Does the a320 neo have anything like MCAS? I am trying to book a flight that will be on an A320 NEO.

Does this have any 'new' systems or features, like the MAX MCAS system?

I'm asking this question also because one airline has just grounded it's NEOs...

Different airplanes, different systems; however, all modern airliners have computer assisted flight controls to some degree.  These include stall protection of various types, of which Boeing's MCAS is one.  Airbus uses different methods of stall protection, but there's still a computer involved.

Do you need to worry about the same issue?  No.  Part of Boeing's problem was that they didn't tell people about their system and pilots weren't trained.  Had the pilots known about the system and how to disable it, the crashes probably would have been avoided.


Why do airplanes lift up their nose to climb? Is it right that basically an airplane just needs to accelerate to climb?

Greater velocity of an airplane leads to greater lift - and since its weight remains constant (or even decreases) - a greater lift leads to a gain in altitude without the need to pitch. But why do airplanes climb by "pointing the nose up"? Is it to climb as fast as possible and to need less horizontal space?

A climbing aircraft needs less aerodynamic lift than in horizontal flight, not more.

Now I have your attention, I hope. The reason is quite simple:

Lift equals weight, and just because the pilot choses a different flight path angle, the weight of the aircraft does not change. The total of all lifting forces must still balance the weight, but in climb you get a small lifting contribution from the engine(s) because its (their) thrust will point upwards just like the rest of the airframe.

Don't let the many arrows and greek letters confuse you. To be in equilibrium, lift (L, dark blue), drag (D, red), thrust (T, green) and weight (m⋅g, black) must add up such that they can be combined into a closed run of vectors. I've done this with the lighter-colored vectors around the weight. Since the flight path points upwards, so does the thrust which now has a small vertical component. The lift vector can be a little shorter now.

Consider the extreme case of vertical climb: Now all thrust supports the weight, and aerodynamic lift is no longer needed.

There is a second, much more subtle effect: When you climb, air gets thinner and engine performance goes down proportionally. At the same indicated air speed, the aircraft will continually decrease its climb speed, and this deceleration frees up a tiny inertial force, which again adds to lift and counteracts weight.

Conversely, at the beginning of a climb phase the aircraft needs to create momentarily more lift to accelerate itself upward. Only then, when climb speed increases, lift must be bigger than weight to overcome the inertial effect which at this moment works downwards. For the supernerds: If you integrate the lift deficit over time of the aforementioned effect and the extra lift over time for climb acceleration, both cancel exactly.

To answer your question directly: To climb you need to increase excess energy, not speed. This is normally done by increasing engine power output, or by trimming the airplane at a lower speed where drag is less, so more power remains for climbing. This question contains more details on how to get an aircraft to climb. Note especially @SteveV.'s bucket analogy.

If you use the airplane's kinetic energy as its source of thrust, the same mechanism can be applied to instationary climbs, where speed is traded for altitude, like in gliders.

The nose-up attitude is simply the result of a different flight path. Since the required aerodynamic lift will be almost the same, the angle of attack will also be almost the same and the whole aircraft needs to fly nose-up. This is similar to a car which has the same attitude towards the road, but when you drive uphill, both car and road will be tilted upwards.

This analogy breaks down when you change speed - flying at lower speed needs more angle of attack to still create the same lift, and this nose-up change will be added to your attitude angle.

According to Wikipedia and what I recall from my earliest days in training as a private pilot:

Relation between angle of attack and lift[edit]
A typical lift coefficient curve.
The lift coefficient of a fixed-wing aircraft varies with angle of attack. Increasing angle of attack is associated with increasing lift coefficient up to the maximum lift coefficient, after which lift coefficient decreases.

As the angle of attack increases so does lift. Exceeding the Critical Angle of Attack further illustrates this point.


Does a conversion for wheel to floats require an STC or Form 337? When you add floats to a tricycle gear (e.g. Beaver) do you need an STC to install the TSO'd floats? Or can this installation be approved with a Form 337 for a single aircraft?

This sounds like a major mod, but I will have to see the design data to really able to come to a conclusion. If its a major mod, it has to be done via an STC.


In a 777, what would happen if the auto-pilot and the altitude hold failed at the same time? I know nothing about a Boeing 777 flight controls.

In general,
I know that the speed of an aircraft is controlled by the throttle on the center console. I have never heard of an automatic speed control. I believe the pilot manually adjusts the speed.
I have heard of altitude hold control. You set it and the system keeps the aircraft at the same altitude. Is this independent of the auto-pilot?
And of course there's the auto-pilot. It makes the aircraft go in a direction you want it to go.

If the pilot does not intervene, what would happen if the auto-pilot and the altitude hold failed at the same time?

Does the aircraft climb or dive?  Dose it oscillate up and down?
Does the aircraft roll over?
Does the aircraft turn?
What about speed?
If it continues in some fashion, what is the effect of the fuel consumption in the different tanks? Is it automatically controlled? What happens if that control fails?

Regardless of whether it's a 777 or any other airplane where the altitude is being held by the autopilot and the altitude hold function stops, whether because of general autopilot failure, just altitude hold failure, or the altitude hold function is inadvertently or purposely switched off; the airplane will seek whatever pitch attitude it is trimmed for.

For example, using the 747-100 and -200 autopilot setup, let's say you are in cruise at 35,000 ft, the autopilot is navigating and altitude hold is on. Further, let's say we're beyond 1990, and many operators of those aircraft had disabled autothrottles because they were a maintenance hog. Thus the airplane is maintaining whatever speed has resulted from where you have positioned the power levers. The altitude hold function is maintaining altitude by using the elevator. You can look down at an indicator on the center console between the pilots to see the degree of up or down elevator being used.

As the flight progresses and fuel is burned, the c.g. moves forward and the altitude hold function adds more up elevator to maintain altitude. When a certain amount of up elevator amount is reached, the system automatically retrims so that no up elevator force is required.  You hear and see it happen because the large trim wheel on the right side of the center console rotates.

If you're a good captain or a good flight engineer, you can monitor the amount of up elevator force being held and trim it out manually before it reaches enough to trigger the automatic retrim, and save the company a little fuel money (or if you're JFK to Tel Aviv in a -100, possibly avoid a fuel stop in Athens).

Now let's say that you reach up and disengage the altitude hold sometime between retrimmings. The airplane will nose down, and actually quite abruptly if it's been awhile since it last retrimmed. So abruptly that normal practice was to always have the yoke in hand before disengaging the autopilot.

Let's say that you that you let the condition persist. The nose is down, so the airplane would descend, of course. The speed would oscillate during the descent. If there was a severe nose down trim ... well, you wouldn't want to go there.

For a humorous account (at least meant to be humorous) of the altitude hold function being inadvertently disengaged, go to http://terryliittschwager.com/hajj4contest.php.

Now for the case of total autopilot failure, I defer to the other answer already here when I posted this. Suffice it to say that the pilots would have to take control in short order to avoid an extremely serious condition, very possibly the loss of the aircraft. You can go to http://community.seattletimes.nwsource.com/archive/?date=19911219&slug=1323954 for information on an incident that involves such. The interesting thing is this airplane had started to do this a number of times (including once to me coming out of Hong Kong), but in previous instances the pilots quickly recognized that the autopilot had failed and had taken control before things got serious.

Following the incident described, the airplane was repaired and reentered service, and we called her Christine.

Nothing radical...fly the plane, navigate, have the copilot fly and figure it out together, trim as necessary, Monitor copilot. Reengage one axis at a time.


For what is VMCL the minimum control speed? I would like to ask which of these options is correct:

  VMCL is the minimum control speed for:

  A) approach in go-around configuration
  B) approach in landing configuration
  C) go-around in approach configuration
  D) go-around in landing configuration

I would choose B but my friends disagree due to Certification Standards CS25.19 Minimum Control Speed stating that:

  VMCL must be established with -
  (6) Go-around power or thrust setting on the operating engine(s).

However that doesn’t mean that my VMCL is the speed that I use for go-around, right? It just says that to establish my VMCL, I need to use go-around power as a reference.

Therefore I think that VMCL is basically just the minimum control speed during an approach in landing configuration.

I would go with B as well.  Minimum Control Speed - Landing is for the critical case where you are in the least favourable possible configuration on approach, gear down, full flap, trimmed at approach speed, C.G. at least favourable location, etc etc, then have one engine fail and the other is put to full power. VMCL is the speed at or above which control can be maintained at that instant maximum asymmetric trust is applied, before the airplane can accelerate or the configuration can be changed.  Go around speed in the approach configuration will be faster than VMCL.  VMCL is the edge of the cliff.

D) CAAS ATPL accepted Go around speed in landing Configuration.


Why is the nose of the Mig-21 shaped so differently compared to other fighter aircraft? If you look at this picture below, you will notice that the nose portion of the Mig-21 has a unique conical shape which is completely different from the nose of the F-16.

(Source)

(Source)

So what explains the conical design of the nose of the Mig-21?

The nose design of aircraft, like any other part, is a result of optimization in response to a number of factors. The Mikoyan-Gurevich MiG-21 'Fishbed' is a supersonic, second/third generation Soviet fighter/interceptor.

The first jet aircraft to enter serice during the WWII, the Messerschmitt Me 262 'Schwalbe' and Gloster Meteor had twin engines in their wings. In these cases, the nose was designed to carry the cannons, which were the primary armament at the time.

"Messerschmitt Me 262A at the National Museum of the USAF" by USAF museum - http://www.nationalmuseum.af.mil/shared/media/photodb/photos/040820-F-1234P-081.jpg. Licensed under Public Domain via Commons.

The first generation jet fighters, like the F-86 and Mig-15 were subsonic and had engines buried into the fuselage to reduce drag. The nose, again carried the cannons (in case of Mig-25, in the lower fuselage).

