Is the flight management system software independent from the hardware? Is it possible to 'mix and match' hardware and software from different vendors to make a flight management system? I want to prepare a study about FMSes and I can see that there are several independent software providers, does that mean their software can be installed on different hardware platforms?

If you are thinking of the analog of installing windows or linux on a given physical personal computer then the answer is more or less no. Not because its not possible but more because thats not how avionics are made or how the avionics pipeline has developed over the years. Avionics also work quite differently than your basic home computer as they are designed to be far more redundant and have far more real time conscious operations. You, as a user a free to run any software you like on your computer as its unregulated and does not matter if say one process blocks another, a process fails, a process produces erroneous outputs or a process all together destroys the machine, these things would not be great in avionics.

There are two basic flavors of avionics "software" components/updates:

Database updates:  these occur regularly when a new dataset is made available and update the waypoints, VOR's, Frequencies, and Maps in the system.

Database updates all ultimately contain the same information (generally speaking). Depending on where you are in the world the information is maintained by various regulatory authorities as well as some other companies. However to play nice with a given FMS the data may need to be delivered in a specific format. As far as I know there are no public FMS data formats and generally you need to get the database updates directly from the maker of the unit.

These could be interchangeable with some coordination but the various makers have a steady income stream from the updates so there is little incentive to change the model.

Data sets from someone other than the manufacturer will most likely not load and may come on the wrong card type or be incompatible with the loading system. Likewise not all units are capable of consuming/making use of the full data set.

Software Updates: these occur perhaps on a schedule or perhaps when needed and change the functionality of the system. Or if there is a bug in the system.

Avionics tend to be quite proprietary largely because it costs a lot of money to certify and design avionics on top of this manufacturers of avionics components have certain responsibilities to upholding certificates. If problems arise with the unit arise they may need to provide a fix, as such its simpler to have control over the whole unit, both soft and hardware. This also helps to cut down on the potential combinations of software/hardware units in the event of an issue either on the software or hardware side, it also absolves you from needing to certify all possible combinations.

One things thats very important is that due to the use case, avionics tend to blur the lines between hardware and software in terms of what is implemented where. Keep in mind that generally anything that can be implemented in code can be implemented in pure discrete logic. Similarly most things implemented classically in hardware can be modeled in software. As such the blurred lines and often tight coupling and required knowledge across the platform makes it almost required to do it all as one.

You can find a lot more about the FAA's hardware and software certification process here as well as some notes on avionics software here. There is also some decent tangentially related info in this answer.

This group seems to be building some kind of open source airplane with open source avionics and might be worth reading up on to see where they are at and how they went about doing it.

But its not all for naught, things like the ARINC standards have been developed allowing for the creation of Integrated Modular Avionics and pushed for standardizing at least parts of the equation and opening future possibilities of at least mixing and matching components.


How is the Density Altitude performance penalty split between propeller and engine? Let's say we have a Cessna 150 with a Continental O-240.

How is the density altitude performance hit split between the engine air intake and the propeller ability to "grab" the air.

Let's say I was able to put a engine on it that would not be affected by density altitude.

What would the remaining penalty be on the aircraft performance due to the propeller still being affected?

There is no reciprocating gas engine or gas turbine which is not affected by density altitude, the density of the air directly affects how much mass of working fluid can be taken in by the engine for a given volume of air and as a consequence the amount of power it can develop for a given fuel consumption.  The less dense the air, the less power or thrust the engine can develop.

Turbocharging or supercharging a reciprocating engine can maintain uniform power outputs for a throttle input provided the density altitude does not exceed the critical altitude of the turbocharger.  Turboprop and turboshaft engine are generally 'flat-rated' ie the fuel controller maintains a uniform power output right up to the thermodynamic rating of the gas generator at altitude.

As for propellors, the thrust they can deliver is directly proportional to the density of the ambient air, so higher density altitudes mean less thrust for a given power input from the engine.

Performance tables for both engines and propellors are available from the manufacturer and vary between make and models.  In general, pilots really don't use this as much as the aircraft performance tables in the POH for a particular aircraft.


What are the alternatives to XFLR? So, currently my team and I are working on a glider project for our senior design.
The design we've come up with causes XFLR to crash for some unknown reason (the issue seems to be at the root airfoil which is wedge shaped). What I would like to know is if there any viable alternatives to XFLR for airfoil and aircraft analysis that won't crash like XFLR does.

Edit: So the main goal of this project is develop an autonomous system to be used in hypersonic glide vehicles. While obviously we're not going to be making a hypersonic glider, my professor is insistent that it at least looks hypersonic. It needs to be able to glide for about 2000 feet after being dropped from a height of 300 feet.

My initial response is that, if you have a wedge-shaped airfoil on a glider, what sort of spec are you designing to?  Most of the time, gliders are low-subsonic aircraft with airfoils similar to Epplers, Wortmann FX, or 4-series NACAs, not wedges.  I associate wedges with massive flow separation or supersonic flows.  Can you provide a picture of what you're talking about, as well as a discussion of what you're designing to?  Also, are you attempting to produce a 3D analysis of a wing that, at its wing box, has this wedge-shaped airfoil?

That said, my short answer is this: XFLR is a panel-method solver, which means that it cannot deal with flow separation save by approximation.  As a result, shapes such as a wedge, which are quite prone to flow separation by virtue of their shape, are very hard, if not impossible, to analyze with these solvers.  Unfortunately, lower-order solvers (i.e., something short of finite-element or finite-volume methods, such as Fluent, CFX, etc.) bank on using these panel methods or other lower-order fluid flow equations that cannot handle flow separation.

If you want to try to accurately model flow separation, you'll need a higher order CFD solver, which brings with it additional complexity, cost, and headache--and getting accurate drag information is a tricky prospect.  There are some freeware solvers out there, but, by far, the most popular (and widely validated) is OpenFOAM.  This is a command-line program at heart, but there are some GUIs developed for it that you may be able to obtain for free or at a reduced cost, such as SimScale.  Some other packages are discussed here as well, if you'd like to have a look.

That said, what data do you need?  If all you need is a sectional drag coefficient, I would highly recommend a look through Hoerner's Fluid Dynamic Drag (not to be confused with his other text, Fluid Dynamic Lift), a vital reference that contains data from a plethora of experiments done on a multitude of shapes.  In it, he describes the drag force on objects from ellipsoids to cones to cylinders and more, all based on size, aspect, roughness, and Reynold's number.  There is an updated copy available, but I haven't found it online as of yet.


Do other countries create the equivalent of a TFR when US VIP's visit? In the US, there's a TFR everywhere a designated VIP (US president or vice president) is going to be. When (most?) foreign VIPs visit the US, I don't think there are TFRs in place for them (unless the location coincides with our VIPs).

Are there TFRs (or international equivalents) in other countries when the US VIPs are there?

Absolutely!  The same airspace restrictions that are in the US are regulated by the FAA and ICAO.  The FAA (or the US) is a signatory to the ICAO standards, and as part of that governing body instituted the same rules worldwide. Those restrictions are also issued through the NOTAM system.

Incidentally, flying in the UK, we had restrictions on where we could fly depending on where the Queen was flying (if our missions coincided with her flights).  They even had a rather unflattering name for those flights in the pilot community.

Here is an article that talks a little bit about th e roles and responsibilities of the Queen's pilots.

You can also check UK NOTAMS (although i don't see any current ones fo rthe Queen at the moment).


How does the FAA define day and night? For the purposes of regulations how do the FARS define daytime? Is it sunrise to sunset, civil twilight, astronomical twilight?

This question was asked before with regards to EASA rules, but FAA was not included.

Day and Night for Pilots

As pilots we often talk about night flying and daytime flying meaning when it is dark or light, but for logging time and for currency there are specific definitions that we must pay attention to.

FAR 1.1 General Definitions

Night means the time between the end of evening civil twilight and the beginning of morning civil twilight, as published by the American Air Almanac, converted to local time.

Day is not defined in the FARs but the definition of night implies that it is the time between the beginning of morning civil twilight and the end of evening civil twilight.

The Air Almanac is published annually on CD-ROM but you can find sunset, sunrise, and civil twilight times for specific locations at the US Naval Observatory website.

The time between sunrise/sunset and twilight is 26-30 minutes depending on the time of year. Since you can easily find sunrise/sunset information in newspapers, the weather channel, etc. you can estimate twilight fairly easily.

Currency
§61.57 (b) (1) … no person may act as pilot in command of an aircraft carrying passengers during the period beginning 1 hour after sunset and ending 1 hour before sunrise, unless within the preceding 90 days that person has made at least three takeoffs and three landings to a full stop during the period beginning 1 hour after sunset and ending 1 hour before sunrise, and…

VFR Weather Minimums
Only Class G airspace has different minimums depending on night and day and they use the standard night definition—end of evening twilight to the beginning of morning twilight.

Aircraft Lights
Aircraft lighting is required between sunset and sunrise.
§91.209 During the period between sunset and sunrise no person may 1. operate an aircraft unless it has lighted position lights, 2. park or move an aircraft in an area of an airport where night operations are being conducted unless it is clearly illuminated, has position lights, or is in an area marked by obstruction lights.

Aeronautical Experience Requirement
In order to obtain a private pilot certificate night training is required. The commercial pilot certificate requires solo night flights. In these cases the standard night definition—end of evening twilight to the beginning of morning twilight—applies.

Special VFR
AIM 4-4-6 g. Special VFR operations are prohibited between sunset and sunrise unless the pilot is instrument rated and the aircraft equipped for IFR flight.

Logging Night Flying Time
Logging of night flight should be made in accordance with Part 1 definitions, which is from the end of evening civil twilight to the start of morning civil twilight. This differs from the definition used for night currency.

