What is the difference between conventional VOR and Doppler VOR? There are two types of VOR (VHF Omnidirectional Range) navigation beacons; the conventional VOR (CVOR) and the Doppler VOR (DVOR).

What are the differences between them? Specifically I would like to know:

Do they generate the same navigation signal?
Can they be used by the same receiver, or do VOR receivers need to be specially adapted to DVORs?
Is one more accurate than the other?
Is one more susceptible to interference than the other?

Short answer:
There are several types of conventional VORs using either rotating or static antennas. What they have in common is:

They are relatively compact.
Bearing is determined from a HF signal rotating 30 rounds per second.
They are very sensitive to multipath interference created by reflection on nearby obstacles, and must be located at isolated places. They are often used for airway beaconing.

There are also several types of Doppler VORs, single or double sideband:

They requires a large 14 m diameter circular array of antennas.
Bearing is determined from the Doppler effect created by scanning the array at 1,300 m/s.
They are less efficient, inactive antennas from the array absorb a significant part of the signal emitted from the active antennas, reducing the effective range.
They are less sensitive to multipath, and are easier to install at airfields. They are commonly used for runway approach.

Bearing is more accurate with a Doppler VOR unless the conventional VOR site neighborhood is exempt of obstructions.
That said both types have the same tolerances from an ICAO standpoint:

The transmitting elements must be accurate to 2°. Most stations are able transmit a signal with an accuracy better than 0.5°. A perfectly sited VOR could deliver this precision to the receivers.

However errors are mostly created by the environment, by reflection and other phenomena changing the signal phase, similarly to a mirror inverting left and right on its reflected image. When direct and reflected waves interfere, an error can be introduced. ICAO limits this error to 6.5° in the volume of service. In practical most VOR stations are well below this limit, possibly using Doppler VORs in most cluttered sites.

A word about these multipath errors: The direct wave propagates along the line of sight (LoS), but the transmitting antenna radiates in other directions. The corresponding rays can be reflected, diffracted and refracted by obstacles and reach the receiver antenna as indirect waves. This can be beneficial, e.g. it extends considerably the range beyond LoS. But waves travel different distances before reaching the receiver:

This means their phase is different on the receiver antenna. Interferences occur, and they change the signal amplitude.
In a volume called the first Fresnel ellipsoid (FE1), centered on the LoS, where the length difference cannot exceed $\small \lambda / 2$, $\small \lambda$ being the VOR carrier wavelength, interferences are constructive, amplitude is increased.

In the second Fresnel ellipsoid where the difference is between $\small \lambda / 2$ and $\small \lambda$, interferences are destructive, amplitude is decreased, and this continues with other multiples of $\small \lambda / 2$. However 80% of energy is in FE1, and the rest is mostly in FE2. Therefore when planning a radio link, only FE1 is taken into account. The ratio between the obstructed areas in FE1 and FE2 determines the ratio of energy with constructive interferences, thus when siting radio stations, at least 60% of FE1 is kept clear of obstacles.
This can be a challenge. For an aircraft at a distance of 20 NM from a VOR located on the airfield, flying at 1000 ft QFE, the radius of FE1 at the middle point of the link is 500 ft. The ellipsoid is already tangent to the ground in the best case, and therefore the ellipsoid between the VOR and this middle point is slightly obstructed.
Limiting VOR errors consist first in removing obstacles from FE1. However as multipath first impacts amplitude, it hits conventional VOR harder, as this type of VOR depends more on a amplitude accuracy.

VOR principles
A VOR receiver, regardless of the technology behind, receives two sine signals repeating 30 times per second: Reference and variable signals, and determines the bearing by solely measuring the difference between their phases.
From a carrier standpoint, only amplitude modulation is used, but to minimize a possible influence of one signal onto the other, the VOR station uses a subcarrier, which frequency is low (9,960 Hz) but significantly distant from 30 Hz. One phase value is conveyed by normally modulating the carrier in amplitude, the other by modulating the subcarrier in frequency. The subcarrier then modulates the carrier in amplitude.
In addition, two antenna systems are used:

The carrier and the reference are send on one or more omnidirectional antenna(s) and all receivers see the same reference phase at the same time.

The variable signal is sent appart to appear different for receivers at different bearings. The type of antenna used depends on the type of VOR.

As explained below, the variable signal is not created by actual modulation of the carrier, but by synthetic sidebands. Modulation and sidebands are anyway equivalent by Fourier transform. Amplitude modulation changes the amplitude of the carrier over time (time concept), but also creates symmetrical sidebands on each side of the carrier (spectral concept):

12 kHz carrier with 500 Hz AM. Sidebands are created at a distance of 500 Hz from the carrier
Conversely, creating carrier sidebands by some method is the same as modulating the carrier.
Phases are equal when the receiver is located north of the VOR (360°M), and show a difference increasing by one degree for each degree of bearing counted clockwise. Therefore the phase difference directly gives the bearing value.
C-VOR and D-VOR differ by how the variable phase is made different for receivers at different bearings. The method relies on amplitude for a conventional VOR and on frequency for a Doppler VOR.
Conventional VOR (C-VOR)
Technologies have changed a lot in the first decades. This explains why C-VOR descriptions also vary a lot, and sometimes contain mixed principles from different generations. Early generations used a rotating dipole to broadcast the variable signal, but they were soon replaced by static antennas or slots on a cylinder, making VOR more simple and less demanding on maintenance.
The static system once used two pairs of Alford loop antennas, more commonly two pairs of vertical antennas. While a vertical antenna radiates equally in all azimuths, a vertical pair tends to increase the field in directions perpendicular to the pair plane.

Conventional VOR antennas for a Thomson CSF TAH 511. Source: STNA
In the aerial above, four vertical tubes form two crossed pairs and the rings below and above the pairs are omnidirectional antennas. A polarizer at the top of the tubes prevents them from radiating in vertical polarization, to increase accuracy.
Reference signal
The reference information is FM embedded into a 9.96 kHz subcarrier ("10k subcarrier") with a modulation index (modulation depth in ICAO parlance) of 16, meaning the subcarrier frequency varies by +/- 480 Hz.
Variable signal
The variable signal is created by artificially creating the sidebands corresponding to the subcarrier. Each pair of antennas receives a HF signal:

Which frequency is f-30 Hz or f+30 Hz (sideband frequencies)
Which phase is proportional to the sine or the cosine of the reference angle. This aspect is explained shortly.

Pairs are directional, sidebands are sent at right angle (image below, left), creating two individual figure-of-eight radiation patterns (below center), themselves equivalent to a larger composite  figure-of-eight along the symmetry axis (below right):

Two phenomena occurs:

Sidebands interfere with the carrier sent on the ring antennas. The result is a cardioid field.

With phase modulated by sine and cosine of the reference angle, the cardioid rotates at 30 revs per second, the frequency of the reference. This is equivalent to a rotating antenna broadcasting a constant signal (the technology used on earlier VORs).

The cardioid EM field which constantly increases and decreases in strength at a given point in space as the pattern rotates is sensed by the receiver as a constant signal modulated in amplitude at 30 Hz, this amplitude variation represents the variable signal.
Bearing determination
Carrier, reference and variable signal sidebands create a spectrum the receiver sees as a whole:

This spectrum has all the characteristics of a HF carrier modulated in amplitude by a 30 Hz signal and a subcarrier at 9960 Hz, itself modulated in frequency by the reference. Phases are finally extracted from this HF wave and compared:

Doppler VOR (D-VOR)
This VOR consists in an array of about 50 fixed Alford loop antennas located on a 14 m circle. Two opposite antennas are activated at a time, and are electronically switched so the active antennas seem to be moving along the circle at 30 rounds per second.

Seen from the receiver one source is moving forward, the other is moving backward, at a linear velocity between -1,300 m/s and +1,300 m/s (Mach 4).

Principle of the Doppler VOR: The variable signal generation
A 110 MHz source moving between -1,300 and +1,300 m/s creates a Doppler shift between -480 Hz and +480 Hz. This value, consecutive to the selection of the appropriate array diameter, is the same than the 480 Hz FM swing of the C-VOR, making the D-VOR compatible.
Reference
The 30 Hz reference AM modulates the carrier which is sent in all directions by an antenna at the center of the circular array.
Variable signal
The actual perceived Doppler shift depends on the direction of the displacement relatively to the receiver, maximum when "side" antennas are activated, null when "front" and "rear" antennas are activated.
Thus all receivers see a frequency variation repeating 30 times per second, and starting at a time varying with their own bearing. This shift therefore can be used as the variable signal.
The repeating Doppler shift being undistinguishable from frequency modulation, the variable signal must be conveyed in FM. However it doesn't FM modulate the carrier, but the subcarrier to be compatible with the C-VOR. To achieve this:

Each active antenna of the array transmit a pure frequency corresponding to a sideband of the subcarrier: f-9.96 kHz and f+9.96 kHz, f being the VOR carrier frequency. When associated with the carrier sent from the central antenna, these sidebands represent a carrier AM modulated by the 9.96 kHz signal.

When antennas radiating their pure frequency are given their angular velocity of 30 rps by the scan, a cyclic Doppler shift between -480 Hz and +480 Hz is automatically added. This shift is equivalent to a FM modulation of the subcarrier by a 30 Hz signal.

Spectrum created
The composite spectrum is identical to a C-VOR spectrum, the C-VOR receiver is able to continue working.

