Is gascolator and fuel strainer the same thing? I am wondering is gascolator the same as fuel strainer, or this two things are bit different. Because sometimes I see one term, sometimes another, and I don't know if I am reading about the same thing.

Yes in practice they are the same thing (it's surprisingly difficult to find the origin of the term "gascolator") and most definitions will mention both terms, although I tend to think of the gascolator part as the gravity water separator bowl/quick drain component, and the strainer as the filter screen covering the outlet.
Back when cars had them (up to the early 60s) they were called "filter bowls" with the bowl part made of glass and without the quick drain.  You just removed the bowl to get rid of any water you saw when checking under the hood (airplane gascolators from the 40s also used glass bowls, although most have been replaced by metal ones).
Most aircraft gascolators use a 75 micron mesh screen (the strainer part - about like the screen on those plunger coffee makers) at the top of the housing to keep particles from passing to the carb.  On my homebuilt I improved on that by using a 30 micron sintered bronze filter made for the filter bowl of a late 50s Chev Impala, which fits perfectly in the standard gascolator bowl.


Does the US military use metric system? Does the US military use the metric system for aviation?

For example, does it use:

feet or meters for altitude?
nautical miles or kilometers for distance?
knots or km/h for speed?
inHg or hPa for pressure?
°F or °C for temperature?

If so, how do they work with ATControllers who are used to using customary measurements?

As the US military primarily flies and trains in US airspace, they use the standard measures associated with the airspace. That is feet (or flight levels), nautical miles and knots, inHg, and °F. Though, using °C is fairly common in the US now since weather reports shifted to the ICAO format.

That said, the cockpit systems can be switched to HPa and meters for altitude and °C for temp for when they fly in airspace where that is the standard. Speed and distance are always in nm and kts.


Rotation direction for adjacent propellers, how do different arrangements compare? (YouTube)

The Airbus A400M uses counter-rotating pairs where the blades meet moving downward (if there is a better description, tell me please).

I played the video frame-by-frame to make sure it wasn't a tricky stroboscopic effect; use <> if you're using the HTML5 player.

How do the different arrangements compare aerodynamically? I think for the three arrangements below, the propeller blade interference will have different characteristics.

Initially during A400M development (when the project was still called FLA), all propellers were supposed to spin in the same direction. The reason for this was the objective to use a single engine in order to minimise logistics costs.

Windtunnel tests soon revealed that the prop wash would create asymmetric flow on the wing, causing uncontrollable rolling moments in low speed flight. Only two options allowed to remedy this:

Use of counter-rotating propellers, like on the Progress D-27 powering the An-70.
Use of two variations of the same engine with opposite direction of rotation.

Counter-rotation resulted in heavier propellers and gearboxes, so it was decided to go with the second option. The exact direction of rotation for each engine was then determined in further wind tunnel tests, with low-speed handling and maximum lift coefficient the determining objectives.


Are you required to disclose medical conditions to your flight instructor? When talking with a local flight school about my interest in starting training, I started asking questions about how the AME process works. The flight instructor then asked me if I had any specific medical issues. Are you required to disclose any health information to your flight instructor? What about if the issue(s) could be disqualifying? Would you get in trouble for lying to the instructor (to avoid judgement or maintain privacy) but NOT lying during the AME?

When it comes to the AME, you must disclose everything fully and completely.  Failure to do so may void any license and insurance and expose you to extraordinary civil and criminal risk.

When it comes to your flight instructor, who is not a medical professional, you do not need to disclose the specifics of your situation.  Saying, "I have concerns about passing a Class III Medical Exam due to certain conditions" is sufficient, and is not the same thing as lying.  Do not claim you are healthy when you know you are not.

Your instructor may decide not to continue training until a physical is passed, or he may decide just to be a little extra vigilant during training, and delay certain elements or maneuvers depending on the information you choose to provide.

For example: If you choose to disclose vertigo problems, he may avoid steep turns until medical clearance.  If you choose to disclose vision issues, he may avoid night-flight.

Regardless, you will need a medical before your first solo flight.

Do not lie to your instructor, but that is not the same thing as disclosing full details of your health with a non-medic.


How do aircraft window size compare to each other? What are some possible improvements on them? I'd like to see a comparison about the window sizes of various commercial aircraft, maybe to give evidence of eventual progress in it over the generations.
For example, I surely know that the B-787 has the biggest ones but it seems strange to me that A350XWB has smaller ones in comparison, considering that it, too, is made with composite materials. Why this difference?
In addition, Boeing increase their window sizes between different iterations of the same model (for example, the first 747s had smaller windows than the later generations, and 777X has larger windows than the original 777), but Airbus seems to not have this approach (neo versions are equal to ceo ones).
Finally, I heard about Boeing Skyview, a very big single windows in Business variants but... is already delivered as solution? Any similar solution from Airbus?
P.s: I found only a link with similar topic but is more general and not specific to a comparison chart between models and/or difference B787 and A350 construction design related to window size

How aircraft windows compare:

  Aircraft windows can be made bigger by improving the materials of the window or fuselage or reducing the amount of Gs the window frames get by changing the exterior shape and design of the fuselage. Another way is making the window surfaces smoother (to reduce surface friction) or changing the shape of the window itself.


Why is a reciprocating engine air intake a reverse bell shape? Why would this inlet for the induction system get wider as the air approaches the filter?
What net effect does this have on intake pressure, and how would an inlet that starts wide and then narrows down perform differently?

It's simply a NACA duct inlet.  On a fully parallel to flow flush surface it has some (but not all) of the effectiveness of a protruding scoop, without the drag.  The curved sides of the ramp act like vortex generators, with the rotation of the vortices on each side pulling air down into the ramp.
On a very clean airplane like one of the RV series homebuilts, that kind of duct can have a measurable benefit.  On a plane like the one pictured, there is a theoretical benefit drag wise, but it would make little detectable difference in that sort of a light plane (with its unfaired nose gear) and is mostly for looks.
In fact since the surface isn't really parallel to the airflow but curves in, the opening is presented more or less directly into the airstream for ram effect and there really isn't a need to create vortices to pull air down the ramp.  A straight sided ramp would work just as well in that particular instance.  Looks cool though, which I suspect is the main reason it's being used there.


Why do the CRJ700 window shades open in different directions? On a CRJ700, the window shades in the rows immediately fore and aft of the exit doors open downward. All the rest open upward. Seen on more than one aircraft. Is there an engineering rationale for this?

Judging by an exit photo here, you're right.

When there is an opening in the fuselage (e.g., where the emergency hatch would go) the surrounding area needs extra strengthening. Below is a high-res example for an Airbus fuselage:

(source) Notice the extra and deeper stringers to the left of the door, and the lack thereof away from the door where the windows would be (yet to be cutout, but you can make out one).

(gettyimages.com) And here's a CRJ700 fuselage (first fuselage actually).

While that's the front service door, not the overwing exit, note the white stringer above the first window to the right. Its depth is clearer on its mirror on the left by the shadow it casts.$^a$

And since a sliding hard blind needs to go somewhere, they typically go into a hidden tray, which takes space. Here is an example from a McDonnell Douglas patent from the 70s.

An upside down unit flanking a hatch could very well be installed that way to make way for a structural element, or to make way for cables/pipes/tubes in the area, especially that the CRJ700 is a narrow plane.

$^a$: It won't affect the first row seats though. Note that the passenger entry door (port side) is taller, so the topmost stringer is already well above the windows. As for the right side, depending on the configuration this area will have either a galley or a lavatory. I tried to check for photos from inside the lavatory, but it didn't have a window (on the outside, the window is there, it's just blocked by the interior panels from the inside – photo below).

(thepointsguy.com)


Why don’t airplanes use turn signals? Why don’t airplanes use turn signals like cars do? Would this improve safety for ground operations at uncontrolled airports? Could a similar concept be used to indicate in air maneuvers?
For example: a specific color could denote a right turn, a left turn, a climb or a descent.

At uncontrolled airports, there is rarely enough traffic for signals to be needed, and pilots should (though are not required to) communicate with each other on CTAF—an option that cars do not have.
In the air, if you're close enough to see a turn signal, you are way too close and need to immediately follow the collision avoidance procedure.
More generally, aircraft are a lot more like boats than cars, and boats don't have turn signals either.


What is the risk of icing with water / moisture on wings prior to takeoff? If a plane without any deicing equipment has water moisture on the wings (say, from sitting overnight) and that plane is then flown to an altitude which will have temperatures below freezing, what is the risk of that initial moisture causing icing concerns?

For the sake of hard examples:

Plane: Piper Cherokee 140
Air temperature on ground: 40°F (4°C)
Air temperature at cruise altitude (3500ft): 28°F (-2°C)
No visible moisture in the air, the only moisture is the moisture on the wings prior to takeoff.

Questions:

Will this be a problem?
If it is a problem, what is the best course of action to protect against the icing concern?

Taking off with wet wings is not a problem, the airflow is going to blow the water off long before it reaches the freezing point. There's no concerns here.

Given the scenario what I would be concerned about would be ice elsewhere on the airframe. 40°F (4°C) could mean that the aircraft was frozen overnight, and there could be ice left over where the sun didn't melt it off. That kind of ice wouldn't necessarily impact the airflow on the wing, but it would make the airplane heavier and therefore impact performance. A simple visual check on the walk-around will confirm this. If there is ice left then deal with it even if it's not on the wing or tail, if it's just wet then get in and fly.


Is there a regulation that requires manufacturers to cover AD's for the life of the equipment? I'm usually pretty good at finding regulations, but I can't find anything in this regard. I'm curious if manufacturers such as Cessna, Piper, or even Lycoming and Continental are required by law/regulation to cover parts and labor for any airworthiness directives (AD) for the life of the equipment.

For example my 1977 Cessna 177 Cardinal II recently got an AD that required a significant amount of labor to complete (16 hours I believe). This AD was covered entirely by Cessna at their expense. This isn't the first AD that I've had like this, but it surprises me that a nearly 45 year old aircraft is still being covered by the manufacturer.

