Why does it take months, sometimes years, for the BEA and NTSB to complete aviation accident investigations? I'm aware that there is a lot that goes into an aircraft accident investigation, so I understand that the investigations take a long time for a reason.

But what I don't know is what those reasons are.  I'm hoping someone with some familiarity can give a high level overview as to why aircraft accident investigations take so much time?

When it comes down to it, accident investigations involve lots of coordination between many different groups, companies, and agencies, often around the world. These groups may range from helpful and responsive to completely uncooperative.

Visiting the Site - First there will be a team that heads to the incident site to collect information. If the site is easily accessible, this may be a fairly quick process. If the site is tough to access, or takes a while to find, this will of course take much longer. This is generally the part most visible to the public, but is only the tip of the iceberg in generating a useful report.

Research - There is also a lot of research that must go on behind the scenes. Especially if a possible cause is not clear, investigators must look into many factors to rule out the options. This can be a lot of information and may involved many different groups around the world:

Previous maintenance done on the plane
ATC and weather information about the flight
Information about the crew, the passengers, and the cargo on the flight
Many individuals may also be interviewed

If any of this initial information provides clues as to possible causes of an accident, they will also be gathering information about related aircraft design and functions. This can be a lot of information and may involve working with many different groups. The process of narrowing the focus of the investigation may involve tracking down different leads which end up being irrelevant. It may take a lot of effort just for the report to end up saying "X was not a factor."

Flight Recorders - Gathering the flight recorder data is not always as simple as plugging it in and reading the data. If there is damage, extracting and repairing the memory may take time. The FDR data must be analyzed and it may take additional work to investigate and verify the parameters. The CVR must be read out and then transcribed. Transcription is also a long process, involving different parties to the investigation, and must be synchronized to ATC and FDR information.

Analysis - Once the information has been collected, it must all be analyzed. Investigators may need to contact and work with many different groups and experts to develop an understanding of parts and processes that took groups of engineers years to analyze and design. Components may need to be analyzed down to a microscopic level. This is generally the longest part of the process. Investigators may realize that they must go gather more information. This may involve running tests on equipment to recreate issues. It may take a lot of work to not only explain what failed, but also the reasons behind the failure and how it could be avoided in the future. Most reports will find issues in many different areas, including human factors, regulations, procedures, and aircraft design.

The Report - The investigators will eventually need to come to some conclusions among themselves. This must all be written up in a report. Some reports can be quite lengthy. If you've ever had to write something like this, you might know that writing the report can easily take much longer than the work that went into it. There will also be an opportunity for parties to the investigation to make comments and provide feedback before the report is released. This is where the investigators get to share the results of all their hard work, and it will be published to get picked apart by the whole world, so it's worth taking the time to get it right.

Law - While most agencies like the NTSB focus on producing a factual report and not assigning blame, lawyers may also need to get involved. Investigations may involve dealing with proprietary or sensitive information, or groups that are reluctant to divulge information (see "completely uncooperative" above). Some accidents may involve criminal investigations as well, in which case organizations like the FBI may also be involved.

Followup - It's not even over after the report has been released. The agency will still need to follow up with regulatory agencies (like the FAA) about recommendations made in the reports and determine whether the responses are adequate.

Additional Duties - On top of all this, many investigators will not be working on one incident full time. Agencies like the BEA and NTSB investigate many smaller incidents as well. So imagine that at any given time, an agency may have many active investigations at different points in the above process. In the case of the NTSB, all of this is accomplished by about 400 people with a budget of around $100 million per year. While aviation safety is the largest part of this with about 130 employees, the NTSB also investigates highway, marine, and railroad/pipeline/hazardous material incidents. Employees also spend time on other things such as educating the public about safety issues, looking for ways to improve safety, and producing additional types of reports.


Why is Airbus proceeding with both the A330neo and A350 XWB? Looking at the specifications for the A330neo and A350 XWB, it strikes me that the two under-development models of the A330neo are relatively similar in specification to the A350-800, one slightly shorter and one slightly longer, with corresponding variances in passenger numbers. List pricing (for what little it's worth) is approximately the same, as well.

As a result, it seems like having two distinct models competing for essentially the same market segment should just increase costs for Airbus, and it's not clear to me what the gains are. Is it easier to sell the A330neo to airlines because of it's relative similarity with the existing A330? Is the A330neo cheaper to operate than the A350 (this seems dubious given cost of operation is one of the big selling points of the A350)?

There's been some rumours about the A350-800 getting cancelled and customers pushed towards A330neo or larger A350 models; this still counterintuitive to me. Surely having a smaller range of aircraft families (i.e., A320, A350, A380) simplifies a lot (manufacturing, certification, etc.), so why increase the number of families instead of a smaller A350 model?

Actually the A330neo is already eating up into the A350-800 orders so much that they have abandoned it.

“Their A350 strategy has failed -- they’re really down to one successful model,” Boeing Marketing Vice President Randy Tinseth told reporters at the Farnborough expo near London. “If they didn’t make this choice, they’d be headed for a 30 to 35 percent share in the 200- to 400-seat market.”
Customer feedback about the A350-800 spurred Airbus’s decision to abandon the plane, said Fabrice Bregier, who leads the airliner unit at the Toulouse, France-based company. Stopping work on that jet will let Airbus focus on the more successful and larger -900 model and respond to some airlines’ concerns for fixes to the biggest version, the -1000.


In a non-symmetric turn, how do the side slip angle and thrust side slip angle affect the equations of motion? I'm doing a problem on Flight Mechanics in which a banked turn is performed. The center of gravity of the aircraft is always within an horizontal plane.

In order to write the dynamic equations, I have to assume some simplifications and conditions. One of them is the following:

  The thrust’s sideslip angle is equal and with opposite sign than the aeroplane’s sideslip angle, that is:
  ($\nu = −\beta$).

  Side slip angle ($\beta$) is defined as the angle made by the velocity
  vector to longitudinal axis of the vehicle at the center of gravity in
  an instantaneous frame.

  Thrust side slip angle ($\nu$) is defined as the angle made by the
  thrust vector to longitudinal axis of the vehicle at the center of
  gravity in an instantaneous frame.
  https://en.wikipedia.org/wiki/Slip_(aerodynamics)#Sideslip_angle

Then, I have to write the dynamic equations for the symmetric flight and for the non-symmetric flight.

My questions are:

In my opinion, the condition written above should not be accounted for the symmetric flight, so $(\beta = \nu = 0)$. Is this affirmation correct?
For the non-symmetric case, I have drawn the following scheme of velocity and thrust. But I'm not sure if it's correct because it doesn't make sense, despite that is what the condition says: $(\nu=-\beta)$. Is the scheme correct according to the condition? (The scheme is the top view of the aircraft.)

Relying on physics, causing a mass to execute a circular path requires a suitable centripetal force. In an airplane in a banked balanced turn, this comes from the inward component of lift due to the bank angle.

However, if the turn is not properly co-ordinated, there can be additional contributions to the centripetal force from the power plant thrust no longer being directed tangentially and sidethrust on the airframe due to slip.

The extreme case is the flat turn where the wings remain level and the power plant thrust has an inward component due to the sideslip.

That said, apart from an airplane having vectoring thrust, the only reason for a thrust sideslip angle I can think of is that many single airscrew airplanes have built-in sidethrust to counteract engine torque. However there is no requirement for the engine sidethrust angle to equal the slip angle, so in that case the assumption that the two angles are the same cannot be valid.

The thrust line of an airscrew doesn't change with slip. The slip causes asymmetric thrust on the blades which precesses gyroscopically so the airscrew creates a couple which tends to increase the slip angle.


Do the effects of turbulence change when banking/turning compared to level flight? Are the effects created by turbulence on the aircraft different when the aircraft is banking or in level flight? By logic I'd say yes but I would like some technical and practical explanation.

When in level flight I can imagine that the aircraft is moved laterally or vertically. What happens when these forces are applied from turbulence when  banking?

What are the consequences of turbulence having the aircraft banked, for example, on the lift produced by the wings?

Turbulence affects aircraft in the same way whether it is banked or not.  The difference however would be the end result of the turbulence.

For example, if an aircraft were to encounter turbulence strong enough to roll the aircraft 20 degrees to the right, the end results would be a 20 degree bank if starting from level, but 45 degrees of bank if they were already in a 25 degree banked turn.  If this were to happen it puts them closer to their stall speed because of the higher bank angle, and if they were already going slow and the airplane is at a low altitude, it could be a problem.

Fortunately, most turbulence strong enough to cause this while at low altitude is caused by the wake turbulence of other aircraft or microbursts, and we have pretty good procedures in place to keep it from being a problem these days.  If they aren't at a low altitude it matters even less because there is altitude for the aircraft to recover even if it does get into an unusual attitude.


Have any large aeroplanes been landed — safely and without damage — in locations that they could not be flown away from? And, what was done with them subsequently?

TACA Flight 110 made a deadstick landing on a grass levee. Engines got replaced and it took off using a nearby NASA facility.

https://en.wikipedia.org/wiki/TACA_Flight_110


What could explain the fact that during 1976-80, I used to hear commercial jets make sonic booms while flying overhead? I've read on this site & on Wikipedia that there have only been a couple of commercial jet planes in history that have broken the sound barrier--either in testing (without passengers) or during an unexpected descent.  However, during the period of 1976-80/81, when I lived fairly close to an international airport, I used to regularly hear commercial jets (I assume 747's) create sonic booms as they passed fairly low overhead. I now live even closer to a much bigger international airport, & never hear this. That's why I started to wonder why. & now that I've read that on record, it's only happened a couple of times, I'm even more curious of what the explanation could be. (It was Bradley Airport in CT, if that matters).