D-VOR frequency spectrum
Receiver
A VOR receiver is looking for 30 Hz and 9.96 kHz signals. We deliver both: 30 Hz signal on the central antenna and 9.96 kHz on the directional scanned array. We had to switch reference and variable signal functions on the carrier because the variable signal is naturally produced as FM, and the FM signal goes on the subcarrier in the standard.
Because of this inversion, the phase values are also inverted, and the result is a wrong bearing angle computation: When the angle is +a, the computation gives -a. The remediation consists in scanning the D-VOR array in reverse direction (counter-clockwise) and generating an opposite Doppler shift.
Accuracy
Both types of VOR (and their different subtypes) are required by ICAO to produce a bearing with a ±2° tolerance. The D-VOR is better in this aspect because it’s easier to produce an accurate Doppler shift than to form a precise pattern with space modulation.
Once the signals are emitted, they are subject to reflection on terrain and obstacles. The final composite error at the receiver location cannot exceed ±6.5°, as ICAO limits the error according to a bent (slow variation) tolerance of ±3.5° relative to theoretical course and to a superimposed scalloping (rapid variation) of ±3°.
On this aspect, the D-VOR is also superior, the variable signal is FM modulated and less subject to multipath errors. The smaller C-VOR is difficult to run on airfields due to reflections on close obstacles, the large D-VOR must be used for terminal VOR. The C-VOR is rather used for enroute navigation and implanted on isolated sites.
Large counterpoises under the antennas limit the reflection problem, and when the site used to built the VOR is carefully selected, the operational accuracy can be far better than the ICAO requirements in a large part of the service volume.
Answer to specific questions
Do they generate the same navigation signal?
There are two differences:

The C-VOR actually sends two modulated signal to generates a cardioid interference pattern which when steered creates an apparent AM modulation. The D-VOR sends only “moving” unmodulated sidebands which create by Doppler effect an apparent FM modulation.

To maintain compatibility with C-VOR, the D-VOR reference signal must be sent in AM, and the scan done in reverse direction of the cardioid rotation.

Can they be used by the same receiver, or do VOR receivers need to be specially adapted to D-VORs?
The C-VOR receiver is used for D-VOR. It computes a phase difference which is wrong (opposed cosine), but because the array is scanned counter-clockwise, the correct bearing is infered.
Is one more accurate than the other?
Wikipedia states, but with no reference, and I’m assuming it’s for a D-VOR: “The predicted accuracy of the VOR system is ±1.4°. However, test data indicates that 99.94% of the time a VOR system has less than ±0.35° of error”.
The same article states about ICAO Annex 10 volume 1: “This document sets the worst case bearing accuracy performance on a Conventional VOR (C-VOR) to be ±4°. A Doppler VOR (D-VOR) is required to be ±1°”. But I can’t find these figures in the version I have.
Annex 10 and Doc 8071 volume 1 (testing procedures) rather give three tolerances:

A maximum VOR equipment signal error of ±2°
A radial bend tolerance of ±3.5° from the perfect course.
A radial scalloping error of ±3° around the bend.

The two last errors are due to the environment rather than to the instrument. VOR are located at places where these errors can be minimized.
So the acceptable total deviation of ±6.5°, as attested by Doc 8071 volume 1 §2.3.48, when the radial is bent by ±3.5° and a scalloping of ±3° is superimposed. However scalloping is a rapid oscillation around the course, and in most cases is ignored by the pilot who keeps working on a mean deviation value (but there are limitations of scalloping when the autopilot is used, because the A/P can react to oscillations).

ICAO VOR tolerances on bearing value
The D-VOR was designed to minimize the multipath effect, the variable signal is frequency modulated for this reason. The size of the counterpoise was increased so that reflection occurs on a controlled surface, rather than randomly. This way VOR could be located on airfields, allowing better VOR approaches and easier maintenance.
However D-VOR introduces a new error: The array antennas are close to each other, therefore the inactive antennas on each side of the active one interact on the signal. First they delay the wave, introducing an error in the phase before the wave is Doppler-shifted. Second they absorb a large portion of the energy, reducing the range. As explained, the 14 m diameter can't be changed to space further the antennas, and they cannot be spaced vertically without impacting the maximum elevation of the signals and increasing the cone of silence, which is already relatively large (100°).
Another error is the discretization of the bearing information due to a scan over only 46-50 antennas (the matter is complex), a fix is the so-called power blending: The two or four antennas around the active antenna are fed with a smaller power HF signal and the transition from one pair to the next is smoothed.
The last error, which has been partially corrected by the DSB D-VOR (the one with two sideband antennas described here) is related to the portion of counterpoise between the antenna and the receiver which varies with the antenna location. If a reflection occurs on the ground, and the one from the reference antenna occurs on the counterpoise, then their path is not equal and the phase difference is altered (however the modulation wavelength being 10,000 km, a path length error of 1 km is not very significant).
It's difficult to quantify a mean error, it really depends on the conditions the VOR is used and at which elevation angle the receiver operates. There are tools for simulation like the Ohio University Navaid Performance Prediction Model (OUNPPM) you may already know. Here is a study of the C-VOR/D-VOR accuracy with this tool.
Is one more susceptible to interference than the other?
For interference from signals or from obstacles, the C-VOR is more prone to errors because of the use of AM for the variable signal. In the D-VOR the reference is AM modulated, but a receiver can maintain a local reference using a PLL oscillator synchronized with the VOR reference when the signal is good, and reject transient spurious values (it’s like maintaining a local time reference, synchronized from time to time with a master clock).
Here is a study of wind turbines interference on D-VOR.
That said:

EUROCAE ED-52 provides a guidance for VOR siting.

For foreign signals, VOR are subject to a requirement from ICAO (Annnex 10, volume 1, §3.3.8.1): "The VOR receiving system shall provide adequate immunity to interference from two signal, third-order intermodulation products caused by VHF FM broadcast […]".


Which wheel or wheels get the chocks? As a quick follow-up question to my earlier one about the retail cost of chocks, which wheel(s) typically get the chocks on a GA tricycle-gear plane? Do you buy one roped pair for the nose wheel (make sure your chocks are away before starting up), or two pair for the main gear, or all three (I doubt this, especially on a small plane)?

To be most effective chocks should be placed on both of the main gear of light aircraft. This prevents the aircraft from rotating or pivoting about the chocked wheel.There's a nice article from the Flight Safety Foundation which talks about this.
The FAA, in an overabundance of caution, advises you to chock ALL the wheels (see AC 20-35C).

Practically speaking, on a flat ramp and a calm day chocking any single wheel is usually enough to keep the airplane where you put it for a short while (say long enough refuel the aircraft, or to get lunch).
When using a single chock my preference in these cases is to chock the nose wheel as it's the most visible (I fly a low-wing airplane, and an inattentive line person who needs to tow the plane could miss a chock on the main gear). With two chocks the main gear should be secured on each side of the aircraft to keep it from pivoting.

For anything longer than that a brief food and fuel stop, or when high winds are anticipated, aircraft should be properly secured (by tying them down and chocking at least one wheel).
In these cases the tiedowns serve as the primary securing mechanism, and the chocks as a secondary mechanism (keeping the plane from rocking fore and aft in high winds and breaking the tiedown ropes).

  Note that there is an exception to the "high winds" bit here: If winds strong enough to blow chocks around on the ramp are anticipated, such as a hurricane, the chocks should be removed unless they can be adequately secured to ensure they don't get blown into an aircraft.
  Of course if winds that strong are anticipated you should really have flown away before they got to you, or you should be looking for a hangar to weather the storm in.


Is data on international air traffic volume in the US freely available? I'm looking for air traffic flow data which has the passenger air traffic from countries outside of the US to every international airport in the US. Ideally, I would like to know how many passengers came from other countries to the international airports in the US but I can also use load factors. I'm only interested in free data. Any ideas would be appreciated. I'm willing to parse together a data from multiple datasets/sources.

Try U.S. International Air Passenger and Freight Statistics Report.

Example of data for Q4 2015:


Which is the difference between IMA (B777) and Open IMA (A380)? The integrated modular avionics concept (IMA) was developed by Boeing for its B777. Open IMA is an improved version developed by Airbus starting from A380. Which are the differences? For example, I got that the network is optical fiber for IMA and Ethernet/Avionics Full-Duplex Switched Ethernet (AFDX) for Open Ima: why?

I know that the question may be too broad and not very easy, so I would welcome even some links to deepen the argument.

Moreover I would like to understand: where is it used IMA nowadays? Only in B777, or even in B787 and new generation B747 and so on? Idem regarding Open IMA: only A380 or even in the A329 Neo?

If Boeing and Airbus have these new systems, what do you have in all other companies? Embraer, Eurocopter, Tupolev etc.

The primary difference is that the B777 is the AIMS (airplane information management system).  It is a Honeywell developed system where all the software on the systems is controlled by Honeywell (closed system).  The biggest downside to the closed system is maintenance and support.

The A380 system is a semi-open IMA system. It has a single supplier hardware cabinet with processor slices and an common operating system.  Different suppliers can develop their applications to run on the platform.

Most newer aircraft designs use the IMA architecture as it reduces the number of LRUs and saves weight.  Boeing and Airbus are going to more open systems.  B787 and B777X are open as is the A350, mainly for competition reasons.  Smaller aircraft (Bombardier, Embraer) are typically closed as they tend to have single source avionics (Rockwell Collins, Honeywell).


How would SLP997 be calculated on a METAR? How would SLP997 be calculated on a METAR? I understand that SLP117 say would be 1011.7 hPa, but I am sure that SLP997 is not 1099.7 as that would be impossibly high.

Refer to FAA document, AC 00-45H Aviation Weather Services

  3.1.5.13.25 Sea-Level Pressure.

  At designated stations, the sea-level pressure is coded in the
  following format: the identifier SLP,
  immediately followed by the sea-level pressure in 1 millibars (mb) .
  The hundreds and thousands units are not coded and must be inferred.
  For example, a sea-level pressure of 998.2 mb is coded SLP982. A
  sea-level pressure of 1,013.2 mb would be coded SLP132. For a
  METAR, if sea-level pressure is not available, it is coded SLPNO.


What is the naming convention for European airways? I know that in the U.S. low altitude airways are called Victor (below 18.000ft, e.g. V123) and high altitude routes are called Jet (above 18.000ft,e.g. J123). Can somebody explain the European airspace routes naming? Thanks!

ATS routes in Europe are designated just like the rest of the world. ICAO publishes guidelines for the designation of ATS routes in Annex 11, which are adopted by almost all countries.

A route will consist of a possible prefix (see below) a letter (see below) and a basic designator (a number between 1-999).

The three types of prefix are:

K (Kopter) to indicate a low-level helicopter route

U to indicate an upper route, available only in upper airspace

or S to indicate a route only used by supersonic aircraft (not very common).

The letters can be:

A, B, G, R for regional routes which are not RNAV routes

L, M, N, P for regional RNAV routes

H, J, V, W for non-regional non-RNAV routes

Q, T, Y, Z for non-regional RNAV routes

In addition, states may add the letters F or G to the end of a route to indicate that the route is in class F or G airspace respectively. To my knowledge, this is not very common (and most ATS routes are in controlled airspace anyway).

