How do hot air balloons navigate? Hot air balloons are quite obviously carried along with the wind, so how can they be navigated?  Choosing the correct launch point relative to the desired landing point would seem to play a major part of this, but logic states that it is not always possible to choose the best possible launch and landing points.

Can a hot air balloon be "steered" by increasing or decreasing altitude, hence selecting just which wind it will be subject to?  Does the direction of the wind vary with altitude, and if so, how much?  How do balloon pilots know how the wind will vary at altitude if that is the case?

That is exactly how balloons “steer” - they pick an altitude where the winds aloft are going the way the pilot wants to - assuming winds at an available altitude exist where the wind is what the pilot wants.

Many balloonists use Ryan Carlton’s wind tool found here to get a good idea of local winds: http://ryancarlton.com

NOAA has a website called RUC soundings that presents actual wind and temperature aloft data from balloon launch sites and then interpolates for locations in between: https://rucsoundings.noaa.gov/

While the pilot can plan a flight and do amazingly well to get near to where they wanted to go, at the end of the day, a balloon, as an unpowered aircraft, is at the mercy of the winds.


How to call a cartesian (END) coordinate system, that is referenced in surrounding air? I'm looking for the correct/usual terminology for a coordinate system, that is moving with the wind.

I do calculations in a Cartesian East-North-Down (END) system. When taking wind into account I'd like to move this system with the wind and transform it back to an earth-fixed END-system afterwards. So basically, the reference point of my coordinate system isn't a point fixed on earth, but an air molecule that is blown with the wind.

Is there a common name for such a coordinate system?

Firstly, I thought of it as the "Wind-Frame", but after some investigations I conclude, that the term "Wind-Frame" is meaning a different system which is also rotated and not only moved in the plane.

So if any body knows, I'd like to hear from you.

I use this because I calculate Dubins paths and want to take wind into account. So when projecting the path of the plane on earth, you will see a trochoid, but the plane itself will fly a plain circle in its surrounding air. This eases calculations a great deal.

Some people call it Amosphere-Fixed reference frame.
(see at: heli-air.net)

Just to add a thought, this name seems to imply a global reference system, whereas the velocity of air molecules may be very local.


Can a DPE do a checkride in any plane of the same class? Do DPEs have to be certified in a specific aircraft type, or can they do a checkride in any airplane of the same class?

For example, if I have done all my training in a Cirrus SR22 and want to do my IFR in the same Cirrus SR22 that I own, can I use any DPE who can do IFR for ASEL?

FAA Order 8900.2B (General Aviation Designee Handbook) sets out the policy on Designated Pilot Examiners (DPE).
Verbiage from Chapter 7, Section 1 states:

Additional Qualifications. DPE applicants must be technically qualified and must hold all pertinent category, class, and type ratings for each aircraft for which designation is sought. All DPEs must meet the requirements of Title 14 of the Code of Federal Regulations (14 CFR) part 61, §§ 61.56 and 61.57, as appropriate.

And from para. 1. f (2) (a) of that section:

(2)    Meet all eligibility and experience requirements for the specific designation sought.
(a)    A designee applicant must have logged at least 5 hours as PIC in each make and model of multiengine airplane and helicopter in which that designee conducts tests.

In specific response to your question (using the guidance shown above in FAA Order 8900.2), it appears that as long as the DPE has been given the FAA authority/Designation to conduct the type of check you are requesting (i.e., Instrument Rating) he/she should be able to do it.
However, some DPE's are only authorized (by the FAA) to conduct Private Pilot examinations, others have additional authority such as Private Pilot/Commercial Pilot/Instrument, etc.
You should pose your question to the DPE directly for confirmation.


Can an aircraft flying VFR with a squawk code enter adjacent class C or D airspace after being handed over to the destination tower? In the US, a VFR aircraft request VFR flight following and is given a squawk code after takeoff.
15nm before arriving at it's destination class D airport, the TRACON facility instructs the pilot to "contact the destination tower".
The pilot keeps his squawk code and change frequency to contact the destination tower. The tower instruct the pilot to enter "straight-in" for the runway in use. However, in order to enter straight-in, the pilot must briefly transit through the class C shelf of an adjacent airport and through the class D of another airport not far from the destination.
Q: Is the pilot cleared to transit through both adjacent C and D airspace since he still squawking the code provided by the local TRACON?
I understand the legal requirements to enter each airspace (AIM 3-2). If the pilot was still in contact with the TRACON facility he would be cleared to enter adjacent C and D airspace since he is squawking a discrete code AND previously established two-way communication. In this case however, the pilot is not anymore talking to the TRACON and switched to the destination tower. I cannot find an official reference that covers this particular scenario.
I came across this question/answer, Does Flight Following automatically include permission to fly through class C or D airspace?, before posting but my scenario is different since the pilot is not talking to the TRACON anymore. It's subtle but makes a big difference.

Trust, but verify.
The pilot must comply with 91.129 and 91.130 unless otherwise instructed by ATC.
ATC of any kind (radar or tower, Class C or Class D) should coordinate with any affected tower if an aircraft they are providing services to will enter another facility's surface area airspace. At least that's how I read the 7110.65 2–1–16, which you will note is in the "General Control" section and not the "Radar" section... though the wording definitely implies that it's directed at radar controllers.
The radar controller should have coordinated with the Class C tower (if necessary) and Class D tower controllers before switching the pilot to the destination Class D tower controller, if they expected the pilot would have to enter the respective surface areas. The destination Class D tower controller should have coordinated with the other tower controllers, if they expected the pilot to enter those surface areas. If coordination was not effected, they should not issue instructions which would imply permission to enter the other surface areas.
The pilot should query whichever controller they happen to be talking to, and follow the instructions they receive ("proceed through the XXX Class Delta airspace" or "remain outside of XXX Class Delta airspace").


Is a light aircraft still usable after a successful airframe parachute deployment? Some light aircraft now have airframe parachutes. If a pilot does have to pull the chute on a Cirrus (for example), is the aircraft flyable or at least repairable after landing or is it a write-off? What G forces are involved in the impact?

I realize that there are lots of possible variables here, but let's assume that the parachute deploys correctly and in plenty of time for a stabilized descent; touchdown is in 'ideal' conditions, i.e. on level, unobstructed ground; and impact forces are as described in the Cirrus CAPS guide:

  The airplane will assume its touchdown attitude to optimize occupant
  protection. The airplane will descend under the canopy at less than
  1700 fpm and ground impact is expected to be equivalent to dropping
  from a height of 13 feet (about 4 meters). The airframe, seats and
  landing gear are all designed to absorb the impact energy.