Note that 747's and other jumbo jets operating out of Bradley could not have produced sonic booms because they do not fly above the speed of sound (they only do 500 to 550 MPH at high altitude cruise) and, in any case, far slower than that (~250 MPH) when near the ground as for landing and takeoff.
Therefore, whatever it was you heard, it was assuredly not a sonic boom from a passenger plane. The last time these commonly occurred was in the 1950's and '60s when the US Air Force flew mock bombing missions across the United States in supersonic bombers at low altitude, to train the pilots and crews for similar missions against targets in the USSR.
Although sonic booms were essentially outlawed over populated zones in the early 1960's, in your case they apparently did happen during flight tests of the F-22 Raptor in your location, which is very interesting! Thanks for @reirab's  detective work which uncovered this.


What are these symbols on the runway? As just a passenger, not a pilot, this may be a very basic question, but when I am on an airplane leaving the terminal, it goes over a symbol on the tarmac that looks like this:

Also I see signs on the side of the runway pointing to those markers.

On a related note, there is a similar sign near the gate that looks like this:

What do these signs mean?

The first one is the holding position marking. It denotes the entrance from the taxiway into the runway. The dashed lines are in the side of the runway.

The second one is the non movement area boundary mainly for vehicles, which divides the movement and non-movement areas of boundary- the movement area is on the dashed line, for moving into which you'll need ATC clearance.

Images from FAA Guide to Ground Vehicle Operations


What does this indication of '10∼15 degree' that points toward the both edge of runway means? While I study FAR AIM, 2-1-1 approach light system, I saw this indication (on the left side) that I couldn't guess what it tried to demonstrate.

It seems like runway end identifier lights, but I can't conclude since there is no explanation about it.

Does someone have a better idea, or is my guess correct?

That image is intended to describe REIL.  REIL are are two synchronized flashing lights. They can be either omnidirectional or unidirectional facing the approach area.  Unidirectional REIL are preferred.  More information is found in AC 150/5340-30.

Installation requirements are in section 7.7.5:

  7.7.5  REIL.

  7.7.5.1 Location.
  Locate and aim the REIL units per Figure A-79.

  7.7.5.1.1 When possible, install the two light units equidistant from the runway centerline.

  7.7.5.1.2 When location adjustments are necessary, the difference in the distance of the two lights to the runway centerline may not exceed
  10 ft (3 m).

  7.7.5.1.3 Each light unit must be a minimum of 40 ft (12 m) from the edge of taxiways and other runways.

  7.7.5.1.4 The elevation of both units must be within 3 ft (0.9 m) of a horizontal plane through the runway centerline, with the maximum
  height above ground limited to 3 ft (0.9 m) (See Figure A-93.)

  7.7.5.1.5 When the centerline elevation varies, use the centerline point in line with the two units to measure the centerline elevation.

  7.7.5.1.6 Orient the beam axis of an un-baffled unit 15 degrees outward from a line parallel to the runway and inclined at an angle 10 degrees above the horizontal.

  7.7.5.1.7 If this standard setting is operationally objectionable, provide optical baffles (per the manufacturer's instructions) and orient the beam axis of the unit 10 degrees outward from a line parallel to the runway centerline and inclined at an angle of 3 degrees above the horizontal.

As described here, the 15 degrees is the horizontal alignment, and the 10 degrees is the elevation alignment.


What is Arctic Control Area (ACA)? I saw that in Jeppesen airway manual but I didn't find a definition for it. What is that?

How to establish it? Who establishes it and for what reason?

from
http://code7700.com/high_latitude.htm

Apparently defined by Transport Canada:

https://www.tc.gc.ca/media/documents/ca-publications/AIM-2018-1-E-ACCESS.pdf

page 192


Why aren't 737s or A320s commonly used for transatlantic flights? Despite newer models of the 737 and A320 families having more than enough range to cross the North Atlantic (and also most of the older models, if they refuel at Gander and\or Shannon along the way; the only one for which this isn't the case is the 737-100, which would require an additional fuel stop in Keflavik, and which is, in any case, no longer in service anywhere), 90% of transatlantic passenger flights are by widebody jets, with 757s accounting for most of the remainder; only 1% of transatlantic commercial flights are by smaller narrowbodies like the 737 or A320.

Given that all A320s and all Next Generation\MAX 737s can fly nonstop between the U.S. east coast and western Europe, and that even the older 737s can fly between the U.S. and Europe if they make a stop or two along the way to refuel, why are the smaller narrowbodies so rare in transatlantic flight, when the prospect of using these smaller, cheaper, more flexible (operationally-speaking, that is, not physically more flexible) aircraft to fly passengers across the Atlantic would seem to be very attractive to airlines, especially low-cost airlines (for instance, Southwest or Ryanair)?

There are many factors that would increase the business cost for taking an operation across the Atlantic/borders:

ETOPS
Crew accommodation overseas
Acquiring airport slots in Europe
Aircraft cycles (two flights for one destination)
Cruise speed (being 10-12% slower is huge over long distances)
Geography, especially latitude.

I will focus on the sixth point, latitude. The comparison of types/distances and geography is a key point.

Looking at FlightAware for JFK to LAX from Sat 07:00AM EDT to Sun 10:43PM EDT, and copying the timetable into a spreadsheet, this is the types breakdown:

Clearly lots of narrow-bodies on that route. Let's do a distances check:

(gcmap.com)

So our best bet is the Gander option, which is 2,043 NM as the crow flies and is comparable to JFK-LAX. Doable, right? Here comes the latitude:

(wikimedia.org)

For most of the time, the polar vortex is strong and doesn't affect the contiguous US that much (watch jet stream forecast animation here). When it weakens, this is when the US weather makes international headlines, and the jet stream drops in latitude. So, for most of the year US transcontinental flights don't face fast headwinds, the story is different for the North Atlantic – compare below:

  When the polar vortex is weak, high pressure zones of the mid latitudes may push poleward, moving the polar vortex, jet stream, and polar front equatorward.

Back to the 2,043 NM distance. We'll add 10% to that for diversion and whatnot – a lenient ballpark figure. Now add 100 knots headwind, and the air distance has become 2,890 NM (at cruise speed of 447 KTAS for the A320).

From the A320 airport planning manual, the 2,000 NM permits almost the full payload of 20 tonnes (181 of 186 seats occupied). 3,000 NM on the other hand drops the utilization to 58%.

Our daring airline will now fly half-empty A320s, has to double the fare because of that, put the passengers through a technical stop, and take at least 80 minutes longer – because of the polar vortex. Add the other 5 factors, and it's a no-go for low-cost carriers.

One of the A321LR's (aka A321neoLR) key solutions is the additional fuel tanks and more efficient engines, giving an initial range of 4,000 NM. This range solves the payload problem, and this kind of specialization is a big deal at the moment, which may render this answer historic in the coming years.


Is there any combination of aircraft and airports where no alternate landing airport would be possible? In the comments on this answer an interesting assertion was made, that you never have a situation in the US where there is no possible alternate airport.  Assuming that:

you're flying an aircraft that is normally flown for commercial reasons,
you're flying to an airport that normally allows flights to land,
you're flying from an airport in the US to another airport in the US,
and you're following the regulation that you have to have enough fuel to get to your destination, then fly to your alternate, then stay in the air for another 45 minutes

is there any combination of aircraft and airports where no alternate landing airport would be possible?

For larger aircraft, likely no. Worst case they can carry enough fuel to return to their origin. If range does became an issue (e.g. Atlanta -> Anchorage) you would just schedule a technical stop somewhere like Yellowknife. Alaska has a ton of small airfields so short-range aircraft would have many alternatives. Wether the alternate has any services is another question.

As the question asks about US airports only, mainland -> Hawaii would be a possibility. Hawaiian Air's 717 planes already need extra tanks in the fuselage to get to the mainland, so a return flight would be weather-dependent. If you take off from Seattle and several airports close for bad weather after you pass the no-return point your options are rather limited. If the weather is bad enough to close every airport in the islands then channeling Sullenberger won't help much. Unlikely any sane pilot would take off with that kind of forecast, and Hawaii's weather is usually pretty good.


Is there any legitimate reason for adding momentary power when descending at idle with full carburettor heat on? Scenario: While demonstrating a simulated engine failure emergency landing a flight instructor puts on carburettor heat and reduces the throttle to idle of a small single engine Cessna. After a couple of minutes descending to the simulated emergency landing site, the CFI adds throttle "to clear the plugs" for a few seconds, then brings it back down to idle to complete the demonstration.

Is this is a legitimate thing that needs to be done for safety?

I've seen several pilots do this, and to me it always seems like cheating, because they are coming in a little short of their landing target.

How much plug fouling can occur in 2 or 3 minutes of idle with carburettor heat at low altitude?
How much good can 3 to 4 seconds of full power do?
Is there something else about this that I'm missing? (I couldn't find anything on this after a brief Google search).

straight out of the Airplane Flying Handbook, pp 9-4

  Operating the engine at idle speed for any prolonged period
  during the glide may result in excessive engine cooling, spark
  plug fouling, or carburetor ice. To assist in avoiding these
  issues, the throttle should be periodically advanced to normal
  cruise power and sustained for a few seconds.

This procedure is common during emergency descents or steep spirals to prevent the engine from cooling off too much.  If the engine mixture is excessively rich, spark plug fouling can occur.  Fouling can be cleaned off the plugs by running the engine at Cruise power settings with a properly leaned mixture in about 10 or so seconds.


Why do turbofan blade tips exceed the speed of sound while prop tips should not? It seems that the tips of the fan of a turbofan engine can and do break the sound barrier:

  The GE-90 has a fan diameter of 3124 mm and a rotational speed of 3475 RPM. Their circumferential velocity is d·π·57.917 = 568 m/s or Mach 1.67 at sea level and ISO atmosphere.Peter Kämpf's answer

While, on a propeller driven aircraft, it seems that having the prop tips exceed the speed of sound is a bad thing - Can turboprop blades break the sound barrier?

Why is it that exceeding the speed of sound is acceptable in one situation but not the other?

