What is the floor of the class E airspace near KRHV when the tower is closed? See the attached diagram snippet for KRHV in Northern California. The chart supplement says that when the tower is closed the airport surface is class G. At this time, what is the floor of class E in areas "1" and "2"?

As you can see, class E starts at the surface around the Fairgrounds visual reporting point. Class E starts at 700 ft. AGL South-West of the airport and at 1,200 ft. AGL North-East of the airport. What happens in the middle in areas "1" and "2"? Does the magenta vignette cut through class D as shown by the red line or follows the border of class D? Again, this question is only relevant when the tower is closed.

Short answer:

When looking at the airspace depiction on the sectional chart, it is logical to assume that the linear portion of the edge of the transition area with 700' floor, shown by the shaded magenta boundary, continues on through the blue segmented circle around KRHV, and this controls the floor of the Class E airspace in that area when the tower is closed and the Class D airspace reverts to Class G.  In that case, the Class E floor in area "1" is 1200' AGL and the Class E floor in area "2" is 700' AGL.  Similarly, it is logical to assume that the arcing circular edge of the 700'-floor transition area located north of KRHV also continues into the blue segmented circle around KRHV, but this section just barely extends into the blue segmented circle before it is intercepted by the linear edge of the 700'-floor transition area coming up from the southeast.

Long answer:

(Click here for a larger view of sectional chart centered on area of interest)

The ultimate authority for the answer to your question is found in the FAA's "Airspace Designations and Reporting Points" document, current edition Order JO 7400.11D.  The class D airspace for KRHV is described on page D-156 under the heading "AWP CA D San Jose Reid-Hillview Airport, CA".  No corresponding E2 airspace is listed-- it would be on page E-134 if it were present.  This confirms what we read in the Chart Supplement-- that the Class D airspace for KRHV reverts to Class G, not Class-E-to-surface, when the tower is closed.  The only exception is the small slice of airspace centered around the "6:30" position of the segmented blue circle around KRHV which does revert to Class-E-to-Surface when the Class D is inactive-- because it is part of an E3 "extension" associated with San Jose International (page E-153).

The magenta shaded border projecting southeast from the word "Evergreen" on the chart is the eastern edge of a "transition area" whose floor is 700' AGL, and your question is essentially asking whether this edge extends on into the segmented blue circle around KRHV, or deviates to include the entire segmented blue circle, or deviates in some other way.  Transition areas are "E5" airspace, and are described starting on page E-220 in the "Airspace Designations and Reporting Points" document.  The specific transition area we are interested in is described on pages E-960 through E-961, under the heading "AWP CA E5 San Jose, CA, San Jose International Airport, CA".  When reading this text, it is helpful to know that "San Martin Airport" (KE16) was formerly known as "South County Airport of Santa Clara County".

Here is the complete text of the E5 airspace description, with the relevant portion highlighted:

  That airspace extending upward from 700 feet above the surface within a 5-mile radius of the San Jose International Airport and within 4.3 miles each side of the NAS Moffett Field TACAN 157° radial extending from the NAS Moffett Field TACAN to 20 miles southeast of the TACAN and within 4 miles each side of the 139° bearing from the San Jose NDB, extending from the 5-mile radius of the San Jose International Airport to 24.3 miles southeast of the NDB and within a 6.9-mile radius of the South County Airport of Santa Clara County and that airspace bounded by a line beginning at lat. 37°30'00"N, long. 121°52'04"W; to lat. 37°22'00"N, long. 122°08'04"W; to lat. 37°22'00"N, long.122°24'04"W ; to lat. 37°30'00"N, long. 122°27'04"W, thence to the point of beginning. That airspace extending upward from 1,200 feet above the surface bounded on the north by lat. 37°30'00"N, on the east and northeast by long. 121°50'04"W; and the southwest edge of V-107, on the southeast and south by the northwest edge of V-111, and lat. 37°00'00"N, and on the west by the east edge of V-27 to lat. 37°30'00"N.

The 8-mile-wide strip of 700'-floor E5 airspace that extends 24 miles to the southeast of the San Jose NDB comes all the way up to the 5-mile-radius arc around San Jose International, and does not deviate either to avoid, or to completely include, the airspace enclosed by blue segmented circle around KRHV.  Likewise the curving edge of the 5-mile-radius-circle of 700'-floor E5 airspace around San Jose International continues a short ways into the blue segmented circle around KRHV, before it meets the linear edge of the 700'-floor E5 airspace coming up from the southeast.  So the edge of the 700'-floor E5 "transition area" does indeed run through the blue segmented circle around KRHV much as was sketched in the question.  Area "1" is outside the 700'-floor E5 transition area and has a Class E floor at 1200' AGL when the Class D airspace is inactive, while area "2" is inside the 700'-floor E5 transition area and has a Class E floor at 700' AGL when the Class D airspace is inactive.

This answer has followed the common practice of referring to E5 airspace with a 700' Class E floor as a "transition area".  This appears not to be actually supported by any current FAR or FAA document, including the "Airspace Designations and Reporting Points" document.  "Transition area" is a term from before the 1993 "alphabet" airspace re-organization, and actually included areas that had controlled airspace floors at 1200' AGL as well as at 700' AGL.  It is an obsolete term now, but still is often used by pilots, most commonly to refer to areas that have Class E floors at 700' AGL.  At any rate, note that area "1" is actually still inside the airspace that is defined as part of the E5 airspace associated with San Jose International-- specifically, it is inside the portion of the E5 airspace associated with San Jose International that has a 1200' AGL floor.  This answer does not intend to imply that there is some definitive reason to say that area "2" is inside a "transition area" while area "1" is not inside any "transition area".  The main point of this answer is simply that when the Class D airspace around KRHV is inactive, area "2" has a 700' AGL Class E floor while area "1" has a 1200' AGL Class E floor.

Note that the "Airspace Designations and Reporting Points" document uses nautical miles and true bearings.  A bearing of 139 degrees true is approximately 126 degrees magnetic at this location.


Why is a combustor in a gas turbine engine asymmetric? As the above question stated, the upper and lower section of the combustor isn't same. Is there any reason behind it? Due to which the cooling of the combustor is also different in the upper and lower section of the combustor.
The below picture clearly depicts it:

That drawing in the question is not really representative, here's a CFM56 combustor:

— faa.gov

The bulge the artist used, is actually a turn/inclination for aligning the combustor with the more outboard first stage turbine.
Here's a more gentle turn in a bigger engine:

— Flight International


What's the relationship between drag divergence Mach number and maximum operating limit Mach number? The drag divergence Mach number, also known as the force divergence Mach number, is the Mach number where drag waves start to form. The drag divergence Mach number is typically between 5 to 10 percents greater than the critical Mach number.

The maximum operating limit Mach number(Mmo) is the mach number beyond which aircraft start to suffer compressibility effects and flutters at high altitude. It's basically the high altitude version of Vne(Vmo).

My question is: what are the two Mach numbers' relationships? Is Mmo always higher than the drag divergence number? If so, how much? Or is it safe to assume that they are more or less the same?

They are unrelated definitions. Mmo is set by the designer with input from actual flight testing, Mmo is a maximum safe speed and is only concerned with practical operation and structural integrity. Mach divergence is a physics phenomena. Mmo can be much lower or higher than the Mach divergence from one aircraft to the next. Mmo has a similar purpose to Vne but Mmo is a more useful measure for high performance aircraft.
It just happens that most commercial and large business jets are designed for high subsonic cruise so the design goal is to push divergence to higher speeds for more efficiency and Mmo ends up very close to Mach divergence.


Is it possible for me to work at NASA or other research companies as aircraft mechanic? I know NASA is huge but is it possible for me to work there or other companies similar to it?  If possible, how?

I currently work at an MRO as aircraft mechanic. My work is mainly on flight controls. The only aircraft that I have experience on is a320 family.

We do some structural works too, knowledgable to SRM.

I'm from Philippines btw.

Probably not, unless you are a U.S. citizen (dual-citizenship should be ok.) According to NASA,

  Other than under extremely rare exceptions, you must be a U.S. citizen in order to work for NASA as a civil service employee.

It's extremely unusual for non-citizens to be able to work in the U.S. in agencies like NASA or the Department of Defense, where there is necessarily lots of equipment and/or information subject to ITAR controls and/or which is classified. This will generally also be true for contractor positions.

At my present job, we are not allowed to disclose anything more than high-level marketing material regarding products subject to ITAR to anyone who is not a U.S. citizen, for example, even though we don't make weapons or anything like weapons.


What pilot certificates were needed to fly the Space Shuttle? Were there specific FAA (or other relevant regulatory body) pilot licensing or certifications required to fly the Space Shuttle? Are they specific to the Space Shuttle, or would it have fallen under an existing pilot license scheme?

FAA considers space shuttle either a military aircraft or spacecraft and hence its rules don't apply on space shuttle.

However, requirements to be a pilot for a space shuttle are:

  ... at least 1,000 hours pilot-in-command time on jet aircraft

It means that you need type rating to operate a heavy jet aircraft (not light jet). Weight of an empty space shuttle is 172,000 lb (78,000 kg)1. In addition, you need the additional requirements mentioned by NASA (link above), which include education and health standards to meet.

Operating empty weight of Airbus A380 is 610,000 lbs.


Do airlines in the US or UK have to pay fuel taxes? Do airlines in the US or UK have to pay fuel taxes?

When looking at Jet-A prices on the Shell website, for example, it's unclear if the listed prices include taxes. Do they?

In the US, yes.

Kerosene [for use in aviation] is taxed at $0.244 per gallon unless a reduced rate applies.
These taxes mainly fund airport and Air Traffic Control operations by the Federal Aviation Administration (FAA), of which commercial aviation is the biggest user (Fuel taxes in the United States).

More information from taxfoundation.org.

In the UK, it depends on the user.

Aviation turbine fuel used for private pleasure flying: £0.5795 per litre
Aviation gasoline (Avgas): £0.3770 per litre

Air transport is exempt.
Furthermore:

Article 24 of the [1944 Convention of International Civil Aviation] requires all contracting states not to charge duty on aviation fuel already on board any aircraft that has arrived in their territory from another contracting state. Further to this, the exemption of airlines from national taxes and customs duties on a range of aviation-related goods, including parts, stores and fuel is a standard element of the network of bilateral ‘Air Service Agreements’ (ASAs) between individual countries.


