How are turbine engines started? What happens to a turbine engine from the time that a start is initiated until stable idle is achieved?

What can go wrong?

The means of starting most turbine engines is high pressure bleed air.  This bleed source typically comes from an APU but may also come from an already running engine (crossbleed start) or an external huffer cart.

In some airplanes the start is completely FADEC controlled and need only be initiated and monitored by the flight crew, and in other airplanes certain steps must be manually initiated.

The process below best describes a turbofan engine.  Read @Falk s answer for information on differences with turboprop engines.

Turbofan basics

Refer to the image below (Credit: K. Aainsqatsi, Wikipedia):

The portions of the engine I will be referring to below are:

The N1 fan, N1 shaft and N1 turbine which are displayed in green and labelled "Fan/Low-pressure compressor", "Low pressure shaft" and "Low pressure turbine".  These units are connected and move as one piece.
The N2 compressor, N2 shaft and N2 turbine, displayed in purple and labelled "High pressure compressor", "High Pressure shaft" and "High pressure turbine".  These are connected and move as one, but independently of the N1 shaft.  Un-pictured is an accessory drive that is geared to the N2 shaft to drive engine accessories.
The hot section, pictured yellow and labelled "Combustion chamber".  This is home to a constantly burning fire in a jet engine.

Engine Start

The process of the engine starting follows this basic formula

Through the opening of bleed air valves, bleed air is sent to an air turbine starter.  These devices typically use the high pressure bleed air to spin and engage a centrifugal clutch connected to the engines accessory drive.  This in turn causes the N2 shaft within the engine to spin.
With the N2 shaft spinning, the N2 compressor and the N2 turbines are spinning.  This begins to force air through the engine from front to back.
With the accessory shaft and N2 shafts spinning, accessories should start working and this can be verified by oil pressure indications on the EICAS.
With increased N2 rotation, ignition will be turned on.  These igniters are located in the hot section of the engine and produce small sparks.  There should be an indication on the EICAS that the ignition is active.
With further increase in N2 rotation, fuel flow will be introduced.  This will be verified on the EICAS.  Once fuel flow is noted, it is important that the next stop happen fairly soon.
Light off!  The fuel is lit by the ignition and now the fire burning in the hot section supplied by air from the compressor is producing thrust across the N2 and N1 turbines.
As the engine is producing thrust across on the N1 turbine, the N1 shaft is spinning the N1 fan and the EICAS will note this increase in N1 rotation.  N1 and N2 rotation speeds increase.
Above a N2 threshold, bleed air valves supplying the the air turbine starter will close and the starter disengage. The igniters will turn off at some N2 threshold.
The engine will settle into a stable idle thrust setting.

What can go wrong?

Hung start

N2 fails to spin up sufficiently for fuel flow to be introduced.
Each start has a time limit and the start will be aborted.

No ignitors

Abort the start and switch igniters.
Give MX a call.

Failure to ignite

Fuel flow is introduced but light off has not occurred in a proper timeframe
Fuel is building up in the engine and if light off does occur, it can be damaging.
The start is aborted and dry motoring is performed to clear the engine.

ITT exceedence

There is usually a limitation in the inter-turbine temperature during engine start.
If this is exceeded the start must be aborted
This may require coordination with MX before another start is attempted.

The air turbine starter fails to disengage

This must be corrected before departing
In some engines, MX can correct this with the engine running.

The bleed air shutoff valve supplying the air turbine starter fails to close

This may require an engine shutdown to remedy
However, in some airplanes, this valve can be manually shut by MX with the engine running
Coordination with MX required.

Runaway N1 or N2

If the FADEC isn't managing fuel flow properly, the engine may not settle but continue to spin up.
Abort the start.
Coordinate with MX before attempting a restart.

What about starting the engine in the air?

If the engine suffers a flameout, an airborne restart may be attempted.  These starts typically happen one of a few ways:

Crossbleed start
APU start
Windmilling start

The APU start is essentially the same process as above.  The crossbleed start, which can also be done on the ground, merely substitutes a running engine at a high power setting to provide the bleed air for starting and is otherwise the same as above.

The interesting start is the windmilling start.  The necessity for this means something bad has happened.  To need a windmilling start, this means that there are no bleed air sources to supply the air turbine starter.  This can mean that all engines are out and the APU is unavailable (BAD!), or merely that bleed valves to a shutdown engine have failed closed and are unable to be opened.

For the EMB-145 that I am familiar with, a windmilling start required descending at an airspeed between 260 KIAS and 320 KIAS and could not be attempted above FL250.  In short, you hope that the mass flow through the engine is enough to spin the N2 compressor as the ATS would.  With an N2 indication within the engines airstart envelope, you introduce spark and fuel and hope that the engine lights.  In the worst case, if you too slow and unable to provide enough airflow prior to light off, the engine can quickly overtemp and be damaged.  For this reason it is especially important to abort this kind of start as soon as an abnormality is detected.


How is the search-and-rescue system for civil aviation over waters agreed and funded? Several accidents in the recent years have revealed how important --and intuitively expensive-- SAR operations over seas can be.

Need for daily government agencies / military flights in the first weeks after the accidents, need for underwater search.
SAR managed by other countries than the registration country of the aircraft.

Crewmembers of an Indonesian Air Force NAS 332 Super Puma helicopter over the Java Sea, Indonesia, 2015.Source

Without entering into too much details:

How is SAR for civil aircraft agreed globally?
Is that under ICAO umbrella?
Is it shared with maritime SAR or other organizations?
How is SAR responsibility shared between countries worldwide?Is a map with responsibility boundaries available?
How is SAR funded?
Are operators (their insurances) liable for costs?
Is it a service provided for free, if so to which extent?
How is the decision to stop active search taken?

Search and Rescue is under the ICAO umbrella, but also with the IMO.

Annex 12 to the Convention on International Civil Aviation gives the international standards and recommended practices (SARPS) on Search and Rescue.
The annex is supplemented by the International Aeronautical and Maritime Search and Rescue (IAMSAR) Manual, which is published by the International Maritime Organisation (IMO)

Together the documents describe:

The organisational structure of the worldwide SAR system concept,
including cooperation between states. (ICAO Annex 12, chapter 2, 3 &
4, IAMSAR volume 1)
The operating procedures for organising and coordinating a SAR
mission (ICAO Annex 12, chapter 5, IAMSAR volume 2)
The operating procedures for those carrying participating in the SAR
mission (Appendix to ICAO Annex 12,  IAMSAR volume 3/ ICAO doc. 9731)

The details of implementing the SARPS are left to the states themselves.


Why are the 737's rear doors unusable in a water landing? The 737's rear exit doors cannot be used to evacuate the aircraft in the event of a water landing, as shown, for example, in this safety card:

(Image from flight-report, via Jordy here at AvSE.)

In contrast, the rear doors on (for instance) the A320 series can be used for a water evacuation:

(Image by Czechnology here at AvSE.)

Why can't the 737's rear doors be used during a water landing?

The bottom of the door opening sits too close to, or below, the water line when the airplane is floating.


Is corrected astigmatism disqualifying for an EASA Class 1 medical? I realize there are similar questions on the site already, but not one specifically dealt with my problem. I reside and plan to work in Europe so I looked up the EASA regulations, but I couldn't really make sense of them. My question is: I have astigmatism, which is corrected by my glasses. I am also shortsighted, which is also corrected. Does this disqualify me for a Class 1 license?

I have a registered astigmatism on one eye that is balanced by the other eye. I have a Class 1 medical w.o. problems. In my medical record, the Doc wrote that my astigmatism corresponds to a .75 dpt on one eye.

He also told me that absolute values are not important, important is that the astigmatism is corrected by either the other eye, some glasses or it is so low that the brain can even correct for it.


What is the difference between the WSUSnn IDs used in convective SIGMETs? When NOAA issues a convective SIGMET, it falls under one of three bulletin IDs: WSUS31, WSUS32, or WSUS33. Below are three examples from the current forecast.
WSUS31:
WSUS31 KKCI 020455
SIGE
CONVECTIVE SIGMET 24E
VALID UNTIL 0655Z
PA
FROM 30NNW JST-20SE EWC
LINE TS 25 NM WIDE MOV FROM 24025KT. TOPS TO FL340.

OUTLOOK VALID 020655-021055
AREA 1...FROM 130SSE ILM-210ENE TRV-TRV-SAV-130SSE ILM
WST ISSUANCES POSS LT IN PD. REFER TO MOST RECENT ACUS01 KWNS
FROM STORM
PREDICTION CENTER FOR SYNOPSIS AND METEOROLOGICAL DETAILS.

AREA 2...FROM 70NNE
ASP-ECK-DXO-CLE-BUF-SYR-BKW-VXV-MSL-TTH-TVC-70NNE ASP
WST ISSUANCES POSS. REFER TO MOST RECENT ACUS01 KWNS FROM STORM
PREDICTION CENTER FOR SYNOPSIS AND METEOROLOGICAL DETAILS.

WSUS32:
WSUS32 KKCI 020455
SIGC
CONVECTIVE SIGMET 30C
VALID UNTIL 0655Z
MI WI LS
FROM 30SSE YQT-40SSE DLH
LINE TS 30 NM WIDE MOV FROM 27050KT. TOPS TO FL310.

OUTLOOK VALID 020655-021055
FROM TTH-MSL-ELD-LFK-DLF-TCC-GCK-RZC-TTH
WST ISSUANCES EXPD. REFER TO MOST RECENT ACUS01 KWNS FROM STORM
PREDICTION CENTER FOR SYNOPSIS AND METEOROLOGICAL DETAILS.

WSUS33:
WSUS33 KKCI 020455
SIGW
CONVECTIVE SIGMET...NONE

OUTLOOK VALID 020655-021055
TS ARE NOT EXPD TO REQUIRE WST ISSUANCES.

