Can a commercial airline continue its flight if its landing gear fails to retract after take-off? So after take-off, due to any reason, the landing gear does not re-tract, is there any standard procedure to be followed? Or can the airline continue with its flight?

Also, I would like to know any FAA regulation on the same (if any), which deals as to the procedure to be followed in such situations.

Usually not. It depends on various factors, most importantly the available fuel. If the pilot decides that enough fuel is available even after accounting for the extra drag due to extended landing gear, he can decide to continue, though this will rarely be the case as the drag penalty is too high and the aircraft speed is limited.

A case in point is the Hapag-Lloyd Flight 3378, which crash landed due to fuel starvation caused by the extended landing gear (which was kept that way as a precaution). The pilot was criticized for his decision to keep on flying instead of diverting to another airfield, and given a suspended prison sentence.


Can airlines schedule more flight arrivals than the destination airport capacity? Takeoff and landing efficiency at an airport seems to depend on a number of factors, like number of runways and gates, infrastructure maintenance, weather, or even notorious traffic congestion in some areas.

Busy approach at Heathrow, Youtube

Is there some process to prevent airlines to schedule more flights than the destination airport capacity? e.g. some coordination between ATC, airlines, and airports management. If so, how are airlines requests handled, is there some rule for fair sharing of the most demanded time slots?

I'll answer for the US. As long as there's no official slot program, airlines can schedule however much they want to an airport, beyond what it should be capable of handling.

Now that doesn't mean ATC lets a free-for all happen. Hopefully, various traffic management units are on it and aware of how much demand is scheduled and already airborne into the airport/region/area that there's too much demand, and will implement various flow control programs to moderate the volume to what can be accepted into a specific sector(Certain airways can get super busy and require these types of actions), or airport. These control programs will either slow aircraft farther out from their destination, hold, or give small to longer delays on the ground, depending on how over scheduled or limitations of weather at the destination.

[Begin edit poriton]
Since the other part of the question wasn't there when I first answered, I'll answer now.
Slot controls vary heavily from airport to airport. In the US, LGA, LGB, DCA, SNA, and at times JFK are slot controlled, with a few others threatened to go to slots due to how many delays they impact the system(SFO, EWR, and ORD). How each airport deals with the slot allocation is different due to how they got slot controls. DCA is controlled partly through congress, LGA and SNA are restricted due to noise controls. In the US, once an airline gets a slot, often times it's considered transferable property, so airlines can sell them to each other if needed.

Now if a slot isn't used and goes back to the airport, the airport can put it up for bid, or allow applications for it, again depending on how their program is structured. AT DCA, some slots are transferable, some require an act of congress to change or modify, and some can only be used for certain routes or types of cities.


What are the rules for right-of-way on final approach: by aircraft category or only by height? I'm a student pilot studying right-of-way and confused about the landing provisions. Right-of-way is determined first by aircraft category, and then by position. That makes sense.

But the last provision, on final, says the lower aircraft has the right away. Does that mean that the lower aircraft regardless of the category has the right-of-way, or does the lower aircraft only have the right-of-way when they are in the same category?

For instance, if a glider was on final but high, and a Cessna 172 was on final but lower/closer, who would have the right-of-way?

The C172 has right of way, it's lower. The rules are in 14 CFR 91.113 and the only place where categories are mentioned is in 91.113(d), which is specifically about converging traffic at "approximately the same altitude". For landing traffic, the lower aircraft has the right of way.

People spend lots of time and energy discussing who has right of way on final, what "on final approach" really means, if it's OK to cut off a faster (or slower) aircraft, if an aircraft on a 5-mile final prevents other aircraft in the pattern from landing etc. But the discussion often becomes a bit academic: practically speaking the point is to be safe, not create any problems, and not cause other aircraft to go around or maneuver to avoid you. Think of it like pulling out of a side street in your car: if another car is coming then you shouldn't cause him to brake hard or swerve to avoid you.


On FSX flight lesson on climbs and descents, what does "free ride" mean? The following is from a lesson on Microsoft Flight Simulator X regarding climbs and descents:

While engine power moves a car uphill, gravity pulls it down. Without your foot on the accelerator, the car's downward speed is determined by the steepness of the hill it's descending. The steeper the hill, the faster it goes. If the hill becomes shallower, then the speed decreases. If the hill becomes too shallow, then some power is necessary to maintain sufficient forward speed.
Airplanes can also move downhill without power.
Just lower the nose, and you'll get what appears to be a free ride (it isn't, but let's not get into that).

I cannot seem to understand what the author meant by the last sentence. Is the author trying to say that descents are not "free" as in descents are not "powered" by the weight of the aircraft and some form of thrust is needed?
I am rather new to the concepts of the physics of flying and may be missing out on something. Hopefully, someone is able to point out what I am not catching. Thanks so much!

If I remember correctly most of those FSX lessons were done by Rod Machado.   He’s a good CFI but has a tendency to speak tongue-in-cheek about things. What he means by that is that by lowering the nose you can maintain the same airspeed but use less power to do it i.e. getting a free ride out of it. In truth what’s happening is that the airplane is compensating for the reduction of thrust by exchanging potential energy for additional kinetic energy, and it does this by descending.  It’s not exactly a “free ride” per se - energy is conserved after all - but the effect is similar to a car rolling down a hill whereby the driver does not need to give the engine gas to maintain a given speed.


Why isn't there a procedure for dual-engine failure in twin-engine airplanes? I'm licensed to fly multi-engine aircraft. I currently fly the DA-42NG.

However, nowhere in my training and in the official POH was I introduced to procedures for handing a dual-engine failure in-flight.

There's no mention of a Best Glide Speed whatsoever.

I'm assuming this is the case for most, or maybe all GA Twin-Engine airplanes. I know jets can glide for some time without any power.

Question is - can GA airplanes? I know it won't fall like a rock - but there's got to be some science to follow here, right? Why haven't the manufactures mentioned it even once? Why isn't it part of the training?

There are.  The Metroliner (SA227) has a dual flameout checklist.  It's possible that the company I flew for developed their own and had it approved, but we DID have a checklist for that.

I think they're rare on pistons twins because there are a very limited number of environmental factors that can cause double engine failures.  It's also possible to simply run out of gas.*  A turbine can ingest water, ice, dust, sand, snow, etc (no filters) that can contribute to a flameout.  The factor that causes one to quit will likely effect the other in a similar way.

I do know a pilot who flamed out both engines by using engine inlet heat on both engines at the same time.  The ice melted off the inlets at about the same time, both engines ingested the ice, and they quit.  He managed to relight both of them and landed uneventfully.  That likely would not happen in a piston twin.  The alt air doors would open and keep the engines running.

*If you find yourself thinking "I'm going to need that double engine failure checklist in about 20mins," you should probably seriously reflect upon the decisions you made throughout the flight.


Does this trip count for the commercial 300NM cross country requirement? I'm an instrument-rated PPL and recently flew (M20J) solo from NJ to Florida with one leg of 280NM and 3+ landings (not counting the return flight because I had 2 passengers).

Will this trip satisfy the commercial cross country requirement of 300NM solo when I start my training next year even though I'm not currently training for my commercial?

Yes.  It counts.  One leg needs to be at least 250NM and you have a 280NM leg.

§61.129   Aeronautical experience.
(4) Ten hours of solo flight time in a single engine airplane

(i) One cross-country flight of not less than 300 nautical miles total distance, with landings at a minimum of three points, one of which is a straight-line distance of at least 250 nautical miles from the original departure point. However, if this requirement is being met in Hawaii, the longest segment need only have a straight-line distance of at least 150 nautical miles;


How are aviation sectionals and enroute charts created? Who exactly handles this?  Is this done by the US Government via one of its printing offices?  Or is this private?  I know Jeppesen does some charts, especially approach plates, but I am not totally sure how all this is done.

I believe the FAA got out of the printing business by implementing a new business model for charts where they license the product to private industry who then take on the risk/reward of the printing process for their customers.

From the FAA AIS website:

  The Federal Aviation Administration (FAA), Aeronautical Information Services (AJV-5), is transitioning aeronautical charts and related products print and distribution operations from existing contract(s) to multiple no-cost agreements with private industry. Digital product files allow industry the opportunity to print, sell, and distribute aeronautical charting products to the public in an Available on Demand (AOD) approach. Any party interested in the opportunity to become an approved print provider should submit product qualification samples from the files below (in accordance with instructions in the Print Provider agreement).

More detailed information about the program is also available through the FAA contract award management site via an official announcement. So to answer your question, the printing of charts is now handled by private industry, not the FAA.

Since you mentioned Jeppesen specifically, note that they are a bit of a different concept because they take raw data from each state's official AIP and then integrate it together in their own way and perform other value-added services. They then print their own end-product for their customers.  It is based on the same raw data but their product should not be considered the same as what is produced by the FAA.


Why does this statement about intrastate aviation in Alaska appear in airworthiness directives? Airworthiness directives typically include a claim that they...

  Will not affect intrastate aviation in Alaska to the extent that it justifies making a regulatory distinction

What's the reasoning behind making this assertion?