Heard on LiveATC that ATC wants to "cancel" something. What did the ATC mean by that? Just heard this on LiveATC:

ATC has cleared the pilot for an ILS approach
ATC then said something to the pilot, to which the pilot replied, "Roger, will cancel with you on the ground, call sign."

What did ATC say to the pilot? What are they cancelling? I didn't catch what ATC said because the audio quality was pretty bad.

The only possible "cancellation" I can think of is the flight plan, but I don't see why they would want to cancel the flight plan if the aircraft has already landed at the destination airport. Any thoughts will be appreciated.

If the airport is non-towered, then ATC may not be able to have radio contact with the aircraft after landing. However, the flight plan still needs to be cancelled or closed after landing. Usually this is done by the pilot calling ATC on the phone, but in this case it seems ATC offered to do it without the call.

Without closing the flight plan within approximately 30 minutes after the scheduled arrival time, the Flight Services will start looking for you. They will try to contact you by phone call and if that goes unanswered, eventually a search and rescue will be started.

On ATC controlled airports the flight plan will automatically be closed after the aircraft landed.


What are good tips for flying across Tejon pass? I will be flying from Northern California to Southern California this weekend for the first time in a C172SP (KPAO to KFUL). My planned altitude is 9500 feet. I had a talked with my former instructor about this flight. We had gone over the flight plan and he told me his tips on flying this route including using extreme caution when flying over the Tejon pass (by Gorman VOR) because of its strong turbulence.

Has any of you flown this path before can possibly give me some tips? Anything is appreciated especially tips about passing the Tejon pass.

I cross that pass on my commute twice a week in my VariEze at altitudes between 5500 and 11500 ft depending on winds and clouds. There's nothing to be particularly nervous about, there's rarely any noticeable turbulence if you're at 7500 or higher.  You can check the Sandberg AWOS and forecast winds aloft, and ask L.A. Center or Bakersfield Approach for ride reports.

I do tend to be flying that route either fairly early in the morning or around dusk, so it may be bumpy more often in the heat of the early afternoon.

If clouds are forcing you down to 5500 be sure not to accidentally fly up the wrong valley when headed north!


Is it possible to split a NOTAM in two messages in case it is too long to fit in a single message? Would it be in accordance with ICAO norms to issue two different NOTAMs with the same year, series and number regarding the same subject and informing //PART 1 OF 2 PARTS// and //PART 2 OF 2 PARTS// in the NOTAMs bodies to inform that they are parts of a single NOTAM?

Multi-part NOTAMs seem to be part of ICAO standard, as far as googling reveals. I can’t seem to find a definitive reference though.

An example - and from experience a relatively reliable one - for a multi-part NOTAM is the infamous Sydney crane list, at time of writing in NOTAM H6002/18, which at the moment comes in three parts and has the part listing in field A):

  H6002/18 NOTAMR H5974/18
  Q) YMMM/QOBCE/IV/M/AE/000/999/3357S15111E008
  A) YSSY PART 1 OF 3
  B) 1811190334
  C) 1811300500 EST
  E) OBSTACLE CRANES AT FLW LOCATIONS
  239FT AMSL BRG 002 MAG 1.58NM FM ARP
  497FT AMSL BRG 002 MAG 3.82NM FM ARP
  220FT AMSL BRG 002 MAG 1.38NM FM ARP OBST UNLIT
  413FT AMSL BRG 003 MAG 3.09NM FM ARP
  410FT AMSL BRG 003 MAG 3.14NM FM ARP
  577FT AMSL BRG 003 MAG 4.65NM FM ARP
  685FT AMSL BRG 004 MAG 4.26NM FM ARP
  249FT AMSL BRG 004 MAG 2.98NM FM ARP
  413FT AMSL BRG 004 MAG 3.18NM FM ARP
  224FT AMSL BRG 005 MAG 1.53NM FM ARP OBST UNLIT
  500FT AMSL BRG 005 MAG 3.42NM FM ARP
  953FT AMSL BRG 005 MAG 5.26NM FM ARP
  623FT AMSL BRG 006 MAG 4.54NM FM ARP
  PART 1 OF 3

Found at FAA pilot briefing site.


Controlling jet engine thrust on airliners Passenger jet airliners seem to control thrust by just adjusting the amount of fuel going to the engine thus affecting the engine rpm. This means it takes a small amount of time to spool up from minimum to maximum throttle and vice versa.

Are there any attempts to allow faster thrust response than this? Are any in current or planned use?

It seems that one could control the compressor pitch, change the gear ratio, or adjust the bypass ratio -- but I'm not sure anyone is doing this. Afterburners and thrust reversers/vectoring don't count. Faster engine respond would help with situations such as loss of rudder control let alone other emergency situations.

Are there any attempts to allow faster thrust response than this? Are any in current or planned use?

First, for turbine engines, the more often used term is thrust lever or power lever rather than throttle. You can Google "throttle vs thrust lever" for that discussion.

I'll use the 727 and the 747 to illustrate what was done prior to when I retired in 1999.

In initial 727-100 sim training, the instructor had us bring the power levers all the way back and allow the descent to stabilize in landing configuration at full flaps. Then, at a given altitude the instructor would tell us to start climbing, at which time we would advance the thrust levers to max power and clean up. From that moment, we would lose hundreds of feet before the aircraft started to climb. The primary reason for the delay was that the engines took 7 seconds to go from flight idle to full power.

In initial 747-100 sim training, we did the same thing. The result was a loss of less than 100 feet, the difference being that engine response was almost immediate, and we also could pitch up immediately without noticeable loss of airspeed.

As I remember being told, the big difference in engine response was because the idle position still had a relatively spooled up engine.

The engines running at that relatively high power output even at idle had the drawback that while taxiing the aircraft would accelerate to a higher than permitted taxi speed, which then required braking.


What are the consequences of throttling up past 100% of N1? The B737 is probably my favorite aircraft and I'm always sure to never throttle past 100% of N1. I was told the aircraft is pretty much totaled if you take N1 past 100% but you can eke out that extra power for emergency purposes. Is that true? What are the consequences of exceeding 100% N1?

And what numbers should I be paying attention to for takeoff in a 737?

The consequences are always explained in the flight manual. It has graphs which specify what you should do if you exceed the speed, temperature, etc., by how much and for how long. For example (this is for FJ33-5A):

Note that the 100% mark is, in a sense, arbitrary. It does not necessarily mean the absolute max (even the 'normal' max), as can be seen from the example. (I don't know how it is for CFM56). This happens for several reasons; typically, the 100% value corresponds to a fixed RPM number for the whole family of engines. As the engine undergoes modifications, the permissible RPM may increase (or, in some cases, decrease), yet the 100% RPM number is usually not changed, moving the red line instead. In some cases, a civil engine is installed on a military aircraft, and is then allowed to run at, say, 108%, at the cost of much reduced lifespan and service intervals.


Does this web page really correctly depict the angle that is called "incidence" in the French language in the aviation context? Does this web page really correctly depict the most common usage of the term "incidence" in the French language in the aviation context, in the context of speaking of an entire aircraft and not just an isolated part such as a wing section in a wind tunnel?  Is the label "incidence" really attached to the correct angle?

I am referring specifically to the second airplane diagram, i.e. the first diagram that shows an airliner.   Note that the text above the diagram uses the phrase "en croisière" which is a reference "cruising", presumably horizontal, flight.  The line x-x' appears to represent the longitudinal axis of the aircraft, so it appears that the angle labeled "incidence" represents the angle between the flight path/ relative wind and the longitudinal axis of the fuselage, not the angle between the flight path/ relative wind and the chord line of the wing, which would clearly be a larger angle.

In fact the text above the diagram explicitly states "L'incidence est définie par rapport à l'axe de l'aéronef et non de la voilure.", which translates to something like "The incidence is defined relative to the axis of the aircraft and not of the wing."

Shouldn't the angle labeled "incidence" be the angle between the flight path/ relative wind and the chord line of the wing rather than the angle between the flight path/ relative wind and the fuselage?

Or is it just a matter of arbitrary convention, meaning that either usage would be equally appropriate?

(One way to concisely answer this question might be "The correct usage of 'angle d'incidence' in the French aviation context is exactly identical to the English-language usage of 'angle of attack' (or replace with other appropriate angle as needed) as noted in this ASE answer (give link)."  Not all ASE answers have given the same perspective on the most correct usage of this term.)

Note that the angle labeled "angle de calage" is the angle that is called "incidence" in American aviation usage and some or most (but not all) British aviation usage-- the angle between the chord line of the wing and the longitudinal axis of the fuselage.  This question is not about whether or not the diagram uses "angle de calage" correctly in the context of French aviation terminology-- it clearly does.

Bonus question-- in the French aviation context, is the term "angle d'attaque" used to mean something different than "angle d'incidence"?

Yeah it's right if we consider that the relative wind is parallel to the ground.

In French, the "angle d'incidence" is the angle between the chord line and the relative wind, contrary to the US and UK which it's the angle between the chord line and the longitudinal axis.(fr="angle de calage")

  In french: In fluid mechanics, "l'angle d'incidence" is the angle formed by the chord of a profile and the relative wind speed vector. In English l'angle d'incidence" is called angle of attack (AOA).
  Attention, angle of incidence in English corresponds in French to the "angle de calage", the angle formed by the reference chord of a wing and the longitudinal axis of the aircraft.
  L'incidence (fr) notes : α

"Croisière" is cruise flight .the picture of the website is not clear because it confusing chord line and longitudinal axis(perhaps to simplify)... other important notion: RELATIVE WIND is the relative movement of air relative to the plane; it is ALWAYS PARALLEL AND SENSE OPPOSITE to the TRAJECTORY OF THE AIRPLANE(path)

Source: (the second link is french because the same page is different in French and in English)
https://fr.m.wikipedia.org/wiki/Incidence_(a%C3%A9rodynamique)
https://www.lavionnaire.fr/AerodynCPFoyer.php


What are the "lumps" in the A380 flight-deck? In this photograph of the Airbus A830 flight-deck there are two large "lumps" sticking up and out from the centre console, next to the engine thrust levers and flight-computer keypads:

I think they're just meant to be wrist-support for when pressing the keypad keys, but it seems odd to single-out that part of the flight-controls in particular for wrist-support. The lumps also seem rather tall to be used comfortably for extended periods (and I assume that's what the pull-out keyboards in the trays are for, so why bother having secondary keyboards down there in the first place?) - and it also hinders access to the 'inner' keys closer to the engine controls.