The WSUS31 is an WMO ICAO communications header. It is not a SIGMET category, it just identifies the basic item and source, in this case WSUS31 is weather-SIGMET united states, 3x is for regional distribution (eg the Americas) x1, x2, x3 are the east, central, and west SIGMET areas in the contiguous USA[CONUS].
Another example: An AIRMET for the far west area would be WAUS46. AIRMETs have 6 areas in the CONUS and 3 in Alaska, 4x means national distribution.
Distribution codes

0x,1x global
2x,3x regional
4x,8x national and bilateral
9x reserved

https://www.weather.gov/tg/awips
https://www.weather.gov/tg/headef
(sections 3.4.1 and 4.3.1) https://www.icao.int/EURNAT/EUR%20and%20NAT%20Documents/EUR%20Documents/EUR%20Documents/014%20-%20EUR%20SIGMET%20and%20AIRMET%20Guide/EUR%20Doc%2014%20%20(EN)%20-%20Edition%202,%202010%20-%20rev%2029Oct2019.pdf


Would the Aeroflot Flight 1492 have been able to dump its fuel first before landing? In the recent Aeroflot Superjet 100 crash, it seems to me that (at least) the landing gear was spiked upwards, penetrating the fuel tanks, which might be one of the factors that lead to disaster.

In my naive mind, dumping the fuel before landing might have mitigated this factor.

Would it have been possible for this airplane to dump its fuel before landing?

This aircraft does not have fuel dumping capability. In general, only large wide body airliners have fuel dumping capability.

Aircraft can land overweight quite easily but getting stopped on the runway safely is the main problem.

Even with fuel dumping, aircraft will often still plan to land overweight. The amount of fuel to be dumped would be planned to make a safe landing on the available runway without excessively heating the brakes and tires.


Do airline pilots identify failed engines in the same way as light aircraft pilots? Do the two old adages of light multi-engine flying, namely "Dead foot, dead engine" and "Raise the dead", still apply when flying transport-category aircraft?  Or do airline pilots need to rely on their engine instruments in order to figure out which engine's kicked the bucket?

For those who aren't familiar with those memory aids, they are from page 12-21 (186 in PDF versions) of the FAA AFM:

  There are two time-tested memory aids the pilot may find useful in dealing
  with engine-out scenarios. The first, “Dead foot–dead engine” is used to
  assist in identifying the failed engine. Depending on the failure mode, the
  pilot won’t be able to consistently identify the failed engine in a timely
  manner from the engine gauges. In maintaining directional control, however,
  rudder pressure will be exerted on the side (left or right) of the airplane
  with the operating engine. Thus, the “dead foot” is on the same side as the
  “dead engine.” Variations on this saying include “Idle foot–idle engine” and
  “Working foot–working engine.”

  The second memory aid has to do with climb
  performance. The phrase “Raise the dead” is a reminder that the best climb
  performance is obtained with a very shallow bank, about 2° toward the
  operating engine. Therefore, the inoperative, or “dead” engine should be
  “raised” with a very slight bank.

Yes, the dead foot, dead engine does apply (but not as much as you might think), and, yes, airline pilots need to rely on their engine instruments in order to figure out which engine has failed, especially when you're flying a 4-engine aircraft. Actually, and with obvious prejudice, I prefer to say that the Flight Engineer will use the engine instruments to tell the Captain which engine has failed. Couldn't resist that.

Sudden loss of power on 727-100s and 747-100s/-200s is not nearly as noticeable as, say, on a Cessna 310. If you lose the middle engine (#2) on a 727, all you're going to notice is the loss of 1/3 of your power. Even the loss of engines 1 or 3 will not produce much yaw because they're mounted close to the aircraft centerline.

On the transport-category aircraft I flew it was unlikely that your foot would notice an in-flight engine failure because you took your feet off the rudder pedals as soon as you lifted off and didn't put them back on until short final. Adverse yaw was taken care of by the yaw damper.

If the loss of an engine came during descent at flight idle, the pilots might not notice it unless there is an obvious alert of some kind. We had one quit on us descending into Miami once and neither I nor the f.o. noticed it. Our alert was the f.e. saying something like, "We just lost #3." My increased work load consisted of simply saying something like, "See if you can get it running again. If it doesn't light off, forget it."

If you deliberately shut down an engine, you of course know which engine it is. That happened to me once. Again another vote for f.e.s. This one informed me that the oil pressure was dropping and oil temp climbing on one of the engines. He recommended shutting it down, which we did.

Generally speaking, when you lose an engine suddenly without warning when climbing out, I think the thing to remember is to take your time, fly the airplane with the configuration you have, and work the checklist for the situation at hand. That checklist will have procedures to ensure you shut down the engine that has failed, not one that's still operating. In other words, just do what you do in the sim every 6 months.


How are wingtips attached to the aerofoil while maintaining structural rigidity? I've been trying to research various methods on the joints between the winglet and the wingtip out of interest. I'm aware that the airfoil is attached to the underbody of the fuselage by means of a butt joint, but with companies like Aviation Partner who offer options such as BBJ's, how are these winglets attached?

There are a number of winglets available in market for retrofitting and their method of attachment will also vary. Boeing details the procedure for attaching a winglet to their BBJ and it is quite instructive. According to the article the main issue is modifying the wing to accommodate the winglet, rather than the attachment itself.

  The more time-consuming part of the retrofit is installation of the
  wing modification to accommodate the winglet.

For this particular aircraft, the following steps are given:

  Removal and replacement of the outboard upper and lower skin panels
  Removal and replacement of rib 25, which is third from the outermost rib
  Installation of stiffeners across rib 25.
  Cutting of the closure rib (rib 27) and trimming of the two spars
  Installation of the new center section of rib 27 and the
  new winglet attach fitting
  Installation of the spar attach fittings
  Installation of the aft-position light.

which is followed by installation of the winglet.

Installation of winglet, from Boeing Aero.


How did the USS Vincennes misidentify an Airbus aircraft? Wikipedia indicates that the USS Vincennes misidentified Iran Air Flight 655:

  Crucially, Vincennes misidentified an Iran Air Airbus A300 civilian
  airliner, Iran Air Flight 655, as an attacking F-14 Tomcat fighter
  aircraft. The Iran Air Flight 655 was climbing at the time, and her
  IFF transponder was on the Mode III civilian code rather than on the
  purely military Mode II, as recorded by Vincennes's own shipboard
  Aegis Combat System. Vincennes fired two radar-guided missiles and
  shot down the Iranian civilian airliner over Iranian airspace in the
  Strait of Hormuz, killing all 290 passengers and crew on board.

Based on the narrative (and any other supportable information): Does the root cause of misidentification comprise:

Failure to follow procedure (Military / Civilian IFF, etc.)?
Equipment Failure?
Human factors (Fatigue)?

The questions are posed because this is the first of at least two Iranian-originating civilian flights that are misidentified by military personnel: I am wondering if there is a pattern, that can produce a lesson-learned (when the final report is published).

tl;dr We don't know.

The US Government has not made enough information available to answer this question. The official Iranian and US reports contradict each other. Inofficial accounts of sailors on other USN vessels operating in the vicinity at the same time contradict both the official US report as well as statements made by Vincennes commanding officer.

There are several possible explanations, many of which have not been officially acknowledged, and probably, the real cause will be a combination of multiple factors. And some of those are easy to address:

User Interface Design: the target tracking system recycles target designations. Shortly before the shootdown, the system had assigned a new target designation to the aircraft and recycled the old designation for a fighter operating over 100 miles away. When the CO asked what the classification for the target designation was, the answer was "fighter" and that it was descending, which was correct for that target designation, but was actually for a completely different aircraft now.

Don't Do That!

No access to current flight plans: the crew only had access to the standard regular schedule, but not to updated flight plans, e.g. including delays or cancellations. On the day in question, the flight was delayed by over half an hour.

Assets used for monitoring mixed-use airspace should be equipped with civilian radios and be in contact with ATC.

Ergonomic Design: the lights were so dark, and flickered every time the weapons were fired, that the crew assigned to monitor the airspace couldn't read the printed out flight schedules.

Better lighting. Or, put the schedules / flight plans into the computer. Even better: integrate them into the target tracking system.

Timezone confusion: the flight schedules were printed out in Iranian time, but the ship's time was Bahrain.

One word: UTC.

Missing Equipment: the Vincennes had no possibility of using civilian frequencies (other than the international distress frequency 121.5), so they had no way of knowing that the "unresponsive" aircraft was in fact in constant communication with ATC.

See #2. Note that directly after the incident, the US Navy did install tunable VHF radio on all ships in the Gulf.

Wrong Frequency: of the 10 attempts to establish contact with the aircraft, 7 were made on military frequencies. Obviously, being a civilian aircraft, the Airbus had no way of hearing this.

Train crew to remember that failure to respond to a military frequency does not imply hostile intent, especially since civilian aircraft won't even be able to respond.

Speed confusion: when the Vincennes adressed the unidentified aircraft, they gave the aircraft's speed in groundspeed as 350kts, but the indicators in the aircraft would have read 300kts indicated airspeed. Since the speed was wrong, the pilots may have thought the calls were made to a different aircraft operating in the vicinity whose speed was closer to the one in the call.

Make it clear in your transmission that you are talking about groundspeed.

A year earlier, another USN vessel was (mistakenly) hit by Iraqi missiles. Her commanding officers received official Letters of Reprimand, effectively destroying their careers, stating that defense of the ship is the first duty. This may have put the CO under additional pressure, fearing for his and his family's livelihood.

Don't punish people for being hesitant in highly complex combat situations involving close proximity of civilians.

Scenario Fulfillment is a psychological condition affecting both individuals and groups where once a situation looks like a certain training scenario, that scenario will be followed to the end, filtering out all Information that does not fit the scenario. The US Government has put forth the possibility that the entire bridge crew may have collectively suffered from this condition.

Psychological training.

The crew was under stress since they had illegally and unprovoked entered Iranian waters, and were simultaneously also engaged in a firefight with Iranian gunboats (which Vincennes provoked by illegally sending her helicopters into Iranian airspace). Either of these two infractions would have been cause for Iran to send fighters to intercept and attack the ship.