It's there because the law requires it. 49 USC 40113(f):

  (f)Application of Certain Regulations to Alaska.—
  In amending title 14, Code of Federal Regulations, in a manner affecting intrastate aviation in Alaska, the Administrator of the Federal Aviation Administration shall consider the extent to which Alaska is not served by transportation modes other than aviation, and shall establish such regulatory distinctions as the Administrator considers appropriate.

Alaska relies on aviation to reach certain communities, and so Congress requires the FAA in its rulemaking process to consider whether aviation rules should be different for Alaska based on whatever it considers to be "appropriate." The cost/benefit ratio for a safety regulation could be different for Alaska—grounding certain aircraft may cut off some areas entirely—, so the FAA is required to at least think about the effects of their decisions on the state.

The above assertion is a statement that they've considered Alaska when issuing the airworthiness directive and decided it should apply the same there as everywhere else.


What is the fourth contact for on the Bose A20 headset's mic plug? Bose mic plug
The Bose twin-plug cable for the A20 headset has a 4th contact.

In addition, the fourth section is rounded somewhat.

Standard GA mic plug
In comparison, the standard microphone plug only has three sections, and they're all smoothly cylindrical.

I can't quite figure out why Bose would have done it this way. Anyone have an answer?

This kind of plug has contacts, not pins, that one on the end of the mic plug's the PTT (Push To Talk) contact for a military spec microphone plug.

This helpful page explains it:

The first aircraft radios used carbon-granule microphones almost
identical to microphones used on telephones. However, a second
function was needed on the microphone in the form of a push-button to
key the transmitter and effect a changeover from receive to talk . . .
hence the name push-to-talk or PTT switch. Telephone companies not
only had pretty rugged microphones, they could offer a nifty 3-circuit
plug to go with it. To this day, the terms "tip", "ring" and "sleeve"
coined by the telephone industry are used to identify the three
circuits. The addition of a "ring" connection allowed us to craft a
PTT microphone companion to the already common headset. Being smaller
than a headset plug made it easy to avoid plugging the headset into
the wrong jack and vise-versa.
This particular plug is a mil-spec critter and appears to have yet
another "ring" between the tip and ring connections I've noted . . .
this may or may not be visible on your particular microphone plug . .
. in this particular plug, it's simply a spacer to fill out the shape
an maintain commonality with the dimensions of other style plugs.

When you watch some WWII movies you see pilots touching their mics or boxes close to their neck to talk, that's because the PTT was wired in-line with the headset rather than being on the control column or throttle. The 'tip' was there to enable that, when the PTT was depressed an electrical connection was made between the tip and the sleeve, signalling the radio to switch to talk mode. Note that the movies aren't always right, some airplanes had a PTT button off the headset, but that's just one of many common inaccuracies.
Nowadays the PTT button is often wired on the other side of the plug so that the PTT button goes to the stick or yoke, but the principle is the same, it's just that the connection is made farther up the line.
The plug on your headset is a slightly older design with a spacer between the tip and the ring to ensure the two stay separate electrically. It isn't an actual contact because it doesn't go anywhere.


Do airlines continue operating in the vicinity of a hurricane? Have hung around some of the aviation interest groups (like airliners.net) and tried to research this but haven't found very clear answers.

Typically when a hurricane (tropical, peak wind-speed in excess of 100 mph) makes landfall, it sheds most of it's energy and water near the coast-line, however the rainfall and wind-speed heat-map (that is elevated beyond the seasonal average) may be over a very large area. Also a hurricane might move at a speed such that the weather conditions might change the large area (covered by the heat-map) over 2-3 days.

So, my questions in view of the above understanding are:

Whether normal flight operations continue (barring the to/from the airports that are directly under the hurricane path), in this vast other region that is part of the heatmap? (Say with airports in areas showing rainfall up to 3 inches, and windspeeds upto 50-60 mph.)
If commercial airlines do operate in such weather, what should I expect the ride to be like?
What are the chances of such flights being diverted?

Here is the WebCite archived webpage (so this link won't go away) of Weather.com that I am referring to.

PS. I plan to take a flight from Bangalore to Delhi to Kathmandu, on Monday, as the tropical cyclone (as it is called here in Indian subcontinent) is about to make landfall on the eastern coast of India around noon, and we are expecting upto 3 inches of rainfall and winds upto 60mph here on Monday morning.

I wanted to see if I should seriously consider rescheduling flights. A call to my airline customer-care yielded no useful information, and they seemed rather clueless. I read in the local newspaper that train services are being shutdown in the affected area, although it seems to be more like trains that pass through the area with the maximum impact.

The cross-wind limit is 35-40 knots for most aircraft with gusts allowed to perhaps 45 or so. The head-wind limit is slightly higher, but not much.

Knot is nautical mile per hour. Nautical mile is 1.852 km, that is 1.15 mile (and for those who prefer metric, knot is just a bit over ½ m/s). So wind more than 40 miles/hour may interrupt airport operations and wind more than 50 miles/hour surely will. I don't think there is a specific limit for rain; it is generally not a big problem if the runways are in good condition.

Problem is that good local forecasts are possible for at most around 24 hours. So it's not possible to tell whether it is likely there will be disruption of operations the day after tomorrow.

For one day ahead, the airport forecasts are publicly available on the internet. Search for TAF ("terminal aerodrome forecast") with the ICAO (the 4-letter one) code of the airport. They are published in strange abbreviations, but there are sites that will happily decode it for you.


Can an aileron stall in-flight? Horizontal stabilizers stall, so I was wondering, is it possible for an aileron to stall? If yes, at what angle of attack?

The aileron itself doesn't stall, being part of the main wing.  But since it alters the camber of the main wing it changes the local angle of attack in effect.  On older airplanes, a down aileron at low speed could trigger a stall separation of the wing in the area of the aileron and if you applied aileron to correct a wing drop at the stall, it would just speed things along and over you go.  This was one of the reasons for slots in front of the ailerons on airplanes like the Globe Swift.

Not sure how it is taught today (I learned to fly in 1975) but long ago pilots were always taught to avoid aileron input close to the stall and keep wings level with rudder, although on modern airplanes with washout and other features to delay stall near the tip you can generally get away with it.


Is aerodynamic flutter speed dependent? Is it possible for  control surface flutter  to occur at low Reynolds and low speed?
If yes,why don't Ultralights have counter weights or tail sting mass to immune the control surfaces against flutter just like how most G.A planes and aerobatic planes do?

Flutter requires 3 factors to come together: flexibility of the structure that a control surface is attached to; the natural frequency of said structure; and an undamped moving mass attached to the structure with an internal CofG offset from the hinge point of the mass such that inertia helps magnify motion of the mass.  If you have an ultralight with a really floppy, flexible wing that can twist easily, with a heavy, unbalanced aileron, and you excite motion in the aileron, which excites sympathetic motion in the wing itself, you can probably get it to flutter at 40 mph.

I say undamped moving mass because a lot of jets with hydraulically operated control surfaces don't use mass balancing but depend on the damping of the hydraulic actuators, and if that isn't sufficient, dedicated flutter dampers that work like motorcycle steering dampers connecting the surface to the structure.

Anyway, ultralights and other lighter airplanes are able to avoid the factors I mentioned because, in designing it to hold up the airplane in the first place, the wing/stabilizer is inherently stiff enough, and/or the oscillating mass attached is light enough, combined with the lack of potential energy in the system at the low speeds they operate at, so it's not a problem.

You see lots of light airplanes (the Aeronca Champ for example) that operate up to 100 mph + without balanced surfaces because the structural stiffness of the strut/wire braced wing/tail and the light control surfaces makes it impossible for the control surface to excite sympathetic motion in the wing/stabilizer, making balancing unnecessary.


Would it make sense to test the performance and handling of a prototype aircraft by mounting a free moving mock up on a track (like a rocket sled)? https://en.wikipedia.org/wiki/Rocket_sled

When an aircraft is designed there is no way to find out if the maximum cruise speed is achievable with the chosen engine + wing + fuselage combination, and at what fuel flow.

Would it make sense to secure a section of high speed rail ( upto 320 kmh at least) to test full scale non flying models of light aircraft to get a better idea of what speeds could be achieved?

The fuselage could be sculpted and  changed repeatedly in a short time to test various drag reducing measures and forces could be measured accurately in real time. Acceleration times to take off speed could also be measured.

Edit: It does not have to be a rocket sled, just a tracked vehicle with the full size aircraft mounted on it as it is in this case with the NASA full size wind tunnel:

https://www.nasa.gov/centers/ames/images/content/109858main_AC91-0255-76.jpg

For designers of kit planes and LSAs, full size tunnel time does not seem to be an option, I don't know. The design team do well to mount their plywood or GRP prototype with its engine attached and run in on the track, controlled remotely and with some capability for movement up and down and limited movement in roll and pitch. An on-board pilot may be an option.

To test a new propeller or a cowling, or fuselage shape, or retractable gear,  wing design even, cycle times would be shorter, I think. The time to build a load bearing aerostructure, wait for good weather, time for take-off, climb and landing, not to mention test pilot time, all these would be reduced to zero - and postponed to a later stage once the design is finalized. All that is needed is to built a mock up capable of standing up to the forces on the track (2km should be OK) and the control system as well as the engine.