For the Cirrus at least, it sounds like that the odds are that the plane will be a loss.  Thus far of 53 CAP deployments, only "9 CAPS Planes that Were Repaired and Flew Again"

Revision A7 of the Cirrus SR22 POH currently states "CAPS deployment is expected to result in damage to the airframe" that updates the earlier language that "The system is intended to saves the lives of the occupants but will most likely destroy the aircraft."

https://www.cirruspilots.org/copa/safety_programs/w/safety_pages/723.cirrus-caps-history.aspx


How does an airline decide when to cancel a long haul flight permanently? BROAD QUESTION WARNING: Obviously the airlines cancel the routes because they are not making money, but would that not have been factored in when they start a route? For example, the current SFO-BLR route seems to be fully booked all the time (a friend flew on it recently), but it would not easily be scrubbed given that Air India is still a government owned airline.
Similarly international airlines would not start new flights to Phoenix because of its proximity to LAX. But there is a sizeable amount of traffic that flows between PHX-LHR (It used to be 2 daily direct flights out of PHX pre COVID)

There are various reasons airlines may chose to stop flying a route. While its often financial there are usually underlying reasons that drive the decision. While financial models are drawn up when planning routes, outside factors may effect the finances in unpredictable ways.
Lack of travel: if a destination becomes unpopular or a city sees diminishing travel an airline may chose to stop flying the route, this may come after various scale backs.
Airframes get decommissioned: The economics of a route are often tied to the airframe used to fly it. Historically with the hub and spoke model smaller short range aircraft were used on quick routes. As airlines decommission old airframes some shorter (or even longer) routes are no longer financially viable.
Geopolitical reasons take hold: Its possible for government actions (generally related to visas and passports) to adversely affect travel and thus make a route either not profitable or completely not viable.
Changing Model: This ties into the airframe issues but over time airlines have changed how they approach travel, both as a company decision as well as a response to technological changes in the industry.
"Can't Land here": Sometimes you just can't get the plane in there
Airport Closures: Airports are by no means everlasting, they do sometimes close down
Bigger, Faster, Farther: There are lots of airports scattered all over the globe that acted as common re-fuel spots during the heyday of the large prop planes and were ultimately not needed during the jet age. While some of them remain as emergency landing spots they dont see nearly the traffic they once did and long distance routes simply bypass them.


What exactly distinguishes a beacon light from a strobe light? Different sources seem to have different opinions:

Wikipedia: Aircraft warning lights:

  These lights include landing lights, red or white flashing beacons, wingtip strobes, and wingtip navigation lights.

Beacons and strobes are flashing lights.
Beacons may be red or white.
Strobes are wingtip lights. I interpret this as strobes being directional while beacons cover 180°.

Aeronautical Information Manual (AIM), 4−3−23. Use of Aircraft Lights:

  b. An aircraft anti−collision light system can use
  one or more rotating beacons and/or strobe lights, be
  colored either red or white, and have different (higher
  than minimum) intensities when compared to other
  aircraft. Many aircraft have both a rotating beacon
  and a strobe light system.

  d. Prop and jet blast forces generated by large
  aircraft have overturned or damaged several smaller
  aircraft taxiing behind them. To avoid similar results,
  and in the interest of preventing upsets and injuries to
  ground personnel from such forces, the FAA
  recommends that air carriers and commercial
  operators turn on their rotating beacons anytime their
  aircraft engines are in operation.

Beacons are rotating lights. They're always referred as rotating beacons in the AIM.
Both beacons and strobes can be either red or white.
I take the sentence Many aircraft have both a rotating beacon
and a strobe light system. as beacons being the lower intensity lights which are constantly turned on during engine operation signalling the danger of an aircraft in operation, while the strobes being the higher intensity flashing ligths with the reason of being seen from great distance.

Wikipedia: Aviation navigation lights

  Aircraft navigation lights are placed in a way similar to that of marine vessels, with a red navigation light located on the left wingtip leading edge and a green light on the right wingtip leading edge. A white navigation light is as far aft as possible on the tail or each wing tip.[3] High-intensity strobe lights are located on the aircraft to aid in collision avoidance.[4]

  In civil aviation, pilots must keep navigation lights on from sunset to sunrise. High-intensity white strobe lights are part of the anti-collision light system, as well as the red rotating beacon.

  All aircraft built after 11 March 1996 must have an anti-collision light system (strobe lights or rotating beacon) turned on for all flight activities in poor visibility. The anti-collision system is recommended in good visibility, where only strobes and beacon are required. For example, just before pushback, the pilot must keep the beacon lights on to notify ground crews that the engines are about to start. These beacon lights stay on for the duration of the flight. While taxiing, the taxi lights are on. When coming onto the runway, the taxi lights go off and the landing lights and strobes go on. When passing 10,000 feet, the landing lights are no longer required, and the pilot can elect to turn them off. The same cycle in reverse order applies when landing.

Beacons are red rotating lights.
Strobes are high-intensity white lights.
Beacons stay on for the duration of the flight including the whole engine run time.
Strobes are added from takeoff until leaving the runway after landing.

Is there a clear definition?

I think there are two points in your question: what is the physical difference between a beacon and a strobe, and what is the operational difference? For the rest of this answer, I'm going to assume that you're asking about an aircraft that has both a beacon and strobes; as you quoted above, it's possible for an aircraft to have neither. I'm also going to assume you're asking for an answer that applies in the US; regulations in other countries may be different.

First, the physical difference is exactly what you've already determined: a beacon is a (relatively) low-intensity rotating red or red/white light; a strobe is a high-intensity flashing white light. (As noted in the comments below, some beacons flash instead of rotating, but they're still lower intensity than a strobe.) This isn't formally defined anywhere (e.g. 14 CFR 1.1 doesn't define them) but the information you found in the AIM is exactly how everyone I know uses the terms. It's also how you find those words used on aircraft part sites, e.g. beacons and strobes. So whatever the 'strict' definition might be, the practical and accepted one is exactly what you've found out.

Second, the operational difference essentially comes down to the question "when do I have to turn them on?" and in addition to what you found in the AIM the FAA gave more details as part of this legal interpretation. The questioner asked two questions about beacons and strobes: when to turn them on, and if they both have to be turned on. The key regulation quoted is 14 CFR 91.209, and note that the FAA considers the beacon and the strobes together to form a single "anticollision system":

  [...] it appears that the strobe light and the rotating beacon are
  part of the same anticollision system.

When to turn them on:

  91.209(b) requires that an aircraft's anticollision lights be turned
  on once that aircraft's engine is started for the purpose of air
  navigation. As a safety precaution, the anticollision lights should be
  on before starting an engine or causing a propeller or rotor to move.

If both have to be turned on:

  [...] because section 91.209(b) does not contain an exception for
  alternative sources of anticollision lighting, turning on the
  anticollision beacon would not relieve a pilot from the requirement to
  turn on the anticollision strobe lights. See § 91.209(b). However, §
  91.209(b), does give the PIC the discretion to turn off the anticollision beacon and/or the anticollision strobe light system if
  the PIC determines that it is in the interests of safety to turn off
  either one or both of these components of the same lighting system.

In other words, the regulations say you should turn them both on, but as PIC it's up to you to determine if using them is safe or not, and if not then you are allowed to turn (or leave) them off.

Practically speaking, I've always been taught to turn the beacon on before starting the engine because it's there to tell people near the aircraft that the engine is running or about to be running. The strobes should go on any time you need to be highly visible (which is most of the time), but not if using them would blind someone else or even yourself, e.g. taxiing or flying in clouds. The AIM 4-3-23 has more details on that, in addition to the parts that you quoted.


Why are some airports not allowed as IFR alternates, even if conditions there are VFR? Why are some airports disqualified for use as an alternate (as listed in a approach procedure for that airport (A N/A)), when there is a provision in part 91 that an airport without an instrument procedure can be used if descent from MDA and under basic VFR conditions are expected using the 1-2-3 rule?
Example: I19 (Greene Co. Airport near Dayton, OH) has a disqualification (A N/A) listed in the procedure. Yet 11 miles away, I73 (Moraine) has no procedures and as I know it there is no specific disqualification.  Albeit, you could only use Moraine for an alternate if descent from MDA and under basic VFR is forecast for the area.
So, why can you not use Green Co. if descent from MDA under basic VFR would be possible?

