Why are ambient pressure and burner can pressure always the inputs on a hydromechanical fuel controlling system? I worked on several of these older systems using a hydromechanical fuel control. I've noticed that the inputs at the fuel control are for the most part the same. Power lever angle, N2(N1 on a single spool), ambient pressure (usually Pamb or whatever the manufacturer calls it), and burner pressure (sometimes Pb4, again depends on manufacturer). My question specifically pertains to the pressures.

Why is it always ambient pressure and burner can pressure that are inputs? Why not compressor discharge pressure and turbine exhaust pressure or some combination of other pressures in the engine?

Hydromechanical Fuel Control Units (FCUs) typically do use compressor discharge air pressure as an input.

As I recall, the FCUs that I am familiar with have had at least the following inputs in addition to the control lever commands:

Compressor Rotation Speed
Compressor Discharge Air Pressure
Ambient Air Pressure

As both a mechanic and pilot I have studied many FCUs, and I do believe the inputs listed above are standard across all those with which I am familiar. This is certainly true of the types that I have studied most recently and the systems which I currently fly. Note that while these FCUs may be older designs—in some cases—they are commonly used on new production turbines.

The following are excerpts from some of my training manuals concerning a Bendix FCU:

  The pneumatic section of the FCU determines
  the flow rate of fuel to the engine for all operations.
  The power levers control engine
  power from idle through takeoff power by operation
  of the gas generator (N1) governor in
  the FCU. Increasing N1 rpm results in increased
  engine power.

  For explanation purposes, consider the N1 governor
  bellows as a diaphragm. P3 air is introduced
  into the bellows in a manner that sets up
  a differential pressure on each side of the diaphragm.
  Therefore, any change in P3 pressure
  will move the diaphragm. When pressure
  is increased, the fuel-metering valve attached
  to the bellows will move in an opening direction
  to increase fuel flow and increase N1 rpm.

  As P3 pressure decreases, fuel flow also decreases
  which reduces the N1 rpm. The N1
  governor increases or decreases P3 pressure in
  the bellows by varying the opening of relief
  orifices in the bellows.

  The FCU controls engine power by maintaining
  the requested N1 rpm through the N1 governor.
  If actual N1 rpm is lower than the desired
  setting, the N1 governor closes the P3 orifice,
  allowing pressure to increase. As the pressure
  increases, the diaphragm moves to open the
  metering valve, increasing fuel flow, which in
  turn increases N1 rpm to the speed requested by
  the governor. When N1 rpm reaches the desired
  speed, the governor adjusts the P3 orifice to reduce
  pneumatic pressure to match the fuel pressure
  required to maintain the desired N1 rpm.


Why is a large flashing "X" placed on a closed runway at Reagan National Airport? Runway 15 at DCA (Reagan National) is closed at night and other times. By "closed," I mean that airport management places a gigantic lit/flashing "X" in the landing zone of 15. I'd estimate the big "X" is 8 by 8 feet, at least. It's like one of those roadside trailer flashing signs, except it's a runway.

The flashing X is very evident to pedestrians, bikers, etc., on the Mount Vernon trail. It's not some bizarre national secret.

My question: Why, in the tightly controlled airspace of Washington, DC, would DCA need to roll out a giant lit "X" to keep planes from landing there?

As if the obstruction were not there, you could fly in? That doesn't calculate, given how tight the airspace is controlled.

Why does this airport in the center of the world's highest airspace security roll out a construction trailer with a big X to keep planes from landing there?

The standard way of marking a runway as "CLOSED" is to put a big giant X on it - for fields which operate at night that X needs to be lighted. The specifications for the runway closure marker are outlined in an FAA advisory circular (AC 150/5345-55A)

The purpose of the marker is to indicate that the runway is temporarily closed (either administratively, as is the case at DCA, or for construction/repair/maintenance).  It is redundant with air traffic control measures (such as NOTAMs) indicating that the runway is out of service, in case some pilots didn't check NOTAMs or somehow managed to stumble into the airspace and happen upon the airport while it's closed.  (Obviously in the case of DCA they would have other problems were they to wander blindly into the area without talking to anyone, but believe it or not it happens far more often than any of us would like.)

The big flashing X doesn't "stop" you from landing on the runway - it just tells you you really, really shouldn't be landing there. There is a United States Senator who has achieved some notoriety in the aviation community after landing on a closed runway.

The X is also quite a bit bigger than you think it is to ensure it's visible from the air  (the arms are 14 feet long):

(I was looking for a good aerial photo of one at night, but unfortunately couldn't locate one. The intent is for the X to be about the same size as runway numbers so there's no good reason for a pilot to not see it.)


Why do the missiles on an F-16 point slightly down? I've been wondering this for quite a while:  Why do the missiles on the F-16 point down a little bit?

I went and did a little searching and found out that the F-16 isn't the only plane that has this feature, so I'm going assume it's not the F-16s frame specifically.  I also doubt it's tactical because all the weapons are pointing down, regardless of the weapons role in combat. In fact I saw a few photos where the bombs closest to the fuselage were pretty level with the ground (and bombs pretty much always go down, so...)

Does it have to do with aerodynamics, or perhaps ease of loading?  Why is the load-out on the F-16 mostly pointed slightly downwards?

If you take a look at the picture again, you'll see that the missiles are in fact lined up quite nicely with the nose of the plane. The missiles are not pointed down, they are pointed forward. The wings and engine (and the entire back two-thirds of the plane) are pointed up, which provides the lift to keep the plane in the air during normal flight. You can see pretty well the alignment in reference to the horizon in this picture (found by @jay-carr):

Just to cut off the potential comments about how planes generate lift, reference is here.


What does 00 mean on a sectional below the airport runway information? What does 00-50 mean on the sectional chart under PHNL (see picture)?

That is the elevation and length of the longest co-located water runway.  Elevation of 00, and runway length 5000 feet.

This information is found on page 16 in the current Aeronautical Chart Users Guide, which states:

  Runway length is shown to the nearest 100', using 70 as the rounding
  point; a runway 8070' in length is charted as 81, while a runway 8069' in length is charted as
  80. If a seaplane base is collocated with an airport, there will be additional seaplane base
  water information listed for the elevation, lighting and runway

(emphasis mine)

In this particular chart of Honolulu Int'l, the first line of airport runway info indicates 13 L 123, which is a 13 foot elevation, lighting in operation from sunset to sunrise, and 12,300 foot longest available runway.

The next line down, which you are asking about, is the "additional seaplane base water information", described by the ACUG.


What is the purpose of these "stickers" in the F/A-18 Super Hornet fuselage? Photos source: screenshot from youtube video ->

I think they can be used as fuselage reference points in flight testing, but I'm not sure.

Are they part of NATO standard symbology?

It may or may not be being used in this application, but they are location markers, usually used in weapons separation tests to record the movement and behavior of stores in the airstream as they separate from the jet.  Camera pods, usually mounted on the wingtips or other optimal vantage points record the process for engineering purposes.


Is there a clear or particular pattern in the mistake-making that leads to a landing at the wrong airport? I'm interested in how decisions and mistakes are made in the cockpit.
According to a brief news report about a recent landing at the wrong airport (see also the Aviation Herald report):

Landings at wrong airports by commercial pilots, while unusual, are still more common than many passengers may realize or airlines would like to acknowledge.
An Associated Press search two years ago of government safety data and news reports since the early 1990s found at least 150 flights in which US commercial passenger and cargo planes have either landed at the wrong airport or started to land and realized their mistake in time.
In most cases, the pilots were cleared by controllers to fly based on what they could see rather than relying on automation. Many incidents occurred at night, with pilots reporting they were attracted by the runway lights of the first airport they saw during descent. Some pilots said they disregarded navigation equipment that showed their planes slightly off course because the information didn’t match what they were seeing through their windows – a runway straight ahead.

Is there a clear pattern in the decision-making process that leads to such landings?
For example:

Does the transition from automated or instrument flight to visual flight represent a vulnerable point in cockpit management?
Is this phase of flight (perhaps after a long day) associated with moments of pilot inattention?
Are there issues in the relationship that a flight crew has with navigational equipment that allow it to be 'disregarded' in this way?

I don't know if any of these are actually involved, they're just examples that I'm suggesting because I'd like a deeper answer than "sometimes pilots are inattentive".

I've been in the cockpit three times in which we realized we were maneuvering to land at the wrong airport in time to avoid so. All three times were at night; all three in VFR conditions, all three with the incorrect runway having the same directional orientation as the correct runway, all three with those runways being separated by just a few miles, and all three being the first time the pilot flying had been into the intended airport.

If I had to characterize the root cause, I would describe it as tunnel vision so to speak, being so focused on what was seen as being where the pilot(s) wanted to go that they failed to take into account that the conditions warranted looking around to ensure that that was where they really wanted to go.

The first and only time I personally almost made the mistake was in the early 1970s ferrying a Grumman American Traveler from the factory in Savannah home to Oregon. Close to midnight, we were under a low but legal ceiling over Mississippi flat land along a Victor airway westbound, navigating by a VOR just beyond our intended airport. The aircraft did not have DME. The airway passed a bit south of our intended airport. It also passed a bit south of another airport 30 or so nautical east of the intended. Both airports had runway lights, both were north-south runways. I contacted the intended airport tower, reported the (wrong) airport in sight, and was given clearance to land. On final I realized that the lights of the town were in the wrong place in relation to the airport, looked on the sectional along the airway, and realized my mistake.

The second time was in the 1980s. I was the captain of a SA-227 Metroliner with a brand new first officer the flying pilot. The intended airport was an uncontrolled field, weather was clear. I called the airport in sight and asked the f.o. if he had it. He replied that he did. We typically made a right-base entry for the runway off our en route course. At the appropriate time, configured to land, he started to turn toward the runway. However, instead of turning right, he started a left turn. I realized that when he had said he had the airport in sight he was looking at the runway ahead and to our left rather the the correct runway ahead and to our right.