Short answer:

Turbofans need supersonic speed at the fan blade tips to create their high thrust.
Turbofans can tolerate supersonic speeds because the intake creates constant flow conditions irrespective of flight speed.
Efficiency for propellers and fan blades is highest at subsonic flow conditions.
Propellers can turn at supersonic speeds, but since flow conditions are less controlled, the penalty for doing so is much higher than the penalty for a fan.

Explanation

It is a bad thing to have supersonic fan blade tips, just like supersonic propeller tips are best avoided. But in turbofans it is a price worth paying, because the faster tip velocity means higher dynamic pressure, and the pressure difference between both sides of the fan blade grows with the square of their velocity. This makes the high thrust levels of modern turbofans possible.

Propeller efficiency over speed (picture source). The plot for fan blades would look not much different. The very thin, uncambered airfoil of a supersonic propeller and the added wave drag lower the maximum efficiency, but hold efficiency up into supersonic air speeds.

Note that the propeller on the XF-84H Thunderscreech did move at supersonic speed. There is nothing inherent in propellers which prevents their tips from moving faster than the speed of sound. On the other hand, the big diameter of a prop requires proportionally more torque to keep the prop rotating against the drag from the supersonic tips. Thus, a fan engine requires less torque per blade to reach supersonic tip speeds on the fan blades.

Also, the shroud of a turbofan engine helps a lot to make the noise from supersonic tips manageable. The XF-84H's noise made people literally sick. But there is more to it: @FreeMan encouraged me with his comment to dive a little deeper.

A supersonic propeller will work well when the direction of flow at every station along the propeller blade is about equal to the local airfoil chord. Since the blade is uncambered, this means that the change in local flow direction at the leading edge can be minimized to the amount which is required to create the desired thrust. But to be able to fulfill this condition you need to match your propeller speed to the flight speed and twist distribution. Also, the angle of attack must be compensated for by sviveling this propeller axis into the direction of flight. It will have no p-factor, but can run at only one speed for a given flight speed.

Contrast this with a turbofan: The intake makes sure that the flow speed and direction at the face of the fan is the same no matter what the flight speed is. This is done by the pressure field in and around the intake which will spill excess air overboard at high speed or suck extra air in from the sides at low speed. In the fan you can indeed match the local angle of incidence to the airspeed so the fan will work well over its design range.

Generally, a fully subsonic fan would be more efficient. But then the diameter would need to be as large as that of big turboprop engines, and the shroud would become impossibly heavy and produce too much drag. The high dynamic pressure on the fan blades is needed to produce the thrust with the relatively small diameter of a turbofan.


How do helicopters hover? I know that helicopters blades are like rotating wings that generate lift in the same way, but how does this make a helicopter hover?

Other question; how does the tail rotor help with the balance of the helicopter and why does it have to be on the left side of the vertical stabilizer instead of in the center?

To understand how a helicopter works (and in fact the mechanics of other aircraft too), it's helpful for you to be familiar with a key concept in physics, called Newton's Third Law of Motion. It says, in general terms, "for every action, there is an equal and opposite reaction".

Here's a simple thought experiment. Picture yourself wearing a pair of rollerskates, standing up, holding a basketball. Now, throw the basketball out in front of you using a two-hand pass (bring it to your chest and push it out in front of you). You'll find yourself moving backwards on the skates. You won't be moving as fast backwards as the ball will be moving forwards, because you have more mass than the ball, but you'll move, because the force of you pushing the ball out forward created an equal force moving you in the opposite direction.

A helicopter, and in fact most powered aircraft, work the same way. when a helicopter's rotor moves through the air, it pushes air downwards through a combination of its airfoil design, which moves air downwards as it passes over the top of the rotor, and an upward angle to the blade relative to the oncoming air that pushes the air with the underside of the rotor. By Newton's Third Law, the force pushing the air downward creates an equal and opposing force pulling the rotor, and the helicopter attached to it, up into the air.

To hover, all that's required is for this force pulling the helicopter up (you can consider it as either "lift" or "thrust") to equal the force of gravity on the helicopter, which is its weight. If these forces balance, the helicopter will remain the same distance off the ground. If lift is greater then weight, it will rise into the air, while if weight it greater, it will sink or fall.

Now, normal aircraft have to move forward through the air in order for their wing to get the airflow needed to generate lift. A helicopter, by rotating its wing, can produce the airflow over the lift surface without the entire helicopter having to move forward (or backward or sideways for that matter). So, it can rise straight up into the air and truly hover over a single spot on the ground.

The tail rotor of a helicopter is necessary to counter another force produced by the helicopter; torque. Torque is similar to force - really it is a force - but it's being produced in a circular direction instead of a straight line. The helicopter's engine uses torque to spin its rotor. Again, by Newton's Third Law, if the rotor of the helicopter is being spun clockwise by the engine, the helicopter itself will begin to spin counter-clockwise.

To counteract this torque, most helicopters have a second, smaller rotor which works the same way as the big one, but directs the force of its thrust sideways in the opposite direction to the way the helicopter's body wants to spin.

This sideways rotor doesn't necessarily have to be on the tail, but it works best if it's on the end of a long lever arm, such as the tail boom of the helicopter. The closer it is to the main rotor's shaft, the more thrust it has to produce in order to counteract the torque of the main rotor.

It doesn't have to be on the side of the tail either; many modern helicopter designs have the tail rotor spinning inside an aerodynamic duct in the middle of the tail:

Helicopters also don't necessarily have to have a tail rotor at all; all that's required is equal, opposing torque to that of the main rotor. A common substitute for a tail rotor is a second, counter-rotating main rotor:


What is the relation between the boundary layer and lift of an aerofoil? Why do we try to reduce the thickness of the boundary layer over an aerofoil as much as possible if the boundary layer is responsible for creating lift?

I wouldn't say that the boundary layer is responsible for creating lift, even if the real world friction enables the creation of circulation and therefore lift. It is mainly responsible for the drag.

Why? Take a look at airfoils in potential flow: they have lift but neither drag nor a boundary layer. Lift is created due to a pressure difference between the upper and lower side of an airfoil and you don't need any boundary layer to explain this pressure difference.

However, you do need a boundary layer to explain drag. The no-slip condition on the airfoil surface creates a layer with a high velocity gradient (from zero on the surface to $V_\infty$- the freestream velocity). Its thickness depends mainly on the viscosity the fluid around the airfoil:

No viscosity at all means no energy loss and therefore no drag.The velocity gradient can be infinite and the layer thickness is zero.
With higher viscosity the particles won't be able to follow such high velocity gradients and the distance between the no-slip surface to the freestream flow around the airfoil will be bigger: the boundary layer will be thicker. The drag will be higher too.


Do we need to know the true track to a VOR? An aircraft can lock onto the location of a VOR and we can see the QDM (magnetic bearing to the station) to the VOR. If this is the case, do we still need to know the true track of that route? And if so, why?

By extension, if we essentially have all we need to get to the VOR in the aircraft, why do we need to know about QTE (true bearing from the station)?

NB: I have no experience in flying a navigation flight

The short answer is no, you don't need the true bearing to the station if you have magnetic bearing.  Presuming of course that your airplane has a magnetic compass to fly that bearing, there is simply no reason to convert to true.


What is the maximum angle F-16 can turn in x seconds flying at corner speed? How can one calculate the maximum turning angle F-16 can turn in x second flying at corner speed. Is it changed with height or weight?

To calculate this, you need to look at the energy Maneuver diagram for the aircraft. This diagram depicts, for a specified altitude and gross weight, the excess power per unit pound of weight the aircraft would have at full afterburner at any g-Loading and true airspeed. There would be a different chart for each aircraft configuration, gross weight and Density Altitude combination.

Instantaneous Turn rate is depicted on the vertical scale, true airspeed or mach number is depicted on the horizontal scale. The concave curved lines that go from upper left to far right represent flight conditions of constant G-loading, while the straight lines that radiate from the origin represent constant turn radius. The peak of the flight envelope, (at about Mach 0.7, 20 deg/sec turn rate and 8 Gs, is corner velocity. The lines that start at the left boundary or at the bottom, go upwards, curve to the right and then back down again, and are labeled with values 600, 400, 300, 0, -200, etc. are called Ps, (pronounced P-sub-S), lines. They depict the specific power, or actually, specific excess power - a measure of how much power per pound of aircraft weight the aircraft would have left over to climb or accelerate at the depicted point on the diagram.
So at the top of the diagram, at the corner velocity, where the turn rate is near 20 deg/sec, the specific excess power is less than -800. The -800+ Ps curve indicates that the aircraft, if it established flight at those conditions, would be bleeding energy (airspeed or altitude) at a rate in excess of negative 800 ft/sec.

The best performance on the diagram that can be sustained, on the other hand, is the highest point on the zero Ps line, which is at mach 0.8, 7 Gs, and it would produce a sustained turn rate of just over 14 deg/sec.

So, in a level turn, at Mach 0.8, 7 Gs, and 14 deg/sec, the F-16 could turn 180 degrees in about 13 secs.

Of course, if the aircraft performs the turn in a descent, it can make the turn in less time. This is indeed a common training maneuver, to turn 180 degrees in the shortest amount of time possible. It is performed by rolling into 135 degrees of bank at or slightly above corner velocity and pulling at maximum G-load. The maneuver is performed at maximum available G-load, in a constant plane tilted at 45 degrees from the horizontal. Bank angle (starting at 135 degrees), decreases throughout the maneuver, reaching 90 degrees bank after 90 degrees of turn, and 45 degrees bank at the end of the maneuver (after 180 degrees of turn). At 15,000 feet MSL, this will generate almost 20 degrees per second, and can be done in about 10 seconds.


What is this flyer in a 1911 short film? In the very first instants of the 1911 comedy short film Robinet aviatore (or Tweedledum Aviator) by Michel Fabre, which can be watched here, on the background some kind of flyer can be seen.

Does someone have a clear idea of what kind of flyer is that? A Wright one?