Is there a regulation that requires this for certified equipment?

The answer is basically no for aircraft not under warranty, but...

I've participated in numerous AD related activities on the OEM side, and I've never seen an AD with a commercial policy incorporated into it that dictated who pays for compliance, kits, or labor.

So strictly speaking, the aircraft operator is on the hook once an aircraft is out of warranty, but the OEM will normally have an internal commercial policy in place that its program office, customer support organization and spares organization uses as guidance on charges.

There is usually a Service Bulletin with a kit that has to be incorporated to terminate an AD and the OEM will decide whether to make the SB and kit available free of charge for some period of time when it's required to comply with an AD, for reasons of morality, politics and marketing. The commercial terms will be included in the Service Bulletin.

That is probably typical, but if an OEM is in a financially tight position and an AD's compliance is really expensive, the OEM may decide to make the operators pay for the SB and kit, or the costs related to a repetitive inspection, and take the heat by getting yelled at during operator conferences.

And sometimes, as in your case, if labor is significant, the OEM may also include a labor charge-back policy that will refund labor costs based on the estimated man-hours quoted in the Service Bulletin.

Sometimes operators include out-of-warranty "AD clauses" in their purchase contracts to avoid getting burned. And sometimes operators, especially those that may be looking for more aircraft, cut their own deals on the side.

Another factor is that, in order to get less onerous compliance terms or limitations in the AD itself (as I suspect in your case), the OEM may convince the regulator that they plan to proactively "campaign" a mod free of charge including labor charge backs, with a campaign completion date, and which may even include sending out dedicated teams to do the work (as with the Cardinal stabilator slot mod).  Sometimes this is enough to avoid an AD being issued at all if the regulator is satisfied that every affected aircraft will be fixed by a certain date.


Why do modern airliners have only two engines? In this terrific question we see the advantages of four engines over two. Namely:

Engine out capability: Losing an engine means losing only one quarter of the thrust, rather than half.
Ground clearance.
Drag: Increased yaw control with four engines in an engine-out scenario means that the vertical stabilizer can be smaller, thus reducing drag.
The wing is loaded more evenly.

If that is so, then why don't new commercial airliner designs use four engines?

Engines are expensive, maintenance-intensive and heavy. You only need 2 to keep a large plane in the air.

In the days of the 747 regulations required at least 3 engines if you ventured more than 60 minutes of flying time away from a suitable diversion airport (in case the second one also failed). However as reliability of engines increased this got extended with ETOPS certificates.


Do pilots know which heading to fly in case of a go around? If the choice to go around is always an option for the pilot as described in Do pilots need a clearance to go around?, is the heading to go around always well-known at every airport?

Is the heading to go around always well-known at every airport?

The initial heading for a go around should always be well known based on a pilot's knowledge and understanding of the procedures associated with the type of approach being made.  Generally, outlined below are the procedures used in U.S. airspace (unless modified by NOTAM, special notice, etc. for a particular location):

Go Around -

Tower Controlled Airport -VFR

Fly runway heading and advise the tower of your missed approach.  The controller will issue further instructions (normally to stay in the traffic pattern for another VFR approach).

Go Around -

Non-Tower Controlled Airport -VFR

Report your missed approach on the VFR advisory frequency (or common traffic advisory frequency [CTAF], as appropriate) and fly runway heading until you turn back into the traffic pattern for another approach or depart the pattern for another destination.

Go Around -

Tower Controlled Airport - Radar Environment- IFR

Aircraft under IFR using a published Instrument Approach will initially start flying the published Missed Approach Procedure noted on the Approach Chart for the runway and procedure in use. Then, after reporting the "missed approach" to the control tower, the controller will normally assign a heading and altitude (i.e., alternate missed approach instructions) to fly putting the aircraft back into the traffic flow for another instrument approach or clearance to some other airport.
Aircraft under IFR flying a "Visual Approach" will report the Missed Approach to the tower.  Since a "Visual Approach" has no "published" missed approach procedure the tower controller will normally issue a heading and altitude to fly for re-sequence into the IFR traffic flow or, if weather conditions and traffic allows, keep you into the local traffic pattern for another landing attempt.

Go Around -

Tower Controlled Airport - Non-Radar Environment- IFR

1.Aircraft under IFR using a published Instrument Approach will fly the published missed approach and contact the controller for further instructions.

2.Aircraft under IFR flying a "Visual Approach" will report the Missed Approach to ATC and will be issued further instructions by the controller.

Go Around -

Non-Tower Controlled Airport - Radar Environment- IFR

Aircraft under IFR using a published Instrument Approach will initially start flying the published Missed Approach Procedure noted on the Approach Chart for the runway and procedure in use. Then, after reporting the "missed approach" to the radar controller, the controller will normally, after radar contact is reestablished, assign a heading and altitude (i.e., alternate missed approach instructions) to fly putting the aircraft back into the traffic flow for another instrument approach or clearance to some other airport.
Aircraft under IFR flying a "Visual Approach" aircraft are expected to remain clear of clouds and complete a landing as soon as
possible. If a landing cannot be accomplished, the
aircraft is expected to remain clear of clouds and
contact ATC as soon as possible for further clearance.
Separation from other IFR aircraft will be maintained
under these circumstances [ref: AIM/Aeronautical Information Manual, para. 5-4-23 e.].

Go Around -

Non-Tower Controlled Airport - Non-Radar Environment- IFR

Aircraft under IFR using a published Instrument Approach will fly the published Missed Approach Procedure noted on the Approach Chart for the runway and procedure in use. Then, after reporting the "missed approach" to ATC, the controller will issue instructions putting the aircraft back into the traffic flow for another instrument approach or clearance to some other airport.
Aircraft under IFR flying a "Visual Approach" aircraft are expected to remain clear of clouds and complete a landing as soon as
possible. If a landing cannot be accomplished, the
aircraft is expected to remain clear of clouds and
contact ATC as soon as possible for further clearance.
Separation from other IFR aircraft will be maintained
under these circumstances [ref: AIM/Aeronautical Information Manual, para. 5-4-23 e.].


How can I calculate distance based on altitude and glideslope angle? How do I calculate the distance to touchdown when the glideslope angle is different from 3°? For example, you are 670ft AGL on a 3.2° glideslope approach; what do I change in the formula to calculate the distance?

Since the 1 in 60 rule of thumb yields a solution of 300 feet for every NM from the touchdown point for a 3 degree slope, use 320 feet for a 3.2 degree slope.  So 670ft, gives you a nadgers whisker over 2 nm.

To be a little more precise, 2.09375 nm ($\frac{670}{320}$)


What are these holes in my Cessna 172, just in front of the elevator? Been wondering about these for a while. Student pilot working on my PPL. When preflighting my Cessna 172 the other day, I noticed these holes just in front of the elevator. What are they for? The image shows the crease between the elevator (white) and the horizontal stabilizer (red) on the left side of the fuselage.

Those are called "Lightening Holes". The name refers to the weight reduction brought about by removing part of the material—lightening—and should not be confused with anything to do with electrical discharge—lightning.

From the FAA's AMT Airframe Handbook, in Chapter 4, page 4-82:

  Lightening holes are cut in rib sections, fuselage frames, and other
  structural parts to decrease weight. To avoid weakening the member by
  removal of the material, flanges are often pressed around the holes to
  strengthen the area from which the material was removed.

The particular part depicted in your photo is the left hand rear spar assembly for the horizontal stabilizer, No. 32 in this figure from the 1975 Cessna 172 Illustrated Parts Catalogue (IPC):

As you can see, these lightening holes are present throughout much of the spar and rib structures in the horizontal stabilizer, as well as the vertical stabilizer, wings, and fuselage.

In addition to the gains in weight reduction, lightening holes also serve as openings to allow the routing of electrical wiring, control cables, hydraulic tubing, and other system components. If you look at the same location on the right side of the horizontal stabilizer, you should see the elevator jack screw passing through one of the lightening holes, in the location marked "C" in the Cessna IPC figure above.


Is there statistical evidence of the benefits of CRM? Seeing there's apparently now a consideration towards allowing single pilot commercial aircraft, I figured a fairly good counterpoint would be the benefits gained from crew resource management (which I've often seen pointed to as something that might have prevented earlier accidents).  Has any empirical evidence been published showing a clear reduction in accidents linked to the development of CRM?

The benefits gained from CRM are not really applicable to a single pilot situation although solo pilots can apply CRM Ideals in their own regard. This FAA study touches upon it well in this study (numbers provided in the figures on page 2 of the study)

  Concern with the factors underlying these accidents led NASA
  researchers in the 1970s to conduct a series of interviews with line
  piLots to investigate their perceptions of aviation mishaps. Charles
  Billings, George Cooper, and John Lauber found that one mishap
  component consistently mentioned by pilots was inadequate training.
  Even more interesting, these researchers found that it was not
  technical training that these pilots felt they lacked, but training in
  leadership, communication, and crew management. In other words,
  traditional training had done an excellent job of imparting stick and
  rudder skills, but these pilots felt that they needed more training in
  crew oaordination. A subsequent analysis of jet transport accidents
  between 1968 and 1976 revealed more than 60 that involved problems
  with crew coordination and decision making (Cooper, White, & Lauber,
  1979).

CRM solves the problem of their being two brains in the cockpit. In other words one of the primary issues they found surrounding aviation incidents was the fact that there were two pilots who had communication troubles in the cockpit (with each other). In some regards a counter point can be made that removing the second pilot is safer by eliminating these possible issues. The study makes it clear that pilots across the board had satisfactory skills in identifying issues and flying the plane but encountered issues efficiently communicating the issues in the cockpit.

This is a tough topic as there are currently no single pilot certified airliners but there are some single pilot certified biz jets which makes that the next best place to look for info. A study was carried out on the difference in accident rates between single pilot and dual pilot situations which interestingly does not show a huge lean either way. The article does not talk about CRM but it could be a starting point for a meta study on CRM as it applies to that group of accidents.

On any note Captain Sullenberger makes it clear that good communication and CRM were key to the successful outcome of his ditching. There is a great interview where he talks about it here.