Finally, in the late 1990s I was jumpseating on a UPS 757 (as I remember) into Miami. It was around 04:30 or so, still dark, clear weather, no traffic. Neither the captain or the f.o. had been into Miami (or at least so they said later). The captain called the airport in sight and Miami Approach cleared them for the visual. My first clue that something was wrong was when the captain then told the f.o., who was the flying pilot, that he needed to get down, get configured. I figured, correctly, that they had made the mistake many, many others had made. They has mistaken the Opa Locka airport for the Miami Airport. Both have multiple runways, both the same pattern. As politely as I could I asked them if they could see a small smudge of blue neon around 10 miles in front of the nose. They said they could, and I told them that was the Miami Sofitel which was completely outlined at the time in blue neon and was alongside the runway they would be using.

Experience is the teacher, which is why when going into Hunter Army Airfield in Savannah for the first time and at night but in clear weather, when asked if I had the airport in sight, I asked for the ILS.


Is flying as a post-retirement occupation possible? Is it possible for a non-professional pilot to pursue a post-retirement career as a professional pilot? Of course I'm not talking about airline jobs but what about bush piloting or missionary/non-profit work?

It depends on your jurisdiction. A lot of places mandate a retirement age of 65 for scheduled commercial pilots (part 121 here in the USA). You are allowed to fly 91 and 135 (charter) operations over 65. While you state you don't want to fly for the airlines, it's worth noting that this retirement age causes a large influx of older out of work pilots many of whom still want to fly. As such there are plenty of high experience older pilots that are primed for flying 135 operations. These may be the people you are competing against for a job which as a low time, potentially inexperienced pilot would be an issue at the bigger outfits. In reality it will depend on a bit on if you are getting into it to make a living or just to fly and bring home some extra cash.

With that in mind there are plenty of commercial operations that seem to always be looking for people:

All of the flight schools near me seem to constantly be on the hunt for instructors. If you are willing to go that route I would think you should have no issue finding work.
There is a small charter op run out of the FBO I fly from. They run 3 King Airs and seem to always be short of qualified pilots. A lot of people use these as time building/jump off points so turn over is high. Presenting yourself as someone willing to stick around, has no interest of going on to the airlines, looks pretty good. There are lots of these smaller outfits, generally at local airports.
If your willing to move to somewhere potentially far far away mission flying is an option. This episode of Omega Tau covers it in great detail and is worth the listen.
If you are looking to spice up retirement, ferry flying can be high pay for the right situations.
Depending on where you are there is a fair bit of Ag Flying you can do.
If you are in or near a beach area and like to fly low and slow, towing banners is always an option.


How do I obtain permission to fly an airplane that isn't airworthy? How do I get permission to fly an airplane with a non-safety-related airworthiness issue, like being out of annual or having an inoperative radio in order to take it somewhere that it can be fixed?

You must request a Special Flight Permit from the nearest FSDO (Flight Standards District Office).

You'll need to fill out Form 8130-6, Application for U.S. Airworthiness, appropriately calling out the reasons you need a SFP (ferry flight, etc). Once the form is submitted, you may be subject to an inspection by an FAA official or representative, verifying that your aircraft is in fact in a condition for safe operation.

Avemco, the insurance company, has a good article on ferry permits that might be worth an extended read and which I don't intend to copy here.


KSEE LOC-D conundrum Consider the LOC-D at KSEE and note the Alternate Minimums criteria.

99.9% of the time, the winds strongly favor 27R;
The tower closes at 1900 PT currently (usually at 2100 PT non COVID times);
LOC-D is a circle only approach with a 6.88º final segment;
LOC-D to 27R not available to at night at all I think since it is a circle only approach (given the steepness). However, you can cancel IFR and continue visually usually;
DEBEY to Apt Elev in 3.1 nm is over 1,500 ft / min descent rate at 120 kts (top of Class B approach speed and common for a small turbo jet aircraft such as a Phenom)
Stabilized approach criteria for a Phenom is no more than 1,000 ft / min decent rate within 1,000 ft of the ground;
Circle NA with tower closed or to the northeast;
Local custom is to start on the LOC-D approach and cancel IFR prior to DEBEY. That makes the approach a 2,400 and 3 mi approach.

With the following conditions:

Part 91 in a light turbojet, class B aircraft (a Phenom);
Night with 1,800 Broken / 3 (so below the altitude at DEBEY and beyond where it is practical to cancel IFR even though KSEE is VFR);
Wind from the west at 10 kts (most turbo jet aircraft have a 10 kt tailwind limitation including the Phenom);
Tower closed (so no circle to land 27R) and Class G around KSEE;
There are two RNAV approaches to 9L and 17. If you do one of these, you still have the 27R circle limitation for night and tower closed but they each have lower minima. 17 / 35 is 1200 feet shorter with a cross wind. 9L would have a limitation busting tail wind.

Questions (and my concern are the REGULATORY aspects here) with the airport 1800 and 3:

Can the LOC-D be flown with the tower closed at all? (The Alternate Minimums clearly state Circling is NA with the tower closed and LOC-D is a circling only approach. But aircraft are commonly cleared LOC-D approach with tower closed...)

Can you land on 27R with some interpretation of IFR rules?
a. If you fly LOC-D with with tower closed, is completion of that approach NA? As a practical matter, on LOC-D, you would break out at 1800 about 1.5 miles from the airport decending at 1500 fpm at night trying to break in to cancel IFR with SOCAL... You can descend to a VFR pattern height and complete the pattern VFR and buy time to cancel.
b. Can you fly one of the approaches and cancel IFR and complete the approach VFR?

What are the limitations on when during an approach you can cancel IFR and legally complete the approach VFR?

Question 1: Can the LOC-D be flown with the tower closed at all? (The Alternate Minimums clearly state Circling is NA with the tower closed and LOC-D is a circling only approach. But aircraft are commonly cleared LOC-D approach with tower closed...)
Ans: The restriction eliminating the option of flying the LOC-D with the tower closed only applies when designating KSEE as a required alternate.
Question 2: Can you land on 27R with some interpretation of IFR rules?
Ans: At least 2 options:
(1)-Tell approach control (ATC) when they clear you for the approach that you intend on cancelling IFR when you get below the clouds (assuming it's still VFR/VMC). When VFR, cancel IFR and land at your discretion VFR/VMC. If, for some reason, the frequency is overwhelmingly busy and you can't get through in order to say "November**** Cancelling IFR" (hard to imagine) fly the published missed or land on another (none restricted) runway. OR
(2)- Request, at an appropriate time, a "Contact Approach." You would then be responsible for terrain avoidance (still under IFR) and land.
Question 3: What are the limitations on when during an approach you can cancel IFR and legally complete the approach VFR?
Ans: You cancel IFR on the approach when you are operating in legal VFR minimums (Class G in your example).


Did the "feeler" ailerons of the B-52A-F make air-to-air refueling easier than with the B-52G/H? The B-52G/H uses 8 spoilerons (so it has 8 burning and 8 turning on its wing) and a shortened vertical stabilizer.  Spoilerons seem to be very effective for this design, further reducing the need for a conventional rudder and ailerons to yaw and roll the aircraft.

The B-52A through B-52F had what have been described as "feeler ailerons".  But their elimination meant that the aircraft no longer has pure roll control, making maneuvering up to a tanker a bit more cumbersome, as inputs from the spoilerons would swing the nose from side to side.

It did occur to me that the tanker, and its boom, would do most of the adjusting, but was the "D" easier to handle in these situations? A response from someone with actual experience would be greatly appreciated.

The earlier variants were indeed easier to handle. The H-variant featured an independent spoiler panel for finer control to make it easier:

In practice, the short fin combined with spoilers-only lateral control induced a tendency to Dutch-roll and low level handling was more sensitive than on earlier B-52s. Raising the spoilers also caused a slight pitch-up movement which was considered a real problem for inexperienced pilots when flight-refuelling. A later modification (used on the B-52H) the 'Airbrake 1' position gave a 10 degree independent movement on the outer spoiler sections for minor corrections, particularly during flight refuelling. The spoilers were powerful control devices. A B-52G from Robins AFB (28th BS) was landed using only throttles and its spoilers after total failure of the elevator controls. This feat won Crew E-21 the Mackay Trophy for 1982. [emphasis mine]
— Davies, Peter E., Tony Thornborough, and Tony Cassanova. Boeing B-52 Stratofortress. Crowood, 1998.


If the pilot cabin loses pressure, can the pressure difference lock the cockpit door? I think, if there is only a 0.1 bar pressure difference with a single square meter door, around the weight of a ton would be needed to open it - if it is sealed hermetically and opens outward.

Is it possible?

Firstly: Flightdeck doors are to the best of my knowledge not hermetically sealed.

Secondly: Doors will normally have one of several solutions employed to safely handle explosive decompression:

Some doors have panels that pop out to equalise the pressure, especially inwards.
Some doors unlock automatically in one or both directions.

Needless to say, you need one solution in either direction. Whatever pressure difference there is it will most probably very quickly be equalised and there should not be any difficulty in opening the door if need be.


Is a cambered or symmetrical propeller airfoil more efficient? Is an cambered propeller more efficient than a symmetrical propeller for a low speed airplane?

Cambered airfoils are used on propellers as they create less drag for a given Cl than a similar symmetrical airfoil.

The primary use for uncambered or symmetrical airfoils is on flight surfaces that must provide lift in both directions equally well, as in a vertical tail or aerobatic aircraft wing. Propellers only provide forward lift or thrust (ground reverse is too little used to matter) so camber works better.


What are endplates? How do they work? Winglets have been discussed fairly regularly, but not much can be found on the topic of endplates. What are endplates, how do they work, and how do they relate to winglets?