Examples:

KY80 ("Kopter Yankee 8-0)

UN872 ("Upper November 8-7-2)

T54 ("Tango 54")


Why would all passengers be asked not to eat peanuts when there is one allergic person on board? In this review of BA British Airways Club World London City flight there is one thing I don't understand:

  ... it was announced that a passenger onboard had a severe nut allergy, so they asked people not to consume nuts on the flight.

I've never seen this in a restaurant or any other setting. I gather it's usually the responsibility of the person suffering from allergy to avoid what they are allergic to (usually with a legally mandated help, like known allergens listed on the menu).

I understand that having a person have an allergic reaction to nuts (which can get very bad) itself is a risk to the whole flight. What I'm missing is how other people eating nuts may endanger the one person with allergy.

The only thing I can think of is perhaps some loose nuts flying into the allergic person's meal (or, more directly, mouth) in a severe turbulence. Is that it? Is it a normal procedure to ask passengers not to eat nuts when there is an allergic person on board?

The problem with a severe peanut allergy is that you don't have to eat a peanut to be affected.  With a severe enough allergy, inhaling peanut "dust" can trigger a life-threatening emergency.  In a confined space, any number of events could cause an issue: people dumping peanuts into their hands, dusting their hands off, accidentally sneezing while chewing the peanuts, etc.


Where did the US 'N' registration letter come from? Why is the first letter in US registration numbers 'N'? Other countries seem to use a letter significant to their country, for instance 'G' for Great Britain, 'F' for France, 'D' for Germany (presumably for Deutschland), and 'JA' for Japan.

Does 'N' have any significance at all?

The origins of this can be traced back to CINA (the Commission Internationale de Navigation Aerienne / the Convention for the Regulation of Air Navigation) established as part of the Paris Peace Conference immediately after WWI.

A part of this conference was the adoption of a system of international aircraft identification still in use today. The U.S. delegation was allocated "N".

A number of theories exist as to why "N" was chosen specifically, and there's a great article about it over at the American Aviation Historical Society.

Theories range from, the largest number of states begin with the letter N; to the recognition of the development of wireless communications by the U.S. Navy that had been using "N" as the prefix to its station call-sign identifiers since 1909.


Do hours flying "advanced ultralight" aircraft contribute towards your license in Canada? I'm interested in the business possibilities of offering flight training in Southern Ontario, in particular using advanced ultralight aircraft. I realize that this is uncommon, of course, but my question is one of regulations.
How many hours flying an advanced ultralight aircraft can count towards a student's:

Recreational license?
Personal license?
Commercial license?

I'm not sure how to read the CARs here in 421. Would a Pipistrel Alpha Electro (classified as an Advanced Ultralight in Canada) or Pipistrel Velis count as "aeroplane"?

It looks like you can count the flight hours towards a recreational license if you logged the hours in an advanced ultralight with an aeroplane certificate of airworthiness.
For the private pilot license only 10 hours in three-axis ultralights can be counted.
For a commercial ticket a maximum of 25 hours pilot-in-command flight time in three axis ultra-light aeroplanes can be counted towards the 200 hours total flight time requirement but this time does not count towards the 100 hour pilot-in-command flight time.
This is based on my cursory reading of the requirements. I would suggest you talk to a reputable flight training organization or Canadian aviation authorities for confirmation.


What is the purpose of flutter testing? All I am aware of is that flutter testing involves the aircraft shaking violently. How is a flutter test performed and what is its purpose?

Flutter is a phenomenon that can occur when a structure is subjected to aerodynamic forces. It occurs not only in aircraft but also for example in buildings, power lines, road signs and bridges. Flutter is an oscillation caused by interaction of aerodynamic forces, structural elasticity and inertial effects.

Perhaps the best known example of flutter is the bridge over the Tacoma Narrows ('Gallopin' Gertie')  that collapsed due to flutter in gale force winds.

Flutter in aircraft causes the wings and / or stabilizers to oscillate.
When the airspeed increases the energy added in each oscillation to the structure by the aerodynamic forces increases. At some speed the damping of the structure may be insufficient to absorb the energy increase from the aerodynamic loads and the amplitude of the harmonic oscillations will grow until the structure breaks.

A flutter test is performed to determine what speed flutter occurs yet is still damped. Theoretically an aircraft should be able to stay structurally intact up to the design dive speed ($V_d$) which is at least 1.4 times the design cruise speed. In flight tests, the $V_d$ is not always demonstrated as this is very risky since there would not be any margin from breaking up. The maximum speed is slowly increased in subsequent flight tests with careful data analyses in between up to a point where the test team decides that it is no longer safe to continue. This establishes the maximum demonstrated dive speed ($V_{df}$); the published maximum operating speed ($V_{mo}$) and never-exceed speed ($V_{ne}$) are well below $V_{df}$ to give margin from disaster.

This video shows flutter in a Hawker 800. The incident occurred not during testing but was caused by inadequate fitting of the ailerons(FAA PDF).


Why don't they build airplanes from 3D printer plastic? I'm not an expert in this field.

My assumption is that there are plastics lighter and stronger than the materials used to build planes. So that would make plane lighter and thus would consume less fuel which pollutes less and so on.

Maybe it would be more maneuverable, go faster, be safer as you may be able to safely land it with a number of parachutes in case of engine failure for example.

If these are true, why are planes not built from such a lightweight plastic?

My assumption is that there are plastics lighter and stronger than the materials used to build planes.

That is not a correct assumption.

Typical 3D printer plastics have a best-case tensile strength of 45-50 MPa.
Aluminum 7075, a common aerospace alloy, has a tensile strength of 500-570 MPa.

After dividing by specific gravity, that's at a 1:4-1:5 ratio of specific strength in favor of metal. There is no significant application in which 3D printer plastics, the properties of which are driven by viscosity, adhesion, and other printing qualities, would offer better strength-to-weight than aerospace metals and fiber-reinforced composites.

Some amount of 3D-printed plastics will likely appear in cabin interiors, for low-volume parts or complex hollowed-out parts, not subjected to significant stresses. But load-bearing parts require high strength and high strength-to-weight ratio. If it's too heavy, it won't take off, and if the material's too weak, it won't stay in one piece.

So the brief answer is, they don't build airplanes from 3D printer plastic (or clay, or plaster, or thatch) because they want them to fly.


When can I start an approach if I lose comms and my clearance limit is not an initial approach fix? Here is the AIM's definition for a clearance limit:

CLEARANCE LIMIT− The fix, point, or location to which an aircraft is cleared when issued an air traffic clearance

Assume a clearance such as:
"Cleared to Los Angeles Internal Airport (KLAX) via..."
This means our clearance limit is KLAX.
But what does this mean if I follow the instructions in 91.185?

If the clearance limit is not a fix from which an approach begins
[it's not], leave the clearance limit at the expect-further-clearance
time if one has been received [it hasn't], or if none has been
received, upon arrival over the clearance limit

A pilot should fly until the last fix on the route and then direct to their clearance limit: KLAX at their last assigned altitude (let's assume FL280).

and proceed to a fix from which an approach begins

Now fly direct from KLAX, with no assigned route, to an Initial Approach Fix (CRCUS or SEAVU).

commence descent or descent and approach as close as possible to the
estimated time of arrival as calculated from the filed or amended
(with ATC) estimated time en route

Hold at SEAVU or CRCUS (for which there is no published hold--so they can make one up), UNTIL their ETA into LAX. Then, descend in the hold and fly the approach. Or, realizing these fixes are 35nm away from KLAX, would a pilot turn around half way between SEAVU and KLAX to return to SEAVU at their ETA to descend?
Is that crazy to anyone else? To follow this regulation, a pilot would fly over their destination airport and then return to an IAF to do an approach. Does ATC really want us to do this in a lost comm situation? At a minimum, this doesn't seem like a prudent use of fuel which brings safety of flight into the mix.
When and where can I legally start an approach in this scenario?

Note: this may be a dupe of this question. However, you seem to be saying that you've read and understood the regulations on what to do, you just don't believe that ATC or the FAA really expects you to follow them.

In the scenario you describe you are indeed expected to fly from the airport to an IAF before beginning an approach. There's a long and detailed article in IFR Magazine about clearance limits, which discusses the regulations and the practical options. It makes a similar point to yours about lost comms:

Since the clearance limit is the
destination airport, very few approaches start there. An airport is
never used as a fix in IFR. A fix is an intersection, waypoint or
NAVAID. Moreover, receiving an EFC time in advance is simply silly.
This would also presume the issuance of holding instructions. Why
would a controller issue these things since lost communication cannot
be predicted?

It also acknowledges that many pilots share your opinion on the lost comms action:

Many pilots disdain these rules as onerous, unnecessarily
time-consuming and complex.

The article then notes that there have been multiple attempts to change the FAA's mind:

Since 2009, there have been about five challenges to this rule. In the
latest iteration, our past editor, Jeff Van West, wrote the Office of
Chief Counsel in late 2017, arguing that 91.185 (c)(3)(ii) is
inconsistent with current air traffic practices and creates an
unnecessary hazard.

But, you can read that 2017 legal interpretation yourself and you'll see that the FAA really does expect pilots to follow the regulation as written:

As you correctly state in your letter, the requirements of §
91.185(c)(3)(ii) are rarely in effect thanks to the improved technology ensuring that communications between pilot and ATC are not
lost. However, the requirements of (c)(3)(ii) are necessary to ensure
the safety of the NAS when a pilot is unable to communicate with ATC.
[...]
we affirm our previous interpretations of § 91.185(c)(3).

So that's the official answer for now (unless I missed a more recent interpretation).
Finally, if you want an alternative course of action, IFR Magazine's suggestion is to fly from the airport to an IAF and then invoke emergency authority to start a descent immediately, without holding:

ATC does not want you flying a holding pattern while it’s diverting
traffic everywhere to avoid a conflict. You have unintentionally shut
the airport down. When you reach an IAF of your choosing, ATC will
know which approach you intend to use. At the IAF, use your emergency
authority and begin descent.

That complies with the regulation and although it burns more fuel your priority should be acting predictably and landing safely. An IFR reserve should be plenty to allow for the extra flying time: KLAX to SEAVU is about 45NM, which isn't much time at jet speeds.