"F86Sabre" by Kowloonese at the English language Wikipedia is licensed under CC BY-SA 3.0

However, the second generation jet aircraft were the first operational jets to go supersonic. The Mig-21 was designed in response to a Kremlin specification, which called for Mach 2 level speed (at altitude), while carrying a simple radar and option for future air-to-air missiles.

As the jet engines require airflow to be subsonic at entry, the flow has to be decelerated before reaching the engine. Early in the design (from Ye-50-3), Mig decided to use a conical centerbody for this purpose, as it was decided that the aircraft would be single engined with engine in the fuselage (the engine was supposed to be the Mikulin AM-9B, however, the aircraft ended up using Tumansky R-11).

This nose design decelerated the flow using two oblique shocks and a normal shock, giving improved pressure recovery at high supersonic Mach numbers. The center-body (cone) moved axially according to the Mach number. Also, the center body housed the radar and associated equipment.

The first generation Mig 21s only had a range finder, and the intake diameter had a smaller cone.

"Mig21F13web" by Newresid stephanelhernault@yahoo.fr - Own work work vector drawig travail personnel dessinn vectoriel. Licensed under CC BY-SA 3.0 via Commons. (Image cropped)

The following image shows the range finder used in early models of Mig 21.

"MiG-21F-13 radar Keski-Suomen ilmailumuseo" by MKFI - Own work. Licensed under Public Domain via Wikimedia Commons.

The photo you've shown are from the later versions (Mig-21 bis from IAF), which had the radars from the "Sapphire" family. To fit the radar antenna into the cone, the cone had to be made bigger, therefore the whole front fuselage had to be redesigned, the diameter of intake got more than 200 mm higher, and the cone itself got longer, wider and moved forwards.

"Mig21fishbedHfamilyweb" by Newresid stephanelhernault@yahoo.fr - Own work work vector drawing travail personnel dessin vectoriel. Licensed under CC BY-SA 3.0 via Commons. (Image cropped)

The following figure shows the enlarged nose cone section housing the radar. Interestingly, the nose cone seems to be made out of (metal tipped) wood to prevent interference.

Source: toad-design.com

A number of aircraft from that time had conical body inlets, like the British Electric Lightning.

"Lightning.inflight.arp.750pix" by Arpingstone - Own work. Licensed under Public Domain via Commons.

The F-16, on the other hand, has a simple normal shock diffuser. By the time of F-16, the radars had become bigger and more important (AAMs have become the primary combat weapon, replacing guns), and needed more space in the nose. As a result, the inlets of most of the aircraft had moved to the sides/downwards. The following figure shows the AN/APG-68 radar in F-16.

Source: defenseindustrydaily.com

One point not mentioned here, but crucial to this discussion, is the inescapable fact that, all other factors, i.e. sophistication of technology,"Moore's Law", etc., being considered, the effectiveness of a radar, not unlike the lens of a camera, is determined by the sheer physical size of the antenna, with performance actually increasing EXPONENTIALLY(!!!), the greater the diameter.  Which is why both the MiG-29, and the Sukhoi Su-27/35 series all have such large, bulbous noses, the better to make up for a deficiency in chip design, and thus general electronic performance and capability.  Needless to say, with it being a most basic law of physics, that two objects cannot occupy the same space at the same time, the larger the antenna, and its accompanying radome, the less space available, circumfirentially speaking, for air delivery to the engine, whose needs in this regard, cannot be compromised. Accordingly, and with BOTH(!!) requirements increasing, somebody had to move, and, with the radar antenna having, for obvious reasons, "first dibs" on the nose of the aircraft, the inlets had to "re-locate" to to the flanks. ala, F-102, F-104, F-105, F-106, and F-4, F-111, F-114, F-15, etc., not to mention Migs "23" to "31"! I could say "Lightning" replaced by "Typhoon", or "Mirage" by "Rafale", but you get the point.


Is AMDAR a required system on aircraft? I was intrigued by the assertion that COVID-19 depressing commercial aviation has lead to lower quality weather forecasting

  The aircraft observations are a key piece in the jigsaw of national and global weather data that is fed into computer models through a process called data assimilation. Multiple studies have found that aircraft are among the most important data sources for reducing the error in forecast models.

After some poking around, I found out the system is called AMDAR

  The AMDAR system predominantly utilises existing aircraft onboard sensors, computers and communications systems to collect, process, format and transmit meteorological data to ground stations via satellite or radio links. Once on the ground, the data is relayed to National Meteorological and Hydrological Services (NMHS), where it is processed, quality controlled and transmitted on the WMO Global Telecommunications System (GTS).

Is this system required by aviation authorities anywhere? Or is there merely some incentive system to encourage participation?

AMDAR (Aircraft Meteorological DAta Relay) is a program established by the World Meteorological Organisation to gather weather data from around the world. It's run through a number of local and regional AMDAR organisations who negotiate with partner airlines arrangements to use existing aircraft sensors to gather and report weather data on each flight.

The gathered data is relayed by satellite or radio to ground stations and then forwarded on for processing and distribution.

(I've paraphrased from this source)

So, there is no specific AMDAR equipment. The AMDAR system is implemented by arrangement with partner airlines, and may be installed on some or all of the airline's aircraft that already carry suitable sensors.

There is no mention of a requirement that an airline partner with a regional AMDAR organisation, and thus no requirement for their aircraft to carry the system.

It's not clear from the pages at the WMO what the nature of the collaboration between the local AMDAR organisation and the airline is, so there may be some payment to the airline, or there may be some benefit in kind: free or reduced cost access to meteorological reports, perhaps.

Short answer: No. It depends on the type certification of the aircraft. For example, helicopters don't even have radars! Also, many old planes (e.g., DC-3, DC-8, MD-80) aren't equipped with AMDAR. So no, not ALL planes have to be equipped with AMDAR, but AMDAR is quite useful.

Usually the rule on AMDAR is the higher and faster your aircraft goes, the more an aircraft weather monitoring system is required. F.e, fighter jets and modern long range jets have to be equipped with some kind of weather monitoring system.  Basically, sometimes weather radars in general are required.


What do flight attendants do if a passenger asks what is going on in case of a potential emergency? This is related to, but not the same as, another question I asked on Interpersonal Skills.

I was on a flight last year, on a route I fly on a fairly frequent basis. Shortly after takeoff, I heard the three double chime signal, which is commonly used by airlines to indicate to the crew of a potential problem. The crew quickly marched up to the front of the passenger cabin and was briefed by the pilots. I also noticed that the plane was going off course. Some time later, I used the onboard Wi-Fi service to query an online flight tracker about the flight I was on, and it said we were diverting back to our origin airport.

Throughout the whole incident, all the crew kept quiet about the whole thing, and didn't let passengers know about the diversion until just a few minutes before landing back at the origin airport.

Before the announcement, while the seat belt sign was turned off and while the crew weren't making any emergency preparations of any sort (just casually chatting with other passengers), I got up and asked the crew what was going on, and they said "nothing". I then showed them the tracker page which indicated the diversion, and they just asked me to return to my seat.

What's the general protocol for cabin crew, when asked by passengers who notice potential issues like this and get curious? Is it common for them to simply say that "nothing" is going on until the flight deck makes an announcement? What if a passenger really insists on knowing what's going on? (As an aviation enthusiast, I feel more comfortable if told about the issue; not knowing about it can make me feel tensed.)

What's the general protocol for cabin crew, when asked by passengers
  who notice potential issues like this and get curious?

The flight crew and pilots are under no obligation to inform the passengers about non critical issues and broadly speaking it's often better to provide only needed information so as not cause some kind of panic. In the vast majority of situations on an aircraft there is nothing the passenger can do other than evacuate when told to do so.

Turning an aircraft around and heading back to the point of origin is not necessarily an emergency although it can be there is nothing to say it is or is not from a passenger point of view.

Even if a passenger insists the cabin crew will likely ask them to take their seats, buckle up and await any further instructions. It's possible that the cabin crew is not even informed of anything as the pilots try and work the problem.

The later part of your question is answered here and the general answer is, unless you are a trained pilot it's hard to actually know if something is going wrong. There is a very interesting example of this from the Air Florida Flight 90 incident which is the only incident I know of where a non flying pilot spotted an issue and took action, this would be a fairly rare case;

  Survivors of the crash indicated the trip over the runway was extremely rough, with
  survivor Joe Stiley – a businessman and private pilot – saying that he
  believed that they would not get airborne and would "fall off the end
  of the runway". When the plane became airborne, Stiley told his
  co-worker (and survivor) Nikki Felch to assume the crash position,
  with some nearby passengers following their example.

This passenger would be second guessing the flight crew AND the cabin crew and insisting to them that they know better than them.

This passenger is going to be treated like the annoyance they are, told to go back to their seat and follow crew instructions.

They're not just obstructing the professionals from doing their jobs, this passenger is potentially causing serious harm by panicking other passengers.

If this passenger keep insisting on causing trouble, the  crew may well be forced to physically restrain them, with the help of any air marshals that may be on board.

If and when there's something the passengers need to know or do, they'll be told.


Why do some commercial flights start off unpressurized? In this video, the B738 starts takes off without the plane's pressurization system engaged.  The video specifically notes that the craft is being pressurized fairly soon after the takeoff has happened.

Is this because of the icing conditions they had on the ground?  Or is there another reason why it would take off unpressurized?

Screen capture for the extremely busy:

The 737 like most modern airliners (notable exception, the 787) is pressurized by bleed air, from either the engines or the APU. Drawing bleed air from the engines reduces the thrust available for takeoff.

