Is there a maximum airspeed to deploy a ram air turbine? Is there any airspeed limit for deploying a ram air turbine? Can airspeed be determined from the rate of its propeller rotation? Could that data be used to determine altitude?

Is there a maximum airspeed to deploy a ram air turbine?

The ram air turbine (RAT) can be extended and used at any speed above a minimum speed, because under this minimum speed, power is difficult to generate.

Generated power may be decreased below 130 knots, and extension is prevented below 100 knots because of additional drag produced for nearly no power obtained.

The RAT can be extended automatically (loss of engines or pressure) and manually, e.g. logic for RAT extension on A330 (note the inhibition by airspeed below 100 kt and by on-the-ground sensor:

Source: Airbus A330 FCOM - Hydraulics

  Can airspeed be determined from the rate of its propeller rotation?

No, the RAT turns at constant speed to produce a constant AC frequency or hydraulic pressure or both. The rotational speed is stabilized by a governor which adjusts the angle of attack of the blades according to airspeed.

If the governor fails to maintain the speed, there is a security to prevent overspeed and blade damage/release.

Emergency Airplane RATs, Michael J. Zolidis, Hamilton Sundstrand, 2006.

A ram air turbine from Hamilton Sundstrand has a mechanical speed governor to vary the RAT blades angle according to the airspeed, and maintain a constant rotational speed.
At low speed, the blade angle is maintained near-perpendicular to the airflow to extract the most energy possible. When the ram speed increases, the angle is progressively reduced.
HS seems to measure the RAT power at 130 KEAS (Knots Equivalent Air Speed), e.g. the A380 RAT is 62” (1.57 m) diameter and delivers 85 HP (63 kW) at 130 KEAS. This mean at 130 KEAS or above, the full power is delivered.

Uncommanded Ram Air Turbine (RAT) extensions - Airbus

The RAT auto-deploys when both engines fail, or manually from a panel overhead. It's prevented to deploy on the ground, and below 100 KCAS
The speed value is provided by the ADIRU.
The RAT is able to be extended in all flight envelope conditions.

Embraer 190 - Airplane Operations Manual

There is no maximum altitude or speed for RAT deployment
Deployment occurs whenever AC buses are not powered or manually.
RAT deployment takes 8 seconds.
RAT has its full capacity at 130 KEAS or above.
Below 130 KEAS, only the AC bus is powered. DC buses are powered by the batteries, as well as the standby AC bus through a DC/AC converter.

ETOPS CAA

For ETOPS, three electrical power sources are required. If the RAT is one of them, it must be demonstrated as reliable (extension and generation).
The extension mustn't rely on engine power :-)

The most popularized RAT use may be for AC143 Gimli Glider, with a dual engine loss.

More:

RAT article on Wikipedia.
A320 RAT extension and retraction on Youtube.

Bombardier BD700-1A11 Global 5000 (source)
Airbus A320 Flight test (source)
Bombardier CRJ700 (source)
US Navy T-45A (source)
Airbus A330 (source)
Boeing B747-8 (picture by Gregor Schläger, source)
Boeing B777, RAT extension switch (source)


How do I plan for my PPL checkride which will involve a diversion? My CFI has told me that in my checkride I will begin a planned cross country flight and will be diverted to another airport shortly into the flight. My question is, how do I effectively plan for this? I am unable to get for example NOTAMS, weather predictions, runways and their lengths etc. for the airport I'm going to (because I don't know what it is)

From what I have read I will be acting as PIC on the checkride and as such I don't feel like I can comfortably satisfy CFR 91.103 when I don't even know where I will be flying to.

This thread should be a great source of tips and tricks :)

The way to think about this is to think about the purpose of being asked to divert during your checkride.

What the examiner will be looking for is not that you have all of the information for every possible airport you might be asked to fly to.  The examiner is wanting to see that if you had to divert unexpectedly for whatever reason, that you are able to do this safely.  That's the bottom line.

In order to do this, you should start working on the problem during your ground planning, and for the purposes of your checkride, this will be no different to planning any other flight.

Plan for your alternate.  You should have charts, frequencies etc and of course, enough fuel.  Your examiner is not going to ask you to divert to somewhere when you reach your destination, it's going to be somewhere en-route.

As part of any good plan, you are going to familiarise yourself with possible diversions along the route.  If you had an urgent situation (not a dire emergency where nearest available is the only choice) requiring you to divert when you were flying solo after you gained your license, where would you go?

This doesn't mean that you need every possible piece of information for every possible airport but it does mean:

Do I have enough fuel to make possible diversions?
Do I have charts on board covering the areas to the left and right of my plan?   - Have I folded my charts so that it's easy to see what possible diversions there are easily?
Do I have Jeppesen (or whatever) on board and is it up to date?
Have I checked the METARs and NOTAMs for anything significant for those likely diversions.
Do I have my E6B or other planning tool and do I know how to use it fully?
Do I know what ATC agencies I would talk to along the route if I need assistance, even if flying in uncontrolled airspace?

In your notebook for the planned flight, write down the likely diversion airfields with their key details.

The list above should be part of any plan, not just for your checkride.

One of the key things you're going to need to figure out is "how long will it take me to get to the diversion"?  In order to know this, you're going to need to know the wind at the altitude you are going to be flying at. The way I handled this was to draw a circle on my chart, marked with the wind at altitude, then the corresponding ground speed already worked out on my E6B and written into the circle for each cardinal and mid-cardinal point on the compass rose.  You can glance at this little chart to instantly see that if, for example, the requested diversion needs me to fly a heading of 320, I will be doing 86 kts for an airspeed of 100 kts.  This saves you having to actually use your E6B in the cockpit to do this.  Mark off 0, 45, 90, 135 etc.

If you think about it, doing this in planning will prepare you for any *sensible" diversion you might be asked to make.

When it comes to the time of the diversion, the primary thing your examiner is looking for is do you get "aviate, navigate, communicate"?

The second thing the examiner is looking for is "can you safely divert from en-route"?

If you have planned thoroughly, and you follow aviate, navigate, communicate, then almost by definition, you will safely divert.

So your examiner suddenly says, OK, see that completely unexpected giant sandstorm ahead, you need to get down soon.  Please divert to "Mark Watney- Space Pirate" airport.

Avoid the single, most important thing in this whole exercise at this point.  Do no go into heads down mode.  It's easy to do if you are unprepared.  Your head should be down for at most 15 seconds.  Do each thing one step at a time, then scan and lookout.  If you are well prepared and planned, then not going heads down will be easy.

You now need 3 things immediately - everything else can come later.

What heading do I need to fly?
How long will it take me to get
there?
Can I make it?

For the heading, grab your chart, find the airport, then take a rough heading you need.  You don't, at this stage, need to be super accurate.  Within 10 or 15 degrees will be good.  The important thing is to begin flying to towards the diversion.  You can get the ruler out and refine your heading once you've got the initial diversion sorted out.  Don't forget to aviate.  Keep your head moving, keep your scan and lookout going.  When you set up for the new heading and turn on to it, remember the gross error check as you roll out.

How long will it take?  Again, you don't need to be super accurate.  Grab a quick measure of the distance from the chart and your ruler.  Then look at that wind chart you prepared earlier.  Get your estimated ground speed.

Can I get there?  You should know the aircrafts' fuels consumption numbers so do the quick calculation in your head.

During all of this, remember to aviate at all times.  Also, remember to conduct your normal en-route and turn check lists.

Now it's time to communicate.  If you are in controlled airspace, let them know you've diverted then start looking for who you might need to talk to along your diversion and get the next frequencies into the box.

When you are safely flying towards your destination, you can start to do some more detailed in-the-air planning to refine your estimated heading and fuel use if needed.  You can also now deal with "do I have the NOTAMs and METARs" I need?  It's OK not to have them all for every possible airport (you should have them for the most likely ones) because you can always call up ATC.  That's one of the reasons they are there - to help pilots dealing with unplanned contingencies.

Remember, the examiner is looking for prior planning and aviate, navigate, communicate.  If you do this, I hope that you will see that the unexpected diversion is not actually that scary.

This is primarily a planning exercise, not a flying exercise.  Arrive in plenty of time.  Recognise that every minute you spend planning will reduce your stress and workload in the air and aim to be ready to go, twiddling your thumbs and itching to get airborne, 15 minutes before your planned time to walk to the aircraft.

You might notice that I've repeated myself a lot.  That's deliberate.  Prior planning and aviate, navigate, communicate it what this is all about.

Good luck!


Why is the NAV ADR 1 ECAM caution a NO GO as per the MEL on the A320? There isn't much more I can post about the question but in the MEL out of the 3 ADRs if ADR 1 fails on ground the MEL doesn't allow for a dispatch.

It is to prepare the aircraft for a possible Emergency electrical configuration. I hope you are aware of the fact that in an A320, if the AC BUS 1 and AC BUS 2 were to fail in flight for some reason, the RAT (Ram air turbine) extends which in turn powers an emergency electrical generator. When the aircraft is in emergency electrical configuration, only the very essential systems are powered and the others are shed. Some of the systems that are shed include the ADR 2 and ADR 3, leaving only the ADR 1 functional. The ADR 1 will continue to supply air data to captain's PFD. In this situation, the first officer's displays goes blank and the captain assumes the flying duties, if the first officer was the flying pilot when the failure occurred.

If the aircraft is dispatched with ADR 1 deferred, and if it undergoes an emergency electrical configuration, as soon as the ADR 2 and ADR 3 are shed, all the flight displays will go off, including the captain's side instruments which are supplied by the ADR 1. Then you will have to rely on standby instruments to fly which would not be the most ideal condition to be in an already crippled aircraft. Remember, this configuration will force the aircraft into alternate law. Both auto pilots, autothrust and even the flight directors would not be available.


What does "clear of clouds" mean in FAA FAR part 103? In FAR part 103 when they are talking about visibility requirements for flying an ultralight, sometimes instead of giving exact distances, they will just say "clear of clouds".

For example:

                                   Minimum
                                  flight
                                visibility
      Flight altitudes             /1/       Minimum distance from clouds
1,200 feet or less above the
surface regardless of MSL
altitude:
(1) Within controlled airspace      3       500 feet below, 1,000 feet above, 2,000 feet horizontal.
(2) Outside controlled airspace     1       Clear of clouds.