See #9.

The CO was known to be a hot-headed aggressive guy looking for fights, and even creating them if there was none. He may have been looking too hard and found one where there was none.

Don't hire such guys, filter them out using psychological evaluations.


Why is the Airbus Beluga XL based upon the A330, and not upon the A350 or A380? Airbus is developing the successor of the Beluga, called Beluga XL.

The original one was based on a standard A300, while the new model will be based on the A330.

Why is the new model based on a quite old design like the A330, and not the more modern A350 (which could generally be more efficient and have more modern avionics)?
In addition, I saw that Boeing built an equivalent aircraft, the Dreamlifter, based upon its biggest model, the 747, so... obvious question: why doesn't Airbus base the Beluga XL off of its giant, the already-tested A380?  This could offer a much better payload capacity, and, maybe, even the ability to carry fuselage sections of future A380s (which, currently, must be transported by trucks due to their size).

Considering that (one of) the main reason(s) for introduction of larger Beluga XL is to meet the demands of the A350 XWB production, it doesn't make sense to have a modified A350 for the next transporter: Airbus would prefer to sell A350s to customers than to modify them for internal use.
A380 is not supported by airports near most of the Airbus production centers- defeating the very purpose of having the Beluga XL fleet.
In the end, it boils down to which aircraft can satisfy two requirements- payload and runway capability at Broughton. From caan.asia/en:

Airbus wants an aircraft which not only meets high payload capabilities - including capacity to carry two fully-fitted A350 wings - but can operate within airfield landing limitations at its UK wing facility at Broughton, to which it will deliver A350 wing covers. Broughton's declared available landing distance for the shorter runway 04 approach is 1,663m (5,460ft).
Airbus considers this restriction to be too tight for a modified A330-300 or A340-500, while the payload requirement is too high for an A300-600. It believes an A330-200 variant - tentatively designated the A330-200XL - could potentially cope with the landing criteria at projected weights of around 135t, and is the most promising option.

Boeing Dreamlifter, on the other hand, is purpose built for B787 transport- wings and fuselage, while the Beluga transports only the wings. The distances involved in the B787 production (compared to the only European production centers of A350 XWB) means that Airbus can afford to transport only the wings, rather than fuselages too.


What is the aerodynamic centre and how does it relate to the pitching moment? Okay so I have been trying to get my head around the Aerodynamic centre and the Pitching moment. Wikipedia really isn't helping much but from what I can gather the Pitching moment is a force caused by the lift from the aerofoil acting upwards from the Aerodynamic Centre (lift) and which acts around the centre of gravity (hence the tail must be configured to counteract this. Can someone please help me out here?

A pitching moment is every moment acting around the lateral axis. Since a moment is the combination of a force and a lever arm, the magnitude of the moment depends on the choice of reference point, the point around which the pitching moment is defined. For flight mechanics, it helps to choose the center of gravity for all pitching moments, because then the weight force will not add a pitching moment of its own. Also, the center of gravity is special because this is the point around which the airplane rotates while in flight.

I guess you mix up aerodynamic center and center of pressure. For me, it helps to use the term "neutral point" instead of aerodynamic center. Why?

Center of pressure describes clearly what it is: If you integrate all the pressures acting perpendicularly to the airflow, the resulting force acts in the center of pressure, just like all masses are summed up in the center of gravity (which, therefore, should be better called the center of mass).

In contrast to the center of mass, this center of pressure is not fixed, but moves when the angle of attack changes. If the airfoil has positive camber, the center of pressure moves forward with increasing angle of attack. If you now move your point of reference away from the center of pressure, you need to replace the lift force by the combination of the lift force and a moment (cogging torque). The motion of the center of pressure is such that at one point the cogging torque is constant regardless of angle of attack and lift. This is the aerodynamic center or neutral point, and I think "neutral point" describes much better what it is: The one point where the cogging torque behaves neutrally regarding angle of attack changes.

The real reason for this name is that static longitudinal stability is neutral (neither positive nor negative) if the center of gravity falls on the neutral point.

In stable flight the pitching moment around the center of gravity has to be zero; otherwise the airplane will display an accelerating pitch motion. To zero the pitch moment, the center of pressure is shifted onto a vertical line through the center of gravity. This shifting can be done by adding or subtracting lift at the tail, which in turn is done by adjusting the elevator deflection or the stabilizer incidence (if the plane has a moveable stabilizer)

Background

In potential flow theory, lift can be calculated as the linear superposition of a contribution from camber and one from angle of attack. While the camber-related part of lift is constant, the angle-of-attack related part varies linearly with this parameter. The center of pressure of the camber part is somewhere at mid-chord (details depend on the camber line; with a Joukowski airfoil the center of pressure is precisely at mid chord). The center of pressure of the angle-of-attack dependent part is at the quarter chord (the center of the area below the chordwise Birnbaum distribution of lift). The important part is the self-similarity of Birnbaum distributions for different angles of attack: The center of pressure of the angle-of-attack dependent part is constant.

Since lift at zero angle of attack is solely from camber, the center of pressure is at around mid chord and moves forward towards the quarter chord point as angle of attack increases. The cogging torque of the camber-related lift contribution around the quarter chord point is also constant, and since the angle-of-attack dependent part of lift has its center of pressure in exactly this quarter point, it will not add a pitching moment of its own at this point. Ergo, the cogging torque of lift in potential flow is constant if the reference point is the quarter chord point.

Fun fact: The center of pressure will move into infinity as the angle of attack is reduced to the zero-lift angle of attack.


How to pronounce ICAO? How to pronounce ICAO, correctly?
Civil Aviation students claim that their teacher told them to pronounce it as

  /ˌaɪˌkeɪˈoʊ/, eye-KAY-oh

but when I look at Cambridge Dictionary it pronounces ICAO differently: https://dictionary.cambridge.org/us/dictionary/english/icao

So, how do you pronounce it correctly in Aviation?

I have usually seen people in the industry pronounce it as eye-kay-oh. Technically, the correct way would be to pronounce the letters individually as per the English language which is why the dictionary has that but I have never seen anyone pronounce it that way.


Why is FL398 the REC MAX altitude on the A320? On the A320 PROG page and in our limitations the REC MAX/ MAX FL is listed as FL398. What is the reason behind this ?

I just came across the answer in the AFM it states

"THIS IS THE MAXIMUM ALTITUDE AT WHICH IT IS POSSIBLE TO MAINTAIN CABIN PRESSURE ALTITUDE BELOW 8000 FT"


Is Touring Motor Glider included in the term "aeroplanes"? The EASA definition goes as follows:
‘Aeroplane’ means an engine-driven fixed-wing aircraft heavier than air, that is supported in flight by the
dynamic reaction of the air against its wings.
‘Aircraft’ means a machine that can derive support in the atmosphere from the reactions of the air other
than the reactions of the air against the earth’s surface.

To me a TMG could go under that definition but not sure though...
Basically I'd like to know whether the 15 hours that are needed to go from LAPL(a) -> PPL(a) can be done on TMG
https://www.caa.co.uk/General-aviation/Pilot-licences/EASA-requirements/PPL-SPL-BPL/PPL-(A)-requirements/

To my understanding of Part-FCL, yes.
While aeroplanes is a broad term used in the FCL, they use it in some cases to include both, SEP and TMG, e.g.

  FCL.105.A LAPL(A) —Privileges and conditions (a) The privileges of the holder of an LAPL for aeroplanes are to act as PIC on single-engine piston aeroplanes-land or TMG with a maximum certificated take-off mass of 2 000 kg or less, carrying a maximum of 3 passengers, such that there are never more than 4 persons on board of the aircraft.

and hence

  FCL.210.A (b)  Specific requirements for applicants holding an LAPL(A). Applicants for a PPL(A) holding an LAPL(A) shall have completed at least 15 hours of flight time on aeroplanes after the issue of the LAPL(A), of which at least 10 shall be flight instruction completed in a training course at an ATO. This training course shall include at least 4 hours of supervised solo flight time, including at least 2 hours of solo cross-country flight time with at least 1 cross-country flight of at least 270 km (150 NM), during which full stop landings at 2 aerodromes different from the aerodrome of departure shall be made.

Source: https://www.easa.europa.eu/sites/default/files/dfu/Part-FCL.pdf


Why are taildraggers considered more rugged than tricycle? Not trying to get into the age old debate of which is better. From mechanical perspective, all landing gears are just long cantilevered beams. With a greater instability, one would expect tail draggers to not be preferred for a rough ground surface.

To expand/clarify upon the other answer, bush planes and the like use tail wheels because imagine if when landing on a rough runway, your little tiny nose wheel hit a rock.  That could be catastrophic.  However, on a taildragger, the big main landing gear can go over some obstacles, and the little wheel on the back won't pose a big problem with small rocks and such.  The little wheel will just bump over the obstacle, instead of possibly skidding on it and throwing the whole plane off.  Effectively, the plane is dragging the tail wheel over the obstacle vs. pushing the tail wheel into the obstacle.  So, that's why I think that tail draggers are preferred for a rough surface.

Feel free to correct me if I'm wrong... I've never really flown a plane in my life.  I'm just an enthusiast.


Is there a forced retirement age for Part 135 pilots? I know that international Part 135 operations have a set retirement age of 65, however if one was to stay within FAA jurisdiction is there a set retirement age for Part 135 operations?

There is no FAA mandated retirement age for part 135 operations, although there was in 2017, a proposal in Congress that would limit the maximum age but only for certain operators. As of the date of this answer there is no regulation for 135 pilot ages.

It's up to the operator then to decide if they want to hire somebody who can only fly domestic routes. For some this may not be an issue, for others it may be a deal breaker.


What is the average climb gradient of an aircraft during the takeoff and early phase of a departure procedure? On chart plates it is written the minimum climb gradient with which an aircraft should climb for obstacle clearance or after ATC request (for traffic flow management etc.).