They are a different design of computer mouse:

As far as I can tell, the front disk is a track pad and the model in your picture has the mouse buttons on the front instead of the sides:


Could a tail rotor serve as a spin breaker for winged aircraft? It seems that yaw, more than pitch or roll, creates the greatest wing asymmetry in a spin.
If the spin progresses to the point where it cannot be broken, some aircraft are equipped with parachutes to try to stop rotation and to get the nose pointed down. Some cannot be saved.

Tail rotors work well in helicopters, and are part of the design to control the (spinning wing) rotor yaw, and, such as the 180 knot MH-65 Dolphin, have the rotor built into the tail to save drag.

Could this work as a safety feature for GA aircraft?

At least one of two possible devices is regularly added before spin testing:

Jettisonable mass, for example by fixing a sandbag to the tail, or
a spin chute.

Spin chutes do what you propose in yaw, but what they mostly do is to pull the tail up so the angle of attack over the whole wing is reduced. This is equally achieved by jettisoning that extra mass at the tail: Now the more forward center of gravity will add a nose-down moment.

In both cases the lowered angle of attack restores roll damping on the wing. This is really what stops a spin, yaw is less of a problem here.


Bypass ducts and spinning blades I want to start out by saying these questions will make me look a fool but i simply haven't found answers for them anywhere so i'm hoping you could help me!

What is the purpose of bypass ducts? If the air is going around the turbine then what even is the point? Why not just make jet engines simple consisting only of the turbine and skip out on the bypass duct?
What makes the fan blades in a jet engine keep spinning? I know how they are started but what keeps the blades constantly spinning with enough inertia to keep compressing air? Is there like a small motor connected to the fan blades via a crankshaft or is a portion of bleed air used to keep the blades in motion?

Thanks in advance for answering my questions :)

Well, let's tackle the second question first: What keeps the fan spinning? It is connected by a shaft to the low pressure turbine and the gasses expanding from the high pressure turbine towards the outside keep it spinning. Look at a good diagram and you'll see two (or three) concentric shafts that connect the low pressure turbine and the fan and the high pressure turbine and the compressor.

As for why bypass, pure jet engines where all the air goes through the combustors are really fuel hungry. You have to have a certain air/fuel ratio to get combustion. You can't lean it beyond a certain point or the fire goes out. Using all the air would use really a lot of fuel. The high-bypass ratio turbofan only takes some of the air through the combustors and just sucks the rest in with the fan and blows is out the back. The difference between that and a turbo-prop is mostly the cowling around the fan.


How are sensors in the wheels connected to power and data buses? In this question the sensors to measure the tyre pressure are described.

But how do such sensors receive the electrical power they need, and how are the signal values transmitted back to the relevant computer systems?

Since the wheel rotates, one would presume that transferring power and data electrically with the reliability needed for aviation use would pose specific demands on the technology.

For small planes simple systems can be installed that fit on the inflation tubes and replace your standard cap. They use small batteries in the sender units and a little read out.

It looks like Boeing gets their tire pressure/break temp systems from Crane Aerospace. The latest and greatest systems are all wireless

  The Crane 777 Tire and Brake Monitoring System (TBMS) provides
  continuous real-time monitoring of aircraft tire pressure and brake
  temperature. The design incorporates our SmartStem® wireless tire
  pressure sensor with integrated fill valve. The SmartStem uses sensing
  technology with triple redundant sensing channels to provide high
  reliability and accuracy. The Crane TBMS replaces TPMU and BTMU units
  (from the legacy system) with a single Tire and Brake Monitoring Unit
  (TBMU) that interfaces with the existing brake temperature probes. The
  existing wheel interface unit is replaced with an in-axle transformer
  and relay transformer hubcap assembly that allow the tire pressure
  signal to be transmitted magnetically with no physical contact between
  the components. Retrofit of the Crane TBMS requires no change to the
  AMC, EICAS, and CMC system interfaces.

That does not shed to much light on how it all works though. Their handheld system is RFID based and presumably their built in system is similar.


Why is Boeing being blamed for the recent 737 Max crashes? Boeing has received more than 5,000 orders for the aircraft, it has delivered 350 so far and only 2 of them have crashed. That's not a very high crash rate. The FAA, until just a day ago, was very confident that the aircraft is "fly worthy".

The Ethiopian crash investigators haven't even ascertained if the crash was due to a problem with the aircraft or if it was pilot error and already the whole world is assuming it was Boeing and has grounded flights worldwide. Why is this?

Why is Boeing being blamed for this? Flights crash all the time! Sure, not as much today as they did in the beginning, but they still do! We can't go on grounding every aircraft that crashed during flight! Plus the aircraft was in development for 5 years - I'm sure buyers were allowed to test the aircraft to their satisfaction before placing orders, Boeing themselves would've rigorously tested the aircraft, it was even approved by the FAA!

Shouldn't we make sure it was not the pilot's fault before we blame the manufacturer? Or did they already do that? I tried to find articles that explained WHY everyone is rallying against the company, but couldn't find anything concrete.

The Ethiopian crash was in a new plane, in good weather, with multiple witnesses describing rattling noises and a smoke trail.

We can rule out weather, and pilot error seems unlikely to cause that.
The plane is so new that maintenance is not likely to be a factor either.

Blaming Boeing may not be fully justified at this point, but caution over the literally hundreds of thousands of passengers who fly on them every day is not inappropriate either.


How common are mayday calls? How often does an aircraft make a mayday call?

I assume when confronted with an emergency on board, they will first deal with it, and not waste time contacting any one who would not be able to help anyway. And when they have time for such a call, there's no emergency anymore.

So, when does making a mayday call make sense?

From the point of view of a private pilot, the answer is that mayday calls are not terrifically common. I've certainly never heard one made in anger in a couple of hundred flying hours.

However your assumptions are correct in parts and wrong in others. First lets define what an emergency requiring a possible mayday call is, which answers your question about when it makes sense.

  Mayday - A condition of being threatened by serious and/or imminent
  danger and of requiring immediate assistance.

That said, some of your assumption is correct:

  I assume when confronted with an emergency on board, they will first deal with it

Absolutely! Pilots are taught to "Aviate, Navigate, Communicate" in that order. Any emergency while airborne requires you to keep the aircraft flying as a first priority. You'll notice Communicate is last after "knowing where you are and where you're going" (Navigate).

  not waste time contacting any one who would not be able to help anyway

As pointed out in comments, this is an incorrect assumption. Once the pilot has some bandwidth to communicate there are numerable ways ATC could help in an emergency, such as (but not limited to):

Clearing surrounding airspace
Aiding with navigation, such as giving vectors to the nearest runway
Prioritizing landings
Helping you once you're (hopefully) safely on the ground - see below.

  And when they have time for such a call, there's no emergency anymore.

Again, an incorrect assumption. Take the example of an engine failure. The aviate part calls for you to set up for maximum glide ratio, and do some checks to see if you can restart your engine. The navigate part could require you to find a suitable field to make an emergency landing. At this point (depending on your altitude) you might have a number of minutes before touchdown. Here's where you tell ATC the problem ("Mayday mayday mayday. G-ABCD, engine failure, 2 miles east of [city], 2,000 ft heading 180 degrees. emergency landing on field beside [big road]"). This has the benefit that they can communicate with emergency services - or at very least send someone out in a car to help you.

As you can see from the above example. The emergency still persists once the pilot has time to tell ATC about it.


How do I get an FAA CPL from an EASA PPL? Im looking into getting a PPL, but feel I need some more information since there are a lot of hours involved so I need to expand my idea of the different possibilities. I am from Sweden but work and plan to do the PPL in Italy, and as I understand it there will be no problem getting a PPL in Italy/Tuscany ( anyone heard of the Lucca Areo Flight School ? ) since I can get a PPL anywhere in Europe.

The plan is to move to the States in approx 2-2 1/2  years from now. There I will need to apply for an FAA PPL but will it be possible to continue on to the CPL in the US as a foreigner ?

As I understood from reading the threads I would need a PPL anyhow to do the CPL, and as I'm not 100% sure I'll be doing the CPL, is a step-by-step way preferable?

First, this question covers converting an EASA PPL to an FAA one. Based on what you said, I'd strongly suggest getting a full private license rather than a foreign-based one. That will probably require some flight training, which means you'll need TSA approval.

Next, when you have the private certificate then you can continue to CPL. In the US an instrument rating isn't required for a CPL but most people get it because otherwise the CPL is very restricted. You'll need TSA approval again for instrument training but not for commercial training. If you do multi-engine training at any point that's another TSA approval, by the way.

Assuming you have the time and money for all the training, your biggest issue will probably be legally entering and staying in the US. You need an appropriate visa or green card for flight training, plus the TSA approvals that I mentioned.


Dimensional analysis with wingspan length? I need some help in understanding the fundamentals of dimensional analysis.
The following is is from "Fundamentals of aerodynamics" by John D Anderson, fifth edition:

Why is the wingspan length not added to the variables that the aerodynamics force R depend on?

In page 38 of the book you're quoting, the derivation goes on replacing $c^2$ with $S$,   the planform area of the wing, implicitly introducing the wingspan...


Why is an outward spinning propeller better in theory on the North American F-82 Twin Mustang? In this question the Wikipedia article of the F-82 Twin Mustang is quoted. In the third paragraph of the article it says:

  In this arrangement both propellers would turn upward as they approached the center wing, which in theory would have allowed better single-engine control.

There was a comment in the other question that questioned this statement:

  according to that article, an outward-spinning engine configuration is better in theory. i don't see how this would be. in a single-engine
  scenario, wouldn't the working engine torque push the non-working
  engine side down?