Can I use radar service instead of DME or GPS for this ILS approach? At the top of this approach chart for KDNN in the briefing section, it is stated that "Simultaneous operation of I-DNN and GQO DME required."

If my aircraft is not RNAV/GPS or DME equipped can I fly the full ILS approach and rely on "Radar" to identify ROLTE INT (IF)?

Tl;dr: This is really an edge case and I can’t come up with any specific wording that says “yes” or “no”. But from the following info I’d say you cannot unless ATC authorizes it.

Since the chart specifically indicates it as required it would be illegal to use the approach. Paragraph 5-5-4 a 2 of the AIM lists under pilot responsibilities:

  Follows the procedure as shown on the IAP, including all restrictive notations

But according to this answer ATC can approve an approach even when some equipment is inop. The answer seems to be concerning inop. NAVAID equip, rather than inop. equipment on the aircraft. Also, the section of the AIM he refers to (5-4-7d) does not include what he says. Paragraph 5-4-6d states:

  The name of an instrument approach, as published, is used to identify the approach, even though a component of the approach aid, such as the glideslope on an Instrument Landing System, is inoperative or unreliable. The controller will use the name of the approach as published, but must advise the aircraft at the time an approach clearance is issued that the inoperative or unreliable approach aid component is unusable.

This would suggest that ATC can approve an approach with inop. equipment.

If you consider telling you when you arrive at ROLTE to be “vectoring” then ATC can give you vectors as far as the FAF. FAA order JO 7110.65W, which gives instructions for ATC indicates in paragraph 5-9-1 a 2.

  If specifically requested by the pilot, aircraft may be vectored to intercept the final approach course inside the approach gate but no closer than the final approach fix.

Note that where you have highlighted “RNAV 1-GPS or RADAR or DME REQUIRED” is on the IAF at GQO, but not on ROLTE. This would indicate to me that you can count on any of those to get you to the IAF, but not beyond it. The word RADAR on the chart at ROLTE and EWADA indicate that those fixes are depicted on the ATC radar screen. This would certainly make it possible for them to tell you when you’ve reached the fix, but I don’t know if you can count on them to do it. And without that or DME you would have no accurate way of identifying the FAF. They may not have time to monitor you after you’ve reached the IAF, so that’s why I say it would require ATC approval.


What is the step-by-step process to become a ground instructor in the US? I would like to know about the whole step-by-step process to become a ground instructor in the US.

My understanding is that any previous pilot or CFI certificates are not needed. So, are only needed the FAA written tests (FOI/BGI/AGI/IGI)? And that's it? What about endorsements?

After passing the FAA written test, do I need to submit an application in the IACRA system to request the card, or it is done automatically?

You may want to check out this document from the FAA also linked in that document is this document which may shed more light on the matter

  The general qualifications for an Instructor Rating require you have a
  combination of experience, knowledge and skill. Title 14 of the Code
  of Federal Regulations (14 CFR) part 61 requires that pilots must be
  able to read, write, speak, and understand the English language. If
  you cannot meet these requirements of English fluency, an airman
  certificate cannot be issued. For medical reasons, an appropriate
  limitation may be placed on the certificate.

  You must pass the Fundamentals of Instructing Knowledge Test and a Flight or Ground
  Instructor Knowledge Test specific to the instructor rating sought.
  You may take these tests on the same day, and you do not have to take
  them in any particular order. An instructor rating obtained by passing
  the Military Competence Instructor (MCI) exam does not require the
  candidate to take the Fundamentals of Instructing (FOI) exam.

  When
  applying for any additional instructor rating, you are not required to
  take the Fundamentals of Instructing Knowledge Test again. Once you
  have acquired a Flight Instructor Certificate, you are eligible to
  give ground instruction required for a Pilot or Instructor Certificate
  or rating, based on the ratings on your Flight Instructor Certificate.
  Because of this, it is not necessary to obtain a separate Ground
  Instructor Certificate since you would already have these privileges.

AskACFI breaks it down nicely here.


Is it OK to decorate a log book cover? I'm a student pilot and am thinking about putting a tasteful decal on my log book, if for no other reason than to identify it as my own.  Is that OK, or would that be frowned upon?  Thanks.

I don't belive there is any regulation against it. Keep in mind you may need to show the book to officials at some point so keeping it professional is not a terrible idea

  (1) Persons must present their pilot certificate, medical certificate,
  logbook, or any other record required by this part for inspection upon
  a reasonable request by -

  (i) The Administrator;

  (ii) An authorized representative from the National Transportation
  Safety Board; or

  (iii) Any Federal, State, or local law enforcement officer.

The FAA is more concerned with what you log than what's on the cover of your book. I can't say I have ever seen a log book with a bedazzled cover but I'm sure they are out there. If you are talking about putting a decal that says "Ryan's Log Book" across the cover, that's fine, but a giant glow-in-the-dark unicorn sticker might get you some looks although technically OK.


How do "tip jet" helicopters cancel the torque effect of the main rotor? Some helicopters use "tip jet" on the rotor blades tips such as the McDonnell XH-20 Little Henry and Hiller YH-32 Hornet.

How do they cancel the rotor torque (often canceled by the tail rotor)?

This is a basic physics question, involving Newton's third law of motion  (For every action, there is an equal and opposite reaction.) When a centrally mounted engine applies force to turn the rotor, the equal and opposite reaction creates torque on the fuselage.  With a tip jet, the force is applied by the jet shooting its exhaust perpendicular to the blade, so the reaction is that the blade moves in the opposite direction.

So the answer is that tip jets don't CANCEL the torque, they simply don't create the torque in the first place.


What is the validity duration of FAA Medical for international flights? FAA Rule:

The duration of FAA medical certificates is specified in 14 CFR 61.23.

An example would be for:

A first-class medical certificate
Applicant is under age 40
Applicant is an airline transport pilot certificate for pilot-in-command privileges

In this case:

  Then your medical certificate expires, for that operation, at the end of the last day of the 12th month after the month of the date of examination shown on the medical certificate.

So this clearly states that if I pass my medical on January 1st 2014 then my medical is good until the end of the day on January 31st 2015.

ICAO Rule:

However, I have been told that ICAO rules state that the medical expires 12 months to the day from when it was issued, which would mean that it would no longer be valid as of January 1st, 2015.  (A reference for this would be great.)

Question:

As the holder of an FAA pilot license, with the above FAA issued medical, may I legally fly outside of the US after January 1st 2015 (but before February 1st 2015)?

I believe the ICAO regulation you are thinking of is this one:

  Excerpts from ICAO Annex 1- Personnel Licensing

  “1.2.5.2 Except as provided in 1.2.5.2.1, 1.2.5.2.2, 1.2.5.2.3,
  1.2.5.2.4 and 1.2.5.2.5, a Medical Assessment issued in accordance with 1.2.4.5 and 1.2.4.6 shall be valid from the date of the medical
  examination for a period not greater than:

  60 months for the private pilot licence — aeroplane;  12 months for
  the commercial pilot licence — aeroplane;  12 months for the airline
  transport pilot licence — aeroplane;”

  It also indicates the following in a note:

  “Note 2 — When calculated in accordance with 1.2.5.2 and its
  sub-paragraphs, the period of validity will, for the last month
  counted, include the day that has the same calendar number as the date
  of the medical examination or, if that month has no day with that
  number, the last day of that month.”

  In ICAO Annex 1, 2.4.1.6, the medical requirement for a commercial
  pilot is prescribed. It states:

  “2.4.1.6 Medical fitness

  The applicant shall hold a current Class 1 Medical Assessment.”

  In ICAO Annex 1, 2.5.1.6, the medical requirement for an airline
  transport pilot is prescribed. It states:

  “2.5.1.6 Medical fitness

  The applicant shall hold a current Class 1 Medical Assessment.”

  “6.1.1 Classes of Medical Assessment

  Three classes of Medical Assessment shall be established as follows:

  a) Class 1 Medical Assessment; applies to applicants for, and holders
  of:  — commercial pilot licences — aeroplane and helicopter  — airline
  transport pilot licences — aeroplane and helicopter  — flight
  navigator licences  — flight engineer licences

  b) Class 2 Medical Assessment; applies to applicants for, and holders
  of:  — private pilot licences — aeroplane and helicopter  — glider
  pilot licences  — free balloon pilot licences

  c) Class 3 Medical Assessment; applies to applicants for, and holders
  of:  — air traffic controller licences.”

However, ICAO is not involved in enforcement but rather coming up with standards, which would then be enforced (if adopted) by the member country's aviation authority.

From the FAA:

  There are many differences to be aware of when flying outside the
  United States (U.S.). International Civil Aviation Organization (ICAO)
  rules prevail. Member states follow ICAO guidelines as published, with
  differences noted, in their official Aeronautical Information
  Publication (AIP).
  http://www.faa.gov/air_traffic/publications/ifim/intl_overview/

For example, the EASA (European Aviation Safety Agency) has rules very similar to the FAA:

  MED.A.055  Validity, revalidation and renewal of medical certificates
  (a)  Validity  (1)
  Class 1 medical certificates shall be valid for a period of 12 months.
  (2)
  Notwithstanding to paragraph (1) the period of validity shall be reduced to 6 months for pilots
  who:  (i)
  are engaged in singlepilot commercial air transport operations carrying passengers and
  have reached the age of 40  (ii)  have reached the age of 60
  (http://easa.europa.eu/rulemaking/docs/npa/2008/2008-17/NPA%202008-17c.pdf)

However, according to this report: http://dspace.mit.edu/bitstream/handle/1721.1/35725/FlightOpsICATfinal2.pdf,

  Air carrier operations are generally regulated by the country of
  registration and the sovereignty in which the operation is conducted,
  including the Federal Aviation Administration (FAA) in the USA and the
  Joint Aviation Authority (JAA) in Europe. International flights may
  also fall under the jurisdiction of ICAO (International Civil Aviation
  Organization) when operating abroad (U.S.-based carriers are governed
  by both FAA  and ICAO regulations when conducting international
  operations.)

So you might be legal until you hit the international waters.  At the very most you might be able to go abroad, but then not be legal to fly back.