However, since this is the minimum required climb gradient, I am curious about what practically happens during real flights. For example, if a chart plate instructs an initial climb with a minimum climb gradient of i.e. 320 feet per nautical mile, will the aircraft try to maintain this minimum climb gradient until the termination altitude? Will it climb with the maximum climb gradient that its performance characteristics allow?

In other words, given an assigned climb gradient from a chart plate (i.e. from DEEZ5: "Standard with minimum climb of 250' per NM to 300), what would the average climb gradient of an aircraft during the initial climb phase be, provided that this value is taken into consideration not only for a lower but also for the calculation of an (hypothetical) upper limit?

The upper limit is a function of the airplane's performance at rated climb power at the normal speed used, modified somewhat by the wind (the gradient is based on ground speed).  What actually happens on a departure is simply whatever numbers that airplane's performance produces using the standard speed and power setting for that airplane.

In a jet you are generally going somewhere around 200 kt once the flaps are up, then accelerate to 230-250 kt once past 3000 ft up to 10000 ft.

From the table below, assuming no wind, an airliner climbing at 3000 FPM at 200 kt will have a gradient of roughly 1000 ft/nm between the initial acceleration altitude (say 1000 ft) and 3000 ft:


How should I log total hours flown in different countries? Let's say you have an EASA-style logbook with European flight time, and then, you start flying in the USA, so you buy an FAA-style logbook and begin logging hours for your flights in the USA.

I don't think it is a good practice to mix foreign hours, since if both logbooks are still open you can have inaccuracies and inconsistencies in the transferred hours.

The question is: is it mandatory to bring your flying hours from the European logbook to the "AMOUNT FORWARD" section in the American logbook, or is it optional?

What is a good practice if you have multiple foreign logbooks?

Is it mandatory to bring your flying hours from the European logbook to the "AMOUNT FORWARD" section in the American logbook?

No, it is not mandatory to bring your flying hours from the European logbook to the "AMOUNT FORWARD" section in the American logbook.

In the USA, logging time is not required at all other than information for required recent experience and check ride prerequisites.  Also, there is no reason the EASA logbook is not an acceptable document for that purpose so long as it contains the needed information such as landings.

What is a good practice if you have multiple foreign logbooks?

Consolidate them into one logbook that best fits the system in which you do most of your flying and keep only specific additional requirements for the other systems logged elsewhere.

If you need to keep the total flight hours separate, I would use one of the customizable columns that I have seen in most logbooks and label it with whichever system you fly in less.  Then you can simply subtract that column from your grand total to deduce the other system's total time.

Although, based on how much I get picked on by my German friends for not using the metric system, I could understand the assumption that we must be different.


How does the Boeing 747 smoke evacuation work? (source, inset source)

I recently watched Mayday's dramatization of UPS Airlines Flight 6.

Then I recalled the Boeing 747 having a SMOKE EVAC handle.

How does the system work?
Why wasn't it used to better allow the crew to see? Or was it used but didn't work?

Looks like the smoke evacuation handle was used, but had little effect on the outcome. From the Final accident report of Boeing 747-44AF N571UP:

  The Captain called for the smoke evacuation handle to be pulled as the smoke accumulated in the cockpit. ... The smoke evacuation handle remained open for the remainder of the flight.

The report also has a note on its working:

  The smoke evacuation handle when pulled opens a port in the cockpit roof, which if the smoke is sustained and continuous, will draw smoke through the cockpit as the pressure is reduced by the open port ...

There is also a mention of it in the preliminary report:

  Smoke  Evacuation Handle –a  handle immediately  aft  of  the  P5  overhead panel that when pulled opens a circular, manually displaced vent in the  overhead fuselage section of the flight deck.

The final report also has an image of the exhaust port.

Smoke Evacuation Port (cockpit ceiling); image from Final accident report of Boeing 747-44AF N571UP


Why do few small planes have reflexed flaps? Reflex flaps capability is very common in flapped gliders, but outside of gliders I am only aware of the Maule which has this feature. https://aviation.stackexchange.com/a/37753/20394 shows the advantage gliders gain from reflex position, so presumably this would hold for more aircraft than just gliders.

I can see how with certain types of flaps, such as fowlers, the mechanism would be impossibly complex. But for other types with a simple pivot this must be more attainable.

I'd guess that it's because gliders are optimised for low speed in rising air and their aerofoils have lots of camber. Reflexed flaps allow them to reduce the camber for high speed flight, but the resultant aerofoil isn't as good as a proper low-camber, high speed aerofoil.
RC power models generally have plenty of power to spare and either don't care about drag or it only matters at high speeds. Their aerofoils are generally low (or zero) camber already so they don't need reflex flaps to achieve it.


Can you identify those parts (sensors), on test aircraft and the purpose? I have seen many photos with those sensors attached to the test aircraft, Can you provide why they are used and what do they measure?

Here is another example on SuperJet:

On the super jet that's a pitot tube rather large but still it's a testing aircraft. Aircraft's use pitot tubes to measure airspeed. The example, from an Airbus A380, combines a pitot tube (right) with a static port and an angle-of-attack vane (left). Air-flow is right to left. A pitot (/ˈpiːtoʊ/ PEE-toh) tube is a pressure measurement instrument used to measure fluid flow velocity. And so on, The basic pitot tube consists of a tube pointing directly into the fluid flow. As this tube contains fluid, a pressure can be measured; the moving fluid is brought to rest (stagnates) as there is no outlet to allow flow to continue. This pressure is the stagnation pressure of the fluid, also known as the total pressure or (particularly in aviation) the pitot pressure. Go here, for evidence.


What aircraft are parked in this naval air station? In May 2020 I saw C-130 Herculess on a naval air station in Ventura County, California. Later, I decided to use Apple Maps so that I will remember what I have seen.
Apple Maps showed some C-130 Herculess, F-18 Hornets, P-3 Orions, and a few other aircraft. But when I zoomed into one of the air stations, I noticed some strange aircraft parked next to the P-3 Orions. They appear to be either a foreign aircraft, or some kind of experimental aircraft that I do not know.

Six of the unknown aircraft have a large swept wing, while two others have a delta wing featuring what looks like a canard.

At the right end of the row of eight fighters, the two delta wings look like Dassault Mirages.  Trailing edge with a slight reverse sweep.  Ordnance just visible mid-span.  Upper fuselage flared towards the engine inlets.
The six fighters at left look very much like Hawker Hunters, but those are now flown only at air shows.  That guess led me to discover that they were stationed at Point Mugu AFB for a 2015 air show.
A video of the maybe-Hunter taxiing at Point Mugu in 2015 also
shows that one of the delta wings has registration N401AX,
which identifies it as a 1980 variant of the Dassault Mirage 5,
an Israel Aircraft Industries KFIR-C2.
Later, the video also shows the maybe-Hunter's registration, N330AX, confirming it as a 1959 Hawker Hunter Mk.58.


How airworthy was the BV 141? How did the BV 141 fly? It looks like it has very uneven weight distribution and the overall design is asymmetric. I'm surprised that it could even take off.

Why would you think the weight was not correctly distributed? If the center of pressure and the center of gravity coincide, there is no problem. Every pilot needs to bring the center of pressure right above or below the center of gravity when flying; this is commonly known as trimming the aircraft. Almost all aircraft have small asymmetries which need to be counteracted by small control surface deflections or trim tab settings.

Note that the fuselage of the BV-141 is offset to the left and the cockpit is offset to the right. This keeps the spanwise center of gravity location near the center of the wing, so any resulting rolling moment is small. What remains (maybe due to an unusual high or low loading of the cockpit) can be trimmed away with the ailerons. A yawing moment due to asymmetric thrust can also be corrected by rudder trim, and the engine was placed on the left so the p-factor of the propeller (which creates more yawing moment at low speed) would counteract the yawing moment due to its out-of-center position.

The BV-141 was designed as an observer platform with an unrivaled field of vision. By using an offset fuselage, only the left side was obstructed by an engine or tailboom. If you compare the BV-141 with its competitor for the same tender, the Focke-Wulf 189, the advantage should become obvious.

Focke-Wulf Fw-189 (picture source)

Note that the BV-141 was a private entry in this contest and was not selected.

A similar aircraft with an asymmetrical mass distribution was the Flyer I of the Wright Brothers. Here, the right wing was 4 inches wider than the left to create additional lift for the heavy engine which was positioned to the right of the pilot.

Front view of the 1903 Flyer I (picture source). Note the offset engine position.


Is the maximum lift-drag ratio found at minimum drag? Figure 10-5 of the FAA's Pilot's Handbook of Aeronautical Knowledge shows:

I didn't think $L/D_{MAX}$ coincided with $D_{MIN}$. Is this Figure accurate?

Well, for all L/D curves and D curves, the assumption is that the weight of the aircraft is constant and that there is no acceleration. Therefore the lift equals the weight (neglecting the small vertical component of thrust). So lift is a constant in these curves.

The rest is simple mathematics; the maximum of $\frac{1}{f(x)}$ occurs at the minimum of $f(x)$ (when $f(x) > 0$), so the maximum of $\frac{L}{D}$ coincides with the minimum of $D$.


What do the gyroscopes used in commercial aircraft actually look like? I pretty much grew up watching Air Crash Investigation and Seconds From Disaster and every other episode had a mention of the aircraft’s gyroscopes, but I always wondered how did FAA rated industrial long use gyroscopes actually look like and where were they physically placed inside the aircraft?

The first gyros were mechanical: A spinning wheel with gimbal mount and driven by air pressure. The picture below shows the innards of one which was used in the Supermarine Spitfire (picture source). The black disk on the right is the instrument background and the arm on top moves the vertical needle sideways in accordance with the turn rate of the aircraft. The white coating on the needle is phosphor to make it glow in the dark.