The air doesn't notice or care that we humans use so many different names for those wingtip extensions. They all help to keep the pressure difference up between both sides of the tip and add some friction drag.

Since giving basically the same thing such a variety of names is a pettifoggery and there is no standardization for naming them, it is hard to give a clear, distinguishing feature. If I now say that endplates extend to both sides of the wing and are smaller, while winglets point up only and are larger, I am sure that somebody will rightfully point out an exception to this rule. Just look at the latest monstrosity Boeing added to their new 737NG.

Boeing scimitar winglets (picture source)

When the term endplate is used, the transition between wing and extension is sudden and sharp, while winglets tend to have a smooth, rounded transition. Maybe this would be a better guide, but also here exceptions can be found.


Is part 141 ground school really supposed to be 35hours? I'm in a part 141 program and in ground school. My instructor dismisses class very early almost every day, but in the logbook he keeps for us he writes a lot more time than we actually meet on any given topic.  Is that okay?

A Ground School Syllabus needs to be checked and approved by the FAA.  As part of that approval, they will decide if it meets minimum requirements, and is expected to take the required hours.

If the actual delivery of the material in ground school takes a bit less (or more) time than approved, that is OK, so long as the approved syllabus is closely followed.

Source: https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_141-1B.pdf


Why are lower VHF frequencies used for towers? So, why are usually lower VHF frequencies (around 118MHz to roughly 120MHz) used for towers and higher frequencies (around 130MHz to 136.975MHz) for ACC? What is the advantage of using lower frequencies for towers and higher for ACC since the wave propagates as a line of sight in both bands, that is, the maximum distance of the radio wave should be the same regardless if the frequency is 118MHz or 136MHz?

There's no specific reason why the lower frequencies are used for towers, but it's not a coincidence that they are grouped together (mostly, there are tower frequencies that are not at the lower end.)
Spectrum management is a complex effort to make maximum use of the fixed amount of frequencies available for use. In the US this falls under the FAA Spectrum Engineering Group AJW-1C.
One method of ensuring reliable safe communication is the intersite analysis. Basically, frequencies have to be used by multiple ground stations based on the airspace volume that the frequency needs to cover. This airspace is referred to as a frequency protected service volume (FPSV).
The goal is that an aircraft in the FPSV will only be able to communicate with the intended ground station. Since towers have a relatively small FPSV, typically 5,000' high (AGL) & 15 nmi radius, the tower frequencies can be reused closer together than a high altitude sector frequency that may cover a 150 mi radius at 45000 feet. A frequency that was used for both high altitude and a tower would be more difficult to de-conflict.
There are also other considerations that can affect the assignment of frequencies. It's all spelled out in the 6050.32B - Spectrum Management Regulations and Procedures Manual. It's rather lengthy at 475 pages. The details of VHF/UHF Comm frequencies is in Appendix 2.


Is the main landing gear of a large airplane designed for sideways (crabbed) touchdowns? Is it just my imagination, or is it a fact that many large airliners actually touch down "crabbed" on difficult crosswind landings?

Here's what I mean in this video, or as shown in this picture:

Is the main landing gear specifically designed to allow this? Is it recommended or discouraged by the manufacturer?

The landing gear is indeed designed to cope with crabbed crosswind landings.

The recommendation is to avoid crab on landing however in severe crosswind conditions it is sometimes impossible to decrab completely without introducing excessive bank. Therefore some residual crab has to be allowed.

Airbus recommends less then 5 degrees of residual crab on landing, but aircraft are designed to cope with more.

An exceptional design is found in the B-52, where the main landing gear can rotated to be aligned with the direction of travel to deal with extreme crab angles.


Can general aviation use UHF to contact ATC? In the US, if a civil aircraft has a UHF radio are there any regulations against it performing ATC communication on the UHF bands?

Pointers to the appropriate CFR's would be appreciated.

This question does not concern operating under an emergency state of any kind. The aircraft is assumed to be in compliance with all regulations otherwise at the time.

The reason for excluding emergency status, is that in an emergency the FCC states you can use whatever methods available to obtain help.

The UHF air band operates in AM in a general range of 225.0–399.95 MHz. Many ATC functions have both VHF and UHF frequencies. For example, Newark Liberty Tower uses 118.3 and 257.6. ATC will often broadcast on both the VHF and UHF frequencies.
You can look up these frequencies on the FCC frequency allocation table to see who is allowed to use these frequencies. This is also located in CFR Title 47, §2.106.
According to the table, the the non-emergency allocation of these frequencies is Federal use:

In the bands 225-328.6 MHz, 335.4-399.9 MHz, and 1350-1390 MHz, the fixed and mobile services are limited to the military services.
The bands 235-322 MHz and 335.4-399.9 MHz are also allocated on a primary basis to the mobile-satellite service, limited to military operations.

There are no non-Federal uses cited for those ranges. Also, per Title 47 §2.102(c):

Non-Federal stations may be authorized to use Federal frequencies in the bands above 25 MHz if the Commission finds, after consultations with the appropriate Federal agency or agencies, that such use is necessary for coordination of Federal and non-Federal activities

So it seems that if you don't have a military purpose, outside of special agreements you are not allowed to use these frequencies. For more information, the National Telecommunications & Information Administration (NTIA) has reports on the usage of the lower portion and upper portion of this band.

Technically there are also limited non-Federal uses but they don't apply to this question:

The frequency 243 MHz is the frequency in this band for use by survival craft stations and equipment used for survival purposes.
...may also be used, in accordance with the procedures in force for terrestrial radiocommunication services, for search and rescue operations concerning manned space vehicles.

For the gap in the ranges mentioned above:

The use of the band 328.6-335.4 MHz by the aeronautical radionavigation service is limited to Instrument Landing Systems (glide path).

And additionally for 322-328.6 MHz:

...all practicable steps shall be taken to protect the radio astronomy service from harmful interference.


What qualifications does a commercial aircraft pilot need? I have been considering becoming a pilot or first officer but I am unsure as to what qualifications are needed to pass the exams etc. Could someone please tell me?

To pass the exams—written and practical—you need training and need to study.

Training is provided by flight schools, airlines, or your country's air force (if you're young and don't mind flying cool jets for a while before moving on to the civilian world).

You also need to be medically eligible for the license you're after.


How to handle seeing someone online claiming to be a pilot or pilot in training, who one feels shouldn't be flying, in the EU? Suppose that on some aviation-related Internet discussion forum, one comes across contributions from a user who claims to either be training for a pilot's license, or to have a pilot's license.

However, the nature of their contributions are such as to call into reasonable doubt whether that person should be flying at all, or at least flying without an instructor closely monitoring from the next seat over in the cockpit.

Not being a forum administrator, there is no way for the person seeing these contributions from being able to access detailed records of the user's activity, such as IP addresses they are browsing from or e-mail addresses associated with their account. However, it stands to reason that the forum records these details.

The user making the claims says to be within the EU, and for simplicity's sake let's assume that the user noticing the claims is within the EU, but the two are not necessarily within the same EU country, so it's not as easy as just contacting one's national authority and be done with it. The forum itself may be hosted outside of the EU, but with a worldwide audience.

If one wants to, for the sake of aviation safety, bring such a situation to the attention of the competent authorities to be looked into, then how would one go about doing so?

How does one determine which authorities to contact? For example, which country's authorities should be contacted initially, and how to locate the proper authority/authorities within that country?
Who (which function) at those authorities should/does one likely interact with? (Basically, if hypothetically calling their switchboard phone number, what to ask for?)
What information is likely to be needed in an initial report, so that one can compile it prior to contacting the authorities in question?

In general, one wouldn't.

If the user in question has never touched the yoke, there is no issue - it's not illegal to lie on the internet.
If they're in training, it's on their instructor to set them right.

This leaves the case where they do hold a current license. Presumably you want to notify the local aviation authority that they might not satisfy its requirements.

Now put yourself in the local FAA-equivalent's shoes. Supposedly a certified pilot has posted on the internet that the artificial horizon is a lie and one should always trust their gut over it. What recourse, exactly, do you have against them? They're not under any obligation to teach flying to the general public, and there's no regulations or prescribed penalties for publishing incorrect information on the internet.

NB: It would be very different had they identified themselves as a commercial pilot for a specific carrier. In that case, they'd be presenting their airline in a bad light, and the freedom of employment (in the US, varies in the EU) would allow their employer to take action to protect their reputation.

A PPL, OTOH, is a more exclusive cousin to the driver's license, and merely indicates that its holder has at some point convinced their instructor that they were capable of flying at that moment, while meeting a number of formal requirements, and has renewed it since at required intervals.

The forum's administration might want to take action to keep false information away from their board, if you inform them, but interaction with them is a subject far removed from aviation.


What is the purpose of the fin at the Boeing 787 APU exhaust? The fin is located under the Boeing 787 APU exhaust as shown in the picture below. Does anybody know the application of this thing or it is used for 'guiding' the APU exhaust? Thanks.

As mentioned in the comments, this is indeed an "aerodynamic fence."  Fences of this sort serve two purposes:

Direct airflow; or
Energize (or trip) boundary layer airflow.

The latter are normally perpendicular to the surface on which they are mounted, allowing them to protrude directly into the boundary layer of air flowing over the surface.  You can picture the effect of these types of devices by looking a how water flows over and around a boulder in a stream or river.  "Tripping" the flow mixes the boundary layer with the more energetic air outside the boundary layer.

It is most likely the former, a device used to direct the airflow.  By the time air gets to the tail of an airplane, to the aft most part of the empennage, it is quite unsteady flow. (In this case, imagine the water flow behind a large ship.) The turbulence characteristic of this type of flow can wreak havoc for designers who want to vent exhaust gases or airflow out of the aircraft's APU. This turbulent flow can create stagnant zones which would block the air from exiting the way intended, as described here.  By directing the flow of the air around the exhaust duct, this can be minimized or avoided altogether.  There is, however, probably a small amount of the boundary layer that gets energized by this device, which would further help the designers manage the flow.