Summary

Position lights – sunset to sunrise

Special VFR – sunrise to sunset unless instrument rated

Carry Passengers – 1 hour after sunset to 1 hour before

Everything else – twilight to twilight


How are performance variables accounted for when testing solar-powered aircraft? With so many factors that could affect performance (wind, visibility range (amount of light), angle of the sun, etc.), how do they accurately test solar aircraft flight time? Any tips for doing my own experiment for a small solar RC plane (vs non-solar of same type)?

Thanks for any help!

Usually when test results are potentially affected by many factors, standard test conditions are defined. When tests are performed under these standard conditions, the results can be compared between products.

Since these standard conditions rarely exists in nature, testing under standard conditions is not possible. Instead, a test programme is developed that tests under a number of non standard conditions to identify the effect of individual factors and correct for that. In addition, components of the system under test can often be tested in an isolated controlled environment. In this way, standard conditions can be achieved for individual components and the effect of deviations for the standard conditions can be determined as well.

For the example of a solar aircraft, the efficiency of the solar panels could be determined independent of the aircraft. The same holds for the battery, the engine, the propeller and other components that the propulsion system may depend on. Not only the performance under standard conditions can be determined, but also under non-standard conditions.

The power requirements of the aircraft under a range of conditions can be determined by test flights. This could involve horizontal cruise flight segments at various speeds, altitudes and temperatures, and also gliding tests.

The maximum achievable flight time under standard and non-standard conditions can then be calculated from the results of all the acquired test results, without ever having flown under these standard conditions.

For validation of the methodology used, a test flight can be done do determine the actual flight time under non-standard conditions. When the results of the test flight agree with the calculated flight time under the same non-standard conditions, one can assume that the methodology is correct.

For you own RC plane such a test programme is probably out of scope. A simple way to gather some data is to perform two flights with the same aircraft. Both time start with a full charge (I assume there is a battery involved). Test how long the flight last with the solar panels. For the second flight, disconnect the panels and see how long the flight last then. You now know how much the solar panels contribute in terms of power production. Then fly with the non-solar plane and see how long that lasts. It will probably last longer than the solar plane with the panels disconnected because it doesn't have to carry the extra weight of the panels. This way you learn what the addition of solar panels costed in terms of flight efficiency.


What are the best practices for gathering preflight weather and information? As a VFR student pilot, I'm still developing a pre cross-country flight routine. Weather has without a doubt been the most difficult portion of my preflight information to digest, as there are so many different sources and formats for it.

What are the generally acknowledged best practices (and sources) for assembling a complete understanding of all weather pertaining to a cross-country flight in a timely manner?

EDIT: This question is primarily focused within the continental United States, although answers pertaining to any region are more than welcome.

At least in the US there are plenty of ways to get a flight briefing.
My usual sources of pre-flight information are, roughly in order:

The Weather Channel
No kidding, if I'm planning a long/multi-day trip I'll start looking at the long-range forecasts 10 days before my flight using The Weather Channel's iPhone app or their website.
As far as weather information goes it's pretty decent (which means "frequently wrong up until 24 hours before go-time, but still worth paying attention to").
Charts (VFR or IFR), Airport Diagrams, and the A/FD
If you're planning more than a hop around the local pattern you should familiarize yourself with the airspace you'll be passing through, landmarks (and obstacles) on the ground, and navaid / airport frequencies. Charts and other FAA publications provide a great way to do that, and you can also usually pick up a phone and call the airport you're flying to for additional information.
All of this documentation is available in a variety of forms - Paper, electronic downloads direct from the FAA (as linked above), or as part of flight-planning software like Foreflight, Garmin Pilot, WingX Pro, etc.
The National Weather Service
A few days before a planned flight it's worth reading the forecaster's discussion to see how confident the people predicting the weather are about their guesses. This is also something you should check the day of departure if there's any uncertainty about the weather.
Electronic briefing tools (DUAT/DUATS/Foreflight/etc.)
About 24 hours out you can get official briefings from DUAT/DUATS/Foreflight and a bunch of other flight planning tools. Get them and learn to read them.

  Electronic briefings from many of these tools are recorded and count as an "official briefing" - a record is made that you requested and received the information. You are responsible for understanding all the information that just got dumped in your lap however, and that's a huge responsibility, especially for a student pilot!

Flight Service Briefings (1-800-WX-BRIEF)
The day of departure your final briefing should be a phone call to flight service to speak with an actual briefer to review your flight. If you can sit down and have your electronic briefing from #3 in front of you it's very helpful because you can follow along with the briefer to be sure you didn't miss anything.

  Calls to Flight Service are recorded and count as an official briefing. If you're unclear on anything you're being told you can ask for clarification.

Of all the tools available I personally think the best one is calling flight service and speaking to a briefer. If your instructor has never made you do this I'd say they're skipping out on a critical bit of your training, and you owe it to yourself to pick up the phone and .

This is your big chance to talk to a live human being and ask any questions - big ones that I always ask are "Are there any TFRs along my route of flight?", and if I'm anywhere near a restricted area I'll check its status ("Is R-12345 active?").


Who to call for flight following? I was up this past weekend on my first solo cross country and decided to request VFR flight following and was a bit confused at what happened. For this question I will set up the actual situation as an example.

I was over the Pottstown VOR (PTW) heading to Lancaster (KLNS) on the 269 radial. I decided to call Reading (KRDG) approach for flight following as they were the closest approach or so I thought. They informed me that I was still in the Philadelphia airspace and advised to contact them. Now in the past (with my instructor) on the same flight in just about the same location we had taken flight following from Reading approach.

So,

How do you know who to hail for flight following?

I was in the Philadelphia Mode C veil, is that why they sent me to Philly Approach?

When you request flight following generally you contact the facility (either approach or center) responsible for the airspace you're in, so your real question is "How the heck do I know whose airspace I'm in?!"

The answer can usually be found on the charts, or in other FAA publications.
Let's look at your example (I was over the Pottstown VOR (PTW) heading to Lancaster (KLNS) on the 269 radial.) in detail with some convenient visual aids.

Preflight Planning and the A/FD

You don't tell us what airport you took off from, but I'm going to assume KPTW (Heritage Airport) as a convenient starting point.
If we have a look in the Airport/Facility Directory for KPTW we'll get an answer very quickly from the "Communications" section:

PHILADELPHIA APP/DEP CON 126.85 (800-354-9884)

So if we're planning a flight out of KPTW and intend to pick up flight following our call to ATC should be made to Philadelphia Approach, on 126.85 (and if we're going IFR and need to talk to them on the ground there's a convenient phone number).

If you have an application like Foreflight or Garmin Pilot this information is readily available to you in the cockpit as well, so if you're unsure who to contact you can always pull up the A/FD information for the nearest airport and use that as a starting point.

In-Flight - Using the Charts

Let's say you didn't remember to look in the A/FD to see who you needed to talk to while you were on the ground, and the battery in your iPad is dead so Foreflight is out of the picture in the air. You can pull out your paper charts and get most of the same information in flight.

If we plot PTW ... KLNS it puts you on the very bottom of the New York Sectional Chart, and on the Philadelphia Terminal Area Chart for part of the flight, so let's take a closer look at the route on each of those.

First the New York Sectional:

Not much help here - or at least nothing glaringly obvious.

Let's look at the Philadelphia TAC:

AHA! There are helpful white boxes with blue text on this chart that tell you CTC PHILADELPHIA APP ON and list frequencies, altitudes, and active runways.
This looks promising: Since the little box says to contact Philadelphia Approach that's who you should probably call first.

In your case there happen to be two helpful boxes, one above your route of flight and one below it. Both boxes are roughly equidistant from the route of flight, so it's not obvious which one you should pay attention to.   In cases like this you can call on either frequency (at least you're calling the right facility - they may make you call on a different frequency and talk to another controller, but you're in the right neighborhood at least.

You can also go to the Airport/Facility Directory (A/FD) as a tie-breaker (though you're probably less likely to pull the book out mid-air, and if you did you'd probably use the nearest airport like I described above).

The blue boxes are talking about the Philadelphia Class B airspace, so if we look at the entry for the Class B airport (Philadelphia International - KPHL) we'll get more details on which radio frequencies we should use:

If you're flying along the 269 radial from PTW you're somewhere "northwest of the airport", so you would call Philadelphia Approach on 124.35 / 128.4 if you're above 5,000 feet, or 126.85 (the same frequency we got from the A/FD entry for KPTW)if you're below 5,000 feet.

I'd Like To Phone A Friend

There's one final way to figure out who you should talk to, and that's to call someone else and ask. If you're opening your flight plan with Flight Service over the radio they will usually sign off with "For flight following try Philadelphia Approach on 126.85" and the usual plea for PIREPS, and if they don't offer a frequency you can always ask them.


Why does ETOPS not apply to older 4 engine aircraft? This is a follow-up to my previous question: What is ETOPS and how does it work?
There is a related question here, but it does not specifically answer this new question.

Facts:

Since February 2015, all new aircraft are required to get ETOPS
approval to fly ETOPS 180+ routes. Source.
The 747-8 has ETOPS 330. The 787 has ETOPS 330. The A350 has ETOPS
370.

Why does ETOPS not apply to the 747-400?

I think it's because the last 747-400 was built in 2009.

  §121.162   ETOPS Type Design Approval Basis.

  Except for a passenger-carrying airplane with more than two engines manufactured prior to February 17, 2015 and except for a two-engine
  airplane that, when used in ETOPS, is only used for ETOPS of 75
  minutes or less, no certificate holder may conduct ETOPS unless the
  airplane has been type design approved for ETOPS and each airplane
  used in ETOPS complies with its CMP document as follows:

  (a) For a two-engine airplane, that is of the same model
  airplane-engine combination that received FAA approval for ETOPS up to
  180 minutes prior to February 15, 2007, the CMP document for that
  model airplane-engine combination in effect on February 14, 2007.