Given that the short film was produced in Turin (according to the Italian Wikipedia), it is likely that that the Aeroclub of Turin (1908) has more information on this aircraft.

On their website they describe the history of aviation in Turin in the 1909-1915 period(in Italian). Around that time, Turin was a center of aviation in Italy (and it still is).

There were several aircraft manufacturers, including the automobile factory FIAT (Fabbrica Italiana Automobili Torino) which at some point produced Farman aircraft under license.

One of their first employees (employee no.3) was Alessandro Cagno. He was, among other roles, the company's racing team driver. In 1909 he lost interest in car racing and turned to aviation. He became the 10th pilot in Italy, on a Farman aircraft. There are several pictures of him in his Farman III on the internet, which looks very much like the aircraft in the short film.

Below is a picture from 1911 of Cagno in his Farman III in Venice.

By Unknown - over 100 years old. Source: wikipedia

Especially this picture looks very similar to what can be seen in the film, including hills in the background.

More video material of the Farman III can be found here:

You can see that there were several variations on the model.

It may be Cagno's aircraft in the film, or another Farman. Looking at the list of early aviators in Italy, the majority of them got their license in either a Farman or a Bleriot. The latter aircraft looks very different.

Source: Contact! The Story of the Early Aviators, Henry Serrano Villard ISBN: 0-486-42327-1


How is the area of flaps determined? While may be possible to look up the dimensions of high lift devices in an aicraft's documentation, there is no information on what the underlying design choices are.

Using Wikipedia, I found out that flaps are used to increase the wing camber, to increase the wing's lift coefficient and decrease stall speed. However, there is no information on how much extra camber is desirable, and how the surface area of the flaps relate to the camber increase.

So, how exactly are the dimensions for flaps on an aircraft chosen? While I'm specifically wondering about large airliners, such as an Airbus A380, I would also like to know if the method for determining the flap size is generally the same for all aircraft, or if there are differences depending on size or mission profile.

The area, or as originally written, length and width*, are but two of many parameters that define the flaps and slats.

The final parameters are a result of an iterative process, as shown above. You try a set of parameters, if they don't work, you go back one step, or even two steps (redesigning the wing).

For example when the A320 was stretched to become the A321, the extra weight meant a change to the flaps was needed. If that had failed, they would have changed the wing or part of it (like they did with the A350-1000).

The basic initial design goal is to work out the parameters that achieve the condition below. The parameters on the right-hand side are a given at this point in the design.

$C_L$ is the lift coefficient. $f$ and $s$ denote flaps and slats. The different parameters, including the deflection angle and type of high-lift device used, define the $\Delta C_L$. $\Delta$ (delta) is the increase from the clean wing state brought about by the slats/flaps.

If the design choices don't work, you try something else. In the A321 the double-slotted flaps worked. In the A350-1000 they had to redesign the wing.

Below you see with the lack of inboard ailerons (decided in step 7), the span of the flaps is defined. If the ailerons are too narrow, you risk aileron reversal. If there were inboard high-speed ailerons, that flap area would then be divided further. Generally the slats cover more span than the flaps.

  The spanwise reach of slats and flaps has to be established, as must the flap type and the angle of deflection of slats and flaps. As already mentioned, it will not generally be possible to set the parameters without an iterative approach.

* The terms chord and span are better and less confusing.

Source: Hamburg Open Online University (.pdf).

For a paper on the Airbus A380 wing and flaps design, see: Aerodynamic Design of Airbus High-Lift Wings in a Multidisciplinary Environment.


Can some IAFs be skipped if more than one IAF exists? Take, for example, this FAA official IAP plate (ILS RWY 13L CAT II JFK). Its Initial Segment consists of more than one Initial Approach Fix (IAF): COVIR, KMCHI, and BUZON. As far as I can interpret this, when an aircraft enters from the en route structure, it is obliged to follow the route COVIR → KMCHI → BUZON → TELEX etc.

My question is, is the aircraft supposed to follow this particular route or, depending from where it comes, it can "skip" e.g. the first Initial Approach Fix, and follow the route KMCHI → BUZON → TELEX (instead of COVIR → KMCHI → BUZON → TELEX)?

Also, if the answer is yes, does that mean that it can even ignore all the IAFs and enter Intermediate Segment directly, provided that this serves its purpose better?

Any initial approach fix (IAF) is a valid point at which an aircraft can start the procedure. Many procedures also have IAFs on multiple paths to choose from to get to the final approach. Standard Terminal Arrivals (STARs) sometimes include a certain IAF so that pilots can go straight from the arrival to the approach. Aircraft not on one of these STARs could use any other IAF.

Aircraft can also start even later in the procedure at an intermediate fix (IF), such as TELEX in the above example, provided it is coordinated with ATC and certain conditions are met.

After entering a procedure, aircraft are expected to fly the procedure as published. While it's not as common as with a SID or a STAR, ATC could certainly give an aircraft instructions for a shortcut on an approach, for traffic or other reasons. ATC would need to authorize this to ensure clearance from traffic and obstacles and compliance with restrictions such as noise abatement.


What is a typical altitude for a dogfight? At what altitude(s) do dogfights typically occur? How has this changed from World War I up to now?

At what altitude(s) do dogfights typically occur?

All of them.

Throughout history dogfights have generally started at one of the aircraft's "best altitude", which depends on the aircraft, and then descended as the pilot's trade altitude for airspeed.

Altitude disparity can be so great that one or the other will simply not engage, or do so at a serious penalty if they are forced to. This occurred during the Falklands when the Argentinian aircraft had much more performance than the UK's Harriers, but only at higher altitudes. The Harriers simply refused to fight them, so if the Argentines wanted to get to the ships they had to fly down where the Harriers had the advantage. The same occurred during WWII when US B-17's flew at altitudes where German fighters were struggling, allowing the escorting P-51's to chew them up.

It is not uncommon for extended dogfights to end with troops on the ground shooting down some of the aircraft, as was the case with the Red Baron (or so the Australians will claim).


How should I deal with a passenger experiencing hypoxia over the Grand Canyon? I am taking my mom for a trip over the grand canyon. My mom lives at sea level, whereas I live at 5000ft, and workout at 8000ft daily.

The VFR lowest route over the Grand Canyon is 11,500ft MSL. If I am flying over this with my mother and she starts to exhibit signs of hypoxia, what are my options?

It is the law to remain at the prescribed altitudes and headings while flying around the Grand Canyon. That being said, obviously passenger safety comes before anything else. If my mom gets sick, I would have to drop in altitude, but what kind of consequences would I face for this?

In the event of hypoxia in one of these corridors, what would be the best way to deviate while remaining safe and courteous?

First, let's be crystal clear on something: A person experiencing symptoms of acute hypoxia is an emergency which requires immediate action to ensure the safety of that person. In an in-flight emergency requiring immediate action, the pilot in command may deviate from any rule …  to the extent required to meet that emergency. (FAR 91.3 (b)).

So if you're over the Grand Canyon at 11,500 feet and your mother starts showing signs of hypoxia you key the mic and let ATC know you have a passenger showing signs of hypoxia, tell them you are descending to a lower altitude, and ask for vectors to an airport where you can land. If they give you any trouble about it you respond with "N12345 is declaring a medical emergency".

All that said, there are sensible things you can do to mitigate the risk of hypoxia and avoid the need to declare an emergency.
If you intend to spend an extended period of time at altitude (which I personally define as "Over 10,000 feet" for an average healthy non-smoker):

Bring a portable oxygen system
Ideally with enough cannulas/outlets for yourself and your mother/other passengers).
If a full oxygen system isn't an option bring one or more "boost cans"
These can provide temporary/limited relief for symptoms of hypoxia – probably enough to get yourself back on the ground, or at least to a lower altitude.
Carry a relatively inexpensive pulse oximeter
Check your SpO2 periodically to catch hypoxia early - before clinical symptoms develop.


What's the difference between the Multi Engine Instrument Rating and Instrument Rating in Canada? Are the requirements for the Multi Engine Instrument Rating the same as Instrument Rating in Canada or is there a separate exam for each of them?

Thanks!

Your IFR is either Group 1, 2 or 3.

All aircraft, including single, multi, multi centerline thrust (like a Skymaster).
Multi centerline thrust and singles.
Singles only.

For group 1 you have to do the ride in a conventional twin, which means you need a multi-engine rating first.  There is no written exam for the multi. It's just the training course and recommendation from the instructor for the check ride.

You can do a Group 3 IFR in a 172, but for the Group 1 you will still have to do a new check ride in a twin, so there is not much point in doing a Group 3 unless it's just to fly your own airplane IFR.

Just about everybody incorporates their multi engine training into the IFR training, does the Multi checkride at some interim point, then the IFR checkride in the same twin later on.

The main difference between the IFR checkride done in a single, vs one done in a twin, is the examiner gives you an engine failure drill to do on a missed approach when you do it in a twin. Otherwise they are about the same.


What is the difference between rate of climb and climb gradient? I am currently trying to study aircraft performance and I have some difficulties distinguishing between rate of climb and climb gradient.

Can someone explain what are the differences between the two of them?

The climb gradient is the percentage of the rise over run (100% if you are climbing at 45 degrees) that your aircraft is climbing at while the rate of climb is the speed at which you are climbing based off the airspeed and climb gradient (given in feet per minute).


Can a pilot initiate an enroute descent to an IAF without ATC 's approval? An IFR flight is cleared DIRECT to a published IAF for an approach at the destination airport. The cruising altitude is 10,000’, the IAF crossing altitude is 2,000’ and the T/D begins about 24nm prior to the IAF with standard rate of descent.

Since route has been previously cleared to that IAF waypoint, can the pilot commence his descent upon reaching the T/D, or wait to hear from controller or request descent instructions just prior to the T/D?

You are never allowed to simply vacate an assigned IFR altitude without clearance.  When you were cleared to the IAF your clearance should have included "pilot's discretion down to ..." of "cross IAF at or above..." or similar words.  If you don't get this, just ask.  Never presume that you can just start down on your own though.