State of the art is to use a ring laser gyro. This is an optical device which sends a laser beam around a triangular or square track in both directions. Rotations will make the light path shorter in one direction and longer in the opposite direction, so the interference between the two beams shifts the place where the waves cancel each other. This shift is registered and interpreted as a rotation. An alternative design uses optical grade glass fibers for the light path.

The placement is important because flexing of the fuselage will give different results for different mounting positions. To my knowledge, in airliners gyros are mostly part of the avionics suite below the cockpit.

See here for a list of sample applications.

Ring laser gyro assembly with three gyros, one for each spatial axis (picture source).

More modern MEMS sensors are on the advance but mostly to be found in backup systems or on unmanned aircraft. They are much more compact and use less power, but their accuracy is lower than that of ring laser gyros.

Silicon Sensing CRS03 MEMS gyro (picture source).


Have B-25's and B-26's been converted for private business use? In the movie Cash McCall, the main character, McCall, owns an aircraft that looks remarkably similar to a B-25 or B-26, but is painted yellow and has no turrets.

Have these aircraft been converted for private business use or were there business aircraft based on the design of WWII bombers?

IMDB:

  McCall's plane is a demilitarized Douglas A-26 Invader, a type used in WWII.

Since the film was made in 1960, I imagine there were plenty of them around.

(The A-26 was known a the B-26 from 1948 to 1965, according to Wikipedia. The B-25 is easily distinguished because it has the twin tail.)


How heavy are modern cantilever monoplane wings? Aircraft need to reduce weight in order to reduce induced drag.  The modern shallow cantilever beam wings carry a massive weight penalty, as most of the material is wasted inefficiency absorbing the bending moment. However, with advancements in materials,  their mass has reduced to the point that parasitic drag benefits outweigh induced drag losses.
But I would like to know how much structural efficiency still influences wing design. Compared to the total empty weight of the aircraft, how heavy are the wings if modern cantilever monoplanes? This includes large airliners and small GA planes. An example of a design from each class is sufficient.

Wing structure is roughly 20% of empty weight, which is roughly half of gross weight. I clipped the two sources some time ago and no longer have references.


How safe is the Certified Rotax 912 versus the Continental O-200? I'm thinking of buying a taildragger LSA, many of which have a Rotax engine. Continental and Lycoming are the major suppliers of certified piston aircraft engines, and they are considered to be safe engines (for pistons!). I'm wondering if I should consider the safety and reliability of the certified Rotax engine to be substantially worse than that of the Conti O-200 (the only other certified LSA engine), and if there is any evidence one way or the other.

As far as I can find out, no one knows. There's no good data available on engine reliability from the manufacturers - although they usually don't share that information anyway - and nothing substantial that I could find from any third parties.

There is some information online, although it's mostly opinions and there's no real, consistent data to support it. This 2008 article compared LSA engine options including the Rotax and said that there were more incidents involving Rotaxes than Jabiru engines (excluding non-engine related causes), but there were also many more Rotaxes in service so the comparison isn't meaningful.

In fact, the article said that any comparison is difficult because the Rotax was (is?) primarily used in experimental aircraft:

  The great problem in identifying engine-specific problems is that in
  the majority of installations, the engines power
  experimental/amateur-built category aircraft, where differences in
  mounting, accessory placement, cooling and vibration variations can
  instill issues that vary from one installation to another

And it also made the point that there are plenty of engine-related incidents involving Continentals:

  And accidents involving Continental O-200-powered craft were as
  numerous as you'd expect for the length and depth of its presence in
  general aviation aircraft. Here again, many occurred through no fault
  of the engine. Still, numerous reports involved engine stoppages,
  heat-related power loss and other engine problems.

The article's conclusion seems to be that a Rotax engine is not (was not) significantly different from any other engine:

  To paraphrase the words of one long-time Rotax service-center
  operator, the main problems involving the engines stem from many of
  the same types of problems—poor judgment, misuse, mismanagement and
  poor maintenance—befalling all aircraft.

I found various other forum discussions about engine noise (no conclusion), fuel efficiency (Rotax is better), maintenance costs (some preference for Rotax) and so on, but nothing authoritative. I suspect that a detailed, data-based comparison simply doesn't exist; finding anything for Lycoming vs Continental is difficult, even with the much longer history and larger installed base.

In general, engine comparisons seem to be mostly based on opinion and anecdote (as described here). That doesn't mean the information is useless, but you do have to spend some time sifting and weighing the opinions to reach your own conclusions.


Why does the attitude indicator gyro not precess the same way that a directional gyro does? The directional gyro needs to be realigned every so often, but the attitude indicator does not, and I have a hard time finding why.

The self erection device in the attitude gyro that levels it when you start up on the ground also keeps it erect (its axis pointed at the center of the earth) when precession tends to send it off kilter during flight.
Air driven gyros use a pendulous vane arrangement that controls the exhaust ports for the air being sucked through, and which always work to keep the gyro aligned with vertical when stabilized in non-accelerated flight.  This system is imperfect, because the pendulous control system is influenced by accelerations and causes its own errors, but works well enough for light aircraft.


Can I count simulator hours towards a commercial flight certificate training? I attend a Part 141 training school and have a total of 98.5 hours of flight training towards a commercial certificate, with 8 hours of simulator training, also for the commercial certificate. Can I count both the flight and the sim hours towards the aeronautical experience for the commercial certificate? It would be a lot cheaper and faster to reach the required 120 hours this way. The Beech Baron is not cheap to rent!

According to the FAA, yes you can count those hours, but they can only count for only

Under FAR part 141:
7 hours(35%) of 35 hours of flight training towards a private pilot certificate
17 hours(50%) of 35 hours of flight training towards an instrument rating
36 hours(30%) of 120 hours of flight training towards a commercial pilot certificate
10.5 hours(30%) of 25 hours of flight training towards a multi-engine rating
12.5 hours(50%) of 25 hours of flight training towards an ATP cerfificate
2.5 hours(10%) of 25 hours of flight training towards a flight instructor certificate
1.5 hours(10%) of 15 hours of flight training towards an instrument flight instructor rating.

From http://www.dctaviation.com/#!sim-faq/ccj4
From what I see, you can probably fill up your remaining hours with sim time because you only have a little over 20 hours left and you can have 28 more hours of sim time towards your certification.


Is it possible to communicate an everyday computer with the ARINC bus? Lately I've been wondering if it's possible to interface an everyday computer with the ARINC buses (either 429 or AFDX).

This would be very useful for simulation, testing and prototyping purposes. For example, we could write a computer program that sends ARINC labels to the bus and see how the avionic systems react to it.

But I think that the greatest challenge would be in the physical layer.

The image on the left shows some connectors that we can typically find in everyday computers. The image on the right shows the connectors that we can find in the front panel of an avionic system.

At first glance making such a connection does not look straightforward.

Nevertheless I've done some research and I have found devices which seem capable of interfacing a computer with the ARINC bus via the USB port:

  These pocket-sized USB adapters are the easy and portable way to interface your computer to ARINC 429 and ARINC 717 Avionics
  databuses.

  Source: Astronics

So connecting a computer and avionics is possible in theory. Still, I don't see how I would be able to connect this USB-ARINC adapter to the avionics box, since the connectors are different.

So there must likely be an access point somewhere in the avionics where this adapter can be connected.

This is all I could find.

So again,

Is it possible to communicate an everyday computer with the ARINC bus?
If so, what is the access point where we would connect the wire?
Would there be any other challenges I didn't take into account?

Is it possible to communicate an everyday computer with the ARINC bus?

Sure. there are appropriate controllers to be plugged in a slot - or even as USB, like the one you found. After all, basic USB is alread way faster than ARINC 429.

  If so, what is the access point where we would connect the wire?

Whatever connector the interface card/box offers. More often than not this may require some special-to-type cable. If you're able to handle a soldering iron and/or crimp pliers, building one is a reasonable job. If not, that's where you may ask the interface supplier to take even more money to sell you a fitting one.

On ARINC 664 (ADFX) it's even less an issue, as there are as well equipment using standard plugs.

  Would there be any other challenges I didn't take into account?

Software. As always it's the software there the main cost and effort is hidden. While basic drivers are usually included (for ARINC 429) or default (ARINC 664), any layer above will be specific to the task you're intended to handle - and usually not exactly low priced.

For ARINC 664 it depends even more on the task intended. While basic communication runs on standard Ethernet layer, 664 adds a quality of service at layer 2. Something you OS default driver may not support. Ofc, one may (buy and) install a driver that does, still this might bring trouble on the 'regular' networkside. Due this (and to avoide collisions) adding a separate interface card with fiting drivers may be advised.

ARINC 664 opens another can of worms depending on the application intended. Basically it is a virtual implementation of a bunch of ARINC 429 busses over Ethernet. To make applications work some translation layer may be needed.

Bottom line, buying and pluging an interface in/to your PC is the least complicated step here. And everything beyond that needs in depth knowledge of what is intended to be archieved.


Can a human be blown away by jet engines of an A380? Can a human be blown away by jet engines of an A380 at full throttle? If so what is the largest object that it can blow away and cause significant damage? Can it blow away another parked Airbus A380 and cause damage?  Can it perhaps blow away the A320 and cause damage?

If so what is the safest parking distance between aircraft, with regards to jet air at full throttle.  What are the safest recommendations?

Absolutely. The jet engines used in airliners are quite powerful and can easily blow away human beings, vehicles and small aircraft. Other (large) airliners, not so much.
It depends on the aircraft's size, weight and distance from the engine actually. There are records of a F-16 being tipped over by a B-1B Lancer; as the thrust of an A380 engine is quite higher than that of the Lancer, the damage would be worse.
The minimum safe distance between the aircraft varies depending on the aircraft and engine type. For example, according to the Australian Civil Aviation Order 20.9 - Air service operations - Precautions in refuelling, engine and ground radar operations:

An aircraft engine shall not be started or operated:
...
(b)   within 8 metres (25 ft) of other aircraft;
... turbine engines, in addition, shall not be operated within the appropriate distance specified below of any other aircraft, fuelling equipment or exposed public areas which lie to the rear of and within a 15 degree arc either side of the exhaust outlet axis of that engine:

Minimum distance between aircraft for operation of engines; image from Civil Aviation Order 20.9 - Air service operations - Precautions in refuelling, engine and ground radar operations


How can someone get FAA commercial flight training as part of an aviation degree? If someone can't afford to pay for flight training directly, is it possible to get commercial flight training with financial aid as part of a college degree?