According to this paper poor CRM was one of the largest human factors in commercial accidents.

  Within the preconditions level, CRM failures were associated with the
  largest percentage of accidents. Approximately 29% of all
  aircrew-related accidents were associated with at least one CRM
  failure.

I can't find a whole lot of direct evidence that CRM has made airplanes safer but the FAA tends to take the approach of identifying the large issues (of which CRM seems to be) then working the problem through training. It is far harder to isolate and subsequently measure human factors. Engines that stop running, brackets that fail, wires that short, etc. are much easier to study...


What do these ramp markings mean at KIFP? As a pilot, what do I need to know about these ramp markings at KIFP? Are they operationally significant?

They are helicopter parking markers, as per the AC that defines them:

I was never taught about this in my training and it was not on the fixed wing PPL exam nor is it on the FAA's quick reference guide but its a good idea to know what they are.

Although interestingly they are not where the airport diagram denotes the "Helicopter Parking"


What are these symbols in Garmin Pilot? When I start editing a flight plan in Garmin Pilot, if I have a distance that is farther (like 1,000 nm or farther) I get these two symbols in the map on the Flight Plan pane:

One is a tower and the other is an oval.

Here is the entire pane view:

Any idea what these two symbols are?

The tower looks like the same symbols as 'obstruction' from the Garmin Pilot manual, but note that the filed altitude is 39,000 feet (ie, no obstacles that high around here.)

What about the little oval?

Those are the highest obstacle and highest terrain point along the route, respectively. They're both grey because they're well below your planned altitude, so they're no factor.

You can see them by going to "Flight Plan", "Details", "Highest Point".


How much actual difference does fixed pitch propeller make in takeoff distance? So it's possible to buy fixed pitch propellers which are either optimised for takeoff or for top speed. I guess most airplanes have a compromise.

Considering a training aircraft like a Cessna 152, what would be the difference in Ground Roll and Total to Clear 50ft obstruction between different props?

As an example the Ground Roll and Total to Clear 50ft Obstruction  at 20 deg C for a weight of 1670 lbs at Sea Level is listed as 755 and 1390 feet respectively. How much numerically  would they change with different props?

Please note this is just a hypothetical question. I'm not in the market for propellers!

With my old VariEze (not a training aircraft; in the same power class as the Cessna 152 but lighter and with much higher wing loading) I had a cruise propeller and a climb propeller that I could exchange on the ground with about 30 mins of work. I measured ground roll at max gross weight and calm wind to be around 1500' with the cruise prop and 1100' with the climb prop. I could usually get around 1500 fpm climb with the climb prop and 1000 fpm with the cruise. Cruise speed was 10 to 15 kts slower with the climb prop depending on altitude; you'd usually have to throttle back quite a lot to avoid exceeding redline RPM.

The difference in takeoff performance is more dramatic when a constant-speed (variable pitch) prop is compared to a fixed-pitch prop. I'm presently in the process of upgrading my Lancair 360 from a cruise/climb compromise fixed-pitch prop to a constant speed and I expect that to decrease the ground roll to less than half the current 1500'. I'll report back with data once it's flying.


What is this airplane used for? Every satellite picture I've ever seen of carriers in port usually shows a lot of equipment on the flight deck, presumably involved with servicing and overhauling the ship between cruises.  This example is from NAS North Island in San Diego.

A closer inspection of the stern of the ship shows what appears to be a derelict F-18 airframe parked on the flight deck and stripped of its engines, LE and TE flaps.

Usually the airwing is launched back to naval air stations on shore prior to the ship reaching port, then fly out again to trap aboard when the ship goes out to sea again and this jet doesn't exactly look flight ready.  What exactly is this aircraft used for?  Is it some kind of training device for shipmates or aircraft handlers or for training on firefighting techniques?

While I'm not sure about the condition of the aircraft, there are uses for a non-flight worthy aircraft in a carrier deck. For example, the crash and salvage team can train salvaging the aircraft, or the sailors can train craning the aircraft abroad the deck.

For example, in the image below, U.S. Navy sailors use a crash and salvage crane to lift a non-functional McDonnell Douglas F/A-18 Hornet during flight deck drills aboard the aircraft carrier USS Ronald Reagan (CVN-76).

By U.S. Navy photo by Mass Communication Specialist 3rd Class Jonathan Nelson - This Image was released by the United States Navy with the ID 150415-N-WO404-124 (next).This tag does not indicate the copyright status of the attached work. A normal copyright tag is still required. See Commons:Licensing for more information.

It may also be used for firefighting and damage control training, as can be seen in the image below.

Sailors assigned to the crash and salvage crew on USS George H.W. Bush (CVN 77) spray foam on an F/A-18 Hornet training aircraft during a firefighting drill; image from warbirdsnews.com, credited to USN

The article notes:

  Since active jets are precious assets, they use specially-prepared training airframes, like grounded F-18 Hornets ... these former frontline fighters are often antiquated models of current equipment or planes that have been damaged beyond the point of repair. These days the trainers are usually represented by earlier models of the F-18 whose variant has been retired, ... (they serve) as training aids for firefighting and crash retrieval and salvage operations, letting crews hone their skills using real world items, without risking damage to expensive operational flyers


Isn't it dangerous for a soldier to sit on the outside of a flying helicopter? AH-64 during an extraction exercise at Camp Bondsteel, Kosovo in 2007 with a soldier on the avionics bay.

I lit upon this image on Wikipedia. I see that the soldier is harnessed fastened to the helicopter, but what if the harness tears? What if the soldier falls? Or if he gets sucked into the helicopter engine intake?

To answer your question of is this dangerous, yes it is. It is very dangerous to be in a job where you voluntarily go into an environment in which you risk your life to combat other individuals who are actively trying to kill you. It would be much safer to never join the uniformed armed services.
On the other hand, in every activity, a certain amount of risk must be accepted while as much risk is eliminated or at least mitigated as possible. After reviewing the original picture from the Wikipedia link in your question, risk mitigation has been performed. The soldier on the outside of the aircraft has been tethered to the aircraft by safety lines attached to at least two points on the aircraft. These are the green high-strength webbing straps attached to two different handholds on the fuselage. These are clearly seen in the higher resolution original picture. You can also clearly see what looks like some type of safety tether deployment bag on his chest while the leg straps of his safety harness are also clearly visible.
Although safety measures have been taken, It is not very likely that the soldier on the outside of the aircraft could not hang on through sheer body strength. During regular maneuvers, his body weight alone should keep him in place.
Case in point, while serving as a paratrooper, I have jumped from UH1s, UH60s, and CH47s. It was quite common to sit on the floor of the aircraft with our feet dangling out of the open door. At other times, we would stand on the skids. Sometimes, the aircraft would be performing combat maneuvers. Only our left hands would be free to hold onto anything available while our right hands were protecting our reserve chute handles. Most likely our left hands were also occupied hanging on to rucksacks or weapons cases. Only a single webbing strap loosely stretched across the door served as our safety line. The load forces induced by gravity and the maneuvers kept us firmly seated during some very extreme banking.
Also, having done civilian skydiving from various Cessnas and Twin Otters, I can attest to the fact that the wind blast/slipstream, on the outside of the fuselage, while not quite pleasant, is not unbearable. It is not very difficult to hang on to the outside of an aircraft at cruise speed.
Although, never having to test a safety harness like this one, I do know that a tether similar to this one should be able to securely tow a fully kitted paratrooper, with a full combat load behind a fixed wing aircraft traveling in excess of 200 knots indicated airspeed. Just as long as his chute does not open. And military transport crew chiefs wear them all the time when moving around on the open tail ramp of an aircraft in flight. Some personnel also had similar harnesses to insert and extract personnel hanging from rigging lines or Fast ropes (SPIES/FRIES). You would literally be hanging under a helicopter in flight with less than the soldier in your picture keeping you alive.
As far as getting sucked into the intake of the turboshaft engine, I don’t think it would happen. It appears that the intake is shrouded enough to decrease or eliminate FOD (human or otherwise). It certainly is not as big and open as a high-bypass turbofan. But, I would have to defer to others with that particular knowledge and expertise.
Edit:
To respond to your edit of your question, there is very little danger that a harness inspected and approved for use would just tear. The webbing used to make the harness has a long and safe history. As I have pointed out above, it has been documented and proven to be able to handle loads many times greater than the weight of a human being in many safety and aviation related fields such as skydiving.
The webbing may be cut. But it would take a deliberate act or a very sharp projection to cut it. A projection like that on the aircraft would be noticed as being dangerous and far more likely to cut the soldier.
A more likely scenario is one where the bindings and buckles on the harness are not properly done when the soldier puts the harness on. The two leg straps and the chest harness gives you three separate failsafes. I would hazard a guess that a safety inspection of the harness, it’s donning and wear are accomplished by a specifically trained senior enlisted soldier like a crew chief, load master, jumpmaster, or rappel master before an operation such as this.


Why limit the bank angle to 10° when passing through FL300 on a B737-800? When passing thought FL300, we are instructed to set the bank angle limiter on the MCP to 10°.

I know one of the reasons for this is that we are thrust limited so maneuver capability decreases.

Are there any other reasons?

One reason that comes to mind is as you get closer to the coffin corner, the extra G force due to maneuvering could cause a stall.  Quoting from "Stall the Pig",

  In the thin air at altitude, jets operate within a very narrow
  airspeed band between MMO (redline) and the low-speed limit, typically
  a yellow arc that provides a warning zone prior to a stall, indicated
  by a lower red line. At high altitudes and high weights, this
  band—known as “coffin corner”—can be quite narrow, leaving you a mere
  10 knots of usable airspeed range, for example. Load up the wing in a
  turn and that lower redline will quickly move upward toward your
  airspeed.

By limiting the bank angle, you also limit the G forces, and stay farther away from an accelerated stall.


Why is it not recommended to hold the nose up on the A320 after touchdown? I was recently told by a trainer in my airline that on the A320 if we hold the nose up after main gear touchdown then the flight control laws logic will memorise that pitch attitude after 5 seconds and will hold it there. Can anyone provide clarity on this? I have read the FCTM and know this is not a recommended procedure.