Or here:

                                      Flight
          Airspace                visibility        Distance from clouds

Class G:
1,200 feet or less above the
surface (regardless of MSL
altitude)                       1 statute mile   Clear of clouds.
More than 1,200 feet above the
surface but less than 10,000
feet MSL                        1 statute mile   500 feet below.
                                                 1,000 feet above.
                                                 2,000 feet horizontal.

What does "Clear of Clouds" mean in this context?  Just that I should remain clear of the clouds, or does it mean that the sky must be clear of clouds in the defined space?

And if it does just mean I need to stay "clear of the clouds", how exactly is that defined?  1000ft?  100ft? 10ft?  What exactly?

It means you have to stay outside the cloud while flying. You're expected to use your own good judgment (remember it is illegal to fly into the cloud, and if you don't have proper instruments and know what you're doing, it's downright deadly) but there is no minimum clearance as there is at other times, so if you really felt like a daredevil you could reach out and touch a low-hanging "popcorn cloud" with your wingtip. This term is often used in situations where vertical separation minima from clouds is not practical (to stay 500 feet underneath a VMC-friendly cloud layer would require altitudes as low as 500 feet AGL; there are a lot of hazards to navigation at that height from radio antennae to city skylines)


Could an electric airliner be aerotowed to cruise altitude by an electric "tug" aircraft? The low energy density of batteries make electric aircraft need a high ratio of battery to payload. Take off and climb to cruising altitude could account for a substantial fraction of the energy required for a short haul flight. The point of aerotowing would be be to have less battery (and maybe motor?) requirement and more payload in the towed craft for cruise and landing whilst the tug aircraft could return to the take-off point. There would be the downside of needing to handle the tug landing of course.

Yes, a tug would help, but not greatly so. If your goal is zero-carbon air travel, the tug will stretch the possible range, but the result will still be much too low for practical use.

The principle is similar to using a catapult to save the energy needed for acceleration on the ground. This topic was covered here and shows negligible gains. We also have covered the problems of fully-electric airliners and the weight disadvantage of electric engines, so I will not cover this here again.

If we only look at the energy needed to lift a conventional airliner to its cruise altitude, the magnitude of the problem should become obvious. Here, only the tug is electric while the airliner is a normal A320. We have lots of answers with A320 data, and assuming that less fuel is taken onboard since we get some help in climb, the take-off weight used here is 72 tons. Cruise is in 30.000 ft, so we need to lift 72.000 kg by 9144 m. Energy $E$ is mass times height times gravitational acceleration, or 1.8 MWh or 6,456 MJ. Add to that the acceleration to Mach 0.8 which is 240 m/s at altitude and we need $\frac{1}{2}\cdot m\cdot v^2$ = 2,074 MJ more.

The sum of 8,530 MJ is the energy content of 200 kg of jet fuel, but for a realistic value we need to divide that by the efficiency of the jet. The same has to be done for the electric propulsion case, but efficiency is much better here. If we assume an overall efficiency of 80% in case of fully electric propulsion, the electric energy need to lift an A320 to cruise conditions is 10,662 MJ. To overcome drag and keep systems running, we need maybe another 25% more, so the total energy need will be 13,328 MJ.

Let's consider a tug which carries half its weight in batteries and has the same take-off weight as our A320. Its 36 tons of batteries will hold 25,200 MJ of energy which is just enough to bring both of them close to cruise conditions. On its way back it will glide, so we can save the fuel for lifting the A320 up. How much is that? If we assume an overall efficiency of 33% for jet propulsion, the savings are 600 kg or one twenty-fifth of overall fuel consumption over a 5000 km trip.

Even with the better efficiency of electric propulsion, a heroic effort is needed to save a comparatively small amount of jet fuel. It does work, but the gains are small compared to the effort needed - just consider that the turnaround time for the tug is similar to the flight time of our A320, so as many tugs as A320s are needed to make this system work for all flights.


Someone's shooting at my plane out of the blue! What do I do? Let us assume that you are in cruise flight in normal, civil-accessible airspace (i.e. not any sort of restricted, prohibited, warning, controlled firing, or other specialized airspace area used for firing containment or security reasons) on an IFR flight plan and in contact with the appropriate ATC agency.  Suddenly, without any warning, notice, or provocation, you see tracers whizzing by your plane!  Assuming you are taking appropriate evasive maneuvers, how do you communicate your situation and your responses to ATC in an unambiguous way? What do you squawk?  7500? 7700?  How does this change for air-to-air fire vs ground-to-air fire?

Furthermore, what evasive maneuvers could a civil aircraft reasonably perform in response to a) air-to-air and b) ground-to-air fire?  Or are you better off not trying to evade fire?

For my answer I'm going to assume that someone is genuinely trying to shoot you down for some reason, it's not some sort of legal intercept. If you ignore a legal intercept then I can see a warning shot being fired to get your attention, in which case I would tell ATC I've been intercepted and get on guard (121.5) and communicate with them and follow their instructions, evasive maneuvering in this case is a bad idea. I'm also assuming that no missiles are involved because if you are against a missile equipped enemy in a PA-28 the missile's going to win. It may be called a Warrior but let's face it, it ain't.

In the incredibly unlikely event that someone is trying to kill you without warning then communication with the ground would be my last priority in the situation you describe because ATC cannot help you and you don't have time to explain it to them anyway. If you have a one-button squawk emergency button by all means hit it, but first and foremost you need to keep positive control on the airplane. If you exceed your critical AOA and end up in a spin you are in a worse emergency and if you rip the wings off you are dead.

If it is at night then turning off your lights would be a smart idea, this won't help if the fire is radar guided but it will if the fire is visual. If there's a cloud very close by going into it is probably a great idea.

Next you need to determine whether the fire is air or ground based. If it's ground based you will know because the tracers will be going from below you to above you (hopefully not through you) then your best bet is to throttle up and clear the area as quickly as you can by staying on the same track so you get away from the guns. Diving will increase your airspeed allowing you to clear the area faster but keep it below the vne! Some small left/right turns may help to throw of the aim of the guns, but large turns will only serve to keep you close to the guns for longer. If there's terrain nearby which you can put between you and the guns then use it.

If the fire is air based then the tracers will be closer to the horizontal. If you are being shot at from another aircraft then flying in a straight line is likely the worst possible idea, you need to maneuver. If your airplane is faster than theirs then dive and outrun them, but chances are you aren't going to be able to do that, so personally I would corkscrew down and cling to the nap of the earth. Use your short turning radius to its best effect and don't fly a predictable path. Ideally I would use terrain and/or clouds to try and break visual contact so I can escape.

If you can spare a few cycles in all this you should make a mayday call to ATC and tell them you're being shot at, and whether it is another aircraft or someone on the ground. Say your intentions, your aircraft condition, and the number of people on board. This isn't likely to immediately help you, but it may help to keep someone else from flying into the same situation if there's a nutcase on the loose with an anti-aircraft gun or someone's strapped a 50 cal to their SR-22 and is playing red baron with passing aircraft. If you're lucky local law enforcement or the military may be able to scramble something fast and take the heat off you, but most likely it's all over by the time they get there.


How can I know where wind is coming from by looking at water? For ground reference maneuvers, I know there are many ways that I can know wind direction: smoke, circling, weather reports from nearby airport and so on. However, how can I determine the wind direction by looking at water? I've tried to look for detailed explanations about it but I have found nothing useful. Can somebody help me to understand this issue? I would appreciate if there is any graphic materials.

The easiest way to tell the direction of the wind when you're near the water is to look for something on the shore that indicated wind direction (beaches often have flags on them)

Barring that there are a bunch of other clues that should be familiar to any sailor (or seaplane pilot) which you can borrow:

Boats lying at anchor weathervane and automatically point into the wind
This isn't 100% reliable: Some boats will set two anchors (fore and stern) and won't weathervane. Also when the tide is shifting boats will swing to align with the tide if it's stronger than the wind.
Boats lying at anchor sometimes have a flag on them
Flags on a boat at anchor work the same way as flags on land - they're excellent indicators of wind direction.
On calm bodies of water the wind creates visible surface ripples
The concave side of these ripples is the windward side.

(Visualize the water as being a large bowl of soup - now blow on the soup. The ripples will have the same shape.)
This same principle applies to larger waves as well (other factors could cause the dominant breeze along a shoreline to not be quite perpendicular to the waves, but if your concern is ground reference maneuvers it's "close enough").
"Wind Streaks" on the sea indicate wind direction
Wind streaks are somewhat ambiguous in that they're aligned with the wind, but don't tell you which way it's blowing: You have to figure that out for yourself (for example by looking at the shape of the waves as described above).

Surf spray gives wind speed and direction
Waves breaking will produce spray that blows downwind - I couldn't find a good illustration for this, but the finer spray tends to blow, while heavier drops just fall. The distance the spray blows gives an approximate indication of wind speed.
It would take some pretty heavy seas to produce visible spray at altitude though, and you're more likely to see foam and whitecaps in that case
Foam or Whitecaps provide wind speed and direction
Foam or whitecaps provide an indication of direction (the foam appears to move upwind - into the wind) and speed (it generally takes winds of 10-15 knots or more to produce whitecaps and foam).


What fomula use for calculating pressure altitude? I'm having some trouble making my calculations of pressure altitude match those in apps and text books.

I'm using the formula from Wikipedia:

  (29.92 - altimeter setting) * 1000 + airport elevation

In the app I'm using, the altimeter setting is currently reported as 29.70 with an airport elevation of 22. Using the above formula I would assume:

  (29.92 - 29.70) * 1000 + 22 = 242

Yet the app is telling me it is 229

Even more confusing, when looking at the Airman Knowledge Testing Supplement for Sport Pilot, Recreational Pilot, Remote Pilot, and Private Pilot (FAA-CT-8080-2H), figure 8, page 2-8, the pressure altitude for altimeter 29.7 is listed as 205. I assume this is using an airport elevation of 0, but then I would expect the answer to be:

  (29.92 - 29.7) * 1000 + 0 = 220

So my questions are:

Which answer is correct? Wikipedia, the app or appendix 2?
Why are there 3 different answers?