A spinning propeller should also produce more lift on the wing section behind it as it is increasing the airflow over that section. Forgetting about the torque for a second, this would already push the other wing (with the failed engine) down.
[EDIT: As answered in the comments, the lift generally has way more effect then the torque.]

So what exactly makes it more favorable to have a outward-spinning configuration in theory?

Also: Does this only apply to this aircraft, or is it valid in general?

Why does it say that the outward-spinning engine configuration is better in theory? What am I missing?

The theory is actually quite simple and straightforward. It should go like this:

In one-engine flight, the asymmetric prop position will pull the aircraft into a sideslip. The sideslip-induced rolling moment will then proceed to roll the aircraft such that the airplane rolls over the dead engine - something every multi-engine pilot learns to avoid early, because it will be hard to get the airplane back to level flight in this configuration.

If the single operating propeller will give the center wing an increased angle of attack due to the propeller swirl, and the outer wing a lower angle of attack, the prop produces a rolling moment which works against the sideslip-induced rolling moment, and should make it easier to avoid rolling over the dead engine. Engine torque will work against this moment, but the induced rolling moment of the wing is stronger, leaving a net moment which rolls the aircraft over the operating engine.

This should apply to all multi-engined aircraft. My reasoning why it didn't work for the F-82 can be read here.


How are winter weather operations different if they are based on an aircraft carrier instead of a runway on land? I am guessing that naval aircraft carriers do not have room for conventional deicing trucks and snowplows.  If they need to have frequent takeoffs and landings, time for clearing precipitation may be very limited, and there may be no alternate runways.  How do they deal with winter weather?

I am interested in treatment of both the carrier deck and the aircraft.

It's true, carriers typically don't have snow removal and deicing equipment (like trucks, but they do have fluid and spray equipment). They don't have this because they regularly avoid weather that could cause significant icing or snow (carriers move pretty quick and weather is somewhat predictable).
But it certainly isn't unheard of that they encounter snow or ice.
The carrier deck
The deck is somewhat cleared using tools like shovels:

Source: TheDrive.com
They also have a "sweeper" truck that can be used to sweep smaller amounts of snow off the deck:

Source: TheDrive.com
This is an older picture, but the equipment is still on modern carriers. They use it primarily for cleaning the deck and after incidents requiring broad FOD removal.
So one thing is in abundant supply on carriers, manual labor, and a lot of snow is removed doing just that. Teams working with shovels and dumping it overboard.
The Russians have a tool primarily used for FOD clearing, but is pretty effective at deicing the carrier deck:

This is basically a jet engine (same one used in MIG-15's) that is mounted to the front of a tractor with a diffuser on the front.
Aircraft
The aircraft have an advantage that most of them can be stored inside when they have icing conditions. Aircraft that are caught outside are manually cleaned using things like brooms and even baseball bats.

Source: TheDrive.com
They also have manual de-icing spray systems:

Source: US National Archives


Can a passenger plane stand still in the air, or hover at a fixed location above a ground? This Gizmodo link shows that a commercial passenger aircraft can stay at single location without any movement with respect to ground. (Is it real, an illusion, or faked?)

I have heard a friend saying that this happens for flights into Heathrow airport when the runway is busy with many aircraft required to land. I have argued with him about the holding circuit which basically requires airliner to follow a path around a airport, he is for sure that he has experienced such a thing happening when he was on board and also saw it live many times.

NO, at least not during landing. And especially not an Airbus.

Two reasons:

While up in the jet stream a 150 knot wind is normal, wind over 100 knots (185 km/h, 115 mph) near the ground only occurs in hurricanes (and tornadoes) and would be so turbulent that landing it it would be most likely out of question.
When landing in strong head wind the pilots will use higher air speed. This is because strong winds have a nasty habit of changing in strength or direction quickly and if the head wind reduced suddenly, the plane would loose lift and crash. So the pilots maintain some minimum ground speed to have a safety margin for that case.

Airbus even has a minimum ground speed warning exactly to keep the pilots out of this risky flight regime and that would be blaring in cockpit if the A330 in the video really almost stopped in midair. There must be something wrong with it (the linked article does not link to a video, only a screencap and one can't tell from screencap what is going on).


Why do modern aircraft tend to have angular tails? In the WWII-era and earlier, many (most?) planes had rounded tails, even high-speed and high-performance fighters such as the Bf 109 K, Ta 152 (though it is more square-ish), P-38, Hawker Typhoon, and even the F-80. A notable exception to this trend is the P-51.

Modern aircraft, on the other hand, tend to have very angular tails. High speed fighters, to airliners, even relatively slow aircraft like the Cessna 152 or Piper Archer have very angular tails.

What is the reason for this change in trend?

The rounded or elliptical design was found to be the cleanest aerodynamically in non-compressible subsonic airflow, which is why it's very common on aircraft of that era.  While the design is very slippery for speeds of Mach < 0.6 or so, it is more difficult to manufacture, which is why, near the end of the war, Spitfires had the 'clipped' wingtips as opposed to the original pure elliptical planforms.

The modern low aspect, sweptback, trapezoidal tail design is a better choice for higher airspeeds and supersonic flight ie Mach > 0.8 and mitigating flight control flutter due to compressibility effects, the same reasons we use sweptback wing.  Note as well that modern fighters use the same kind of planform for their wings and tail planes as they offer a compromise between acceptable supersonic aerodynamics and good trans sonic maneuverability.


What education is needed to become a civil pilot? I'm from Croatia and I'm intersted in becoming a pilot, but however, I'm not going to the college deisgned for that (I'm studying IT, not aeronautics).

Nevertheless, I contacted Croatia Airlines and they told me that I needn't have an aeronautics college degree, but I do need these qualifications to apply for the First Officer (Co-pilot) position:

hold a valid CPL (A)
hold a valid multi-engine instrument rating (airplane) (ME-IR(A))
successfuly completed a Multi Crew Coordination (MCC) Course
hold a Category 1 Medical Certificate
hold a valid Associate Degree
hold at least English Proficiency Level 4
hold a certificate of passed ATPL (A) theoretical knowledge examinations according FCL.515
be minimum of 21 years of age
total flight time:

Ab-initio pilots: at least 250 hours total time, to include 100 hours as pilot-in-command of airplanes
Pilots with valid type rating: a minimum of 500 hours on respective type

So, I have a few questions.

Does someone know where I can get my licences for being an civil pilot in Croatia?
About theoretical knowledge (physics, mathematics):

Could I watch MIT OpenCourseware on that (and if I do, should I watch this or this?
I stumbled upon Flying Academy website (can't post the link because I'm new here) and it says "Sufficient level of knowledge of Mathematics and Physics".
What is sufficient and what would I have to learn?

I know I have a lot of questions, but I would really like to become a pilot one day and I believe I am self-disciplined enough to learn on my own. Can someone show me the way?

First, does someone know where I can get my licences for being an civil pilot in Croatia?

I'm afraid nobody here can help you with that: You will need to find a flight instructor or flight school in your area. (Google can probably help you locate candidate schools, and we have some general advice on selecting a school and selecting an instructor that might help you narrow down your choices.)

  Second, about theoretical knowledge (physics, mathematics), could I watch MIT OpenCourseware on that (and if I do, should I watch this or this? I stumbled upon Flying Academy webiste (can't post the link because I'm new here) and it says "Sufficient level of knowledge of Mathematics and Physics".
  What is sufficient and what would I have to learn?

To begin flight training you don't need to know anything about math or physics: Your initial training will be about manipulating the controls of an aircraft to make it do what you want it to do, and for the moment you don't care how or why it works, you just need to learn the physical technique of controlling an airplane.

At some point in your training you will learn the physics of flight - this is generally part of "Ground School" but your flight instructor may introduce the concepts to you as you approach lessons where they will be relevant.
A basic understanding of the laws of motion and air pressure will be helpful, but everything you need to know can be found in the various FAA handbooks (the Pilot's Handbook of Aeronautical Knowledge, the Aeronautical Information Manual, and the Airplane Flying Handbook are good starting places - regulations will probably differ in Croatia, but the basics of flight will be the same, and are explained in fairly simple language in those books).

You will also need to be able to work basic flight planning calculations as you advance in your training, which means you will need some basic mathematical knowledge: The ability to add, subtract, multiply, divide, and do simple algebra will cover nearly everything you need to do as a pilot, and higher math is generally not necessary unless you start getting into the Why of aerodynamic theory.


Does North Korea's aircraft registration prefix allow for only 500 aircraft? In the Wikipedia page about aircraft registration prefixes, we can see that North Korea has P-500 to P-999. Does that mean that it’s only allowed 500 planes? What happens when the registry is all used?
(Oddly enough, I visited that Wikipedia page after reading an article about Star Trek’s starship Enterprise, also on Wikipedia.)

Civil aircraft tail numbers almost always follow ITU radio prefixes. North Korea has been allocated six ITU prefixes: HM and P5-P9.
Many countries with consecutive 2-letter prefixes will move the dash so it looks like they have a 1-letter prefix, but they still only use the allowed subset. So in this case, rather than P5-00 to P9-99, they write P-500 to P-999. They could have just as easily chosen P-50000 to P-99999 if they wanted, or gone alphabetic for even more possibilities.
However, in practice North Korea only has a handful of very old civil aircraft. While there is a humanitarian exception for spare parts to keep their airlines safe, the country can’t buy any more planes, which means they don’t need more tail numbers than they’re currently using. Heck, they could probably knock off a digit and still have more than they need!


What does the Airspeed indicator show when your pitot tube is blocked? So the question in the topic.
I want to clarify whether the speed indications is maintained or go to 0.

Depends on how much blockage. If fully blocked, as in air tight, the pitot side becomes like the sealed aneroid side of an altimeter and it only reacts to changes in static pressure, indicating the difference between ambient static and the pressure trapped in the pitot side.

If the blockage is not air tight, like you usually get with bugs, somewhere between zero and actual, in proportion to the blockage.  If the blockage is something that can move around, like a slug of water in the pitot line, you get wild and crazy fluctuations.


Is it legal to compensate a CFI for more than 8 hours of his services per day? A CFI can only log 8hrs of in-flight dual given in a 24hr period (FAR 61.195).  In my scenario, a CFI is required to be aboard a plane to satisfy insurance requirements.  This CFI will put in a 17hr day, all of it in a plane that a non-student customer is flying as PIC.  The customer has a valid medical, is current, and is appropriately rated in category and class.