From most common to least common, takeoff configurations are:

Engine bleeds on (supplying bleed air to the pneumatic system), APU off. This is a pressurized takeoff & generally the most common scenario.
Engine bleeds off, APU bleed supplying air to the pneumatic system. This also results in a pressurized takeoff, with more engine thrust available. Used when max thrust is desired, typically due to heavy weights, short and/or contaminated runways, close-in obstacles requiring steep climb gradients, and similar circumstances.

In the case that the APU is inoperative but taking off with the engine bleeds off is still required, you get:

Engine bleeds off, APU bleed off. This results in the unpressurized takeoff referenced in the question.  At a suitable altitude (typically 2000 to 3000 feet into the climb, a minute or two after takeoff), the engine bleeds are turned back on & the aircraft pressurizes normally.

This is uncommon, but still considered a normal procedure (not an abnormal one out of the QRH).

Edit:

Link to Pneumatic System description for the 737

Link to PDF discussing pneumatics & pressurization on the 737

The air pressure outside decreases as the aircraft climbs. However up until a certain altitude, which I happen to forget, you can fly without the aircraft being pressurized. This is why we don't need to throw on oxygen masks while flying light aircraft (up until a certain altitude anyways)


Does a CFI need an Instrument Rating https://www.ecfr.gov/cgi-bin/retrieveECFR?gp&n=14y2.0.1.1.2&r=PART#se14.2.61_1183

The or below is very confusing.  Doesn't it mean I need an Instrument rating or one of the things that follows it in the list?  Or means one or the other, not both.
Furthermore, when would one of the things that follows in the list NOT apply?

(2) An instrument rating, or privileges on that person's pilot certificate that are appropriate to the flight instructor rating sought, if applying for—

(i) A flight instructor certificate with an airplane category and single-engine class rating;

(ii) A flight instructor certificate with an airplane category and multiengine class rating;

(iii) A flight instructor certificate with a powered-lift rating; or

(iv) A flight instructor certificate with an instrument rating.

For most people, the answer is yes—you need an instrument rating to be a CFI or CFII for the categories that are listed.

It is possible to become an ATP by using military experience. In that specific case a person has instrument privileges but may not have an instrument rating.

You do not need an instrument rating to become a Certified Flight Instructor, as the regulations you quoted state. You just have to be rated for the type in which you are instructing.


Why does condensation form on the wing especially during take-off and landing? To start off, yes this question was asked before, yet I don't find the answers satisfying and here is why:

It appears to me that this phenomenon only appears during the approach phase of a flight and during low speed turns, or rather when the angle of attack is rather high. Also, usually the flaps are deployed when it happens, yet I'm not sure if that makes a difference.

Considering this, the answers wouldn't necessarily answer my question. They all talk about how there is a lower pressure above the wing, which causes the dewpoint to drop and thus makes the water condense. But is there a "lower" lower pressure when the angle of attack is higher and therefore making this phenomenon occur more often? Or is the point at which the laminar airflow gets turbulent (which moves forward as the aoa is increased) an important factor here?

Here is a picture to show what condensation I mean:

And a more extreme one:

Yes, speed and flaps do make a difference.

The lift created by the wings is approximately constant over the duration of a flight. With full tanks, it is higher at the beginning of the flight, and when the aircraft banks, it is again higher to create the centripetal force for changing its course. But the difference is small¹.

Lift is caused by a pressure difference between the two sides of the wing. In cruise, this difference is low but extends over much of the wing's chord. At low speed, however, the suction on the top surface has a peak right aft of the leading edge, so the maximum suction is bigger than it is in cruise. Exactly this changed pressure distribution causes the humidity to condense, because it lets the air's relative humidity rise above the condensation point. In cruise, the pressure change is lower and the dew point is not exceeded. Also, since the airplane flies slower when close to the ground, the air has more time for the condensation to develop.

See below for a color-coded plot of the speed distribution over a typical airliner airfoil in the landing configuration. Red symbolizes the lowest speed (highest pressure), while purple stands for the highest speeds with the lowest pressure. Such suction peaks must be avoided in cruise to enable the aircraft to fly at a high cruise Mach number.

Airliner airfoil with high lift devices in landing configuration (picture source)

¹ The fuel fraction of airliners rarely exceeds 40%, and the added lift in a 30° bank is only 15%.

it appears to me that this phenomenon only appears during the approach phase of a flight.

Flying at high altitudes where it is -40°F fuel in the wings cold soaks.

That is my answer for the first two pics of the commercial aircraft above, the one pic of the vapor bubble or whatever about the fighter jet I would remove from the discussion too many unknowns about the picture regarding speed and the maneuver.  Commercial Jet aircraft flying > 30,000 feet altitude for X amount of time the wing becomes a nice cold plate increasing the likelihood and making it more common to see during the approach/landing phase of a commercial flight.


How close do you have to be to an underwater black box to detect it? The news keeps talking about the black boxes on aircraft that end up in water, and one thing that keeps coming up is the underwater locator beacon that transmits a signal for 30 days if it gets wet.

What kind of signal does it transmit and what kind of range does it have?  I'm guessing that the depth of water that it is in will affect how far away that it can be detected, but by how much?

This excellent explanation is taken from Avionics News in 2006:

FDRs are equipped with an Underwater Locator Beacon (ULB). If you look at a picture of an FDR, you will almost always see a small, cylindrical object attached to one end of the device.

If a plane crashes into the water, this beacon sends out an ultrasonic pulse that cannot be heard by human ears but is readily detectable by sonar and acoustical locating equipment.
There is a submergence sensor on the side of the beacon that looks like a bull's-eye. When water touches this sensor, it activates the beacon.
The beacon sends out pulses at 37.5 kilohertz (kHz) and can transmit sound as deep as 14,000 feet (4,267 m). Once the beacon begins "pinging", it pings once per second for 30 days.

Newer FDRs can now transmit as deep as 20,000 ft.
The following table is taken from a fascinatingly detailed article on Hydro International about the retrieval of black boxes. It shows the radius you can pick up the signal of a pinger from:

Notice that if pingers were replaced with more powerful transponders, the range could be drastically improved!
The article also points out, that in very deep water:

under normal conditions, the existing pinger would not be detectable from the surface in depths exceeding 2km

I think it does -- per the table in Danny Beckett's answer you have a maximum of 7km range. If the black box is 4km deep in the water, you would have to be no more than 3km from it to hear it.


Could an airliner exceed Mach 1 in a zero-G power dive and safely recover? (I looked for duplicates. I really did.)
Being as it is that "safety" and this are mutually exclusive:
I am stupid. I take a cruising A320, apply TOGA power, and push zero Gs until I exceed Mach 1. How do I get out of this in one piece? And how much faster can I go before I need to start this process of getting out in one piece?

There is actually some data (albeit limited) on this scenario:
On August 21st 1961 this test was performed in a DC-8. When this test was performed they were supersonic for about 16 seconds which took a lot of planning to pull off. You first need to climb higher than the plane typically does to have enough altitude to pull this off, then make sure you understand how the control surfaces are loaded in the dive. You get out in once piece by planning for it and understanding exactly what's going on:

We took it up to 10 miles up, 52,000 feet—that’s a record—and put it
in a half-a-G pushover. Bill maintained about 50 pounds of push. He
didn’t trim it for the dive so that it would want to pull out by
itself. In the dive, at about 45,000 feet, it went to Mach 1.01 for
maybe 16 seconds, then he recovered. But the recovery was a little
scary. When he pulled back, the elevator was ineffective; it didn’t do
anything, so he said, “Well, I’ll use the stabilizer,” and the
stabilizer wouldn’t run. It stalled, because of the load. What he did,
because he was smart, is something that no other pilot would do: He
pushed over into the dive more, which relieved the load on the
stabilizer. He was able to run the [stabilizer] motor, with the
relieved load, and he recovered at about 35,000 feet.

Remember you're diving fast, really fast, so you likely can't go much faster as you will ultimately run out of time to accelerate:

The Mach number itself isn’t used in a dive as a target because it’s
much more accurate to use airspeed. So every thousand feet I would
read off to Bill the airspeed [he needed] at the next altitude. As we
were coming down, I was talking almost all the time because at a
descent rate of 500 feet per second, every two seconds we were 1,000
feet lower. Looking out the window—which I stopped doing—it looked
like it was straight down.

The trick is to not over stress the airframe.

Mach 1 is approximately 67,000 feet per second.  At a max ceiling of maybe 40,000 feet, an airliner couldn't even get close to Mach 1 speed in that distance.  Given enough height it could do it but it would be starting the dive from Space or very close to it.


Why don't commercial jet aircraft have a break-apart, parachute escape system? Imagine that the pilots on a jet aircraft determine that it will crash. Consider what would happen if the design of the craft allowed it to:

Break into four pieces
Each piece is pressurized independently
Each piece is attached to large parachutes, similar to how they bring down Soyuz or other space crafts returning to Earth

Would that not work so that passenger jets are brought down safely instead of crashing?

wouldnt that work for keeping a majority of passenger jets from crashing?

The majority of passenger jets don't crash.

Designing an aircraft like that would incur very substantial weight penalties. The Space Shuttle booster rocket parachutes weight 990kg, each (it needs 3) plus 550 kg for the drogue chute needed to pull out the main canopies. Plus another to pull out the 550kg drogue. Where are you going to put that much nylon?

Then there's regular maintenance of stuff that large and heavy - you will need an entire empty hangar to repack things along with a crew and a crane.

Also consider how you are going to break up a commercial airliner in an orderly manner. It would have to be designed for it and lined with explosives. That's going to be really popular.

Finally, parachutes need time to work. Large parachutes need considerable time. So this whole process only helps if there's a problem in cruise flight, and that's the phase with the lowest accident rate. Parachutes below 1000 feet are just excess weight.