The formula from wikipedia is a rough estimation. Think of it as a rule of thumb. It's useful if you need numbers for rough calculations. However, the exact formula is as shown below:

According to that formula, I calculated pressure altitude difference for 28.92 and it's 938 feet, as opposed to 1000 feet. Additionally, as you can tell from the formula, the relationship is not a constant linear value. So difference of 1 inch of HG is not always 938 feet, it's changing.

So, the FAA guide is accurate. And I would say your app is accurate enough also, however probably omitting some numbers after decimal, hence the small difference. Of course, you need to add field elevation on top of those numbers as well.


What is "Hotel Mode" on a turboprop engine? I have heard that some aircraft that do not have an APU can run an engine in "Hotel Mode".

What is hotel mode? Are there any advantages to having it instead of an APU?

Hotel mode is a feature on ATR 42/72 turboprops replacing an APU by locking the right-hand #2 engine (PW100) with a 'propeller brake' while allowing the turbine, and therefore also the generator, to run, providing electrical power and bleed air.
ATR describes this as the following:

The propeller brake is fitted on a countershaft on the RH engine reduction gearbox in order to stop the propeller (and the power turbine)

HP (High Pressure) spool drives the DC generator.

Bleed pressure is available downstream the HP compressor and supplies both packs.

This picture should give you sort-of an idea of how it works:

If I gather correctly, the propeller drive shaft is locked, and the (HP) compressor shaft is free to run.
Here's another pic of a PW100 engine:

Hotel Mode seems to be generally disliked for a number of reasons:

It's very loud, especially if you're lifting baggage next to it
It consumes a lot of fuel, since you're running a full engine.
It could be dangerous if the propeller brake is in poor condition and suddenly loses its grip.

This configuration is rare, if not unique. The rival Dash-8 has a separate APU, as does the Saab 2000. It was an optional feature on the Fokker 50. The smaller Jetstream 41 only has a battery.
Source: SmartCockpit ATR-72 documents.


How does VDL relate to ACARS and CPDLC? I know that ACARS and CPDLC are 2 different systems, so I can compare ACARS vs CPDLC, but can I do the same comparation between CPDLC vs VDL? Or a CPDLC it’s a VDL?

If CPDLC it is a VDL, ACARS it is a VDL also?

TL;DR : according to the most usual meanings of these acronyms :

ACARS and CPDLC are applications
VDL is a point-to-point communication technology

To give an everyday-world analogy, the relationship between VDL and CPDLC/ACARS is the same as the relationship between 3G/4G and the web browser/facewhatstime app of your smartphone.

More detailed answer

From a telecommunication point of view, we represent the different functions of a network by different layers. Ideally, one can replace the technology used to implement a given layer by any equivalent technology without impacting the other layers.

The VHF Data Link (VDL) is a technology used to implement the functions of the physical and datalink layers. It means that it is a technology designed to carry any digital data directly from one "device" (aircraft or ground station) to another (resp. ground station or aircraft), independently of its actual content. There are different versions of VDL, namely modes 1 to 4. The current deployments of VDL in europe by ANSPs use VDL mode 2.

CPDLC is an application (application layer). It is directly facing the user, and can use any layer below it (in particular, it can use VDL, HFDL or satcom as layers 1/2)

ACARS is ... a more ambiguous word. It predates the OSI model, and at first it described both the application (text-oriented transmission) and the point-to-point communication technology. Nowadays, pilots use the word ACARS to talk about the application (the printer in the cockpit), and that particular application can, as any application, use any underlying link layer (VDL, HFDL, satcom...). But the old meaning of "ACARS" to describe the original blob of "point-to-point  technology + network + application" can still be found today, for example in the acronym POA (plain old ACARS). By the way, the  point-to-point technology originally used by ACARS is also called VDL mode 1.


Is it always advisable for passengers to wear seat belts when a 747 is on final approach? I noticed in this recent video that some of the passengers are not wearing their seat belts. I realize this is not a typical commercial flight, but is it advisable to wear seat belts when a 747 or similar aircraft is flying so close to the ground, (apparently) during a final approach? Or are the safety precautions here so thorough that it's not actually necessary in this case?

Yes, it is always advisable for passengers to wear the provided safety belts in all phases of flight. This is especially true for aircraft on takeoff, landing, in low level flight, or in any other flight regimes that are especially prone to turbulence or other risk exposure.

A large, heavy aircraft—such as a B747—will be less affected by wake or mechanical turbulence than would a smaller aircraft—such as a CRJ200 or a C172. However, even large, heavy aircraft can be subjected to severe turbulence that could result in injury or death if passengers are not restrained by appropriate safety belts.

Additionally, for flights conducted under 14 CFR 121—which I am confident is a majority of the US operated passenger flights involving the B747 (though not, obviously, Air Force One pictured in the question above)—passengers are generally required to:

  occupy an approved seat or berth with a separate safety belt properly secured about him or her during movement on the surface, takeoff, and landing
  Excerpted from 14 CFR 121.311 (b)


Are any online resources available for ATC recordings? liveatc.net is available, but the voice quality on there, I am given to understand, does not represent the quality of voice available to someone actually sitting in an ATC tower. So I am looking for a source which offers more representative recordings.

EDIT: I intend to use these recordings to evaluate which speech to text engine (Non comprehensive list) works best in the context of aviation, so recordings which best mirror what happens in reality are important to reduce pre-processing.

LiveATC is probably your best shot. The quality you'll get on the stream depends on where the receiver is setup. Since aircraft communications are in VHF or UHF (military) reception is basically within line-of-sight range. This is why often you'll hear the aircraft side of the conversation without hearing ATC.

I would just browse the various streams on LiveATC until you find a good one. OR, if you're near an airport, set up your own receiver!


Why does Chicago O'Hare have a penalty box? I was reading What information does a pilot have about aircraft operating on an intersecting runway? and noticed this on the map:

(airnav.com)

Why is a "penalty box" marked on the map? What is it? What is it used for?

In addition to what vasin mentioned in his answer, a mechanic from O'Hare mentioned hearing ATC direct aircraft to go there when they weren't ready for takeoff by the time they got to the runway in a comment on the video that prompted the linked question:

  They [the pilot of the aircraft not yet ready for departure] sheepishly called and told the tower that they'd need another moment or two before takeoff. The controller goes..."Uh....yeah, no.....cross Runway two-seven left and hold in the penalty box. We'll be in touch."

Apparently ATC doesn't like you holding up the line of departing traffic at ORD.

As mentioned in the comments, the concept of having a paved area on or near the taxiways for planes to park while waiting to be ready for departure, waiting for a gate, or other similar uses is not unique to O'Hare. Most significantly-sized commercial airports have such areas. The primary thing that is unique about O'Hare's is just that it's named and the name is on the airport diagram. And perhaps also this particular controller's snarky sense of humor.


Do left and right mic buttons control both headset microphones? The aircraft I was flying today has a push to talk integrated button on each control yoke. I was sitting in the right seat, but my headset was plugged into the jacks on the left side of the cockpit. When I pushed the right mic button, the tower could hear a carrier wave but no voice transmission.  It was only when I pushed the left mic button that they could hear my transmission. Is this normal?  Seems like pushing either mic button should allow a transmission from either headset.

This is the expected behaviour. The other pilot might make some sound or even talk to someone else. You don't want any noise interfering with your own voice during transmission.  Two microphones picking up your voice might also decrease the sound quality because of the small delay between the two locations.


What is the maximum altitude allowed to fly a model plane/helicopter in England? What is the maximum altitude I'm allowed to fly a model plane or helicopter in England?

According to the UK CAA, a model aircraft is defined as:

  any ‘Small Unmanned Aircraft (SUA)’ (0-20 kg) used for sporting and
  recreational purposes and a ‘large model aircraft’ is defined as any
  ‘Unmanned Aircraft’ (over 20 kg) used for sporting and recreational
  purposes.

The following rule applies to all "small unmanned aircraft", i.e. up to 20kg:

  (3) The person in charge of a small unmanned aircraft must maintain
  direct, unaided visual contact with the aircraft sufficient to monitor
  its flight path in relation to other aircraft, persons, vehicles,
  vessels and structures for the purpose of avoiding collisions.

The following rule applies between 7kg and 20kg only:

  The person in charge of a small unmanned aircraft which has a mass of
  more than 7 kg excluding its fuel but including any articles or
  equipment installed in or attached to the aircraft at the commencement
  of its flight, must not fly the aircraft:

  (a) in Class A, C, D or E airspace unless the permission of the
  appropriate air traffic control unit has been obtained;

  (b) within an aerodrome traffic zone during the notified hours of
  watch of the air traffic control unit (if any) at that aerodrome
  unless the permission of any such air traffic control unit has been
  obtained; or

  (c) at a height of more than 400 feet above the surface unless it is
  flying in airspace described in sub-paragraph (a) or (b) and in
  accordance with the requirements for that airspace

So in theory, a model aircraft weighing less than 7kg could be flown to any altitude, with the only limitation being the requirement to keep in it sight. From 7kg to 20kg the altitude is 400ft, unless you meet the airspace requirements. In practical terms, the requirement to keep the aircraft in sight "unaided" is the main limitation and that restricts the altitude of smaller models in particular.

If it's over 20kg, the model aircraft is subject to all the regular UK aviation rules but in practice a written exemption is required:

  Large model aircraft having a mass between 20 kg and 150 kg are
  subject to all of the Rules or Articles of the Air Navigation Order.
  As many of these Rules are practically impossible for the model
  operator to meet, the modeller must request a specific written
  Exemption to allow the model to be flown

The CAA homepage for model aircraft is here.


What are the services that MROs provide for corporate jets (private jets)? What are typical Costs/Rates of Private(corporate jets) MRO Services in the Middle East/North Africa region?

In general, the MRO services for corporate jets includes, but is not limited to:

Aircraft major and minor inspections and overhaul
Aircraft defect rectification and trouble shooting
On-site defect rectification (away from base).
Compliance of regulatory directives.
Replacement of avionics units.
Aircraft engine maintenance.

The costs associated with these activities will vary depending on the model, location and aircraft condition. If you want actual costs, it would be best to contact the service provider directly.