There is a little bit of a misunderstanding in your premise. There is a difference between an alternate airport and a diversion airport. An alternate airport is your listed optional destination for the purposes of filing a flight plan. A diversion airport is the airport to which you head when you can not land at your original destination. They may be one in the same. For instance, when you divert to your alternate airport.
It is not that the airport can not be used as an alternate. It is that the approach can not be used to qualify the airport as an alternate. You can not use the standard precision approach, standard non-precision approach, nor non-standard approach alternate minima. You can, however, use the VFR weather minima to qualify the airport as an alternate. That means that both I19 and I73 are treated the same when filing. This is for filing purposes only.
Once airborne, the situation changes. If the weather or any other circumstance dictates a diversion to airport I19, you can use the procedure to shoot an approach down to the IAP minima regardless of if you filed it as an alternate or even if it qualified as an alternate when filing.  Therefore, you could possibly effect a landing at I19 in IMC, but not at I73 in IMC. You could divert to either one in VMC. Even if your filed alternate were an entirely different airport.


What is the reason for different engine configurations seen on Solar Impulse? In various images of the Solar Impulse aircraft, I see the engines mounted in different positions along the wing.  Am I looking at SI 1 vs SI 2, or are the mount positions capable of reconfiguration depending on conditions/experimentation?

Solar Impulse 1 had 2 engines right next to the fuselage, and the other 2 further out where the wing bends upwards.

Solar Impulse 2 has a pair of closely spaced engines on each wing, located partway out onto the wing.


How do I determine the engine thrust required to give a specific climb rate? New pilot here and I am playing around with a flight simulator game for the B737-800. I need some help understanding where/how one can find out if one has enough engine thrust (%N1) to meet a required climb gradient in feet per minute, not in degrees.

If an airport has a SID that requires, let's say, 1100 feet per minute climb how do I know that the thrust setting (%N1) that I get from the OPT program is enough to give me that 1100 feet per minute when I takeoff? Where do I find that information? Is it in the OPT or is it in performance manuals and, if so, which performance manual? Please explain it in simple terms and with references. Thank you.

How do I know that the N1 that I get from the OPT is enough thrust to meet the required climb gradient in feet per minute published on the SID?

You can't, but read on please.
Variables
A few things out of the way first. A percent N1 is not a percentage of the engine's max thrust. 95% N1 at 20°C at sea-level is different from 95% N1 at 35°C at a 4,000 feet MSL airport in terms of thrust force.
Likewise for the lift; airport elevation, temperature, and pressure, also affect the lift. So for the same runway and SID, you'll get different climb rates at a given speed on different days. And since lift counters weight in a steady climb, how heavy you are plays an important role (as well as how the plane is loaded, i.e., center of gravity).
Gradient and OPT
A SID that shows a climb rate, will also show the corresponding ground speed (put together that's a gradient), in fact it will be multiple rates vs. speeds. Climb rate on its own is not a performance parameter. And while an angle of climb (flight path wrt air) does not depend on the wind, the climb gradient (wrt ground) is affected by the wind (yet another variable). Another variable, turns (bank angle) while climbing.
I'm not sure what OPT is, if it is the free Onboard Performance Tool app from Boeing on the App Store, then note that it requires contacting a Boeing representative for the configuration files, etc. If it is an OPT-like software in the sim, then I highly doubt it can calculate the climb rate; even relatively expensive performance calculators for PC flight sims don't go there.
If you have all the variables, you still can't know the gradient or climb rate at a speed. While a real Boeing 737 comes with an AFM or FPPM (manuals that include performance data), climb gradients with all engines operative are typically not included. The FAA AC 120-91 (Airport Obstacle Analysis) discusses this point:

(...) It is recognized that many AFMs generally contain only the one-engine-inoperative performance for loss of an engine at V1 on takeoff. All-engines-operating performance must also be considered to determine the airplane's flightpath in the event of an engine failure at a point on the flightpath after V1. The best available all-engines-operating data should be used consistent with best engineering practices. Operator's may find appropriate acceptable data in various sources, such as: community noise documents, performance engineer's handbooks, flight characteristics manuals, and manufacturers' computer programs.

How is it done?
So what do you do? Unfortunately not much. In the real world a program like the Boeing Climbout Program (BCOP) -- an example of the aforementioned "manufacturers' computer programs" -- is used to analyze each SID individually (this is different from the three or four takeoff limiting weights pilots are accustomed to).
But even then the analysis may not be presented to the pilots. The airline that is operating out of airport x -- your day-to-day typical not-in-a-hot-valley airport -- would have already checked the extremes (temperature, weight, etc.) against the SIDs for its fleet, and concluded early-on that airport x is not limiting.
The pilot will normally be presented with runway specific thrust setting / weight limit. If you're below this weight, then you may have more than one thrust/flaps setting to choose from. SIDs for the most part (for an airline flying a 737) are not limiting except in extreme airports. Note that the SIDs are designed with the planes/airlines that use them in mind, especially that noise is another important factor.
If you are not an airline pilot and you have your own business jet, then this is a different matter. But because business jets have limited payload/fuel compared to jet-liners, the performance tables are not as complex and indeed can be printed. In other words, those SID figures are more important to general aviation pilots (you may also notice that some SIDs are for turbine aircraft only).
Flight sim
For the purposes of a flight simulator, you can take this as an opportunity to test the impact of each condition one by one. If your 737 allows VNAV arming on ground, you may get "unable next altitude" if the plane thinks it can't make the first restriction, although this is not good practice, as the actual climb is divided into segments, each with a different performance, and the first waypoint may not be representative of the most demanding segment.
You can also test all the extremes at once and see what vertical speed you get. 1100 FPM can be achieved by a 737 in a wide range of conditions, if it can't get to 1100 FPM close to the ground, then getting to cruise will be quite the challenge, i.e., test the conditions to put that value in perspective.
I recommend browsing the aircraft-performance and performance-calculation tags, as well as checking the Airbus publication 'Getting to grips with aircraft performance'.


Is it possible to drop a payload via anchored parachute? Apologies if this is not the proper forum for this question -

Here's my situation:

I'm trying to drop a payload via parachute with some accuracy.  I'm worried that in the above setup, the line will interfere with parachute deployment or - if not deployment - operation during flight (imagine wind pushing the chute into the line).

I haven't tested this yet but plan to.  Does anyone know how the payload <> anchor connection might be engineered to ensure full deployment throughout the descent?

I'm trying to drop a payload via parachute with some accuracy.

Cut a hole in the middle of the parachute, make its edge smooth and install a pipe through the center of the box that contains the payload. Run the line through the pipe and parachute and let the payload fall from the balloon. I believe the trick will work for small parachutes able to deliver up to 10 kg to the ground.


Would it be feasible to build a jet fighter plane based on a wooden construction? I read about the de Havilland Mosquito recently and that it was a quite successful British bomber in WW2 due its lightweight wooden construction. As far as I understand it, usual planes at that time were built mainly with metal parts already, thus heavier than the Mosquito and hence uncatchable for them. Furthermore it was too fast for getting hit by heavy anti air, namely the German 88mm cannon.

With this traits of a wooden construction, I wonder if it is feasible to build jets mainly of wood and give them a boost in speed. I have doubts however that the wooden construction is stable enough for resisting the hefty g-force mid-air while flying in mach 3 speed.