In flight mode the stick commands a load-factor. Which means it will be impossible to flare the aircraft, because as you pull on the stick, you'll be commanding a positive g-load.

Because of this the Airbus has a flare mode which activates at 50' RA. At 50' the pitch angle is stored (memorized). At 30' the aircraft commands a 2° nose down (it takes 8 seconds). The pilot would gently counter this by pulling back, resulting in a nice flare and no increase in the auto-thrust.

If the pilot did not float for way too long (they should not), the plane will touchdown before the 8 seconds pass, further eliminating the need to push forward on the stick to keep the nose gear planted.

The logic reverts to ground mode when two conditions are met: on ground for 5 seconds and pitch angle <2.5°.

If the 5 seconds pass and the nose is still +2.5°, the logic will remain in the flare mode and the THS will not reset to 0°. The pitch will revert to the one set at 50'. As the plane continues to slow down this may result in a nasty nose landing gear slam or a tail strike depending on the stored pitch angle and any gusts (kind of like this funny TV ad).

I do recommend you check your company's Flight Crew Operating Manual (FCOM) and to not use the internet for flight. If your instructor does not like too many 'why' questions during class, you can try and ask them after class. When you get your answers, try to validate them from the FCOM.

Some companies that fly extreme approaches have custom logic set by Airbus. So the installed logic may differ.


What is the clearance between a fan blade and the nacelle? What is the distance between the tip of a fan blade and the inside of the nacelle for a turbofan like the Rolls Royce Trent 900? Does this distance change significantly during cruise due to thermal expansion?

Can't say for sure without specific information from the manufacturer, which would be proprietary, but it's probably somewhere between 0.010" and 0.100". As you make the clearance tighter, you run the risk of a heavy rub between the blades and the case.  But as you make the clearance more open, you lose efficiency.  Somewhere in between there is a sweet spot where efficiency is fairly good and risk of a rub is low enough.  The exact clearance may vary significantly between different manufacturers and models, depending on what type of blades they have.

And yes, this distances changes significantly as you go from idle to takeoff to cruise.  Thermal expansion is a player, but most of it is mechanical loads (i.e. centrifugal force).

also, very minor point, but the clearance you are looking for is between the fan blades and the fan case.  The nacelle is a separate structure that is outside of the case.


Why does Boeing 247D have reverse slope windows when they were removed from the D models? Have a look at this article on a famed example of the 247D, DZ203, the first aircraft to make a completely blind landing. The first image is the aircraft during its flights with the RAF, which places it after 1942. Note the reverse-slope windows that are a hallmark of the early 247's.
However, this is a D model, and the D model of the 247 is noted as having had these removed and replaced with normal slope-down windows. This can be seen in the images of the other 247Ds on the same page, which were produced in the same batch of aircraft.
Does anyone know what's going on here? Were certain batches one way or the other?
NOTE: No, this is NOT a dup. The original answer from a while back states that all 247D's had forward slope windows, but this example clearly does not.

The Boeing 247D, DZ203 has construction number 1726 and was built in 1933.
The first production Boeing 247D produced made its first flight on September 5. 1934 and was scheduled to be delivered to United Air Lines late September 1934. (It didn't enter service with United immediately, instead it participated in the 1934 MacRobertson Race first, where it finished third.)
So DZ203 was built as a standard Boeing 247, and then later converted to the 247D standard. In the conversion the engines, cowlings and propellers were changed, but the windshield remained in its original style. This was common for 247D conversions.


What's required for the ADS-B to function? A GPS or Mode S Transponder? Jeppesen defines the ADS-B as a surveillance system broadcasting GPS-derived positions and other information such as velocity over the data link. Yet, the Wiki article on ADS-B relates it to the Mode S transponder system. So the ADS-B operates either on a GPS or on Mode S. Is my understanding correct?

ADS-B, Automatic Dependent Surveillance - Broadcast, is a  broadcast of the aircraft's position and other information.

The position is determined by a GPS receiver. It is possible to use another qualified position source, but today it is de facto GPS. Other GNSS (Galileo, GLONASS, Bei-Dou) are other likely candidates in the future, but as far as I know, none have been certified for ADS-B yet.

The broadcast is usually by the Mode S transponder but can also be done by a dedicated transmitter / transceiver in the Mode S format and frequency (1090 MHz).

In the USA below 18 000 ft, in addition to the Mode S based ADS-B, a system based on Universal Access Transceiver  (UAT)  is used. This operates on 978 MHz

A third broadcast system was VDL mode 4, it was never rolled out on large scale.

So ADS-B uses GPS to determine the position and it operates either  on 1090 MHz (a frequency also used by Mode S)  or 978 MHz to broadcast information.


How are sector capacity constraints set in the current US ATC system? My understanding is that in ATC, one of the constraints when considering the distribution of flights is the number of aircraft occupying a sector. Each sector can have different capacities.

I have read many academic approaches on how to calculate these capacities, but my doubt is: what is the method used right now, on February the 6th 2017?

I think January 25th, 2017 is close enough.
For Eurocontrol—

To evaluate sector capacities, the Network Manager uses the Air Traffic Control (ATC) Sector Capacity Analyser (CAPAN) methodology – using a fast-time computer simulation model that calculates the capacity of an ATC sector based on the controllers' workload. CAPAN is used with the Reorganised ATC Mathematical (Model) Simulator (RAMS) simulation engine.

Above quotation answers the question in a general form. The workings of CAPAN are laid out in this PDF, titled Capacity assessment and planning guidance document.

The FAA (US) isn't much different—

... the US and Europe use a comparable methodology to balance demand and capacity.

More on that here (PDF), titled 2015 Comparison of Air Traffic Management-Related Operational Performance: U.S./Europe.


How much fuel did this Boeing 787-9 have on board for this flying display? Once I saw how an Airbus A350 did a validation flight prior to an airshow and flew back to Toulouse from London Farnborough without landing/refuelling (distance: 550.57 mi (886.06 km)).
I thought that these aircraft must be very light to perform at airshows.
I then saw a video of the All Nippon Airways B787 at the Farnborough Air show 2016.
How much fuel did it carry to perform such a steep climb?

Looks like he is zooming after taking off: gain as much horizontal speed as he can, then pull up very steeply to convert some of the kinetic energy into potential energy. He only spends about 4-5 seconds at the crazy steep angle.

For zooming at these speeds, the mass is not very relevant: it appears in both kinetic and potential energy terms and cancels out.

$$\frac{1}{2}\cdot m \cdot \Delta V^2 = m \cdot g \cdot \Delta h \Rightarrow \Delta h = \frac{\Delta V^2}{2 \cdot g} $$

He just needs to take a longer take-off run at higher take-off weight to reach the same speed.


How does the mechanical linkage of the airspeed indicator convert dynamic pressure to KIAS? I understand the underlying principle of an airspeed indicator, ie. that it uses the Pitot-static system to measure the dynamic pressure as the difference between total pressure and static pressure.

Knowing that the dynamic pressure is $p_{d} = \frac{1}{2}\rho u^2,$ any linear variation in the measure will be a linear variation in $u^2$, not in $u$ alone. Yet the airspeed indicator markings are themselves uniformly spaced and still, they show $u$, not $u^2$. Therefore: how does the mechanical linkage convert a linear displacement (variation) in the dynamic pressure measurement $\propto u^2$ into $u$?

That is, how is the square root transformation of the dynamic pressure performed at the clockwork level of the airspeed indicator to obtain the indicated air speed?

My guess is that one of the gearwheels will be responsible for this but I haven't actually been able to find any information on this online.

(YouTube)

As the diaphragm inflates, it pushes a levered arm up, which drives a gear via a hollowed curved track (not via the cogs). The bigger the inflation, the smaller the rotation of the gear (arm increasing radius) compared to the piston displacement. It's the only variable in the mechanism that is not a fixed ratio.

Full disclosure: this is my analysis of the video, I haven't designed one before.


How is the pressure difference in passenger plane toilets generated? The toilets on passenger planes flush with an impressive amount of force - Is the negative pressure inside the tanks generated by a pump or are the tanks connected to the outside air pressure? Considering that the toilets should also work on the ground, I presume pumps are used - on the other hand, maybe the low pressure is stored inside the tanks from the last flight? Also, pumps would mean the toilets don't work when the aircraft is not powered up  - is this true? Also, how was the engineering problem solved of keeping the pumps or the tubes connecting to the outside free from waste?

How is the pressure difference in passenger plane toilets generated?

The pressure in flight is generated by using the vacuum outside. This dosen't work on the ground or at low altitude, so there's a pump as well to draw out the air to create an artificial vacuum.

  Considering that the toilets should also work on the ground, I presume
  pumps are used - on the other hand, maybe the low pressure is stored
  inside the tanks from the last flight?
  Also, pumps would mean the toilets don't work when the aircraft is not
  powered up - is this true?

Not sure about this one, but since the aircraft is seldom not powered when a person is onboard (maintenance can't do much without power either), I can't think of this being a significant problem. There might be a little bit of leftover pressure.

Airbus states that the vacuum pump is powered off the AC power bus, so it may be powered from the ground or the APU when the engines aren't on.

  Also, how was the engineering problem
  solved of keeping the pumps or the tubes connecting to the outside
  free from waste?

As is seen in the picture below, the tank is rinsed out through with the help of a second port on the access cover to clean it out. The rest of the system I believe is designed to last until the next maintenance, when (I think) it's connected up to a high pressure hose to thoroughly clean it out.

A320 Toliet System:

A320 System Details.


Why in certain airports the windows are blocked while others not? In certain airports, like the T1 of MMMX the windows are blocked or semi-blocked

while in others are not (MMGL)

I understand this could be done to avoid debris hit the windows, but then why?

Keep the sun out if facing south or west, help keep the temperature down.