The National Business Aviation Association (NBAA) recommends that pilots comply with the strictest interpretation of the law (so in this case, have the appropriate compliance with ICAO standards) to avoid having to explain the nuances between the two sets of regulations.
(http://www.nbaa.org/admin/personnel/medical/medical-certificates.php)


Why is a clock necessary for IFR? According to FAR 91.205 (d)(6), one instrument required for IFR is:

  A clock displaying hours, minutes, and seconds with a sweep-second
  pointer or digital presentation.

Why is it necessary to time things in the cockpit, or know the time?

There are several reasons:

For departure clearances. An IFR clearance may have a void or release time so that clearance is only valid between certain times.
For holding pattern legs. A standard holding pattern is based on a time of one minute at or below 14,000' MSL and 1.5 minutes above 14,000' MSL on the inbound leg.
For holding pattern clearances. Holding instructions include an EFC (expect further clearance) time, so that if you have a communication failure while holding then you know when you can safely leave the hold and start an approach.
For timed approaches, where an aircraft is cleared to start an approach at a specific time
For timed turns. A standard rate turn is 360 degrees in 2 minutes, so with only a timer and a turn coordinator you can turn a specific number of degrees.
For en route reporting and general time/distance calculations. Especially in a non-radar environment (i.e. when ATC can't see you on radar) you may be required to give ATC actual or estimated times for passing certain fixes. (This is not strictly IFR only, but it's still relevant.)

All of these scenarios are discussed in detail in the FAA's Instrument Flying Handbook and in the AIM.


Does the speed of the air molecules matter in aircraft performance? Does the fact that air molecules move slower in cold weather and faster in hot weather also affect the aircraft's performance or no? So if its cold there is a higher chance or air molecules hitting the wing and engines because the air molecules are compacted and slow moving and in hot weather they are spread out and faster moving, so less of a chance of air molecules hitting the wings and going into the engine. So in cold weather the molecules move slow and in hot weather they move faster, does this also effect aircraft performance. I know that the fact that in cold air the air is more compacted and that increases aircraft performance but does the fact that it moves slow also have an effect on aircraft performance? Same with hot air, the air is more spread out which reduces aircraft performance but does the fact that the air molecules are moving fast have an effect on aircraft performance?

In some sense, yes it does.  But we usually don't think about it in those terms.  You usually only need to think about individual air molecules when the object you are talking about is very small.  For example, if you are trying determine the aerodynamics of an airplane whose length is 1/100th diameter of a human hair, then you might start caring about individual air molecules. For realistic sized planes, the planes are so big relative to the air molecules that we can just pretend that air is continuous. So instead of thinking about the motion of individual air molecules, we think about continuous variables such as density and temperature.  i.e. when your air molecules "spread out and faster moving" we say that is a higher temperature with a corresponding lower density, and when they are "compacted and slow moving" we say that is lower temperature and a higher density.  By doing that, we've taken the motion of a quadrillion individual air molecules and reduced it down to one single number. And that one single number, density, does have an affect on aircraft performance.

For completeness, you also sometimes need to consider individual air molecules at very low pressures.  e.g. if your air pressure is a millionth of an atmosphere, then there are not many air molecules to go around and so each individual molecule's motion becomes more significant.  But airplanes generally do not fly at such low pressures.  Even at 40,000 ft, there's a lot more air pressure than that.


What would happen if you turn on all air vents simultaneously? Sitting on the plane yesterday, wanting some fresh air and boom it hit me [literally]. What would happen, let's say both static and mid flight, if everyone turned on there air vents at the same time?

Could the unit handle all of it simultaneously, would it effect pressure, I'm not privy to the working of air units of aircraft so it may be a silly question but it's still a question that I'm interested in knowing the answer to.

@Casey is correct. Nothing will happen under normal operating conditions. The FAR §25.831 Ventilation requires,

  ... the ventilation system must be designed to provide each occupant with an airflow containing at least 0.55 pounds of fresh air per minute.

In general, the amount of air available is far greater than the requirement. On the ground, compressed air for the Environmental Control System, which supplies air to crew and passengers can be obtained from an APU, a GCU, airport high-pressure hydrants, or the aircraft engines. In flight, however, compressed air is obtained almost exclusively from the compressor stages of the aircraft engines.

The pressure would not be affected by this. According to FAR §25.843, Tests for pressurized cabins, the pressurized cabins are tested to show the performance of

  ... the pressure supply, pressure and flow regulators, indicators, and warning signals, in steady and stepped climbs and descents at rates corresponding to the maximum attainable within the operating limitations of the airplane, up to the maximum altitude for which certification is requested.

Note that in some aircraft the air conditioning system is switched off during climb- this is to do with the load on engine and not the air supply.


Why does the A320’s maximum allowable aileron deflection decrease, rather than increase, when the flaps are extended? According to this answer to why the A320 uses mainly spoilerons for roll control during landing, rather than conventional ailerons, the ailerons can’t extend as far when the flaps are extended, for fear of stalling the wing:

Downward aileron travel must be restricted when flaps are deflected. Since flaps change the local incidence on the flapped part of the wing, the outer wing will experience an increase in its local angle of attack. The increased suction over the inner wing will accelerate not only the air flowing over the inner wing, but also that air which will flow over the outer wing as well. Left to itself, the outer wing would stall if powerful Fowler flaps are deployed on the inner wing.
Adding slats will push the stall angle of attack up, and now the outer wing is back in business. However, if the aileron is deflected downwards, the stall angle of attack is reduced again. The outer wing could stall simply due to the aileron deflection!

Which would make sense - after all, if the trailing edge of the wing is already angled more down than usual, then it can’t safely extend as far further down for roll control than it would be able to do otherwise - if not for the fact that the ailerons aren’t located on the portion of the wing with the flaps on it (they’re located near the wingtip, where they’ll be more effective at rolling the aircraft, whereas the flaps are located near the wing roots, where there’s more space to store them and they won’t increase the bending stresses on the wing as much), and, since extending the flaps increases the amount of lift produced by the wings at a given speed and vertical load factor, thereby allowing the aircraft as a whole to fly at a lower angle of attack than it would be able to do with the flaps retracted, the A320’s allowable aileron deflection should increase when the flaps are extended, since the lower attack angle of the unflapped, aileron-containing portion of the wing should allow the ailerons to deflect further without stalling.  Indeed, the A320’s direct competitor, the 737, exhibits precisely this behaviour, where higher flap settings increase the allowable aileron deflection (and, thus, the lateral control authority available) for a given indicated airspeed and vertical load factor1 - so why does the A320 behave in precisely the opposite way?

1: This means, for instance, that the 737’s crossover airspeed, like that of essentially all aircraft, decreases as the flaps are lowered, whereas, if the aforementioned quote were accurate, the A320’s crossover airspeed would increase at higher flap settings!

You assume that

  the lower attack angle of the unflapped, aileron-containing portion of the wing should allow the ailerons to deflect further without stalling.

but that only looks at the geometric angle of attack. What counts, however, is the induced angle of attack. Since the flaps on the inner wing create much more lift, the induced angle of attack is much higher than for the clean configuration at the same geometric angle of attack. Consequently, the outer wing will stall at a much lower geometric angle of attack, and adding trailing-edge-down aileron deflection will stall the outer wing with only a medium angle.

Add to this that the spoilers are much more effective for creating rolling moments once the flaps are deployed and will avoid the adverse yaw of an aileron deflection due to their high drag on the down-going wing, and the spoilers are a much safer option for roll control that the ailerons are in landing configuration.


Is there a minimal legal ground clearance to use an international airport? The question arises while I was looking at the evolution of the B737 engines and the lower and lower space available between ground and engines. Then I realized that ground clearance is also low for other small airliners we can find in international airport (e.g. Embraer 175, ATR-42,...).

I imagine ground clearance is designed taking into account tailstrike, FOD, runway irregularities.

My question is: can an aircraft legally be excluded from using an airport because of its ground clearance?

Let's restrict this question to international airports and airliners transporting at least 8 passengers

For propellers, there is a minimum ground clearance according to the EASA Easy Access Rules for Normal, Utility, Aerobatic and Commuter Category Aeroplanes (CS-23):

  CS 23.925 Propeller clearance

  Propeller clearances with the aeroplane at the most adverse combination of weight and centre of
  gravity and with the propeller in the most adverse pitch position, may not be less than the following:

  (a) Ground clearance. There must be a clearance of at least 18 cm (7 in) (for each aeroplane with
  nose wheel landing gear) or 23 cm (9 in) (for each aeroplane with tail wheel landing gear)
  between each propeller and the ground with the landing gear statically deflected and in the
  level, normal take-off, or taxying attitude, whichever is the most critical. In addition, for each
  aeroplane with conventional landing gear struts using fluid or mechanical means for absorbing
  landing shocks, there must be positive clearance between the propeller and the ground in the
  level take-off attitude with the critical tyre completely deflated and the corresponding landing
  gear strut bottomed. Positive clearance for aeroplanes using leaf spring struts is shown with a
  deflection corresponding to 1.5g.

  (b) Aft mounted propellers. In addition to the clearance specified in sub-paragraph (a) an aeroplane
  with an aft mounted propeller must be designed such that the propeller will not contact the
  runway surface when the aeroplane is in the maximum pitch attitude attainable during normal
  take-off and landings.

So 18cm seems to be the minimum ground clearance for propellers on most aircraft (e.g. ATR-42).

It is hard to prove a negative, but the section about turbojets and turbofan engines does not list any minimum.


Based on this fuel flow chart, why isn't it more optimum to remain at an intermediate altitude rather than climbing? I am having a bit of confusing as to why people say planes gets more efficient as they fly higher. Because on a typical long haul flight the Fuel Flow of the aircraft will obviously be much more that when it was lighter as it was heavy but my main question is since aircraft FF decrease with weight but at the same altitude isn't it more efficient to keep flying at the same altitude instead of climbing further? Here below are some charts on the B737 FF getting lesser with the altitude as it gets lighter. Notice how the FF goes up as you climb higher even though its lighter. Looking at the charts I suppose isn't it more efficient to keep flying at the same altitudes? Can anyone help me clarify this? Thanks

When airplane mass, altitude, N1 (engine spool speed) and Mach number change together, it is very hard to come to a meaningful conclusion what is better for fuel flow. However, you see that the grey boxes tend to show the smallest fuel flow and they sit at the upper altitudes, so altitude seems to help. Going above 90% N1, however, seems to increase fuel flow again.
With increasing altitude, the flight Mach number needs to be increased to keep indicated airspeed constant. I expect that the chart lists trim points at or near the optimum polar point for cruise, at least that is what the almost constant indicated airspeed for each mass suggests. With increasing Mach, drag goes up but so does the distance covered per time, so there is again an optimum where the transsonic drag increase is still tolerable and outweighed by the higher speed over ground.
Therefore, higher flight speed is one reason why airliners like to climb to the tropopause. But there is more:
The thermodynamic efficiency of a heat machine grows with the ratio of temperatures in its thermodynamic cycle. Since the lowest temperature is determined by outside air, and outside air temperature drops with altitude while the top temperature is limited by the engine's materials, flying higher improves the thermodynamic efficiency of the engines.