The article previously cited calls them vortex generators, which are explained in more detail here and correspond to 2 above.  Fuel that was pooling in the APU was a result of the stagnation of the flow.


Is there a benefit to representing a SID/STAR in 3D? There are several examples of 2D representations of SIDs and STARs on the web.  I have yet to encounter a 3D representation of one.

Does one currently exist?  Are there any benefits of representing a SID/STAR in 3D as opposed to 2D?

I have flown aircraft with Augmented Enhanced Reality built into their PFDs. They represent a desired flight path on the PFD with a rectangle whose unit of measure is dependent on the phase of flight. For example purposes, you would see a box on the PFD roughly 200 feet high by half a mile wide with 1 to 5 miles between each box in the enroute phase of flight. Your goal is to fly through each box. There is a dot or crosshair target on the screen to represent your actual current flight path based on trend vectors and statistics like airspeed, ground track, vertical speed, and rate of turn. Keeping the target centered in the boxes will keep you on your flight plan entered into the system. I have seen this system in Garmin and Dynon equipped aircraft.

Flight Directors and autopilots with Flight Directors can give you visual cues for pitch and bank corrections based on your programmed flight plan and actual flight vectors.

Also, apps such as Foreflight will graph out your entire flight plan including instrument procedures in virtual reality. It will then allow you to virtually fly the plan in 3D for preflight planning.

I don’t find this last resource useful in actual flight. Any other tablet based 3D representation would be just as bad. A simple piece of paper would be preferable in actual IFR flight. Any technology that would increase pilot workload any further than it already is in IMC would be dangerous. More than a couple of seconds to look at the information you need clearly displayed would be too long. The current charts facilitate rapid information retrieval by using standardized formats for every chart. There is no need to fiddle with gadgets unnecessarily.

One way this can be very useful is for at home training. Get a few pictures as large as possible taped under your tv or monitor. Have all of your charts, sectionals, and checklists applicable to a real, normal flight out and ready. Then, chairfly the entire flight from preflight planning to hangaring the aircraft in detail. Play the 3D virtual reality representation of the flight on your tv or monitor when it comes time for the flight phase.

By the way, your standard ILS or GPS approach in a linked standard six-pack already represents the information in 3D. You just have to be able to interpret it as such.


Why is the AWACS' rotodome located at the back and over the aircraft? Browsing this website, I found this question dealing with torque due to the huge piece in motion, and its answers also speak of drag.

The rotodome is located above the aircraft and at the aft of the aircraft. For me it would have been logical to put this huge mass as closely as possible to the CG for stability reasons. For this aircraft, the CG is located close to the main gear, a little in front of them. When I look at an AWACS, I can see that the rotodome is located well behind the main gear.

AWACS image courtesy of airliners.net

Moreover, it seems logical to put the rotodome under the aircraft. Its mission is to observe airspace under the aircraft to detect hostiles flying low enough to avoid detection by ground radar. By mounting the rotodome above the fuselage, the aircraft's wings may disturb the radar mounted above them.

This position is also shared with other airborne radar such as the A-50 or the E-2C.

It's mounted dorsally in large part because it's simply too large to fit beneath the fuselage.

The rotodome has to be that large because inside is actually a planar array. The radar itself isn't round, nor aerodynamic, so it's wrapped in a smooth fairing that presents the same profile regardless of which direction the array is facing.

Caption: The Northrop Grumman AN/APY-1/2 AWACS multi-mode radar inside the E-3D rotodome. (Credit: Scott Carson. Twitter.)

Some airborne radars do not rotate and can indeed be mounted below the fuselage, like the E-8 JSTARS' APY-7 (primarily a ground surveillance radar):

(Credit: USAF. Link.)

Pave Mover, an APY-7 prototype:

(Credit: Daderot. Link.)

The cancelled E-10 (planned E-3 Sentry and E-8 JSTARS successor) also had a similar under-nose longitudinal array.

(Credit: Defense Industry Daily. Link.)

However, most larger, non-rotating arrays are mounted dorsally and longitudinally, like the Boeing 737 AEW&C:

(Credit: Seattle Aviator. Link.)

  [Question:] Moreover, it seems logical to put the rotodome under the aircraft. Its
  mission is to observe airspace under the aircraft to detect hostiles
  flying low enough to avoid detection by ground radar.

Not exclusively. Low-altitude penetrators aren't the only targets. AWACS is also tasked with finding medium to high altitude aircraft, both watching for enemies (eg firing "AWCAS killers") and keeping track of friendlies.

  [Question:] By mounting the
  rotodome above the fuselage, the aircraft's wings may disturb the
  radar mounted above them.

You don't need a lot of depression to observe things at medium to long range. At 30,000 ft, the horizon sits just a few degree below level, and even at 30 miles (which is very close) a low-altitude target is just -10 degrees. There's also a fair bit of clearance between the elevated dome and the fuselage/wings, which reduces how much of the ground is masked (roughly -20 degrees from radar to wingtip). Together, there's probably fairly little that an E-3 wouldn't be able to see. You'd have to be practically underneath it at close range. And then you'd have to deal with the fighter escorts...


Hot air balloon toilet? I have never been in Hot air balloon

But today I was wondering, what if someone in Hot air balloon wanted to pee?

how will they do it??

if there are no toilets in there, can they just do it from there to the ground? what if there was people down there?


Why don't smaller powered airplanes have better lift-to-drag ratios? Many airliners have LDRs near 20, and it sounds like the electric Eviation Alice may have an LDR of 24 at 240 kts, but many small planes typically have LDRs of only 8-10.  It seems like they could easily increase the ratio with e.g. larger wingspans with higher aspect ratios and save a lot of fuel - why don't they do this? What are the tradeoffs? Are there any commercially successful 4-20 PAX planes that have LDRs over 20?

There are plenty of smaller power planes that achieve those numbers; motorgliders.  And motorgliders with L/Ds in the high teens and low 20s are pretty efficient cruisers.

So the real question is; why aren't all light aircraft made to be like motorgliders?

Well, motorgliders have their disadvantages.  The long wing span is a problem fitting in on the ground.  The long wings are heavy, which limits payload.  The long wings result in slow roll rates and general controlability problems.  So if you are going to live with the hassle of long wings, it has to be really worth the trouble.

And probably the biggest one; the long wings stop being an aerodynamic advantage and become an impediment when you want to cruise at significant margins above speed for best L/D.  This is the case for aircraft that cruise at low altitudes if you want to cruise at 2-3 times max L/D speed efficiently.  In this case, < span = better.  WW2 fighters modified to be optimized for low altitude combat had their wing spans reduced.

Airliners are more like the motorglider, and benefit from the L/D benefits of high aspect ratio because of their operating environment.  They cruise at very high altitudes where indicated airspeeds are low because of the thin air.  At FL400, an airliner might be cruising in the thin air at only 280 kts indicated, maybe only 2X its flaps up stall speed (going 500+ true, but it's the indicated airspeed that matters - if you could stick your hand out the window, you'd feel a 280 kt wind blast, not a 500 kt wind blast).

It's cruising a lot closer to its max L/D speed than the low altitude airplane that flies at 3-4 times its stall speed, and so it benefits from the span and area like a motorglider.  To take that to it's most extreme, you have the Lockheed U2, which needs all that span and area to make it up to 75000 ft (where the indicated airspeed is only about 80 kt going, say, 200 kts true or whatever it is).

You do see some aircraft like the Diamond light twins with quite long aspect ratios for what they are.  This is done mostly for rate of climb. because in a light twin, single engine climb performance is critical, and the high aspect ratio really helps (climbing close to max L/D speed) and that's factored into the balancing act of deciding just how long the wings need to be for good single engine performance without giving up too much controlability or taking on too much weight (helped there by composites) or too much space on the ramp.


Does the flight always switch to TRACON on a go-around in class B airspace? I have been listening to class B go-around ATC recordings.  After the initial climb of the go-around, the tower gives the flight a heading and altitude.  Then, on some recordings I hear the tower say "contact departure" and a frequency.  But on others I don't hear that.
I can't tell whether:

It's optional for the tower to hand off the flight to departure in a
go-around and the tower can keep control the whole time until they
land, or

The tower always switches the flight to departure, but sometimes
that hand-off is left off of the recording.

Which is it?

It depends. As a rule oh thumb, a missed approach will be handed over to approach (TRACON) to get a new approach clearance. Some places have local rules that allow approach to delegate this responsibility to the tower when it makes sense, which means the aircraft can then stay on the tower frequency for the new approach. This would normally require a few things, such as appropriate equipment being available in the tower (radar) and having a tower controller that is actually rated to be allowed to perform approach control.
In any case, when a go around is initiated, the tower will immediately call approach and coordinate what to do. One of the results of this coordination is the "heading and altitude" you have heard the tower give to some flights. Typically, approach will request to get the flight at a specific heading and altitude, and the tower will give those instructions before handing over the flight. Some airports will have very specific local regulations about which steps to follow, others allow the controllers to come up with a solution that fits the specific situation.


Materials usually used in dorsals fins specifically in the ATR 72 I am an aerospace engineering student and I am having problems finding information about the materials usually used in the dorsal fin of an aircraft. I would also like to know the kind of stress and forces this part of the aircraft is under. The project I have to do is about replacing the material the selected part of the image is usually made of.
So my question is if anyone knows the material typically used in this part and if you may know any other alloy or material that could be used.