The wings and a few parts of the body of the Heinkel He 162 jet fighter were made of plywood.
https://de.wikipedia.org/wiki/Heinkel_He_162#Konstruktion_und_Ausr.C3.BCstung

The Bachem Ba 349 'Natter', a rocket-powered interceptor, was built almost entirely of wood.  https://en.wikipedia.org/wiki/Bachem_Ba_349


How does an engine work when an airplane has $v=0$ on the ground? I mean, for a turbofan:
$$ T= \dot m_{air,h} (1+f) v_{e,h}+ \dot m_{air,c} v_{e,c}- (\dot m_{air,h}+ \dot m_{air,c} ) v_0+ (P_{e,h}-P_{amb} ) A_{e,h}+ (P_{e,c}-P_{amb} ) A_{e,c} $$

but
$$ \dot m_{air}=\rho Av_0 $$

do I have to impose  $\dot m_{air}$?
in this case how the thrust expression change (in particular the terms with $v_0$)?

To start the engine, the fan blades have to be spun up. This is typically handled by either blowing air through them from some outside source, and/or by using an APU to generate power to drive the shaft they're connected to.

Once the engine is running, it sucks in enough air to keep going on its own.


What are the (new?) FAR Part 141 rules for simulator hours for private pilots? My son has started on his own at a Part 141 school in Vacaville CA that claims that mix of 18.9 hours flight and 36.3 simulator hours both with instructor will allow him to check-ride.  (Note that 18.9 allows only for 5 hr solo, 3 hr cross-country, 3 hr night, 3 hr instrument, and 3 hr prep check ride.

Are they blowing smoking knowing that he will need at least 16.1 hr more flight time to meet minimum FAR requirements? And knowing the national average is 60 hrs flight time. Isn't this just a marketing job to lower the total package price ($7,611) with more simulator time?

First, the new rules you're - probably - thinking about are for an instrument rating, not a private pilot certificate. So, that means that your question is essentially this: how much sim time can be credited towards a part 141 private pilot certificate?

Assuming that your son is doing ASEL (airplane single engine land), then the requirements are in 14 CFR 141 Appendix B. You can use a sim for 15% or 20% of "the total flight training hour requirements of the approved course, or of this section [of part 141], whichever is less", depending on the capabilities of the simulator:

  (2) Training in a full flight simulator that meets the requirements of
  §141.41(a) may be credited for a maximum of 20 percent of the total
  flight training hour requirements of the approved course, or of this
  section, whichever is less.

  (3) Training in a flight training device that meets the requirements
  of §141.41(a) may be credited for a maximum of 15 percent of the total
  flight training hour requirements of the approved course, or of this
  section, whichever is less.

A part 141 airplane private pilot course must have a minimum of 35 flight hours training (a school can require more hours, but it can't require less than 35), therefore sim time can be credited for either 5.25 hours (15%) or 7 hours (20%). I don't see any way to reconcile those numbers with the ones you gave, although if your son is doing part of a much longer study course that includes instrument, commercial or ATP training then it could theoretically be a result of how his school organizes training time. That seems very unlikely to me, though.

As for your concern about lowering the package price, that's exactly why simulators are used in training (among other reasons) and there's nothing inherently wrong with using sim time instead of flight time for training. Just ask an airline pilot! But it has to be within what the FAA allows, so I can only suggest that you ask his school to put their claim in writing with references to both the FARs and their FAA-approved training program documentation. If they still make the claim, then forward all the docs to the local FSDO and ask for their confirmation.


How does a labyrinth seal work when the engine isn't rotating? I believe I understand how a labyrinth seal in a turbine engine works when a the engine is running.

Any oil that makes it past the first part of the seal is thrown outwards due to the centrifugal force, forms vortices and therefore cannot pass the second part. I know there's a bit more to it, but to me that seems to be the important part (please correct me if I'm wrong).

However I can't understand what stops the oil passing through when the engine stops rotating. Can anyone explain this?

An example of oil labyrinth seal use

I'm taking the bearing sumps example. There are several bearings to maintain the engine rotors and shafts centered within the core and the stators. Some may use labyrinth seals.

Source.

Pressurized cavity during operation

In a bearing sump with classic dry design, oil is provided directly to the bearing, and labyrinths seals maintain oil within a first cavity (the sump). There is another cavity around the first where compressed air is injected. Air is tapped for internal use from a compressor stage (bleed air).

Source.

This way if oil escapes the first labyrinth of the oil seal, it is contained by the pressure of air coming from the outer cavity on the other side of the seal.

Actually air, which is provided at a higher pressure than oil, will enter the inner oil cavity and mix with oil to form a mist. This is why scavenged oil must then be filtered to separate air when returning to the oil tank (oil must also be cooled has the bearing generates a significant amount of heat).

Oil is directed to the bearing using jet nozzles, the sump is not completely filled. Someone more knowledgeable may explain why, perhaps an oil boundary layer would appear and create unnecessary friction:

Source: Gas Turbines, A Handbook of Air, Land and Sea Applications

In today's engines, oil is circulated using pumps. There are two pumps: One to supply with oil and one to scavenge oil. To ensure oil doesn't accumulate into the sump, the scavenge pump has a higher capacity. Both pumps are driven by the rotation of the engine.

Non operating engine

The pumps are mechanical and driven by one of the engine shafts.

When the engine is not operating, the pumps stop, oil is not supplied any more and it leaves the sump by the scavenge pipe. Bleed air isn't necessary any longer.

When the engine is started, the pumps also start. Oil is therefore injected again into the sump.

The bearing can sustain lack of lubrication for a short time, and there can be an emergency system if oil supply from the tank is interrupted.

Residual leakage

As there will be some limited leakage anyway, oil is extracted by the cavity drain and disposed overboard (or returned to the oil tank).


How does MCAS compare to stall protection systems installed in other aircraft? How is MCAS in 737 MAX 8 different from the stick pusher in MD80 or DHC8 and from the Airbus alpha protection, in terms of overall safety?

All these systems will push the nose down at high AoA and all of them rely on the AoA data, which can become corrupted?

If all of those systems perform a similar function, why is only MCAS currently under scrutiny?

(this is an operation safety question, not related to Boeing's apparent lack of proper disclosure and training)

MCAS is currently under scrutiny because it has apparently caused two crashes resulting in 346 fatalities. Other similar systems have undergone scrutiny in the past. For example, the flight control system in the Airbus A330 was under the microscope after suffering a number of very similar failures. On Qantas flight 72 the computer received faulty AoA data causing a sudden nose-down. They were fortunate enough to have enough altitude to recover, but it resulted in some serious injuries. It was determined that the incident was not completely isolated.

As to why the A330 was not grounded where the 737 Max was, that is probably due to the fatalities involved. Airbus just dodged a bullet in that the crews had sufficient time to recover. Timing was everything.


What is the name of the Instrument that indicates roll? What is the name of the instrument that would indicate whether the wings are level or tilted (one higher than the other) as when flying IFR? Is it the inclinometer?

The only1 instrument that directly indicates the bank angle is the attitude indicator, also (especially formerly) known as the "artificial horizon".  As another answer has noted, many other instruments give indirect indications of bank angle, and by using them appropriately, it is quite possible to keep the wings level even with no direct indication of the bank angle.