How much drag does a RAT deployment add? How much drag does a RAT deployment add?

I was watching a simulator video of an A320 dual engine failure at low height during climb out and one step in the protocol was the pilot manually deploying the RAT.

Simulator Video

Since he doesn't manage to make it back to the runway from his 2000 ft engine flameout run I was wondering if not deploying the RAT would make any difference due to reduced drag?

Would the on-board batteries and windmilling engines be able to provide sufficient power for control surfaces?

Also, are there real life incidents of a 2000 ft (or lower) dual engine failure that made a safe return to the runway? Sully Sullenberger's A320 had reached approx. 3,000 ft, yet he was forced to ditch rather than return.

Does the energy management differ drastically from type to type? i.e. Among dual engined aircraft would some be easier to land from a 2000 ft dual engine failure than others? For typical climb profiles, weights etc.

Since he doesn't manage to make it back to the runway from his 2000 ft engine flameout run I was wondering if not deploying the RAT would make any difference due to reduced drag?

No, because it deploys automatically. Note that in the video in the first attempt the step is not done because there is less time. It is probably included in the checklist just in case the automation didn't do it's job.

Nevertheless, let's try to estimate the drag. All I could quickly find about the RAT is that the attached electric generator provides 5 kW, but that should be enough. We need to take into account the hydraulic pump and power losses, but the generator wouldn't be insignificant part of the load, so we could guess that the turbine does not have more than 50 kW of drag.

Now potential energy is $E_p = mhg$, differentiating by time we get $P = v_{vert}mg$ and solving for vertical speed $v_{vert} = \frac{P}{mg}$. Taking some “median” weight of 60 t (A320 has MZFW 62.5 t and MLW 66 t) and substituting we get:

$$v_{vert} = \frac{50\ \mathrm{kW}}{6\cdot10^4\ \mathrm{kg}\cdot 9.8\ \mathrm{ms}^{-2}} \approx 0.085\ \mathrm{ms}^{-1} \approx 17\ \mathrm{ft/min}$$

So the deployed RAT increases the rate of descent by less than 20 ft/min.

Now the video mentions the best glide speed would be 205 knots (I suppose it is for the 1+F configuration; for clean it sounds too low, though I don't have a reference for this). Since the L/D ratio is around 18, that would give the total descent rate about:

$$v_{vert} = \frac{205 \mathrm{knot}}{18} \approx 11 \mathrm{knot} \approx  1150 \mathrm{ft/min}$$

Except, well, 18 is clean L/D. The L/D at 1+F is a bit lower. I don't have reference for that either, but something like 10–12 sounds right, so:

$$v_{vert} = \frac{205 \mathrm{knot}}{12} \approx 17 \mathrm{knot} \approx  1730 \mathrm{ft/min}$$.

That is about 100 times more. So the RAT might increase drag by 1%. It was very rough estimate, so it may be 2% or 0.5%, but it definitely isn't that significant.

  Would the on-board batteries and windmilling engines be able to provide sufficient power for control surfaces?

The training manual mentions that

  If engine wind milling is sufficient, additional hydraulic power may be recovered.

without saying at what speeds that would be, but generally the speed for wind milling engine restart are significantly higher that the best glide speed. I'd say the necessary speed would be more than 250 knots.

  Also, are there real life incidents of a 2000 ft (or lower) dual engine failure that made a safe return to the runway? Sully Sullenberger's A320 had reached approx. 3,000 ft, yet he was forced to ditch rather than return.

I can't find any other incidents involving dual engine failure on A320-family aircraft besides US Airways 1549. And I am not aware of any incidents on any other aircraft that would fit that criteria either.

It should however be noted, that flight 1549 likely had enough altitude to return to the runway—if the manoeuvre was executed perfectly. A small mistake and they'd crash into populated area since the airport is in the middle of a city. The Sullenberger's great airmanship was in that he chose the worse option that he was certain he can make over the better option where he was not.

  Does the energy management differ drastically from type to type? i.e. Among dual engined aircraft would some be easier to land from a 2000 ft dual engine failure than others?

Principally it's the same for any type. But since turn radius increases drastically with speed, slower aircraft can turn faster and thus could return from lower altitude.

Here's a related question that discusses the manoeuvre; and it's dangers: Is it even remotely feasible to turnback a single engine aircraft with an engine failure?


Is some sort of clearance, such as a clearance to enter nearby controlled airspace, required to legally fly in IMC in Class G airspace? In the US, is some sort of clearance, such as a clearance to enter nearby controlled airspace, required to legally fly in IMC in Class G airspace?
Or to put the question another way, in the US, may an instrument-rated pilot flying an IFR-equipped aircraft in Class G airspace violate the VFR cloud clearance requirements without an IFR clearance, without violating any FARs other than (the rather ambiguous and subjective) FAR 91.13?
Does it make any difference to the answer if the pilot is NOT following any specific established instrument approach or departure procedure?  For example, if the pilot is taking off from an airport for which no instrument approaches and departures have been established?  Or if the pilot is flying in one of those now-rare bits of airspace where the class G ceiling is well above 1200' AGL?

An FAA-appointed Designated Pilot Examiner has recently told me that it is legal to fly an airplane or glider in clouds in Class G airspace with no clearance, if the aircraft is appropriately equipped and the pilot has an instrument rating in airplanes.
On the other hand, here is a case, originally noted in an answer to a related question on ASE, where a pilot  who took off from
an uncontrolled airport into clouds without a clearance or
release from air traffic control (ATC) was found to not be in violation of FAR 91.155(a), the VFR cloud clearance and visibility requirements, but was found to be in violation of FAR 91.13(a), the prohibition against operating an aircraft "in a careless or reckless manner so as to endanger the life or property of another."  An interesting aspect of the pilot's defense in this case is his suggestion that by departing immediately after another aircraft which had received an ATC release and clearance, he assured himself that there would be no other IFR aircraft in the airspace above the airport 1.  Other aspects of the pilot's defense were the fact that  he broadcast his departure intentions on the Unicom frequency, and he monitored the ATC frequency for other traffic.
The FAA and NTSB did not find these arguments to be convincing.
There definitely seems to be a grey area here as to exactly what precautions, other than receiving an IFR clearance for adjacent controlled airspace, would satisfy the FAA as far as FAR 91.13 is concerned, in the context of operations in IMC in uncontrolled airspace.  Also, one can easily imagine situations that are clearly compliant with all regulations and all accepted practices, and yet clearly create significant risks, arguably more so than the case linked to in this answer.  For example, one could argue that any time any aircraft operates in IMC in uncontrolled airspace, this creates a significant risk of collision with VFR traffic which may be legally flying just outside the edges of clouds with no radio or transponder.  Yet IMC in uncontrolled airspace is an accepted practice-- many airports are located in airspace that is Class G up to at least 700' AGL, yet have established instrument approaches with minimum decision heights much lower than that.
Footnotes--
1-- Page 4 of the finding says that the respondent claimed that by following this procedure the respondent "assured himself that there would
be no other IFR aircraft in the controlled airspace above the
airport".  This may be a typo-- it should perhaps read "uncontrolled" rather than "controlled"-- since there seems to be no dispute that the respondent was able to observe the prescribed VFR minimums once he reached controlled airspace.


High performance endorsement in airplane modified by STC I had trained for my complex and high-performance endorsements in an airplane that was certified with an engine that does not meet high-performance criteria but had been modified by STC such that it did meet criteria.

The logbook endorsement mentions the model of the airplane and that it had been modified such that the aircraft produced more than 200 horsepower. The question is do I need to actually track down the STC information just in case of a ramp check or when going for a more advanced pilot certificate?

Edit:

This question was posted due to a conversation with a flight instructor who had balked at the legality of the endorsement. His argument essentially went like this:

1) If you have an aircraft with a "200 HP" factory new engine, you put it on a dyno, it generates 205 HP. It's still a "200 HP" engine as per the FAA.

2) If you have an aircraft with a "200 HP" engine, you do a top-of-the-line overhaul, you put it on a dyno, it generates 205 HP. It's still a "200 HP" engine as per the FAA.

3) If you have an aircraft with a "200 HP" engine, you apply an STC that changes the cylinder and piston configuration to intentionally generate 205 HP, you put it on a dyno and it does make 205 HP, now because the intent of the STC being to generate more than 200 HP and the FAA approval via STC as a "more than 200 HP" engine the aircraft only at this point meets the high-performance criteria.

His argument was that in cases 1 and 2, since the engine was not "modified" with the specific intent to generate more than 200 HP you merely won the horsepower lottery but it's still certified as a 200 HP engine. He had questioned whether the STC was intended to bring the power output above 200 HP or if it was just an accidental byproduct and it was still therefore certified as a 200 HP engine.

No.  All that’s required is that you received ground and flight instruction in an aircraft which meets the requirements for a high performance airplane in 14 CFR §§61.31 (f) and received an high performance endorsement from an authorized instructor in their logbook.  If the approved STC makes alteration to the engine such that the power out is now rated to exceed 200 bhp per the terms of the STC, then the airplane would be considered high performance under §§61.31.


Can instruments be fixed via a swift punch? I remember reading a book about private piloting techniques, (I can't remember the title; it has been so long; perhaps I can check my library history or something to see later), and I saw something bizarre.

The author was discussing instruments, and what to do in case of failures. He wrote something about how, in the case of a failure of a critical instrument, in a situation where you really need it, that one should punch out (or otherwise destroy) the glass of the gauge, to allow air into the system.

What?

Is there any way something like this could be useful, or at least theoretically logical? Can anyone deduce any sense out of this?