The loads on section of a dorsal fin are minor, just from the dynamic pressure of airflow that may be striking the panel from the side during yaw excursions in turbulence.  It's a "lifting" surface, insofar as it's contributing to the restorative yaw moment being part of a stabilizing fin, but the loads aren't super high and it may even just be attached like a fairing using dzus fasteners or camlocks or  similar if there is something inside that needs ready access.
Can't speak for the ATR specifically, but the material is probably either 2024 Alclad sheet like the adjacent structure, or if the part has compound curves, you might see a more formable alloy like 6061 or even 5052 in a non-structural part like that (you will see 6-series alloys in heated leading edges for example).  On newer designs it's more likely to be composite, usually Kevlar or a fibreglass/Kevlar blend (fibreglass is better in compression being stiffer, so it is sometimes mixed in with the Kevlar) and most recently carbon fiber.
If I was tasked with redesigning the part to a new material, it's likely because it's aluminum and the goal is weight saving, and I would likely choose carbon fiber as the replacement.  The optimum would be carbon fiber skins sandwiched over a nomex honeycomb core, the way interior floor panels are made.
An important caveat about using CF, is you cannot let it live right beside aluminum where there is a potential for direct contact. They are well apart on the galvanic scale and if there is water present the carbon will destroy the aluminum. If that's a problem it might be better to go with Kevlar composite.


Do fighter jets have forward-looking radar warnings for missiles, and when was this first implemented? Let's imagine a swarm of fighter jets intercepting another swarm. Both groups are moving head-on towards each other. Once they get in range, they will probably lock on and fire missiles.

Do fighter jets have radar that will show and warn of a missile coming head on? Or do they only scan their tails?

I'm interested in when, if ever, such capability was implemented. To me it seems like the 50's and 60's and maybe even the 70's, they would only worry about scanning their tails. It would also be good to document this for both NATO and Warsaw Pact jets.

Radar Warning Receiver systems (RWRs) used by military aircraft are omnidirectional. However, they do not warn of incoming missiles (unless that missile is at least semi-actively radar-guided, like an AMRAAM). What they warn of are various patterns of radar activity, including a radar lock (which is a constant, high-intensity scanning of the aircraft's position, more than just a "blip" as the antenna passes by on a wide-angle scan pattern).

If another aircraft has a radar lock on you, you should be expecting an incoming missile of some kind. However, IR missiles (AIM-9 Sidewinder, AA-11 Archer, MICA IR, ASRAAM) do not emit any EMR that indicates they're incoming; they use a passive FLIR sensor to identify and track the heat source they were told to kill (they don't even require a radar lock; the seeker can be cued to a pilot's helmet, or it can be "uncaged" and will lock on to the most significant heat source in front of it). Passive radar-guided missiles like the old AIM-7 Sparrow also do not emit their own radar; they track the radar returns from the firing aircraft. Only semi-active and active radar-homing missiles emit their own radar noise that can be used by the RWR to know one is on the way. A few older passive missile systems used radio control to guide the missile to the target, and RWRs can also detect these "sideband" radio signals as a clue a missile has been launched.

More modern Missile Approach Warning Systems (MAWS) have additional features that can help detect and track incoming missiles of multiple types. The biggest clue of a missile launch is a new heat signature, especially in the direction of an incoming radar lock; a suite of IR sensors can be used by MAWS to put 2 and 2 together and warn you of the missile launch.


Do I need complex endorsement in each class or type of aircraft? I have experiences with PA28R and got a complex endorsement from my instructor.
Now, I am working on multi add-on and flying DA42 Twinstar.

Do I need another complex endorsement that specifies the class and the type of the  aircraft for DA42 checkride?

You only need one complex endorsement under FAA regulations,

  §61.31   Type rating requirements, additional training, and
  authorization requirements.

  (c) Aircraft category, class, and type ratings: Limitations on the
  carriage of persons, or operating for compensation or hire. Unless a
  person holds a category, class, and type rating (if a class and type
  rating is required) that applies to the aircraft, that person may not
  act as pilot in command of an aircraft that is carrying another
  person, or is operated for compensation or hire. That person also may
  not act as pilot in command of that aircraft for compensation or hire.

  (e) Additional training required for operating complex airplanes. (1)
  Except as provided in paragraph (e)(2) of this section, no person may
  act as pilot in command of a complex airplane, unless the person has—

  (i) Received and logged ground and flight training from an authorized
  instructor in a complex airplane, or in a flight simulator or flight
  training device that is representative of a complex airplane, and has
  been found proficient in the operation and systems of the airplane;
  and

  (ii) Received a one-time endorsement in the pilot's logbook from an
  authorized instructor who certifies the person is proficient to
  operate a complex airplane.

In your case a class rating is only required for the "multi" aspect of the DA-42 as the DA-42 has no type rating.

The FAA further more defines complex aircraft as

  Complex airplane means an airplane that has a retractable landing
  gear, flaps, and a controllable pitch propeller, including airplanes
  equipped with an engine control system consisting of a digital
  computer and associated accessories for controlling the engine and
  propeller, such as a full authority digital engine control; or, in the
  case of a seaplane, flaps and a controllable pitch propeller,
  including seaplanes equipped with an engine control system consisting
  of a digital computer and associated accessories for controlling the
  engine and propeller, such as a full authority digital engine control.

No part of this definition stipulates how many engines the aircraft has.


How can I get a ride in the jump seat as a non-professional pilot? A couple of years ago, I had a strong fear of flying. Now, I really enjoy it. In fact, it is a dream of mine to sit in  the jumpseat of an A320 during takeoff. I've had a handful of flying lessons.

If I took my logbook and explained my interest to the captain, is there any chance this could happen? If not, how could I make it happen?

It's hugely unlikely. Almost vanishingly unlikely, with few exceptions perhaps for something a little smaller than a passenger-carrying A380 (like a private jet on a repositioning flight where you know the captain well)

You used to be able to go up and see the captain on the flight deck - I did it a few times as a kid. Even then asking to sit in the jump seat was usually met with a smirk.

And then 9-11 happened.

  With effect from 1 November 2003, ICAO Annex 6 was amended so that under Chapter 13.2.2 “all passenger-carrying aeroplanes of a maximum certificated take-off mass in excess of 45 500 kg or with a passenger seating capacity greater than 60 shall be equipped with an approved flight crew compartment door that is designed to resist penetration by small arms fire and grenade shrapnel, and to resist forcible intrusions by unauthorised persons. This door shall be capable of being locked and unlocked from either pilot’s station”.

And with that came locking of the cockpit door, and no more visits to the cockpit during flight (incidentally, if you ask nicely, the captain will often let kids take a peek when they're deplaning the passengers)

And then germanwings happened, and they had a rethink. But still no visits to the cockpit during flight at all for the average Joe.


Why don't FMCs automatically include up-to-date oceanic route definitions? In modern FMCs, flying an oceanic route requires inputting coordinates directly, often in obtuse formats (which are arguably prone to typos, but following proper procedure and a step through the route map generally prevent this being an issue).

Working with an example: North Atlantic Tracks, or NATs, are a set of roughly parallel airways in the North Atlantic, generally spanning from Canada's maritime provinces in the West to the Irish coast in the East. Because of frequently changing conditions in the North Atlantic, these routes undergo changes every few days, which are conveyed to pilots before each transatlantic flight.

Having said all that: modern FMCs are pretty clever, and they can (and regularly do) pull down data from the network, including in-flight weather data, for example. Why don't modern flight computers use this to also download oceanic route definitions if manual input is required rather than using a company route?

Much like 'Why can't flight management systems receive instructions directly from the controller?', the answer is it should be coming soon (mid/late 2020's).

    FMCs are pretty clever, and they can (and regularly do) pull down data from the network.

You're right, but the issue is "the network". They do that already off private networks, as opposed to a common public network (Aeronautical Telecommunication Network). ATN is now at the heart of the data-link modernization.

Having the option to access and uplink common flight plans and routes to an aircraft's FMS should become a reality (Boeing):

But as the above 2016 presentation shows (starting from the 'B2 Ground Deployment' slide), some old hurdles are still there. A 1994 Flight International article might shed some light on why it's been taking so long:

  It is increasingly clear is that different regions, operators and manufacturers are going to find their way to the ATN by different routes via different steps, and that is giving rise to a variety of concerns. The most avid proponents of the ATN fear that some entities will become content with incremental communications improvements on the way and lose the desire to see the project through.

  Airlines are reluctant to make the necessary investment until civil-aviation authorities (CAAs) make their intentions clear. In a classic chicken-and-egg paradox, however, the CAAs say that they cannot go ahead until they are certain which equipment the aircraft will carry in future. Exasperated service providers are reduced to pleading with the user community to do something, at least.

ATN has been a dream since at least the early 1990's, but reluctance is the reason. But whether the route is oceanic or not, the pilots are supposed to check the FMS entries whether manually typed in or uplinked.


What is the purpose of using 8.33 kHz instead of 25 kHz frequency spacing? What is the purpose of using 8.33 kHz instead of 25 kHz frequency spacing?

The purpose is to accomondate more dedicated frequencies within the airband VHF range (117.975 to 137 MHz).

Increasing number of stations made this necessary, if the smaller division was not implemented, it was estimated that only 70% of future requirements for frequencies in Europe can be met.

833radio.com has further information and an nice table describing the channel spacing:

For simplicity, the actual 8.33 channels are displayed as rounded to .005 values.
For example to use the frequency 118.0083MHz, you dial 118.010


Why are the power and drag curves called polars? See Wikipedia:Drag polar and Wikipedia:Polar curve (aviation) for example.

These curves are not on a polar coordinate system. Why are they called polars?

It is an historical name.

The first polars were drawn by Otto Lilienthal in polar coordinates.