For the UK answer, see: Do any UK universities include PPL/Commercial flight training as part of an aviation degree?

In the US, there are 2 ways to become a certificated civilian pilot: Part 61 and Part 141.

Part 61 is done in informal classes and flights at a local flight school.

Part 141 is a professional pilot training program, with uniforms, classrooms, a full-time staff, and a uniform fleet of aircraft.

There are numerous US universities that offer bachelors' degrees using a part 141 program. You can find a list of such programs here.

Furthermore, many of these schools, such as Embry-Riddle, take the FAFSA, which is the  process for obtaining financial aid as for any other program.

After graduating from one of these programs, you will have obtained all the training necessary to work as a flight instructor, or as a commercial pilot under Part 119

Private Pilot Single Engine
Instrument Pilot Single and Multi-Engine
Commercial Pilot Single and Multi-Engine
Flight Instructor Single Engine
Flight Instructor Instrument
Multi-Engine Flight Instructor

You will have also earned either an Associates or Bachelors degree, usually in something like Aviation Engineering or Aviation Operations.

You will not, however, have flown enough hours to get a job flying air taxi or cargo under Part 135, which requires 500 hours to be the pilot-in-command.


Are en-route ATC callsigns standardized? I've seen different callsigns for en-route air traffic control, including Center, Radar, and Control (and Radio?). I suspect the only difference is the geographic location - Center in the U.S. (e.g. Salt Lake Center) and Radar and Control in Europe (e.g. Langen Radar, London Control).

Are there any other differences besides location? (is the location-assumption correct?) If not, why is it not standardized then?

The 'Center' suffix is indeed more common in the US for the en-route call-signs under radar control. There is also New York Radio, for example, for the non-radar service over the Atlantic. Another example is the 'Director' suffix that is not common in the US, but is common elsewhere for the final approach controller.

In this case we need a referee, enter ICAO Annex 10 Volume II Communication Procedures:

  5.2.1.7.1.2 The unit or service shall be identified in
  accordance with the table below except that the name of the
  location or the unit/service may be omitted provided
  satisfactory communication has been established.

Unit/service available                Call sign suffix

area control centre                   CONTROL
approach control                      APPROACH
approach control radar arrivals       ARRIVAL
approach control radar departures     DEPARTURE
aerodrome control                     TOWER
surface movement control              GROUND
radar (in general)                    RADAR
precision approach radar              PRECISION
direction-finding station             HOMER
flight information service            INFORMATION
clearance delivery                    DELIVERY
apron control                         APRON
company dispatch                      DISPATCH
aeronautical station                  RADIO

Above are the standards, but nations are free to deviate. Below is from the UK AIP listing the differences:

And from the US AIP:

Facility                                         Call Sign

Airport UNICOM                                   Shannon UNICOM
FAA Flight Service Station                       Chicago Radio
Airport Traffic Control Tower                    Augusta Tower
Clearance Delivery Position (IFR)                Dallas Clearance Delivery
Ground Control Position in Tower                 Miami Ground
Radar or Nonradar Approach Control Position      Oklahoma City Approach
Radar Departure Control Position                 St. Louis Departure
FAA Air Route Traffic Control Center             Washington Center

  The U.S. does not use the term "area control service" to indicate controlled flight in controlled areas. The U.S. equivalent facility for an Area Control Centre (ACC) is an Air Route Traffic Control Center (ARTCC).

Related: Where to find the callsigns of the en route controllers?


How efficient would an airliner be if it did not have to carry its own fuel? Hypothetically, if all the fuel was supplied externally or pulled from the atmosphere to where the plane had never to carry any fuel on board, how much more efficient would an airliner be? The plane would not fluctuate in weight.

Short answer is about twice as efficient for a mid range route,(3000 nautical miles) when based on fuel used per ton of cargo per mile traveled.

Explanation:
I will use the 737-400 as an example because I have an operational manual for it. First we need to define terms. I assume we are talking about fuel burn per something: per mile, per hour, or per payload ton-mile. Gross weight is the total weight if you set the plane on a scale in some flying condition. Max gross weight is the maximum weight at which the aircraft is considered safe to fly. Operating empty weight is the lowest gross weight achievable in a flying condition, no cargo, no extra crew or passengers, and no usable fuel. Useful load is the difference between max gross weight and operating empty weight. Payload is useful load minus fuel load and extra crew.(that is load that pays, aka cargo and passengers)

The thrust required(and thus fuel consumption) for level flight is determined by aerodynamic drag and the majority of drag is broken into parasitic drag and induced drag; parasitic drag comes from shape or texture and dynamic pressure,(basically speed if you keep the density constant) go faster get more parasite drag, this does not change with gross weight.

Induced drag is caused by the lift created by practical wing designs, for a set wing design and speed the induced drag increases with weight. So high gross weights have higher induced drag and so require more thrust.

Now for the example. A 737-400 has a maximum gross weight of 143500 pounds and a typical operating empty weight of 77100 pounds(typical airline equipment with seats and such) giving a useful load of 66400 pounds. This weight can be split up however needed between fuel and payload depending on the length of the flight.(In practice other factors can limit gross weight such as available runway length, and payload as some engineering optimizations assume a lower landing weight than takeoff weight to save on structural weight.) At least up to the limit of installed fuel tank size, this model can hold 37708 pounds of fuel.

Some reserve of extra fuel is required for safety, diversions, holding and such, so this is usually extra fuel at landing. This is typically 4000 to 9000 pounds depending on specifics of the flight.

Assuming flight altitude of 33000 feet and mach .74 cruise(430 knots). I am using nautical miles and short tons(2000 pounds) for all of this.

A the most exaggerated case will be maximum range with reserve fuel of 9000 pounds.(maximum fuel at start, reduced payload) Payload will be at most 28692 pounds or 14.3 tons. Fuel burn at the start will be 6234 pounds per hour for 1.014 pounds fuel per ton-mile of payload (6234/(14.3*430), and at the end of flight 5066 pounds per hour for 0.824 pounds fuel per ton-mile of payload (5066/(14.3*430). (geometric mean of .914 pounds fuel per payload ton-mile. Change in rate is non-linear.)

If all of the useful load could be used for payload as in the case of an external fuel supply, or an infinitely short flight with no reserve fuel, you get 66400 pounds or 33.2 tons of payload. The fuel burn will still be 6234 pounds per hour but you get .437 pounds fuel per payload ton-mile. 6234÷(33.2×430)

So cruise fuel consumption with an external fuel supply will be approximately .437/.914 = 47.8% or about half of the fuel consumed per unit of cargo. Actual results will depend on variables if I must state the obvious. Longer flights would see more improvement, shorter flights less, payloads less than maximum allowable will also see less improvement, flights requiring less reserve fuel will also see less improvement.


What is the traffic pattern altitude at KSQL? According to some online sources (https://skyvector.com/airport/SQL/San-Carlos-Airport and https://www.airnav.com/airport/KSQL) TPA at San Carlos Airport is 800 ft AGL. However, reading the Chart Supplement / AFD entry (pg. 205 of Chart Supplement Southwest US, pg. 207 of the PDF version available here: https://www.faa.gov/air_traffic/flight_info/aeronav/digital_products/dafd/), I don't see it explicitly noted so I would assume it's the standard 1000 ft AGL. The Garmin Pilot app also concurs with my reading and lists it as 1000 ft.

I know from being a student pilot based out of KSQL the altitude is in fact 800 ft. But how would you arrive at that short of asking tower or airport management? Am I missing something or could this be an error on the part of the FAA (perhaps because 800ft used to be the standard TPA - related question that mentions this: How do I determine the VFR pattern altitude at an airport?)?

I am based at KSQL, the TPA is 800 AGL. The A/FD er, excuse me, I mean the Chart Supplement, says "Helicopter TPA--806(800)" which seems like a typo; it's the TPA for fixed-wing also.


What is the range difference between LEAP and PW1000 powered A320 and A321 NEOs? Mounted on the same aircraft, PW 1000G and CFM LEAP are two very different engines, with different performances, that should have an impact on range. And we know range is a very important aircraft parameter, since Airbus is developing longer and longer range versions of the A321.

So what is the difference in range on the same aircraft between the two engines?

According to Airbus
Airbus quote a single range figure of 6300km for the A320neo
This is 100km more than Airbus claim for the A320ceo with sharklets but the difference is probably due to increased fuel capacity in the A320neo and possibly to revised wingtip arrangements.
The difference in range between older A320 (~5700km?) and A320 with sharklets (~6200km) appears to be 500km. This implies the wing sharklets are more important than larger fuel capacity and both these features are more important than engine differences alone.
Superficially at least, the choice of engine does not affect the range claimed by Airbus.

This raises the question, what benefits are provided by the new engine options alone?
The only relevant claim by Airbus appears to be

The A320neo also offers significant environmental performance with nearly 50% reduction in noise footprint compared to previous generation aircraft.

I guess airlines choose between NEO engine options mostly based on commercial factors and maybe on fleet characteristics, maintenance arrangements, etc. Factors other than range.

According to others
Forbes has a comparison beween these two engines which suggests the geared-turbofan arrangement of the PW1000 offers large advantages in both fuel efficiency and noise.


Is it possible to 'derate' a plane as a safety measure? Assuming a type of plane has a technical issue that must be fixed related to its flight behavior, could the plane be derated to add safety margin (instead of banning it).

What I have in mind is having longer runway requirements, lower airport T, higher air pressure, softer rate of climb, lower take off weight, etc.

