B used for voice communications? Everyone knows the radio communications doesnt sound great altough they work perfectly.

But can the brand new ADS-B communications be used for carrying audio signal? Would it be clearer?

The ADS-B will be mandatory by 2020 (At least for anyone that wants to fly at the controlled airspaces) so why dont we ditch the old radio system full of parasties and use ADS-B instead for voice communications instead?

Why dont we ditch the old radio system full of parasties and use ADS-B instead for voice communications instead?

Well, why don't we use televisions for washing dishes? Because televisions don't wash dishes.

Likewise, ADS-B doesn't carry an audio signal, so it can't be used for voice communications.

Perhaps ADS-B could be modified to carry voice signals, but this is probably not a good idea. The reason for this is that, while aviation voice communications currently use a band which is 19 MHz wide, the band that ADS-B uses is only about 1 MHz. (The Signal Identification Guide says, "There are two types of ADS-B: one [...] with about 50 kHz of bandwidth;
[and] one that transmits at 978 MHz [...] using a larger bandwidth of about 1.3 MHz".)

Transmitting voice signals digitally is a good idea, but I don't know of any reason why this would be done using ADS-B. It would make more sense to simply design a new protocol from scratch.


Which altimeter setting is used to define airspace boundaries? Let's say that we're flying VFR over the top of Class D airspace at 3,000 feet. The Class D extends up to 2,900 feet - we're above it, but just barely with a 100' buffer.
We're also talking to approach control for VFR flight following. Approach has given us the QNH for their nearby Class C airport, say 29.90", which we've dutifully and correctly set into our altimeter's Kollsman window.
However, it turns out there's a strong pressure gradient today. The QNH at the Class D airport underneath us is 29.80". According to that pressure setting, our altimeter would read 100 feet lower - placing us within the upper bounds of their airspace.
In a situation like this, which pressure setting actually defines the upper boundary for the Class D airspace? Would this aircraft have inadvertently busted the Class D airspace?
(One one hand, everyone within the Class D would be using the QNH reported by the local ATIS, and would expect nearby aircraft to be participating with the Class D tower. On the other, approach control would expect you using their given altimeter setting in order to comply with cruising altitudes and for vertical separation. The only rule I can find is FAR 91.121, which just requires using an altimeter setting within 100 nautical miles.)

Airspace boundaries are not defined by altimeter settings or Indicated Altitude. Like the field elevation, they are at True Altitude. This is defined as the actual height above the 19-year average level of the sea surface. Some boundaries are defined by the height above the surface (field elevation) which is in turn at True Altitude. The MSL vertical dimensions of the boundaries do not change based on barometric pressure or altimeter settings. They are relatively constant.
Your Indicated Altitude shown on your Altimeter may be different from the True Altitude due to barometric pressure changes, erroneous settings, or atmospheric anomalies. This does not change the boundary dimensions.
For further clarity, look at how the FAA Pilot’s Handbook of Aeronautical Knowledge defines these terms:

Types of Altitude
Altitude in itself is a relevant term only when it is specifically stated to which type of altitude a pilot is referring. Normally when the term “altitude” is used, it is referring to altitude above sea level since this is the altitude which is used to depict obstacles and airspace, as well as to separate air traffic.
Altitude is vertical distance above some point or level used as a reference. There are as many kinds of altitude as there are reference levels from which altitude is measured, and each may be used for specific reasons. Pilots are mainly concerned with five types of altitudes:

Indicated altitude—read directly from the altimeter (uncorrected) when it is set to the current altimeter setting.
True altitude—the vertical distance of the aircraft above sea level—the actual altitude. It is often expressed as feet above mean sea level (MSL). Airport, terrain, and obstacle elevations on aeronautical charts are true altitudes.

Mean sea level.
The average height of the surface of the sea at a particular location for all stages of the tide over a 19-year period.