Why are the pitot tubes on supersonic combat aircraft so long? I've noticed that on combat aircraft the forward (nose-mounted) pitot tube is usually very long, on the order of half a meter to well over a meter on some aircraft. Why are they so long? Surely the body of the aircraft is not disturbing the air in front of the craft, neither during subsonic nor supersonic flight.

Example, from an AIDC F-CK-1:

Example, from a Mirage III:

Note that I couldn't find any good pictures of the Mirage in which the entire pitot tube actually fit in the photo!

The length is not needed for supersonic flight, but for subsonic flight at high angles of attack. Due to the high wing sweep, a high angle of attack capability just happens to coincide with supersonic configurations.

In subsonic flow the air ahead of the aircraft is influenced by the aircraft's pressure field, and at high angles of attack and high wing loadings this reaches out quite a bit. The pitot tube can only measure total pressure when it points into the flow direction. Ahead of the aircraft, the local flow angle increases the closer you are to the aircraft, and this increases measurement errors, because now the pitot tube sits at an oblique angle to the airflow. A longer pitot tube reaches farther out into still relatively undisturbed flow, so less compensation is needed to arrive at good values for total and static pressure. In early flight test, the pitot tube is much longer again, because the compensation factors are not yet established.


Can the cracks found on the A380 wings tear the wing apart? Given all the press given to the cracks found on some A380 a few years ago, I am concerned about the safety of the current fleet of A380 owned by major airlines, although the planes are fairly new (less than 10 years), and are, I hope, well maintained.

Could their be today a catastrophe resulting from these cracks, especially between the 2-year revision period?

The issue has been fixed, for both the old and new A380's. Before the fix, the first 120 A380's did not face any danger according to Airbus.
From begadistrictnews.com.au:

"The aircraft is absolutely safe because there are so many ways for the loads to travel within the structure of the wing," [Airbus's head of engineering, Charles Champion] said.
"As it really is not a safety issue, we will inspect them over time ... within the next four years – some of them before."

From Wikipedia:

High-strength aluminum (type 7449) reinforced with carbon fiber was used in the wing brackets of the first 120 A380s to reduce weight, but cracks have been discovered and new sets of the more critical brackets will be made of standard aluminum 7010, increasing weight by 90 kg (198 lb).

From aviationweek.com:

Airbus has developed two fixes it says will permanently deal with the cracking of some rib-feet, which has already resulted in an airworthiness directive requiring enhanced inspection intervals and fixes where component cracking is found. One solution addresses the retrofit fix while the other alters the production process so the problem never occurs. The fixes should restore the aircraft to 19,000 flight cycles and regular inspection intervals, says [Tom Williams, Airbus’s executive VP-programs].

From flightglobal.com:

[21 March, 2014] LHT and Ameco to complete A380 wing-rib fixes next year.

Related: How strong is the A380 fuselage-wing joint?


What are the advantages and disadvantages of mixing the bypass flow with the core flow? Many Aircraft engines mix the bypass air with the core gases before exhausting to atmospheric pressure through a propelling nozzle. However, some do not mix and have separate nozzles for the flow of each. What are the advantages and disadvantages of each?

PS: I hope that I am clear now. Sorry if the question wasn't clear earlier.

In simple terms, mixing the exhaust flow (with any bypass ratio) is good for all the reasons except for construction and weight. It is aerodynamically more efficient; it reduces noise (exhaust noise makes most of the jet noise); it cools combustion chamber (and other downwind parts) more efficiently, etc.

However, making the mixing chamber on a high bypass / big engine would require enormous outer nacelle to cover the whole engine (and extend somewhat beyond), and the weight penalty and complexity/cost negates all the benefits.


Should an aircraft registration match the flag next to it? More specifically, I have noticed that on several of the aircraft of Blue Panorama Airlines, even though they are an airline based in Italy and the Italian flag (together with the EU flag) were on each of the aircraft's tails, they all had an aircraft registration prefix of "EI", which is obviously the prefix for Ireland.

Why do the flags and registration prefixes contradict?
Even if there is a reason for that, why does an Italian airline have aircraft registered in Ireland?

That's because the aircraft (some of them at least) are leased from Aerotron Ireland Ltd., an aircraft leasing company in Drogheda Ireland.

I only looked up one. It was EI-FVA.
Here it shows it being registered to Aerotron on Aug 23, 2016.
And here it shows it entering Blue Panorama's fleet on Dec 8, 2016.


How should I interpret this raw SID data from the FAA? I am trying to make sense of the SID structures from the FAA's 28 day NASR subscription files (SSD and/or STARDP, raw data in txt files), and I have two questions.

First, I notice that there are SIDs without any path: no transition FIX/NAVAIDs and no main bodies. What's the point of referencing a SID that does not contain anything else except the airport(s)? Take this SID for example (no other records exist for BELLEVUE SID):

D0075     NA N4729353W12212567RNT     BELVU3.BELVU BELLEVUE THREE
D0075     AA N4729353W12212567RNT

Second, another thing that prevents me from interpreting these SIDs is the difference between "NA" airports and "AA" airports. From the layout file which explains how to read and interpret the records, I read that "If there are airports served by the DP that are not served by any body, there will be one or more records describing these airports, with the FIX/facility type code field containing an 'NA'".

The problem is that in each SID where an 'NA' record exists, another one 'AA' record exists for the SAME airport described by the 'NA' record, so I cannot really understand if they are served by the SID's main body (if any). I am not sure how to interpret this, or the fact that SIDs like the one already mentioned (BELLEVUE) contain neither a main body nor any transition paths.

Another example is this SID; every "NA" airport seems to be also an "AA" airport:

D0161     NA N3832426W08950067BLV     CARDS1.CSX   CARDS ONE
D0161     NA N3844553W09022121STL
D0161     NA N3834133W09009183CPS
D0161     NA N3853237W09002456ALN
D0161     NA N3839436W09039074SUS
D0161     AA N3832426W08950067BLV
D0161     AA N3844553W09022121STL
D0161     AA N3834133W09009183CPS
D0161     AA N3853237W09002456ALN
D0161     AA N3839436W09039074SUS
D0161     ND N3845099W09021395CSX     CARDS1.BDF BRADFORD TRANSITION
D0161     R  N3921383W09013256SKYPE K5
D0161     R  N4004061W09003391SKUTR K5
D0161     NW N4109350W08935163BDF
D0161     ND N3845099W09021395CSX     CARDS1.LEBOY LEBOY TRANSITION
D0161     R  N3922076W09033098DEECE K5
D0161     R  N3926003W09034230LEBOY K5
D0161     ND N3845099W09021395CSX     CARDS1.NEENS NEENS TRANSITION
D0161     R  N3923033W09025555MYKEY K5
D0161     R  N4014535W09031538NEENS K5
D0161     ND N3845099W09021395CSX     CARDS1.SPI   SPINNER TRANSITION
D0161     R  N3919223W09000200TEWHY K5
D0161     NW N3950230W08940398SPI

Am I missing something here? I apologize for the lengthy post but I would really appreciate if someone could point me to the right direction.

To your first question, some SIDs exist to provide a basic set of information that will almost always be given as part of a clearance, rather than a path to fly. This allows a controller to not have to state that part of the clearance verbally, saving time and confusion.

On the Bellevue Three Departure from KRNT, the departure is as follows:

  Climb heading 350°, maintain 3000, expect RADAR vectors, expect filed altitude within 5 minutes after departure.

There's no location to code in the procedure (other than that from the Lost Communications section) so while the SID exists, there's not much to code for an automated system to interpret.


Can a Bombardier CRJ derate the takeoff thrust? I have recently been flying a Bombardier CRJ 700 in a simulator and wondered how to derate the engines for takeoff.

I know how the takeoff thrust derating is selected in Airbus and modern Boeing aircraft via the (M)CDUs (see also How do pilots set the exact amount of thrust needed for a reduced power takeoff?) and I have also seen panels for setting engine modes including a flex temperature in aircraft like the MD-80 or the Avro RJ. However, I could not find anything like this on the CRJ (at least not in the simulator).

Can the CRJ even derate the thrust for takeoff? And if, how does it work?

I saw the thrust levers have detents labelled SHUT OFF, IDLE, CLIMB, TOGA, MAX POWER:

(image source)

I assume TOGA would result in less thrust than MAX, but how is this selected?

Indeed the CRJ can use reduced takeoff thrust setting.

  Flex power is selected by entering an assumed temperature on the PERF MENU page of the FMS CDU. If the FMS is not available, the assumed temperature can be entered on the EICAS menu page using the EICAS control panel.

It's set up using the CDU or the EICAS control panel. That control panel is on the pedestal aft of the thrust levers, between the radio panels. Do note:

  The FLX indications on the EICAS menu page are only displayed if the FMS has failed or is not available.

As for the activation:

  When programmed, the FLX power setting is activated by the FADEC when the thrust levers are in the TOGA detents.

Source: CRJ700 FCOM

Note on terminology:

Derate and assumed temp/flex are not interchangeable. In derate the takeoff calculations are done based on the derated value remaining the highest even when an engine fails. It can be used to lower the Vmcg/a and in turn the V1 in certain situations (related post).


Why did some aircraft use hand-crank instead of gravity for alternate gear extension? I wondered whether the final scene in The Memphis Belle where they hurry to extend the gear by hand crank (because their electric system failed) is realistic, but according to this answer the B-17 indeed used a hand crank for manual gear extension.

But why did it (and other aircraft of the era that used similar system) need to manually crank the gear all the way down rather than just pull a latch out and let gravity do the rest, like modern systems generally work?

They had to manually crank down the gear because the electric system was damaged.

"As the B-17 limps closer to base, Dearborn orders the landing gear dropped. Only one wheel descends due to electrical failure caused by battle damage, but the crew are able to manually lower the malfunctioning wheel just before landing."

Free fall only works for hydraulic powered landing gear systems. The B-17 uses an electrically driven motor to raise and lower the gear.

Not all hydraulic landing gear can free fall. PBY-5A's have hydraulic gear and emergency gear extension used a backup hydraulic pump. Additionally you could manually break the up locks and then manually push the gear to the locked position.