If the static port gets blocked in an aircraft with no alternate static port, you can break the glass of the VSI (Vertical Speed Indicator) to allow air from inside the cockpit in the static system. By doing this you will sacrifice the VSI in favour of the altimeter and airspeed indicator

Due to venturi effects, air inside the cockpit has usually a slightly lower pressure than the pressure measured by the static port outside your aircraft.

This causes your altimeter to indicate a higher altitude and the airspeed indicator will also indicate a greater speed. The VSI is useless after you break it.

Needless to say this does not apply to pressurized cabins nor to glass cockpits...

This works because the inside of the VSI contains a diaphragm in a pressure chamber. The diaphragm is connected to the static system through an unrestricted tube. The chamber is connected to the static system through a  restricted (calibrated) leak. If the static pressure changes, the pressure in the diaphragm  changes instantly, while the chamber pressure lags slightly behind. This causes the membrane to expand / retract which drives the needle on the instrument.

When the glass is broken, the chamber will be at the same pressure as the cockpit. Through the calibrated leak, the static system will be levelled with the cockpit pressure, but of course with a delay as well. The VSI will now work in opposite direction (if you didn't destroy the needle).

The inner workings of an IVSI

Some VSI apparently have the calibrated leak into the cockpit already. For such VSI's smashing the glass does not work. Here the diaphragm should be destroyed as well.


Do any newer production aircraft use venturis as a backup vacuum source? I began my flight training in a Cessna 120 with 2 venturis as the source of vacuum for my DG and TC. They worked well in flight.

Are there any aircraft with deployed/deployable venturis out there? Other than my 1946 vintage C-120 which is also my birth year.

Not as far as I know. Even Vacuum pump systems are quickly becoming a thing of the past. Electric AI's are available and I have seen plenty in use. However with glass cockpits making their way into general aviation AHARS units are becoming more and more common place over traditional vacuum systems. There are even some small drop in units intended to replace traditional vacuum systems like DG's and Attitude Indicators. Venturi vacuums, while simple have down sides like potential icing risks and needing sufficient airflow to function.


Do Blue Angels jets have a snap-to-angle feature in their control sticks? So, in most drafting/modelling software, we have a feature called Snap to Angle or Snap to Edge; its function is to snap the control(cursor) to the nearest most obvious angle/edge to relieve strain on operator to carefully move the cursor to that exact point.
If you haven't seen it try Right Click on Desktop > View > Align Icons to Grid & then move the icons around.

Now on to my question:
When performing the maneuver Opposing Knife Edge it is crucial that the roll angle (w.r.t. level) should be very close to ±90°.

Especially considering the high speed (& probably high G-Force) situations is a feature equivalent to CAD's Snap-to-Angle employed in air-show modified jets?

Short answer: No.

Long answer: No way!

This would be a feature which pilots would never accept and for good reasons.
There are many instances where you want to fly at a slight angle to exactly horizontal or vertical to make corrections. Just think of flying an approach with crosswind.

The designers have made the cockpit glazing transparent to enable the pilot to check and adjust his/her attitude, and this feature works really well. There is no need to add something which will be in the way of proper flying at some times.

What you do find sometimes on small aircraft with manual controls, however, is a trailing edge modification which helps with centering the rudder and/or the ailerons. See below for an example: This is the tail of the Klemm 35, and the rudder has two narrow strips which are deflected slightly to the left and the right, respectively. This increases the force gradient over deflection for the first few degrees when the rudder is moved away from its centered position.

Klemm 35 tail detail (own work)


Why aren't there simplified fly-by-wire helicopter controls? I was discussing helicopter control with relatives over the holidays, particularly regarding how difficult it is to fly one and how changing any control requires adjusting the other two main controls. One of my relations asked whether any helicopters have a computer control system that automatically compensates, allowing simplified controls that almost anyone could fly.

I replied that I had not heard of such a thing and could only guess why not:

Reliability concerns and possibly pilot training concerns (i.e., you'd have to know how to really fly in the event of a computer failure anyway, so why even have the computer?)
Subtle complexities of the control interactions not lending themselves to reasonable computer automation.

Are there actually no systems like this? Why not? Were my guesses any good?

Regarding the possible duplicate, I saw that question and it seems to indicate that automatic simplified controls would be possible, but it doesn't seem to fully answer the question of why not have a psuedo autopilot that allows a pilot to just push forward on the cyclic to go forward (for example) without having to constantly adjust the collective and rudder at the same time.

Helicopter manufacturers seem to have been slow to adopt fly-by-wire systems. I used to work in the General Dynamics group which designed the fly-by-wire system for the F-16. That was the first production aircraft which had full-authority fly-by-wire (without mechanical backup systems). By the time I started working there, they were in process of updating the system to incorporate a digital flight control computer. The production required extensive coordination between multiple disciplines. As an electrical engineer, I regularly interacted with software engineers, control-law designers, test engineers, and "mechanization" engineers. It took many years for the company to develop such a culture, where each member is concerned with the efficiency and safety of the aircraft. I speculate the helicopter manufacturers didn't catch up for a couple of decades because funding was limited.

Here is an article which describes the Army's experience: Army Slow To Adapt Fly-by-Wire Controls for Helicopters

Funding aside, helicopters are ideal candidates for fly-by-wire systems. The obvious goal is to take a marginally controllable aircraft and make it both stable and maneuverable. That would dramatically reduce pilot workload. Most helicopter fly-by-wire systems accomplish hands-free hover and decoupled control inputs (i.e. sideways flight without needing rudder inputs).

The first helicopter which demonstrated a great fly-by-wire system was the Sikorsky RAH-66. It even achieved sideways flight at 60 knots and backward flight at 25 knots, using only cyclic stick inputs. Unfortunately, that program was cancelled in 2004. The first production military fly-by-wire helicopter is the NHIndustries NH90, which was the first helicopter to fly without mechanical backup controls, in 2002, and entered service in 2007. The first civilian fly-by-wire helicopter, the Bell 525 is currently under development.


How can a private pilot prepare for a long cross country flight in an unfamiliar area? TL/DR: What are common preparation tips or techniques for low-hour private pilots planning long cross country flights in unfamiliar territory?

I got my private pilot's license in November 2016 in Hawaii. I've since moved back to the mainland to continue working and flying here. I'm currently in Phoenix and have been checked out for Cessna 172 rentals at a local airfield.

Over MLK weekend (Jan 14-16) if the weather is nice I hope to fly from Glendale (KGEU) to San Luis Obispo (KSBP) then to Rancho Murieta (KRIU) near Sacramento, and back to Phoenix. My girlfriend plans to come with me and I want to do everything that I can to prep and plan this flight to minimize our risk.

I have about 75 hours total time, mostly in 172s and DA40s and all my cross country time has been on the Hawaiian islands where it is nearly impossible to get lost and there are few airspaces enroute.

I'm very comfortable with VOR navigation but I'm not yet accustomed to the smaller Garmin G430 GPS unit in the Cessna here (I'm spoiled, used to the G1000) so I don't want to stress with the GPS unit.

I'm most concerned with the strength of my pilotage and dead reckoning and whether they are up to the task, especially considering that this will be my first flight in the region. Since VOR is line-of-sight and there more than a few mountains in the region I want to feel confident that I can get us there safely in case the VOR signals aren't being received for the duration.

I have the routes planned, altitudes selected, waypoints and frequencies written down, performance planning and W+B done, etc. and I plan to speak with my local flight instructor to go over all of these materials before the flight.

In any case, it would be great to hear additional tips/tricks/things to be aware of/mistakes that you made early in your flying career so that I can be as prepared as possible moving forward!

I'm in a similar boat to you and I just did my first XC from KDYL to KDDH a few months ago. Which was the first time I had been to an airport I did not go to during training. It was a lot of fun but here are a few things to consider,

Get the G430 simulator as Ron mentions. You should always familiarize yourself with all systems in an aircraft before flying it. While you don't need to know the IFR capabilities of the 430 you should understand its VFR functions well. This video covers it well.

If you don't already use it, get ForeFlight or some similar app for your phone/tablet. This will provide you all the charts and calculations you need. Most pilots are using something like this these days but often times it's not allowed during training and many new pilots don't yet have it.

Use flight following if you can. If your instructor never went over that ask a local CFI about what it is, how to get it, and why you should basically always use it when you can.

Since it's a new airport for you, watch videos of others landing there to get an idea of what the terrain and airfield looks like.

If you have, or can get access to a simulator, fly the flight in the simulator using the intended aircraft so you have an idea of time, and basic terrain features en route.

Perhaps most importantly, this is no time to push your limits both physically and mechanically. Don't depart with "just enough fuel + minimums". Don't make this a "just above VFR minimum weather flight". You will most likely be flying a contiguous leg longer than you have flown yet, understand the human limitations in a situation like this. Understand that the plane has far more endurance than your body and understand when to say "I won't be making the flight today".

Most importantly, Have FUN!


Can a commercial pilot rent an airplane and use it for hire? Can the holder of a commercial pilot certificate rent an airplane (with a recent 100-hour inspection) from a fixed-base operator and use it to carry passengers for hire?
I believe the answer this is a "NO" since this pilot would be holding out by providing the airplane to the passenger, thus, this pilot would illegally be acting as a commercial operator / air carrier. Basically, the pilot and the airplane would be coming from the same source, even though the pilot doesn't actually own the plane and is renting it from somewhere else.
EDIT: Sorry, yes, I'm asking in regards to US regulations (FAA).

It doesn’t matter whether the pilot rents, leases or owns the plane; if they are offering “aviation services” to the “general public”, then they are “holding out” and would need an Air Operator Certificate.


Why don't rudders stall at 30 deg deflection, as they don't have downwash to reduce local AOA like flaps and horizontal tails do? Why don't rudders stall at 30 deg deflection, as they don't have downwash to reduce local AOA like flaps and horizontal tails do?

or do they?

I understand flaps and horizontal tails don't stall at 30 deg deflection as the downwash from the wing reduces the local Angle of Attack, so flaps and horizontal tails aren't seeing an angle of attack
 of 30 deg even though they are deflected by 30 deg.

However, there is no "vertical downwash" from the wing to help the rudder.  Why don't rudders stall at 30 deg deflection when most classic NACA airfoils stall at about 15-20 deg?