If you are on flight following, or an IFR flight plan, it is up to the controller to clear you through an airspace or hand you off to the controller with jurisdiction. If you are not on flight following, or an IFR flight plan, don’t fly so close to the boundary without giving the local tower a courtesy call to “request” transiting their airspace at your desired altitude. It is not a bad idea to do so even if you are well above their airspace. They may know about conflicting traffic of which you are not aware.


ExpressJet IATA code before "merger" with Atlantic Southeast? Before 2011, Atlantic Southeast had the IATA 2-letter code "EV". Then,

  On November 22, 2011, both ExpressJet and Atlantic Southeast Airlines achieved a single operating certificate that allowed them to operate as one carrier, using Atlantic Southeast's former call sign "Acey". Effective December 31, 2011, all flights began operating under the name ExpressJet.[7] ExpressJet currently operates as United Airlines Express.

(so says Wikipedia.)

What IATA code(s) did ExpressJet, or airlines which became ExpressJet, use until that time?

By looking at the Wikipedia article history, one finds that on 8 November 2011 (before the merger), the IATA code for ExpressJet was XE, the ICAO code was BTA and callsign was JET LINK.


What is the difference between APV I and APV II? Been reading all these ICAO documents about APV I and II and none of them clearly describe (from a pilots perspective) the difference. Please help

The difference between APV-I and APV-II "... lie in the signal-in space performance requirements..." (see this presentation, in particular beginning on page 12: ENAV presentation).

This means that APV-I/II refer to navigation signal performance requirements for APV approaches. Note #8 on page 13 of the presentation referenced above is clarifying:

  The terms APV-I and APV-II refer to two levels of GNSS approach and landing operations with vertical guidance (APV) and these terms are not necessarily intended to be used operationally.

Therefore, look at APV-II versus APV-I as providing for lower APV minimums based on signal performance (horizontal and vertical alert limits) at locations where this is possible. Similar in concept, but not in value, as the difference between RNP .3nm and RNP .1nm approaches.


Why was blue hydraulic system chosen for RAT? Q1. Why is blue hydraulic system chosen for RAT out of the three.
Q2. If in case of hydraulic emmergency if I push RAT switch on Emer Elec pannel what will happen

Because in A320 is the only hydraulic system independent from the engines and isolated from the other two hydraulic systems (while G and Y have the PTU in common). Also the B hydraulic system is able to control both elevators and ailerons, while Y cannot control ailerons and G controls only the left elevator. That's a design choice taking in account all the possible failures to reduce the risk of a triple hydraulic failure.

There are two switches that allow you to open the RAT:

The RAT MAN ON (on HYD panel), which open the RAT and feeds the B HYD
The RAT MAN ON (on EMER ELEC panel), which has the same effect of the previous one, but it also connects the emergency electrical generator

Please also note that in case of a dual engine loss, the RAT is automatically deployed.


What are these bomb-shaped things attached to some propeller aircraft? I've seen them on a few prop machines and searched here and via Google but couldn't find anything.

That is a weather radar pod.  On multi-engine aircraft, it is typical to install radar in the nose.  But that is not possible in a single engine propeller plane.  So, when radar is installed in one, it is most common to hang it under a wing as shown in the photo.  Here's a link to such a pod


In calm winds, which runway should I select at an untowered airport? In calm wind situations, approaching an uncontrolled airport with no other aircraft reporting on CTAF, which runway should I select that would cause the least safety hazard?

Especially at an airport with one runway, I don't want to set up to land head-on with an aircraft flying without a radio.

Often uncontrolled fields will publish a preferred calm wind runway in the Airport/Facility Directory. When one isn't published the calm wind runway is usually the longest runway, which gives you a 50/50 chance at guessing right.

To further reduce your likelihood of winding up face to face with another arriving aircraft you should self-announce on the CTAF and overfly the field to observe the traffic pattern. Also, turn on all the external lights 5 miles out. If there is traffic in the pattern you should work yourself into the same pattern everyone else is using.