Why do the British not produce anymore aircraft? Minus Airbus which is a group of companies, why does the United Kingdom not produce aircraft anymore ie, the VC10.

The root of the reason is the fact that aircraft design has become very expensive and the world economy cannot support more than a few companies anymore.

Look at other industrialized countries: They all used to have scores of aircraft companies, which all merged or went down over time. Russia might seem an exception, but the Russian design bureaus are not very productive anymore and kept alive artificially. By now, a national economy the size of Great Britain is too small to support even a single commercial jet builder.

In Augustine's Laws, Norman Augustine shows how aircraft prices have historically accelerated at a faster rate than the economy, and driving this to it's ultimate conclusion, he predicts for the US military:

  In the year 2054, the entire defense budget will purchase just one
  tactical aircraft. This aircraft will have to be shared by the Air
  Force and Navy 3½ days each per week except for leap year, when it
  will be made available to the Marines for the extra day."

There is no conspiracy about it, economics is enough for a convincing explanation. If there is a culprit for the early death of many British aircraft makers, it would be the British Government bureaucracy itself, with a helping hand given by BOAC management. Britain effectively nationalized her aircraft industry at the onset of WW II, and left it to Government bureaucrats to decide which aircraft to build next. This produced aircraft like the Saunders-Roe Princess or the Bristol Brabazon which incorporated many innovations, but were conceptually completely behind their times. When they once tried to be visionary, they steered all efforts into supersonic airliners, which also proved to become a dead end.

When British designers tried to design jet airliners, BOAC management saw no market for a jet airliner but bought the Boeing 707 less than a year later. If you desire to see a conspiracy behind the early death of many British airliner projects, maybe start looking here. The EU certainly has nothing to do with it.


How are Mode 2 pulses encoded? I'm working on a research project looking at Mode 3A/C replies and have noticed some pulse patterns that look very similar which I suspect are Mode 2 replies.  They appear to differ by just one pulse.

I'd like to extend my decoder to decode these as well but I'm struggling to find out how Mode 2 pulses are encoded.  I know that mode 3A/C is encoded using the Gilham code but that excludes the extra pulse that I am seeing.

Is there a publically available document which explains how Mode 2 pulses are encoded ?  I've search high and low and haven't found one yet.

I think the problem is that you see a Mode 3/A (identity) reply, but you try to interpret it as Mode C (altitude reply).

In Mode C, altitude is Gillham encoded, using all pulses except for D1 and X. This gives a range of -1200 to 126700 ft in 100 ft increments.
If you see a D1 pulse, you are not looking at a Mode C reply.

In Mode A, a 12 bit identity (squawk code) is transmitted, using all pulses except for X. In Mode A, the D1 pulse is commonly used (in fact, evey squawk code where the last digit is odd uses the D1 pulse).  It is simply the octal conversion of bits / pulses [A4 A2 A1], [B4 B2 B1], [C4 C2 C1], [D4, D2 D1].

For example, if you would encode squawk code 2345 you would set pulses [A2 = 2], [B1 & B2 = 3], [C4 = 4] and [D4 & D1 = 5].

Note that in case of Mode A, there may be an addition pulse for radar IDENTificaton. This is the Special Purpose Identification (SPI) pulse and it occurs 4.35 microseconds after the start of the closing framing pulse, with a duration of 0.45 microseconds.

source: www.radartutorials.eu


What was the commercial speed of Concorde? I work on time-space cartography in a historical perspective and need to establish a commercial speed of Concorde aircraft flights based on timetable data. This issue differs from the issue of the maximum speed of planes, because in a time geography perspective I want to consider speed from the point of view of the user, the traveller, i.e timetable commercial speed, and not maximum aircraft speed.

I found some indicative timetables of London-New York in 3,5 hours for 5 850 km which turns into an approximate value of 1 600 km/h. Could anyone confirm these data and this figure?

A related problem is that time-tables are not symmetric, because of trade winds, so that transatlantic routes take longer from Europe to USA that the contrary. I want to use the longest value since it provides a consistent value for minimum time-distance.

The Concorde cruised at 1350mph (~Mach 2.05 at 55,000Ft.)

Concorde’s fastest transatlantic crossing was on 7 February 1996 when it completed the New York to London flight in 2 hours 52 minutes and 59 seconds.

When it flew the average flight time (was) around 3 hours 30 minutes, but can be slightly longer if the aircraft (needed) to hold before landing at the local airports.

Wind is a huge factor in flying. A headwind or tail wind can mean a big difference in flight time. The Concorde cruised at a significantly higher altitude than most airplanes ~55,000Ft. which means it was subject to very different wind than its sub sonic lower flying counterparts. At that altitude winds in excess of 100Kt are common place. So you could see a 200Kt difference in speed depending on direction.

Also of note the speed was often called out using Mach's Number (the Concorde flew a bit over Mach 2). However since Mach's number accounts for air density,  Mach 1 at 55,000Ft. is 660MPH which is significantly lower than the often quoted Mach 1 = 760MPH (which is the speed of sound at sea level).

One of the best sources of info on flying the Concorde is this podcast interviewing one of the pilots.


What is the purpose of these odd "control surfaces" on the BAE Taranis? I was looking at a video of the BAE Taranis, and noticed these weird control surfaces:

There is a matching pair on the underside. They don't seem to move at all throughout the video, even on landing, and yet they seem to be slightly extended.

What are they?

They look like spoilers but are more precisely called drag rudders. They are not meant to reduce lift like regular spoilers, but increase drag in order to create a yawing moment.

Regular aircraft have a vertical tail for yaw control. Without this, you need some force acting at a lateral distance from the center of gravity for yaw control, and this is what these speed brakes do. They are opened only on one side, and keeping both slightly open increases control power because then one can be closed while the other can be opened further.

The Northrop B-2 uses split ailerons to the same effect, and the Horten IX had a two-stage wooden speedbrake which could be extended near the wingtips. By raising only the smaller brake with small rudder pedal movements, yaw control could be tailored to flight speed. At high speed only small input was needed, and at low speed both brakes could be fully opened for maximum yaw control.

Horten IX V2 3-side view (picture source). Note the two extended speed brakes near the wingtip in the front view. The real speed brakes were on the lower side of the center wing and right behind the rear landing gear bay (in the drawing called spoilers).

Thanks to @RedGrittyBrick for the hint: Yes, the X-47A and X-47B also seem to have drag rudders. I guess their large chordwise dimension helps to limit the lift loss when they are extended.

Northrop-Grumman X-47B in flight (picture source)


How are the services kept running on a plane without an APU? I have seen several aircraft that do not have an operative APU, so how are lights, air, and other systems kept running?

The aircraft is connected to a ground-based supply.

The ground-based air conditioning is connected using a large yellow pipe, and electricity is connected using a set of cables. In the photo below you can see both connections.

image source

In the cockpit, the pilot can select the power source for the aircraft. The proper procedure is to start the APU before disconnecting the ground power supply, otherwise the whole cabin will go dark once ground power is switched off! If you are a passenger boarding, you may have noticed that the cabin lights flicker for a very brief moment. This is when the power source is switched from ground power to APU, as part of the start up procedure.

If the APU is inoperative, things get a little complicated. Typical electricity source include ground-based supply, APU, engines and battery. The battery is only a backup for very essential flight instruments; it is not even capable to
power everything in the cockpit, let alone the cabin. The ground-based supply unit must be disconnected before the aircraft starts moving. So that leaves the engine(s) as our only power source.

However, getting a turbine engine started without an APU is a tricky matter in its own: it requires another ground-based unit to blow air into the engine. The only remaining option is to keep at least one engine running during the turnaround, since the running engine can be used to power up all other engines, at the expense of fuel.


What is the capacity of the vent surge tank in an A320? If the wing tanks of an A320 are fully filled and the fuel expands due to high temperatures then the fuel overflows into the vent tank. My question is, does the fuel get stored in the vent tank? If yes, how much? If not, does all of the fuel just spill on the ramp?

From Airbus flight crew operating manual (FCOM):

The expansion tanks above the center tank allow the center tank to be filled to the maximum. Tanks capacity is 23,858 liters.

The FCOM says the fuel can expand up to 2 % without spillage in the vent/surge tanks. That's about 239 liters per surge tank.

The volumetric expansion of the fuel is about 0.095% per °C. 2% allows for a 21°C temperature increase.

The vent/surge tank communicates with the outer tank on the same side, and fuel can flow back by gravity, when conditions permit.


How do the European ATC strikes affect us as pilots? So every once in awhile I see an article talking about the air traffic control strikes in Europe like this one:  European air traffic controllers to strike.

How does this affect me if I am flying to Europe?  Do they just close the doors and all airspace becomes uncontrolled airspace?  I'm guessing not, but that's what I envision when I hear that!  What happens if they go on strike while I'm over the ocean on my way there?

Since these strikes are announced in advance, you will not be caught by surprise half way accross the ocean. If you try to file a flightplan through the soon to be closed airspace, the CFMU will not accept your plan. There will be no IFR traffic in the airspace before they close down the service.

I don't know about VFR.


Why don't bypass ducts in jet engines narrow down the flow to accelerate it? Since decreasing the flow area increases flow velocity, why don't turbofan bypass ducts narrow down to produce more thrust?

if you decrease the duct cross-section, you must apply work to accelerate the flow through the smaller duct. this means the fan driving the duct has to work harder (it must absorb more shaft horsepower) against that constriction in the flow and you derive no benefit- unless you mount the fan on a more powerful engine, in which case you are burning more fuel to drive the fan-and-duct system. So, there is no free lunch available here.


Is it legal to do a barrel roll? Is it legal to barrel roll a plane?
Are you allowed with any pilot license?
Are there any requirements for the plane to be allowed to barrel roll?

This answer is for the US. A parachute is required of everyone when the aircraft is carrying someone who is not a crew member.  The maneuver must not be prohibited by the aircraft flight manual. (Or must it be specifically permitted?)   (Future edit needed.)  And of course you must not exceed the permitted airspeed and G-load parameters.