A typical test cycle would be as follows:

Build mock up
Test run on track and obtain data
Perform modification (replace cowl, wings, propeller etc)
Repeat the above

Considerable time and cost would be saved on the aerostructure, pilot time, fuel cost and safety would be very much better. Handling and stall behavior also could be safely tested out.

No, it doesn't make sense because there are better alternatives:

Computer models: fluid dynamics programs are very good at simulating airflow over a 3d model
Wind tunnel testing: In a wind tunnel the airplane model stays in the same place and air is blown over it. Smoke can be added to show vortices, and cameras can record it

There are practical problems with rocket sleds:

A rocket sled would be much harder to get video from
It would be challenging to keep a rocket sled at a completely consistent speed
Rockets only last a few seconds, you'd only get a bit of data at a time


What were the effects of the oil crises on the Concorde ticket prices? One of the things that is considered to have greatly hampered Concorde's success were the dramatic oil price increases due to the 1973 oil crisis (the 1979 one surely didn't help either, but it was too late already).

Wikipedia tells me that the 1973 oil crisis resulted in crude oil prices being multiplied by four. How much could this have affected Concorde's projected ticket prices ?

This is a very complex question, because I'm really interested in how much this affected the commercial case of Concorde, meaning a standard occupancy rate would need to be considered (ideally what was considered initially for Concorde if anyone has any idea...). But due to the difficulties of Concorde, the occupancy rate was usually very low (surely much lower than projected without the oil crisis), to the point that actual ticket prices surely ended up reflecting that. But that is a triggered consequence I would like to be able to distinguish from the original factor (after that we can of course add the calculation when the occupancy rate gets reduced as a result).

Basically :

Do you know what were the pre-crisis projected stabilized (ie non-initial) ticket prices of a given long range Concorde flight ? That would be immensely helpful ;
Do you know how much a 4x increase in crude oil prices at the time would have affected this projected ticket prices, all other things being equal (same occupancy rate, etc) ? If we knew typical jet fuel prices at the time (pre- and post-crisis), seems like an estimate of the additional "first degree" cost per ticket could be reached by dividing fuel capacity over expected number of passengers. Adding benefit margin and we would have an estimate of price increase.

Thanks.

The Concorde started service only in 1976, so there never were actual pre-crisis prices. This makes your first question impossible to answer. Of course the airlines which ordered the Concorde had their plans how much to charge, but kept that a commercial secret.

When service started, the plane lost money. What happened next is an interesting lesson in economics. From A Pricing Lesson from the Concorde:

  The Concorde team decided to do some market research. They asked
  businessmen how much they thought a Concorde ticket cost. The answer,
  “Most of them didn’t know. It was their secretaries or travel
  companies doing the bookings. When they were asked to guess, because
  they were senior, very important people, they all guessed that the
  fare was higher. ” – explained Captain Jock Lowe, Concorde resource &
  Planning Manager.

  This insight led to a new pricing strategy. Captain Lowe described “So
  very simply, we said, we’ll charge them what they think they are
  paying. And so we put the fares up”.  There was a discrepancy between
  what the company was charging and the value customers saw in the
  product.

  Concorde ticket prices were doubled to over $7,000,  one way, in
  today’s prices. As a result, Concorde was repositioned to provide a
  super-elite class for bankers, the rich, and the famous. Concorde
  became the place to be seen.

Generally, ticket prices were 1st class + 20%. So what affected ticket prices most was the all too human tendency to show off; the mechanism that makes luxury brands possible. Fuel became less significant.

Now let's look at the fuel cost. This table only starts in 1975 (but covers the full operational history of Concorde), and when I apply your factor of four, the pre-1973 price of jet fuel would had been 8 cent per Gallon. This means the nominal price has gone up by a factor of 50 when compared to the peak in 2008.

The Concorde typically needed 214 Gallons of fuel per passenger on the Paris - New York route (see my comment for evidence; using @mins much better source gives 236 Gallons), so that means fuel cost per ticket would look like the plot above, multiplied by 214 or 236. At the start of operations in 1976 that would had been about 70 USD per ticket, would had jumped to 200 USD per ticket at the start of 1981, would had dipped below 100 USD briefly in mid-1986 and again in 1998. The peak would had been above 800 USD in mid-2008 had the Concorde still been in operation at that time and would today be nearly 300 USD.


How does a VOR or a VORDME affect the coding decision between CF or IF-TF respectively? I was reading of the following case in ARINC 424-17 spec. Unfortunately the image is copyrighted and I can't paste it here, so here is a low(er) quality image of mine replicating the situation:

The text says that the path after the VI has to be coded as a CF if the XYZ is a VORDME but if the navaid is VOR only then it should be an IF-TF sequence. My question is not why is that sequence by how does the collocated DME affect the decision? The document mentions

This will allow a segment to be constructed, from one fix to the next fix, using an “intercept” where coding would otherwise not be possible.

But it doesn't explain why is it "not possible" to code this path as a CF if the station doesn't have DME. How does DME help here? In my mind, FOOBR is on a radial, let's say 55 from XYZ so if the airplane intercepts and follows this radial it will arrive to FOOBR, no DME involved. Is there something that I'm missing here?

VI vector to intercept
CF course to fix
IF initial fix
TF track to fix
Clarification:
Ralph J asked "what's the difference between CF and TF paths?" That's actually a good question. The spec is quite laconic:

Course to a Fix or CF Leg. Defines a specified course to a specific database fix.
Track to a Fix or TF Leg. Defines a great circle track over ground between two known databases fixes.

To my understanding, TF is more accurate as the course is derived from the previous fix while CF requires the course and recommended navaid to be coded in the aircraft's database, hence making the TF a simpler choice when available.

First; you have to understand that ARINC 424 is an industry standard.  It is not regulatory.  The regulatory documents are published by RTCA (and EUROCAE in the EU).  The basic database coding requirements of it are generally well accepted and used by the industry as those are essential to its primary function of interoperability.  But there's a lot of flexibility in how strictly developers follow the standard.
The example you give is one of application of the standard.  Both of the leg combinations are valid, though the IF-TF is preferred.  Note that ARINC 424 uses the word 'should' and not 'shall'.
Having worked FMS, I can say that the VI-CF could be coded but there are potential issues if XYZ is not a VOR/DME.  How is FOOBR defined if there's no DME?  It would have to be defined as an intersection with a radial from another VOR and the XYZ radial or as a Lat/Lon fix.
If it's a Lat/Lon fix, you can't reliably use the CF leg to get to it even if it's nominally on the radial as the radial error is quite large and could result in 'missing the fix' while flying the radial.  And since the Lat/Lon fix is the RNP standard, the preferred leg type would be an IF-TF leg with the IF at XYZ.
If FOOBR is an intersection, it can be workable once you are established on the CF leg - by tracking the crossing radial.  But the VI leg intercept is a floating fix which complicates the path generation as the relative positions of the intercept and FOOBR are not easily computed.  That problem is much simplified if FOOBR is a Lat/Lon.
In my experience, I would expect the CF leg to be coded as a IF-TF.  That provides fixed start and end points and a much simplified intercept computation.  And it wouldn't be unusual for an FMS to convert the the original CF leg (based on the VOR/DME) into a TF leg.


How do pilots detect and respond to windshear while landing and taking off? How does wind shear affect aircraft while landing and taking off? How do pilots detect that they are encountering wind shear and what would they have to do to prevent it from turning into a bad situation?

The most dangerous form of windshear for planes is the microburst. This is a downdraft that after it hits the ground spreads out in all directions. It is dangerous particularly for planes low to the ground (on takeoff and landing)

When a plane coming in for a landing approaches the microburst it will enter a headwind and see and increase of airspeed and lift, the inexperienced and unsuspecting pilot may then reduce engine power to slow down and keep himself aligned. After the plane passes through the burst it will enter a tailwind decreasing lift which may cause the plane to crash into the ground short of the runway.

To prevent crashing the pilot would need to keep power and possibly abort the approach to wait out the burst.

Detecting windshear from the ground is done with doppler radars (TDWR) and multiple wind sensors (LLWAS) which can detect the changes in wind which will be relayed to pilots in accordance with regulations (3-1-8).

All turbine powered airplanes used in §121 operations, except for turbopropeller powered airplanes, must have a windshear detection system installed, this is detected in one of 2 ways, using the onboard weather radar (predictive) or using the wind sensors on the aircraft like the angle of attack and airspeed (reactive).


What is the difference between "anywhere" and "other than congested areas" in regard to minimum safe altitude? Just missed a PPL written exam practice test question that asked me what the minimum safe altitude was over areas "other than congested areas". I chose "An altitude allowing, if a power unit fails, an emergency landing without undue hazard to persons or property on the surface."

It turns out this is the answer to the question for the area of flight called "Anywhere". The answer for the area of flight called "other than congested", however, is "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."

I can now handily regurgitate the correct answers on the written exam for either stated scenario/area. However I'm wanting to know, is the FAA trying to tell me something here? What is the difference between "other than congested" and "anywhere"? Is "other than congested" presumably more congested than "anywhere"? Anything to take away from this hair splitting other than grumbling about the FAA?