If the pattern is empty my personal practice is to pick the approach to the longest runway with the fewest obstructions, and ideally one that doesn't overfly residential areas (where it's practical to avoid doing so).


What would reasonably take to get current to fly general aviation aircraft after many years What would it take to become current? I was a fairly proficient pilot and accumulated around 5000 hours. In 1984, I changed careers and haven't flown since. I was licensed for commercial and instrument operation of airplanes (single and multi-engine). I had an instrument rating and AGI, IGI, CFIA, CFII and I even  got an ATP certificate (although no type ratings and at 74 years old, I don't think that would be usable). I also have an airframe and power plant mechanic certificate.
For 16 years I lived and breathed aviation. I couldn't make a reasonable living at it so I went back to school and switched to computer science. I am  now retired, still in reasonably good health and I am considering getting back into aviation as a hobby.
I know the rules have changed. Airspace categories are different and airplanes have become incredibly more expensive (holy cow). And the avionics make the stuff I was using look like they should be in a museum.
My question is, "What would it take to make me legal to fly?" Could I ever be a safe pilot again?

I am a private pilot and rent old planes, like 73 Cessna 172, with exactly the old instrument panel.
I am a 74 years old retired civil engineer. and fly only VFR.
Here in our airport, Van Nuy, there are many CFI's who would get you up and going in a few hours and will sign you off when you're ready. they charge $30 per hour; and are much younger than our kids.
you would want to look at an airport near an aviation colleges, those kids need hours as CFI. And are very up to date on the latest technologies and what gear is the most reasonable. Like what navigation on which iPad, headsets, what not.


What is this twin engined jet? I was barely able to get a shot of this plane so it's not great quality. I was hoping someone could identify it for me. I've never seen one like this.

It's one of NASA's three WB-57F aircraft attached to Johnson Space Center in Houston, Texas, and operating out of nearby Ellington Field Joint Reserve Base. The B-57 was a tactical bomber that first flew in 1953, and the WB-57F was a modified version that the US Air Force used for strategic reconnaissance. The three aircraft with NASA are the last flying examples of the type and are used for Earth science, and are very versatile as they can fly up to 60,000 feet or higher.

The image below from Wikipedia shows one of the aircraft with pods on each wing.

Source


Can a GPS signal sent to a plane be spoofed? Related to What effect would an air-to-air GPS jamming system have?, I'm wondering whether it is possible for a terrorist (or likewise, law enforcement) to manipulate GPS signals received by a jet, re-routing it elsewhere?

I gather this would be far from a simple task, but how feasible is it?

Let's assume that this is in uncontrolled airspace, so atc can't spot the change in flight path.

Spoofing GPS means broadcasting a false GPS signal - This is harder than jamming GPS which can be done relatively easily by broadcasting a strong random signal at the relevent carrier frequencies.

GPS receivers use GPS ephemeris tables which tell them where exactly they should expect each satellite to be. So the false GPS signal has to look enough like a real GPS signal that the receiver will accept it and use it's transmitted data in it's calculations.

Of course, if, for example, the expansionist president of a country with advanced avionics capability decided to supply sophisticated equipment and the associated personnel to a separatist group in a neighbouring country, it might be possible for them to bring about this kind of result.

There have been reports of this kind of spoofing actually happening, so it appears to be possible.

  The U of Texas students built a GPS spoofing device for about $3,000. A pair of students, the “attackers,” then sat aboard the upper deck of the White Rose, where their GPS spoofer emitted a counterfeit signal slightly stronger than the real GPS signal.

This was a yacht at sea, presumably out of sight of land on a featureless ocean.

It may be more difficult to achieve this with an airliner, which have a variety of navigational instruments, including radio navigation beacon receivers. Inconsistent indications may alert the pilot to a problem.

Non-GPS navigational instruments/systems that may be found in an aircraft include:

VOR
DME
NDB/ADF
TACAN-DME
ADIRU