  (b) For a two-engine airplane, that is not of the same model
  airplane-engine combination that received FAA approval for ETOPS up to
  180 minutes before February 15, 2007, the CMP document for that new
  model airplane-engine combination issued in accordance with
  §25.3(b)(1) of this chapter.

  (c) For a two-engine airplane approved for ETOPS beyond 180 minutes,
  the CMP document for that model airplane-engine combination issued in
  accordance with §25.3(b)(2) of this chapter.

  (d) For an airplane with more than 2 engines manufactured on or
  after February 17, 2015, the CMP document for that model
  airplane-engine combination issued in accordance with §25.3(c) of this
  chapter.

  §25.3   Special provisions for ETOPS type design approvals.

  (a) Applicability. This section applies to an applicant for ETOPS type
  design approval of an airplane:

  (1) That has an existing type certificate on February 15, 2007; or

  (2) For which an application for an original type certificate was
  submitted before February 15, 2007.

  (b) Airplanes with two engines. (1) For ETOPS type design approval of
  an airplane up to and including 180 minutes, an applicant must comply
  with §25.1535, except that it need not comply with the following
  provisions of Appendix K, K25.1.4, of this part:

  (i) K25.1.4(a), fuel system pressure and flow requirements;

  (ii) K25.1.4(a)(3), low fuel alerting; and

  (iii) K25.1.4(c), engine oil tank design.

  (2) For ETOPS type design approval of an airplane beyond 180 minutes
  an applicant must comply with §25.1535.

  (c) Airplanes with more than two engines. An applicant for ETOPS
  type design approval must comply with §25.1535 for an airplane
  manufactured on or after February 17, 2015, except that, for an
  airplane configured for a three person flight crew, the applicant need
  not comply with Appendix K, K25.1.4(a)(3), of this part, low fuel
  alerting.


What are these four little things between the horizontal and vertical stabilizer on the B737? I was looking at some photos today and came across this one:

Image source

I noticed four little things in between the horizontal and vertical stabilizer. Could somebody explain me what those are?

The objects are vortex generators. In general, vortex generators serve to introduce turbulence which helps to prevent flow separation. More information here:

  This was to reduce elevator and elevator tab vibration during flight to increase their hinge bearing service life.

As mentioned on the site, you can see these on any 737 version from the original -100/-200 up through the NG. Better image from same site:


What causes aileron and elevator flutter? This video shows a Hawker jet with the wing fluttering up and down like it's about to break. What can cause flutter like that? Can it actually cause a wing or stabilizer failure? How can flutter be prevented? What should be done if something like this happens?

Imbalanced or loose (and, in extreme cases, structurally weak) control surfaces can cause flutter, a type of harmonic motion. Flutter is a very dangerous condition; if it is not stopped, it can cause structural failure and potentially lead to a fatal accident. V-tail Bonanzas had a series of such accidents related to flutter of the butterfly ruddervator tail.

I understand that prevention is a combination of good maintenance and keeping the aircraft below Vne (never exceed speed), or possibly other speeds in some configurations.

The appropriate reaction would be to slow down, first and foremost. Descending is probably also a wise choice.


Who decided that the Boeing 737 MAX planes that were airborne when the grounding was issued cannot enter and land in EU air space? On March 12th, 2019, EASA grounded the Boeing 737 MAX series by publishing their Emergency Airworthiness Directive 2019-0051-E (AD):

  Effective Date: 12 March 2019, 19:00 UTC

   [...]

  Required Action(s) and Compliance Time(s):

  From the effective date and time of this AD, do not operate the
  aeroplane, except that a single non-commercial ferry flight (up to
  three flight cycles) may be accomplished to return the aeroplane to a
  location where the expected corrective action(s) can be accomplished.

The PDF document was created at 17:12 UTC and went into effect practically immediately. The AD does not specify any particular instruction for actions concerning flights already airborne.

Of course there were a number of long-haul flights en-route, that clearly started before the publication, and were scheduled for landing in the EU hours after the effective date/time of the AD. Closely related questions have already been asked on Avitation SE:

What happens to an airborne plane when its type is grounded by an authority?
Why would a flight no longer considered airworthy be redirected like this?  (Smart Wings QS 1201 was scheduled for DXB 15:30 UTC - PRG 23:20 UTC)

After March 12th, many people were convinced that EASA has forbidden entry or landing for the 737 MAX in EU air space. I cannot read that from the directive or any other reliable source.

We all agree that operation of a plane shall not be finished mid-air. The AD could not be followed literally for flights like QS 1201. Unless this case is covered by a different applicable document, EASA failed to give a clear directive.
Emergency ADs shall always serve the purpose of aviation safety. I cannot see how diverting numerous flights on very short notice can be safer than allowing landing at the planned destinations.

For comparison, this is how the FAA worded their AD on March 13th in this corresponding part:

  This Order is effective immediately. This Order prohibits the
  operation of Boeing 737 MAX airplanes by U.S. certificated operators.
  This Order also prohibits the operation of Boeing 737 MAX series
  airplanes in the territory of the United States. Boeing 737 MAX series
  airplanes covered by this Order, if in flight at the time this Order
  is issued, may proceed to and complete their soonest planned landing,
  but may not again takeoff.

  Special flight permits may be issued [...] including to allow non-passenger carrying flights, as needed, for purposes of flight to a base for storage, production flight testing, repairs, alterations or maintenance.

FAA's AD covers the case of airborne 737 MAX explicitly. On the contrary, the EASA AD requires interpretation at this point, and therefore this is my question:

Who had the right and duty to interpret this AD and to decide what should happen with the B737 MAX in flight?

Was it ATC in the role of an executive authority?
Was it the Airline that is risking its certification or wanting to minimize storage fees?
Was it the PIC who is risking a hefty fine?
Or am I missing something entirely?

The operator's airworthiness department interprets the AD and informs the operations department and senior management.  Ops decide how to deal with airborne aircraft.

The EASA AD actually had more generous continued flight provisions than the FAA issued AD.  It was in no way intended to prevent aircraft in flight from landing.  Airworthiness would immediately talk to operations.  Operations would decide what to do, though in most cases a few phone calls would be made to senior management.  If the aircraft can't make it back to a 'home' port, that pretty much dictates what is going to happen next (continue to destination).  In the subject case, a number of aircraft were airborne and capable of returning to a home port.  So you need to figure out what to do next - continue flying to your EU destination and get your passengers there with minimum inconvenience (with possible adverse publicity for not discontinuing the flight as soon as possible), or simply get the aircraft back to base so that you don't have it stuck somewhere needing maintenance (and reading between the lines, Ops and Airworthiness would be concerned that the recovery might become more complicated than the 3 flight cycle limit ferry suggests).  So better to get your pax down ASAP, at a port where you can easily carry out whatever rectification is needed, and importantly too, also one where you have more aircraft available to get your passengers to their destination without having to do positioning flights.

In some cases, such as TUI, they elected to divert the aircraft to the nearest suitable port, regardless of destination or home port convenience.


Has any aircraft ever been designed such that it could descend safely with no control input? Has there ever been any aircraft of any type that could glide safely with no control input simply based on the way the frame of the aircraft was designed?

I was trying to think of requirements for building an aircraft that would be accessible to the masses and the first thing I thought of was safe landing in the event of engine failure or other catastrophic mechanical breakdown.

It seems to me that it would be possible using modern composites to create some type of aircraft whose default flying configuration is a safe, slow descent. NOT including parachute equipped such as cirrus, has any such craft been designed/flown?

Broadly speaking most (if not all) light GA aircraft can "glide safely with no control input" - aircraft are generally designed to have positive dynamic stability, such that they will return to a stable equilibrium condition (e.g. "level cruise flight") in the face of most modest upsets. Once configured for cruise flight they can maintain it with little input from the pilot (and if equipped with even a basic autopilot "little input" can often be reduced to "no input" for extended periods of time).
Whether or not the engine is producing power is largely irrelevant here, save for the fact that if the engine isn't producing power you will eventually be descending.

Positive stability alone will not make aviation "accessible to the masses" however, nor will autopilots: As with driving a car or riding a motorcycle there are certain "aeronautical decision-making" skills which a pilot must possess in order to safely fly (and land) an aircraft when everything goes right. If you introduce problems (like engine or instrument failures) the need for a real live pilot becomes even more critical: technology can not yet replace the critical decision making capabilities of a trained human mind.

Particularly in regard to your question about a default flight mode of a controlled descent, even a simple autopilot can already do what you describe: Planes will continue to fly the last autopilot-commanded heading or route until they run out of fuel, at which point they'll start descending (while still attempting to fly the programmed profile).
What they cannot do is select a suitable landing site, update their flight profile, and fly themselves to a safe landing. For that to happen without human intervention requires a huge amount of luck.

In a particularly famous example of this kind of luck a Piper Comanche "landed" itself in a field after running out of fuel, the pilot being unconscious at the time due to carbon monoxide poisoning. The pilot survived and in fact literally walked away from the accident scene, and the aircraft in question is, as best I can determine, still flying.


Are there pictures of unassembled planes being transported around? My google-fu is failing me here.

A friend was telling me about the assembly of carbon-fibre planes, and how the huge parts of these need to be transported long distances between countries.

Are there any photos of this?

Here you have pictures of wing upper cover being handled and transported:

(Image Source: www.airbus.com)

Wing upper cover is biggest single composite component on A350XWB.

Additionaly try google: "wing upper cover A350", "wing lower cover A350". Those are the biggest. And you can see them in various stages in google.


Turbine blade manufacturing/assembly process I want to know the process for manufacturing turbine blades and the companies that are involved.