The CFI might (or might not, he doesn't need the time) log a few hours of dual given to complete a checkout with this customer but then just sit there for the next ~15hrs staring out the window as the ground slides by and the customer racks up the hours he needs.

At the end of a very long day the CFI hands the customer a bill for 17hrs and is rewarded about as handsomely as a CFI can be rewarded.  The CFI walks away with a fat stack of $20s and maybe 3hrs in the logbook.

Has the CFI broken a rule?

In my scenario, a CFI is required to be aboard a plane to satisfy
  insurance requirements.

This is the important line and you need to reference the policy for the exact wording. I happen to have some quotes from when I was shopping for an M20C about a year ago and here is the exact wording from my aircraft owner policy,

  Named Pilots and Additional Pilot Requirements

  You are to receive a minimum of 5 hours dual flight instruction in the
  make/model by a CFI who meets all the requirements of the policy and
  receive a written endorsement in your logbook from the CFI prior to
  solo; then 5 hours solo in the make/model prior to carrying
  passengers.

In this case it clearly states that the time is all flight instruction and not simply "CFI present" time if your policy is written this way then its pretty clear the FAR would be broken in your scenario. I think its safe to assume most policies are written this way although if the policy simply states CFI on board then its tough, although I agree with Ron's comment its going to be hard to explain as a CFI that you just "sat there".


How to not converge or diverge from the runway when there aren't checkpoints? When flying circuits under VFR, if there is no clear distinct checkpoint available, what can you do/use as a checkpoint? I suspect the runway but please correct me if I'm wrong. How do you make sure you don't converge, diverge from the runway or stray away from the centreline?

I'd like to add something to Ron's answer.  Use of geographic checkpoints is used a lot in initial training but it can become a debilitating crutch that leaves you in the lurch as soon as you go to another airport.  I teach in gliders where getting the circuit right is fairly critical the first time, there being only one chance to land.

The really important checkpoint or turnpoint is the turn from downwind to base.  Learn to recognize the presentation of the runway when at a 45 degree aspect to it, which is normally the proper turn point for downwind-to-base unless you are extending or shortening your downwind for a specific reason.  I always weaned my glider students from dependence on geographic points as soon as possible, and certainly before solo.

You are at 45 degrees to the runway when the extended line of the lengthwise edge and an extended line of the threshold are "even" relative to the horizon.   This can be pretty tricky to discern at first but over time you'll learn to recognize this just by the appearance from your vantage point, and you will no longer care about ground landmarks.


Aircraft Turns - is there a 'pre-turn'? I've travelled from Vancouver to London often enough to see this phenomenon as something that happens regularly enough to notice. I'm just not sure why.

So... the route from Vancouver to London is basically a series of right-hand turns. I guess it follows a set of rhumb lines or whatever. But what I noticed was that most right-turns are preceded by a smaller left turn.

ie the aircraft banks and turns left for a couple of seconds, then straightens up and goes straight into the longer right hand turn I'm expecting.

So my question is, why does it do that little turn in the opposite direction? I can't imagine it's navigational, not when it's cruising at high altitude. Is it something mechanical? Say to make sure everything is working and not iced up? I imagine the aircraft is on autopilot at that point, so it's not a pilot thing.

Does anyone know what this is? In fact, has anyone else even noticed this?! I think I've noticed it most on Vancouver-London because when you're over Iceland and the aircraft starts to turn north, you start to wonder where you are headed!

In cruise, there are no opposite turns that precede every turn.

Human senses and the inner ear are very good at playing tricks, in fact pilots can't judge turns if they have no visibility (e.g., in clouds) without using their flight instruments.

Judging an aircraft's bank from a passenger seat is almost impossible at night, in clouds, over sheets of ice, over hazy oceans, etc.

On a commercial flight, the water in a cup remains level in the lateral during coordinated turns, that's because the load pulling down on the aircraft will still be pulling down perpendicular to the floor.

A shallow roll to the right or left could be just the plane correcting its course in a gust or so.


Is the 737-800 circular PFD for AOA or RA? So, I have seen some people on the Internet showing the 738's PFD circular gauge for RA, but others show that the gauge is used for AOA(angle of attack). Which one is true? Is there a switch to change the circular PFD gauge between RA and AOA?

It’s a customer option (i.e. the operator can choose and specify) to switch between the two; presumably by pin programming the computer responsible for generating the display symbols.


When should an Obstacle Departure Procedure (ODP) be used? Buried away in the front matter of the FAA charts is a section titled "IFR TAKEOFF MINIMUMS AND (OBSTACLE) DEPARTURE PROCEDURES".  Note that this is not a graphical departure procedure that is in with the rest of the approach plates.

Knoxville, TN (KTYS) contains the following departure procedure in that section:

  DEPARTURE PROCEDURE: Rwy 5L, climb heading 048°  to 3400 before
  proceeding on course. Rwy 5R, climb  heading 048° to 3500 before
  proceeding on course. Rwy  23L, climb heading 228° to 3500 before
  proceeding on  course. Rwy 23R, climb heading 228° to 3500 before
  proceeding on course.

Question: If I receive an IFR clearance along the lines of "*N1234, cleared to XXX as filed, climb and maintain...." and I didn't file any kind of departure, am I expected to fly the above ODP, and will ATC know what I'm doing if I do?  Does it matter if it is VMC or IMC?

According to the definition of the FAA it is a recommended procedure, so there is generally no need to follow it.

  OBSTACLE DEPARTURE PROCEDURE (ODP)- A preplanned instrument flight rule (IFR) departure procedure printed for pilot use in textual or graphic form to provide obstruction clearance via the least onerous route from the terminal area to the appropriate en route structure. ODPs are recommended for obstruction clearance and may be flown without ATC clearance unless an alternate departure procedure (SID or radar vector) has been specifically assigned by ATC. (Source: FAA Pilot/Controller Glossary)

According to FAR 91.175 you are responsible to ensure sufficient obstacle clearance if the airport is IFR (of course also if the airport is VFR).

  (f) Civil airport takeoff minimums. This paragraph applies to persons operating an aircraft under part 121, 125, 129, or 135 of this chapter.
  (1) Unless otherwise authorized by the FAA, no pilot may takeoff from a civil airport under IFR unless the weather conditions at time of takeoff are at or above the weather minimums for IFR takeoff prescribed for that airport under part 97 of this chapter.
  (2) If takeoff weather minimums are not prescribed under part 97 of this chapter for a particular airport, the following weather minimums apply to takeoffs under IFR:
  (i) For aircraft, other than helicopters, having two engines or less--1 statute mile visibility.
  (ii) For aircraft having more than two engines--1/2 statute mile visibility.
  (iii) For helicopters--1/2 statute mile visibility.
  (3) Except as provided in paragraph (f)(4) of this section, no pilot may takeoff under IFR from a civil airport having published obstacle departure procedures (ODPs) under part 97 of this chapter for the takeoff runway to be used, unless the pilot uses such ODPs.
  (4) Notwithstanding the requirements of paragraph (f)(3) of this section, no pilot may takeoff from an airport under IFR unless:
  (i) For part 121 and part 135 operators, the pilot uses a takeoff obstacle clearance or avoidance procedure that ensures compliance with the applicable airplane performance operating limitations requirements under part 121, subpart I or part 135, subpart I for takeoff at that airport; or
  (ii) For part 129 operators, the pilot uses a takeoff obstacle clearance or avoidance procedure that ensures compliance with the airplane performance operating limitations prescribed by the State of the operator for takeoff at that airport.

In this case it seems to be the easiest way to follow the ODP, but it's not binding.

Lnafziger  correctly commented that this is not applicable for part 91 operation. That's why I like to add a part of this Article, which I've found on the AOPA website, to my answer.

  [...] We cannot assume that ATC will assign any special routing or altitude based on the ODP. They expect the pilot to fly the procedure if necessary without further clearance. FAA Order 7110.65R, Air Traffic Control--the controller's handbook--states, "If a published IFR departure is not included in an ATC clearance, compliance with such a procedure is the pilot's prerogative." In other words, you have to decide whether you need to follow a specific route or procedure and fly accordingly. Now, we might think this is wrong, dangerous, and dumb, but it is the way procedures are arranged.[...]

According to all this information ATC would expect you to follow this procedure, at least in IMC. If you like to fly it in VMC and it does not disagree with your ATC clearance you are also welcome to do so. If there is any confusion I tend to ask and clarify the situation.

In most cases an ODP says that you should climb on runway heading at least until passing xxx feet before turning in a direction. I would always comply with it and if there is severe CAVOK and ATC then asks me to turn earlier, I would do it, so everyone is happy and on the safe side.


Why do all commercial aircraft have carpets? When flying I noticed that all the commercial aircraft I have been on use carpets as a floor covering. But why? If you fly in an older aircraft it looks worn out and it is susceptible to stains etc. Why do they not use one of the hard flooring options like linoleum?

helps prevent slips and falls
contains spills (your spilt soda won't ruin your neighbors bag)
more easily removed and replaced
helps reduce cabin noise


What is the weight of ballistic recovery systems? How much does a Ballistic Recovery Systems parachute system weigh?  I wouldn't want to use a personal quadcopter or jetpack without one.  I wonder if they could be made small and light enough for a small JB-9 type jetpack.

The smallest BRS listed here is certified up to 600 pounds (272 kg) of aircraft weight. That should be more than enough for a small jetpack or personal quadcopter. This system weighs about 22 pounds (10 kg), not counting anything required to install it.

As GdD mentioned, altitude may be an issue. The FAQ for a Cessna 182 mentions an altitude loss of about 300 feet, and that is with a rocket deployment.

They make systems for many different types of aircraft and ultralights, some probably smaller than the 600 pound limit listed above. You should contact them if you have a serious interest in such a system.


How is metal fatigue detected in an aircraft? There have been many accidents involving metal fatigue. How do the engineers, maintenance team, etc. know if an aircraft has metal fatigue? What is done to "minimize" metal fatigue or repair it?

How do the engineers, maintenance team, etc know if an aircraft has metal fatigue?

First of all, is not an "aircraft" that has fatigue, but a component.