There is no relation to the license (certificate) the pilot holds.

Actually, this related answer indicates that the airplane or glider must be in the "acrobatic" category: What are the US definition and restrictions on aerobatic flight?. But it's not clear what specific FAR is involved, if any.


Can spatial disorientation in low visibility situations lead a pilot to fly upside down? In this comment it's mentioned that pilots in instrument conditions may wind up in a situation where they're inverted due to spatial disorientation, and be completely unaware of it until they fly out of the cloud.

Is that really something that can happen so easily?

The short answer is "Yes", if the pilot is not properly trained, doesn't trust their instruments, or has an instrumentation failure.

Without a visual reference (such as the real horizon or artificial horizon) it's very easy for a pilot to place their aircraft in an "unusual attitude" -- something other than the expected straight-and-level flight or commanded turn.
As humans we naturally rely on our inner ear and sense of balance to tell us what's "up" or "down", but in a moving aircraft you can move through a whole range of attitudes in "1G maneuvers" (where your body thinks down is where your seat is).
Little micro-movements we unconsciously make on the controls (or larger movements we may make consciously in response to turbulence or other perceved disturbances in the aircraft's attitude) based on what our ears and butts are telling us will eventually get us into trouble.

It's so easy that often instructors will have students create their own unusual attitudes in training by having the student close their eyes and simply try to fly straight and level - within a few minutes at most the student will invariably no longer be in level flight.

There's an exercise you can do on the ground to illustrate how imperfect your sense of balance and direction is, but it requires a large, flat, open area. We'll use an American Football field for this example:

Stand on one of the goal lines
Have a friend stand at the 50 yard line (about 45 meters away)
Close your eyes or put on a blindfold, count to ten, and walk directly toward your friend
Stop when you reach your friend (or your friend yells "STOP" because you're about to walk into a goal post)

Most people will not make it to their friend on the 50 yard line, because without a visual reference it's very hard to walk a straight line: You will veer off one way or the other, and some folks will even manage to walk in a complete circle (which is what eventually tends to happen over a large enough distance).
The same principles apply to flight, except there's a third dimension (vertical) to contend with.


When will the Canadian ADS-B satellite system be implemented? It is interesting that ADS-B is not mandated in Canada as of yet. If you fly in the US you quickly realize the benefits. Now as I understand it Nav Canada is the largest shareholder in Iridum but ADS-B in the SDA (Southern Domestic Airspace) is still far off.

Some people may hate the idea of a mandate but I fly in the south and it is crucial to be able to see other traffic. XM is great for WX but expensive. I am curious as to why Nav-can is not hot on the ADS-B trail other than the politics of mandated dollars for Mode-S transponders.

Does anyone know the timing for implementation of the ADS-B satellite system for Canada?

This Advisory Circular, although from 2011, is still current and indicates that there will no Transport Canada ADSB mandate (being regulatory, it's not up to Nav Canada).  It appears the policy is to foster voluntary adoption of ADSB over time, and Nav Canada will create an environment where aircraft operators will get operational benefits by adopting it.

So the commercial world will likely switch over fairly quickly, while GA operators and private owners will do it gradually as the costs of the systems come down, and anyone who doesn't want to doesn't have to, and can continue using Mode C. I imagine that later on, when the system is mature, say in 5+ years from now, and GA ADSB systems are dirt cheap, TC/Nav Can will likely decide it's time to phase out surveillance radar completely, and then it'll be mandated for anyone that wants to operate in transponder airspace.


Why does a pilot bank up to 5 degrees into the operating engine following failure of the other engine? If a multi-engine aircraft suffers an engine failure while near minimum control speed (Vmc), one of the solutions is to bank up to 5 degrees into the operating engine to increase rudder effectiveness to maintain control. Why is it up to 5 degrees? What happens if the pilot banks more than 5 degrees into the operating engine?

The 5 degrees of bank is to create a side slip component that offsets the skewed thrust line created by the asymmetric thrust, and the rudder input made to counteract the asymmetric thrust.

You have the live engine on one wing that wants to make the airplane turn.  You apply opposite rudder to stop the turn.  With the rudder moment pushing sideways, you end up with a resultant thrust line that is offset, and the airplane proceeds forward with a lateral skew toward the dead engine even though you think you're going straight.
By banking into the live engine, bank angle makes the airplane want to side slip toward the down wing, which is in the opposite direction to the skew effect mentioned above.  The 5 degrees of bank is roughly what gives the necessary amount of side slip tendency.  Close enough in other words.

The result is that you will be flying with 5 degrees of bank, but actually proceeding straight through the air.  The skid ball will be offset into the bank because you are actually still in coordinated flight and the offset location of the ball is the true "centered" location.


What are the meanings of those SFO Taxiway Marking? I'm studying aviation and pulled up a Google Map satellite view of San Francisco International Airport (KSFO) and was wondering if someone could shed some light on what a few of the taxiway markings meant.

What do the straight lines starting from the taxiway edge marking towards the "median" area mean? Probably that it's not usable for aircraft taxiing - but I couldn't find out what the name of these lines were.
What is the number inside the small pink / purple used for?
What are the white numbers inside the blue boxes used for?

For 1, what is slightly harder to see is that the line which runs parallel with the taxiway is a double line. This denotes the taxiway edge and the thicker lines running perpendicular to the double lines shows which side of the taxiway edge isnt suitable taxiway. They are often coloured differently too, and in SFO case the unusable part of the ramp is green.

The pink circles with black text are geographic position markings, and are used by the airports Surface Movement Guidance Control System (SMGCS) in low visibility.

The white numbers in blue squares are not are not mentioned in the FAA Standards for Airport Markings but I suspect thy might have something to do with the skybridges.


What kind of waypoints/routes are used to prepare a flight plan in practice? I have noticed that FAA provides data delivery service where both waypoints and ATS routes are available to download. By looking at the files, I realize that there are a variety of waypoints and routes. I really want to pick the particular type of waypoint, which are used for pilots to prepare a flight plan in reality. Could you please let me know which types of waypoints/routes are used in practice?
For reference, I am attaching the screenshot from which the types are categorized.

Types of Waypoint:

Types of ATS Routes:

In real life the flight planning process starts with where you are, where you are going, and then you make decisions on routing based on considerations such as weather, terrain, alternate airfields, airspace, VFR vs IFR, etc.  Looking at the chart you will then choose appropriate waypoints along that route of flight based on the aircraft navigation equipment.  You don't generally start planning by making a blanket decision on what category of waypoint you would like to use.


What would be the likely repercussions of flying into the Air Force One temporary flight restriction area? I just saw this video on YouTube where a guy flies his plane into Air Force One's temporary flight restriction.

It's very clear that ATC are not amused and that he's caused a good deal of trouble. What would likely happen:

To his license? (lose it?)
Would he be fined?
Would he be arrested?

The answer to each of the points in your question is "Maybe".
A pilot wandering into a presidential TFR (and many other "VIP Movement" TFRs) potentially faces some pretty severe consequences. Quoting the standard language from one such TFR NOTAM:

  THE FEDERAL AVIATION ADMINISTRATION (FAA) CLASSIFIES THE AIRSPACE DEFINED IN THIS NOTAM AS 'NATIONAL DEFENSE AIRSPACE'. PILOTS WHO DO NOT ADHERE TO THE FOLLOWING PROCEDURES MAY BE INTERCEPTED, DETAINED AND INTERVIEWED BY LAW ENFORCEMENT / SECURITY PERSONNEL.
   ANY OF THE FOLLOWING ADDITIONAL ACTIONS MAY ALSO BE TAKEN AGAINST A PILOT WHO DOES NOT COMPLY WITH THE REQUIREMENTS OR ANY SPECIAL INSTRUCTIONS OR PROCEDURES ANNOUNCED IN THIS NOTAM:

  A) THE FAA MAY TAKE ADMINISTRATIVE ACTION, INCLUDING IMPOSING CIVIL PENALTIES AND THE SUSPENSION OR REVOCATION OF AIRMEN CERTIFICATES; OR

  B) THE UNITED STATES GOVERNMENT MAY PURSUE CRIMINAL CHARGES, INCLUDING CHARGES UNDER TITLE 49 OF THE UNITED STATES CODE, SECTION 46307; OR

  C) THE UNITED STATES GOVERNMENT MAY USE DEADLY FORCE AGAINST THE AIRBORNE AIRCRAFT, IF IT IS DETERMINED THAT THE AIRCRAFT POSES AN IMMINENT SECURITY THREAT.

That's a lot of MAYs, so what does it mean in practice?

The pilot will be detained and interviewed by law enforcement
May is a nice word, but in practice if a pilot flies into one of these TFRs they will be held and questioned once they're on the ground to find out why it happened. It's kind of a big deal.
The pilot will face some kind of Administrative Action from the FAA
Suspension or revocation of their certificate is certainly possible (especially if it's not the first time).
A stern talking-to from someone at the FSDO and/or a reexamination ("709 ride") is almost certain.
The pilot may face Civil Penalties (a nice way of saying "fines")
$10,000 used to be the magic number for these fines as defined in 49USC, the law now refers back to 18USC (which I'm not going to read through because reading the US Code makes my head hurt), but I assume it hasn't gone down. The point is it could be an expensive error.
The pilot may face Criminal Charges (arrest and imprisonment)
I can't recall a case of a pilot accidentally violating a TFR and being locked up for it, but I imagine willfully violating a TFR could land you in prison pretty easily.
Use of deadly force may occur (the pilot may be shot down)
Again, I can't recall a case where a pilot has violated a TFR and been blown out of the sky by a missile from an F-16 (though there are plenty of cases where aircraft have been intercepted and diverted), but it is an option available if the aircraft poses an "imminent security threat", however that determination is made.