Why would a C150 tachometer bounce so much that the needle fell off? On a long flight in a C150E, the tachometer started bouncing a little bit and the severity of the bouncing gradually increased until it was extreme: The tachometer was spinning in loops and making a loud screeching sound.
 The counter continues to increment.

Here's a video of the tachometer in the last 10min of our flight. Just after that video, the needle fell off, but the screeching sound persists and the metal pin at the center still seems to be spinning:

What could cause this?

I understand the tach needle is not powered by any gear mechanism, but rather a small alternator that converts the angular velocity of the tachometer cable into a current which exerts a force on the needle.  This should be highly reliable and I don't see how it could cause this behavior.

Cessna 150s have a mechanical tachometer driven by a mechanical tach drive cable geared to the engine.

The tach needle is moved by sensing spinning magnets driven by the tach cable.

They do wear out over time and yours has reached the end of its life.


What does the last digit mean in a Piper Arrow model number? The Piper Arrow's model is PA-28R-201. At first, I thought that 201 means horsepower but the Arrow's HP is 200 so I figured that's not the case. What does it stand for?

The number notes the model

PA-28R-180 180bhp Cherokee Arrow with the ‘Hershey Bar’ wing.

PA-28R-200 200bhp Arrow II with the lengthened fuselage.

PA-28R-201 200bhp Arrow III with the tapered wing.

PA-28RT-201 200bhp Arrow IV with the tapered wing and T tail.

PA-28RT-201T Turbocharged Arrow IV.

The Arrow III was introduced in 1977 with the tapered wing and larger stabilator.  This improved low speed handling characteristics and increased the total fuel capacity from 50 to 77 gallons.


Why is the ILS16 approach at KSKF not available in my Garmin 430W? I am doing flight instruction on the San Antonio area (Texas) and I've been shooting different approches on the vecinity airports.
One of the approaches I usually execute is the ILS 16 at KSKF, which is a military and civilian airport. Yes you can land there and do fuel on the self service pump.
Everything was okay until the last garmin database update in which they removed the ILS approach. When you select the approaches on the GPS the only available ones are the RNAV approaches. I looked into the NOTAMs and there is nothing published there, I am still able to request the approach and do it with the VHF Nav Instruments, but was cool for students to monitor what was going on on the GPS as well.
Does anyone know why the approach is not able to be selected on the GPS?
Note: The GPS Database is current

There are two ILS approaches for runway 16. Both of them had amendments on 13 Aug 20. Therefore, the IAP charts that were in the database are no longer valid. They expired. It would be interesting to know the effective date of your last Garmin update. That could affect what approaches you are able to see.
I am unable to pull up the former IAP charts at this time. It would also be interesting to see what has changed. At the KTKI airport, the decommissioning of the MELISA NDB was enough to require a complete change of the ILS approach. Melissa was the Final Approach Fix. You were to notify ATC when you were Inbound inside of the FAF. The NDB has been replaced by the JIPUK waypoint.
This is a good lesson for new pilots. Read the entire IAP chart (including the borders) and check the effective dates.


Can supersonic conditions be replicated on the ground? In a previous question the P&W J 58 engine for the SR-71 was discussed. The engine was a new and innovative design combining the characteristics of a turbojet and a ramjet.

Before flying with such a new design I would think they would want to test it on the ground as much as possible to ensure the safety of the pilot and the aircraft. Otherwise you're sending a guy up with things that should work but so far only on paper. (I know that's what test pilots signed up for but they don't want to be reckless about it.)

J-58 ground test. from Wikimedia commons

From what I know a pure ramjet won't even operate at zero airspeed. What I'm wondering is how much can be learned from ground testing on such a radical new design, or any supersonic design for that matter? Can supersonic conditions be replicated on the ground?

Yes, supersonic conditions can indeed be replicated on the ground for purposes of airframe and engine testing.
Arnold Engineering Development Complex (AEDC)
The U.S. Air Force and NASA both operate supersonic wind tunnels, as do Lockheed, P&W, and others. The most advanced of these facilities are probably those at Arnold Engineering Development Complex on Arnold Air Force Base. I won't mention any specific numbers from memory because they've likely changed since I worked there and I can't remember exactly which ones were classified/FOUO/otherwise-not-public, but let's just say they're pretty good.
AEDC has test cells designed both for testing jet engines as well as for testing scale models of airframes (or full scale airframes if it's a small enough airframe, such as a missile.) Additionally, it has facilities for testing upper-stage rocket motors. Lower-stage rocket motors don't need the facilities at Arnold, as those are designed to operate in the atmosphere and can just be lit up out in a desert somewhere.
According to Wikipedia (which I believe is sourced from publically-available information,) Hypervelocity Wind Tunnel 9 can generate air flow of Mach 14 with simulated altitudes from sea level to 173,000 ft.

AEDC Tunnel 9 (with test article)  Source: Wikipedia
In case that's not enough, G Range can fire projectiles at roughly the speed of low Earth orbit. However, this one is kind of stretching the definition of "supersonic," since it's typically pumped down to such negligible air pressure that Mach number isn't really defined before a shot at that kind of velocity. Still, as the wiki article indicates, it's capable of shots at up to 1.7 atmospheres, so it definitely counts as legitimately supersonic on those shots.

AEDC Range G  Source: Wikipedia
Holloman Air Force Base
In addition to wind tunnels and other facilities at AEDC, the U.S. Air Force also occasionally uses rocket sleds, such as the one at Holloman Air Force Base, which currently holds the speed record for any type of non-air/space vehicle at 6,416 mph / 10,326 km/h (Mach 8.5.)

Holloman High Speed Test Track Source: Wikipedia

Land Speed Record Rocket Sled at Holloman Source: Wikipedia

The "Speed Limit" at Holloman Air Force Base
Source: some guy's website, which got them from publically-released images from Holloman AFB


What is the difference between fuel exhaustion and starvation? Is there any technical difference between fuel exhaustion and starvation? And what does it mean if a pilot says he has a "fuel shortage"?

Fuel exhaustion means there is no more fuel on board the aircraft. Fuel starvation means there is fuel somewhere, but it isn't available to the engine(s) for any one of a number of reasons: pilot error, blocked fuel lines or valves, malfunctioning fuel pumps etc. You can read a study of exhaustion and starvation incidents here.

A "fuel shortage" isn't a formal aviation phrase as far as I know, but "minimum fuel" is a formal phrase with a specific meaning. This is from the FAA's AIM 5-5-15:

  Advise ATC of your minimum fuel status when your fuel supply has reached a state where, upon reaching destination, you cannot accept
  any undue delay.
  Be aware this is not an emergency situation, but merely an advisory that indicates an emergency situation is possible should any undue
  delay occur.
  On initial contact the term “minimum fuel” should be used after stating call sign.

  EXAMPLE− Salt Lake Approach, United 621, “minimum
  fuel.”

This question has some more information.


How much fuel is used for the different phases of the flight of a typical airliner? An Airliner flies from LA to JFK in 5 hours. In the first 30 minutes the plane climbs to about 30,000ft. For the next 4 hours the plane flies at about 30,000ft. For the next 30 minutes the plane descends to JFK.

What % of the total fuel used for the flight is consumed in each of the 3 phases  of the flight, i.e, the climb out, the cruise, the descent?

From this site by Boeing for the B737-800: fuel used for TO and climb = 2,300 kg.
From this site: fuel burn in cruise for B737-800 is 2,500 kg/hr
From this site: fuel burn at idle of a CFM56 engine = 300 kg/hr, so for the half hour descent two engines burn through 300 kg.

Total fuel for a 4 hour cruise flight is therefore 2,300 + 4 * 2,500 + 300 = 12,600 kg. Percentages:

TO & Climb =  19%
4-hour cruise = 79%
30-minute descent at idle: 2%


Has anyone built a paragliding simulator? I am searching for a manual on how to build a paragliding simulator, where you can practice controlling the paraglider. My idea of the project is that you sit in a paraglider seat and you can experience the behaviour of the seat in a flight.

If you have any references to already built projects, it would be awesome.

The popular simulator X-Plane allows you to build your own aircraft models it looks like some people have built paraglider models that you may want to take a look at. As for controls you can build all kinds of custom interfaces to simulate the controls of a paraglider but it will take some work.


Do raked wingtips reduce drag of a hang glider? Do they realy reduce drag or improve performance?  If so, how?

The main effect of the ranked wingtips is not improving the glider performance but change handling characteristics during thermaling. Such wing tip changes the stall pattern of the inboard wing during the circling in a thermal. They are optional.
Pros:

Whit this wingtip installed, you should be able to climb better in weaker thermal. Due to a change in the wing stall pattern and bigger area.
Glider should have a higher glide ratio at a lower speed. Thanks to the higher aspect ratio. See. this answer https://aviation.stackexchange.com/a/8797/54674

Cons:

Such wing tips adversely affect roll rate. Especially if you need to quickly change your bank angle in "wild thermals".

In theory, they should decrease your glide performance characteristics in high sped flight.

It is always a pilot choice. Glider looks much better with them ;)


How does the size of each stage vary in a high pressure compressor? Is it true that in the high pressure compressor the stages and blades on the stages get smaller as it goes on?

Yes, the volume of the annular air channel goes decreasing after each stage. When air is compressed it takes less volume. Each stage compresses a bit more, hence the volume is constantly decreasing. This is also true for the low pressure compressor.

In this cross-section, the two spools, low pressure in red, and high pressure in green, display clearly this progression.

Turbofan compressor section (GE90), source

The first stage of the high pressure compressor is longer than the last stage of the low pressure compressor, but note the annular space of the high pressure section is smaller than the low pressure section due to the mean diameter reduction. In addition the HP spool rotates at a higher RPM.

Engine from the same family, in 3D:

Turbofan cutaway, source

The reduction of volume can be achieved by decreasing the outer radius of the air channel, by increasing its inner one, or by adjusting both. The number of blades/vanes can also be increased as pressure increases, to prevent deformation.


In order to become a pilot, should an individual have an above average mathematical ability? I would very much like to become an airline pilot however maths has never been my strongest subject. Are most pilots mathematically adept or can I get away with being average?

In short, no.