The magnetic compass (even of the simple "wet" type) could be added to the list of instruments that indirectly indicate bank angle, though its use is very limited.  (For example, at mid-latitudes in the north magnetic hemisphere, it is generally not feasible to rely solely on a magnetic compass for bank attitude control, even in very smooth air, on headings that lack a significant southerly magnetic component.)2  It would be very challenging to use a magnetic compass to keep the wings level in any significant amount of turbulence, even if the pilot were free to choose a target heading that gave optimal perfomance of the compass.

The inclinometer doubles as a bank angle gauge if the aircraft is kept on a linear flight path.  Since any deviation from wings-level flight generally causes the flight path to curve, the inclinometer is of no practical value for keeping the wings level in clouds.

Beware of the term "turn and bank indicator".  This is another name for the needle-and-ball turn rate indicator, or its vintage British equivalent that has a second pointer arm in place of the ball.  But the ball-- also known as the "inclinometer"-- or the second pointer arm-- really just indicates sideslip, not bank angle.  As noted above, only if the flight path is constrained to be linear does the inclinometer reading correlate to the bank angle, and that is not a realistic constraint for most cloud-flying situations.  A better name for this instrument is "turn and slip indicator".  A more common name in modern times for this instrument is simply "turn rate indicator", with the fact that a slip-skid ball (inclinometer) is mounted in the same housing going unmentioned.

Footnotes:

1-- Here's a notable, but rarely-seen, exception to this statement-- the "Bohli" compass is a specialized compass for use in gliders.  One of its many advantages over a more conventional magnetic compass is that it provides some direct indication of bank angle.  See these related ASE answers for more about it-- How can pilots fly inside a cloud? , Is it normal for gliders not to have attitude indicators?

2-- Same as footnote 1!


Why is Reverse thrust more effective at higher airspeeds? It might seem logical at first but why is reverse thrust actually more effective at higher airspeeds?

If we assume that engine performance will not change during a 100 knot deceleration on landing roll-out, and engine is kept at constant reverse thrust throughout the whole landing then the engine will produce a constant force to slow the aircraft down. It won't be more effective at higher airspeeds because we are continuously redirecting a constant amount of air at specific velocity. Even if we include an engine performance change on landing roll-out, thrust will probably not change by more than a percent. Am I missing something?

From "handling The Big Jets" by D.P.Davies.

Reverse thrust is much more effective at high aircraft speeds than low speeds for two reasons. Firstly, the net amount of reverse thrust increases with speed because the acceleration imposed on the (constant) mass flow is greater. This is because the aircraft forward speed is additional when in reverse thrust as opposed to subtractional when in forward thrust. Secondly the power produced is higher at higher speeds because of the increased rate of doing work. In this context it means that the kinetic energy of the aeroplane is being destroyed at a higher rate at higher airspeeds.


Who said "A little of all of us goes with every pilot we lose"? The only attribution I’ve ever seen for the quotation below is “Anonymous FAA Inspector.”

  Whenever we talk about a pilot who has been killed in a flying accident, we should all keep one thing in mind. He called upon the sum of all his knowledge and made a judgment. He believed it so strongly that he knowingly bet his life on it. That his judgment was faulty was a tragedy, not stupidity. Every inspector, supervisor, and contemporary who ever spoke to him had an opportunity to influence his judgment, so a little of all of us goes with every pilot we lose.

Who originally said or wrote these words? What were the motivating circumstances?

William Garvey in "Viewpoint"
The authoritative reference is in this article:
Aftermath: Lessons Learned  (Aviation Week)
Excerpt:

The last words of William Garvey's January Viewpoint -- ". . . so a
little of all of us goes with every pilot we lose." -- struck me
("Aftermath," page 7). I had just returned from the small town of
Vesoul, France, where I attended a ceremony marking the 40th
anniversary of the death of a Mirage III pilot. Lt. Patrick de
Barbeyrac Saint-Maurice died while flying an intercept training
mission near Vesoul on Nov. 3, 1966. The cause of the accident was
never fully determined, other than the ...
THIS CONTENT REQUIRES SUBSCRIPTION ACCESS
Paywall stops reading more of it.


Do Special MEA altitudes and routes in Alaska require WAAS? Low Enroute IFR charts in Alaska (and maybe elsewhere?) have blue routes and MEAs for GPS equipped aircraft, such as T266, 7000G MEA, below. Is an IFR GPS sufficient to use these, or is WAAS required?

The answer appears to be yes. The FAA document that describes this rule says:

  TSO C145a and TSO C146a GPS WAAS navigation systems are authorized to
  be used as the only means of navigation on Federal airways and other
  published ATS routes in lieu of ground-based navigation aids in Alaska

The IFR chart legend says:

  To utilize these routes aircraft will need to be equipped with IFR
  approved Global Navigation Satellite System (GNSS). In Alaska,
  TSO-145a and 146a equipment is required.

And both TSO C145 and C146 specifically mention WAAS in their titles.


Why doesn't a full yoke deflection also change the stabilizer trim on the Boeing 737 MAX? Various websites have stated that during the 737-MAX crash in Indonesia, the pilots could not pitch up because of a faulty AOA sensor pitching the plane down.

The stabilizer has a rear fulcrum and front jack screw. The elevator, positioned by yoke, is hinged to the stabilizer.
If the yoke is pulled back, the elevator moves up. Then the stabilizer must move down, either automatically or manually, to remove the yoke loading.
However, if the yoke is fully pulled back, why doesn’t this force the stabilizer down directly so that the pilot always has total control of pitch without checking the flight manual or pushing switches?

The yoke does move the elevators, whereas the trim moves the horizontal stabilizer. The stabilizer is much larger than the elevators, and therefore is more effective than the elevator at extreme angles. Even with full backpressure, the nose would continue to pitch down.

Nonetheless, all 737NGs/MAXs have trim cutout switches, 1 for the autopilot and 1 for the normal electric trim. Using these would immediately disable the electric trim. These are generally part of a standard trim runaway situation, but the crew did not recognize the situation and failed to use them.


Why did flying boats in the '30s and '40s have a longer range than land based aircraft? I just learned that until shortly after world war 2, flying boats had a longer range than land based aircraft

In the 1930s, a flying boat route was the only practical means of transatlantic air travel, as land-based aircraft lacked sufficient range for the crossing. (link)

Why was that? I'm not aware of any reason why land based aircraft should have a shorter range than seaplanes.

Since fuel volume in aircraft is a large factor in range, and the volume of an aircraft increases faster than the linear size, larger aircraft have a big advantage for range. In the 1930s, the biggest hurdle for large land-based aircraft was infrastructure. Most airports in the 1930s were not very large, and many parts of the world did not have any at all. The common airliners at the time carried around 20 passengers.
Designing an aircraft that could land on the water allowed aircraft to get larger and have longer ranges without the need for large runways to be built to support them. Aircraft like the Sikorsky S-42 carried almost 40 passengers. It wasn't until at least the late 1930s that land based aircraft were able to reach this size, and after World War II the devolopment of infrastructure and aircraft technology made long-range land-based aircraft much more feasible.


Why do airplanes use AC electric power? Primary electric power on larger airplanes is provided as AC. What aspects of aircraft make AC a better choice than DC?

AC is easier to produce with the engines, that act as generators.
The engines have a rotating shaft that it is easily equipped with magnetic dipoles all around.