Ailerons deflection of the F16 in take off and landing gain? Let's say you are at a safe altitude and landing gear is down and the aircraft is in To/L gains and you want to do aileron roll and apply full  left (or right ) stick to do the rolling maneuver.The F16 doesn't have any ailerons only flaps moving up and down  .But because is in the  take off /landing gain's with the flaps deployed at maximum angle only one moves other stand still at 20 degrees down .Will the raised flaperon go above the wing cord or not , meaning will  rise up above the cord line of that wing or not passing the wing line ?

As per flight control diagram from General Electric 1975:
The aileron control can command +/-21.5 degs.
The flap control can command +21.5 degs down (even though the HUD will say 20 but there is in this control a +1.5 electrical bias which will be neutralized by the mechanical bias). This is added to the aileron control output.
Then one should subtract the 1.5 degs mechanical flaperon bias.
The flaperons can move +20 to -23. (remember negative is up)
So one flaperon will be at +20 down while the other will be at -1.5 up above the cord given that the aileron produces max aileron roll.
So the question is will the aileron control command max deflection if you are airborne? Most likely no when the aircraft starts rolling, as when the gear is commanded down, internally in the roll system the command will be decreased due to roll rate, and the command is only about half with gears down.
But when you are weight on wheels and the roll rate is zero, you will get one of them 1.5 degs above the cord line, when you command max roll.
Source document: Diagram in AD-A055-417.


How Does the FAA Define the Dimensions of the Touchdown Zone? Does the FAA give a regulatory definition of the term "Touchdown Zone" for use within the context of landing operations?

In 14 CFR 91.175 the FAA requires—in certain cases—that pilots must be in a position to land within the "Touchdown Zone":

(c) Operation below DA/DH or MDA. Except as provided in §91.176 of this chapter, where a DA/DH or MDA is applicable, no pilot may operate an aircraft, except a military aircraft of the United States, below the authorized MDA or continue an approach below the authorized DA/DH unless—
(1) The aircraft is continuously in a position from which a descent to a landing on the intended runway can be made at a normal rate of descent using normal maneuvers, and for operations conducted under part 121 or part 135 unless that descent rate will allow touchdown to occur within the touchdown zone of the runway of intended landing;

Is this zone explicitly defined? If so, where is the applicable definition found?

No definition is offered in 14 CFR 1.1. However, several uses or definitions of this term do exist in various FAA advisory documents. These uses or definitions are generally similar, but include variances. A few of these include:
AC 91-79A (referencing an obsolete document):

the TDZ is referred to as a point 500-3,000 ft beyond the runway threshold not to exceed the first one-third of the runway

AIM 2–1–5:

3,000 ft beyond the landing threshold or to the midpoint of the runway, whichever is less.

The Pilot Controller Glossary:

The first 3,000 ft of the runway beginning at the threshold.

Also of note, the runway touchdown zone markings on long precision runways generally extend to 3,000 ft beyond the threshold.

Found this definition on an FAA website today:

The runway touchdown zone is usually defined as 1000 feet from the runway threshold or 1/3 the total available landing distance. This provides runway “underrun” in case the pilot comes up short of his/her aim point, as well as increased obstacle clearance while on final approach.


Is it OK to move a light aircraft by pushing or pulling the propeller? It's very common to see pilots moving a light aircraft by pushing or pulling on the prop, either because there's no tow bar available or simply out of preference or convenience. Is this a reasonable thing to do or can it damage the prop or engine in some way?

A couple of my CFIs have asked me to help them park the airplane (in absence of a tow bar) when I was pushing the airplane by putting one hand on the hub and the other on the propeller near the hub, and them (the CFIs) pushing the tail down and nose wheel elevated. But according to AOPA, it is not a good thing:

  ... never push or pull on the prop blades. Forget what anyone has told
  you about pulling near the hub or the strength of the propeller.
  Aluminum blades can bend, and it doesn’t take much to put the blades
  out of track with one another.

This PDF says the same thing:

  Avoid pulling the airplane around by the prop. Yes, this seems the
  perfect solution to a vexing problem of how to change the airplane’s
  position without having to walk around and get the tow bar, but it’s
  worthwhile to make the extra effort. Neither the engine nor the prop
  particularly benefit from the loads imposed by horsing the whole
  airplane around.


Is it possible to add "planets" to the gearbox of a Trent 1000? The gearbox of a geared turbofan engine has 4 reducing gear small wheels being spun by a larger wheel or gear, simultaneously spinning the shaft that is attached to the fan.

That is 8 points of contact, two for each small wheel/gear meaning 8 the points where friction and subsequent heat would result.  I gather the use of 4 small wheels/gears instead of one is for reducing the load on the teeth at each given point.

Would increasing the smaller gear wheels (i.e. the "planets" ) from 4 to 8 or 12 or 16 for a gearbox designed for an engine the size of a Trent 1000 or more render the gear teeth less likely to break or fail?

With some reinforcement on the teeth, would it be possible to make a gearbox for this large engine?

As for the extra heat, cooling and rotating the oil through a cooler or along the length of the aircraft several times over, exposed to the  atmosphere at cruising altitude using a high pressure oil pump passing oil through a sealed gear box would take care of cooling.

With the ambient energy loses to heat would this render the engine a lot more fuel efficient and possible?

The fundamental question you seem to be asking is whether adding more planets to a planetary gear improves the load carrying capability of the gearbox.  The answer to that question is yes... to a point.

Take a look at a picture of the PW geared turbofan gearbox.  You'll note that there are five planets in there, and they are packed in pretty tightly.  There's really no room to add any more.  Although adding more planets would distribute the load such that each planet takes less load, it's impossible in this configuration because there is no space.  Let's say that you really really wanted to make it six planets instead of five. The only way to make enough room would be make the planets smaller. As you make the planets smaller, then either the ring gear has to get smaller too, or the sun gear has to get larger.  Either way, that is going to change the gear ratio (see formulas here). Specifically, the gear ratio is going to get closer to 1, which means the gearbox no longer does the job it was intended to do (namely reduce speed and increase torque).

So you can't have your cake and eat it too.  If you want 16 planets in a planetary gear, you can do it, but the gear ratio will be something like 1.02:1 which is not useful.  You might as well forget the gearbox and just do direct drive at that point.  If you need a decently high reduction ratio like 2:1, you can do it, but you will be limited on the number of planets that you can fit in.


What areas of a commercial airliner are pressurized besides the cabin? For example, what about the baggage compartment? Landing gear housing? Avionics?

Baggage, yes, landing gear, no.

The fuselage of an airliner is typically "capped" by two bulkheads, the forward and aft pressure bulkheads. These are roughly spherical sections that seal the central "cylinder" of the aircraft's fuselage.

Here's a 787's forward bulkhead:

... and a 767's aft pressure bulkhead:

Practically all the space in the fuselage itself between these two bulkheads is pressurized during high-altitude flight. This includes the baggage compartment.

Gear assemblies, however, are typically not pressurized. For some jets like the 737, this is fairly obvious:

Other designs with full doors for the gear assemblies aren't as obvious, but in general it's neither feasible nor desirable to pressurize the landing gear housings when airborne.


Does a straight missed approach require all turns to be less than or equal to 15 degrees? I am studying ICAO's PANS-OPS 8168 manual, and I am having trouble understanding the criteria applied to straight and turning missed approaches. In the manual, it clearly states:

  I-4-6-2 Types of missed approach.

  There are two types of missed approach:

  a) straight missed approach (includes turns less than or equal to 15 degrees)

  b) turning missed approach.

When there is a turn more than 15 degrees, it takes into considerations three cases (1. turn at altitude/height, 2. turn at at fix/facility, 3. turn at MAPt). As far as I can tell, each one of them concerns only a small initial portion of the whole missed approach. An example can be seen in the following picture.

Taking the above points into consideration, I would like to know if the requirement for turns less than 15 degrees does not concern all the legs of a straight missed approach, only those which are between the MAPt and the (potential) Turning Point. In other words, it seems strange to have, for example, only one turn more than 15 degrees near the end of the missed approach, which can be many miles away from the MAPt, and suddenly the whole missed approach to be considered a turning missed approach, instead of straight, with all the subsequent rules of a turning missed approach applied from the MAPt until the last waypoint.

A straight missed approach can have a combination of both straight and turning parts. The straight part is called the intermediate missed approach, while the turning part is called the final missed approach. When a straight missed approach starts a turn of more than 15°, the turning missed approach criteria applies, as stated in Part I, Section 4, Chapter 6.3.4 of ICAO DOC 8168 Vol. II:

  Wherever practical the missed approach track should be a continuation of the final approach track. Missed approaches involving turns are permitted (see 6.4, “Turning missed approach”), but should only be employed when an operational advantage may be obtained.

Take this approach from Ålesund Airport in Norway for example:

In the straight part you have a track change of 6°, which satisfies the criteria for a straight missed approach. This allows a reduced Minimum Obstacle Clearance (MOC) of 30 m, among other things. When AL821 is reached, the turning missed approach criteria is applied, and the MOC is increased to 50 m.


What is an “aeronautically qualified witness”? Many older NTSB AARs, in their history-of-flight-and/or-accident-sequence sections, make mention of observations by an “aeronautically qualified witness” or witnesses, without any further explanation of what this term means.  Example (AAR 76-04, page 3 [paper]/6 [PDF]):

  An aeronautically qualified witness, who was standing near the base of the radio tower when the plane struck, stated that the sky was overcast and that the bottoms of the clouds were obscuring the top 30 feet of the tower.  [...]

What, exactly, is meant by an “aeronautically qualified witness”?  Does it mean “a witness who is themself a pilot”?

It means a witness with credentials and knowledge that makes the witness competent to give a reasonably accurate description of an event, or an informed opinion, to an investigating authority or a jury.  Likely a pilot witness to a crash as in this case, who knows more about weather than the average person, or a mechanic witness in an investigation or lawsuit over maintenance.