Here (sorry, German link) we find an example:


What details do EICAS systems provide? I was reading this article about EICAS:

  Engine-indicating and crew-alerting system (EICAS) includes
  instrumentation of various engine parameters, including for example
  revolutions per minute, temperature values, fuel flow and quantity,
  oil pressure etc. Typical other aircraft systems monitored by EICAS
  are for example hydraulic, pneumatic, electrical, deicing,
  environmental and control surface systems. EICAS has high connectivity
  & provides data acquisition and routing.(source: Wikipedia)

Wikipedia article doesn't explain EICAS functionality very well, specially on the matter of the Crew-alerting System.

I'm interested to know more about this system... So here is my questions:

I'm correct to assume that EICAS is a vital instrument for glass cockpits?
Is every fault displayed there? (ie. Radio failure, air packs malfunctioning, etc...)
What is the difference between red messages and yellow messages?
How much detail can a pilot get from its messages?

The EICAS will have the engine instruments and the crew alerting system in one display.  It is a vital instrument because it displays engine parameters, fuel, the crew alert system and other systems information depending on the specific airplane.

The CAS (crew alerting) functionality of the EICAS replaces the illuminated fault buttons in older airplanes.

YSSYguy CC-BY-SA 3.0

The electronic CAS that is part of an EICAS display is a superset of these old panels and can display a much bigger set of alerts.  The specific alerts that can be shown will cover most error and failure modes the airplane systems can reasonably encounter.  Cautions are yellow in color and will illuminate the master caution and sound an audible chime.  Warnings are red in color and will
illuminate the master warning and sound the triple chime (and the fire bell for certain conditions).  There may also be advisory messages displayed in another color, e.g. cyan, on the EICAS.

 EMB-145 EICAS.  The CAS is the upper right portion of the display

The messages themselves are terse and not detailed, though detail can be inferred from the pre-defined message text.  Warnings and cautions that are displayed can be addressed with memory immediate action items (memorized checklists) and/or the QRH (quick reference handbook) which defines the procedures for dealing with problems in a verbose checklist flowchart.  The QRH will be indexed by the messages on the CAS so they can be easily found and referenced.


What type of batteries are used in airline planes? In Embraer 145 and Boeing 777
I mean material, recharge cycle,  nominal current and voltages. From the comments I don't understand the difference if the plane is turboprop or turbofan.

From this Concorde battery page, the Embraer E-145 can use a 44 Ah, 24 VDC Lead-Acid batter: Concorde RG-422

The Embraer E-145 can also use Ni-Cd batteries.

The Boeing 777 uses Ni-Cd batteries as well: Boeing 777 Saft Batteries


Would turbine blade twist change if all conditions except the density of the fluid remained the same? While designing a turbine, the blade twist is apparent from the velocity triangles, and this analysis only depends on the velocity.

However, would there be any difference for different media? When all conditions stay the same but the density of the fluid changes, would the twist stay the same?

A classic comparison would be boat props vs aircraft at various RPM.  A higher density (viscosity) fluid would put more stress on the blade tips, hence shorter and more robustly built blades.  The amount of twist would depend on loading of props and would include chord length.  A tapered prop may have a different twist from an untapered or reverse tapered.  Diameter and RPM are also factors in loading.  And, as in aircraft, twist would also play a role in cruise efficiency or acceleration from standing still.

So there is no one rule about this going from one fluid to another (rare application).
Variations of design and performance in one fluid are much more common.


Are turn rate indicators calibrated to a certain speed? If so, what speed? Are turn rate indicators calibrated to a certain speed? If they are, what speed are they calibrated to, and why aren't all the turn rate indicators calibrated for the same speed?

They are not calibrated for a certain speed.

If by "calibrated", you mean they deflect together / to the same side, then you're using the instruments wrong. The two instruments have are not linked to each other, they operate independently and they operate on different principles. They are located next to each other in the cockpit out of convenience.

The "slip indicator" is a ball in a U-shape tube. It tells you whether gravity (or experienced acceleration) is pointed down, or to the side. Period. It is as simple as that.

The "turn coordinator" (little white plane / white needle) indicates your yaw rate. It operates by using a spinning gyro; the precession effect of yawing causes the gyro assembly to roll.

The roll is restricted by a spring, which is calibrated to indicate standard rate turn when the yaw rate is 3 degrees per second. The turn coordinator works at any airspeed (part of the preflight check is to turn the plane while taxing and verify the turn coordinator works).


Are there cases of a thrust reverser used on a turbojet engine? In the case of a turbojet (with no "cold" bypass flow), the airflow being directed forward by an hypothetical thrust reverser can be really hot.

Depending on the location of the engine, this flow may be dangerously redirected towards the empennage and the fuselage.

For instance, for a fighter this would be a hazard for sensors, equipment, payloads including missiles, likely many other elements, and pilots:

General Dynamics F-16C (source: Wikipedia)

Are there turbojet engines fitted with a thrust reverser? Which aircraft are they used for? How is this problem dealt with?

Yes.

The Rolls-Royce/Snecma Olympus 593 [Wikipedia] were pure turbojets and they had thrust reversers.

Source: Wikimedia

Also, T/R on Concorde were also used in flight (If I remember correctly, only the inboard ones were used in flight) because Concorde didn't have spoilers.

Being a civilian aircraft, with the engines mounted under the wing, Concorde didn't have any real problem with thrust reversers


Is it legal to use GPS to navigate VOR Airways? A previous question concludes that it is legal to fly an aircraft in the US with only an IFR-approved GPS/WAAS system and no other navigation equipment on an IFR flight plan. My question is about how the pilot is then allowed to navigate.
Specifically, must a pilot fly on GPS (T and Q) Routes? FAA Advisory Circular 90-108 discusses using RNAV systems on conventional routes, so it seems that a pilot could also fly on VOR airways, for instance. In fact, 90-108 specifies exactly what a pilot can use their RNAV system for:

Determine aircraft position relative to or distance from a VOR, ... DME fix, ...
Navigate to or from a VOR,  TACAN, NDB, or compass locator.
Hold over a VOR, TACAN, NDB, compass locator, or DME fix.
Fly an arc based upon DME.

Navigating on a VOR airway involves navigating to and from VORs, which is covered by point 2. However, the list does not include navigating to a DME/radial fix off a VOR. After taking off IFR the departure controller may clear an aircraft direct to a fix on the airway e.g. "cleared direct BOONE". Could a pilot legally use only GPS/WAAS to fly to BOONE or any other VOR radial/DME point?

It's legal if you have a suitable and acceptable RNAV system as described by FAA Rules.
Also realize that it is only RNAV capability that provides for 'direct routing' without recourse to DR - Dead Reckoning - or Radar assisted DR needed by traditional Radio Aid based navigation.
When an RNAV system navigates to an out of service VOR, it is flying a computed course from it's position vis a vis the VOR to the VOR position. This is no different from flying from any point 'A' to any point 'B'. That is the whole purpose of the Advisory Circular being quoted. A few more extracts from the AC (quoted below) should make it amply clear.

FAA AC 90-108 extracts . . .

PURPOSE. This advisory circular (AC) is intended for the following purposes:

a. Provides operational and airworthiness guidance regarding the suitability and use of Area Navigation (RNAV) systems while operating on, or transitioning to, conventional, i.e., non-RNAV, routes and procedures within the U.S. National Airspace System (NAS). This guidance material applies to two broad categories:

(1) Use of a suitable RNAV system as a Substitute Means of Navigation when a very high frequency (VHF) omni-directional range (VOR), distance measuring equipment (DME), Tactical Air Navigation (TACAN), VOR/TACAN (VORTAC), VOR/DME, non-directional radio beacon (NDB), or compass locator facility including Locator Outer Marker (LOM) and Locator Middle Marker (LMM) is out-of-service, i.e., the Navigation Aid (NAVAID) information is not available; an aircraft is not equipped with an automatic direction finder (ADF) or DME; or the installed ADF or DME on an aircraft is not operational. For example, if equipped with a suitable RNAV system, a pilot may hold over an out-of-service NDB.

(2) Use of a suitable RNAV system as an Alternate Means of Navigation when a VOR, DME, VORTAC, VOR/DME, TACAN, NDB, or compass locator facility including LOM and LMM is operational, and the respective aircraft is equipped with operational navigation equipment that is compatible with conventional NAVAIDs. For example, if equipped with a suitable RNAV system, a pilot may fly a procedure or route based on operational VOR using that RNAV system without monitoring the VOR.

b. Qualified RNAV Systems. Describes the types of RNAV systems that qualify as “suitable RNAV systems”

DEFINITIONS. For the purposes of this AC, the following definitions are provided:

b. Area Navigation (RNAV). A method of navigation which permits aircraft operation on any desired flightpath within the coverage of ground- or space-based navigation aids or within the limits of the capability of self-contained aids, or a combination of these.

g. Substitute Means of Navigation. The use of information from an RNAV system in lieu of that from out-of-service conventional NAVAIDs and/or inoperative or not-installed navigation equipment compatible with conventional NAVAIDs.


What is the IATA code for the A320neo family? I was looking for A319neo, A320neo and A321neo IATA code all over the net but I could't find it, can someone help me with this.

(As of 9 March, 2018, the answer with the highest up-vote count (from April 2016) states "will likely be the same as". A more definitive answer should be available now.)

The IATA three letter code for the Neo will likely be the same as for the regular model.
Unfortunately the IATA code list is copyrighted, and I can't find a public document that confirms it.

The more commonly used ICAO type designator, a four letter code can be found in  ICAO doc 8643. It contains a list of all common aircraft and their codes.

The ICAO type designator for the neo will be the same as for the regular versions. So A319, A320 and A321. Only if the performance of the Neo aircraft significantly differs from the originals, then a dedicated designator will be created.


In a 747 is it normal for the Vr (takeoff speed) to vary greatly depending on fuel load and ambient temperature? I was reading one of the documents linked on this question, particularly I was reading case study number 8 of this particular document.