Semi-related Addendum: After Challenger went boom the Space Shuttles were fitted with a crew escape system. It was intended to allow the crew to exit when the craft was under control but unable to reach a survivable landing site. Re-read that carefully: when the craft was under control. The crew exits at reasonable altitudes and the Shuttle crashes under remote control.

Parachutes simply haven't been a viable option for commercial air transportation since the DC-3 era.

The bottom line for most operators is that modern airplanes simply don't crash.  In the West, the probability is just about zero, so no emergency devices like this are needed.


If a Boeing 707 hits turbulence that registers as +5 G on the FDR, would the 787 experience lower G forces due to the flexibility of their wings? A 707 being a much older plane with relatively stiff wings compared to the 787. What percentage would the g forces be reduced on a 787 given its wing flex?

And yes, I mean if the 707 and 787 were flying through the exact same turbulence at the same time.

The 787 will not experience lower G-forces, it will experience them later. If the turbulence is of short duration, the 787 might not register much while a 707 is shaken thoroughly. If the updraft persists, both aircraft will eventually feel the same forces.

When an aircraft enters turbulence, the wings experience more lift and start moving upwards. If the wings are heavy (full tanks) and floppy, it takes quite a while before the fuselage experiences any forces. After the wings reached their upper bending limit, the fuselage starts moving upwards together with the wings. In an aircraft with lightweight, stiff wings, the fuselage follows any wing movement immediately.

G-forces caused by turbulence are instantaneous. The wings will not "cushion" the aircraft to mitigate the force of the turbulence. The additional flexibility of the wings means that they will absorb more energy and dissipate them without damage to the structure.


What's the purpose of yawing? I've never understood the purpose of yawing, i.e., rotating around the vertical axis by activating the rudder. Provided that airplanes have ailerons that allow banking (used for turning), why do they actually need to yaw? Furthermore, I've read that yawing induces an undesired banking because of the different lifts generated by each wing, due to the fact that one wing "feels" a higher airspeed than the other (a similar effect as a car's wheel spinning faster than the other during a turn). So, if yawing is so "useless" or bothering, why do airplanes have rudders? Moreover, could an airplane takeoff, fly and land without rudder?

From a totally practical standpoint, let's say you're in a small tricycle gear aircraft with a freely castoring nose wheel (or a tail dragger) and you're starting your takeoff roll in a calm wind. When you bring the power up, the aircraft is going to want to turn left (why is another question), in other words to yaw about its vertical axis in a counter-clockwise direction, and head for the grass off the left side of the runway. You counteract that adverse yaw by using right rudder to keep the airplane straight. Initially you might have to use some right brake as well until there's sufficient air moving past the rudder. If you had a steerable nose gear, you wouldn't need the right brake.

You reach flying speed, apply up elevator, and lift off. As the airplane rotates about its lateral axis, there'll be some additional adverse yaw as a result of that rotation (again another question). Even if you had a steerable nose gear, that would now be useless as the nose gear is no longer on the ground. Your means of continuing to fly straight ahead is to counter the adverse yaw with rudder, and you would continue to use right rudder as you climb out. If you don't, you'll start turning left.

You reach the altitude you want, level off, and trim for level flight straight ahead. Then you decide you want to turn left. You start the turn briskly with left aileron, but you forgot to use any rudder. If you were looking at the ball on the bottom of the turn and bank indicator, you would see it shoot left. If you had used left rudder while initiating the turn, that wouldn't have happened. You would have started a coordinated turn.

Now you're coming back to the airport, and there's a crosswind from the left. You decide you want to counter that crosswind by slipping into it. In other words, you want the airplane to travel sideways at a speed that matches the crosswind while still having your nose pointing straight down the runway. So, you lower the left wing and to keep the airplane from turning, you use right rudder to keep the airplane aligned with the runway. You match the crosswind by adding or decreasing your bank.

There are other uses of rudder, and especially in aerobatics.

I once flew a few loads of skydivers. The jumpmaster sat behind me, and to help him in positioning for the drop zone, he wanted flat turns. In other words, he wanted the airplane turned while keeping the wings level. So, if he wanted a left turn, that meant left rudder and right aileron. Uncomfortable from a pilot's standpoint.

Finally, back in the 1960s when I was working on my instrument rating, I had an instructor who taught that the best way to track a localizer in close was to use rudder only for small corrections. Personally, I don't like that method, but it's one way of doing things.

A useful thing, the rudder. You need to be able to directly control movement about all three aircraft axes.

There are two main reasons: control on the ground and efficiency in flight.

When an aircraft is rolling on the ground, the only way to control its direction is with the rudder. When a pilot both takes off and lands an aircraft they use the rudder to steer. If the aircraft had no rudder, it would likely roll off the runway.

In flight, the rudder is used to keep the fuselage parallel to the line of travel. For example, if the pilot makes a turn without using the rudder air will hit the side of the aircraft and the drag on the plane will be significantly higher.

Another cause of inefficiency in propeller aircraft is what is known as P-factor. This is a yawing of the aircraft due to asymmetrical force in the propeller causing drag. The pilot must hold down the rudder constantly to prevent this. It can become quite tiring to do so in long flights.


How accurate is the barometric altimeter in the Tu-154? If the Smolensk disaster was to be traced down to a single decision (other than attempting landing in the first place), it would probably be the choice of radio altimeter to control altitude over a very unfortuitously shaped terrain (a wide valley, with steep slopes). This made the airplane to descend to 80 meters above the bottom of the valley, instead of 80 meters above the runway located 60 meters higher.

Someone mapped the black box recordings of the navigator's altitude readouts to speed and terrain profile, interpreting them as barometric altimeter readouts and it came out as an unreasonably bumpy ride (the orange line). I tried to follow up with mapping these same readouts at the same intervals, but relative to ground surface - treating them as radio-altimeter readouts - and it follows the blue line; judge for yourself which can depict a large passenger plane trajectory more accurately.

An unbiased comparison would include both advantages and disadvantages of the two types of altimeters. In this specific case (unknown, uneven profile terrain) the one main disadvantage of the radio altimeter is obvious: it doesn't provide accurate information about altitude of the airplane relative to the runway. I wonder though, what redeeming properties does it have - what are the advantages (if any) of using a radio altimeter over a barometric altimeter during landing - any inherent flaws of the barometric altimeter, like accuracy, reaction speed, or such, in which one type excels over the other?

(yes, I'm asking for a biased comparison; one with focus on superiority of one of the other. I realize both have their correct applications, both have strengths and weaknesses, applications where one or the other is better. Here I'm specifically asking for one side of this argument; half of the full image; look at it not as "why is A better than B" but "which traits of A are better than B")

A barometric altimeter is required to meet certain operational standards for use in an aircraft under instrument flight rules. We talked a little about this in another question with references to the relevant FAA requirements for the instrument.
I'm certain there's an equivalent in the Polish regulations, and while I don't know where you'd find it I would bet it's broadly similar in its requirements.

A radio/RADAR altimeter is typically accurate to within 20 feet within its operating range (typically <= 2,500 feet AGL). There are varying TSOs for radio altimeters, so you'd have to look up the standard a specific unit was built to in order to get exact numbers.

One of the core issues underlying this accident which you highlighted in your question is that a barometric altimeter and a radio altimeter are two different devices, measuring two different things, so it's not really reasonable to compare them.

Barometric altimeters measure altitude above a standard reference (usually sea level) by using a known/standard pressure lapse rate (~1 in.Hg per 1,000 feet) and measuring the difference in pressure at the instrument.

The readings given by a barometric altimeter are affected by weather conditions (mainly temperature), so the displayed altitude may be 'incorrect' (relative to say GPS altitude above mean sea level).
The readings given by a barometric altimeter are not affected by the local terrain, so peaks, valleys, and tall buildings won't change what it shows.

Radio altimeters measure the distance to whatever radio-wave-reflecting object is below the unit (typically "the ground" - whatever terrain happens to be under you) by detecting how long it takes a radio pulse to be reflected back.

The radio altimeter reading is not affected by weather conditions (temperature) as these don't affect the pulse reflection time.
The radio altimeter is affected by local terrain (peaks, valleys, etc.) as this changes the distance the radio pulse has to travel.
The radio altimeter reading is affected by any object that reflects radio waves (buildings, other aircraft passing below you).
The radio altimeter reading may be affected by "slant range error" just like DME, (in practical terms this is less of an issue for radio altimeters: The radio altimeter points "straight down" so the slant range error is generally small unless the aircraft's pitch or roll attitude is extreme).

So to directly answer your question, barometric and radio altimeters aren't comparable in the way you're asking: Because they measure two different things it's not possible to say one is "superior" to the other. They are different tools, serving different purposes: It's incumbent on the pilot to be aware of the limitations of whichever tool they happen to be using at the time (and to ensure that they've selected the correct tool for the task at hand).

A radio altimeter is probably better because of its independence from weather-related pressure systems which barometric altimeters are really horrible at. There are many small pressure variations in a given area which the barometric one cannot compensate for all the time. The radio altimeter works batter in this area because a pilot would not need to reset it as often and when it encounters weather, it will not mess up.


Is there any particular reason the A380 doesn't have a centre wing tank? Today I learnt something new, but apparently the A380 has no centre wing tank, which leads me to ask, is there a specific, design reason for this? Or did Airbus just think those huge wings were big enough to hold all the fuel they'd need?

Although, I've heard rumours that the A380F if built would have had a centre tank (no idea how true this is), but this shows the engineering is possible, Airbus just chose not to go with it for the passenger version. Any reason why?