To the naked eye, there is no way to detect metal fatigue until it starts being too late: you can only see cracks that are already forming and/or propagating.

There are tools available to allow for early detection, my bachelor's thesis was about one of these: the photoelasticity of certain materials is used. A light coat of one such material is applied on the new component and the photoelastic properties and exams done during the lifetime of the component tell the maintenance people what is the current status of the inner layers of the piece.

Another method uses electric resistance, as metal fatigue, by cracking the metal, increases the resistance.

Depending on the scenario, X-rays could also be used.

  What do they do to "minimize" metal fatigue or repair it?

You cannot minimize fatigue, once it starts setting in, it is an irreversible process. You can delay the likely catastrophic failure by applying strengthening elements around the affected one, but the safest course of action is to replace the component and recycle the old one.


Why can the A-10’s engines flame out merely from ingesting smoke from its gun? Apparently, firing the A-10’s GAU-8 cannon can sometimes cause its GE CF34 engines to flame out from ingesting the smoke from said gun.

It’s easy to see how the gun’s smoke could be ingested by the engines:

(Image by 67blackcherry at The Gear Page, via @Koyovis here at avSE.)

Even when the gun is firing and its smoke is blowing into the engines, though, the vast majority of what’s going into the intakes is still air; even though it is true that, to quote Wikipedia, "[g]un exhaust is essentially oxygen-free", this exhaust is immediately forced into (and diluted by) ambient air the moment it leaves the barrel, and is blown back towards the engines (and diluted still further) by yet more air.  And modern high-bypass turbofans like the CF34 are - indeed, have to be - designed to keep running even when quite a considerable proportion of the incoming air is not, in fact, air (I think I remember reading somewhere about small high-bypass turbofans being tested, successfully, for their ability to keep running when given a half-and-half mix of air and rainwater, although it’s possible that I might be misremembering).  So how can gunsmoke ingestion be enough to flame out the A-10’s engines?

I found a 1955 NACA research memorandum entitled "STALL AND FLAME-OUT RESULTING FROM FIRING OF ARMAMENT", specifically looking at flameouts in the F-86, F-94, and other aircraft associated with the firing of guns or rockets (especially in the case of the F-94, which had a nose-mounted rocket pod).  While the analysis in the paper does concern itself with a high speed (Mach 0.9) and high altitude (45,000 ft) scenario, I think that we can reasonable interpret its results for the A-10.

The paper points to the following factors following, from the aircraft firing a weapon, which could lead to an engine flameout:

(1) Increased inlet temperature

(2) Changed inlet pressure

(3) Distorted inlet-pressure and temperature profiles

(4) Entry of combustibles into engine

(5) Reduced oxygen content in gases entering engine

Of all of these, the first item was noted as the most significant, and the first step in the chain of events that results in reduced oxygen in the combustor, or, if you'd like it stated another way, an increased fuel-air ratio.  Since the exhaust gas from the gun is much hotter than ambient (anecdotally, the gas block of an AR-15 can hit up to 600 deg F after firing 600+ rounds, so I'd imagine the barrels of the GAU-8 would be at least that) and does not cool completely before entering the engine, the engine has to deal with its effects -- and the first stage to see it (ignoring the fan) is the compressor.

The compressor of a jet engine is, essentially, a fan, but one that spins fast enough to compress the air coming into the engine such that you can burn fuel in the combustor and push the maximum amount of gas as quickly as possible out the back of the engine.  However, in order to operate, the combustor needs a low enough fuel-air ratio to allow combustion (i.e., enough air to burn the fuel it's dumping in).  Similarly, the combustor is a fan, made up of a series of airfoils -- if these airfoils stall, the combustor doesn't work anymore...again resulting in too little oxygen in the combustor to allow for combustion.

Considering inlet temperature first, we can think about it from a gas-law point of view.  If I heat a volume of air, its density will decrease.  Hence, if I'm taking the same volume of air into my engine and compressing it, I'm taking in significantly less oxygen on a per-molecule basis.  If I take the ideal gas law as a rough estimate and double the temperature, my density is cut in half -- so now my engine has access to half the air.  According to the NACA study (and your picture), gun gases typically spread out in front of the aircraft, leading to a greater heating effect in the surrounding air, even if that is more spread out.  Between this and a momentum exchange between the gun gas and the ambient air, as the gun exhaust is slowed by the still, ambient air, the NACA study found that firing four 20 mm cannon reduced the inlet pressure to their study aircraft (an F-94, I believe) by as much as 9%.

So, this is a lot of hand-waving, so let's look at the effect all this on the jet engine in the NACA study.  The temperature increase on the plot is an inlet temperature increase -- and it doesn't take much of a temperature rise to significant decrease the mass flow rate of air through the engine...and stall the compressor.

Compressor stalls can also occur due to distorted inlet air velocity profiles (a fan is typically designed for air to come in axially and uniformly), another side effect of exhaust gases non-uniformly mixing with the inlet air.  Similarly, if burning particulate matter is ingested, this could change the velocity profile inside of the compressor itself by artificially decreasing the pressure ratio across the compressor.  Naturally, if combustion is delayed until the combustor, these particles will have little effect.

You can also look at this from the perspective of the downstream effect of having less air moving through the engine, or the fuel-air ratio in the combustor.  This could also be affected by a decrease in the available oxygen in the gun gases as well.

As we can see, though, changes in inlet temperature in the compressor appears to be the more sensitive parameter for this particular engine.  As mentioned in the NACA report:

  The increase in compressor-inlet temperature during armament firing
  is probably the most important single factor affecting engine performance. This increase in temperature is sufficient by itself to account
  for the observed occurrences of compressor stall and flame-out.

Hence, according to this article, the final solution to the A-10's problem (while gun gas deflectors and the like were considered) was a reformulation of the propellant used in its shells and the addition of a link between the gun trigger and the engine ignition system.


Has a general aviation twin-engine turboprop with counter rotating propellors ever been built? In my experience with general aviation twin-engine turboprops I've never heard of one with counter rotating propellors. I've never seen any data about an engine manufacturer building left-rotating turboprop engines.

I'm also curious if any counter rotating twin-engine turboprop aircraft exist outside general aviation as well.

The only aircraft with turboprop counter rotating propellers that I can think of is the Piaggio P 180 Avanti, whose design is unusual in so many ways.

Check out http://www.mpa.piaggioaerospace.it/, which gives the specifications of a Maritime Patrol Aircraft(MPA) based on the P 180.


How is the center of mass controlled in planes with multiple tail engines? My understanding is that, for flight stability, the center of mass must be ahead of the aerodynamic center.

There have been some rather big jets with 2 or 3 jet engines in the tail. Tu-154 and Boeing 727 have 3 in the tail. The DC-9 has 2, and there seem to be countless small private jets with twin engines in/near the tail, like the Learjet 45.

Another example is the Concorde and Tu-144 which had a whopping 4 engines very near the tail. If I'm not mistaken those were some extra-heavy engines too since they had to be supersonic.

So if we're putting the heavy engines in the tail, what is done to compensate? Do they just use ballast in the nose? How is the center of mass kept under control?

A few more details: Engines at the tail requires stronger (heavier) empennage, which also adds more weight in a direction we do not want our CG moving. Wings still hold the fuel, so moving the large wing/fuel mass backwards just to move the aerodynamic center backwards doesn't seem like enough.

I noticed that those tailed trijets and large tailed twinjets seem rather old. There don't seem to be any new designs of large commercial aircraft with tail jets. This makes me suspicious that the configuration is inefficient. However, small private jets seem to always be tailed twinjets, whether new or old designs.

The wings are placed sufficiently far aft.

Yes, moving the wings aft moves the C/G aft as well, but since the fuselage has some weight, eventually the centre of lift overtakes the centre of gravity and there you place the wings.

A slight problem is that C/G of cargo gets quite a bit ahead of the C/G of the airframe, causing a large difference in overall C/G position between empty and loaded aircraft and a larger horizontal stabilizer is required to maintain control over the whole range. And that, of course, reduces overall efficiency.

When you look at aircraft with tail-mounted engines, you'll see that it has wings further aft compared to one with wing-mounted engines.

Note that Concorde additionally could transfer fuel between forward and aft fuel tank in flight to adjust the C/G in flight to reduce the needed deflection of the elevators. But that was not because of the overall aft C/G—the centre of lift was correspondingly far aft—but because the centre of lift moves quite significantly aft in supersonic flight.


What vertical speed at touchdown makes a 'perfect' landing? Is there a general vertical speed that pilots shoot for, or is it entirely by feel/trial-and-error?

I would argue that the way to think of the perfect landing is not in terms of vertical speed but rather in terms of the G-forces involved.

Thinking in terms of G-force, the perfect force depends on what you're landing on and how long it is. The various conditions I can think of offhand are:

long dry runway, no wind or straight down the runway -- try for a greaser if you want, although arguably a greaser is not the safest landing.
cross wind -- the higher the xwind the more you want a firm touchdown.
short runway -- firm so you will have effective braking.
wet runway -- firm, especially if the runway has standing water. The two times that I blew tires on landing was when there was standing water and I didn't plant it firmly enough. In the first case the tires blew before I used the brakes. It was an F27 and one of our pilots was in back at a window seat. He said the two right wheels never rotated at all. I had touched down with a greaser on a puddle.
carrier -- I once checked out a Navy carrier pilot in a 182. It was really hard for him to flare for a landing, since they don't do that. As I remember, he said that they wanted a 4G landing impact.


What aircraft "don't respond well to tarmac runways"? On the Shoreham Airfield Website they wrote, they have a tarmac runway for most aircraft and a grass strip (actually two) for "aircraft which need a grass strip".

Quote:

  We appreciate that older, more fragile planes don’t respond well to tarmac and that’s why we offer both grass and tarmac runways to cater for a wide range of aircraft.

Page link

What aircraft are those not responding well to tarmac? What does it mean they don't respond well to tarmac? I could imagine this to be old WW2 Aircraft or similar.