FAR 91.119 is as follows:

  Except when necessary for takeoff or landing, no person may operate an
  aircraft below the following altitudes: Anywhere. An altitude
  allowing, if a power unit fails, an emergency landing without undue
  hazard to persons or property on the surface. 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. 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.

The difference is subtle, but here it is:

anywhere means anywhere: At all times you need to operate at an altitude where, should you lose power, you can put your aircraft on the ground without "undue" hazard to anyone on the ground.
Ignoring all airspace considerations, say you're operating over a city (a congested area), and keeping to the bare minimum requirement for altitude and distance from obstacles. Your engine now fails, and your only "landing" options all involve slamming nose-first into the side of a building. You were not operating "at an altitude allowing, if a power unit fails, an emergency landing without undue hazard to persons or property on the surface".
Since we all want to be able to make safe emergency landings this rule is largely common sense with the force of regulation.

other than congested areas is stuff like farmland or open beaches: you COULD operate much lower and closer to obstacles here and still be within the rules above (you're 300 feet AGL over an open field with a barn 300 feet to your right -- The engine dies, you set it down in the field, and everything is cool), but the FAA (and Farmer Brown in the barn milking Bessie) would prefer you not be that close to the barn in the event of say a flight control malfunction.  Most pilots also wouldn't want to be that close to the barn at that low an altitude (unless engaging in an approved aerobatic demonstration with appropriate waivers) anyway, so it's usually a non-issue.

That leaves congested areas - cities, suburbs, crowded beaches, etc - where the FAA bumps up the minimum obstacle clearances / altitudes for the comfort and safety of folks on the ground.
One could contrive a scenario where you could safely fly at 1500AGL next to a 2000-foot building (like a long, clear, mostly-empty park adjacent to it that you could fly over & use for the "anywhere" emergency landing requirement), but again if something else went wrong you might go into the side of the building. As there are more people in "congested areas" to be freaked out by an airplane flying at a safe-but-rather-close distance, and more people who could be hurt by an unexpected departure from controlled flight, the margins are increased to provide a higher minimum level of safety.
As with Bessie in the barn, most pilots probably don't want to be this close to buildings full of people (and the associate mechanical turbulence), and while circling your friends house in the suburbs is fun it doesn't have to be done low enough to pick out the individual bricks in their driveway and you really should be high enough to land on their street safely if your engine quits, which these minimums will likely allow.


Is it normal that an ELT activates during a strong up draft in flight? I was flying a PA 28 181 Archer on a nice clear day at cruise speed level flight 3000ft. Suddenly, from nowhere it was hit by an up draft that lasted I would  say less than a second. I got pain in my back. Then I noticed that the led in the RCP of the ELT (Kannad 406 compact AF) was triggered.
Is this normal? Did anyone experienced anything like this?
Should I take the unit to the repair shop? It is only 3 years old.

The manual for your ELT doesn't say exactly what triggers it (or I overlooked it) and the EUROCAE ED 62 standard is behind a paywall. The FAA ELT standard TSO C-126 isn't on the FAA site, possibly because it seems to be based on a commercial standard RTCA DO-204A, which is also behind a paywall.
However, your ELT complies with C-126 and I found a thesis called The sensitivity of aircraft emergency locator transmitters to nondistress impact events about false activation rates for ELTs that includes this (p.27):

TSO-C126 ELTs follow the specifications of RTCA DO-204, Minimum
Operational Performance Standards for 406 MHz Emergency Locator
Transmitters [15]. In these documents, the RTCA defined a crash as
when the longitudinal axis of the aircraft experienced a velocity
change of -3.5±0.5 feet per second (fps), with a minimum of
deceleration of 2±0.3 Gs.

If the turbulence you encountered exceeded those tolerances then I assume it would set off the ELT. I don't know if your unit needs repairs or a new battery, you would need to check with your repair shop. In the US there are required inspections and rules on when to replace batteries (14 CFR 91.207) but if your aircraft isn't a US one then that wouldn't apply to you.
I would get someone to look at your back before you worry about the ELT, though :-)


Could a turbofan have two adjacent fans? Is there any a point where it becomes possible/ideal to run two large front fans (side by side) powered from a 'single' core? Otherwise shoot this to pieces and explain the ways this is a bad idea.

This inspiration for this question is from the design of some rocket motors which utilize a single turbine driving both pumps on a single shaft to feed multiple combustion chambers and nozzles.  Example would be the RD-180.

Generally, it is more efficient to have one large than two small devices.

The twin fan solution not only needs a gearbox and driveshafts that a single fan solution does without, it also has more intake and nozzle surface area per cross section than the single fan. This will cause more viscous losses and lower efficiency. The only advantage would be if size limitations make a single fan impossible, but in that case it would be more straightforward to have each fan driven by its own core engine.

Famous examples of aircraft which used a single engine and two "fans" would start with the Wright Flyer models, all of which had a single engine drive two propellers via bicycle chains. But the list is short.
The list of opposite designs where two engines would drive a single propeller or fan would probably be longer, and my favourite from this list is the LearFan.

@jwenting correctly reminds me that for completeness a single power plant driving two contra-rotating propellers should also be mentioned. This is indeed the only way on airplanes of one engine driving two propellers, albeit not adjacent, that has seen wider adoption, from the RR Griffon on the Avro Shackleton to the NK-12 of the AN-22, Tu-95 and Tu-114.

Of course, all single-engine helicopters also use this one engine to drive their two propellers …


Why does manifold pressure increase when you turn on carb heat? So everyone knows that carb heat decreases engine performance. Yet when we check the heat during run-up, the manifold pressure increases.

Why is that? Shouldn't adding carb heat cause the intake air to become hotter and therefore thinner, and cause the manifold pressure to decrease?

Because manifold pressure sucks! Seriously though, the manifold pressure measures how much the engine is able to reduce the pressure between throttle and inlet valve by sucking air into the cylinder.

When you apply carb heat the air gets routed over a heat exchanger that uses some of the excess heat from the exhaust system to heat up the intake air, however the reason it becomes less dense, is because the pressure stays the same. If you look at the so called ideal gas law, you'll notice that pressure is a function of density and temperature, if you have a closed system, where the density can not change, increasing the temperature would indeed increase pressure. This is not a closed system however, so the pressure actually stays more or less the same and the density decreases, and it's not the reason for the manifold pressure increase.

The thinner air leaves the engine with less oxygen to burn and thus it produces less power, the RPM drops, causing the engine to "suck" less air into the cylinder, this gives the air more time to sneak passed the throttle, and the manifold pressure rises. For the same reason the manifold pressure rises (slightly) when you reduce the RPM for cruise. Any reduction in RPM, for whatever reason – engine damage for example – as long as the throttle doesn't move (or if you have carb ice, which has essentially the same effect as closing the throttle), your manifold pressure will actually rise. Remember, it seems counter-intuitive, but the engine is fighting a battle with the throttle, trying to keep the manifold pressure down by sucking the air out, while the throttle is trying to increase the pressure back to atmospheric by letting air in.

When the throttle is anything but wide open, the situation looks like this (image borrowed from the linked article)

(source: avweb.com)

It's related to the fact that the manifold pressure gauge, when the engine is stopped, will read ambient pressure, i.e. 29.92 inHg on a standard day at sea level, which is usually interpreted as "full throttle", it doesn't matter how the throttle is positioned. So it's not really showing how much fuel/air mix you're shoving into the engine. In fact, we're not shoving at all, the engine literally sucks it into the cylinder as the piston moves out of the way during the intake stroke. In this particular case with the engine off, it just means that enough air was able to sneak by the throttle and equalize the pressure. It is not flowing nearly fast enough to equalize the pressure as soon as the engine is running though.


What is the thrust balance between compressor and exhaust nozzle for a turbojet engine? I had this question asked in university and the teacher was unable to provide more than a theoretical estimate. The ratio I was given was 15/85.

Obviously in the case of a turbofan this ratio increases.

Is there any professional pilot or engineer able to tell even on a real example, what is the ratio of thrust distribution between compressor and jet for a known reactive jet engine, turboprop or turbofan?

I believe that helicopter turboprops produce no measurable thrust in the jet. Anyone?

The answer depends on two major factors: the engine design, and the flight speed.

Engine design. As mentioned in this answer, there are four major types of turbine engine design: turbojet, turbofan, turboprop, turboshaft. The turbojet has all air flow through the engine itself and derives all thrust from the combustion gas jet exhaust. At the other end of the spectrum, the turboshaft has negligible thrust from the hot exhaust and transfers all useable power to the output shaft.

Flight speed. At high speed (case a in above picture) air streams into the inlet at high velocity and is decelerated before it hits the compressor, which sees a static pressure at the front that is higher than ambient pressure. No suction at the compressor from end at high speed! Only at the lower speed of case b is the static pressure at the front of the compressor lower than ambient.

To start with the last question:

  I believe that helicopter turboprops produce no measurable thrust in the jet. Anyone?

Helicopter engines are turboshafts, which transfer all useful power onto the output shaft. No thrust from the exhaust stream here, ratio 100/0

Then the title question, which is a bit confusing because of the use of the word suction. IF we take the question as posted in a comment, it seems to focus on turbofans, and on the thrust ratio between hot stream and cold stream:

  The compressor acts as a tubed multi blade propeller. It compresses the airflow and the reactive effect is thrust on each rotor blade. What is the ratio between the thrust developed in compressor and the thrust developed in the exhaust nozzle?