It simply doesn't need one. Depending on the source, the A380 has a range from 8200 NM1 to 8477 NM2. The current longest scheduled flight is AKL-DOH, which is 7848 NM3. So the current configuration is capable of flying any of the current routes.

As far as the A380F, it really wouldn't make sense to add a center tank there either. The extra fuel weight would mean less cargo capacity available.

 1 Wikipedia

 2 Aerospace Technology, 11/19/2013

 3 Wikipedia

The A380 simply does not have enough space left on the lower deck, which is why they moved all the fuel into the wings. That is likely the reason for the poor performance of the A380, as the wings turned clumsy and produce a lot of drag, which than again requires a large empennage.

With an A380F, where you do not have crew accomodations on the lower deck and no "luggage" to be placed there, you would have enough space. So you could install a center fuel tank and add stream lined wings, but that would mean new wings just for the A380F, which is a way pointless.


What's the reason for the local flap extensions at the shockbody locations? This weekend I was on a Airbus A319, and I noticed that the flaps have small extensions at the location of the shockbodies (indicated in the picture with the red circles)
I was wondering what the reason is for these extensions?
My guess is that it could be to compensate for the lower local lift generation caused by the presence of the shock bodies, but I'm not sure. I'm also interested in knowing why they have different sizes at different locations.

The anti-shock bodies also serve as fairings for the flap actuators. When the flaps are extended, the anti-shock bodies move down as the flap mechanisms extend. The upper surfaces of the anti-shock bodies are open to allow room for these mechanisms to extend.

The extensions to the flaps are to cover the openings of the anti-shock bodies when the flaps are retracted to provide a more aerodynamic surface. Evidently the outer locations have larger openings to cover.

Below is an image of a different aircraft and flap track design, but the principle is the same. You can see some of the hardware that sits in the fairings, and the covers that allow the hardware to extend out of the fairings.

Source

When the flaps are retracted, you can see that the flaps close out the top of the anti-shock bodies, and the outer position is closed out further aft.

Source

I'm not sure, but I think that those are trim tabs.


Seating distribution in passenger aircraft Recently I was checking in to a flight and was asked if I'd like a window or aisle seat as usual and choose a window seat. I was then told that there are no more window seats available but I could get an aisle seat without someone sitting next to me and then just take that window seat. The plane was an ATR-72 so the rows were 2+2 seats.

I know about weight distribution to the front/back but I couldn't come up for a good reason to do this. What could be the reason for not giving me that apparently free window seat right away?

There are certain restrictions due to which the airliner didn't give you the seat even if you were ready to pay extra for it (Depends on the operations policy by the manufacturer and the aircraft).

It's mostly the weight restrictions for the flight to take-off as there might be some obstacle for the flight during take-off(hoarding on the end of runway, climate etc.). If the weight is too much then it will result in a disaster so equal weight distribution is mandatory.

Moreover in the end it's airliner which has to suffer because the seat occupancy get's affected and it has huge losses incurred by not leaving to its capacity.

The only plausible reason is that the airline charges a different rate for the window seats, and you didn't purchase a ticket at the proper price point to get it.  It has no effect on the airplane whatsoever.


What are good resources for learning more about communications? As title says, which book/web site/etc.. are available for learning proper communication (for Private Pilot License)?

Phraseology is standardized by the ICAO (but countries can notify differences to the standard) in Annex 10 and other documents. The ICAO quick reference guide presents phraseology examples for various situations (taxi, approach, emergency,...). If you are interested in recommendations concerning radio communications in general (not just what directly concerns the pilot), Eurocontrol released a European Action Plan for Air Ground Communications Safety.

Many CAAs also have some form of phraseology reference manual available for free. The general procedures and the phraseology will be almost the same from one country to the next, but variations do occur.

US:

The AIM has a section dedicated to radio communications which details procedures, phraseology and provides general recommendations. Communication examples illustrate the general principles.
The FAA also published an order prescribing ATC procedures and phraseology (but this is a very dry read. Not where I would start)
The Instrument Procedures Handbook contains information regarding radio communication procedures specific to instrument flying (e.g. how to receive a clearance at a non-towered airport)

EU:

Eurocontrol released a guide to phraseology for GA pilots describing good communication practices, phraseology for different flight phases and aviation acronyms. It also has pictures (picture books are always better ;-) ).

UK:

The CAA release a radiotelephony manual describing the phraseology for different flight phases with examples at the end of the manual. It also describes the differences between ICAO and UK radiocommunications procedures (eg FL ONE HUNDRED instead of FL ONE ZERO ZERO).

France:

The SIA has a phraseology training manual with phraseology examples for each flight phase and for using different flight services (ATC, AFIS,...)
The official text for radiotelephony with phraseology in French and English

And many more...

Knowing the phraseology is one thing, but understanding what is being said on the radio can be quite difficult. If you want to practice listening to and understanding radio exchanges, you can find ATC recordings on YouTube or go to LiveATC for ATC communications from all over the world.

VFR Communications for Idiots (West Wings)

Radio Mastery for VFR Pilots Workbook (book)

FAA safety circular on phraseology

The FAA holds regular safety seminars on communication

ICAO Standard Phraseology

Phraseology Guide for GA Pilots in Europe


In case of a drone strike with an airplane below 400 feet, who is at fault? If a plane is flying VFR (see and avoid) below 400 ft, and the pilot collides with a drone due to not seeing the drone until it's too late to take evasive action, then would the pilot be at-fault for insurance purposes? Would the drone operator (or the pilot) have violated any federal regulations for not keeping clear of the other craft?

Conditions:-

Class E or G airspace
out of the 5nm radius of an airport
sparsely populated area
operator of drone is not within 500 ft of where the collision occurred (i.e. for the purposes of FAR 91.119 (c)).
I have a smaller piston engine plane in mind, but I'm assuming that the outcome would be the same for faster jet aircraft too

The FAA has some rules pending about this, you can read them here but for drones under 55 LBS one of the proposed rules is,

  Must yield right-of-way to other aircraft, manned or unmanned.

and since you bring up class E it should be noted that

  Operations in Class B, C, D and E airspace are
  allowed with the required ATC permission.

if/when this goes through it looks like its the drone operators fault since the plane had the right of way

According to the FAA's website in relation to model aircraft they state that,

  (4) the aircraft is operated in a manner that does not interfere with and gives way to any manned aircraft;

this is pretty much a blanket statement that maned aircraft have the right of way but the FAA handles most things on a case by cases basis so in the end of the day it could go either way.

Drone strike with plane below 400 feet - who's at fault?

According to this article (FAA to Drone Operators: Keep Off Airports, Stay Below 400 Feet) it appears that the pilot of the plane is guilty for the collision. If the drone operator respected the FAA rules (line of sight, below 400 ft and max. allowed weight, far from the airports) he can not be declared guilty for the accident.

Federal Aviation Administration (FAA) chief Michael Huerta says the agency already has regulations in place to ensure safety in the skies.
Huerta says the agency already has rules that prohibit operators of personal drones from flying into airports and soaring over 400 feet in the air., Source


How can the lift induced drag for a wing be calculated? I have found a lot of information to calculate drag coefficients and I know that total drag can be calculated by
$$ D = \frac{1}{2} \rho u^2 S C_d $$
However I was wondering, if I substitute the zero lift drag coefficient into this equation is it correct to assume the value produced for the drag force would be the parasitic drag whilst the remainder of the total drag is made up of lift induced drag?

Induced drag is the portion of the lift force that opposes motion.  Induced drag exists even when the drag coefficient CD in your equation is zero.

Lift is perpendicular to the air flow relative to the wing.  Imagine a wing moving right to left across your screen.  The air is moving left to right relative to the wing.  If there's no vertical induced airflow then the lift is vertical and there's no induced drag.  However, lift deflects the air down, so typically the air relative to this wing is not moving exactly left to right, but is tilted down slightly.  Hence, the lift, which is perpendicular to that airflow, is actually tilted back (right) slightly.  That means a (typically small) portion of the lift is "pushing this wing back," opposing its right-to-left motion.
If you know trigonometry, induced drag is lift times the sine of the inflow angle, $ L\sin \phi $.  The inflow angle is the angle of the airflow relative to the horizontal in this picture.
There's a picture of exactly this at the bottom of this page in the induced power section.  (Induced power is the power required to overcome induced drag.)


How do wings generate lift? Just the basic question that every aviation enthusiast must be curious about: exactly how does a wing generate lift?

To get to the bottom of it, it might help to look at lift at a molecular level:
Every air molecule is in a dynamic equilibrium between inertial, pressure and viscous effects:

Inertial means that the mass of the particle wants to travel on as before and needs force to be convinced otherwise.
Pressure means that air particles oscillate all the time and bounce into other air particles. The more bouncing, the more force they exert on their surroundings.
Viscosity means that air molecules, because of this oscillation, tend to assume the speed and direction of their neighbors.

Flow over the upper side of the wing
Now to the airflow: When a wing approaches at subsonic speed, the low pressure area over its upper surface will suck in air ahead of it. See it this way: Above and downstream of a packet of air we have less bouncing of molecules (= less pressure), and now the undiminished bouncing of the air below and upstream of that packet will push its air molecules upwards and towards that wing. The packet of air will rise and accelerate towards the wing and be sucked into that low pressure area. Due to the acceleration, the packet will be stretched lengthwise and its pressure drops in sync with it picking up speed. Spreading happens in flow direction - the packet is distorted and stretched lengthwise, but contracts in the direction orthogonally to the flow. This contraction is needed to make space for that wing; in supersonic flow it will decelerate for the same purpose. Once there, it will "see" that the wing below it curves away from its path of travel, and if that path would remain unchanged, a vacuum between the wing and our packet of air would form. Reluctantly, the packet will change course and follow the wing's contour. This requires even lower pressure, to make the molecules change their direction. This fast-flowing, low-pressure air will in turn suck in new air ahead and below of it, will go on to decelerate and regain its old pressure over the rear half of the wing, and will flow off with its new flow direction.
Note that lift can only happen if the upper contour of the wing will slope downwards and away from the initial path of the air flowing around the wing's leading edge. This could either be camber or angle of attack - both will have the same effect. Since camber allows for a gradual change of the contour, it is more efficient than angle of attack.
Flow over the lower side of the wing
A packet of air which ends up below the wing will experience less uplift and acceleration, and in the convex part of highly cambered airfoils it will experience a compression. It also has to change its flow path, because the cambered and/or inclined wing will push the air below it downwards, creating more pressure and more bouncing from above for our packet below the wing. When both packets arrive at the trailing edge, they will have picked up some downward speed.