Who makes the turbine blades? Who applies the thermal barrier coating? Who repairs the blades?

Let's take the General Electric GEnx as an example. Does GE make the blades themselves, or do they buy them from a supplier? Where do companies like MTU Aero Engines come in?

You'll have a hard time finding an exact answer, as that's unlikely to be public information, but here are some general trends:

In the case of the high pressure turbine, the blades are one of the key company jewels.  These are one of the highest technology pieces of the engine, and contributes a large part of the competitive advantage of one engine over another. Thus, this technology tends to be kept as a trade secret, and the parts are generally manufactured by the engine OEM themselves, and not outsourced.

For example, let's just say that tomorrow P&W discovered some new material that would increase EGT margin by 50 degrees.  That would give them a huge advantage over GE.  So they would want to keep it as closely guarded as possible.  If GE ever found out how to make that material, the competitive advantage is gone. So they want to keep all of the information as closely guarded as possible.  What's the best way to do that?  You make everything yourself.  If you outsource the manufacturing, then your material is out there in a place where you don't have control over it.  One or two blade might "walk away", and suddenly show up somewhere else.  You don't want that to happen.  So you keep it all in house.  In fact, you probably keep the information on a "need to know" basis.  I.e. the engineers who design the compressor or the fan aren't told the details of this new material.  They know it's there, and maybe some general information, but the details of how to make it aren't even widely known within the company.

Now that's for new engines. Ones that are actively being sold, where there is a competition, and customers are willing to pay a premium for performance.  Now consider on the other hand a very old engine.  Something like a CFM56-2, or a JT8D. That's ancient technology, so there's not really any competition on performance.  But there are still a lot them flying around, and they do need spare parts from time to time. The key driver for the spares market is going to be cost.  No one will pay a premium for performance here.  So you might see some of the manufacturing outsourced in this case.  You'll even see 3rd parties selling aftermarket parts for these engines (look up "PMA").


At what age may a student log time and use that time to obtain a rating? A few years back the FAA was upset about young pilots attempting to set records and crashing in the process.

Were there any rules instituted regarding logging of time with a CFI / instructor? May a 9 year old or 12 year old log time flown with a CFI and use that time to qualify for a rating?

FAR § 61.83 states:

To be eligible for a student pilot certificate, an applicant must:
(a) Be at least 16 years of age for other than the operation of a glider or balloon.
(b) Be at least 14 years of age for the operation of a glider or balloon.
(c) Be able to read, speak, write, and understand the English language. [...]

A student pilot certificate enables you to fly a plane solo or on a solo cross country.
In other words, you need to be at least 16 years old to fly a plane (non glider/balloon) solo.

Now, back to your initial question. If you go through FAR §61.83 - §61.95 you will find all the regulations about student pilots (which would be the kind of pilot you are referring to ).
I have found no age restriction going through them for the pre-solo instruction. All it says that it must be done before soloing which does require a medical exam and certificate (but these don't have age restrictions either).
Summing up, a 9 or 12 year old child is legally able to take flying lessons with an instructor, but may not solo before his/her 16th birthday (no glider/balloons).


Why is flying in a slip uncomfortable? It seems that flying a plane in a slip can make passengers uncomfortable.

What is it about that configuration that is unsettling?

A slip is uncoordinated flight and this shifts the effective gravity vector you experience.  Passengers in the back are also at a disadvantage without a visual horizon in front of them.  This can induce a mismatch between what the passengers can see versus what they are physically experiencing.  In some people this can cause discomfort and potentially vertigo.

Other discomfort can be psychological in nature that the airplane isn't behaving how they expect.  Passengers expect if a plane isn't turning that the wings are level.  If you are flying when the plane lands in a crosswind with a slight bank and touching down with one main gear, then the other main gear, many passengers will comment that the landing was incorrect because the main gear didn't all touch down together and the pilot was flying "sideways".  They don't realize the wind requires this technique and that the landing was in fact correct.  The perception of things not being right, however, can cause discomfort in some passengers.


Is there a standard word or phrase in the English-speaking world to describe the angle between the fuselage and the flight path / relative wind? Is there a standard word or phrase, or several alternative commonly-used words or phrases, in the English-speaking aviation world to describe the angle between the longitudinal axis of the fuselage, and the flight path/ relative wind/ undisturbed free stream airflow?

Also, is one particular greek letter commonly associated with this angle in engineering texts and papers, much as "alpha" is commonly used to describe what the English-speaking aviation world usually calls "angle-of-attack"?

Basically the angle we are asking about is conceptually much like angle-of-attack, but modified to mean the angle-of-attack of the fuselage rather than the angle-of-attack of the wing.

Note: this question is asking about an angle that we would see when looking at the fuselage and flight path in a side view, as the aircraft flies with the wings level.  This question is not asking about a yaw angle or sideslip angle.

It is just angle of attack.

Most anything can have an angle of attack. If you must be specific, you mention 'angle of attack of ...' Due to complexity of aerodynamics, most external elements of an airplane have their own local angle of attack. AoA sensors measure their angle of attack, and it is usually not even converted to 'wing' or 'fuselage'; it is dubbed 'indicated' or 'measured' and all limits are set with respect to that local AoA.

All these angles are usually designated as $\alpha$ (alpha), but with an appropriate index, which should always be explained in the nomenclature.

When we talk about airplane as a whole, usually the 'default' angle of attack is the one between the wind and the body frame (in the vertical plane). How body frame is defined depends on the aircraft designer, but normally X goes along the fuselage. Therefore, the angle of attack is exactly what you say: the angle between relative wind and the fuselage -- and not that of the wing (even though it is arguably more important).

Yet when we talk about aerodynamics, we may redefine the angle to mean 'angle of attack of the wing'. And even offset it to be with respect to zero lift. This is all fine as long as it's explicit. When we talk about just wing or airfoil, then the default angle of attack will be that of this object.


Are weather-reporting requirements for an airport in Class D airspace more stringent than for an airport in surface-level Class E airspace? In the US, are weather-reporting requirements for an airport in Class D airspace more stringent than for an airport in surface-level Class E airspace?
Are there other requirements that would cause an airport with an operating control tower to be eligible for surface-level Class E airspace but not for Class D airspace?
The intent of the question is to understand why any airport with an operating control tower, whether "temporary" or otherwise, would have surface-level Class E airspace rather than Class D airspace during the hours that the tower was operational, if in fact this ever occurs-- apart from the obvious case of a temporary (or new) control tower going into operation in pre-existing surface-level Class E airspace.
Related ASE links: In the US, are there any operational control towers located in surface-level Class E airspace or in Class G airspace?
This outside link appears to describe the establishment of temporary surface-level Class E airspace concurrent with the establishment of a temporary control tower-- but may just be an example of inaccurate or unclear writing.  The surface-level airspace at this airport is normally Class G, and the same was true in 2016.  The only NOTAM turned up during an archive search for this airport at this time references the temporary control tower, but no temporary change in airspace designation.

Your First Question: In the US, are weather-reporting requirements for an airport in Class D airspace more stringent than for an airport in surface-level Class E airspace?
Answer: The "Primary" airport within active Class D airspace requires (Ref: FAA Order JO 7400.2M, paragraphs 17-2-9 and 17-2-10:

That a Control Tower be currently in operation;
That a certified and approved weather observation and reporting system (for the primary airport) be in place and operational; and
Communications capability must exist down to the runway surface area (for the primary airport).

However, a primary airport that is within the surface area of active Class E airspace will not have a Control Tower currently in operation.  (if there are airports with a currently operating Control Tower within the surface area of active Class E airspace, I am unaware of them).
With respect to your specific question above, if the airport in question (within the surface area of active Class E airspace) is meant to accommodate instrument procedures (e.g., instrument approaches, IFR arrival/departure procedures, etc.) then the exact same requirements (Ref: FAA JO 7400.2M, paragraph 18-1-3) for communication and weather observation/reporting must be available as are required for Class D surface airspace. (But there will not be a Control Tower operating)
There are a dwindling few airports that have Control Towers that operate while the airspace is designated as active Class G. But, as I mentioned above, the same is not true for primary airports located within the active surface area of Class E airspace. In that case, the Control Tower, if there is one, is not operational (e.g., closed/not staffed - usually in the later evening as traffic warrants).  If the Control Tower was currently operating the active surface airspace would be Class D.
Your Second Question: Are there other requirements that would cause an airport with an operating control tower to be eligible for surface-level Class E airspace but not for Class D airspace?
Answer: Again, as mentioned above, if the primary airport has a currently operating Control Tower, the active surface airpace would be Class D (or in a few cases Class G), not Class E. Therefore, parsing the eligibility requirements between Class E and Class D airspace, both of which (with respect to your question) might have operating Control Towers, is not possible.
Typically, when/if the Control Tower closes (not staffed/closed for the night) at a primary airport in Class D surface airspace, then that airspace surface area reverts to Class G or Class E.
Lastly, my response above excludes special occasions where a temporary Control Tower may be operating in active surface airspace designated as Class E.  This would be a circumstance where a NOTAM or similar would exist identifying a particular event taking place.


Why do pilots' masks have more oxygen? When a commercial passenger airliner suffers a rapid decompression, it is critical that everybody on board gets oxygen quickly. In the passenger rows, oxygen masks connected to chemical oxygen masks will drop. In the cabin, the flight crew will pull out their oxygen masks, which are connected to pressurized oxygen canisters. The chemical generators will last for 10-15 minutes, but apparently the flight crew's oxygen supply will last for a couple of hours.

Why would the flight crew's supply last for so much longer? If the plane isn't at a breathable altitude after 30 minutes, it seems like it'd probably be unrecoverable, and the passengers will be in irreversible comas anyway.