Could this work technically? Legally?

This is inspired by the recent crashes of Boeing 737 MAX-8s, but the question is about types in general.

The answer is yes, if there is an operational procedural restriction limitation that effectively mitigates the risk, without adding its own risks, and is something that is operationally feasible, pending a design change.

Examples would be an AD that:

Imposes a speed, altitude, weight or temperature limitation.

Imposes additional reserve fuel requirements (this was done for CRJ200s that had a problem with the flaps getting stuck while extended following a missed approach).

Limits operation in icing conditions (although for most airline operations this effectively grounds you, because "legal" icing conditions exist in any cloud above the freezing level).

All sorts of other system restrictions.


At what rpm does the tip of a 54" propeller start to incur mach losses? At what rpm does the tip of a 54 inches propeller start to incur mach losses? The max rpm of my engine is 3600.

A 54 inch propeller would start to incur efficiency loss at approximately 4300 rpm.

At 4300 rpm a 54 inch propeller would have a tip speed of 691 mph which, relative to the 767 mph speed of sound, is about the maximum which still allows propeller efficiency.

You can calculate the variables using this tool: WarpDriveProps.com Propeller Tip Speed Calculator


Were there ever instrument approach procedures utilizing only Four Course Range Navigation? Looking for information on 4 Course Range instrument approach procedures.  I am aware of their navigational use as we developed the airway system, but were they ever used for final approach segment navigation? Does anybody have access to such an approach plate?

Yes such approaches have existed.

As early as 1944 the North America Low Frequency Radio Range (aka Four-Course Range and Adcock Range) network was quite developed. There are several approach plates using this type of radio aid, e.g. this one from May 1944 for Meridian:

Source

The station is used for IAF and FAF. The approach is done using 334°/154° headings. None of them, nor the station are aligned with a runway, this looks like a circling maneuver.

Other plates:

Fort Chimo (Quebec)
Joliet (1957)

Some editions of the AAF Radio Facility Charts can be bought online, but the edition of June 1944 has been scanned by North Texas University:

On pages 38-39 we can see the overall coverage.
Other pages show details by area.

This is the page for Mississipi with Meridian, the airfield we discussed above, at the center:

We see that two of the four identified directions are not connecting airway segments. This is the ones used to approach the airfield where the station is located. They cannot be aligned with the runway because they play their role in the four-course range: There are four beams radiating over about 90° in azimuth, with small areas overlapping (about 4°). The middle axis of such areas is the actual path:

While the station location can be selected, and there is a certain possibility to have unequal quadrants, the adjustment is still limited. One or two directions are used for the airway(s), they determine the overall orientation of the other antenna system (angle bisector), and it's anyway difficult to create a small aperture (i.e. a very directional beam) at this frequency. This explain why the approach is a circling one.

Complete list of US approaches

At some point modern standardized plates were issued:

(Source)

The image below can be found on this site dedicated to simulation, which lists about 400 approaches in the US and Alaska.

More:

On Youtube: The Four Course Radio Range.
On Wikipedia.


Do pilots have a generally preferred "traffic" resolution? For aircraft cruising along at altitude, it is common for the controller to assign an aircraft a new course or altitude or speed for some reason such as "for traffic". My question is, would most turbojet/turboprop pilots rather have a vector, say 20 degrees off course for 10 minutes, or have a different altitude, or have a speed assignment? What is most efficient for the airplane? Do companies have a preference? Are certain actions easier for the pilot? I suppose there is a fuel-use vs. time-en-route trade off in some cases, and many other factors as well, and personal preferences might vary widely, or maybe people don't really care?

If ATC offered me a heading change or an altitude change and I was happy with the altitude I was at, I'd take the heading change in a heartbeat.  Compare:

Altitude change:

Dial the alt preselect up.
Select speed or VS mode (usually speed).
Set climb thrust.
Monitor the capture.
As the AP captures and pitches over, start bringing the thrust back to keep from speeding up until the original thrust setting is restored.

Heading change:

Select Heading Mode if in Nav mode.  If on vectors, it's already set.
Twirl the heading bug and monitor the turn.
When told to, dial the heading bug to a new heading as instructed or to a suitable intercept angle and reset Nav mode if told to resume self navigation.

Notice that with the heading change I don't have to screw around with power, which can be more hassle or less hassle depending on if you have FADEC, but in any case a lot more work than twirling the heading knob and pushing a button.


what type of sensors does the Boeing 737 MAX use for MCAS? I can imagine there are several different ways to measure angle of attack (accelerometers, relative pressure measurements between pitot tubes, etc), but I'm curious which sensors the 737 MAX uses for its MCAS system since it's been in the news recently.

The pitot tube has nothing to do with the angle of attack. It is used for measuring pressure which in turn gives you the airspeed.

Accelerometers are used for the Inertial Navigation System.

The angle of attack is another sensor (shown below): the principle is that it rotates and reads the angle between the current position and the reference position.

Regarding the 737 MAX, there are two AoA sensors one on the captain side and one on the first officer side.

The MCAS reads the AoA from the captain side.


Backup airspeed indicators (lack thereof) This recent aviation.SE question asks why isn't GPS used as a backup speed indicator. The answers given mention that GPS cannot indicate airspeed. However, there are other methods to indicate airspeed. At the very least, a small anemometer and vane might be deployed in a fashion similar to how a ram air turbine is deployed. Or at the very least, deploy the ram air turbine and measure the RPM or voltage.

Another creative method might be to release a small red sponge ball, and have a camera/sensor mounted in the top of the tail (where the A380 already has a camera) determine the vector that it flys away. Image processing for this type of work has been available for years already.

Of course, these solutions would only be deployed when necessary. I wager that using the ram air turbine to determine the airspeed could be done in software with no added weight or mechanical components added to the vehicle. Assuming that the vehicle already has a camera in the tail (such as the A380), adding the ability to deploy a small sponge ball would be less of a retrofit than adding cellular telephone service.

In order to answer your question first we need to figure out what we're trying to accomplish with airspeed. For the most part the goal is "envelope protection" - keeping the pilots from either stalling the aircraft or overspeeding (and overstressing) it.

So the first thing to know is thaton modern transport category aircraft there are already backup systems to compensate for a failed airspeed indicator.

For starters there are usually at TWO (visible) airspeed indicators (one for each flight control station - pilot & co-pilot). The airspeed indicators are usually using two different pitot (ram air pressure) sources, so that if one pitot system or indicator fails the aircraft can still be flown on the others.
In addition to those two indicators there is often a third "tie-breaker" system on modern aircraft which is used to determine which system has failed (if two systems agree the third is declared insane and ignored).

In the unlikely event that all of the pitot-based airspeed indicators fail they aren't the only system providing envelope protection: Angle-of-Attack vanes are used to determine when the wing is approaching the critical angle of attack (and is in danger of stalling). These operate independently of the pitot system as a redundant form of stall protection, and as with the pitot system aircraft usually have more than one AoA vane installed.

Both the pitot-based airspeed indicators and the AoA vanes are critical systems, and are heated (to prevent ice from accumulating and interfering with their proper operation) and monitored (by onboard computers and/or the pilots).

Finally in the face of a failure of all of those systems there is the ultimate fallback method that others have described: Pitch + Power = Performance.
A pilot should be able to at the very least maintain level flight, descend, climb, and make standard-rate turns within a safe flight envelope by reference to engine power and aircraft attitude.
While that's far from an ideal situation it is one pilots are trained for.


Are intersection takeoffs less common in the USA than in other countries? On a recent trip through Australia I did a number of intra-oz flights.  In at least three of the cases we performed intersection takeoffs, a couple at MEL/YMML and one at BNE/YBBN.  I have at least a thousand domestic flights within the USA, and although I wouldn't bet my life on it, I can't remember ever doing an intersection takeoff there.

The MEL/BNE runways are quite long - even with the intersection takeoff the available runway was over 8,000 feet in each case.

Am I wrong that this is super rare in the USA?  Are there airports where intersection takeoffs are commonly used, and maybe I just never fly through those?  The advantages are obvious, it saves taxi time and fuel, and a 737-800 on a 75 minute stage can't be anywhere near gross weight anyway.  In the USA, airports like HOU/MDW have runways that are shorter than our takeoff roll, which strongly suggests there's no outright safety issue... and these airports handle hundreds of 737-800s a day identical to the QF/VA ones I was on here.  What other things am I missing here?  Are the aussies just more time/fuel conscious than us yanks?  ;-)

US airlines are extremely fuel conscious. They have software that calculates the exact throttle and flap settings required for the exact length of runway available so that they don't burn any more fuel than necessary, and that is all typically computed before they even push back from the gate.

If the pilots know in advance (e g. from the ATIS) that intersection departures are in use, they'll calculate for that. However, if they're already taxiing out to the end and ATC asks if they can accept an intersection departure instead, they'll need time to rerun "the numbers" and reconfigure the aircraft. US ATC has learned from experience that this delay often negates whatever trick they were trying to pull off, so they usually don't bother asking unless there's a really good reason.

Also, unlike light planes, for safety reasons airliners are required to have enough runway available to accelerate to V1 (nearly rotation speed) and then brake to a stop again before the end if they need to abort. This means they'll rarely use more than about half the runway available. This is factored into "the numbers", of course, and is another reason why they need to be checked before accepting an intersection.

As to why intersections seem more common in Australia, perhaps there is some difference in how their airports are designed, or perhaps their ATC is just more willing to do it, or perhaps Qantas pilots are faster at running "the numbers" or have a habit of running all likely options instead of just the expected one.


Could a rotor head wing be plausible? Could a helicopter support a detachable wing with no controls on top of the rotor head in place of a radar dome? Could the rotor head be made to support more weight? Would it be more fuel efficient at higher speeds, add a level of redundancy, or increase speed?

I did consider clearance and the drawn pictures is not to scale. The wing may need to be drawn longer, further back or placed higher. This would be a payload in itself for extending the range of the helicopter under lighter loads.