I bet many other WWII era aircraft with hydraulic gear were similar. Free falling hydraulic gear probably came much later.


Where can I find ATC Guidelines for handling Airport Incidents? Immediately after an airport incident (e.g. a crash, runway overrun, fire etc.) it is fascinating to hear in recordings the ATC handle various duties so deftly . e.g. Ground vehicles, Fire, Go arounds, the actual aircraft involved, police, medics, tugs, closing runways or airports etc.

Is there any training material on this? I want to read more (My day job is in Chemical Plants & I'm thinking there is stuff we could learn from Aviation Incident Response Procedures).

I imagine these incidents are rare so any given controller doesn't get much by way of prior experience. So the best way to readiness would be via learning from past incidents or guidelines etc.

NTSB reports & past ATC tapes do help a lot but has anyone compiled these learnings into advisory documents? Just like pilots use checklists for difficult situations are there any similar ATC checklists?

I'll answer from US ATC perspective having worked ATC at 3 different airports. First, I'll describe the alerts, then I'll describe training

As with all things, each airport has different procedures for how they handle emergencies or accidents. For each airport, the airport operator and the ATC Tower will come up with numerous Letter's of Agreement for how they want to handle things from lighting to emergency services. My first airport had 2 alert conditions, Orange and Red. Orange was go to standby positions, something is inbound requesting emergency services to be ready in case something happens. These are relatively common. Red was an actual accident/crash.

The more common alerts are broken up into 3 categories I, II, and III. Alert I alerts are usually, a heads up to the crews to just be ready, but not go to the runway. Alert II are go to the standby positions, somebody's inbound with an issue and services are needing to go there. When this alert is declared, often as soon as the plane lands the runway is closed automatically until the airport inspects it(making sure no debris fell off the aircraft on landing). And Alert III is an actual crash. Most of the times, this is an immediate closure of the airport. This is due to the emergency services focusing on the accident and can't be available if something else were to happen on the field. Note, super large airports can have enough spare capacity to keep portions of the field still operating, depending on what all they have and how their command/control works.

Training wise, it's often just on the job training and usually the light emergencies, where people just need to get back or gear stuck or similar non-crash emergencies. Usually in the course of a controller's training at their facility they'll get a couple of these and know how to react. There are discussions of past issues as well, when there's time and resources available to do these types of discussions. Full on crashes, as stated are rare, so likely the first time a controller has to deal with it, they'll have seen small issues in the past to help prepare them.


What is the drag of helicopter rotor at jet speed? I wonder if a jet plane can have helicopter rotor for vertical take off and then, when moving forward just stops that rotor and uses lift from wings like normal plane.

Since rotor blade seems thinner and smaller than wings, I guess when turned off, its drag should be much lower than wing.

So why doesn't that type of hybrid plane exist?

Or the drag of the rotor at the jet speed would be so high? If the drag is high, why is it high, since the rotor blade is also airfoil like wing?

There were actually some experiments with stopped rotor. Furthest with the actual implementation was probably the Boeing X50 Dragonfly:

  By Source, Fair use of copyrighted material in the context of Boeing X-50 Dragonfly

The main reasons I can think of why nothing like this reached production yet are:

When the rotor spins, the blade on one side moves aft and needs to have its leading edge face aft, but when the rotor is stopped, both sides need the leading edge facing forward. So either the airfoil must be symmetric, but that has really poor efficiency, or some blades have to turn somehow, which is complicated.
To be light, rotor blades are normally very flexible and rely on the centrifugal force to keep them straight under load. But when they stop, they won't have such force, so they must be much stiffer, which makes them bit too heavy to spin.
Having separate wings and rotor would add a lot of weight, especially since the rotor would still have to be made strong enough to resist the aerodynamic loads when stopped.


Are there any electric ultralight aircraft? Are there any electric, FAR part 103 aircraft?

FAR part 103 aircraft are unique in that they don't need a license to fly.

ElectraFlyer offers a Part 103 legal trike, and at least as of two years ago, had a flying prototype of a more conventional designed single-seat Part 103 legal ultralight.

Realistically, given the weights of engines and batteries compared to the weights of the Rotax or similar engines usually used on ultralights, it's possible to turn many Part 103 designs into electric power, provided you're willing to do the engineering work yourself. For a fairly extreme example, see Dale Kramer's eLazair, a twin electric motor conversion of the Lazair ultralight that retains its Part 103 status.


What general aviation single-engine piston pressurized airplanes are there? Finding a general aviation single-engine piston airplane that's pressurized is a bit rare. What airplanes that meet these specifications have been produced? Also, which ones are still in production?

The ones I know of

Mooney Mustang M22 (out of production)
Piper Mirage (they claim its the only pressurized piston single on the market)
Cessna P210N (out of production)
Lancair IV-P (falls under experimental but is in "production" none the less)

For what its worth this is a pretty small category of plane to begin with. The M22 was not very successful (although it was ahead of its time) and there are not that many left flying (less than 20 I think). The P210N saw some better success and the Mirage seems to be selling but in the end of the day extra maintenance and complexity of the plane its self does not lend to a very practical plane considering there size and performance numbers.

If we are talking about the less produced or experimental designs we can add,

Junkers Ju 49 - One of the early test beds for pressurization
Farman F.1000 - Altitude record plane
Airco DH.9A - Another early frame used for testing


What qualifications are required to become chief instructor at a 141 flight school (FAA)? Under the FAA jurisdiction flight school operations can be conducted under the provisions of part 61 or part 141. If a flight instructor wanted to become a chief instructor at a part 141 flight school, what would they need to be qualified?

The requirements are in 14 CFR 141.35, Chief instructor qualifications. They're too long to quote here in full and the exact requirements depend on the type of instruction, but in summary:

Hold a commercial or ATP certificate
Hold a CFI certificate
Pass knowledge and proficiency tests
Meet minimum flight time requirements (depending on the type of instruction, e.g. 1000 hrs PIC time is required for private pilot instruction)
Meet minimum flight training time requirements

For training pilots for an instrument rating, the chief instructor also needs an instrument rating, instrument flight time and instrument training experience.


Is it possible to get permission to fly a quadcopter around the St. Louis Arch for non-professional means Is it permissible to fly a small quadcopter (<1 kg) around St Louis Arch for non-commercial means? If so what permit/permission is required?

The Superintendent's Compendium for Gateway Arch National Park says

  Launching,  landing,  or  operating an  unmanned  aircraft  (UA)  from  or  on lands  and waters administered  by  the  National  Park  Service  within the  boundaries  of  the Jefferson National Expansion Memorial  is  prohibited  except  as  approved in  writing by  the  superintendent.

Since drone flight is not listed under activities that require a permit they clearly don't approve such activity on a regular basis. The only way I imagine they would approve non-commercial activity is if there was some sort of organized event. On an individual basis I expect the answer would be no.


What is meant by Manual Tuning of ADF/NDB using BFO? As NDB transmission is either N0NA1A(requires BFO to be turned on for Manual Tuning, Identification and Monitoring) or N0NA2A(BFO turned on only for Manual Tuning).

My question is what exactly is meant by Manual Tuning and how does BFO help in Manual Tuning of ADF/NDB.

Thank you

How (and when) to use the BFO button on an ADF? This post explains when to use it, But I want to understand the concept of Manual tuning and Why N0NA2A needs the BFO turned on for Manual tuning?

Manual tuning is like the old style analogue radios with a dial or rolling switch for tuning, similar to old AM/FM radios in your car, etc. Old Automatic Direction Finder (ADF) systems still have a tuning knob that does the same thing.
BFO stands for Beat Frequency Oscillator. There is a bit of electrickery going on, but basically, the ADF radio receiver processes the incoming signal and splits it in two, and just about halves one of those signal's frequencies. These two signals are then layered on top of each other so you can hear them on the headset. You then proceed to tune the radio until you minimise the pulsating sound coming from the headset.
The best analogy of how this works is how a guitarist tunes by ear by comparing two strings. When they pick two strings at the same note, if they aren't in tune there is a pulsing harmonic that doesn't sound nice. When the string is tuned properly, this pulsing goes away. Same concept is happening in your ADF radio with BFO selected.
So in summary, BFO help you tune to the exact NDB frequency using your own ear as a guide.


For electric aircraft, is MTOW = Empty weight + Maximum payload? Electric aircrafts and most drones have simple powertrains, and their weight does not vary along the flight. After reviewing this thread I assume that:

MTOW = Empty weight (batteries incl) + max payload ?

I have reviewed some drone specs, and sometimes the numbers match, others don´t. Am I missing something?

A maximum payload may be specified to be less than tested MTOW minus empty weight in some cases, as a precaution against conditions that may reduce MTOW -- which depends on strip elevation, barometer, and temperature.

The thinner (higher and hotter) the air, the less a given amount of power can lift, in the case of a quad-copter or similar aircraft, or the longer it will take to reach takeoff speed and the slower climb will be, in the case of a conventional winged drone (electric or otherwise, though at least electric motors don't lose power with altitude).  Responsible drone manufacturers may (and should) specify a maximum payload spec that will keep gross weight below the least MTOW for foreseeable conditions.

There may also be cases where, for one reason or another, payload is based on testing conditions different from your flight configuration -- for instance, if you're using a heavier battery pack than the one used for testing, you'll have less margin below MTOW than the test condition.  Payload limits may also be specified below MTOW minus empty weight for reasons of center of mass location, payload restraint limitations, or other engineering reasons.


Obtaining Captain's name on historical flights? Is it possible to find out the name of the Captain on a previous flight?

Generally, no.  As a matter of protecting employees' privacy, that sort of information isn't typically made available beyond what a passenger may notice (nametags) or remember from a PA ("This is Captain Smith...").

In an unusual situation, it might be possible to get a name by contacting the airline, but it's probably unlikely that you'd get an answer back unless the pilot happened to call or write back to you.  Which could happen, but not often.


Why are the in-flight refueling probes of French-built fighter aircraft non-retractable? French-built fighter aircraft seem to have in-flight refueling probes that are not retractable, as seen from the linked images below. What are the advantages of a non-retractable refueling probe that make it worth the increased drag?