The pilots also need to use oxygen in case of smoke, fumes, or fire in the aircraft.  Thus, they need enough oxygen to be able to get down and land in a fire scenario, which is much more than a decompression!

Fire procedures have the crew on 100% oxygen at positive pressure to prevent them from breathing in smoke and fumes, while in a decompression, their masks mix oxygen with cabin air, in much the same way the cabin masks do.  This is also why the cabin masks are not used in smoke/fumes scenarios.


How are "preferred routes" assigned if there is more demand than capacity on a route? There might be multiple routes, belonging to the “Preferred Routes” class, connecting the same pair of airports.

However some of them might be more appealing for non-urgent circumstances such as less turbulence, more favorable winds, etc. Therefore there will be a route (as long as I understand) that is the desired one by many airlines at the same time.

Let’s suppose we have airlines A, B, and C requesting a flight on route x, but the capacity is one per route, or stated another way, only one of the three airlines can take the route and the other two must choose another route.

Which is the protocol followed to decide if the route x is assigned to A, B, or C?

Air traffic services (at least in the US) are handled on a first come first serve basis. That's the overarching protocol. Beyond that, it's situation dependent.

In the air, controllers give pilots what they want if possible. In practice the situation is quite fluid. Maybe all three can't go on the same path now, but in a minute there will be enough clear airspace to make it happen. Or maybe they go on a route very close to but not exactly what they requested.

If (for some reason like a prominent jet stream) many airplanes are filing the same (or very similar) flight plans so that certain airspace will be overwhelmed, there is an entire division of the FAA dedicated to deciding where and when aircraft need to be rerouted. Here's some info @mins linked to in a comment.

Also, your question seems to assume competing airlines. For all ATC cares, A, B, and C could all be flights of the same airline.


Is there any form of checklist that a pilot needs to go through before they use their ejection seat? Obviously, the use of an ejection seat is a last resort tactic but is there anything at all that a pilot must consider, any buttons they need to hit or something similar before they may eject?

Obviously not including anything such as arming the ejection seat or removing any covers over the ejection seat handle or anything.

Yes there are checklists but a lot of the training is done by practice exercises so the procedure becomes instinctive during an emergency.

The exact procedures to be used vary based upon airframe, cockpit configuration, and ejection seat make and model.  Here are two examples, one from the F-16A/B aircraft and the other from the F/A-18E/F aircraft.

From the F-16 USAF Flight Manual.

And from the F-18 NATOPS Manual.

Again there are a lot of mitigating factors here, specifically, airspeed, altitude, attitude, aircraft controllability and imminent danger to the flight crew which must be taken into consideration to order to make the decision to eject.  Since an ejection seat is nothing more than a device to provide an additional velocity vector to the aircrew in order to provide time for the main parachute to open and safely lower the occupant to the ground, they have specific altitude, airspeed and attitude envelopes in which they may be operated to ensure maximum chance of aircrew survival.  This should be reviewed and thoroughly understood by the aircrew prior to use.

There have been a few instances where the seat was used outside of the envelope.  One notable instance being Soviet test pilot Anatoli Kobachev when he punched out of a MiG-29 during a low altitude, high AOA pass at the 1989 Paris Air Show.  His delay was to direct the stricken aircraft away from the crowds and very fortunate that he didn’t die.  He walked away from the accident.

The checklists above should be used only IF TIME AND WORKLOAD PERMIT.  Again flight crews practice ejection procedures separate from aircraft operation in order to become uncounsciously competent in the operation of the seat.  They typically order the cockpit and workstations for aircraft egress prior to situation where there is an increased probability of needing to abandon a disabled aircraft.  These include takeoff, landing, and entering a theater of combat, etc.  Checklists will be use here prior to these events and crews will probably brief ejection procedures here as well.  Carrier operations, in partcular will have crews ready to eject at a moments notice and anticipating emergencies such as a cold cat shot or arresting gear failure during launch and recovery operations, both of which will probably require an immediate ejection to save the lives of the aircrew.

Correct cockpit preflight procedures must be done by the aircrews prior to operations to ensure safe ejection as well.  Crew must attach the leg restraints as well as correct attachment of life support umbilicals such as oxygen, anti-G, radio and HMCS data lines to ensure they separate properly during ejection without causing serious injury or death.  Shoulder straps must be attached into the occupant’s parachute harness to connect them with the seat’s recovery parachute (some seats do not have this; the pilot will wear a separate parachute system as part of their life support garb in this case).  Charts, kneeboards and other foreign objects must be placed such that they do not interfere with the operation of the ejection handles or the seat safing handles.

The ejection process again is going to be based upon the cockpit configuration and seat type, but typically if the aircraft commander says EJECT! EJECT! EJECT!, you will pull your legs and extremities clear of the legwells and flight controls, head back against the seat headrest, grasp the ejection handles, disengaging the grip safeties and PULL HARD.  The ejection itself will happen fast and very violent with a BANG! BANG!  The canopies will either break away with a pyrotechnic charge or be fractured with a similar charge sounding like a shotgun blast at close range.  This is followed a split second later with a jolt and explosion as the pneumatic catapult throws you clear of the cockpit and the seat rocket motor ignites, giving you an approx. 20g acceleration clear of the cockpit.  After this, the recovery process becomes pretty automatic.  Air data sensors feeding a small computer in the seat right the occupant using a drogue chute, followed by seat frame separation and deployment of the main recovery parachute.  The pilot may be required th pull an additional handle for deployment of the seat pan and life raft for a water egress as well.

Wind blast will be a major factor and all material suggests that an ejection be intitiated at the lowest airspeed, if possible.  High speed ejections will invariably result in serious injuries as due to wind blast, as this chart from an F-16 flight ops manual suggests.

Ejection at supersonic speeds is usually fatal, with very few exceptions.  This pilot was very fortunate to survive a supersonic ejection, but was seriously injured in the process.


Why does this Garmin GMA340 have an Airway/Inner marker indicator? On this Garmin GMA 340:

the outer marker is blue and is designated O
the middle mark is amber and is designated M
the inner marker is white and is designated A and placed on the far left.

I looked at the GMA 340 Manual and could not find an answer although it does say Airway/Inner Marker.

Why would it say Airway if this is what the A indeed stands for and why even have an inner marker because that Garmin can't do a Category II approach?

The "A" is not an inner marker. The A is an airway marker. Airway markers were part of a now-obsolete system of "red" airways. They were placed along the enroute path and they could be picked up at cruise altitudes. The red airway system was mostly abandoned in the 60's and few "A" markers are still operational. Here's a map showing where they were located. They weren't at aerodromes.

Source

The airway markers transmit the same 3000 Hz audio frequency as inner markers so the airway marker can be used to pick up the inner marker. Since you say that unit is not certified for cat II it makes sense that they labeled it "A" instead of "I" although it can be used for inner markers.


Why is a contra-rotating High Pressure section more efficient? In the Rolls Royce Trent 900 marketing material, the use of contra-rotating HP system is described as increasing the efficiency of the engine. Can anyone explain why/how that increases the efficiency?

These marketing type documents don't always mean "efficiency" in the true technical definition of the word, nor is it clear if they are talking about turbine stage efficiency (i.e. efficiency of the nozzle/turbine blade expansion process), or overall engine thermal efficiency.

The main advantage of contra-rotating is the removal of the nozzle guide vanes (NGVs) between the high pressure turbine and low pressure turbine. These LPT inlet nozzles require cooling air, that needs to be from a reasonably high pressure source because it has to be at a higher pressure than where it is being introduced back into the hot gas stream. Hence, it is usually bleed from within the high pressure compressor exit. (See reference below to "HPC S7 Air" - which means stage 7, this is the GE90 engine which has 9 or 10 HPC stages depending on the model).

In comparision, HPT inlet nozzle guide vane cooling air has to be bleed from the HPC exit, as an even higher pressure is needed. (see reference to "HPC exit air", or "CDP", compressor discharge pressure).

(Pic from here)

Given the LPT nozzle guide vanes require cooling, removing them reduces the cooling air required, and hence this air, which has been compressed which required turbine energy to do so, and hence represents an energy investment by the engine, is still available in the combustor, and for extracting (recovering) work from in the high pressure turbine. Therefore, the thermodymanic cycle efficiency of the engine is increased, as parasitic cooling air requirements have decreased.


What is the correct name for clearance delivery at KSAN if the tower is called "Lindbergh Tower"? In the departure and instrument approach charts for KSAN, they reference Lindbergh Tower" for KSAN tower. Does this mean that we should be calling up "Lindbergh Clearance" to pick up our flight plan?

Lindbergh is used as an identifier shortcut because "Lindbergh Field" is the official name of the airport. So I would call in with "Lindbergh Clearance Delivery".


Can I obtain a license over several years? How long does training for student, sport, recreational, or private licenses "count" toward your license, before it's considered outdated/expired?  Can you start the process, intending to spread out the expense over something like 5 years, or in that situation, do you need to "save up" and do it all within a year or two?

Bonus question - My luck that I'm just starting to look into this, and there's a private pilot ground school course starting tomorrow nearby.  Is it premature for me to take this class, not having taken any other steps?  Would it be over my head, or would I need to take it again if I don't get the private license within a certain amount of time taking the class?

I'm assuming you're asking about the US, since you mentioned sport/recreational licenses.

You can take as long as you like to learn to fly, although spreading it out over multiple years will actually cost more, not less. The reason is that you forget things and take a lot longer to develop the right reactions, muscle memory and feel for the aircraft. So try to fly as much as possible and do your license as quickly as possible, within whatever time and budget limits you have; I know that not everyone has the time and money to learn to fly in one month or even one year.