Then, depending on the instrument, the current is either used directly or, by the use of converters, in DC form as not only it is easier to produce, it is also easier to convert. So electronic devices that uses 12, 5 or 3V may contain their own voltage converter (though this is less and less true with modern efficient switch-mode converters). If DC conversion was as much efficient as AC conversion, we wouldn't see high-voltage lines. Last but not least, it's easier to switch, because the current is null twice per cycle. DC must be switched at full current, which is expensive and weight costly. (thanks mins)


Where does it say that type certificates are required? I am doing research and looking for a regulation (from FAA, Transport Canada, ICAO or anywhere else) that explicitly states that a type certificate is required for aeronautical products (aircraft, aircraft engines, aircraft propellors). I have looked around on google and at the CARs and FARs but haven't found it yet.

Can anyone help me find a specific reference to this regulation?

I guess I was thinking about it the wrong way. I was hoping for a single regulation to cover it. These sections of the FAR seem to be enough to say that type certificates are required for aeronautical products.

14 CFR §21.45 states the privileges bestowed to type certificate holders including the ability to obtain airworthiness certificates for aircraft, install engines and propellers, obtain production approval or replacement part approval.

14 CFR §21.6 states the need for a type certificate in order to manufacture new aeronautical products

14 CFR §21.9 states replacement and modification parts need to be produced under type certificate

14 CFR §21.132 states that a type certificate is necessary in order to be eligible for a production certificate.

14 CFR §21.183 states that in order to get an airworthiness certificate the aircraft must conform to its type design.

There are probably more examples in other sections. Any other answers appreciated.


Lindbergh's panel-- Ryan NYP-- what is this instrument and how was it useful? Lindbergh's panel-- Ryan NYP-- what is this instrument and how was it used?

See this link-- it should allow you to zoom in by mousing around

https://www.amazon.com/Instrument-Successfully-Atlantic-Charles-Lindbergh/dp/B077RBRZTT

Consider the "T" shaped instrument at the lower center--

The top (horizontal) part is a bubble level -- it acts exactly like a slip-skid ball except the bubble deflects in the opposite direction as a ball would--

The lower (vertical) part is some sort of pitch level.  It is calibrated to show pitch attitude.  The glass tube may possibly have a part that we can't see, that disappears into the panel.

So why how was the vertical glass tube intended to be used?  Was it intended to provide useful information in cloud?  If so, would it actually have provided any useful information, or not?  Or was it just intended to display a precise measure of the aircraft's pitch attitude and thus angle-of-attack, during unaccelerated straight-and-level cruising flight in visual conditions, for the purpose of optimizing the airspeed and angle-of-attack for long-range cruising flight?

The calibration suggests that the instrument was intended more to detect large deviations than for fine-tuning the angle-of-attack in cruising flight in visual conditions, but it is hard to see how this would be of much practical use during actual cloud flying.  It's pretty much analogous to a simple pendulum, but with more damping.

Its an Inclinometer which provided pitch and roll information

  In the early 1920's, the US Government contracted Rieker Instruments
  Company to produce bubble style pitch and roll indicators for the fast
  emerging aircraft market.

  One of the most famous inclinometer fluid filled vial type
  installations - if not the most famous - was the use of a pair of
  Rieker glass tube instruments on the panel of the Ryan NYP "The Spirit
  of St. Louis".  In 1927 Charles Lindbergh chose the lightweight Rieker
  P-1057 Degree Inclinometer to give him climb and descent angle
  information.

(source)

This was useful to the Spirit of Saint Louis as it had effectively no forward visibility with the exception of the periscope. He may have also chosen this in the interest of weight as it would be much lighter than an early gyroscopic instrument.


In a part 91 formation flight within a mode C veil, are all the aircraft required to have their transponders on? Two aircraft are planning on conducting a standard formation flight (aircraft remaining within 1 mile of each other) as follows in the U.S.:

Maintaining VFR below 10,000 MSL;
Remaining outside/clear of Class B/C/D airspace;
The route will be totally within the 30 mile mode-C veil of an airport listed in appendix D to Part 91, for example - Houston or Atlanta; (FAR 91.215)
FAR 91.111 will be complied with: see below:

§91.111   Operating near other aircraft.
(a) No person may operate an aircraft so close to another aircraft as to create a collision hazard.
(b) No person may operate an aircraft in formation flight except by arrangement with the pilot in command of each aircraft in the formation.
(c) No person may operate an aircraft, carrying passengers for hire, in formation flight.

No flight plan will be filed;
No communication with ATC will be established. (takeoff/landing will be at non-towered, uncontrolled airports in Class G airspace);
Both  aircraft will be equipped with a properly certified operable (4096 3/A, w/Mode C) transponder in accordance with FAR 91.215;

Question: Is it legal for only the agreed upon formation leader to have his/her transponder on with the other aircraft's
tansponder set to "standby?" Or do both airplanes have to have their transponders on?

The way 91.215 is written, you must operate your mode C transponder in rule airspace unless ATC tells you not to.

The reason ATC tells you not to squawk in the case of a formation flight is to avoid triggering a constant stream of Collision Alerts between members of the formation, which is useless, annoying and may distract them from an actual problem elsewhere.

However, the CA is suppressed if all the aircraft involved are squawking 1200 (VFR) because there's no point warning the controller about a possible collision between multiple aircraft they're not talking to.


What is the fuel source for the APU on a B737? Where does the fuel come from that powers the APU on a 737? My understanding is that it is from the left front main fuel tank, but I've also heard, hearsay, it can have it's own source. I know that the methods for getting the fuel to the APU can vary: GPU, gravity feed, main tank switch. But where does the fuel come from?

Thank you

It comes from the left side of the fuel manifold, which means it is most often fed from the #1 main tank, typically by turning on either or both boost pumps in that tank. However, it can be fed from the center tank (using the left center tank boost pump) or from the #2 main tank using a boost pump there and opening the crossfeed valve.

If no boost pumps are running, it suction (not gravity) feeds from the #1 main tank. This would be the case when starting the APU with only battery power and no external AC power. It isn't preferrd to do this for longer than necessary, though, because it puts more wear on the fuel control unit with the suction feed than when the fuel is being supplied from a boost pump.

There is no separate fuel tank dedicated to the APU. Gravity feed wouldn't work because the APU is higher than the main tanks (in the wings) and the center tank (below the cabin floor).  (The exception to that would be if the aircraft is inverted, although that situation is considered undesirable for several reasons unrelated to providing fuel to the APU.)


Why do we call it an apron? Where did the term apron come from?

Follow up question as suggested by @Pyritie.

Airport apron refers to the area of an airport where aircraft are parked, unloaded or loaded, refueled, or boarded and looks like this:

Image from airplane-pictures.net
This probably originated from the word defining theatrical apron:

1903 A. B. WALKLEY Dramatic Criticism 108 The ‘apron’ is the technical name for the stage-area in front of the curtain. In the Elizabethan theatre it jutted right out among the public, who surrounded it on three sides. This ‘apron’ slowly shrank..till at last in our day it has altogether disappeared.