Behind the wing, both packets will continue along their downward path for a while due to inertia and push other air below them down and sideways. Above them, this air, having been pushed sideways before, will now fill the space above our two packets. Macroscopically, this looks like two big vortices. But the air in these vortices cannot act on the wing anymore, so it will not affect drag or lift. See here for more on that effect, including pretty pictures.
Lift can be explained in several, equivalent ways
Following the picture of a pressure field outlined above, lift is the difference of pressure between upper and lower surface of the wing. The molecules will bounce against the wing skin more at the lower side than at the upper side, and the difference is lift.
Or you look at the macroscopic picture: A certain mass of air has been accelerated downwards by the wing, and this required a force to act on that air. This force is what keeps the aircraft up in the air: Lift.
If you look at the wing as a black box and only pay attention to the impulse of the inflowing and outflowing air, the wing will change the impulse by adding a downward component. The reaction force of this impulse change is lift.
Either way, you will arrive at the same result. By the way: Most of the directional change happens in the forward part of the airfoil, not at the trailing edge!

Lift is a matter of definition
Lift and induced drag are both part of the pressures acting on the wing. If you add up all the pressure forces acting on a wing, their resulting vector will point slightly backwards. The streamwise component is drag, and the component orthogonal to the direction of movement is lift. This is just a defininion, made for simplicity.

A plane flies by several mechanisms. The first is the Bernoulli effect caused by wing camber that generates a pressure differential pushing the wing upwards as it moves forwards through the air. Note that birds have cambered wings. However, it is possible to have a plane with completely flat wings and no camber at all, so it is a mistake to think this is the only source of lift (as some of the answers above have done).

The angle at the wing root is also important. If you stick your hand at an angle out of car window, you will feel it forced upwards. This same effect is accomplished in an aircraft by angling the wings slightly upward relative to the plane of the fuselage.

Finally, you should be aware that the reason a plane stays aloft has nothing to do with lift, but with the surface area it presents to the ground. The primary force holding a plane up is air resistance which is a function of this surface area. The force of this air resistance is much greater than the force generated by the previous two effects. For example, a major design criteria for a plane is whether it has a square fuselage or a round/oval fuselage. A square fuselage will present more surface area to the ground, thus having greater efficiency in staying aloft. For this reason, nearly all early aircraft had square fuselages. However, a round fuselage will be more efficient moving forwards than a square one, so in a plane built for speed, round is better. An aircraft with a round fuselage goes faster, but is less fuel efficient than one with a square fuselage.

The same argument holds true for wing area. The larger the wing, the more air resistance. For this reason, gliders have relatively large wings compared to powered aircraft. The drawback of a large wing is the same as that of a square fuselage: the plane goes slower.

So, to recap, there are three factors that keep an aircraft aloft: vertical air resistance due to downward facing surface area, the angle of the wings at the wing root, and the Bernoulli effect associated with the camber in the wings.


Why does airflow separate from the wing during stall? What causes the airflow separation from the airplane wing, that triggers a stall?

To be more precise, what is the detailed explanation of the physics for why flow separation occurs at certain speeds & angles of attack?

Air flowing underneath the wing at an angle is pushed downwards, regardless of the shape of the lower surface: high pressure has few practical limits.

Air flowing over the upper surface cannot suddenly change direction though because it is driven by an under-pressure gradient. It can follow a slowly curving surface to the limit of the pressure differential between ambient and suction, but too steep a curve and the airflow cannot follow and has to separate: a stall occurs.

Picture source

The answer it's about the DECELERATION  of  the airflow over the wings, due to the Increased AOA  above  the stall margins, then separation takes place from the wing roots and closer  to the trailing edges and moves across  the wings and   towards leading edge and spread outward until reaching the wing tip  (this is done by aeronautical engineers  to preserve the ailerons efficiency little  time after the wing started to stall) , at any speed . There are many videos on Internet that have wings  with " taft's" on top on them  for visualization of  turbulence. At this highest level of the AOA (17-30  degrees depending on the wing profile) the first layer of the airflow is  deflected from the wings surface because it is not energized enough to follow the upper side and unstuck from it. So the airflow is not accelerated on top of the wing 's surfaces .


Why are videos call and voice calls prohibited on airplanes? I'm taking a flight to Japan this summer and noticed that on United, they may have wifi but it says everywhere that no voice calls or video calls are permitted and strictly prohibited during flight. They don't say why, but out of curiosity why is that such a big deal?

Voice/video calls have not been approved by the FAA, and no one is particularly interested in having them approved, due to the frustration it would cause amongst passengers, having to listen to a multitude of conversations in a confined space, throughout the flight. Not to mention the fact that it would clog the limited bandwidth if even a sizable chunk of the passengers wanted to do it.

Virgin comes right out and says it with something along the lines of "For the safety and comfort of our guests, VoIP and Video Chat is also prohibited".

The FCC does not approve of cell use and airplanes. One of the reasons is it wreaks havoc on cell systems because of frequent cell changes.


In general terms, is a Constant Speed Propellor equiped aircraft more expensive to maintain? I've been looking at possibly buying a used Mooney M20 or a used Cessna 172.  One of the big differences between the two is that the Cessna is a fixed prop, and the Mooney is a constant speed propellor.  While CSPs sound really nifty and efficient...I can't help but wonder if they would be more expensive to maintain.  Both in terms of regular maintenance and just the fact that it has more parts that can break.

Is a CSP more expensive to maintain than a fixed pitch prop?  And why? If you can include some numbers that relate to the planes mentioned, that'd be cool too...

Yes, they are more expensive because they are more complex.  I would not avoid buying a plane simply because it has a CS prop because, in the grand scheme of airplane ownership, CS prop maintenance has a small impact on your hourly cost.  Maybe ~$1/hr for a piston single with repetitive ADs.

Now, the maintenance of a CS prop can range from a simple visual inspection of about \$100 USD to a complete replacement of the prop (up to \$15,000 USD, maybe more for large props).  An owner will likely not do an "overhaul" when the prop reaches TBO but will instead opt for an IRAN (Inspect, Repair As Necessary).  This is typically a little cheaper than a full blown overhaul and, from a practical perspective, extends the life of the propeller as an overhaul would.  At some point you'll end up grinding blades and balancing the prop but that's not annual maintenance.  I've seen the cost quoted at around \$1,500 USD for a high performance piston single IRAN which comes to less than $1/hr for a private owner.

All in, a CS prop only adds a small amount to the hourly operating cost.  In my opinion, the performance gains are worth the cost in most cases.

A fixed prop is relatively low maintenance. Basically, all you do it file out cracks for maintenance.

A constant speed prop has moving parts. There is usually an oil linkage. Usually, a constant speed prop has to be overhauled at regular intervals like the engine.


Why don't tanker aircraft have ejection seats? Apparently, the KC-135 has no ejection seats (they used to have parachutes to allow the crew to manually bail out, but those were removed in 2008 to save money), and, according to this Quora discussion, that's the case for all tankers (presumably excluding the ones converted from bombers), not just the KC-135.

This seems somewhat illogical to me, as tankers act as potent force multipliers; to quote the linked post:

  It is quite possible that a sophisticated opponent will go after the tankers, as an easy way to disable a lot of aircraft without actually having to shoot them down. Doesn't really matter if they go down from a missile hit or lack of fuel. The math on that one looks very good - shoot down a tanker, and you have probably shot down four or five smaller, agile, hard to hit strike aircraft.

Not only that, but tankers are big, slow (for military aircraft), and generally devoid of any defensive armour or armament, making them easy targets relative to combat aircraft.

Even in peacetime, the role of a tanker aircraft inherently places it at a much greater risk of a midair collision than most aircraft are ever exposed to (example) - and, with most MACs, the only way to survive is to abandon aircraft.

So why don't tanker aircraft have ejection seats for their crew?

When I was flying the KC-135 tankers - A model and Q models - all crew members had parachutes, and all parachute packs had supplemental oxygen bottles that were good for at least 10 minutes - which was enough time to descend to the point where you did not need supplemental oxygen. If you had to bail out, it would be through the crew entry hatch, on the port side just behind the pilot's seat and in front of the boom operator's seat. If you had to pull the handle for bailout, the crew entry hatch would be jettisoned and a metal air dam would be pneumatically deployed about 4 feet down at the leading edge of the hatchway, to provide a wind block to allow crew members to fall free of the aircraft before getting into the slipstream. This prevented crew members from being blown back onto the body of the aircraft.

I have never heard of any tanker crew ever having to bail out of a KC-135, so perhaps this is why they got rid of the parachutes? Of course, I retired more than 20 years ago, and much has changed since then. But the KC-135s are still flying, even though they are older than anyone flying them today.

To answer the original question - both the KC-135 and the KC-46 are modifications of civilian aircraft, which do not have ejection seats; whereas fighters and bombers are designed for their specific mission.