Two sources for the answer:

From The Jet Engine 5th edition by Rolls Royce, page 94:

  A compressor is a device that raises the pressure of the working fluid passing through it - in this case, air. A fan is a large, low-pressure, compressor found at the front of most modern aero engines.

  For a modern large civil engine:the fan passes over one tonne of airflow per second; this flow produces around 75 per cent of the engine thrust

Gas Turbine Theory by Saravanamuttoo a.o. example 3.2, finds a ratio of 73.5% at sea level:

   Thrust of a twin-spool bypass engine with the following data:
   * Overall pressure ratio           25.0
   * Fan pressure ratio                1.65
   * Bypass ratio                      5.0
   * Total air mass flow             215 kg/s
   * Fan thrust (cold stream)     52,532 N
   * Exhaust thrust (hot stream)  18,931 N

These above percentages are from the engine itself - but in cruise flight, a large part of thrust is developed by different structural parts of the engine, notably the engine intake.

A supersonic turbojet engine with central intake cone, from an old paper format uni lecture book. The inlet starts developing thrust at below M = 1. A subsonic engine has its inlet optimised for lower velocities and contributes more to the thrust in cruise.


How do airline pilots relieve the physical stress and discomfort of sitting for long periods of time? Airline pilots are required to sit in the cockpit for quite a considerable amount of time during their day. For example, during the preflight, climb and descend portions of the flight, there are many events going on in the cockpit that requires both pilots' attention. The amount of time they are required to spend sitting in the cockpit is, surely, longer than that of a passenger on the same flight.

How do they relieve the physical stress/discomfort and other physiological issues associated with sitting for a long time? For example, during cruise, is it normal for one of the pilots to unbuckle the seatbelt, get up and stretch his legs in the cockpit? Do they do some simple exercise for a few minutes during the turn around?

Note: This question is not about how pilots deal with the mental stress of boredom in a long flight. This is about how they deal with the physiological discomfort associated with remaining in the sitting position for a long time.

I was on an EMB-145. The longest flight we usually had were 3.5 hours so my experience doesn't compare to Trans Pacific routes. As a crew-member I could get up to use the restroom, but there wasn't enough room to stand on the flight deck. You learn to sit different ways (one leg under you) to makes adjustments. Then the other leg under you later and so one. Some sort of seat Yoga I guess you could call it. My strategy was to walk, walk, walk, and stay off the plane as long as I could between turns. Your body adapts to the environment after awhile regardless of your body being in great shape or not.


What is (or was) the "international frequency"? I have recently read a book about Douglas BADER. This pilot has lost his legs (because of accident in 1931) but after (thanks to his single-mindedness) he takes up the "broomstick" again and became a ace with ~30 victory...
After he is shot and captured by the enemy: the Germans. Germans contact the UK in the "International frequency" to send prostheses. The Germans propose a deal but the RAF drops it during a bombing raid with 11 messerschmitt shot in the process.(at the same time)

What information are available about this frequency? (name, usage, frequency).

Have you question about this story?
Bonus :

The international distress frequency has been 500 kHz, since 1908.
Copious details are at https://en.wikipedia.org/wiki/500_kHz.

During the war, this frequency was used for reporting distress and for monitoring distress, by the Germans and the British.  It was also used before and after the war for this purpose, by many countries, by aviators and mariners and others.


Why does Airbus not display the exact airspeed on the PFD? On every other PFD (I know), the exact airspeed is displayed as big number on the PFD. To clarify what I mean, here are two pictures:

Source, added square, Boeing PFD

Source, added square, D10A EFIS

Now, when we take a look at the Airbus PFD, we can see that there is no exact speed display:

Source, added square, Airbus PFD

This is one of the biggest differences between the Airbus PFD and other PFDs. What led Airbus to this unusual decision? Is it maybe because Airbus pilots don't need to watch airspeed as close as other pilots, because of the numerous flight envelope protection systems and the fact that the autothrottle controls the speed until 20 feet above ground?

Is there just no need to know the exact airspeed and Airbus wanted to remove a source of distraction?

Is it possible to turn an exact speed display on if the pilot wants or needs it?

Where it came from (history)
The Airbus-style airspeed tape on the A320 onwards comes from the A310 (Flight, 1987).

The present scale convention is similar to that used on the A310, and pilots have obviously readily adapted to it, but it does show that it may take a little time to shake off an old, ingrained response.

What the author is referring to is the speed-deviation indicator, an indicator like that on the 767 shown below that shows how fast/slow the plane is compared to the target speed.
(commons.wikimedia.org)
The A310 had this design when Thomson-CSF (later became Thales Group) took over the forward-facing crew cockpit (FFCC).

Thomson-CSF has been developing its A310 CRT symbology in close cooperation with Airbus and the customer airlines, and many details have changed since the company's selection as A310 supplier in September 1979 (Flight, 1980).

(Emphasis mine.)
Based on the above, Thomson-CSF reached the final design through usability engineering.
The A300 had a circular attitude indicator. The A310 change was to crop the sides to allow for an airspeed indicator.

The electronic attitude director indicator (EADI) which forms the basis of the PFD is no longer round, allowing more airspeed information to be presented on the sliding scale on the left.
(...)
The aircraft's indicated airspeed is shown by a yellow circle, the arrow through it indicating the speed trend. The airspeed symbol and trend remain stationary while the scale moves.

My opinion: This is the closest thing to the old "clockwork" cockpits, where an instrument's hand position was enough to glean the required information. Here the pilot would keep the yellow line (or circle on the A310) away from the too-slow and too-fast regions.
Not just Airbus
Below you can see the different versions on the 737 Classic, the one on the right featuring the "rolling digit cursor."

Something I found during my research I think is worth sharing about Airbus' philosophy that I haven't heard before:

The coach driver gives a command and the horses take care of the road, the A320 pilot makes a control input and the aircraft takes care of the flightpath (Flight, 1986).

I think the Airbus airspeed tape follows that, showing only what's relevant at a glance, as Radu094 wrote in their answer.


How does deploying flaps change the gradient and rate of descent? My understanding is:
Using the gradient formula "(T-D)/W x 100", we can see that with the deployment of flaps, the gradient would reduce (due to the drag added). And since Rate of Descent (RoD) = gradient x Ground Speed (GS), the RoD will naturally decrease.
However, when doing questions, it is apparent that the gradient increases rather than the reduction I expected.
Can anyone provide some explanation on it? Am I using the wrong formula or viewing it in the wrong way?

Yes you’re viewing it the wrong way.  Deployment of flaps changes all sorts of flight parameters, not just one.  The wing area may increase, the camber and angle of incidence of the wing increase and so the engine thrust line is effectively tilted downwards.  The aspect ratio changes, as does the relative angle of the horizontal stabiliser.  The net result is that the flight efficiency is reduced (i.e. the amount of energy required to maintain height increases) but the stall speed is reduced.  There’s a lot happening and you have to take it all into account.  Typically on approach you’ll want a low airspeed and relatively high rate of descent but without compromising control authority, so the flap layout is designed to provide this.


What is the third airport near Dubai visible on Google Maps? I know Dubai International (DXB) and Dubai World Central (DWC). What is the third Dubai Airport, not named on Google Maps?

Is it military, GA or commercial. Why there is no clear access road to it?

The airport is Al Minhad Air Base:

  Al Minhad Air Base is a military installation in the United Arab Emirates. The base is located approximately 15 miles (24 km) south of Dubai and is operated by the United Arab Emirates Air Force. It is currently the headquarters of Joint Task Force 633 and supports Australian operations in the Middle East.

If you turn on Google Earth view, you can see the single road leading into the airbase from the east:


How do I improve navigation with a VFR sectional chart? I am doing my PPL atm. I am struggling to navigate with a VFR sectional chart, I am getting lost more often. How do I fix this issue? Any tips?

I have trouble identifying small towns, identifying places if there are no big landmarks.
How do I identify places more accurately?

The trick is not to fixate on small details, but to scan on the chart along your route for landmarks and features that combine into large geometric shapes that are easy to pick out from the air (while cruising the higher the better).

Like; highway, river, and railway line that form some shape like a large 5 mile long triangle so that there is a unique pattern, with a town at some point on the triangle that makes it especially distinctive, to the left of your track.

Note that configuration on the map.  Try to mentally compress it in your mind to allow for foreshortening because you will be initially viewing it at an angle.  Look for its match on the ground, allowing for its location to be farther left or right than expected if you've drifted off track.  As you find it and know where you are, scan ahead on the map for another easy to spot shape, as close as possible to your current position, note its distance, estimate the time to get there based on your ground speed and wait for it to appear.

Beyond that, it's mostly about establishing the correct heading to stay on track and holding it well, staying on top of your position and not allowing distractions to divert your attention too long as the world slides by below, and getting good at mentally projecting your progress based on known ground speed (like, you've been distracted for 5 minutes since your last known position, and if your ground speed is 2 miles per minute you should be between 9 and 11 miles away from it, so start looking for a recognizable geometric pattern ahead of you, say, 12 to 15 miles from last known).