No airplanes absolutely need a grass strip, but for some taildraggers (airplanes which have a tailskid instead of a wheel) it's a real benefit because the grass is softer on the skid, and the friction of the grass improves control on the ground and helps slow the plane down. Pavement isn't that big a problem for skids make from more modern materials, but you can imagine it's not going to do a slab of wood much good. Many vintage designs have no brakes or poor brakes, so having grass makes a big difference when landing, on pavement you'd end up rolling a lot longer and have less directional control at low speed.


What is a Simultaneous Offset Instrument Approach (SOIA)? I have heard about Simultaneous Offset Instrument Approaches (SOIA), special procedures for runways that are spaced particularly close together. How exactly do they work? What are the requirements for an airport to be eligible for the procedure? What special requirements are there for pilots flying the approach?

SOIA (Simultaneous Offset Instrument Approaches) allow airports with parallel runways that are 750 to 3000 feet apart to conduct (almost) simultaneous approaches to the two runways. At an airport, one runway uses the ILS PRM approach, while the other runway uses an offset LDA PRM approach (with glideslope). SOIA refers to the LDA PRM approach, where another aircraft is flying the ILS PRM approach ahead. PRM stands for Precision Runway Monitor, which is a high-update radar system allowing for "equivalent" safety with reduced margins.

For a PRM approach is conducted, there must be two frequencies per runway:

a primary frequency for both the transmission and receipt of instructions
a "monitor" frequency, only for ATC to transmit on

The reason for the "monitor" frequency is just in case the primary frequency is blocked and breakout instructions have to be provided. The tower controller will communicate to aircraft on both frequencies, both in normal PRM operations and when providing breakout instructions.

There is also a "monitor" controller that ensures that the two aircraft never get dangerously close together -- if such a situation occurs, the "monitor" controller overrides the tower controller on both frequencies to allow for immediate breakout instructions to be given.

Of the two approaches, the more interesting of the two is the offset LDA PRM approach. In the LDA PRM approach, aircraft fly an approach course that is 2.5 to 3 degrees offset from the runway heading, following the glideslope until the MAP (this course does not meet up with the runway threshold), at which point the pilot should proceed visually to the runway.

The MAP on a LDA PRM approach is 3000 feet away from the ILS approach course, meaning aircraft have to manoeuvre towards the extended runway centreline to be stable by 500 feet -- the less spacing between the two runways, the more aircraft will have to turn. This does mean that it is less suitable to larger aircraft, due to the manoeuvring required at higher speeds (than other aircraft), though most SOIA approaches are designed for larger aircraft as well. Before reaching the MAP, the pilot must have have:

the runway in sight;
the aircraft on the adjacent ILS PRM approach in sight; and
notified ATC that traffic is in sight.

This means that the aircraft on the ILS PRM approach should be ahead of the other aircraft. To allow time for visual contact, aircraft should be clear of cloud before the MAP, which is taken into account when deciding on the minimum cloud ceiling allowed for the approach.

The NTZ (No Transgression Zone) is a 2000 foot wide area between the two approach courses which aircraft must not enter at any time. ATC would immediately issue breakout instructions to both aircraft if an aircraft breaches the NTZ, as there would be very little horizontal separation between the two aircraft. [The FAA AIM][3] states that:

  In the unlikely event that an aircraft "blunders" off its course and makes a worst case turn of 30 degrees toward the adjacent final approach course, closing speeds of 135 feet per second could occur that constitute the need for quick reaction.

Special training requirements vary from country to country. In the US, SOIA special training requirements are:

Parts 121/129/135: operator training as agreed to by FAA and educational video
Part 91 transport category: read about PRM approaches in AIM, video
Part 91 other: read about PRM and SOIA approaches in AIM, video

An example of a SOIA approach is the SFO runway 28R LDA PRM approach:


What exactly is an "engine surge" in a jet engine, and what causes it? Surge suggests that something speeds up, yet I read elsewhere that in fact in jet engines, an engine surge is actually a compressor stall.

Whether that is correct or not, what exactly is doing the surging in the case of an engine surge?

What kind of fault within the engine or conditions of its environment causes an engine surge?

The surge is the increase in rpm of a stalled compressor.  The compressor blades are airfoils not unlike propellers and wings. They will stall if airflow is not maintained at the proper angle of attack.

Interruption of airflow in jets can be caused by abrupt maneuvering, ingestion of foreign matter, or excessive application of throttle.  Much has been done to eliminate this issue in modern jets, but the nature of the design still makes it possible. If air flow is interrupted to the compressor, the jet can literally backfire, creating a loud "bang".  A large yellow flame may also be seen coming from the back of the jet as the fuel/air mixture is now excessively rich due to insufficient air.

If the engine is not damaged, it can be re-started the same way we unstall a wing, by re-establishing proper airflow angle of attack.  This is done by lowering pressure BEHIND the compressor.  Throttle is reduced. Provided the engine is not damaged, throttle can be carefully restored.


Why does the Embraer E-Jet Family have doors of different sizes? I just noticed yesterday that the right and left forward doors of all E-Jet Family aircraft have different sizes (both in height and in width). What is the reason behind this design difference?

It's actually more common than one might expect, and not just in the E-jet family.

The de-facto standard is that passengers board from the left and the right side doors are only used to load logistical stuff (ie catering) during the turnaround or during an emergency evacuation.

As such, the left side door(s) must fit certain FAA standards (so it fits jet bridges or the average human height, for example).

For example, on the Boeing 737 (all models), the left forward door is 0.86 x 1.83 meters while the right forward door is 0.76 x 1.65 meters, 20 percent smaller (by area).

Now you might ask "ok, so make both doors the size of the left door". It's beneficial, from engineering/structural point-of-view, to have each door as small as possible.

(http://www.boeing.com/assets/pdf/commercial/airports/acaps/737.pdf pages 73 and 77)


How do different training paths to multi-engine rating compare? I am going to be initiating my private pilot license shortly and wanted some feedback and comments with regards to utilizing single engine (minimum) and multi-engine to obtain my multi-engine rating quickest.

I know that most people start and stay with a small single engine to obtain their license. Then start putting some time in (later) to get their multi-engine.

However, I am thinking that after a little time in a single—doing most of time in a twin (even though the cost is significantly more) because my time in the twin will apply later on towards the multi-engine will be more efficient.

If it's been objectively compared before, I'd like to know the different paths taken, and which is better when?

At the end of the day the choice might be made for you, as many flight schools will not let you fly their multi-engine aircraft until you have a private licence.

People almost always begin on single-engine aircraft not just for cost, but also for efficient training. Multi-engine aircraft are complex beasts that require a lot of theoretical knowledge and practical skills to fly safely. If you're trying to get a grip on all that at the same time as just learning the basics of flying, you'll no doubt struggle and have to repeat lessons. Your first solo will definitely come considerably later, and many would agree that you learn the most about flying when you're up there by yourself.

Granted, the more multi-engine time you can get, the better your future job prospects (generally speaking). Just remember that doing your early training like that will increase the time it takes to get your ticket. For a qualified pilot, a multi-engine rating only takes 10-15 flight hours of training anyway, so to me there isn't a huge advantage in getting one before your private licence.


How do changes in certification requirements affect previous type certificates? How does the 2016 part 23 airworthiness requirements rewrite affect older type certificates?

If some aspect of an aircraft does not meet the new requirement do all of those aircraft have to be updated accordingly?
If so, what if the aircraft can't be made to meet new requirements, such as climb rate, etc.
If one of the new rules are less restrictive than the old can those aircraft take advantage of that?
Do newly manufactured aircraft of the same type have to get recertified?
If old type certificates are still valid and the FAA wants one of the new rules to be retroactive will they have to issue airworthiness directives for each type that doesn't meet the new standard?

New rules don't affect t existing designs....

Certification basis is declared by the maker and agreed with the certifying authority...Or authorities... ( ideally it's a common certification basis to avoid extra testing, or building aircraft to  different standards) That basis must reflective rules in existence at the time of application. New or pending  rules may be imposed by Special Conditions or equivaent. Any modifications to that approved design are normally to the same certification basis.

But if a new design comes along, it's the applicable rules at the time of application..

If a change is needed to all aircraft of a certain "class" e.g. Introduction of TCAS, ACAS , then that is imposed by operational requirements, such as Parts 91, 121, 135 etc or their equivalents.


On a axial flow turbo fan or turbo jet engine what comes first the rotor or the stator? I've been let to understand that one stage consists of a row of rotors and stators. But I'm not sure which comes first? Does the front fan blades make the first part of the stage (rotor) with a stator section behind? And so on.. Or on a fan engine with a booster the first stage is the stator and then rotor (after the fan blades).
Secondly do all engines have inlet guide vanes? I'm assuming not or we would physically see them in front of the the big fan engines or do they appear later on.. Maybe in the HP section?

Hope this makes sense and any images with an explanation would be appreciated.

Thanks

There are two aspects to consider here:

The aerodynamic principle:

The simple aerodynamic principle requires a compressor stage to have first a rotor followed by a stator.
The constructive aspects:

Constructive aspects to be considered are:

a) Pre-rotation of air before the rotor: in order to reduce the relative speed of the airflow on the rotor blades (to avoid the shock waves of supersonic airflow) a set of stators can be placed in front of the rotor; this will rotate the air towards the direction of rotation, reducing by this the relative speed of the airflow on the rotor blades; even in such cases a stator stage is required after the rotor.

b) Bearing location: some designs put the bearing behind the rotor, other designs put the bearing in front of the rotor; in such case the bearing before the rotor needs to be supported by a system of vanes.

Consequently, many smaller diameter (or high speed military design) engines will take advantage of a) and b) above and have a stator in front of the first stage compressor.

To answer the same questions on turbines, there the aerodynamic principle requires to have first a set of stators and then a rotor.


Is the induced drag independent of wing span? I am a new aviation student and I was reading about induced drag the other day. I know that it is produced as a result of the tip vortices and that the greater the aspect ratio of an airplane the less the induced drag force. But when it came to the equation of the force, it is equal to:

$D_i = \frac{1}{2}\rho V^2 S \frac{C_L^2}{\pi  AR \epsilon}$

If we substitute aspect ratio $AR$ with span/chord $\frac{b}{c}$  and plan area $S$ as $b\cdot c$, the span term will be cancelled and the induced drag will be affected by the chord length only.

It kind of contradicts the effect of aspect ratio on the induced drag force, doesn't it?