To quote Patrick Smith, veteran pilot and author of Cockpit Confidential and the blog  "Ask the Pilot,"

  There's a lingering assumption that airline pilots are required to demonstrate some sort of Newtonian genius before every takeoff- a vestige, maybe, from the days when airmen carried slide rules and practiced celestial navigation...
  The basics are what pilots encounter. Routine arrival assignments require some quickie mental arithmetic.

So basically, it doesn't involve super complex math. You need to be able to do some moderate arithmetic and geometry, but nothing so complex that it can't be done, as Smith says, on

  my $6.95 calculator from CVS- the one flight-bag accessory more indispensable than an emergency checklist, aircraft deicing guide, or a bag of ramen noodles.


How does density altitude affect performance, temperature, and pressure; and how is it calculated? I'm trying to better understand density altitude. If the density altitude at Rand Airport (for example) is 8300 ft:

What does the 8300 ft mean? Does it mean that at that altitude, aircraft performance will be at its lowest?
What does the 8300 ft mean in terms of air quality? Does it mean that at that altitude, the pressure will be at its lowest and the temperature at its highest?
And why 8300 ft specifically? Was it calculated? If so, how?

The International Standard Atmosphere (ISA) gives “average” values of air pressure and density by altitude. It starts by defining standard pressure 1013.25 hPa (29.92 inHg) and standard temperature 15°C at sea level, and derives the values for higher altitude from physical laws.

A “density altitude” is altitude in ISA at which air has the density you are observing. This is analogous to “pressure altitude”, which is altitude in ISA where the pressure you are observing occurs.

You can measure pressure altitude easily by setting your altimeter to the standard pressure of 29.92 inHg/1013 hPa. However you don't have any instrument to directly measure air density, so you have to calculate density altitude from pressure altitude, temperature and humidity.

  And why 8300 ft specifically? Was it calculated? If so, how?

This AOPA document provides approximate formula:

  Density altitude in feet = pressure altitude in feet + (120 x (OAT - ISA temperature))

  Pressure altitude is determined by setting the altimeter to 29.92 and reading the altitude indicated on the altimeter.
  OAT stands for outside air temperature (in degrees Celsius).
  ISA stands for standard temperature (in degrees Celsius).

  Keep in mind the standard temperature is 15 degrees C but only at sea level. It decreases about 2 degrees C (or 3.5 degrees F) per 1,000 feet of altitude above sea level.

I have also found a calculator, which uses more accurate equation, also taking humidity into account. It comes with detailed explanation of the physics involved.

Giving it current METAR FAGM 301600Z 33006KT CAVOK 27/00 Q1022 it calculates density 0.967 kg/m³, which is expressed as density altitude 7 866 ft (2 397 m).

It's already late afternoon, so earlier in the day it might have even 8 300 ft (if it was 31°C, which might have been just past noon)

  What does the 8300 ft mean in terms of air quality?

It is simply another way of expressing the density 0.954 kg/m³. You are normally familiar with how the performance decreases when you climb, so expressing density as altitude allows you to easily reference the loss of performance due to the hot weather to that.

  What does the 8300 ft mean? Does it mean that at that altitude, aircraft performance will be at its lowest?

It means aircraft performance will be as if you were at 8 300 ft on a standard day.

Both aerodynamic and engine performance depend on density. For aerodynamic performance higher density altitude means you'll need higher true airspeed for the same indicated airspeed, and for engine higher density altitude (lower density) means lower maximum power.

For an average single-engine piston aircraft, 8 300 ft is quite high. The performance will be poor.


Would a two-seat light fixed-wing aircraft with a landing speed of 20 knots and a top speed of 180 knots be technically possible? Watching helicopters come in to land, on occasion, I have noticed that they approach with a forward speed of a few knots, never land straight down. If there is sufficient landing space, would it be possible in some cases to replace the helicopter with a small fixed wing aircraft with low stalling speed?

The Helio Courier is an aircraft which is capable of flying slowly:

With a minimum-control speed of around 28 mph, the Courier is perfectly suited for confined off-airport operations. The first one was certified in July 1954 and powered by the 260 hp Lycoming GO-435-C2B2. - Wikipedia

I want to design (on paper at least), a tricycle retractable aircraft which is capable of the 20-200 knot speed range. Why has no one developed such an aircraft, and can the helicopter be replaced in certain situations by such an aircraft? Will it be technically feasible but commercially infeasible?  (Edit: can I do this with increasing wing area and power only?)

EDIT: What I am looking for is an aircraft that can meet these helipad specifications, see page 25 in the document : https://www.faa.gov/airports/resources/advisory_circulars/index.cfm/go/document.current/documentNumber/150_5390-2  and the image titled "Figure 2–7. VFR Heliport Approach/Departure and Transitional Surfaces: General Aviation". 4000 ft approach and 500 ft obstacles outside that. I can fire up my favorite flight sim and try the approach. Stopping within the helipad could be a problem.

At least one airframe close to these specs already exists, its a highly modified Wilga by the name "Draco". It can get off the ground in 120 feet and has a stall speed of ~37mph and cruises at ~180mph. With its epic 4000 ft/min climb rate it can get out of tight spaces fast as well. The only thing it lacks compared to your specs is the retractable gear as it was designed as a big gear bush plane.

(source)

The same guy (Mike Patey) also built a pretty wild Turbolance experimental that has some epic short field and climb performance as well and its a retract.

His overall secret sauce is effectively putting a PT-6 on the front end of a small airframe to add a huge amount of power to a light airframe.


Would shooting the tyres prevent a takeoff? In the movie Fast & Furious 6, among other questionable parts of one scene, they try to prevent a very large aircraft from takeoff.

As opposed to whatever they tried, how effective would it be in preventing takeoff to shoot the tyres?

(FAA takeoff safety)

If a tire failed/burst during takeoff at high speed, it is recommended to continue the takeoff.

The Face/Off method may work however, quickly grab a helicopter, shoot one of the engines, when that fails, land the helicopter on the tail. In Hollywood, haste is not required as they have endless runways.


What are those little rods that stick out of a planes fuselage? I noticed quite a few of them around the nose and cockpit area of a plane when I was at the airport and wondered what they were for, could someone please help.
THERE'S A PHOTO BELOW.

Thanks

Generally speaking you are most likely looking at the Pitot tubes

Some angle of attack indicators also look quite similar and in the case of some of the A380 the Pitot tubes and angle of attack indicator are combined into one unit.


What does ATC mean when they refer to "company"? Listening to LiveATC there are references by various ATC entities (towers, approach, etc) to "company". To what does this refer?

Generally when used in ATC movement instructions the word "company" means "The other aircraft operated by your company".
In this context it's a convenient shorthand for controllers and pilots: If two aircraft from the same operator are going to the same place on the airport (one may be told "Follow company"), or to assist with visual separation and sequencing on approaches.

In other cases it can mean "the airline (company) you work for" (such as being instructed to taxi to a ramp and "call company for your gate assignment" - the distinction is made based on the context of the request or instruction).

Note that this is not standard phraseology: despite being widely used the term company does not appear in the pilot/controller glossary or the Air Traffic Controller's Handbook .


Is a wind speed of 150 km/h dangerous during a flight in an Airbus A321? I am just curious about this... during one flight on Airbus A321 we experienced turbulence and the pilot told us that the wind speed is 150 km/h, so we won't get drinks and snacks due to safety reasons. The question is: Was that wind speed 'normal' or 'dangerous'? What could happen?

High windspeeds themselves are not a problem, but the environment surrounding them may be.

For example, in the wintertime it is not uncommon to find a strong core of fast winds embedded within the polar jetstream.  We term this windspeed maximum a 'jet streak'.  There are a couple of meteorological phenomena associated around these jetstreaks, such as regions of ascent and descent in the entrance and exit regions of the jetstreak and often times turbulence in the periphery.  You'll also find regions of turbulence on the lateral extent of the jetstream (polar side in particular).  Lastly, if you are flying at an angle to the jetstream or perpendicular to it, you will often experience changing wind direction along with speed, and this can be turbulent.

There is nothing dangerous about that wind speed alone.  What likely happened is that other airplanes were reporting turbulence and the pilots were being cautious with you and just offered that wind speed up as an easily understood number to justify the precaution.


Why do some aircraft have symmetrical tip airfoils while others do not? On some aircraft, the tip airfoil is symmetrical, while others carry their root foil all the way through the tip. It would seem an aerodynamic disadvantage to have a non-symmetric airfoil at the tip since it is not making much (any?) lift.

It doesn't seem to be simply for manufacturing purposes since it is on planes with tapered wings as well as straight wings.

Why is it incorporated into wing design?

Camber shifts the airfoil's section of lowest drag of the drag polar to higher lift coefficients. In order to create the least amount of drag in level flight, an airplane wing benefits from moderate camber. Most of the lift is created in the mid section, but enough lift is left towards the tips to justify camber there, too. In case of elliptical or tapered wings, the design lift coefficient for lowest drag at a given lift will be equal over the whole span (elliptic wing) or even peak near the tip (highly tapered and untwisted wing with no regard given to stall behavior or spar mass).
Normally the tips carry less load than the inner wing, details depending on wing taper and twist. This helps to prevent the tip section stalling first at high angle of attack. Good aileron effectiveness also requires an airfoil which equally produces positive and negative lift at low drag.
One example would be the Me-262. When Ludwig Bölkow designed the wingtip, very little was known about transsonic effects and a thin, symmetric airfoil with an elliptic nose was chosen because it showed a late onset of transsonic effects in wind tunnel tests.
When North American later designed the F-86, the outer wing design of the 262 was copied over because it had worked well in the German design.
Many Horten flying wings used symmetric tip airfoils because the bell-shaped lift distribution needed for stability resulted in a slightly negative lift at the tips at low angle of attack and very little positive lift at high angle of attack.
With some designs I am sceptical that a symmetric airfoil has been used even if it is claimed so in David Lednicer's outstanding collection. The Lockheed P-3 is there listed with NACA 0014 at the root and NACA 0012 at the tip - no, the Lockheed engineers 60 years ago knew better than that!


Why are the cockpit displays swapped between the captain's and first officer's sides? This question focuses on Airbus, like the A320, but is not restricted to those aircraft as the situation seems to be the same for other aircraft.