In the conclusion the author notes that the aircraft flight characteristic calculations had been messed up to the point that all V-speeds were calculated for a 747 100 tons lighter than their actual Take Off Weight (TOW).  Thus, they tried to rotate too early, couldn't get enough lift and the tail of the 747 struck the ground.

When reading that brief description, I had assumed that perhaps they were off by 5 to 8 knots, or something along those lines.  So, I was surprised to see the author later note that Vr was actually off by close to 30 knots!

I'm really curious suddenly, how much can a 747's rotation speed change?  I was told that rotation speed was generally somewhere around 130 knots for that class of plane, but if there is a 30 knot variance. Can it really be anywhere from 115 to 145 depending on the weight of the plane?

As Henning Makholm's answer discusses, the weight difference between the lowest and highest weights is significant. The operating empty weight (OEW) of a 747-400 is 394,100 lb, while the maximum takeoff weight (MTOW) is 875,000 lb. This means there is a difference of about 400,000 lb between the lightest and heaviest weights at which a 747 may be taking off, making the MTOW about twice as heavy as the OEW.

The rotation speed Vr is the point at which the aircraft can pitch up and develop enough lift to climb. So at MTOW, the 747 must develop about twice as much lift than closer to OEW. Most of this force is lift from the wings.

Lift can be calculated with the following equation:

L = 1/2ρv2sCL

L = lift
ρ = air density
v = airspeed
s = wing area
CL = lift coefficient

The air density will certainly play a role. Higher altitudes and temperatures reduce the amount of lift. But this example pertains to the other variables.

An airliner can use flaps and slats to increase the CL and s of its wings.

The CL will also depend on the angle of attack α of the wings. An approximate curve for the 747 can be seen here (it's for a 747-200, but it should be close enough). When an aircraft rotates, it is changing the AOA, which increases the lift. It is very important when designing an aircraft to make sure it can pitch up enough while on the runway to achieve the pitch angle needed for takeoff. A 747-400 rotates to about 10 degrees on takeoff. Based on the approximate CL-α diagram, the lift coefficient changes from about 0.3 to 1.25 when α changes from 0 to 10 on rotation.

When the aircraft weight is increased, flaps may be increased from 10 to 20. However, flaps 20 may be standard because these guys said so, so lets assume that CL and s will also not change. This leaves the airspeed v as the only parameter left to increase lift.

In this study, figure A-7 shows a distribution of ground speed at liftoff that lies between 140 and 190 kts. These numbers will probably be a little higher than Vr due to the acceleration between Vr and liftoff, and an average headwind. This means that at weights at the lowest end, 130 kts would be a reasonable estimate for Vr.

So now lets make up some numbers. Lets take the weights 475,000 lb and 875,000 lb. Assume that the aircraft needs a lift 10% higher than its weight to take off. This gives us lift values of 522,500 lb and 962,500 lb. Using the lift equation and a low end speed of 130 kts to find the unknown portion.

522500 = 1/2ρ1302sCL

ρsCL = 61.8

Since we are assuming none of those vales will change, we can solve for v at the higher lift value.

962500 = 61.8/2v2

v = 176 kts

This is not too much lower than the high end liftoff value of 190 kts. So there you have it. Lift must be increased to account for the additional weight, and lift is proportional to the square of the airspeed.


What is the proper air strip closure procedure with the FAA? I own a grass airstrip that was registered for me by a good friend.  I want to sell my land and the guy that registered it is dying and can't help me.  What do I need to do to have this airstrip closed?

It looks to me like you need to file FAA Form 7480-1, Notice of Landing Area Proposal.  There is a checkbox for "Deactivation or Abandonment".

The form explains that you have to give 90 days advance notice.  So you shouldn't make any changes until 90 days after filing the form.  This presumably gives them time to update charts, so that pilots know the airstrip is no longer usable.

The form has the address and phone number for your FAA regional office, who might be able to help if you have questions about how to complete the form.


aircraft display Processors what kind of Processors and GPU are used for Aircraft display ? Is it possible to use single processor to run all three displays (Primary flight display, Navigation display and EICAS)?

Airplanes have a long history of evolution, and so do computers.

But some latest developments seems to suggest that, yes, people are working on it to use a single computer system to display and control everything, but right now the innovation front is in the automotive industry where regulatory complexity is lower.


Can an armed door be opened from outside an airliner? This is a continuation from this question, whereby it discussed the meaning and significance of an armed door.

Now, is it possible to open an armed door from outside, for example, if for some reason the passenger or crew are incapacitated, due to inhalation of poisonous gasses etc.

This depends on the aircraft:

DC9, MD80, B727, B737

On some (especially older model) aircraft doors such as the Boeing 737 for instance this is directly dangerous, since the slide is attached on the inside by hand with the means of a girt bar to the aircraft.

There is hence no way to open the door without the slide going off should it be armed. There is a helpful notice in red on the outside to "stand clear" when the red banner is crosses the window, the indication that it is armed. Judging by the space required and force the doors have, this is still most probably very dangerous idea that should not be used unless absolutely necessary.

Source

Airbus, B757, B767, B777, MD11, E-Jets

On more modern aircraft, this is safe: opening the door externally will push the arm handle to the disarmed position before proceeding to open it. This is for instance the case on all Airbus aircraft.

This video provides a nice example.


What can I do to prepare for private pilot training? (India) I am an aviation enthusiast from India. I am 24 now and want to be a hobby pilot after 1 or 2 years (I need to save money to afford training).  I want to move up to twin engine aircraft as well.

Since I have fair amount of free time and can understand the concepts clearly with no time pressure, what should I start doing now that will help me tremendously when I train to be a pilot (reading books or doing any other stuff)?  What should be my plan of action?

It's hard to give you specific advice for India because I'm not familiar with the regulations and standards there (your best bet would be to give the DGCA a call and ask if they have any publications you can review).

Broadly speaking all countries are going to expect you to know much of the same material however (because all airplanes essentially fly the same way). Along those lines, the FAA publishes some of the best flight training resources out there, and it's all available online for free.
I would recommend two of the publications to anyone considering flight training:

The Airplane Flying Handbook
This is where I'd generally suggest starting - a basic "How does all this flying stuff work?" textbook on a par with any of the commercially-produced materials.
Details on specific regulations, procedures, how to read charts, etc. may vary, but all of the material on aerodynamics, systems, flight controls, and maneuvers will be applicable.
If you're interested in helicopters there's a Helicopter Flying Handbook as well.
The Aeronautical Information Manual (direct PDF link)
This will be less useful to you as it's written with US regulations in mind (and stuff like aeronautical charting is probably different in India than it is in the US), but again there are large sections that are broadly applicable: Chapters 1, 2, and 8 in particular.

In addition to reading you can gain some experience using simulators if you use them effectively - even relatively inexpensive home simulation software & equipment can be helpful, though it's not a substitute for the real thing. We've got a good Q&A on using simulators to help in training which addresses some of the strengths and weaknesses of learning in a simulator. To help keep you from developing bad habits you would have to un-learn in a real airplane there are also companies providing what's effectively a private pilot flight course via simulators for free, and that will help you get started doing things right - following all the procedures as you would for a real airplane.


Given the same engine, why install a gearbox on a turboprop but not on a turbofan? I am reading the book Mechanics and Thermodynamics of Propulsion, by Hill and Peterson. I found out this image while reading the chapter 5, "Thermodynamics of Aircraft Engines":

Why would there be a gearbox in the turboprop but not on the turbofan? Was this just a result of a simple, quick, representative sketch? Or did authors forget to add the gearbox to the turbofan?

Later in the text, it says:

  The gearbox is necessary so that both propeller and core engine can operate at optimum rotational speed.

There it says "optimum rotational speed". Is that the speed of the compressor? The speed of the fan? Or maybe an intermediate, flight-airspeed-dependant speed? How does the gearbox know which is that "optimum speed"?

The bigger the diameter, the lower the optimum speed. Generally, fan and propeller blades should run at a high dynamic pressure, but still at subsonic speeds to avoid the higher losses involved with supersonic flow. Since the tip will be the part with the highest speed, and propellers have bigger diameters than fans, propellers run at lower speeds.

The high pressure compressor and turbines of an airliner engine will run at above ten thousand RPM, while the propeller wants to run at about 1800 to 2200 RPM. The propellers on the Tu-95 even run at only 750 RPM. Both the fan and the propeller are powered by separate low pressure turbines which also have an optimum speed, and the faster the turbine runs, the more torque it will produce for a given size. For that reason, the low pressure turbine and the shaft of a big airliner engine run at between 2500 and 4000 RPM, and the turbine of the PT-6, a classical turboprop engine, at 30.000 RPM. Since power is torque times RPM, a faster running shaft will be lighter than one running at low speed, so the speed is only reduced directly at the propeller mount.

A fan's optimum speed is between that of the compressor and the propeller and would ideally also need a gearbox, but here the transmitted power is so high that a compact gearbox will be hard to design. Even if it runs at 98% efficiency, it will produce waste heat in the order of several hundred kilowatts in case of a big airliner engine. Some small engines with just a single turbine use gearboxes already (e.g. the Lycoming ALF507), and now the next generation of efficient fan engines are also introducing gearboxes. But so far, most engine designs have preferred to run the fan faster than what would be ideal. Note that the tip speed of a modern, ungeared fan is already well above Mach 1.

Their bigger diameter makes propellers more efficient. The more air mass is involved in thrust creation, the higher the propulsive efficiency will be. Fans need to be smaller precisely because they will run with the speed of the low pressure turbine, and to convert the available power into thrust, they need a much higher solidity ratio, which translates into a higher wetted surface, which increases friction losses.


What does YF stand for? I know that F=fighter, A=attack, F/A=fighter/attack, B=bomber. I can not find any information on what YF stands for. This type of aircraft is usually an experimental aircraft, but why do modern aircraft use X instead of YF?