A home computer flight sim like FSX or Xplane is really great for practicing this sort of thing on your own time.


How do AHRS systems meet the "gyroscopic" requirement of 14 cfr 91.205.d? EDITED
Among the instruments listed as required for IFR operations in the US FAR is are various "gyroscopic" instruments, including those for the turn coordinator, attitude and heading. In modern avionics, though, there are no gyros. All the inertial sensing is done through some sort of non-spinning resonator (see https://en.wikipedia.org/wiki/Vibrating_structure_gyroscope). How are these things "gyroscopes" within the language of the FAR? Am I misunderstanding what the term means? I thought the "gyro" root meant "to turn in a circle" (as in "gyrate" or the making of the Greek sandwich), which is how heading/attitude/rate-of-turn devices all used to work. Obviously this is a nitpick since the point is to  sense  rotation. But then why does the FAR specify "gyroscopic" as a modifier for the various instruments?
ETA:
The origin of this question was a Sheppard Air test prep q referencing the FAR. Supposedly, all of these questions are on actual FAA exams. Here's another one, which in light of the comments I marked "B" for. But according to SA, the correct answer is "C". So (if SA is correct) the FAA seems to think here that a gyro is actually a spinning object.

(Also, thanks whoever downvoted this, while a People Magazine question about JFK Jr's IR training gets upvotes.)

In regulations, instruments are always defined functionally. They say what the instruments must measure, not how. Any actual implementation then has to be certified, but that certification concerns with accuracy of the instrument, its reliability and ability to detect its failure – because the pilot can only handle the failure if it is obvious to them – not it's principle. So anything that can locally (without external reference) measure attitude and rate of turn qualifies.
Note that the "gyro" root does mean “circle”, but don't forget the other half of the word:

[…] from Ancient Greek γῦρος (gûros, “circle”) and σκοπός (skopós, “watcher”).[1]:

It means, and always did, an instrument for observing rotation, though it was only used to describe one of the methods for doing so known to the person that coined the term (that person was Leon Foucault and the other method was obviously Foucault pendulum).


Can airlines recover costs if they dump fuel for a medical emergency? As per the title, can airlines recover costs if they dump fuel due to a medical emergency on board shortly after takeoff?

You are overestimating (by asking) the cost of fuel in such a worst-case scenario diversion that requires fuel dumping.

With this week's jet fuel price, 50 tonnes (approx. half of what is loaded on a 787 bound for a long-haul) would set you back \$31,000.[a] But,

  A single flight diversion can cost Emirates anything from US\$50,000 to over US\$600,000, depending on the nature of the diversion which includes fuel, flight catering, landing and ground handling fees, air navigation cost, passenger rebooking costs and onward connection, as well as other associated costs to care for crew and passengers.

Since 50 tonnes can be considered an upper limit, and Emirates' upper limit is \$600,000, fuel is just 5% of the cost. Further,

  Adel Al Redha, Emirates' Executive Vice President and Chief Operating Officer, said: "We can never hope to recover the costs of a flight diversion, but the wellbeing of our customers is always our number one priority (...) [emphasis added]

Source: Emirates reveals the real cost of medical diversions for an airline, www.airlineratings.com, 2017

[a]: Also, for reference: An A380 returned to SFO not long into a flight due to a medical emergency, and dumped "40 tons" on the way back (avherald.com).

Related: How much compensation does an unruly passenger have to pay to an airline if the flight has to be diverted to remove them?


What is situational awareness and why is it important? What is the definition of situational awareness? In which phase of flight is situational awareness the lowest, and why?

A simple definition of situational awareness that you are aware of the different situation happening around you, know why they are happening and can think of an action you need to take to tackle with those.

In aviation, situational awareness means:

  For a pilot, situational awareness means having a mental picture of
  the existing inter-relationship of location, flight conditions,
  configuration and energy state of your aircraft as well as any other
  factors that could be about to affect its safety such as proximate
  terrain, obstructions, airspace reservations and weather systems. The
  potential consequences of inadequate situational awareness include
  CFIT, loss of control, airspace infringement, loss of separation, or
  an encounter with wake vortex turbulence, severe air turbulence, heavy
  icing or unexpectedly strong head winds.

As far as your second question, hypothetically speaking, one can say that going through the preflight checklist, pilots are more focused inside the cockpit mostly and the situation outside the airplane is not too much of concern until they pay attention to that.

Generally speaking, when the airplane is not moving, situational awareness can be lesser. It is same as when you are driving, at what time you have lesser situational awareness?


Can I fly a practice LNAV approach with an iPad? I'm doing training for an instrument rating, and I'm thinking I'd like to do some solo VFR cross country flying and do some practice instrument approaches.  The C152 I'll be flying doesn't have a GPS installed, but I'll have ForeFlight on my iPad.  Since I'm VFR, could I request a practice LNAV approach from ATC and use my iPad to navigate the approach?  I realize this isn't quite as good as doing hood training in an aircraft with GPS, but I think it will be of some use to me in my training.

In the US, there are no regulations prohibiting you from using an iPad for navigation while flying VFR. There are also no regulations specifying what equipment you must use for a practice approach. The key to this is that it is a practice approach. Therefore, it is flown VFR. Even if you were an IFR-rated pilot in an IFR aircraft under the hood/foggles, your safety pilot would be VFR.
If you fly that same approach IFR (whether IMC or VMC), then it is an actual approach even when done as a practice approach. Just the ATC expectations are changed. Flying IFR would require the proper TSOed navigational equipment.
One word of caution would be that this might not be a safe practice flying solo. It would be best to have your iPad mounted somehow to make it hands-free. You should also practice this with your CFI (preferably) or a safety pilot first.
It would also be unwise to have to switch back and forth from the approach chart to your Foreflight  AHRS screen on the same iPad. You are in a critical phase of flight. Doing what you plan would be an unnecessary distraction and a violation of the Part 91 sterile cockpit strong recommendation (not a regulation for Part 91, yet). Either print your approach charts or carry two iPads.
Some guidance for practice approaches is provided in AIM 4-3-21.


Do runway markings vary from country to country? I understand that most of the airports should follow FAA/ICAO for runway markings but most of the countries have their own standardization orgs. So, how much do the runway markings vary from USA to Europe?

Edit: We are mainly looking for the big commercial airplanes and not the smaller and private strips which handles only big jets for commercial operations.

Do runway markings vary from country to country?

Yes, examples are touchdown zone markings and runway number sizes.

How much do the runway markings vary from USA to Europe?

Europe is too big to manually check each country, but it doesn't vary by much. Numbers are still numbers and TDZ markings still follow the same pattern.

Even smaller airports, say in the US, don't necessarily match bigger airports.

Difference are submitted to ICAO to be included in supplements to Annex 14 when it comes to international airports (typically). And each country's AIP will list the differences from ICAO Annex 14. So if you are interested in a certain country, check its AIP. If interested in the recommended standards, check Annex 14.


Are there any places I can take an FAA written test in Japan? I want to ask FAA in person. But, I was not able to reach them. I tried phone call 8668782498, sent e-mail to local FSDO. But nothing coming back.

I guess I have some possibility to take it in military base placed in Japan.
Do you know something about this?

According to this list, there are three Airman Knowledge Testing Centers outside the 50 states (listed as "Out of US" on that document.)  All of them are in US outlying territories, and none of them are in Japan.

You could conceivably arrange do the written test at the center listed in Guam (Barrigada).  There are regular airline flights to Guam from Tokyo, Osaka, Fukuoka, and Nagoya, and the 4-hour flight to Guam is better than the 8-hour flight to Hawaii or the 9+ hour flight to the continental US.


Do large non-pressurized metal planes have a maximum fatigue cycle? For example the DC3. The way I understand it, the only thing that "ages" the airframes of DC3 is the landing/takeoff cycles and the accompanied periodic force loading/unloading. Do planes such as this really have a meaningful definition of lifetime of its airframe?

As a side note, is loading/unloading cargos on the floor another kind of cycle too?

Yes they do, and here is why.

Airplanes are made mostly of aluminum rather than steel. It is possible to design a steel part in such a way that it will never succumb to fatigue failure (crack propagation at a stress significantly below the yield stress) but this is not true of aluminum and its alloys. For this reason it is necessary to periodically tear down and inspect aircraft for fatigue cracking of their aluminum structure- in essence, safety is inspected into (aluminum) aircraft because from a design standpoint, it is not possible to design fatigue failures out of their structure.

During that teardown, any part that shows fatigue cracking (or corrosion, or physical damage, etc.) is removed and replaced with a new part that is certifiably fault-free. To some extent this means that a DC-3 with 40,000 hours on it has had so much of its structure replaced over the years that the joke is told that the only part that actually has 40,000 hours on it is the serial number plate.

Flexure of the structure during turbulence in flight is a more significant source of fatigue cycling than cargo loading & unloading cycles.


Why overhead bin was put on top of passengers head? Hello I'm just curious about the reason to why the overhead bin was most commonly being put on top of our seat and head.

Because it is the most efficient use of space.

Due to the physics, specifically the way pressure differential is spread in a container as stress, a perfectly circular tube is the best shape for the body of an airplane, and a rectangular box is way, way, worse. Modern airlines have an oval cross-section, but it is still a lot closer to a tube than a box.