In front of the left seat, the navigation display is displayed at the right of the the primary flight display, and it is the inverse of the right seat.

Is there a technical reason to do so? An historical one?

It's hard to see from the angle that your example photos were taken from, but the main reason is that they want the primary flight instruments (which are on the PFD, or Primary Flight Display) directly in front of the pilot, no matter which seat they are in.
The PFD gives the most critical information which is used to actualy control and fly the aircraft, so is designed to be in the pilot's direct line of sight.
Less critical information is put on the MFD (Multi Function Display).  Since the pilots sit close to each side of the cockpit, this usually means that there isn't room to place the MFD on the outside of the PFD.  Even if there was room, the extra display is used partially for redundancy, so they don't want to put it further away from the other pilot.
Since the PFD is directly in front of each pilot, it doesn't take any effort to switch between seats because of that aspect.
This photo (it's night, so a little dark but I think that you can see what I'm referring to) was taken from my head level while sitting in the right seat, which should make it pretty clear:

own photo


What is the airflow across and below an elevator? So when an airfoil creates lift. The air above the foil moves faster. This creates lower pressure in tip of the wing and relatively speaking higher pressure under the wing this create lift l. Along with meetings 3rd law of motion. You know it deflects aid downward the reaction is forcing the wing up. But how did this work with an elevator to my understanding. When the elevator goes up so the airflow across the top speeds up, so this creates low pressure. And the air below the elevator is relatively speaking higher pressure. But this would cause the elevator and tail of the plane to go down along with the pitch of the plane. But in realty when the elevator goes up,  the tail of the plane goes down and the pitch goes up. Same with when it goes down the the airflow below the elevator speeds up and become low pressure and the air above it is higher causes the tail of the plane to go down and the pitch up. But in reality when the elevator goes down the pitch also goes down. Really confusing, someone please help.

When an elevator moves (trailing edge) up, it partly moves in the way of the airflow. That means pressure goes up.The elevator is an airfoil itself, in the shade of another airfoil. If it moves up, the same thing happens when a wing moves trailing edge up: lift works downwards.

Image source

Picture above shows an airfoil with trailing edge down: lift is upwards.

Upper aft side of the airfoil: air only moves faster if the surface moves out of the way of the stream, if the shape moves away gently enough the air still tries to follow. Note that the nose of the shape had pushed air out of the way, so there is less air along the upper aft side of the picture: lower pressure.
Lower side of the airfoil: air tries to stream like it did before, but now there is a shape in the way of the airstream. The air needs to stream through a narrower stream tube: higher pressure. When the stream bumps into the airfoil at a shallow angle, it gets deflected downwards: impulse lift.


What are ATC's considerations when they instruct to intercept final approach course instead of simply clearing for approach? When ATC provide radar vectors for an instrument approach, they sometimes instruct pilots to intercept the localizer or final approach course before giving an approach clearance, and other times give an "early" approach clearance with the final vector for the interception while the aircraft is still heading to intercept the localizer or final approach course. What are ATC's considerstions when they "delay" the approach clearance until the interception of the localizer or final approach course?

The main reasons I will instruct a pilot to intercept and follow the localiser instead of clearing him for the ILS are separation and minimum safe altitudes.

In a busy approach environment, it is often beneficial to let two aircraft intercept the approach with 1000 ft vertical separation. Maybe the aircraft are slightly too close horizontally but the first one is faster than the second one. I can then have then both follow the approach course, and descent number two on the approach once horizontal separation exists.

As for minimum safe altitudes, if you are approaching an airport on a heading straight in toward the runway, maybe there is room for you to intercept the approach course a large distance from touchdown. However, at this distance it might not be possible to descend to the approach altitudes, due to terrain or airspace restrictions. In this case I will also clear you to follow the localiser and then give the approach clearance later.


How does security and baggage checking work in regards to a private jet? I was told recently that if you are flying on your own private jet, you can drive your car directly on to the runway, park next to your plane and board without any security checks.

This can't be true can it?

I don't own my own private jet so I'm afraid I can't check for myself.

How does security work around privately owned planes landing in public airports?

Here in the US (you didn't specify where, and this is different in other countries), traveling domestically in your own private aircraft is much like traveling in your own private car.

Except in very specific situations, you are not generally required to go through security, and at many, many smaller general aviation airports airport security is almost non-existent, or at the very least they are not checking passengers and their luggage.

If the police have a reason to suspect that something illegal is taking place (they have reasonable cause) then they can search the airplane, but again, much like in your car, this doesn't usually happen.

International flights are a very different matter though, and the airplane, crew, passengers, and luggage must all clear customs at departure and arrival airports where they will be inspected.


How quickly should heading changes be accomplished? While airborne if there needs a change in heading, then what is the rate of change of heading with respect to time?

Like, I want to change my heading from x degrees to y degrees, where the difference is 45 degrees, do we have some specific time limit in which we have to get this change and do we have some regulation/standard for specific rate of heading change?

According to Wikipedia, a "Standard Rate Turn" is three degrees of heading change per second.

The bank angle required to achieve this depends on your true airspeed; at a low TAS a standard rate turn is easily achievable with normal, comfortable bank angles (say, 20°, plus or minus).  At high true airspeeds, the bank required becomes excessive, and "half standard rate" is used if anything is used, but at least in airline flying it's not particularly common to use either.  We just reference an angle of bank — but what that gives you in degrees per second is variable (as a function of TAS again).

The upper limit of what an airliner (or pretty much any IFR aircraft) is going to give the controller in terms of turn rate is whatever you get with a 30° bank.  And if that produces less than standard rate or whatever, then so be it.  At high altitude (say 35,000' and above), even 30° can be on the edge of problematic (mainly, with regard to wing loading and Mach buffet), and controllers are used to rates of turn that are less than what you'd see down low.

But if you're looking for a ballpark, 3 degrees per second at low airspeeds (say, under 200 knots), then 2 degrees per second up to maybe 300 knots, and 1 degree per second above that.  Ballpark, but reasonable numbers.


61.129 (a)(3)(v), can it be with multiple instructors? My question is can the 3 hours in prep for the check ride be done with different instructors, or does it have to be all 3 hours with the same instructor? Thanks.

There’s no requirement per se that multiple instructors cannot do this.  However, the CFI giving you the logbook endorsement to take the practical will probably want to log that time with you for liability reasons.


Why do some airport towers avoid monitoring 121.5? In the USA airport facilities directory (AFD), some towers (eg KSJC) are listed with the note:

  Emerg frequency 121.5 not avbl at tower.

Why do these facilities not monitor guard? Does the note actually mean that they cannot even talk on 121.5 in an emergency?

I am assuming it is because a different facility in the area (eg a TRACON) is monitoring guard, and they don’t want two facilities taking responsibility for guard. But suppose an airplane is landing in an emergency, does that mean the tower couldn’t even listen to the emergency communications?

How does this work practically in emergencies?

It seems to come down to the point that as long as someone is monitoring 121.5 in a specific airspace then not everyone needs to. And it helps avoid multiple ATC facilities responding to the same call. This is from the FAA's Facility Operation and Administration orders (my emphasis):

  3-3-4. EMERGENCY FREQUENCIES 121.5 AND 243.0 MHz

  [...]

  d. When facilities are in proximity and no derogation of services will
  result, transmit/receive capability should not be provided for each
  facility. The following requirements shall be maintained:

  Geographical area coverage shall not be derogated.
  DF-equipped facilities shall have transmit/receive capability on 121.5 MHz.
  Facilities without emergency frequency capability shall have appropriate landlines for rapid relay of emergency information.

Looking at KSJC, there are a lot of other airports close by, so the potential for confusion or conflict on the frequency seems high. My guess is that they leave 121.5 to NorCal TRACON; KPAO is 10 miles from KSJC and also doesn't have 121.5 available, for example.


Do I need to keep my foreign based PPL after passing an FAA instrument checkride? I have a foreign based PPL (PPL issue on the basis and valid only as long as my foreign PPL is valid). I'm going to go for an instrument rating checkride very soon.

Assuming I pass the checkride successfully, does my license become valid regardless of my foreign one or do I still need to keep both?

I lived in the US for the past 10 years and I am a US citizen.

Adding an instrument rating doesn't change the fact that your FAA private certificate is foreign-based. The IR is an add-on to a pilot certificate, it isn't a certificate itself. If you don't keep your foreign license current then you can't fly on your FAA foreign-based certificate.

To get rid of your foreign-based certificate, you can either do a regular FAA private checkride (including the written exam) or get an FAA commercial certificate (which replaces your private one). In both cases you'll also need an FAA medical to replace your foreign medical.

Source: I did an FAA IR while holding a foreign-based private certificate. I later did the private checkride to get a 'full' FAA private certificate. See this answer for a few additional details on going from foreign-based to 'full'.


What is the reason for this engine oil service procedure on a Bombardier CRJ? Someone told me that servicing the engine oil on a Bombardier CRJ900 aircraft with the APU on could lead to the particular engine being overserviced. He then advised that the engine-oil service be done within 20 minutes of aircraft shutdown.

What's the reason for this?

The Aircraft Flight Manual or Flight Crew Operating Manual will specify the timeframe during which engine oil may be checked after engine shutdown. For the CF34-3B engine on a Challenger 605, checking must be done between 15 minutes and 2 hours following shutdown.
If done outside of this window, the engine must be dry-motored (cranked without introducing fuel) for at least 30 seconds.
Otherwise the oil level may (incorrectly) show too-low (the oil tank is not at the bottom of the engine), which could lead to overfilling. Overfilling is said to be worse for jet engines than operating them with slightly too-low oil levels.


Is there a specific aviation term for suicide by pilot? CFIT, controlled flight into terrain, refers to an aircraft being unintentionally flown into the ground.

Is there any term specific for suicide by pilot?  CFIT would not apply to that situation.

According to the German Wiki article about CFIT a pilot's suicide is indeed not a CFIT. It is instead denoted as SEC.
They refer to the document CAST/ICAO Common Taxonomy Team: Aviation Occurence CategoriesPDF (Rev. 4.7, page 21)
which says

SECURITY RELATED (SEC)
Criminal/Security acts which result in accidents or incidents (per Annex 13 to the Convention on International Civil Aviation).
Usage Notes:

While security-related acts can lead to accidents as defined as by Annex 13 to the Convention on International Civil Aviation, they are not considered accidents by some organizations. Regardless, these events have similar consequences in that they result in serious injury or death to person(s) and/or substantial damage to the aircraft. For these reasons, they are categorized as security-related occurrences for prevention purposes only.