Rafale, and Mirage 2000.

According to Dassault, this configuration was chosen in order to reduce complexity and therefore avoid deployment/retraction problems:

Failure-prone systems have been eliminated early on in the design process:
... and the refuelling probe is fixed in order to avoid any deployment or retraction problem.

There are some other advantages as well:

A non retractable probe takes up less space in the forward fuselage (where space is at a premium) compared to the retractable one. For example, when the F-16 was fitted with a retractable probe (Conformal Air Refueling Tanker/System (CARTS)) for the Indian MMRCA competition, it had to be done via a change to the forward section of the right conformal fuel tank.

Modifications for retractable probe in F-16; Lockheed Martin photo , image from f-16.net
Another good example for this is the French Mirage F1s supplied to Libya, which had their radars removed to accommodate the retractable probes and the Mirage F1C-200 version, which necessitated the lengthening of the fuselage to accommodate the (non-retractable) probe.
The French aircraft, especially the Rafale are not exactly known for their large noses. in such cases, it is better to have a fixed probe, thereby saving the space required for the deployment/retraction mechanism.

It weighs less as the system is simpler- basically, you are eliminating the deployment/retraction system of the probe.

This system offers increased fuel flow and reduces maintenance requirements.

One thing to note is that the Mirage 2000's refueling probes are removable (it appears like Rafale's too is removable), so the drag penalty is not there when the mission doesn't call for it. At the same time, this reduces the weight penalty. Interestingly, it means that the number of probes can be less than that of the aircraft itself, with the probes installed as per requirement.

Another thing is the French doctrine- Unlike US, the Armée de l'Air  doesn't put too much into mid air refueling or stealth requirements.

It can also be interpreted as a design choice- all the French aircraft, right from Mirage F1 have had fixed refueling probes (while some were modified to accept retractable ones).


How are large cargo aircraft loaded at airports? Passenger aircraft are accessed at gates, or using buses. While they are parked waiting for passengers to board, the area they use is billed by the airport.

I was wondering what is the procedure for loading large cargo aircraft, whose payload must be moved slowly, using relatively complex equipment, and fastened to the airframe carefully.

Source

This takes time and if the area used is also billed, the cost could also climb a lot.

Do shipping companies have specific reserved areas to do that? Are these areas specifically reinforced?
What kind of fees are paid to the airport?

They will be loaded/unloaded on the ramp somewhere,

In the case of a facility like the one UPS owns in Louisville KY. they will have a large amount of ramp space in and around the facility which is on the field.

(source)

The aircraft will pull to the facility as they would a gate and be loaded there

(source)

In the case of just more generic cargo loading and unloading at an airport where no shipper has a facility the airport authority or FBO may have a facility set aside for cargo like the one at JFK. You can find a full list of the airlines/operators who have facilities at JFK here as an example. You can find a full map of the JFK cargo facilities here.

Keep in mind that some cargo will go on passenger planes and may be loaded at the gate. Along with everything else. In this case the cargo will be accepted and sorted (most likely at one of the above example buildings) and then towed over to the aircraft.

Airport fees here in the states are often charged by weight so the fees to the field will be judged on that. The fees for the cargo operations will most likely depend on what you need done such as loading/unloading, storage, customs, refrigeration, live stock services etc. I dont see any explicit prices listed but here is another one of JFK's cargo handlers CAS, I would assume you could contact them if you wanted some pricing on a given transaction.

I would not think the reinforcement is any different than anywhere else, a fully loaded aircraft be it cargo or people is the same weight.


Why do you never see any other planes in the sky whilst flying? I was just wondering as I passed the airport this morning why, whilst we are flying, do we never see any other planes nearby? There must be millions of planes and millions of people flying each day, I appreciate the sky is massive but these planes must follow roughly the same routes so how is it that they never seem to pass by any other aircraft?

If you're not seeing them, you're not looking.

I see planes all the time when flying commercial.  Obviously, I see them a lot more when close to a major center, and a lot less when in the sparse parts of the Pacific Northwest (Montana, Idaho, Oregon, Washington).

I think spotting them may take some practice. Visually, a plane 10+ miles away is a very small dot, and easily missed.   Try looking for contrails and be sure to look at altitudes above and below you.  Scan the sky in narrow, 10°  concentrated "fields of view" to scan from left-to-right all the way across the sky.


Non-Towered Airport Operation Logs Do general aviation non-towered airports have to submit any types of logs to the FAA regarding total number of take-offs and landings in a given year?

I'm trying to figure out how busy a small airstrip near a property might be, I'm not having any luck getting the airstrip owner on the phone.

Thank you!

Look up the airport at http://www.airnav.com/airports

It'll show info such as:

Airport Operational Statistics

Aircraft based on the field:        66

Single engine airplanes:        65

Multi engine airplanes:     1

Aircraft oper  ations:  avg 70/day *

52%     transient general aviation

48%     local general aviation

for 12-month period ending 07 April 2015


What is the longest period of time an aircraft type has been grounded due to safety concerns? Obviously inspired by the current 737 Max situation, what is the longest period of time that any individual type of airliner has been grounded for safety concerns (excluding those that never returned to service)?

The Yak-42 was grounded from June 1982 to October 1984 (26 months) for a cause similar to Alaska Airlines Flight 261.


What sort of debris has been found in 737 Max fuel tanks? There have been numerous reports of Boeing finding "foreign object debris" in the fuel tanks of its 737 Max airliners.

It's not clear what this debris is. It could range from a couple of missing screwdrivers and a blowtorch, to perhaps microscopic particles that might contaminate the fuel.

Has Boeing released any details of what these objects are? And, more generally, how unusual is such contamination?

As a generic answer, not unusual. Besides personal objects like bucking bars, clecos, rags and such left in tanks, the biggest contamination source, from my experience working on a production line many many years ago, is "swarf". Swarf is aluminum drill shavings and mountains of it are created during assembly.  You will also get wire cutoffs and other similar bits, shop (bucked) heads of rivets that were drilled and punched out because the rivet was dumped when being driven and had to be removed and reshot.

All that stuff is supposed to be thoroughly vacuumed out before the sealers go in with their goo guns, but nothing is ever perfect.  Even if the wing was cleaned out before the sealing was done, if the wings get modded or repaired farther down the line, where more rivets get drilled out and redone, more swarf or other contam gets introduced and may get overlooked.

The first time fuel flow test runs are done on the completed aircraft, that's when you find out how bad a job they are doing up the line as the fuel screens and filters are removed to check.

Some manufacturers will build special rotation fixtures to put the wing in (not really practical in a one piece swept wing, but easy to do with a straight one) after it comes out of the assembly jig to rotate, barbecue chicken style, while they listen for objects clattering about. It's good for catching bucking bars, clecos and such that get left inside.


Why do airports in the UK have so few runways? Almost all of the major airports in the United Kingdom are single-runway (or functionally-single-runway) installations, with only two of the very busiest (Heathrow and Manchester) having as many as two runways (although Heathrow has a third under construction).

(In addition, even for the three major UK airports that have two runways, the two runways are always a parallel set, with no provision made for crosswind operations.)

This is - with few exceptions - far fewer runways than would be normal for airports of their size.  Taking the seven airports in the UK with more than ten megaemplanements in 2018 and comparing them to similarly-sized airports elsewhere:

Heathrow (two runways, with a third under construction) v. O'Hare (seven runways, with an eighth under construction)
Gatwick (two [functionally one] runways) v. Newark (three runways)
Manchester (two runways) v. la Guardia (okay, two runways)
Stansted (one runway) v. Baltimore-Washington (two air carrier runways1)
Luton (one runway) v. Calgary (four runways)
Edinburgh (one runway) v. Norman Mineta (two runways)
Birmingham (one runway) v. Raleigh-Durham (two air carrier runways1)

Having so few runways not only increases congestion and severely limits the number of flights that can use the airport without infringing on safe separation distances between aircraft, but also poses the risk, for the four single-runway airports,2 of an unserviceable runway (for instance, due to snowplows, potholes, trespassers, flocks of birds, wayward deer, or a disabled aircraft) shutting down the entire airport, potentially for a prolonged period of time.

Why do the UK's major airports have so few runways compared to the norms for airports of their sizes?

1: Plus one general-aviation runway each for Baltimore-Washington and Raleigh-Durham.

2: And, to a lesser degree, for functionally-single-runway Gatwick, as its emergency backup runway is close enough to the main runway for a single debris event to potentially affect both.

There are perhaps 101 non aviation-related reasons why the UK does not have larger airports, such as space consideration (we're only a small island!), politics (NIMBY!), civil engineering (Airports are commonly near urban centres and are often surrounded).

However, the most aviation-related related reason I can think is that we just simply rarely need cross runways. If you look at most large airports in the UK their runway(s) are east-west(ish). The reason for this is over 70% of the prevailing wind direction in the UK is West or SouthWest.

In addition, we rarely have extremes of wind - those exceeding the crosswind capabilities of common commercial airliners. Heavy snow is even rarer. I can probably count the number of times a runway at a large airport has been closed due to any of the reasons you mention in the last 20 years on two hands.

Bottom line; it's just not necessary. There is no socio/political/weather climate to warrant it.


What is the dutch roll filter? How does it work? Some airplanes have a dutch roll filter for the "yaw damper."

What is the dutch roll filter?
When is it used?
Is it ever required for certification or operation?
How does it work?

I assume you know what a dutch roll is, if not here is a brief summary:
At the airplane yaws to one side the wing that is moving forward has a higher speed and creates more lift which causes the aircraft to roll towards the trailing wing. There are also effects like the vertical stabilizer usually being above the center of gravity which at great side slip angles causes the aircraft to roll towards the trailing wing as well. And lastly there are effects like the fuselage causing a disturbance on the trailing wing.
All these effects depend on the aircraft type and wing configurations. But generally speaking a yaw rate creates a roll rate as a side effect. And if you move the rudder left and right constantly then you cause the wings to rock, which is called a dutch roll. This behavior is quite unpleasant for passengers in the back or front because they are accelerated left and right.