At an extreme deflection (like 30º) a rudder is probably stalled. But in that condition, lift does not entirely disappear, and drag increases a lot. The resultant of the two forces (the 'aerodynamic force') pushes the tail sideways, yawing the airplane. Hence, that stall doesn't matter much...


How does the U.S. Overflight Fee system work? After going through the Overflight Fees on FAA.GOV, the following is clear and self-explanatory:

Exact fees
Method of Payment (online, via Pay.gov as mentioned on the page).

What's not clear to me is the following:

  The FAA charges overflight fees to operators of aircraft that fly in
  U.S.-controlled airspace, but neither take off nor land in the United
  States.

Does this mean that international flights that land at any airport within the U.S. are not liable for overflight fees, and that they're only liable to pay the other fees such as airport charges etc.?
How is the invoice/bill delivered to the responsible party? I
believe airlines/commuters have accounts that get billed, but what
about private jet owners?
What would be the circumstances if, say a private jet owner/operator
departs from Canada, lands in Mexico and doesn't pay the invoice?
What if such a trip is made once a month for a long period of time
without paying the due fees. Does that jet "not get permission" to
enter U.S. Controlled Airspace?

Correct. Some countries charge overflight fees regardless of whether you land or not. In the US, overflight fees are charged per 100 nm. You can find the exact fees for 2017, 2018 and 2019 here. The fees can be paid online, and the FAA is pretty modern when it comes to this; it accepts ACH transfers from a US bank account, Amazon account, Dwolla account, PayPal and Debit or credit card.
The aircraft has to identify itself. The flight plan tells the FAA who you are. They look you up in the registry of the country in which your aircraft appears and send you the bill.
Unpaid fees accrue interest, and can result in the aircraft being denied entry into US airspace or impounded if it does happen to land at a US airport. The FAA can also put liens on the aircraft in the country of registration, which would have to be paid before the aircraft registration changes hands.


Minix wingtip vortices mitigation - How does it work? I stumbled upon this article: Minix wing tip device promises 6% gain in fuel efficiency for airliners.

Such an economy is appealing and I must confess the design is "sexy".

Could someone expand a little bit?

The tiny mass of air that this device can affect will in no way have the claimed effect on induced drag. This wingtip vortex pseudoscience is just bullshit. What can be observed as a vortex behind the wing is actually the consequence of the vortex sheet rolling up due to downwash behind a lift-generating wing. But air flowing around the tip has almost nothing to do with it.

I would compare it to those magnetic rings you are supposed to put around your fuel line to save fuel. Snake oil, in other words. There is no way this thing can reduce the wing's vortex, all it will do is to create some more local turbulence.

All it needs is a slick salesperson, a few gullible people with too much money and greed, a big promise, and the scam takes its course. This can easily yield enough investment money to allow all scammers to drive a Ferrari for a year or more. Now they have a year to come up with the next big thing.


Is the location of an aircraft spoiler really that vital? I was wondering that spoilers in most of the aircraft are always placed aft (towards the tail) the CG location. Why aren't they placed ahead of the wings or near the nose of the aircraft? The same is the case with parachutes. For small UAVs, the parachutes are either at the CG location or placed behind it. Is there a really strong design point to this method? Any suggestions/information would be appreciated?

Surfaces sticking out ahead of the Centre of Gravity act in an unstabilising manner: any dissymmetry will want to amplify itself. A dart thrown with the feathers first is in an unstable equilibrium and will very quickly turn around 180º.

Surfaces behind the CoG act as stabilisers, keeping the nose pointing forward. An aeroplane has vertical and horizontal tail surfaces at the back just for this purpose. When spoilers are deployed at low speeds, the aeroplane is in a situation where you don't want any destabilising moments.

Aerodynamic behaviour is stable if a disturbance auto-corrects: a deviation is automatically blown back. Since motion in flight is relative to the Centre of Gravity, it follows that the aerodynamic Centre of Pressure must be behind the CoG.


Is there any certification for Aircraft Security that Software Engineers can accomplish? I would like to ask you if there is any certification that Software Engineers can take for learning the fundamentals or more exeutive concerning the section of Air Safety and Security. I am talking about Safety protocols like DO-178C or DO-178B or any other.

*It doesn't really matter if it is going to be a US certification or a EU one.

Thank you in advance for your time.

I am unaware of any individual certifications for engineers related to avionics - security or general SW development. Caveat: This is based on my experience. That's 24 years of civil avionics development which followed a USAF career in R&D, mostly space systems. I'm an aero engineer by schooling and my work is primarily defined as 'systems engineering' and management.

Fundamentally avionics development is no different than any other product development. We define and develop hardware and software to perform specific functions on aircraft. The skills are essentially the same as the auto industry and even some consumer products. For the software side, this means real-time embedded applications -- not PC, web, or client/server apps.

The biggest differences to other markets is the level of regulation and the life span of the products. Everything we build has to be certificated as part of an aircraft under a Type Certificate (TC) or Supplemental Type Certificate (STC) or as an 'appliance' under a Technical Standard Order (TSO). And even then the TSO'd product installation has to then be certificated under the aircraft's TC or STC. Because of the regulations, change is expensive so the products tend to have a very long life span. There are updates along the way, but you very seldom see wholesale product redesigns until the product is almost unsupportable or there are changes in the regulations.

Certification is about demonstrating that the product complies with the rules. In the US, that's Title 14 Code of Federal Regulations. That means focusing the entire business to meet the rules. That includes internal development processes and procedures and a quality program that's compliant.

Industry standards such as SAE, RTCA, (and EUROCAE in Europe) are the basis for most of these internal procedures. RTCA DO-178C doesn't tell you how to write code. It sets a standard for a SW development process that will produce the necessary artifacts for certification and theoretically result in SW that meets the necessary level of safety and design integrity. The company has an internally defined software development process that is compliant with DO-178.

As for security, RTCA DO-326A, Airworthiness Security Process Specification provides guidance. It doesn't tell you how to build a secure system. It defines a process that will allow you to identify the security risks and ensure that you address the risks.

So what's the best way to learn the avionics business? Seek employment with an avionics company. Avionics is a niche business. There's no big educational pipeline to feed the industry. If you have the fundamental engineering skills and a willingness to learn, you can get a job in avionics. That was the basic criteria I applied when I was a hiring manager at my last employer.

As to the basic skills; For a SW engineer I would look for SW design and coding experience. Real-time embedded experience is a definite plus but not a deal breaker depending on the specific job. Most companies I'm familiar with use ADA, C, C++, etc. Getting familiar with the industry standards helps (and shows initiative) but it won't make you an expert.


Why was the engine of the Ju-87 Stuka not replaced with a more powerful one? Related to this question
Why did the Ju-87 Stuka have a siren?

I would like to know the reasons why they have not changed the engine of the Stuka when they realised it was easy prey for Hurricanes and Spitfires in 1942/43.

Couldn't they have replaced the engine with a bigger one?

It is a heavy aircraft, but certainly could have gone through some improvements in order to increase its speed and manoeuvrability.

Ok it is a bomber, not a fighter, but still...

The Ju-87 Stuka did undergo engine change during its life.

The initial Ju-87A version used the Junkers Jumo 210 A engine, which produced 602 hp. This was almost immediately replaced with Jumo 210D, which produced around 661 hp.

The first production version, the Junkers Ju-87 B-1 used a Junkers Jumo 211D generating 1,184 hp. Note this version had the fuselage and landing gear redesigned from 87A.

The next major version, the Ju-87D, used a Jumo 211J delivering 1,401 hp, after briefly dabbling with Daimler-Benz DB 603 engines.

The final operational version of Stuka, the Ju-87G, used the Jumo 211J engine.

This is more or less the same path followed by other combat aircraft of the era. For example the Hawker Hurricane MkI used a Merlin III engine producing 1,310 hp, while the last major version, the MkIV used the Merlin 24 (or 27) engines, producing 1,620 hp.

However, the main thrust in engine change in Ju-87 was increasing the payload, rather than increased speed or maneuverability like the Hurricanes. For example, Bomb carrying ability was nearly quadrupled from 500 kg in the B-version to 1,800 kg (max load) in the D-version.

Another reason was the aircraft design itself. It was designed to be a rigged dive bomber, and increase in speed would've done it no good (it is to be noted that the fixed landing gear added a lot of drag, though it was study enough to mount a cannon) and it had limited maneuverability at the best of times when loaded (though it had good turn performance at low altitudes). The airframe had reached its limit.

The only reason the Stuka served till the end of the war though its limitations had become apparent by the Battle of Britan was simply because no better replacements were avilable (though the process started in early 1940's), though the Focke Wulf 190 took over some of the duties of Ju-87.


Does my 1st class medical give me 2nd and 3rd class medical privileges after it expires? If a 35 year-old pilot were issued a 1st class medical on January 15, 2012, am I correct that that pilot would be able to exercise privileges requiring a 1st class medical until January 15, 2013? Or would they extend until January 31, 2013? The chart in 14 CFR 61.23 mentions something about it expiring on the last day, but I can't find that exact language anywhere but in the header row of the reference table.

Additionally, after the 1st class medical certificate expires, does it not afford the pilot the privileges of a 2nd class medical for the 60 months listed in 14 CFR 61.23? I'm looking for the part of the FAR that explains how medical certificates of a higher class afford the privileges of a lower class after their original designation period expires.

A first class medical issued to a 35 year old pilot on 15 Jan 2012 will let that pilot:

exercise privileges of an ATP certificate until 23:59 31 Jan 2013
exercise privileges of a commercial certificate until 23:59 31 Jan 2013
exercise privileges of a private, recreational, student or CFI certificate (if the CFI is acting PIC) until 23:59 31 Jan 2017

Your first class medical is always a first class medical -- you don't get private pilot privileges for 5 years because a first class medical grants third class privileges, rather you get private pilot privileges for 5 years because that is what a first class medical grants you.

These durations are from the table of 61.23 (d).  You don't see this language in the text above the table because they are not concerned with the duration of the privileges but only the minimum required medical class for specific operations.

For example, 61.23 (a)(2)(ii) says you must hold at least a second class medical to exercise the privileges of a commercial certificate and 61.23(d)(1)(iii) and 61.23(d)(2)(i) list the duration that each of an first and second class medical can be used to for this purpose.