The question is than how do you allocate the space inside a tube. The widest floor area is in the middle vertically, so that is where the passengers go. Now we have roughly one to two meters of vertical space both above and below the passenger deck, not high enough to accommodate people but enough for cargo and storage.

Naturally you would want the heavy cargo to go below, and passenger storage to go above, for logistic reasons. Putting them on the same deck as the cabin would reduce the usable floor area for putting seats. You'd want maximum floor area to place the maximum number of passenger seats to increased revenue on the same flight.


How to model aircraft fuel consumption during the approach? I am trying to write an algorithm modelling the 'Airplane landing problem'. The aim is to land a sequence of airplanes while minimizing the operating costs and respecting constraints such as the separation between consecutive airplanes.
Hence, I need to be able to quantify these operating costs in particular fuel consumption.

Basically, in my simulation - it's a very simple approach - airplanes can be in 3 different regimes :

the aircraft can be asked to fly faster than it's preferred speed, it's called time advance and it's one of the tools used to reduce congestion
the aircraft can of course fly at it's preferred speed
the aircraft can be asked to fly a holding pattern

I would like to elaborate a function that would give the fuel consumption in function of the time for every mode.
I absolutely don't know where to start. The only information that I find deal with the preferred speed consumption.
How can I model the two others regimes ?

Edit : Indeed, the part concerning holding patterns is similar to this other question. However, I don't think any information on time advance has been given so I would like to focus my question on this. Also, if anyone has more information on fuel consumption in holding patterns than would by very helpful.
Thank you very much

Approaches take relatively little time, and have various throttle ranges, from idle to slow level flight. I would simply model as if the aircraft were flying level for the distance of the approach, you will over estimate fuel consumption for the approach itself, but for even a 60 minute flight the error would be tiny. You simply cannot accurately predict what is going to happen.


Anyone recognize this airport? I found this image on boldmethod.
Where is this? Looks like a beautiful place. Has an instrument approach (from the runway markings.) On a mesa in snow country. It is not Sedona or St George.
Telluride?

Yes, Telluride RWY 9, as can be seen clearly in this video.
Screenshot from video:


Is it feasible to recuperate energy from landing aircraft by using a runway sled with regenerative braking? Would it be feasible to land large (Boeing 747 and Airbus A380) and all other aircraft on a sled on the runway, the kinetic energy of the aircraft is then transferred to the sled, then the sled uses regenerative braking to produce electricity for use by other electric sleds that taxi the aircraft to the runway for taxi, given that a lot of fuel is used during taxi and that fuel is expensive, causes green house gas pollution when burnt. This would save costs on tire wear brake pad wear and if designed properly improve braking safety

What you propose might be technically possible, but that doesn't make it a good idea.

However, any benefits would by tiny compared to the immense cost, the extraordinary engineering efforts required, and the horrendous risk of something going wrong.

Airports have long, wide runways for good reasons. Airliners don't touch down on a single spot. Your "sled" would need to be a very wide and extremely long platform.

The sled would need to be able to bear the weight of a large airliner as it touches down. A large plane can damage a concrete runway. The sled is going to need to be extraordinarily strong.

Your platform will need to accelerate from zero to the speed of a landing airliner in very short order; if it causes the plane to decelerate too rapidly instead, it will tear bits off the plane, or limbs and heads off the passengers.

Good luck designing and manufacturing this huge, strong and and extremely lightweight sled.

(Maybe you can design the sled to match the speed of the incoming plane. That would solve some problems, but only at the expense of introducing some even more exciting new ones, like having just constructed the world's largest and most lethal railgun.)

What's going to happen when something goes wrong? You now have a wheel-less airliner, in difficulties, at landing speed, plus a huge sled also possibly travelling at 300+ km/h. I don't even want to be in the same town as that, never mind at the same airport.

What will you gain? Not much in the way of saved energy from regenerative braking; the energy cost of maintaining the machinery that can cope with such savage braking effects will greatly outweigh it anyway.

And actually, taxiing is good for aircraft engines, because it allows them to warm up before being used at full power (it may even be good for them after landing, to allow them to cool down more slowly).

So, nice idea, but in this case, the wheel, all of 5000+ years old, is an invention better-suited to airliner landings.


Can the V-22 carryout vertical takeoffs with shorter blades? The V-22 has blades that are larger than blades on most helicopters. Could you make them smaller and still have the vertical takeoff effect?

Bonus: Does the V-22 get some of its thrust from the exhaust?

The rotor size helicopter (or a tiltrotor, in this case) is determined by its aerodynamic requirements, most importantly, its hover characteristics. The main constraint is the weight that has to be lifted by the helicopter at a give a altitude.

In this context, it can be seen that the blades of V-22 are actually smaller. For example, V22 has a Max. TOW(Take-off Weight) of 27,400 kg. For achieving this, the V22 twin rotors of 11.6 m diameter, giving a rotor disc area of 212 m². A CH47, which has a Max TOW of 22,680 kg has a rotor disc area of 520 m² using twin rotors.

If we take single rotor helicopters, the CH 53 Super stallion has a 24 m dia. rotor having a disc area of  460 m² to lift a max TOW of 33,300 kg.

This lesser blade disc area of V22 limits is ability to hover at higher altitudes. The V22 rotor blades will have been optimized for required performance parameters. So, if the blade length is reduced (assuming airfoil is kept the same), vertical takeoff is possible though other performance characteristics will be severely affected.

The V 22 uses two Rolls-Royce Allison T406/AE 1107C-Liberty turboshafts, which do not produce any thrust.


Solutions to improve the aerodynamic behavior of a UAV So I'm working at a project of a UAV with the follow characteristics:

Rectangular planform
Conventional tail
The fuselage is just a metal/aluminum rod

So we need to improve its aerodynamic behavior/perfomance.
I thought about: Winglets, big AR, a tapered planform or an elliptical one for reduced induced drag, maybe flaps/slats. I cant think anything about the tail actually.

The UAV is similar to the one in the picture. (The tail and wings)

You want to move a heavy payload at low speeds. This means that induced drag will dominate the aircraft. If we assume a quadratic polar, the least amount of energy for staying airborne is needed when induced drag is three times higher than friction drag. Assuming a quadratic polar, the optimum lift coefficient at that point is $$c_L=\sqrt{3\cdot c_{D0}\cdot\pi\cdot AR\cdot\epsilon}$$
Obviously, you want a small zero-lift drag, but when you combine this with the high aspect ratio for a very efficient configuration, your lift coefficient will also become very high. You need to be careful to pick the right airfoil, and now Reynolds number effects demand to be observed. Once I know the overall size of your UAV, I can become more specific.

Just an example: If the zero lift drag coefficient is 0.02 and the aspect ratio is 12, the ideal lift coefficient is already 1.5. This is beyond most airfoils at Reynolds numbers below 1,000,000 and indicates a too high aspect ratio. Better add some chord in that case.

Also, some design decisions will look counterintuitive at first. I would strongly encourage you to add wing struts, like in a Cessna 172 or the Dedalus human powered aircraft. They help to save wing weight and thus reduce induced drag.

Don't overdo it with an elliptic planform! This will produce too small a chord on the outer wing and give the design undesirable stall characteristics. Better keep some chord and twist the wing so you will achieve the desired elliptical distribution at the design angle of attack. Better yet, save some wing weight by moving to a more triangular lift distribution – however, for small aircraft the optimum looks still quite elliptic.

The model pictured in your question has a lot of dimples on the fuselage - make sure yours will have a smooth surface.

Also look into improving propulsive efficiency. Use low RPM on a large propeller, if possible. You didn't mention your means of propulsion, so again it is hard to be more specific. Judging from the model, you will use electric propulsion. Use a brushless external rotor with a high pole count (low RPM per Volt).

So please provide more details and then you will receive a better answer.


Which organisation deals with Aviation Law - IATA or ICAO? Both Organisations are involved in Aviation Regulation. But which of them deals with Law? Are directives given by both equally applicable to all aircraft & airline operators?

ICAO does deals with law, although not directly.
The Convention on International Civil Aviation and its 19 Annexes form the basis of International Air Law. Although the Convention text itself is not directly a law, the 193 ICAO Member States ratify the ICAO Standard and Recommended Practices, albeit sometimes with minor modifications.
From this answer:

ICAO is the International Civil Aviation Organization, a specialized
agency of United Nations. It was created after the Convention on
International Civil Aviation (the Chicago Convention) of 1944 was
ratified in 1947. The purpose of ICAO is according to the convention:

"WHEREAS the future development of international civil aviation can
greatly help to create and preserve friendship and understanding among
the nations and peoples of the world, yet its abuse can become a
threat to the general security; and
WHEREAS it is desirable to avoid friction and to promote that
co-operation between nations and peoples upon which the peace of the
world depends;
THEREFORE, the undersigned governments having agreed on certain
principles and arrangements in order that international civil aviation
may be developed in a safe and orderly manner and that international
air transport services may be established on the basis of equality of
opportunity and operated soundly and economically;
Have accordingly concluded this Convention to that end."