Finally, I'm not aware of any cargo aircraft that have ejection seats, either.

Ejection systems have saved many lives in non-combat related incidents. When it comes to ejection, These systems should not be restricted to combat craft.  Ejection systems can be devised to work in almost any craft provided that the extra bulk is not an overwhelming part of the useful load.
By not including ejectors in more aircraft, designers are denying air crews the best lifesaving equipment there is. While it’s true that most aircraft go their whole life without crashing, some of them do crash eventually, some suffer from poor designs, malfunctions or pilot error, and yet we expect crews to go down with the ship. The reasons can include, cost, weight capacity and other performance considerations, but these are poor reasons to exclude life-saving technology.
This sends a message that your life is worth less than the cost of the system/design and the cargo capacity that you displace.  Ejection is by far the best option. It's self-contained, requiring only that you strap in to the same seat you always use and put on helmet. It requires far less reaction time. It can save your life far past the point that maneuvers become useless.  Depending on velocity and attitude, you only need a few seconds and a few hundred feet, to deploy the system properly. Even near the ground, ejection can be a survivable alternative to what would otherwise be a deadly crash landing or aborted take off. Good ejection systems are very expensive and sophisticated - operating as gyro-guided autonomous small rocket crafts in their own right.
The best way to think about ejection is to think about a pilot and crew over the span of their entire career. They may only need to use an ejector one time, if at all, but the number of lives it could save warrants it’s inclusion. It obviously makes less sense for passenger aircraft, due to the impossibility of including so many and the moral/ethical restraints against abandoning passengers. Nevertheless, It makes perfect sense for cargo-liners. Ejection systems for entire passenger craft/modules is fraught with difficulty and is not so close to being readily available tech, or nearly as viable as cockpit seats. But even these difficulties might be overcome if not for cost, efficiency, and 'return on investment' considerations. Ultimately, I f we really wanted to make such a craft because we considered lives to be invaluable, we certainly could. That said, it would be much more costly, burn more fuel, be heavier, carry fewer people, and cost more per ticket.
Such ideas can seem extreme, wasteful, or even crazy until you put things into the perspective of a situation where it would be the only thing that can save your life. The truth is, very, very few of us experience those kinds of situations and live to talk about it. Maybe we should give those voices more weight in such discussions - pilots whose lives may have been saved because this expensive, heavy, "crazy" equipment was there. In the end, usually, the main reason we exclude such systems is simply because we don't consider them to be 'worth it', not because we can't do it.


What has happened to make me experience negative G with the control stick FULL AFT near the top of a loop? I experienced negative G with the control stick FULL AFT near the top of a loop.

My questions:

Aerodynamically, what happened? Was the wing meeting the air at a negative-lift angle-of-attack (creating a skyward lift force) at this instant?
How can I change my technique to prevent this?

You were too slow.

Start the loop with more speed and pull more (if the g limit of your aircraft allows) at the beginning, so you have more speed at the top.

  Aerodynamically, what happened?

Without aerodynamics, you feel -1 g at the top of the loop, simply by having inverted the plane. Since the plane feels the same acceleration, both of you move together - until vertical speed picks up and drag will keep the airplane back. This is when you have the sensation of negative gs. In order to stay with positive gs, you need a centrifugal force to compensate for earth's gravity. This is the product of pitch rotation speed squared and the radius of the loop. If your flight speed drops, the radius will drop as well and leave little centrifugal force, even at a high rate of pitch. Dan Pichelman correctly describes how this kind of loop looks to an outside observer.

So there is little aerodynamics involved here besides drag - low speed will reduce all aerodynamic forces. The angle of attack on the wing is insignificant - what counts is the inertial force of the moving aircraft (besides gravity, of course).

If your airplane places you behind the center of gravity, pulling hard will give you the sensation of negative gs even when the aircraft as a whole is still at positive gs. Any maneuvering will add inertial effects which grow with the pilot's distance from the center of gravity.

  How can I change my technique to prevent this?

Fly faster, and be fast enough at the top to push in order to round out the loop, so it will look more like a circle. But make sure to stay within the limits of your plane. Again, Dan is right: It really sucks when the wings fold up.

Negative gs are completely normal at the top of the loop. When I did my first loop in an open-cockpit aircraft (a Boeing Stearman, no less), I did exactly that: Push near the top. However, this did not last long because my instructor immediately whined "pull, pull!". He had not closed the pockets of his flight jacket and started to lose their contents. So make sure that all equipment is secured before doing aerobatics.

Gravity and/or "centrifugal force" don't contribute to force "felt" by the pilot (and by the aircraft structure.) Only aerodynamic forces do. Actually the apparent centrifugal force created by the rotation ABOUT THE AIRCRAFT's CG is "felt" by the pilot, but that would appear to contribute a positive G-load component to a pilot sitting in front of the aircraft's CG during a loop.  This would surely only be significant in an aircraft with the cockpit far in front of the CG, rotating very rapidly about the CG.

For negative G to occur near the top of the loop, the wing indeed must have been at a negative angle-of-attack at that point, even with the stick full aft.  Here's how that could happen:

At the top of the loop, the airspeed was quite low, meaning that the flight path had a very tight (small) radius of curvature of the flight path due to the low airspeed.  Note that gravity and aerodynamic force both combine to determine the aircraft's total curvilinear acceleration through space, and gravity is forcing the flight path to curve earthward at the top of the loop, even if the aerodynamic lift force is very small or even negative (skyward).  Since various molecules of the aircraft are moving in different directions at any given instant (think of a flat spin for an extreme example), the relative wind (meaning the undisturbed airflow-- the apparent wind created by the motion of the aircraft-- the direction the airflow would be coming from if not altered by the disturbance created by the physical presence of the aircraft) "felt" by any given point on the aircraft's surface curves to follow the path of the turn.  This means that the actual airflow will also have a curvature to it. If the loop has a very tight radius at the top, this effect will be extremely significant.

Unless the fuselage is able to bend like a banana (with the "canopy" side being the concave side and the "belly" side being the convex side) to conform to the curving flow, we can visualize (loosely speaking) that the curving flow will tend to "push up" against the bottom ("belly" side) of the horizontal tail and pitch the nose toward the aircraft's belly-- toward the sky in this case.  It's as if we're giving the aircraft some negative decalage.  Due to this pitch torque, full aft elevator may be insufficient to command a positive AOA at the wing. A faster entry speed (or stronger initial pull) increases the airspeed over the top of the loop, increasing the radius of the loop and avoiding the issue with negative G.

Another way to think of the "curvature in the relative wind" is to note that a pitch rotation always leads to some amount of "pitch damping" effect. Pitch damping and curving relative wind are two sides of the same coin.  Either way we look at it, we see that the "free-stream" or undisturbed relative wind tends to be directed "up from below" (i.e. has a vertical component aimed from belly toward canopy) at the rear end of the fuselage during a loop, which tends to pitch the nose "down" (toward the belly), decreasing the angle-of-attack of the wing.  The actual airflow over the rear end of the aircraft will be affected by the wing's downwash, but a given nose-up elevator input will still end up creating less nose-"up" pitch torque when the flight path is curving in the nose-"up" direction (toward the canopy), than it would if the flight path were completely linear and the pitch rotation rate were zero.  The curvature of the relative wind--the pitch damping effect-- effectively reduces the elevator's "purchase" or "leverage" on the air and reduces the amount of nose-"up" (towards the canopy) pitch torque created by the raised elevator, compared to what we'd see at the same airspeed if the flight path were linear.  A normal constant-airspeed turn also involves some pitch rotation, so the same effect is present to some degree-- more on this later.

These dynamics are a reason why an all-moving horizontal tail can be a good thing-- especially in radio-controlled model aircraft where stick force is provided by springs in the transmitter and thus the stick-force-per-G characteristics aren't a concern.  Fully all-moving stabs may be poor in terms of giving a nice increase in stick force with G-loading but look at the tail of this Fox aerobatic glider -- the elevator comprises more than half of the total horizontal tail area.  (This is NOT the glider in which I experienced negative G over the top of the loop!)

In my personal experience, if the loop is in the clockwise direction and 12 o'clock is the top of the loop, and the airspeed gets too low over the top of the loop, the negative G (with stick full aft) will occur from about the 12:30 through the 1:30 or 2:00 positions, not at the very top of the loop.  It appears that the point of lowest airspeed does not occur at the point of strongest negative G, and the G-load may in fact have be positive at the point of lowest airspeed, which probably occurs somewhere between the 12:00 and 12:30 positions.  I don't know the reason for this.  Perhaps I was mis-perceiving the aircraft's position in the loop due to the unusual attitude and un-accustomed sight picture, but I don't think so.  Since pitch torque commands a change in rotation rate, rather than directly governing rotation rate, perhaps there was simply a time lag between the time the tail started "feeling" a strong change in the direction of airflow due to the decreased radius at the top of the loop, and the time that the aircraft's pitch rotation rate had been altered enough by this pitch torque, relative to the (not necessarily constant) pitch rotation rate that would have been required at any given instant to hold the angle-of-attack constant, to drive the wing to a negative angle-of-attack.  This is only a hypothesis.

The negative G was very mild, but enough to make objects rise up against the canopy.

My recollection is that the problem was avoided if I did not let the airspeed drop below 40 mph at its lowest point.