Aspect ratio $AR$ can be written as $\frac{b}{c}$ which is equal to $\frac{b^2}{S}$.

Before we start substituting, note that $C_L$ also depends on the wing surface area $S$.

$L = \frac{1}{2}\rho V^2 C_L S$

or

$C_L =  \frac{L }{\frac{1}{2} \rho V^2 S}$

Substituting all this in the induced drag formula yields:

$D_i = \frac{1}{2}\rho V^2 S \frac{C_L^2}{\pi  AR \epsilon} =
\frac{L^2}{\frac{1}{2}\rho V^2 S \pi AR \epsilon} = \frac{L^2}{\frac{1}{2}\rho V^2   \pi b^2 \epsilon}$

This shows that the induced drag is proportional to the inverse of the square of the wingspan.


What happens when a GA pilot squawks 7500? If you were to put code 7500 into your transponder in a small general aviation aircraft, and you were in a rural area with no one around, and you did not have enough fuel to get to any city, what happens? Would they shoot you down? {edit what I meant was if you were being Hijacked and you on purpose sqacked 7500

Who would shoot you down and why? You are in the middle of nowhere. Who are you endangering? ATC would try to contact you to ascertain your actual condition. You may have accidentally put in the wrong code. They would then offer assistance if needed.

If it was a kidnapping situation, all they could do is follow or track you until you land. You are not going to get far. Even if you went to another country close by, you can still be tracked and local authorities alerted.


Under what conditions may a colorblind pilot fly a Light Sport Aircraft legally? Are pilots of Light Sport Aircraft within the FAA's jurisdiction required to have color vision? Do colorblind LSA pilots have to take the Operational Color Vision Test (OCVT)? Without the requirement for a medical certificate, where does any testing or certification for color vision come into play?

What I assume you are talking about is the drivers license medical loop here in the US that allows you to fly LSA aircraft with only holding a Drivers License (in lieu of a medical certificate). You can find the full regulation here but there are a few things you should know.

First off you need to see what your local state requires (since drivers licenses are issued by states not a federal body like pilots licenses). If your state has color blind restrictions on drivers licenses you may have an issue

  (i) Comply with each restriction and limitation imposed by that person's U.S. driver's license and any judicial or administrative order applying to the operation of a motor vehicle;

If you are stepping down from larger planes into LSA planes you can not use the drivers license if you have ever lost a medical cert

  (iii) Not have had his or her most recently issued medical certificate (if the person has held a medical certificate) suspended or revoked or most recent Authorization for a Special Issuance of a Medical Certificate withdrawn; and

The catch all clause that may make the colorblind condition an issue is the last requirement in the FAR

  (iv) Not know or have reason to know of any medical condition that would make that person unable to operate a light-sport aircraft in a safe manner.

There are lots of light signals used in aviation that a red/green color blind person would have issues with. According to this article color blind LSA pilots are restricted from flying into where color light signals may be used (these signals include but are not limited to tower light signals and ground based warning lights like those in the DC area). If your state issues you a color blind restriction on your drivers license it holds here as well,

  Of course, any limitations placed on the driver's license would also apply to flying, and a person must always be physically able to perform the flight safely.

Furthermore it seems that according to this article you can have the restrictions lifted if you can pass a color blind test (I assume this applies to both the LSA restrictions as well as the regular PPL restrictions)


What pattern of position lights did early Soviet jetliners use? All aircraft that operate at night or in poor weather need position lights to make them visible to other aircraft for the purpose of avoiding mid-air collisions.  On most aircraft, these follow a set pattern: two continuously-illuminated lights on the wingtips (red on the left wingtip, green on the right [a pattern inherited from marine navigation lights], to allow other aircraft to see whether yours is flying towards or away from them), a continuously-illuminated white light in the tail, and high-intensity white anticollision strobe lights on each wingtip, in the tail, and on the upper and lower surfaces of the fuselage.
However, according to the Wikipedia article on the Ilyushin Il-62, early Soviet jetliners did not follow the standard arrangement for position lighting:

The Il-62 entered Aeroflot civilian service on 15 September 1967 with an inaugural passenger flight from Moscow to Montreal, and remained the standard long-range airliner for the Soviet Union (and later, Russia) for several decades. It was the first Soviet pressurised aircraft with non-circular cross-section fuselage and ergonomic passenger doors, and the first Soviet jet with six-abreast seating (the turboprop Tu-114 shared this arrangement) and international-standard position lights.  [Emphasis added.]

What arrangement of position lighting did pre-Il-62 Soviet jetliners use?

That was a tough one. The USSR joined ICAO in 1970.[a] The colors and positions would have been the same, since those carried over from maritime conventions.
What isn't the same, based on checking warbirds, is the viewing angle. The red/green lights in ICAO/Western standards are not viewable from behind, but Soviet aircraft did not have that distinction. They also had separate top/bottom navigation lights, even the license-built DC-3 (Li-2) was modified to have that top/bottom arrangement.[1]
Judging by the Yak-40 (an early Soviet jetliner), they lacked the white wingtip lights[b] that are viewable from behind -- compare with the ICAO-compliant Il-62 (shown on the right):

Both aircraft are stored; sources: scalemodels.ru and elevation.maplogs.com

For the aforementioned warbirds, below shows an American F4F (annotated) and a Soviet Il-2:

Sources: primeportal.net and primeportal.net

1: http://www.dc3history.org/airlinesoftheworld/russianaviation.html
a: I'm not sure whether Soviet transport aircraft that flew internationally and were built prior would have been retrofitted
b: technically those are anti-collision lights, but unfortunately the Wikipedia statement is vague and lacking in-line citation -- the ICAO-equivalent became effective in 1962 according to SARPs Annex 6 part 1


Why does the 747 have 4 engines instead of 2? If the 747 can fly with two engines, why does it have four engines?

What is gained by adding another 2 engines?
Flights over the ocean?
Fuel savings?
Safety?

Simply, more engines = more power, and power is needed for several things, the first of which is, taking off.  At max takeoff weight, a multi-engine aircraft has to be able to lose one engine (after reaching the go/no-go speed) and safely continue the takeoff, which means that if you could just barely fly on 3 motors, you're going to have to have 4 to meet certification (safety) requirements.  For the amazing weights that the 747 can carry, it needs some pretty powerful motors, and all 4 of them, for taking off fully loaded and meeting this requirement.  (Interestingly, if the aircraft is empty and could safely continue the takeoff on 2, it is typically allowed to take off with one engine already inoperative -- to ferry to a maintenance base, for instance.  But this requires no passengers/freight, and thus a very light airplane.)

At cruise altitude, more thrust means a higher cruise altitude is possible, which makes for better fuel efficiency.  So while a 4-engine aircraft can certainly fly on 3 engines, and in many cases (depending on weight and outside air temperature) on 2, it can't fly as high as it could with all 4.  The higher cruise altitude not only makes for more efficient flight, it also keeps you above a lot of the weather out there, and in extreme cases, a 2-engine ceiling might not clear all the terrain on your route.  (Again, this depends on weight & temperature.)

Modern engines have amazing reliability, and it's now considered routine to dispatch the twin engine 777 and 767 and A330 on long overwater routes, but 50 years ago, the reliability wasn't as great, so it was considered essential to have the redundancy so that if one engine failed over the middle of the ocean, there was still a comfortable margin, and you weren't now "one motor away" from going swimming.


How do helicopters handle P-Factor? Propeller-powered aircraft have a "problem" called P-Factor, where the descending blade of the prop is generating more lift (a.k.a. thrust) then the ascending blade due to a higher angle of attack when the angle of attack of the wings is high. (I hope I summed that up properly.)

How about helicopters? For this example let's say the blades turn counterclockwise when seen from the top.  When the helicopter is accelerated, the blades on the right side of the helicopter are faster then the ones on the left side.  Thus they should be generating more lift. The higher the speed, the higher the difference in lift on both sides would be.

What mechanism handles corrections that have to be made due to this lift difference? How does it work?

This was one of the primary problems that needed to be solved in helicopter flight.

In my example, I'll use a 2 bladed helicopter, but this holds true with all helicopters, and I'll explain some of the different rotor types later on. The blade that is moving forward, relative to the direction of the helicopter, is called the advancing blade. The opposite is called the retreating blade, and you are correct in assuming that they would generate different amounts of lift. As a previous commenter noted, the term used for this is "dissymmetry of lift", and is the same thing that limits the maximum speed of a helicopter.

A two bladed helicopter will generally have what is called a "semi-rigid" rotor system. Semi rigid systems are only possible on even bladed helicopters, and are generally only used on 2 bladed helicopters. The two blades are connected together by a hinge on the rotor hub (where the blade meets the helicopter), and if you push down one blade, the other blade moves upward, and vise versa. What happens as you move forward is that the advancing blade (the one generating more lift) will get pulled up with a greater force than the retreating blade (the one generating less lift). As the advancing blade rises up (because of its additional lift), it pushes the retreating blade down. This advancing blade, in pushing up the rotor, is reducing the angle of attack of the blade against the airflow, which in turn is going to reduce its lift. The retreating blade is hinging downwards, which is increasing its angle of attack against the airflow, which will increase the lift it provides. These two forces will work against each other until they are in balance, which means that the advancing blade and the retreating blade will even out in the lift they are generating, which removes the dissymmetry of lift.

The blades in a helicopter are spinning at a some speed, which varies depending on where on the blade you are talking about (the tip or near the rotor hub, for example), but to simplify this explanation, I'm going to assume that the blade is traveling at the same speed along its entire length. Let's say that the blade is spinning around at 100mph at its tip. As the helicopter moves forward, at let's say 50mph, then we have one blade that is moving against the air at 150mph (the advancing blade), and one that is moving against the air at 50mph (the retreating blade). As the helicopter gets closer to 100mph (the speed of the blades), at some point, the speed of the air against the retreating blade will get closer and closer to 0. When it hits 0, it will stop generating lift, and the helicopter will start to roll (now the rotor is only generating lift on one side). This effect, called retreating blade stall, is one of the reasons why helicopters are limited in their top speed.

Just as a side note, I have greatly simplified some of these explanations, so I am well aware that I have glossed over various parts of this explanation to simplify it.