Examples include, (a) hijacking and/or aircraft theft, (b) interference with a crewmember (e.g., unruly passengers), (c) flight control interference, (d) ramp/runway/taxiway security, (e) sabotage, (f) suicide, and (g) acts of war.

Also, (same document, page 9) about CFIT:

Usage Notes:
[…]

Do not use this category for occurrences involving intentional flight into/toward terrain in manned aircraft or intentional ground impact of unmanned aircraft. […] Code all suicides under Security Related (SEC) events.

[…]

(Emphasis mine)
So according to ICAO, all suicides are SEC but not all SEC are suicides.


Will creating a strong back pressure within a ducted propeller enable an aircraft to attain a higher altitude? I would like to know if creating a strong back pressure within a propeller duct will enable an aircraft to attain a higher altitude.

Please reference the conceptual drawing below.

This is showing a ducted propeller with the addition of a centrifugal blower/compressor. This hybrid propeller would consist of four parts sandwiched together and then welded in order to make one piece that rotates as one unit.

The purpose of the compressor is to create a strong back pressure within the duct which should enable the propeller to produce more thrust/lift and should enable the aircraft, particularly a helicopter or drone, to attain a higher-than-normal altitude. I believe that the merging of the airstream from the propellers with the airstream coming out of the compressor is what will create the strong back pressure throughout the duct.

I think one key application for this type of 'pressurized' ducted propeller would be high-altitude rescues such as rescuing stranded mountain climbers, or reaching an airliner that went down up in the mountains above the reach of most helicopters.

Will creating a strong back pressure within a ducted propeller enable an aircraft to attain a higher altitude?

A very creative thought and project - a centrifugal compressor could be used as a means of propulsion if the exhaust stream is properly nozzled. So what you're basically doing is switching on another engine to produce more thrust, but:

The extra engine is in the way of the propeller, blocking its outlet flow.
Propellers and rotors are very efficient thrust generators on their own.
Creating static pressure is not the most effective way of creating thrust, better to convert it into air flow velocity.

Anything that is in the way of air flow creates back pressure and/or friction. The propeller flow is blocked, and the compressor flow runs into the side wall and does not accelerate any air backwards.

The way the air from the centrifugal compressor is normally deflected is depicted below (from an old uni book).

Air flow needs to flow and be guided gently. If it hits an obstruction, it pushes against it and creates negative thrust, like a person in a sailboat pushing against the mast.

It won't fly, I'm afraid...

Starting an extra engine might help in reaching places that are hard to get to. A simple propeller or turbofan is best - but when the extra propulsion is off, it is dead weight. Best to crank up the engines that are there already.


If cleared to cross a runway and expedite but are slow to get away, are you obliged to stop? Suppose ATC says "Big Jet, cleared to cross runway 36, expedite" and you acknowledge "Cross runway 36, wilco, Big Jet". As you start to move forward  you immediately realize that you are unable to go as quickly as you expected (perhaps there's an incline or a gust of wind -- I'm not sure what's plausible). At the point you realize this, you can still hold short the runway. Are you obliged to stop and reply 'unable' or is that ill-advised?

If you feel you cannot safely comply with any ATC instruction, you can simply reply “Unable” and the controllers will amend your clearance.  Remember: you are pilot in command; you are the final authority on the operation of that aircraft.

So the scenario might play out as:

ATC: “Bigjet, cleared to cross Runway 36.  Expedite crossing and report clear.”

Bigjet: “Cross runway 36 and report clear, Bigjet.”

Bigjet: “So-And-So Ground, Bigjet, Unable.  I’ve got a problem here.”

ATC:  “Bigjet roger hold short of Runway 36 for arriving traffic.  Will you be able to taxi after traffic clears the active?”


What is the relation between clouds and radar effectiveness? Recently, India's prime minister Narendra Modi commented on how cloudy weather can help a fighter jet  escape from radar. Is there any technical reasoning to back these comments?

Here is the quote in question:

  In the interview by TV channel News Nation on Saturday, PM Modi said,
  "The weather suddenly turned bad, there were clouds... heavy rain.
  There was a doubt about whether we can go in the clouds. During a
  review (of the Balakot plan), by and large the opinion of experts was
  - what if we change the date. I had two issues in mind. One was secrecy... second, I said I am not someone who knows the science. I
  said there is so much cloud and rain. There is a benefit. I have a raw
  wisdom, the clouds can benefit us too. We can escape the radar.
  Everyone was confused. Ultimately I said there are clouds... let's
  proceed."

https://www.ndtv.com/india-news/controversy-over-pm-narendra-modis-cloud-can-help-us-escape-radar-comment-on-balakot-air-strikes-2036402

Radar relies on electromagnetic wave propagation: from a source, to the target and back to a receiver.

Anything that alters the behavior of these waves along the way will impact the performance of the radar station. For example:

A target hiding behind terrain will be harder (but not necessarily impossible) to detect, because the terrain will absorb the outgoing emissions before they even reach the target.
If the target is in plain sight but shaped in such a way that all the incoming radar energy is reflected in a direction different from that of the receiver, then it will not be detected (this is the method employed on the F-117).
If the target is in plain sight but the return signal comes back accompanied by a lot of duplicates purposefully emitted by the target, it will complicate the task of figuring out which is the correct reflection, delaying or preventing a valid solution.
If the target is coated in a material that absorbs all the incoming energy, the radar station will never see a return, and thus think there is nothing there to detect (another technique used by Low Observability aircraft). This one is relevant to your question!

The media between the emitter and the target needs to allow the waves to travel, and while the best media is vacuum, air is not terrible either. At least normal, ISA air, things get complicated in the high atmosphere, or at high temperatures, or when electromagnetic fields (caused by thunderstorms, the Earth's core, etc.) come into play.

In the case of water suspended in the atmosphere, it can absorb the radar emissions and thus limit their effective range. However, it does so mostly at certain wavelengths, which are the ones at which water molecules can best capture incoming energy. One such wavelength is the one used in microwave ovens, because food tends to contain water, and heating the water is a fast way of heating the food.

So the ultimate answer to your question is, there is some kernel of truth in those statements, but how large it is is very debatable. Some radars, particularly modern high-frequency ones, operating in the millimetre band, will see noticeable losses due to coulds. Other radars, particularly those in the low GHz range or lower, will fare considerably better, although the lower frequencies have their own disadvantages in terms of resolution and antenna size requirements. Ultimately, defense organizations are quite aware of their equipment's capabilities and usually take steps to mitigate any drawbacks, so it is unlikely that some cloud cover will substantially impair a modern IAD network.


What is a general rule for crosswind correction, especially when landing? I am wondering what is the rule of thumb with correction of the bat?

Is it 2° for every 5kts?

Now i know you can use a E6B.
But im talking about landing ILS or visuals without bracketing the approach.

So lets say you landing on runway 06 the magnetic heading is 060, the wind is 080/05kts.
So would the correction be 062?

The aircraft is a C172

Apologies if this is not a valid question, getting back into aviation

What I have learned during my commercial flight training is making use of the speed number.
Take your TAS, devide it by 60. This is your speed number.

Now take you XWC (crosswind component).
Devide the XWC by your speed number. This is the amount of degrees you should crab to stay on track (wind correction angle)

Lets use an example:

We are flying in a C172 at 120kts TAS.
XWC is 18kts from the left.
120 devided by 60 is 2, so our speed number is 2.
18kts wind devided by 2 is 9. Now adjust your heading by 9 degrees to the left (into the wind), and you should stay on track.

Worked perfectly fine for me so far.
Hope it helps! Cheers


What is the rule of thumb for land/taking-off on a sloped runway? Skyvector lists the gradient for KMCI as 0.3%.  What is the rule of thumb for how large a gradient needs to be before you always take off downhill and always land uphill like they do at Lukla?  Assume winds are not a factor.

What does your POH/AFM says?

Ignoring winds and other factors, it depends on effective runway length, not just runway length. If you have a runway long (really long) enough, you can takeoff/land in either direction.

As mentioned here:

  ... advantage or disadvantage of a sloped runway is that a 1% runway
  gradient — an increase or decrease in altitude of 10’ for every 1000’
  of runway length — is equivalent to a 10% increase or decrease in
  effective runway length ...

Example:

Runway length is 1500' with 3% up-slope gradient

Landing uphill on it will give us an effective runway length of almost 2000’ (1500’ x 1.3 = 1950’).
Landing downhill on it will give us an effective runway length of just over 1000’ (1500’ x 0.7 = 1050’).

Just for reference, the runway (6: uphill; 24: downhill) at Lukla Airport has 12% gradient and is 1500' long.

Effective Runway Lengths (using the formula above)

 6: 1500' x |(1+1.2)| = 3300'
24: 1500' x |(1-1.2)| =  300'

Hence, hypothetically speaking, if runway 24 is 48,400' long with no wind, A380 can takeoff too.


Does ducted fan require more engine torque than unducted-fan,at same RPM? Two identical fans, one is unducted and other is ducted,both operate at same RPM.
•Does ducted fan require more engine torque than  unducted-fan ,measured both at same fan RPM?
power=torque x RPM so in my case more torque mean same as more power("induced power")...
(Engine torque is direct indicator which fan has higher  drag at blades.We can make analogy with wall to wall airfoil(represent ducted fan) vs 3D wing (no side walls at wingtips )represent unducted fan.
Here is problem:
I think ducted fan requier more torque for same RPM(maybe I am wrong?),which means it has higher drag than unducted fan,but in theory wall to wall airfoil must has lower drag than 3D wing at same speed and same AoA.
•How explain this contradiction?

Two identical fans […]
I think ducted fan require more torque for same RPM

Yes, a little more. The shroud prevents the air flowing directly around the tips, allowing them to produce more thrust. And this extra thrust comes with induced power.

but in theory wall to wall airfoil must has lower drag than 3D wing at same speed and same AoA.