The curvature in the relative wind is also present in a normal turn and requires the stick to be further aft to command a given angle-of-attack while turning than in wings-level flight.  Due to the low airspeed involved, this effect is extremely noticeable during a thermalling turn in a sailplane.  I know of at least one sailplane in which the total "up" elevator throw is somewhat limited to help prevent stalls and spins, and heavy pilots (who move the aircraft's CG to near the forward edge of the allowable envelope) find it is not only nearly impossible to stall in a turn (absent a sudden sharp gust from below), but difficult to maintain a slow enough airspeed for optimum thermalling, even with the stick full aft.  They simply don't have enough elevator power to put the wing at the optimum (high) angle-of-attack during a steep thermal turn.  During wings-level linear flight, those same pilots have no problem commanding a stall, or putting the wing at the optimum (high) angle-of-attack required to achieve flight at the lowest possible sink rate.

On a more fundamental level, the reason we don't "feel" gravity is that gravity exerts an equal force per unit mass on every molecule of the aircraft and pilot's body, all at the same time, thus creating no stresses or strains with the body or structure, and creating no tendency for the pilot to move toward or away from the seat of the aircraft.  In flight, we only feel aerodynamic forces.  Examples: 0G flight-- total acceleration-- 1G downward-- felt acceleration -- 0G.  Flying straight and level-- total acceleration--0G-- felt acceleration-- 1G upward lift force (per unit mass) generated by wings. Standing still on solid ground-- total acceleration--0G-- felt acceleration-- 1G upward push force (per unit mass) of floor against soles of feet. In all cases "felt" force + gravitational force = "total" force.

IF we adopt the aircraft as our reference frame, THEN we have an accelerated reference frame and we do have to consider centrifugal (inertial) force.  Also, if we consider the aircraft to be a fixed reference point, then it is valid to say that the pilot will tend to "feel" gravity pulling him against his seat in normal upright flight, and against the seat belts in sustained inverted flight.  At any given instant, the total force that we compute that the pilot will end up "feeling" will come out the same whether we choose the aircraft as a reference frame, which requires us to consider centrifugal (inertial) force and gravity, or we choose a true inertial reference frame, in which case centrifugal (inertial) force vanishes and gravity is a force that creates an acceleration but cannot be "felt".  However in an accelerated reference frame it is no longer true that F=ma, so this is not a good choice of reference frame if we want to discover the fundamental cause of the total force acting on the aircraft, the total acceleration acting on the aircraft, and the G-load "felt" by the aircraft and pilot.

To put it another way-- the apparent centrifugal force created by the rotation about the center of the loop (as opposed to the rotation about the aircraft's CG) is a pseudoforce that is simply equal and opposite to the real, aerodynamic centripetal force generated by the aircraft.  That's all it is.  Whether or not we count it in our calculations depends on whether we are using an accelerated reference frame that is tied to the aircraft, or an inertial reference frame such as the earth or airmass (in the latter case, assuming that any wind present is linear and not a rotating such as a dust devil or rotating thermal column etc.)

To help understand the advantage of choosing a true inertial reference frame such as the earth over an accelerated reference frame such as one moving with the aircraft, consider this question-- at an instant in time where the G-load is negative (with the stick full aft) near the top of the loop as described in the original question, if we suddenly took away the atmosphere so that the plane was in a vacuum, while preserving the same initial velocity and the same gravitational force, would the "felt" G-load-- the G-load on the G-meter-- instantly go to zero?  Why or why not?

Outside links pertaining to the curvature in the relative wind in turning flight (not loops specifically)

"Circling the Holighaus Way" by Richard H. Johnson--A key point is that as a glider circles, if the fuselage is tangent to the curving flow near the CG, then it will not be tangent to the curving flow near the nose--and the yaw string will be slightly deflected to the outside of the turn.  There's a bit more to it than that though.

"Spiral Stability and the Bowl Effect" series-- by Blaine Beron-Rawdon-- pertains to stability and control of rudder-controlled rc sailplanes--

Part 1
Part 2


What would be the safest way to drop thousands of small, hard objects from a typical, high wing, GA airplane? The subject pretty much states my question, now I will provide a bit of background.

A family member, who lived on the west coast of Florida Manasota Key, collected tens of thousands of fossilized sharks teeth between the mid-1940s and the late 1970s. I have now become involved in deciding what to do with these sharks teeth. Here is one of the multitude of pictures available showing samples of these types of sharks teeth:

The vast majority of this collection ranges in size between a dime and a quarter and likely has the same level of hardness.

If you've visited one of the beaches in this part of Florida in the last 25+ years, you probably know that finding these treasures is no longer as easy as it used to be.  When I was a kid (late 1970s), I could usually come up with 10+ teeth in about a 2 hours stretch.  However, by the time my kids were of the age where this would be of interest (early 2000s), we were lucky if we found one a day.

What I'd like to do is return these teeth to the area just off shore of this beach thus giving future searchers a better chance of "re-finding" them.

Let's assume for the purposes of this question that the airplane involved would be a Cessna 172S. What would be a good way of doing such a drop without harming the aircraft itself?

I assume just dropping them out the window risks blow back that could damage the aluminum fuselage or tail assembly.

A couple of notes:

This is NOT a question about the legality of dropping items from an airplane in the United States. I am well versed with 14 CFR § 91.15 - Dropping objects, which states:

  No pilot in command of a civil aircraft may allow any object to be dropped from that aircraft in flight that creates a hazard to persons or property. However, this section does not prohibit the dropping of any object if reasonable precautions are taken to avoid injury or damage to persons or property.

I am not interested in a solution harmful to the environment. Thus dropping them in taped boxes or rolled up newspaper would not be warranted, because that would be littering.
I'm certainly aware that renting a boat and dropping them off the side would be an alternative. That said, for the purposes of this question, I am specifically asking how to achieve this using a Cessna 172 (or similar) high wing GA airplane.

Funeral homes sell gum bags for ashes. They dissolve in the ocean, releasing the ashes. You could make satchels and drop them in bundles with the teeth wrapped in kelp.

Inspired by another answer What would be the safest way to drop thousands of small, hard objects from a typical, high wing, GA airplane? (and now I also notice the comment suggesting to freeze the teeth in ice) :  make a giant shark's tooth cookie!   Mix dough and teeth together in barrel, let harden, cut away barrel, and take mister sharktoothcookie for a one-way flight in a plane with door removed.


Does an increase in air temperature actually improve aircraft performance? Mainly because of what pilots learn about density altitude and aircraft performance, any idea that an increase in temperature could improve performance seems counterintuitive. And indeed it is. Here's what got me thinking about it.

In studying for a written test I ran across a question phrased something like this:

  An aircraft flying at a constant power setting flies from a colder temperature to a warmer temperature. What happens to true airspeed and true altitude?

The correct answer turned out to be that true airspeed and true altitude both increased. I knew immediately on the altitude because I remembered reading how very cold temperatures can cause dangerous errors in altimeters, but the airspeed didn't make sense.

I still don't understand why the increased temperature lead to an increase in true airspeed. Obviously a reciprocating engine doesn't perform better in warmer air. We don't install "interwarmers." Does it really mean that warmer air can actually improve performance? Or does this need a deeper explanation?

Drag (and lift) increases with density. Density decreased and so did drag. So at the same power, you can fly faster.

Now I don't know whether reduction of power of a normally aspirated spark-ignition reciprocating engine at constant throttle setting would be higher or lower than the reduction of drag. But the question says power setting.

"Obviously a reciprocating engine doesn't perform better in warmer air."

Why not? Horse Power increases with inlet temperature. Have a look at your engine handbook and look for something like "Sea Level and Altitude Performance". There should be a chart or table that makes that clear. I'm looking at the chart in my Lycoming engine manual for my Mooney, and the chart clearly shows an increase of horse power with inlet temperature.

"We don't install 'interwarmers.'"

No, we don't, but your reasoning is wrong. The premise of the question is that the air temperature changes by itself. By the way, the air pressure increase in a turbocharged/supercharged engine has an increase in air temperature as one component (although the smaller one) to provide for higher engine power. We close the cowl flaps in cruise flight to keep the engine warm, so we get higher engine output when an increase in altitude provides for cooler air to begin with!

"Does it really mean that warmer air can actually improve performance?"

yes, but not much. Air density changes (from altitude change) are much more pronounced.


How can I identify the FAF on this Jeppesen chart? According to this Jeppesen ILS Approach Chart:

How can the FAF be identified?

Would it be the point at which the G/S is intercepted?

What is the difference between FAF and FAP?

The terminology is different between ICAO and the US.
The following definitions are being used by Jeppesen (Introduction to Jeppesen Navigation Charts):

  FINAL APPROACH FIX (FAF) — The fix from
  which the final approach (IFR) to an airport is executed and which identifies the beginning of the final
  approach segment. It is designated in the profile
  view of Jeppesen Terminal charts by the Maltese
  Cross symbol for non-precision approaches and
  by the glide slope/path intercept point on precision
  approaches. The glide slope/path symbol starts at
  the FAF. When ATC directs a lower-than-published
  Glide Slope/Path Intercept Altitude, it is the resultant
  actual point of the glide slope/path intercept.

  FINAL APPROACH FIX (FAF) OR POINT (FAP)
  (ICAO) — That fix or point of an instrument approach
  procedure where the final approach segment commences.

  FINAL APPROACH POINT (FAP) (USA) — The
  point, applicable only to a non-precision approach
  with no depicted FAF (such as an on-airport VOR),
  where the aircraft is established inbound on the final
  approach course from the procedure turn and where
  the final approach descent may be commenced. The
  FAP serves as the FAF and identifies the beginning
  of the final approach segment.

So the FAF looks like this for non-precision approaches:

And for an ILS approach the FAP is number 8 in the following image:

No. You intercept the GS long before FAP.

The FAF/FAP mark the beginning of the last segment. FAF is used for non-precision (non-glideslope) approaches, and FAP for ILS approaches.

The FAP is usually indicated by a Maltese Cross symbol. In the absence of that, the best clue that a fix on an ILS is the FAP is the GS crossing altitude indication.