As the airport apron looks similar to this, it probably go its name. The following image shows an apron stage (The Visy Theatre in Brisbane Powerhouse)

Image from gtaust.com
As for why its like this, the following explanation seems the most plausible:

Waay back in the day, airports were simply 1/2 mile or 3/4 mile squares of flat grass-covered former farm field with a small terminal building in one corner. Planes landed & took off on the grass, and parked in front of the building to load & unload.
Given the reality of rain & snow, the area in front of the building would get muddier faster thatn the rest of the field. Between plane traffic, fuel truck traffic, cargo wagon traffic & passengers (& horses), churning the surface to mud would be pretty much a sure thing.
A pretty obvious innovation would be to pave a more-or-less fan-shaped area in front of the building where the airplanes could park.
Which when viewed from above, would look like an apron

As for tarmac, it is simply a synonym for Asphalt, which was used in apron's construction.
Note: The historical term apron bears similarities to modern ramp, as in 'walk the ramp'


How do you figure out which frequency to contact approach on for a class bravo transition? I'm about 20 hours into my PPL, so maybe I just haven't gotten to this part yet.
Suppose I'm flying KFCM to KRNH and I want to request clearance across the bravo. How do I figure out which approach frequency to contact KMSP on?
From liveatc.net, it looks like approach is 121.2 or 126.5 (for low altitude). At skyvector, 121.2 and 126.5 are listed under Class B. From the Chart Supplements - neither of those frequencies appear. Am I just looking at the wrong information?
I found a similar case for KPBI where the approach frequency (124.6) doesn't show up on the chart supplemental.

The example KFCM to KRNH starts under the Class B shelf, in this case you check KFCM's chart supplement, and it says, "MINNEAPOLIS APP/DEP CON 134.7":

Which also agrees with the sectional (shown below).
Zoom out in the sectional, and you'll note different frequencies to the NW and NE of the Class B, so if you're transitioning through, the frequency will depend on which direction you're coming from.

Minneapolis-St Paul TAC chart via skyvector.com

Definitely don't use liveatc for frequencies, as that's a hobbyist site.
If you're departing during the tower's operating hours, requesting flight following would be more practical. Also, see related:

On a chart, how can I find the frequency for flight following?
Where is flight following available?
Why did the tower at a Class D airport not set me up with flight following on the ground?
Is a VFR flight following request implied when talking to tower and advising them of your intended airport?
How do I contact Flight Service while in flight?


Do any gliders carry GPWS? Do any gliders come with a ground proximity warning system (GPWS)?  I realise that, for a glider, a GPWS probably wouldn't be able to help quite as much as in a powered aircraft, since a glider, by definition, doesn't have any engines which it can apply TOGA power on (unless, of course, it's a motorglider), but it could still warn the pilot if they were descending too rapidly for their altitude or were about to land with the glider in an unsafe configuration, thus allowing the pilot to take the necessary actions for avoiding a crash (for instance, by pulling back on the yoke, jettisoning ballast, lowering the flaps and landing gear if the glider in question is so equipped, etc.).

GPWS is mostly useful for aircraft flying in instrument conditions or at night when there is low visibility preventing a good view of the ground. Gliders aren't designed to fly in these conditions and they don't have the required instruments. They should be able to see the ground and avoid it without GPWS.


125 cc engine, 64" propeller 3 blade, 180 kg gross weight, will it climb? I'm a government teacher in school, currently I made an RC aircraft and flew it, now I'm working on a single engine light weight aircraft, I want to use a Honda CG 125 (single piston) engine, with 64" propeller 3 blade, engine RPMs are 3000, wings length is 29' feet and width is 4'6" approximately, and the length of aircraft is 20', empty weight of aircraft is 130 Kg, gross weight will be 250 Kg.

I want ask you: will this climb?

I found a google site that showed: Honda GC 125 - 124cc, 10.8 bhp, @ 9000 RPM.

Seems to me it would be much less at 3000 RPM. Can you use pulley/belt system to achieve high engine RPM (smaller pulley) and lower prop RPM (larger pulley)?

The frontal area you provide:

wings length is 29' feet and width is 4'6" (54") approximately,

sounds similar to a Cessna 150, which has a narrower cabin (just about two adult shoulder width, 38 inches), and that needed 100 HP to fly, coming from a 200 cubic inch engine.  It's overall weight was higher tho, 1600 lbs gross (in my 1971 model) vs the 250kG/552lb you provided. If the extra 16" of width is all in the cabin, that will be a lot of extra drag to overcome with that low horsepower engine.


Does aviation use "style" designers? When designing a new plane, does aviation industry use style designers like car industry, or are the decisions made by aerodynamicist; will they solely determine what the plane will look like?

Notwithstanding the case that Quiet Flyer mentioned, generally no, because aerodynamic forms are inherently beautiful, so the need for dedicated stylists isn't there because an un-artistic designer striving for the best configuration will tend to produce an attractive shape by default (with exceptions of course, but overall).  This tends to fit in with the old observation that beautiful aircraft tend to fly better than ugly ones.
Sometimes however, a particular contour, especially vertical fin shapes, become associated with a "brand" (since almost all airplanes are identified by their side profile) so the designer will conform to the brand shape to some degree. That doesn't take a dedicated stylist however.
The biggest example of automotive style styling practices infecting aviation I can think of is Cessna's entirely marketing driven change to their single engine line in the mid 60s, going from straight to swept vertical tails.  Swept tails on 120 mph airplanes made a negligible difference to performance or handling (yes there is probably a theoretical benefit, but I've never seen any evidence that they made any practical difference that could be measured or observed and there is a significant manufacturing cost) but were done to look modern, since faster airplanes all had swept tails and they certainly do look sleeker. You will notice that they didn't also sweep the horizontal tail, just the vertical one, because no one cares about the view from below (lots of airplanes have swept horizontal tails; I'm just pointing out that Cessna saw no benefit to changing their single engine line this way).
Another one was "Omni-Vision" where turtle decks were cut down to add a rear window, partly for a more airy cockpit and visibility, and partly to look a bit more like a car. There was a significant drag penalty to Omni-Vision, costing a couple mph in speed when adopted vs the old straight turtledeck, but it was obviously considered worthwhile for both practical and aesthetic reasons as it became ingrained in Cessna's "brand".
In the 50s and 60s Cessna also adopted other (goofy) automotive marketing terms to describe useful engineering changes like adoption of steel gear legs, "Land-O-Matic Gear" (after acquiring Steve Wittman's leaf spring gear leg patent) so I think they probably brought in marketing types from the automotive industry, but I don't think dedicated stylists were necessary.


Under what circumstances does a flying club need to do 100-hour inspections? I am part of a not-for-profit 501(c)7 flying club that owns a handful of airplanes. These airplanes may be used only by the club members. Members pay monthly membership dues; and pay for Tach time to use the airplanes.

Are our aircraft subject to the requirement of 100-hour inspections?

Possible contributing factors:

Some members are flight instructors, who offer flight instruction in these airplanes.
The students (Receiving dual instruction) may or may not be members themeselves.
A club rule says that only approved club flight instructors may offer instruction in club aircraft.

Does one of these bullet points trigger a requirement for 100-hour inspections?

The relevant FAR is 91.409, which says in part "no person may give flight instruction for hire in an aircraft which that person provides, unless within the preceding 100 hours of time in service the aircraft has received an annual or 100-hour inspection".

If we required student pilots to become members of the club prior to receiving any instruction, would we no longer be subject to requiring 100-hour inspections?

AOPA addresses this very matter in their question of the month found here

  A flying club aircraft normally would not need to receive 100-hour
  inspections.  FAR 91.409b requires a 100-hour inspection when a person
  receives instruction from a flight instructor who also provides the
  aircraft.  The FAA guidance further clarifies that the 100-hour is
  required when a person is providing flight instruction for hire in the
  instructor’s personal aircraft.

Your issues arise with these two points

  The students (Receiving dual instruction) may or may not be members themeselves.
  A club rule says that only approved club flight instructors may offer instruction in club aircraft.