The 'Y' in YF stands for prototype according to the Tri-Service aircraft designation system. The 'F' stands for fighter, so YF stands for prototype-Fighter. These aircraft are operated by the US Department of Defense (USAF or USN).

For example, YF-22 is the prototype (technology demonstrator) version of the F-22 Raptor.

The 'X' series is the name given for strictly experimental aircraft; i.e. they are not prototypes.


Who is responsible for aircraft separation in IFR (limited/no visibility)? I was reading how-much-is-the-minimum-safe-distance-between-two-planes-in-flight and realized part of it confused me (or maybe I'm just tired.)
In a low- or no-visibility environment (i.e. under IFR rules AND conditions), who is responsible for separation of planes in flight?
§91.111 Operating near other aircraft and §91.13 Careless or reckless operation are both shown in that question/answer, but if a flight is under ATC guidance, are they (ATC) or the Pilot-In-Command (PIC) responsible?
I'm most interested in the U.S. (FAA Regs), but discussions of other regulatory bodies would be fine.

ATC is always responsible for IFR-IFR separation, regardless of weather conditions. That is their primary mandate, and all other services are provided on a workload-permitting basis.

In visual meteorological conditions, pilots of IFR aircraft are also responsible for seeing and avoiding other aircraft. But for IFR traffic of course this is not always possible, since the aircraft may be going in and out of the clouds.

If a loss of separation (at worst, a collision) occurs between two IFR aircraft, ATC would be held responsible (assuming the pilots followed ATC's instructions). If analysis indicates the pilots could have seen each other, they would also be held responsible.


What are the lateral sensitivities of GPS approaches? What are the lateral sensitivities of each of the WAAS and LNAV approach? Is the lateral sensitivity of WAAS the same as that of the localizer, which is 3 to 6 degrees? What about the LNAV approach?

Check out AIM 1-1-9 for localizer information. Basically, the localizer is positioned so to have a course width of 700' at the threshold. So full deflection to either side is 350'. A CDI has 5 dots on each side, so at the threshold each dot is 70'. Near the Middle Marker, one dot means you’re off course by 150 ft. Near the Outer Marker, a one-dot deviation puts you about 500 ft. from the centerline.

GPS (non-WAAS) approaches have a constant full scale deflection of .3 NM after the final approach fix.

  AIM 1−1−17 5 (e) (5) When within 2 NM of the Final Approach Waypoint (FAWP) with the
  approach mode armed, the approach mode will switch to active, which
  results in RAIM and CDI changing to approach sensitivity. Beginning 2
  NM prior to the FAWP, the full scale CDI sensitivity will smoothly
  change from ±1 NM to ±0.3 NM at the FAWP. As sensitivity changes from
  ±1 NM to ±0.3 NM approaching the FAWP,…

WAAS on the other hand is similar to the localizer.

  AIM 1-1-18 (d) 4 Both lateral and vertical scaling for the LNAV/VNAV and LPV approach procedures are different than the linear scaling of basic
  GPS. When the complete published procedure is flown, ±1 NM linear
  scaling is provided until two (2) NM prior to the FAF, where the
  sensitivity increases to be similar to the angular scaling of an ILS.
  There are two differ- ences in the WAAS scaling and ILS: 1) on long
  final approach segments, the initial scaling will be ±0.3 NM to
  achieve equivalent performance to GPS (and better than ILS, which is
  less sensitive far from the runway); 2) close to the runway threshold,
  the scaling changes to linear instead of continuing to become more
  sensitive. The width of the final approach course is tailored so that
  the total width is usually 700 feet at the runway threshold. Since the
  origin point of the lateral splay for the angular portion of the final
  is not fixed due to antenna placement like localizer, the splay angle
  can remain fixed, making a consistent width of final for aircraft
  being vectored onto the final approach course on different length
  runways. When the complete published procedure is not flown, and
  instead the aircraft needs to capture the extended final approach
  course similar to ILS, the vector to final (VTF) mode is used. Under
  VTF, the scaling is linear at ±1 NM until the point where the ILS
  angular splay reaches a width of ±1 NM regardless of the distance from
  the FAWP.


What does the "visibility" number mean on an approach plate? In the profile view in an approach plate, there is a visibility number next to the MDA or DA. What does it mean? Is it limitation to use the approach?

If this question is about the US, the FAA's Chart User's Guide is a useful source for questions about approach plates or any other charts. It says:

  This section gives the pilot the lowest altitude and visibility
  requirements for the approach. There are two types of landing
  minimums: Straight-in landing or Circling. Straight-in landing
  minimums are the MDA and visibility, or DH and visibility, required
  for a straight-in landing on a specified runway. Circling minimums are
  the MDA and visibility required for the circle-to-land maneuver.

And:

  The visibility values are shown after the DA/DH or MDA. They are
  provided in statue [sic] miles or runway visual range (RVR). RVR is reported
  in hundreds of feet. If the visibility is in statute miles, there is
  an altitude number, hyphen, whole or fractional number, e.g. 530-1.
  This indicates 530 feet MSL and 1 statute mile of visibility. The RVR
  value is separated from the minimum altitude with a slash, e.g.,
  1540/24. This indicates 1540 feet MSL and RVR of 2400 feet.

The number is indeed a limitation: if the required visibility doesn't exist then the pilot can't use the approach. However, there are some differences in what that really means depending on the type of flight: an airline flight (part 121) can't even start an approach if the reported visibility is less than the approach requirements; a private flight (part 91) can start an approach but may not land if the flight visibility is below minimums. This question might be relevant.


How accurately do I need to maintain my altitude while VFR-on-top? Is holding altitude as stringent a requirement when flying VFR-on-top? If the deviation exceeds say 200 feet off a given VFR altitude (i.e. 5500’ heading eastbound) is this as big of an issue for ATC?

Considering, as a pilot, you should be able to maintain an altitude with Less than a 100 foot accuracy, I would say that you should be doing the same when VFR-on-Top. If you change (vacate) that altitude for any reason, you should let ATC know. They are still maintaining aircraft separation. They need to anticipate your current and future position. If it’s a brief departure from the previously reported altitude (say for instance, due to turbulence), reporting the discrepancy is not important if you return to the original altitude immediately. Though, you might want to give ATC and/or FSS a PIREP.


Did Boeing build airliners other than the 7x7 series? What I mean by the 7x7 series is the 707, 717, 727, etc. I took this picture at the Pima Air and Space Museum in Tucson, Arizona.

What type of aircraft is this? Was it an airliner? I know that no 7x7 series aircraft was that small, so were there other airliners made by Boeing besides the 7x7 series?

Yes, Boeing built other airliners, with different numbering, although none of them were jet-powered. Three iconic designs come to my mind right away, although there were others:

The Boeing 247 predated the DC-3 into service, and was a highly advanced twin-engine, monoplane cabin design. It was a pioneering aircraft, introducing all-metal construction, a cantilever wing, and retractable landing gear. It was later surpassed by the DC-3, as the 247's cabin was too small for serious airline service.

The Boeing 314 "Clipper" was a large four-engine flying-boat transport from just before World War II. Not quite as pioneering as the 247D, it nonetheless was massive for its time and heavily influenced later large Boeing designs.

The Boeing 377 "Stratocruiser" was a post-World War II design based on the B-29 bomber, with a double-deck (double-bubble) fuselage and four piston engines. It was large, pressurized, and technologically advanced, but relatively unsuccessful in sales compared to contemporary designs like the Lockheed Constellation.

As others have mentioned, the aircraft in your question is a Sud Caravelle, which was designed to solve the same problem as the later Boeing 737: it was a shorter-range airliner meant for smaller routes. You point out how much the Caravelle's nose looks like the Boeing 787, and you're right - but it is even more similar to the De Havilland Comet; Sud licensed the design from De Havilland.

All photos from Wikipedia.


Why does the F-4's rear seat have a weather scope eyepiece? In the front seat. The pilot has a flat screen radar scope that shows both the planes and the weather.

But on the rear seat. The weather scope has an giant eyepiece. Perhaps glare protection?

(angelfire.com)

That's not an eyepiece, it's a glare shield. The angle of the display made it susceptible to glare from light entering the cockpit. The shield made it easier to see, at night as well. My theory is that they got the idea from Star Trek. Spock had one too on his workstation on the Enterprise.


Was the 737-300's wing an early supercritical wing? I know that the 737 NG borrows the basic wing design of the 777, but I have also heard that BAC 4xx airfoil on the 737 classic (300/400/500) was an early supercritical aerofoil design?

Is this true?

Supercritical yes, but early? Not really.

BACXXX airfoil plot, shamelessly copied from airfoiltools.com.

The plot of the BACXXX above shows typical contour characteristics of supercritical airfoils:

blunt leading edge
very little curvature on the top surface at mid-chord
higher curvature at the bottom, resulting in negative camber around mid-chord
rear loading: Higher camber at the rear, thinner part of the airfoil,

however, this airfoil does not take those techniques to their extreme. It was a redesign on the original 737 wing, extended by 4.4% of chord at the leading edge and overall a compromise between high commonality with the earlier design and improved aerodynamics.

At the time when the "classic" series of the 737 was designed in the late Seventies/early Eighties, supercritical airfoils were already firmly established. They were first researched by K. A. Kawalki in Germany in 1940, who arrived at identical shapes as R. T. Whitcomb at NASA a quarter of a century later. The first operational supercritical airfoils, at the time called rooftop due to the roof-like shape of the upper surface pressure distribution, were employed by Vickers in the VC-10. This remarkable aircraft is to this day the fastest airliner with a maximum cruise Mach number of 0.89 and flew first in 1962.

Boeing became aware of supercritical airfoils only after the original 737 was designed, so the redesigned wing of the classic series carries some of the baggage carried over from the earlier design.