As for a ground school course, they're often planned to end with you taking the knowledge test required for private pilots and that test might even be included in the price. When you take the test it's valid for two years. If you don't pass your final checkride within those two years then you'll have to do the knowledge test again first. But that doesn't mean you have to do a ground school course again, you can work with an instructor and by yourself to refresh your knowledge.

But if you're not sure about how/when to start training then the best thing you can do is talk to an instructor about your situation and expectations. Any good flight school will be happy to have someone sit down with you and answer whatever questions you have. An introductory flight would be a great way to start, if you haven't already done that.


What should I know before getting the KAMRA laser eye surgery procedure as a pilot? I was recently looking into the KAMRA procedure to fix my reading problem. Then I came across some posts that discourage it as it causes one to see halos in night so particularly bad for pilots. I was wondering if anyone else here has done that that what was his or her experience about it? What are the regulations on this as well?

I'm not clear if you are asking about LASIK or KAMRA, the former is accepted by the FAA, while there is no explicit mention of the latter procedure.

The procedure site itself mentions halos as one of the side effects of the procedure:

  The KAMRA inlay procedure may cause blurred vision, difficulties with contrast sensitivity, problems with night vision, double vision, ghost images, glare, halos, and color disturbances.

In general, people with such adverse effects and complications are not allowed to serve as airmen:

  The FAA expects that airmen will not resume airman duties until ... there are no significant adverse effects or complications (such as halos, rings, haze, impaired night vision and glare), ...  and reviewed by an Examiner or AMCD.

The medical certificate for a person who had undergone such procedures is contingent upon the absense of any side effects affecting vision:

  An applicant treated with a refractive procedure may be issued a medical certificate by the Examiner if ... the applicant does not suffer sequela such as; glare intolerance, halos, rings, impaired night vision, or any other complications

It would be better if you consult a doctor to find out if the procedure is suitable for you and possibility of side effects.


Is 'bouncing' an airliner on landing in high winds a deliberate technique, or something always unexpected? Last week, 767 landing at Newark, high winds, a good deal of rocking in the last few minutes, some passengers quite distressed. The landing was harder and noisier than usual, and we immediately floated upwards, must have been a couple of seconds before we landed again.

The question I have is - in these circumstances (high winds), would the pilots have been flying the landing with a little less flare than usual and anticipating the bounce as a way of shrugging off some speed / energy; or, is it something you never quite know if it's going to happen or not, and would rather didn't happen at all?

Bouncing a landing is neither intentional nor desirable. There are several reasons why a student pilot might bounce, but for a professional pilot, it's most likely related to wind gusts, which are a challenge no matter how much training and experience you have.

Gusts are by their nature unpredictable, and if one hits the plane right as it's touching down, it can suddenly lurch upward and/or downward, resulting in a bounce. That's probably also why your plane was "rocking" before landing.


What is the actual range of ICON A5? Does anyone currently own or have experience flying an ICON A5 aircraft?

They claim a range of 300 NM (555.6 km). I would like to know whether this is a theoretical calculated range, or a true/actual number?

I can't speak directly to the ICON A5 as I neither own nor fly one, but for every aircraft I'm familiar with the manufacturer's "book numbers" are generous theoretical values - for example, they typically assume flying perfectly straight-and-level in a no-wind condition, and getting the best possible fuel economy performance from the powerplant.
The Icon folks are openly honest about this on their specs page: Performance specifications are estimates only., and range is certainly "Performance" in my book.

Personally I have no doubt that the A5 could manage 300NM under the conditions for which its designers did the math to arrive at that number - it's a slick little plane with a fuel-sipping engine - but they may have done a "to empty tanks" calculation (leaving you to account for the VFR fuel reserves you're legally required to have), and in the real world the 15-knot headwind you run into will substantially reduce your range (or, conversely, you can fly in the other direction and increase it).

As with all aircraft your mileage will, quite literally, vary depending on the day and direction of flight.


What is the standard way for the ATC to ask a pilot to repeat him/herself? There is a lot of information on how the pilot should ask the ATC to repeat a statement, but is there a standard way for the ATC to ask the pilot to repeat a readback, or any new information that the pilot provides?

Yes, and it is exactly the same: Say again.

  Station calling Georgetown Ground say again your callsign

  Lufthansa 123 say again speed

  Scandinavian 123 say again all after 'good morning'

Or simply

  United 345 say again


How big is the radar cross section of a modern glider? I heard somewhere that modern glider made of plastic and composite materials are less detectable than other aircraft by primary radar. I wonder how much.
What is the radar cross section of a typical modern glider such as the Schempp-Hirth Duo Discus? How does it compare to a typical GA aircraft such as a Cessna C172 and to a typical airliner such as an jet airliner such as an Embraer E190 and to a typical turboprop such as a De Havilland Canada Dash 8?

Smaller than that of a normal aircraft, but very far away from a VLO/stealth one.
The RCS of various light aircraft has been measured and published here: https://apps.dtic.mil/dtic/tr/fulltext/u2/a029262.pdf
The RCS of the human body is on the order of -20 to -5 dBsm: https://ieeexplore.ieee.org/document/7027834
The glider can't hide the human inside. Extrapolating light aircraft RCS down to a glider, my best guess for the lowest-RCS gliders would be on the order of -10 to -5 dBsm, and no less than -12 dBsm or 0.05 m² due to the pilot.
The reason is that a glider still contains a lot of non-radar-transparent parts, which will reflect radar frequencies and produce a sizable RCS.
It doesn't take much to produce a radar reflection. -40 dBsm corresponds to a sphere just 1.4 cm in diameter. Anything that contains metal or water will reflect radar. Even small metal or flesh objects will produce a significant return.
To get seriously low RCS, such as -20 to -30 dBsm, below a bare human, where "real stealth" is considered to begin, you need to specifically work for it, intentionally reflecting the waves in the wrong direction, not avoiding reflections.
In particular, you need to ensure the reflection is directed into specific lobes. This isn't best achieved by radar transparency - in fact, both the F-22 and even non-VLO fighters like the F-16 intentionally coat their canopies with gold to make them radar-reflective, so as to avoid random reflections from the objects inside.


Is there a maximal time to pass a type rating? Let's say you begin a type rating for a long haul carrier (e.g. A350 or B787) at day 1. After few days, your training stops due to external causes (airline paying your training bankrupt, all aircraft are grounded in your area due to Eyjafjöll ashes, or even in a larger area due to a pandemic such a covid19,...).

Is there a time limit to resume your training? If so, what is the maximal allowed time between the first day of your type rating training and the day you pass it?

This question can be restricted to A350 and B787 under FAA and EASA regulations if needed.

Nope.  Not unless your employer refuses to continue training.  Legally all that’s required is that you have accomplished all the training required to meet the prerequisites per §61.39 and meet the practical test requirements per §61.43 plus meet the eligibility requirements for the grade of pilot certificate you are applying for per §61.103, §61.123, or §61.153.


How can the range of an aircraft be calculated given real wind conditions? I am very new to aviation and trying to understand how to calculate the actual range of an aircraft given real world wind conditions.  I understand from this related question that you need  30 minutes of reserve and that tailwind and headwind direction will obviously impact your range.  I've also heard that the altitude you fly at can impact your range because higher air is thinner and allows you to travel faster.  I also would assume that the aircraft load would impact range.  So my question is:

Given the theoretical range of an aircraft (i.e. from specs published at this site) how do you calculate how far the aircraft can actually travel at a given altitude, with a given load, and with current wind conditions?

The best answer: Use the charts in the respective Pilot's Operating Handbook (POH). There you should find correction factors for the parameters which influence aircraft range

Fuel on board: The more, the better. But note that doubling fuel will not double range.
Take-off mass: If you take no payload, the aircraft will produce less induced drag and reach a slightly higher range. See the chart below for an example.
Wind enroute. Follow the link; the wind component parallel to your flight direction will change the range by the product of wind speed times flight time.
Cruise altitude: This depends on the type of engines, jets benefit more from altitude than propeller aircraft.
Temperature

Generally, there should be a chart like this:

It plots the maximum achievable range over the aircraft's payload and assumes that the tanks are filled such that the flight starts with the maximum take-off mass. The chart should also have an explanation that clarifies which altitude and which thrust setting were used.

Or you use approximations like Breguet's range equation, which require detailed knowledge of the aircrafts L/D and the engine's fuel consumption. That will be the weakest point of any range calculation: Sufficient data how changes in the aforementioned parameters affect the result.


How does the Angle of attack vary from the root to the tip of a propeller for a fixed pitch prop? I came across a video while learning about propellers where it showed the angle of attack increased from the root of the propeller to the tip of propeller whose pitch was fixed.
I somehow cannot get my head around it. Is it because the tip moves faster than the root? If so, can anyone explain why moving faster changes the angle of attack at the tip?

I am pretty new to all this so sorry for the stupid question, & I tried searching on the site but could not find answers to this question explicitly.

You are absolutely correct. The "relative wind" at any point on the propeller is a combination of the aircraft's forward motion plus the angular rotation speed of the prop, which is greater at the tips.  This is why, to get the best Angle of Attack, the prop (airfoil) is designed with a twist or "washout" towards the tip.

Notice, with variable pitch props, as the planes forward speed increases, the entire prop AOA
is turned forward to account for change in relative wind.

Fixed pitch props try to find a happy medium between low speed performance and cruise efficiency.  For example, a 10 x 6 (finer pitch) gives better acceleration for take-off, but a 10 x 7 pitch uses less fuel at cruise.


What are concrete examples for class G up to 14500? It is said that there are some places where class G goes up to 14500 and then class E starts. However, I find they all overplayed with some special use airspace by looking at NorCal and SoCal Sectionals. Can anyone point me to some non-trivial 14500' Class G places? It is best to see some civilian airport within it.