A second feature is that the wing could be made to catch the vortex left by the rotor blades in flight increasing air pressure under both the rotor blades and rotor wing.

Similar to the way ducks fly in a v formation the wings would also take this advantage from other helicopters with this extra wing for extra lift.

Could extra lift be created from the rotor wing, the vortex ring redirection and /or flight in a V formation?

There is no need to attach the wing to the rotor head - simply attach it to the top of the fuselage. You could run the rotor through a hollow tube and attach the wings to that - the inner uncovered section of the wing is an interesting idea.

If you are looking for VTOL, a tilt rotor with two electric motors driven by the gas turbine may be a better option.


Would the Concorde have been better off using a tailed delta wing? In one of the answers to this question about the Concorde's lack of high-lift devices on its wings, it was pointed out that the Concorde, using a tailless delta wing, wouldn't have been able to use flaps, since there was no horizontal tail aft of the wing to counteract the downward pitching moment that would result from deploying flaps.
On the other hand, a tailed-delta configuration (a delta wing with a conventional tail mounted aft of the wing) would have been able to use flaps, as it would have had a separate elevator further aft with the ability to counteract the flap-generated pitching moment.  A good example of this would be the design for the Boeing 2707-300, which was to use a tailled-delta configuration and would have had some rather impressive flaps, but was cancelled in 1971 before even the two prototypes had been completed.
Given that it would have allowed the inclusion of flaps, would a tailed-delta configuration have been a better choice for the Concorde than the tailless delta they ultimately went with?
Edit: Better in that it would have greatly increased the Concorde's subsonic efficiency and allowed lower-speed (and thus less potentially-tyre-explodey*) takeoffs.
Quoth the linked question:

...The lack of high-lift devices considerably reduced lift at low speeds, requiring the Concorde to take off and land at higher speeds and angles of attack than if it had been equipped with flaps and slats. As well as greatly increasing drag (and thus fuel consumption) during takeoff and landing, this greatly increased the force carried by the main landing gear and the speed at which its tyres had to spin; as a result, if and when a tyre blew out (due to, for instance, a piece of debris left by the previous airplane to use the runway), the results would be much worse than with a tyre blowout on a subsonic airliner.
...[The addition of high-lift devices], along with slightly larger wings and more powerful engines, would have allowed the Concorde B to dispense with afterburners, considerably increasing its fuel efficiency and range.

* It happened a lot before the fatal accident.

The beauty of the pure delta configuration was you could get a reasonably low supersonic drag configuration in a planform with a lot of wing area, essential for really high altitude cruise and for reasonable landing speeds without high lift devices.  It was a good overall compromise for Concorde's mission.

The Avro Arrow, produced then scrapped in Canada in the late 50s, also used a large pure delta plan form (which is thought to have had some influence on Concorde, a lot of Avro's engineers having joined the Concorde program when Avro Canada vanished).  This allowed it to meet the RCAF's specification that required M2+ while being capable of sustaining a 2G turn at 50,000 feet, something no interceptor could do at the time.


What should I look for / check during an oil change? Piston aircraft engines require regular oil changes, and at least in the US it's something the FARs allow an owner with a private pilot certificate to do.

What are some of the things I should look for during an oil change (or what are some of the things I should be sure my shop is checking when they do an oil change)?

First, a word of caution - Don't attempt your own oil changes on an aircraft unless you're familiar with the process, and have both the tools and skills you'll need to get it done right.
  It's probably a good idea to have your mechanic supervise you on your first oil change, and check your work on the next few until you're sure you've got the hang of  it.

  This isn't an oil-change how-to - just a list of stuff to look at to judge the general health of an engine.

Disclaimers and warnings out of the way, here's what I look for (or ask the shop to check) during an oil change:

Draining that dirty old oil

First, don't forget to grab a sample for oil analysis while you're draining (I'll talk about that a little later!).
Now, while the oil is running out of the drain you're really looking for big chunks of metal coming out with it (or heaven forbid blocking the drain hole) You also want to make sure there is no nasty sludge coming out (that's a car in the video, but the principle is the much same).
Basically what's coming out of the drain should look like oil. It'll be dirty (dark to black, rather than the pretty clear-ish liquid you poured into the engine all those hours ago), but it should still be flowing nicely.

  Obviously chunks of metal here would be bad. If you're noticing them in the drained oil you've got some serious mechanical damage in your engine and you need a mechanic to check it out.

  Sludge generally means you need to talk to your mechanic too - often it means a bunch of low-time oil changes to clean out the gunk from the engine, but if it's severe it could indicate other engine problems that need attention

Checking the Oil Screen

If your engine has an oil suction screen that can be removed and cleaned (as on most Lycoming engines), remove it and inspect it for any pieces of metal, then clean it and reinstall it.

  As with chunks in the drained oil, bits of metal in the screen are often a sign of a serious mechanical problem - if you find any you're going to want to talk to your mechanic.

Inspecting the Oil Filter

As part of every oil change the filter should be cut open and inspected for fine metallic particles in the pleats. There are a few of ways to do this (one is to simply stretch the pleats out under a bright light and look at them, another is to wash the filter in a solvent and strain the used solvent through a coffee filter to see if any particles are left behind).
EAA has a great video on inspecting an oil filter - it's worth the 10 minutes to watch.

  If you find any bits of metal  in the filter you already know what I'm going to say -- you're going to want a mechanic to check things out. A very small amount of metal may not be a serious issue, or it might be the beginnings of an engine on a path to self-destruction.

Run an oil analysis

Some people do an oil analysis every oil change, some people don't ever do one.
Smarter people than me say it's probably a good idea to do them, so I consider it to be cheap insurance and a good window into where those "bits of metal" I keep talking about above might eventually start coming from.
There are plenty of companies that do aviation oil analysis and for an idea on what's in the report check out Blackstone Labs' interactive report explanation page.
There's another EAA video that talks about oil analysis which is worth the 3 minutes to watch too...

  Note that a single oil analysis won't tell you much (unless things are REALLY out of whack) - it's the long term stability or trends that matter here, so if you're going to do an oil analysis be prepared to do them at every oil change from now on...

Do the things that aren't oil-related

An oil change is a good opportunity to do some other regular maintenance - Since the cowling is off anyway why not clean/gap/rotate your spark plugs (which is another mind-numbing task the FARs allow owners with a private pilot certificate to do)?
In fact since the cowling is apart and your engine is naked now's the time to give it a good once over for any loose parts, chafing wires, etc. that might have come up since the last oil change or service that had someone under the cowling.

It's probably also a good opportunity to check all your lights (interior and exterior), and break out the manufacturer's lubrication chart to see if there are any other things that need to be oiled, greased, cleaned, or sprayed.

So what's all this fuss about metal?

You've probably noticed above that I'm really harping on all the ways you can find metal in your oil in this answer.  The simple fact is that all engines wear, and eventually they wear out. That wear shows up as microscopic bits of metal relatively harmlessly suspended in the oil (what the oil analysis picks up), but if that wear suddenly accelerates bigger pieces of metal start getting torn off of the moving parts in your engine, and showing up in other places like the oil filter and screen, letting you know something is wrong with your engine, and hopefully letting you know on the ground rather than in the air.

I don't want to give the wrong impression here though: Not every bit of metal that turns up in an oil filter will be a death sentence for the engine that produced it! In fact brand new engines sometimes produce a few bits of metal during break-in as parts wear in to each other, and they stop after the first oil change or two. The thing to remember is any metal showing up where it shouldn't be during an oil change is definitely something to have checked out by a mechanic.


How does the Airbus ECAM / ND transfer work? On the Airbus A320 a knob on the switching panel says ECAM/ND XFR (Electronic Centralized Aircraft Monitor / Navigation Display Tranfer) and it transfers the either the Engine/Warning Display (E/WD) or the System Display (SD) onto the Navigation Display (ND). The ND gets its information from the Air Data Inertial Reference System (ADIRS) and IT and the ECAM gets its information from the system sensors.

Both ADIRS, IRS and system sensors information get sent to the Display Management Computers (DMC), and I'm just wondering if im correct but when you switch SD or E/WD the DMC when it is processing the data for, in this example the system sensors, it sends the system sensors data to the ND?

And the other way around when you switch the ND to the ECAM. When the DMC is processing the data, in this example ADIRS and IR data, it will send the ADIRS and IR data to the ECAM?

So my question is, is it during the processing the data phase that the DMC sends the data to thd correct display?

All this depends on the A320 generation. On early models all computations are done by the SDACs and the DMCs, and the switching corresponds to data switching in the DMCs, so the screen will display what it receives.

On later models all screens receive all data and on request they can display what you ask when you do the ECAM/ND switching.

In fact in latest models of A320 the displays switching possibilities are voluntarily limited just for conformity with earliest A320’s


Does the required torque to spin a propeller increase with RPM? I‘ve currently been experimenting with different propellers: 12x12 prop, 16x12 prop (both two blades) and a 22x14 (6 blades) prop. They were propelled by a 2.4 kW electric motor with 260 kV on a 6S/5200mAh/12C battery setup.

The 12x12 prop produced 2 kg of thrust at full throttle, the 16x12 produced 4.5 kg of thrust. So I thought the 22x14 would produce around 6 kg because its bigger blade area would be more efficient. However, I got only 0.8 kg of thrust and recognized that the motor would slow down at a certain RPM.

I have to say the big prop is pretty heavy so could it be that the motor would have enough power to spin the prop faster but it lacks enough torque to get it there?

Of course. More and bigger blades is more drag. Drag is also proportional to the velocity squared. Even maintaining the RPM, a bigger propeller (diameter) will have the additional diameter flying faster.

To maintain a higher RPM (or to use a bigger prop) the force to cancel the increased drag is higher, and thus the torque (force times distance) that drives the propeller.

Place the propeller in vacuum, and the engine will have no trouble with the propeller apart from any loads on the shaft (but there won't be any thrust).