Within ICAO, the 191 Member States and a number of global aviation
organizations work together to develop international Standards and
Recommended Practices (SARPs). These SARPs are the reference for
states developing their national civil aviation regulations which are
legally enforcible. This is an important aspect: ICAO SARPs are not
legally binding by themselves, they form the basis of national
regulations which have legal status.
In this way civil aviation regulations are harmonized all over the
world, with slight differences based on the actual implementation in
national regulations. These local differences are then reported back
to ICAO and published.

IATA is a trade organisation representing the interests of their member airlines. They don't deal with law in the sense that their directives are not embedded in law.


Is it cheaper to drop cargo than to land it? Is it more fuel efficient to drop cargo onto a runway from the air en route to a final destination than to land and unload it using a more fuel efficient plane?

That scenario only makes sense if your airplane stays at cruising altitude: although taxi and takeoff does use up fuel it's really the ascent to cruise that takes the most. You aren't really going to be able to drop cargo accurately from cruising altitude, so you'll have to descend pretty low, then you'll need to climb up again, and that would suck up lots of fuel and make it much less efficient a method of delivery.

Add to that the weight and cost of the parachute mechanisms as well as the massive protective packaging the cargo would need to survive the jolt (2-3 Gs when it hits the ground) and the whole thing becomes pretty uneconomical.

The military only air drops cargo when there's no other alternative - now you know why.


Why are older airplanes still in use? It is normal to see older planes (20+ years) quite frequently. In fact, a few months ago I saw a plane over 50 years old (not in a museum but on a runway, about to take off).

Comparing to cars, there are not many cars on the road which are older than 10-15 years.

What are the reasons for this besides the following?

Airplanes are very expensive. A new 172 would be over USD 300,000, and a thirty year old can be around \$50k or less.
Airplanes follow a very strict maintenance schedule and are inspected thoroughly (ideally speaking). Hence their life is increased.
Pilots are very well trained compared to car drivers, so they know a lot more of what they are doing. Hence they are more aware of the condition of the plane.
Cars crash a lot more often than airplanes.

It appears that this holds true for both general and commercial aviation.

Besides the main points you mentioned, I can think of a couple things, the first is sort of related to your point #1.

Airplanes are designed to be easy to service. Cars are less so.
Cars only have a few very expensive parts, mainly the drivetrain (engine and transmission). If either of those needs to be replaced in an older car, it can easily cost more than the car is worth.

Airplanes are much more complex, and have a larger number of expensive components. The engines of most airliners are designed to be removed relatively quickly. Although the engines tend to be the most expensive part, replacing an engine is nowhere near the total cost of the airplane, and there is generally a good pool of engines out there for parts and replacement (just look at how many JT8D engines are still in service).

In GA aircraft, it is easier for a repair to cost more than the airplane is worth. However, the more comprehensive maintenance required on aircraft means that this kind of repair is less likely to be needed. Also, while its usually easy to go out and replace a broken car with a comparable new or used one, the aircraft market isn't as large. New aircraft tend to be much more expensive, and the used market is more limited.

Another reason is that airplanes can have more unique qualities than cars. For example, there are original 737s flying in Canada because they are able to operate from gravel runways. There are just more combinations of sizes and capabilities in airplanes than with cars. Many times, it is only economical to replace those aircraft (both for the builder and the buyer) in very long cycles.


Is it Legal to listen to Air Traffic Control Frequencies in the USA on a computer for entertainment? like listening to scanners an radio frequencies for entertainment and i make it a game because i use a online flight tracker and try to find that aircraft. Is it legal?

Yes it is legal in the US, and you can listen to audio streams on websites such as https://www.liveatc.net


What makes intentional low or missed approaches legal? A common procedure in flight training is the low approach: simulating a landing, but without actually making contact with the ground before powering up and either going around in the traffic pattern or executing a missed approach procedure, sometimes after flying all the way down to an approach's minimums.
In this situation, a pilot flies very close to the ground - one suggested crosswind training procedure suggests flying along the runway low enough that "[i]t's OK if the wheels inadvertently touch down during the exercise."
Contrast this to other operations, including a simulated engine-out procedure away from an airfield. These are governed by FAR 91.119:

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.

Training for missed approaches and going around are important for basic skills, and they are performed very frequently. However, the regulations make no exception for training. For a maneuver where a pilot descends below 500 feet AGL without intending to land, is there legal guidance that makes this OK near a runway, or is it an unwritten exception?

Well, I'm going with "It's a written exception, but nobody thought to include it in 14 CFR 91.119 though".

I say this because there are a number of regulations that require a student pilot or applicant for a license to receive and log flight training for go-arounds.

For example:

14 CFR 61.87 - Solo requirements for student pilots
14 CFR 61.98 - Flight proficiency (Recreational Pilots)
14 CFR 61.107 - Flight proficiency (Private Pilots)
And others

The complete text of the private pilot SEL requirement (and they are all similar) is:

  §61.107   Flight proficiency.

  (a) General. A person who applies for a
  private pilot certificate must receive and log ground and flight
  training from an authorized instructor on the areas of operation of
  this section that apply to the aircraft category and class rating
  sought.

  (b) Areas of operation.

  (1) For an airplane category rating with a single-engine class rating:

  (i) Preflight preparation;

  (ii) Preflight procedures;

  (iii) Airport and seaplane base operations;

  (iv) Takeoffs, landings, and go-arounds;

  (v) Performance maneuvers;

  (vi) Ground reference maneuvers;

  (vii) Navigation;

  (viii) Slow flight and stalls;

  (ix) Basic instrument maneuvers;

  (x) Emergency operations;

  (xi) Night operations, except as provided in §61.110 of this part; and

  (xii) Postflight procedures.


What is a tactical penetration descent? I was flying the other day by a military base and heard a military aircraft (I'm not sure what type it was) request a tactical penetration descent from the controller at a civilian airport. What is a tactical penetration descent?

According to LOCAL FLYING OPERATING INSTRUCTION / 440 AIRLIFT WING INSTRUCTION 11-250 / OPR 440 OSS/OSA:

  5.7.4. ARRIVAL PROCEDURES:
  5.7.4.1. DESCENTS:
  5.7.4.1.1. TACTICAL (PENETRATION) DESCENT (Overhead, Downwind, Beam, etc): High rate (unrestricted) visual descent profile designed to transition an aircraft from a high-level altitude structure to a low-level altitude structure putting the aircraft in a safe position to execute a tactical approach.
  ...
  5.7.4.1.3. TACTICAL (PENETRATION) DESCENT ASSAULT – High rate (unrestricted) visual descent profile designed to transition an aircraft from a high-level altitude structure to a low-level altitude structure putting the aircraft in a safe position to execute a tactical approach to an assault landing zone. Note: A separate penetration descent profile may also be flown to Mackall AAF (HFF), see Pope Aircrew In-flight guide for procedures.
  5.7.4.1.3.1. Arrival Procedures:
  5.7.4.1.3.1.1. When sequenced, commence penetration descent to a tactical approach, ARA, or normal pattern. Request desired approach as early as possible upon switching to Pope Tower.
  5.7.4.1.3.1.2. Remain at or above 2500’ MSL until within 5 NM of Pope. Do not descend below 720’ MSL until given clearance to land from Pope Tower.

See also fooot's answer to another question, where he describes a tactical descent as an extremely steep descent, and a tactical approach as an extremely steep approach.

According to other sources, the technique in question might also be called (depending on the exact landing circumstances) an Assault Landing, a Sarajevo Approach or even a Khe Sanh Approach or an Overhead Approach.


Do some right-handed pilots fail to use the left stick of an Airbus? After years of flying left-hand throttle and right-hand yoke (in the right seat), are there ever first officers who simply cannot transition to the opposite due to particular hand-dominance?

As a corollary, are there any pilots who simply cannot acquire the left-hand dexterity/sensitivity to use the Airbus joystick when transitioning to captain?

And in all cases, are there ever trainees who cannot get used to yoking or throttling with a non-dominant?

In a study titled 'Role of handedness in flying performance', the author notes:

  [Leon had reported] that movements in one limb were not affected by actions in the other limb. It may be for similar reasons that in multi-crew cockpits of transport and passenger aircraft, pilots have not reported any difficulty in operating controls at either the left or right seat even though the layout of the controls is a "mirror image".

From an observation that may or may not have been studied, operating controls is not like handwriting—handwriting requires major shifts in body position to use the other hand. The human brain is really good at ordering one hand to mirror or follow the path of the other hand. If you think of the yoke as a steering wheel, then when switching from right to left seat, the left hand follows the circular path of the now free hand.

It takes getting used to, but unlike handwriting, it's very quick. I've done this experiment years ago. If you have a flight simulator, setup the plane on approach and switch the joystick from your preferred side to the other. In my case, just like the study above, I did not find any difficulty.

https://commons.wikimedia.org/wiki/File:Patria_pilot_training_OH-GSC_Malmi_3.JPG

Above is the cockpit of a Cirrus aircraft, it's often remarked that the stick resembles half a yoke, and would be operated much like any yoke. The same is said about the Airbus stick.

But Airbus also has an armrest, which is very beneficial as the precision increases when the arm is rested, see here: Why don't we fly helicopters with yokes?