It can be difficult to find these areas on a VFR sectional (there are very few of them anyway), but on an (FAA NACO) IFR en route chart they're shaded brown, so they stand out very clearly from the background. Here are a few grouped together in South Dakota.

IFR chart:

VFR chart:

At the western end of those areas there's a public airport, Bison Municipal (6V5):


Is a FAA certified plane allowed to fly everywhere in the world? Following the debate about FAA and Boeing certification practices,  I was wondering whether Europe could potentially require the Boeing 737 Max to be certified by a European agency.
Is a FAA certificate de facto valid in other countries ? Or are all planes required to be certified by local authorities too ?

Update :
Despite FAA certification being valid throughout the world, it appears EASA will conduct its own review of the fixes implemented by Boeing.
It is not a proper re-certification, but the plane will have to comply with EASA in order to be able to fly again in the European airspace.
More about this here (FT paywall).

It's valid in countries that choose to accept it as de-facto valid but sovereign nations are free to require local certification if they like. The reality is that the FAA has a huge amount of resources at its disposal and for smaller nations is advantageous to simply say we agree that those people know what they are doing and we can't afford to do it any better.

However Boeing does hold an EASA Type Certificate for the 737 as well as the FAA issued one but if you dig into it you will find a lot of "see FAA TCDS" notes. With that said the 737 is certified by European agencies currently. A good chunk of regulations even stem from the FAA work, the best example of this is in the EASA TCDS where EASA changed some regulations to the FAA spec.

  However, to harmonize with the FAA, the same requirement was moved to JAR 25.810(a)(1)(ii) at Change 14 which is now in
  CS25.810(a)(1)(ii).


What are the weather requirements to log an instrument approach? So let's assume that I'm the sole manipulator of the flight controls in an aircraft in which I'm rated and that I fly an instrument approach.

What weather does the FAA require (assuming that I'm not wearing a view limiting device) in order to log the approach for currency requirements?  For instance, if I am cleared for an ILS in visual conditions, can I log it?  What if I start the approach in the clouds and break out at 1,500 ft and continue the approach?  1,000 ft?  Before/after the outer marker?  150 feet above minimums?  I think that you get the idea....

Update with relevant info from InFO 15012 (I'm skipping the FTD portions as not relevant to the question, and including the simulated parts but italicizing them as they're useful but also not relevant). Translated, you can log an approach when:

it is flown solely by reference to instruments, and

it is flown in IMC, and Actual Instrument time is logged, or
the PF is using a view-limiting device, and Simulated Instrument time is logged;

you must fly the complete approach from a feeder or the IAP (or Vectors to Final) and remain established the whole time. This means you fly initial, intermediate, and final segments, unless you're on vectors.

if flying the approach in IMC, you may log an approach that:

continues to DA/DH or MDA in actual, or
becomes VMC before DA/DH or MDA, provided you are inside the FAF.

if simulating the approach, you must continue to the DA/DH or MDA under the hood (or other VLD);

That's pretty much it. Here's the source text:

  A pilot may log an IAP for currency or training when the pilot
  accomplishes the IAP in accordance with the following conditions:

  When conducted in an aircraft, flight simulator, flight training device, or aviation training device, the pilot must operate that
  aircraft or authorized training device solely by reference to
  instruments [§ 61.51(g)(1)];
  When conducted in an aircraft, flight simulator, flight training device, or aviation training device, the pilot must be established on
  each required segment of the IAP to the minimum descent altitude (MDA)
  or decision altitude/decision height (DA/DH);
  When conducted in an aircraft simulating instrument flight conditions, a flight simulator, a flight training device, or an
  aviation training device, the simulated instrument meteorological
  conditions (IMC) must continue to MDA or DA/DH; and
  When conducted in an aircraft, the flight must be conducted under actual or simulated instrument flight conditions [§ 61.51(g)(1)].
  When conducted in an aircraft maneuvering in IMC, and the aircraft transitions from IMC to visual flight conditions on the final approach
  segment of the IAP prior to or upon reaching MDA or DA/DH.

Previously, I linked to Rod Machado, who cites the FAA in an answer to this that I quite like, and which was pretty frequently referred to when I was instructing at a flight school:

  Once you have been cleared for and have initiated an instrument approach in IMC, you may log that approach for instrument currency, regardless of the altitude at which you break out of the clouds.

...but this is not the latest knowledge anymore. It's functionally pretty close to the InFo rules for IMC approaches, though!


MD81: Why are there so many lights on the fuselage? Looking at this photo I can see lots of lights on the fuselage of this MD81. It can't be a reflection, can it?

Source: Airliners.net

Why are there so many lights?

I think they are reflection from some light posts in the background environment (green line above the blue "horizon" light), and the reflection of the wingtip position light.


Why is this 737 MAX 8 still flying? I just saw a plane overhead that was flying unusual low and it turns out it was a 737 MAX 8 that left from the Boeing factory in Renton.

https://fr24.com/BOE867/1fdcadbf

Are planes that are not yet operated by airlines exempt from being grounded?

Emergency order issued by the FAA allows for special flights including production flights testing, ferry etc.
The order is available on the FAA website.


Can foreigner fly model aircraft (quadcopter) in US without being part of an organization (like AMA)? The title says pretty much all. I'm visiting Guam very soon and I just found out the FAA is enforcing some rules that are mostly common sense. However, one rule states "the aircraft is operated in accordance with a community-based set of safety guidelines and within the programming of a nationwide community-based organization;"

I have read the rules of AMA, but if i'm not registered with them, does this mean I can't fly my quadcopter in US territory? (non-commercial flight)

Thanks!
Lu

This answer reflects the referenced rules but does not necessarily include all laws that may apply in this situation.

The wording on the picture included in this answer is confusing. If you go to the wording of the bill, it says that the FAA:

  may not promulgate any rule or regulation regarding a model aircraft, or an aircraft being developed as a model aircraft, if--

  ...

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

So this bill does not prohibit you from doing anything, it just says that the FAA can't make a rule specifically about model aircraft that applies to you as long as you are operating according to those rules. You still must follow any other general rules about aircraft. See the interpretation of the rule, as linked from the answer on that question, which says:

  Thus, based on the language of the statute, we conclude that aircraft that meet the statutory definition and operational requirements, as described above, would be exempt from future FAA rulemaking action specifically regarding model aircraft.

  ...

  Thus, the rulemaking prohibition would not apply in the case of general rules that the FAA may issue or modify that apply to all aircraft, such as rules addressing the use of airspace (e.g., the 2008 rule governing VFR operations in the Washington, DC area) for safety or security reasons.

  ...

  The FAA permits aircraft operations below 500 feet when flown over open water and in sparsely populated areas. 14 CFR 91.119(c). Such operations may not be conducted “closer than 500 feet to any person, vessel, vehicle, or structure.”

It looks like there are some such "sparsely populated areas" on Guam, which should meet those requirements. Staying at least 5 miles away from the airports would also be a good idea. You can see that the southern end of the island will be your best bet:

Keep in mind that there are also additional military sites there, including one in the south, that may be sensitive to such things.


Is it safe and effective to have "glider pilot mentality" when landing single-engine fixed-wing aircraft? I am a low-time pilot, of approximately 200 hours. I trained on the DA20 and DA40, designs that are derived from the Diamond touring motor glider design(s) of the early 1990s. I anticipate getting my Glider rating this summer in the US. As I've considered getting my glider rating, I've noticed a habit that I've developed that closely matches the "glider pilot mentality" which does not seem so prevalent in my training for ASEL.

I've always preferred using a forward-slip for landing with the engine idle, as opposed to using the throttle to adjust the descent angle. I attribute this to multiple factors, such as being aware of the design history of the DA20, training with its more "glider-like" characteristics, and a general paranoia of the engine quitting on base or final.

This brings me to the following questions: What are the safety considerations for this type of approach? Are there limitations on the use of sideslip on light airplanes?

Edit: Supplement questions, for possible merge or replacement of above. (Taken from my comment below)

Instead of puttering in using throttle, why don't we use side slips all the time?
Why don't most/more GA aircraft have spoilers or dive brakes?
Is the mentality of "every landing is an engine-out landing" creating more danger than it alleviates?

Diamond aircraft are very low drag and do not have particularly effective flaps, so sideslipping is certainly an effective way to approach the problem. However there are considerations you need to be aware of:

A steeper approach can bring you down on top of another airplane on final approach. Maintaining a more common approach angle is safer as it is less likely to bring you into a potential collision, and keeps you on a path where other pilots are likely to see you
Steep sideslips are not particularly comfortable for passengers, the steep angle and different feel can be frightening
Having your engine idle for long periods can lead to ice buildup in your carburetor, even with the heat on. It also lets your engine cool down quite a bit. Keeping some revs on keeps things warm up front
A steep approach angle makes it harder to round out accurately
A mishandled sideslip can lead to a loss of control. If the ball is to one side and you get past the critical AoA you will be executing a snap roll at low altitude, which = bad

There's nothing wrong with using sideslip and keeping up with the technique - it's very useful if you catch a thermal on approach, are given a slam dunk approach, or need to get on the ground fast. For me it's not the best tool for normal approaches when you have alternatives, especially if you come in at a very steep approach angle.

One technique I've heard of for approaches on Diamond single engine airplanes is to use a combination of both: a slight sideslip dirties up the airflow enough to create some useful drag, and power is used to maintain the approach angle.

I can't think of a light airplane you can't sideslip, or any airplane you can't sideslip for that matter (perhaps the Mig 15). Sideslipping was used successfully in the Gimli Glider incident, and that was a 767! There are limitations which will be listed in the aircraft documentation, for instance you should not sideslip a C152 above 20 degrees of flap. If I'm flying a C150/152/170/172 I follow that rule.