No, it doesn't. The comparison is always made for the same lift, never the same AoA.
For the same AoA the drag should be higher for the same reason as above.


What would happen if multi engines operated symmetrically? What would happen if a multi engine operated symmetrically? So if one engine were to rotate counter-clockwise and the other clockwise. What are the advantages and downsides to this?

A single engine plane yaws to the opposite direction of the engine spinning. This is called the p-factor It's the same with a twin, with both engines rotating into the same direction. Rudder input is needed to fly straight.
When the engines operate symmetrically, this effect cancelles out. The plane is easier to fly.
It's also explained in this video about twins.
An example of a counter-rotating multi-engine plane is the Lockheed P-38 Lightning.

[The P-38] featured two 1,000 hp (746 kW) turbosupercharged 12-cylinder Allison V-1710 engines fitted with counter-rotating propellers to eliminate the effect of engine torque.
Counter-rotation was achieved by the use of "handed" engines, which meant the crankshaft of each engine turned in the opposite direction of its counterpart.

If the engines are turning in the same direction, then if either fails, the net p-factor will not be the same. See: Critical engine.


Why are overwing engines so rare? This comment to a question about underwing vs rear-mounted engines notes the existence of a rarely used third option: overwing engines.

There seems to be very few planes using those. What are the disadvantages that makes it so unpopular, and what are the advantages that made it worth building those few planes?

The biggest reason is the negative (or spoiling) effect of having a body "in the way" and disrupting the flow field above the wing.  A wing makes lift by redirecting a very large package of air downward (actually, up a bit, then down a lot) as the wing moves along, and most of the package of redirected air (which ends up as downwash) is above the wing.  (Otherwise, the wing would just be an air deflector and a flat sheet of plywood would do the job.)  Disruptions to this upper flow have to be minimized.

Look at any tactical fighter, like a Skyraider, festooned with rockets and bombs and tanks under the wing almost across the entire span. The disruptive effects of all those shapes on the underside have minimal effect other than parasitic drag. Put them on top and they act like spoilers and the airplane would never get off the ground.

On airplanes that do put the engines on top, either the engine is so far aft that it minimizes the effect and it might was well be mounted on tail pylons (like the Honda Jet), or the engines are mounted way forward to minimize the effect, plus gain from having the high velocity fan stream across the top, or it's propeller driven and the propeller flow field mitigates the effect, or, it was done anyway and the design was unsuccessful.


Sightseeing in a class Bravo airspace? I went to go fly around DFW today, wanted to do some sight see of the city and such. When I got in the air I contacted approach to get VFR flight following and was going to remain outside of the class B airspace anyways for most of it. When requesting to go closer I was told I would need to have an LOA with KDAL (Dallas-Lovefield), which I did not so I remained outside the Bravo, what is an LOA and or how is the best way to be inside the class B for sight seeing?

Letters of Authorization (LOAs) are authorization to conduct various types of commercial flights in certain airspace.  They are defined and governed by FAA Order 8900.1 and can be obtained from the regional Flight Standards District Office (FSDO) for that area.  It is not necessary for non-commercial general aviation operations.  I suspect (and I don't know the full details as to how you contacted Ft Worth Approach) that the controller thought you were a commercial operation requesting to start doing some sightseeing over the Dallas Ft. Worth Area without having done this paperwork.

Usually as a GA pilot, you can simply contact approach control for a Class B airspace and request a transition through Class Bravo.  This request may or may not be granted depending on commercial traffic congestion that day, etc.  They may also want you to stick to existing VFR traffic transition routes and not deviate from that.  Class B, as a general rule, is not very accommodating for sightseeing and other leisure flying.


Is it possible to reach an A340's fuselage from the ground? There is this ATC recording where an A340 pilot requests to leave the aircraft and close the fuel panel on the bottom of the fuselage, while the aircraft is on a taxiway (the request is made at 2:50). Now, here is a picture to show how to get in and out of an A340 without deploying the emergency slides and causing even more issues:

(Source: http://www.flugzeugbilder.de/show.php?id=695499 and yes, I realize this is technically a A330)

However, the picture also makes it look like it not actually possible for anyone to reach the fuselage from the ground. Is that actually the case? And if so, how would the pilot actually reach the fuselage and close the fuel panel?

Yes, the refuel/defuel service panel can be reached from a person standing on the ground.

From the Airbus A340-200/-300 Aircraft Characteristics - Airport and Maintenance Planning document, the height of the panel in question is just under 2 meters from the ground:

The panel is located on the lower area of the wing/body interface fairing as seen here (item 13):


Why do heavy bombers not carry air-to-air missiles? Imagine a heavy bomber – such as the B52, Tu160 or B1 – is heading toward a hot zone carrying a large number of AMRAAM or longer ranged missiles. Why doesn't it also carry air-to-air missiles?

I got the idea from a TV documentary about the future projection of the air forces but I don't know why they're not already doing this? Wouldn't it be a strong deterrent capability? I'm aware of the fact that such aircraft were not designed to engage hostile aircraft; neither their speed nor maneuverability is enough for that. However, I feel they caould do serious damage to enemy aircraft formations from a relatively safe distance while being under protection of the fighters like F15, F22, Su XX...

Well, of course the enemy would be carrying similar missiles in such a scenario. Or maybe the radar of the aircraft does not have the capability to engage air to air (I don't know if such a thing is possible). But thanks to its great lifting capacity, when compared to a fighter jet, a heavy bomber may have the advantages of getting more missiles and a more powerful jammer into the action at a time. Also, especially if the aircraft was one of the low observable ones, I think it would be a game changer in any aerial conflict even when the missiles were not longer ranged than the ones the other party would be using.

So, basically, why do heavy bombers not carry air-to-air missiles today? And as a side question, what would be the benefits and trade-offs of such an upgrade to existing heavy bombers other than what I mentioned?

Well, actually, they do.

Or at least it has been proposed on several occasions.

The ill-fated A-12 stealth attack aircraft was going to carry 2 x AIM-120 AMRAAMs as part of its defensive package when it went into combat.

Larger fighter-bombers like the FB-111 did in fact carry the AIM-9 Sidewinder AAM for defensive use.  And the Sukhoi SU-34 advanced theater bomber derivative of the SU-27 Flanker air superiority fighter can carry all modern Russian made AAMs, both IR and radar guided in addition to air to ground ordnance.

The EA-18G Growler electronic warfare derivative of the F/A-18F Super Hornet also carries AIM-120s for defensive use.

There is rumored to be an 'Arsenal Plane' in development by the Pentagon, which is very similar to a Cold War proposal for a VC-25 Cruise Missile Carrier Aircraft, a flying cruise missile launch platform based on the commercial 747-200 airplane.  The DoD's new 'Arsenal Plane' is rumored to be capable of carrying virtually every conventional - and possibly air-launched nuclear - weapon in the DoD's inventory, including AAMs.  Exactly what form this aircraft will take is unknown, but is supposed to be adapted from existing large cargo aircraft or commercial aircraft.

Depending on the types of AAMs desired to carry, mounting and launching them from an existing aircraft would not be a terribly difficult task.  Structural modifications would be necessary on primary components to install pylon hardpoints.  Additional infrastructure for power and datalink lines between mission systems and the missile would be necessary, and additional mission systems such as air-to-air fire control radars, IRST systems all would have to be installed.

Now a while a large aircraft could carry such weapons, their use against a fighter would be limited to stand-off launch and use in defensive retreat; the launch aircraft is just not designed to maneuver with a modern fighter in ACM, which limits the application of these systems in war.

So could it be done? Sure.  Is it a wise idea?  Well, that's debatable.

Historically, defensive armamaent for large, high value aerial assets eg bombers, tankers, transports, etc has been very ineffective.  In World War II, heavy bombers were equipped with multiple gun turrets to protect against enemy fighters.  So convinced were Allied planners that this strategy would give the bombers adequate protection, they sent waves of bombers over Germany with horrible results; the slaughter of heavy bombers over German airspace by Luftwaffe fighters nearly cost us control of the skies during the war.  This massacre only ended with the introduction of long range escort fighters to protect the bombers against enemy interceptors.  The terrible record for 'flying fortresses' protecting themselves with guns combined with the introduction of guided missiles convinced planners to eliminate defensive guns from bomber designs.  In the '50s they were limited to a single tail mounted and remotely controlled turret.  By the '60s, they were totally eliminated from new designs.  High losses to bombers from SAMs over North Vietnam convinced planners that the best defense for the manned bomber was to avoid detection in the first place.  Low altitude terrain masking, electronic warfare, passive low observable design features and stand off launched weapons like cruise missiles were the preferred protection for manned bombers in the '70s and into the '80.

Just what the future defensive systems for manned bombers remains a bit of a mystery.  Both the USAF and Northrop Grumman aren't making many public comments about the new B-21 bomber under development, but it appears likely that stealth combined with a the latest net-centric warfare capabilities will be the cornerstones of its design.  Whether this bomber will carry AAMs is unknown.


Is it true that cockpit doors are bulletproof? I read about 9/11 and read somewhere that after 9/11 all aircraft cockpit doors were replaced with bulletproof ones.

Is this true?

For all air transport operating under 14 CFR 121, 121.313(f) requires a door to be installed between passenger compartment and cockpit.
14 CFR 25.795(a) outlines the relevant design requirements for such a door:

(a) Protection of flightcrew compartment. If a flightdeck door is required by operating rules:
(1) The bulkhead, door, and any other accessible boundary separating the flightcrew compartment from occupied areas must be designed to resist forcible intrusion by unauthorized persons and be capable of withstanding impacts of 300 joules (221.3 foot pounds).
(2) The bulkhead, door, and any other accessible boundary separating the flightcrew compartment from occupied areas must be designed to resist a constant 250 pound (1,113 Newtons) tensile load on accessible handholds, including the doorknob or handle.
(3) The bulkhead, door, and any other boundary separating the flightcrew compartment from any occupied areas must be designed to resist penetration by small arms fire and fragmentation devices to a level equivalent to level IIIa of the National Institute of Justice (NIJ) Standard 0101.04.

So to summarize, any airplane operating under 121 rules (i.e. scheduled air carrier operations) must have bullet-resistant cockpit door.