What is hinge moment? What is hinge moment?
Why in the process of calculating it we must calculate the coefficient of hinge in 2D?
Why the distribution of airfoil thickness at 90%, 95%, and 99% of the line should be considered?
Why is the line used for his (cf= line form hinge line to trailing edge) (cb = line from hinge line to leading edge) using a perpendicular line with Λ_(1/4) wings?

The hinge moment is the moment acting about the hinge line of a control surface. Simply put, it is the force that must be overcome to move a particular control surface. At any given dynamic pressure and airspeed, the hinge moment will vary with angle of attack, the amount of control surface deflection, and trim tab deflection. Not an easy concept and not one which is generally taught to pilots, however becomes critical for engineers who design control systems for aircraft.


I've been denied VFR clearance through C airspace, what should I do? If I'm flying along in my C-152 and I am trying to go in a straight line through the "center" of C airspace (to land at a regional airport under the airspace), but the controller tells me to remain clear, what should I do?

Would it be safe to fly under the C, or above it, or would it be best to completely circle around even if it takes extra time and fuel?

If I'm flying along in my C-152 and I am trying to go in a straight line through the "center" of C airspace, but the controller tells me to remain clear, what should I do?

Well, the obvious answer is remain clear of the Class C airspace :-)

HOW you remain clear is entirely up to you - you can go over, under, or around - you just can't go through, and I think that's the more interesting part of your question.

Flying around the class C airspace is usually a safe choice (don't skim along the margins though - give it some reasonable breathing room), but as you've noted it could add a lot of time/fuel. You need to balance that with the time/fuel required to climb above the airspace, or the risks of flying under the airspace (mainly obstacles) to make your decision.

I'm going to use my local class C airspace as an example for an exercise in aeronautical decision making because conveniently there's a VOR you could hypothetically be circling while talking to approach, and an airport on the other side you might want to get to.

In our hypothetical example let's say you're circling Deer Park VOR (A) at 2500 feet, and you want to cut through the Class C airspace to get to Brookhaven (B), but approach isn't cooperating.

Click to embiggen.

I've got three options sketched out here - think about them, then hover over the spoiler boxes for my thinking on each of the three routes:

The dashed line through the center (the route you were hoping Approach would give you).

   A straight line is the shortest distance between two points, but this straight line stinks: Since Approach wouldn't let you go through the class C airspace you're going to have to spiral-climb to 4200 feet or higher (5500 feet if you're playing by the hemispheric rule), and then when you get to the cut-out in the class C on the other side you're going to have to dive down to get to pattern altitude.
That doesn't seem safe, nor efficient to me, so let's toss that idea out the window.

The northern route under the class C airspace.

   Simple enough, we'll split the difference between the ground (roughly sea level) and the floor of the airspace (1500 feet) and fly under the shelf at 1250 feet. Plenty of room above and below (if your altimeter is set right and you're any kind of decent pilot).
 So this is the part where I confess that I'm a big ol' wuss and don't like to be close to the ground. It's like a porcupine, but with radio towers for quills (like the one I marked with a big OUCH - at 1250 feet there'd be less than 500 feet between my landing gear and the top of that tower).
 I'm not happy with the obstacle clearance on this route (and while I could certainly rearrange the line a bit to avoid the obstacles I'm not going to because they serve my purpose) -- the northern route is out.

The southern route under the class C airspace.

   Same idea as the northern route - descend to 1250 feet and fly under the shelf, but I like this route a whole lot better.
 There are really great landmarks here ("Fly southeast toward the looped road, then go to the middle of the bay and stay between the two shore lines until you pass the bridge at Smith Point. At that point you'll see the airport off your left wing and can maneuver to enter the pattern.")
 You're also over water, and we don't tend to have any radio towers sticking up out of the bay.
 You'll need to watch out for traffic from Bayport, students practicing ground-reference maneuvers, and banner-tow planes in the summer, but that's just your basic everyday VFR "See and Avoid" situation.
 This is probably the route I'd pick.


Why can’t the CF34 use wide-cut fuels? The General Electric CF34 high-bypass turbofan (used primarily on the Bombardier CRJ and Embraer E-Jet regional jets), unlike the vast majority of jet engines (both civil and military), is not certified to burn so-called “wide-cut” fuels (gasoline-kerosene blends, nowadays used mainly in cold-weather operations), such as Jet B1 and (formerly) JP-3 - only “narrow-cut” fuels (straight kerosenes), such as Jet A-1,2 Jet A, JP-5, and (formerly) JP-1.  In contrast, CF34s in military service (known to the military as the TF34, and used mainly on the A-10 ground-attack aircraft) do just fine with wide-cut fuels (an absolute necessity back when aircraft so engined entered military service, as the go-to military jet fuel back then was JP-4, aka Jet B with the military’s stamp of approval).

This is a bit surprising, as:

it renders CF34-equipped aircraft unable to operate in very cold places (wide-cut fuels, having much lower freezing points and viscosities than the straight kerosenes, remain useable down to much lower temperatures than their narrow-cut ilk), and
there doesn’t seem to be any obvious technical reason for such a restriction, seeing how, as mentioned above, military CF34s are perfectly happy to run on wide-cut fuel.

Is there some critical difference between the military and civilian versions of the CF34 that renders wide-cut fuels compatible with the former but not the latter (maybe a gasket somewhere in the civilian CF34 that’s dissolved by the gasoline in wide-cut fuels?), or did General Electric simply not bother to certify the civilian version for use with wide-cut fuels?

1: Formerly also often known as “JP-4”.

2: Also often known as “JP-8”.

Actually, the CF34-3B1 engines are certified to use wide-cut fuels, JetB/JP4. This comes straight out of the AOM for the CRJ200. I would venture to guess that all variants from CF34-1A to 3B would have the same certifications.

The CF34-8C5 engines on the other hand are not, again straight from the AOM for the CRJ 705/900. CF34-8C1 to 10E also likely have similar certifications for fuel certifications.

The difference is likely more to do with cost to certification. Seeing as wide-cut fuels aren’t overly common, except in the most remote locations north of 60 degrees of latitude, GE probably said why bother spending the extra money. JetA1 is good to -47*C/-53*F so for most commercial aviation, it’s more than sufficient. Every aircraft I’ve flown to date had an on-ground operating limitation of -40*C anyway.


What is this light passenger prop airplane which crash landed in East Kalimantan, Borneo in 1983? Plane crash landed in Borneo jungle in 1983.

That registration looks like PK-DCR to me. It's a little bit blurry, but especially if you zoom in, it's fairly readable.

A quick web search for that registration and "airplane" brings me Wikipedia's page on Deraya Air Taxi, which indicates that

  On November 1982, Indonesian Aerospace 212-100 PK-DCR of Deraya Air Taxi and PT Pupuk Kaltim was damaged when it approaching Bontang. No fatalities in this accident.

The 212-100 brings us to the CASA C-212 Aviocar.

Looking at the pictures on Wikipedia, it's pretty close, so that's probably it. Note the pretty distinctive tail section, and the relative dimensions:

(source; photo by RuthAS, published under CC-BY-3.0)

(source; photo by John Wheatley, published under under GFDL-1.2)


What is needed to go from a student pilot license to a private pilot license? I will be 16 in a few weeks and I really want to get flying so I am currently thinking that I should get a Student Pilots license and then get a Private Pilot License next summer when I am 17 but I was wondering what is required to advance from an SPL to a PPL? Is it significantly more economically wise to just wait to get a PPL?

You have a bit of a misconception about the way these things work.  Everyone gets a student pilot's license before they get a private pilot's license.  The student license is just a step along the way to the private license.  The requirements for getting a student pilot's license are minimal.  It's the equivalent of a "learner's permit" in the automobile world.  The reason that the requirements for a student pilot's license are minimal is that you will be operating under the supervision of an instructor.  Just having the student license does not authorize you to fly an airplane without an instructor on board.  When you hold a student pilot's license, an instructor has to endorse your license for solo privileges in each make and model of aircraft, and also has to endorse your logbook for solo privileges every ninety days.  An instructor also has to review your planning for every cross-country flight, with exceptions for flights to another airport within 25 miles or repeated flights to another airport within 50 miles.  These and other requirements for solo flight under a student pilot's license are spelled out in FAR 61.87 and 61.93.

Without a student pilot's license, there would be no way to build solo flight time as needed to qualify to take the checkride for a private pilot's license.

This answer is assuming that

1) You live in the USA

2) You haven't already learned to fly, and accumulated flight time, in the military..

Highly related-- essentially the same question in fact-- see all answers--

Am I required to obtain a student license before a sport, recreational, or private one?


Why does a DME ground station wait 50 microseconds? The FAA says that a DME ground station sends a response exactly 50 microseconds after having received an interrogation from an aircraft. For what reason is there a 50 microsecond delay?

The delay is not 50 milliseconds, but 50 microseconds.

It takes some time for the ground equipment to decode the incoming signal, decide it needs to reply, and fire up its transmitter. In order for the distance measurement to be reliable, this inevitable delay needs to be precisely defined and the same for all DME stations. It also gives the airborne interrogation some minimal time to shut down its transmitter and start listening even when it's right on top of the ground station.

50 µs must have felt like a suitable interval to standardize on, long enough for it to be reasonably possible to engineer the ground stations to meet it (given the technology of the time the design was made), yet short enough that one DME station can service an acceptable number of aircraft without needing to handle overlapping delays between different interrogations.

The standard delay also means that a DME station used for ILS can be located midway between the runway's thresholds and adjusted such that aircraft see the distance to the threshold rather than the distance to the physical antenna, by reducing the delay appropriately. (Such a DME does not give useful readings for aircraft not aligned with the runway).

Note, by the way, that the 50 µs is the time between receiving the second pulse of an interrogation pulse-pair and transmitting the second pulse of the resply. So the ground station actually has to start transmitting the reply less than 50 µs after it knows it has received a complete interrogation. For Y channels where there are 30 µs between the two reply pulses, the ground station actually has only 20 µs to react.