Which incidents did not result in accidents because of the actions of the second pilot on board? In accordance with 14 CFR §25.1523 and §121.385c3, commercial airline aircraft must be operated by at least two pilots. This provision mainly bases on workload and pilot incapacitation considerations (see §25.1523-1).

I am looking for any incident reports of events, in which the second pilot (irrespecive of rank) on the flight deck has corrected a (fatal) mistake made by the other pilot or discovered a failure of some sort which was not discovered by the other pilot, and thus averted an accident. So not the daily flight in which everything is normal, but those in which something went wrong which was then corrected by the second pilot.

Mostly, only events in which something goes wrong and which turn out as severe incidents or accidents are reported as such. These events are thoroughly investigated to learn from these events and make aviation safer. I am, on the other hand, interested in the other 99,99..% of events. Those events that are rarely reported, because everything turned out well in the end, "almost-accidents" that were prevented by the second pilot on board.

Besides the obvious pilot incapacitation events, can anyone recall any specific events / flights and direct me to the respective (official or non-official) report, i.e. by the U.S. NTSB, the French BEA, the German LBA, the British & Australian CAA, …?

During the 2005 Logan Airport runway incursion, the First Officer noticed the other plane and realized that they could collide. Telling the Captain to "keep it down", he pushed the control column forward and passed under the other aircraft as it took off.

During United Airlines Flight 232, the actions of the flight instructor for the type, Dennis E. Fitch, brought in additional expertise that significantly contributed to success. E. Fitch joined the crew during the flight as an additional pilot.

On the day before Lion Air Flight 610 crash, that plane, already with problems, has been saved by off-duty pilot who correctly identified the problem (and suggested to disable the flight control system).


What protocol should be followed after accidentally entering restricted airspace with a UAV? This is related to my earlier question.

Delhi has a lot of areas with restricted airspace and no fly zones. Assuming we are able to get the necessary licenses and permissions to fly, what should we do if we accidentally enter no fly zones while in controlled flight?

The altitude will be less than 400 meters.

Once (and if) we are clear of the no fly zone, where should we report the incident?

This is a hypothetical question. I do not intend to break any laws knowingly.

Well this one I can answer even without being an expert on India's airspace regulations: Entering a "no-fly zone" or other restricted area with an aircraft - even an unmanned one - is going to be some kind of a violation.
You local authorities could tell you what kind, but it doesn't matter: it's a situation to be entirely avoided.

You should plan your test flights to occur far, far away from such restricted areas (as well as from airports, population centers, "open-air gatherings of people" (to use the FAA's parlance), or anything else that you might disturb, damage, destroy, or annoy during your testing.
This is almost certainly what the DGCA is going to tell you if you contact them and ask for advice on test parameters for an Unmanned Aerial Vehicle, but more importantly it's just plain good old fashioned Common Sense!

If you cannot exercise such common sense you should rethink & rework your plans until you can.
If after real, honest rethinking you're still in a situation where you feel you may inadvertently penetrate controlled or restricted airspace then coordinate with the agencies that handle that airspace PRIOR TO YOUR TESTING to make appropriate arrangements.

Now if you exercised all due common sense and still the absolute worst happens (Murphy's law rears its ugly head and LITERALLY everything that can go wrong does - even the engine cutoff and the emergency self-destruct didn't work!) you may still accidentally wander into airspace you shouldn't be in.

If that DOES happen your procedures should be effectively the same as they are in a manned aircraft anywhere in the world if you encounter the same situation: Communicate, Confess, and Comply.
Contact the controlling authority (e.g. tower, approach, the military division responsible, etc.), let them know what's happened, tell them where you are (in this case, where your drone is - they'll likely ask you to copy a number if they want to find out where "home base" is), and comply with any instructions they give you.
(This may mean you need a radio and a list of frequencies on the ground with you - picking up a sectional chart would be a good idea. You may also need a radio-relay in your UAV depending on what kind of range the vehicle has...)

Yes, the controller might get a little snippy with you (you are after all somewhere you're not supposed to be. Controllers tend to not like that!), and you might get in a little trouble for the violation (because again, you're somewhere you're not supposed to be), but that's all preferable to the potential alternative of smacking your UAV into a plane full of people at 300 feet on short final to Indira Gandhi International Airport.
As with all aviation operations, safety must be your overriding concern.


Should spoilers and reverse thrust be deployed before nose gear touches down? On airliners, should spoilers and reverse thrust be deployed before nose gear touches down?

I used to thought that deploying them will affect the handling characteristics, so it is best to wait until all wheels are on the ground; but I've seen pilots do it both ways. Does it depend on landing distance and runway condition?

It depends on the aircraft (and conditions). In some aircraft like the MD-11, the deployment of ground spoilers causes a nose up pitching moment- in such a case, the spoilers should be deployed after nose landing gear touches down.
An example is the incident in Hawaii where the aircraft, a MD-11 exhibited a pitch up tendency during landing and the pilot had to initiate a go around. The factual report noted:

The MD-11 Flight Crew Operating Manual, Volume II, Landing Roll Procedure, contains the following note:
Ground spoiler deployment causes nose up pitching moment. This effect is most noticeable at aft centers of gravity. It is important to check the nose up pitching tendency with forward pressure on the control column and smoothly lower the nose wheel to the runway.

In some cases the deployment of thrust reversers could also have similar effect. In such cases, the thrust reversers and spoilers should be deployed after the nose wheel touches the ground, while in other cases, it is done after the main landing gear touches down and before the nose gear touches down. From FAA Airplane Flying Handbook:

... some airplanes tend to pitch noseup when reverse is selected on landing and this effect, particularly when combined with the noseup pitch effect from the spoilers, can cause the airplane to leave the ground again momentarily. On these types, the airplane must be firmly on the ground with the nosewheel down, before reverse is selected.
Other types of airplanes have no change in pitch, and reverse idle may be selected after the main gear is down and before the nosewheel is down.

There are other issues as well- deployment of thrust reversers before the nose wheel touches the ground means the pilot may not have sufficient authority for steering the aircraft in case one of them doesn't deploy. To prevent this some aircraft restrict the use of full reverse thrust till the nose landing gear is on ground (though idle reverse is permitted once the main gear touches down).
Also, for aircraft having engines in rear, the deployment of clamshell type thrust reversers can have clearance and debris ingestion issues which can limit their deployment. Also, the effect of spoiler deployment on the aircraft aerodynamics has also to be considered. For example, Boeing states:

The MD-80 and MD-90 in-flight spoiler lockout mechanism prevents the undesirable flight control configuration of deployed spoilers in either the speed brake or ground spoiler mode when flaps are extended.

There are also other aircraft (like Tu-154) where the thrust reversers were deployed before touchdown. So, all in all, it is better to consult the particular aircraft manual to decide when the spoilers/thrust reversers are to be engaged.


Is this test question correct about the causes of detonation? So detonation is explained brilliantly in the answer of this question. In the accepted answer, NathanG goes on to say the following:

  the octane rating of a fuel is basically the amount of pressure it can take before it detonates

From what I understand, the higher the number on the octane value, the more pressure the fuel can take, which is why it is used in engines with higher compression ratios.

Assuming octane works exactly the same way in aircraft piston engines as in cars, this has left me confused about a question I was faced with on a small test:

  Which of the following situations may lead to detonation in an aircraft engine?

  A: Running the engine at too rich a mixture setting

  B: Running the engine at too lean a mixture setting

  C: Using fuel of too high an octane rating

  D: Using fuel of too low an octane rating

I thought the correct answers to this were B and D, yet the correct answers were apparently A and C. Can someone explain why this is the case? I'm just not seeing it.

Yes, the writers of test questions are human too.  It would appear B and D are the correct answers.

According to the Lycoming website, for pilots, the greatest danger for detonation in aircraft engines is too lean a mixture.  Running rich at full throttle keeps cylinders cooler. Answer B is correct. Excessively lean mixtures can also be caused by clogged fuel injectors or air intake leaks.

Lower octane also increases risk of detonation because it's "autoignition" temperature is lower than higher octane fuel.  Autoignition can happen without spark due to higher temperature and pressure.  This throws the "timing" of piston power stroke and ignition off, causing a "ping" or "knock".  Engine damage may result. Answer D is correct.

So running rich at high power settings, while producing slightly less peak power, greatly extends the life of your all important engine.


Why does a turbine helicopter need to spin a tail rotor? Should not the exhaust of the turbine supply enough byproduct to deflect and maintain yaw with a simple deflector (i.e. rudder/stabs)?

Well, that’s complex. Where should I begin?

The main job of the tail rotor is to use its long lever arm and directed force/thrust (horizontal lift) to counteract the torque of the spinning main rotor. The exhaust gas of a Turboshaft engine does not produce a large amount of thrust for the very large amount of torque the rotor-powertrain combination produces. See the previous topic: Does a turboshaft's exhaust provide any thrust?.
Energy is finite. In simplest terms, any energy taken out of the engine before the exhaust gasses reach the exhaust nozzle will be energy taken out of the thrust generated. Turbofans generate less thrust with their hot-side core exhaust than Turbojets. Turboprops generate a lot less thrust with their exhaust than Turbofans. And, Turboshafts generate less thrust than that. The most important contribution the exhaust has in a Turboshaft is to dispel heat and waste from combustion.
NOTAR (No Tail Rotor) helicopters already exist that use Coandă Slots and ducted thrust instead of a tail rotor. An internal fan is used instead of the exhaust, though.
The anti-torque thrust a helicopter creates must be variable with the ability to fine tune.
If the engine fails, you still need yaw control until you land.
As complex, damage-prone, maintenance-dependent, and expensive the typical tail rotor system is, if it were possible to use your idea with today’s engine technology, it would have already been done.
I am sure there are other reasons. But, great question. Way to think out of the box.