To suppress this side effect of a yaw motion creating a roll motion and a subsequent dutch roll you can add a "durch roll filter" to the yaw damper control system. All it does from my understanding is to combine the normal feedback loop for the yaw rate with a second loop for the roll rate. This causes the yaw damper to reduce rudder deflection slightly whenever the roll rate picks up and increases it again when the roll rate stagnates which can stabilize the dutch roll and causes a more uniform roll rate.
Modern fly by wire aircraft can also use the ailerons to dampen the dutch roll much more effectively. But if the yaw damper can only affect the rudder than this is obviously not an option.

I'm not 100% sure when it's used but I'm guessing that all modern airliners have this because there are people in the far back that would get motion sickness really quickly when the yaw damper allows a dutch roll and the aircraft swings side to side on every turn. For a small general aviation aircraft this may not be needed and development costs can be kept low.

As per all control systems I think the yaw damper with or without this filter has to be certified. And if the system is changed later on will also have to be tested and certified. Depending on the aircraft type you may need redundant yaw dampers


Can I fly for commercial jobs with just my temporary certificate? I just received my temporary certificate and when I called the airman registry to ask how long it would be before I received my permanent copy, they basically told me it was going to take awhile. So my question is, what can I do with the temporary? Are commercial jobs allowed? Can I apply at private companies to fly for them?

A temporary certificate is valid for everything that a permanent one is valid for; it's just, well, temporary.

14 CFR 61.3:

  No person may serve as a required pilot flight crewmember of a civil
  aircraft of the United States, unless that person:

  (1) Has in the person's physical possession or readily accessible in
  the aircraft when exercising the privileges of that pilot certificate
  or authorization—

  [...]

  (iii) A temporary certificate issued under §61.17;

61.17:

  A temporary pilot, flight instructor, or ground instructor certificate
  or rating is issued for up to 120 days, at which time a permanent
  certificate will be issued to a person whom the Administrator finds
  qualified under this part.

(See this question for what happens when the 120 days are up.)

As far as the FAA is concerned, your temporary certificate is no different from a permanent one. I suppose it's possible that an employer might decline to hire you until you get a permanent certificate but I think that's highly unlikely within the US (employers abroad might be a different story). I've seen people pass a CFI checkride and start instructing within a few days, for example.


Can the lift fans used on a F-35 be driven by a turboshaft engine instead of the jet engine? If yes, which one? This is for a sci-fi story I'm writing, so the answer doesn't have to be perfect, just close as possible.

Can the lift fans on a F-35 be driven by a turboshaft instead of the jet engine If yes, which one? The jet engine that drives the lift fans in a F-35 is called Pratt & Whitney F135  engine. The engine dumps 20,000 shaft horsepower onto  shaft that spins the fans. But i need a way to do this with a turbine, not jet engine with thrust coming from the rear.

I'm assuming that it takes a certain amount of shp (shaft horsepower) to spin the lift fans at the correct rpm.  The fictional vtol is to have 4 lift fans driven by four turbine with little heat signature to avoid infrared.

There is no difference between turbofan, turboprop and turboshaft engine except for what is mounted on the shaft. There are many cores that are used in all of turbofan, turboprop and turboshaft engines. So yes, they can be driven by turboshaft. In a sense, the engine that drives them qualifies as turboshaft simply because it drives them.
That said, the lift fan of F-35 is absurdly inefficient. The thing is that lift is equal to mass flow through the fan/propeller times change of speed of the air, but the power required is equal to mass flow times square of change of speed, plus drag that grows with RPM.

Now the fan is small, so it has small mass flow and so it needs to accelerate the air to great speed and to do that it also needs high rpm, both greatly increasing the power required to spin it.

F-35 can live with that, because it only spends very short time in hover and a lot of time at high speed, so it can trade efficiency at hover for low drag at speed. But anything that should work like a helicopter should better have a large rotor like a helicopter, because it takes much less power to spin it (and thus has much lower fuel consumption).


Could the wing struts on the SUGARVolt cause problems? On Boeing's concept aircraft, the SUGARVolt, there are wing struts connecting the fuselage and the wings, which is for making sure that the wings do not bend too much during flight.

Could the wing struts cause aerodynamic instabilities, and could this make the aircraft more efficient, or less efficient? In what ways?

Struts like those on the SUGAR Volt and SUGAR Freeze have been used on gliders and propeller aircraft without problems. Since they are loaded in tension, they can oscillate like the string on a guitar. Note that they are braced at two thirds of their span to reduce their free length and to increase their resonance frequencies. A coupling between the strut bending motion and oscillating aerodynamic forces can be expected, but only at speeds above the SUGAR Volt and SUGAR Freeze design speed.

Henschel 126 with a very similar strut arrangement. Only with the strut it was possible to reduce the wing chord at the root in order to give the pilot better upward visibility (picture source).

Those struts do indeed reduce drag. They cause friction drag but allow to build the wing much lighter, thus reducing the required lift and the inevitable induced drag.

Modern gliders have very similar wings but do not use struts. This might seem puzzling, but can be explained by the low payload of a glider, which is at most two humans and their equipment. In order to fly faster, gliders use water ballast to make their wings even heavier. Therefore, a glider will not benefit from a lighter wing.

Nimeta single-seat glider (picture source)

In contrast, a revenue-generating aircraft needs to pack as much payload as possible. It cannot afford to carry unnecessary weight around in its structure. Also, a lot of its mass is concentrated in the fuselage, which increases the wing's root bending moment. A strut will help to reduce the root bending moment greatly and will enable a much lighter wing structure.


What are the states that the landing gear can be in? What are the valid set of enumerated states for landing gear?

My current working set is:

DOWN
DOWN & LOCKED
STOWED
STOWED & LOCKED
INOPERATIVE
CYCLING_UP
CYCLING_DOWN

Also, are there any definitions in which UP is distinct from STOWED?  (I can't find any.)

Any instruments always show only three states:

Down and locked (green)
Up/stowed (extinguished)
Anywhere in between (red)

If you want to simulate it, remember that while the pilot can only command one of the two end states, the transition is a continuous process and you need to represent exact position of the gear in each frame of the simulation. So you need a value that will smoothly transition between 0 (stowed) and 1 (down and locked). Any value in between will indicate red on the instrument, but will correspond to different state of the gear animation.

The exact steps during gear extension (and in reverse for raising) differ by aircraft, but generally the animation will have three parts that you will map to suitable ranges of the gear state value:

opening the gear door,
lowering the gear and
closing the main gear door.

The last step actually complicates issues a bit, because the gear is already down and locked when the main gear door close and in case you do gravity extension the main gear door remain open.

So the suggested mapping is actually something like:

opening the gear door 0.0 to 0.3
lowering the gear 0.4 to 1.0
closing the main gear door 1.1 to 1.4

When you extend the gear normally, the value will transition up to 1.4 (and show green past 1.0), when you extend the gear via alternate mechanism (gravity drop), it will only transition to 1.0. If you want to simulate alternate extension, of course.

Tweak the values to make the animation look appropriate. The relative speed differs by aircraft. Some aircraft also don't have gear door (e.g. 737 only has one panel that is attached to the strut on main wheels; it still does have nose gear door, so the process will be slightly different for each leg).

Which leads me to note, that if you want to simulate failures, you definitely need separate value for each leg, because some failures, like jammed actuator, only affect one gear. Also in reality the legs take slightly different time to extend, so you can add some variability to the transition time if you wish.


Should I avoid testing unnecessary equipment? Suppose you are on a day VFR flight and you are testing your aircraft lights. If you discover that the bulb for one of your nav lights is blown, then you can turn the switch off and tape it off, placard it as inop, and fly anyway. However, if you don’t placard it, my understanding is that you are not legal to fly, even if it is day VFR and you leave the switch off.

My question: should you avoid testing unnecessary equipment? Presumably if you did not test the nav lights during your preflight (not intending to use them) then you never knew they were broken, therefore you didn’t need to turn off and placard as inop. What is best-practice here? My question is specifically about nav lights, but I am also interested in other optional equipment (eg an autopilot).

(This is in the USA as a Part 91 flight.)

The best practice is to pre-flight everything for every flight:

If you have different pre-flight procedures for different situations then sooner or later you'll use the wrong one and miss something that you should have found. Consistency is really helpful in procedures.
Even if something isn't needed for the flight, checking everything gives you an accurate picture of the state of the aircraft. One broken light is probably just a light bulb, but 3 broken lights and inop pitot heat may be a more serious electrical problem. If you don't know the state of the aircraft then you can't make informed decisions.
Plans change. You might set off for a day VFR flight on a clear, sunny day intending to be home hours before sunset. But if the weather changes quickly or you get delayed then your flight home might have to be night VFR or IFR. If you have equipment issues that restrict your options then it would be best to know that before you depart.

There's nothing wrong with flying with inop equipment provided that you know about it, you've complied with the rules in 91.213 on minimum required equipment and deactivating and placarding, and you've made a conscious assessment of the risk. But not inspecting the aircraft properly or deliberately ignoring inop equipment is a really great way to put yourself in an "up there wishing you were down here" situation.

And from a regulatory point of view, if you don't preflight properly then you're probably in violation of 91.103 ("become familiar with all available information concerning that flight") and of course 91.13 ("No person may operate an aircraft in a careless or reckless manner").


For a given airfoil, with known Cl and Cd curves, how can I calculate the autorotation AoA range? I'm trying to tabulate the differences of (vertical) autorotating behavior for rotors of equal chord and span, but with different airfoils. Of course, they can be studied case by case, but there may be a simpler, less laborious way... Hence my question...

This NACA report may help you further.

Basically, determine $v_i$ = the induced velocity in the hover, then vertical autorotation speed is around:

2 * $v_i$ for a rotor with 12 degree blade twist.
1.8 * $v_i$ for an untwisted rotor.

More detailed information in Prouty chapter 2, although the annoying non-metric constants pop up all the time.