As the answer goes on to state

  Some clubs require a flight instructor to be a member prior to giving
  instruction in club aircraft.  In this case, the FAA doesn’t view this
  as an issue as long as three conditions are met:

  There must be no contractual relationship between the member-instructor and the flying club for the provision of flight
  instruction.
  The member-instructor is not recommended or given preference by the flying club.
  The club members are free to choose instructors who are not club members.

  If any one of these conditions is not met, then a 100-hour inspection
  would be required for the club aircraft.


Why hasn't the US military performed aftermarket modifications on certain aircraft? The US military emits more CO2 annually than several countries. Winglets have been proven to work well in the commercial sector to reduce fuel burn, therefore reducing both CO2 emissions and fuel cost. The US military doesn't really lack research or production/modification capability, so why have winglets not been installed on non-fighter/attack aircraft? (Think C-130, E-3, KC-135...) They would reduce CO2 emissions and fuel costs, so why not implement them?

I think the main reason is that many of these planes were produced before winglets were common
Look at a list of USAF planes and see what years each one were produced (I am not including every plane, but most of the common ones)

C-5: 1968–1973, 1985–1989
C-17: 1991-2015 (has winglets)
C-130: 1954-present
E-3: 1977-1992
KC-10: 1979–1987
KC-46A: 2013-present (does not appear to have winglets, even though recent)
KC-135: 1955–1965

But when you look at this story about winglets, there is the sentence

The first 747-400 was delivered to Northwest Airlines in 1989, the
first commercial aircraft with proper winglets.

So for the most part you are talking about adding winglets to an existing airframe, rather than aircraft with winglets as part of the design.  This increases the expense of adding winglets, which reduces their cost-effectiveness. Look at this article on modifiying the B-52 to use four modern engines and the problems with that (not all of these would apply to winglets).


Are some tail wheels made out of solid plastic? Are any tail wheels on small planes made of hard, rounded, plastic-like material?

You can see that sort of thing on ultralights that land at 25-30 mph where they may use a solid once-piece wheel made of some elastomeric plastic or rubber.  Smaller airplanes however, will use a rubber tire on an aluminum wheel with proper bearings, due to the very high rolling RPM once you are landing above 40 mph (or at least a bushing that can take high speeds and loads).
The smallest ones usually have solid rubber tires and once you get to a certain size, say on airplanes over 1500 lbs or so, they will be pneumatic tires.  For example, an Aeronca Champ usually has a solid rubber tailwheel, but it's heavier and faster Citabria descendant has a pneumatic tailwheel tire.  You can browse typical tailwheel tires here.


Vintage army Kollsman altimeter - any info? I have a vintage Kollsman altimeter A.C. U.S. Army. I can't read the text on the front because of the needle arms are in the way, but might state:

Type 5
Serial No A 464.

Back plate is very hard to read, but does state:

Kollsman Brooklyn NY.
Then possibly: Order No.  W. 636 AC 4708  or W. 635 AC 4798

Any info on it or what aircraft it came from?

You should think about selling that altimeter to a museum because you have a piece of history. Kollsman was one of the first people to make barometric altimeters and a Kollsman was used on the first deomonstrated instrument flight by Jimmy Doolittle.
Excerpt from Wikipedia:

Paul Kollsman (February 22, 1900 in Germany – September 26, 1982 in Beverly Hills, California) was a German-American inventor. He invented barometers and instruments for instrument flight in airplanes.
Kollsman studied civil engineering in Stuttgart and Munich (Technische Universität München). In 1923 he emigrated from Germany to the United States. He worked as a truck driver until he found a position at Pioneer Instruments Co. in Brooklyn, New York. In 1928 he founded his own company, Kollsman Instruments Co., with $500 of seed money.
He spent a long time searching for the right opportunity to launch his product, then Jimmy Doolittle flight-tested his instruments. His instruments were later used in the NASA Apollo program. The altimeter setting window of the sensitive aircraft altimeter is named the "Kollsman window" after him.


What is the immediate cause of stall? The direct cause of stall is unclear to me.

I heard about exceeding maximum angle of attack (around 40°) ;
I heard about reaching the stall speed in the current configuration (flaps, etc).
I heard about load factor which can lead to a stall.

Are these three parameters both direct causes of stall? By "direct", I mean for example that pitch is not a direct cause to stall, since pitch let AoA vary which causes stall.

It's unclear because there is a relation between angle of attack and speed. When we increase the angle of attack, we lower speed. But at the end, what will be the cause of stall?

If both causes are direct causes, are they independent?
- It should be possible to fly very fast (faster than stall speed) and have an angle of attack of 40°.
- It should also possible to have a very low speed (lower than stall speed) and have an angle of attack which produces lift.

What parameter will win and how are they related together?

When an aircraft is on the ground, taxiing at 10kt, the speed alone makes the plane stall, regardless of the angle of attack, am I right?

I would like to know necessary conditions to stall, and sufficient conditions to stall (all conditions being direct causes).

The immediate cause of a stall is the detachement of the airflow from the wing:

Image from NASA

This happens when your Angle of Attack is too high.

How can the AoA become too high?

--For level flight:

Given a certain velocity, you will have a certain AoA that will provide the lift needed for level flight. The lower the velocity, the higher this AoA.
Given a certain wing (configuration) you will have a certain maximum allowed AoA (in the picture is the AoA for wich you have the highest value of the plot):

Image from Wikipedia

Given these two tidbits of information, you can see what is the answer to your question:

If the velocity is too low, to fly straight you need an AoA that exceeds the capabilities of your wings (or a vectorial thrust that exceeds the weight of your veichle, but I would say that it is not quite common)
If the AoA is too high, well, is quite evident that you have stalled.

--For curved flight:

During a turn you need to use a component of your lift vector to actually turn

Image from here

As you can see the lift you need to turn is larger that the lift you need to fly level (given the same speed). And to have a higher lift you need a higher AoA.

And once again back to the AoA we are: if you want to turn too much (high load factor) you need a lot of extra lift, meaning that you have to increase your AoA.

If you exceed your wing limits, you stall

Dynamic stall

This is not exactly my cup of tea, but reading from the already linked wikipedia article:

  Dynamic stall is a non-linear unsteady aerodynamic effect that occurs when airfoils rapidly change the angle of attack. The rapid change can cause a strong vortex to be shed from the leading edge of the aerofoil, and travel backwards above the wing. The vortex, containing high-velocity airflows, briefly increases the lift produced by the wing. As soon as it passes behind the trailing edge, however, the lift reduces dramatically, and the wing is in normal stall.

I would say that once again we fall in the "too big AoA" case, even if for different causes.


What is an NTAP when referenced in a NOTAM? When reviewing notices to airmen (NOTAMs) for the KDNL airport today (08 April, 2016) there's a particular NOTAM that references an NTAP with a number. What's an NTAP? How does one go about looking one up?

!DNL 03/008 KDNL SVC SPECIAL EVENT MASTER'S GOLF TOURNAMENT SEE NTAP 1604031100-1604112359

The Notice to Airmen Publication is an FAA publication, currently available in PDF or print form, published every 28 days. The NTAP contains airway, airport, facility, procedural, general, and international NOTAMs. As voretaq7 notes, this includes long term NOTAMs that a flight service brief won't include if you don't ask. There is also a section with graphic notices, including general notices, special operations, airport and facility notices, and major sporting and entertainment events.

That last section is the one relevant for the NOTAM listed above. This lists information and procedures for any airports affected by special events, which is nice to have in one place rather than looking up long and complicated NOTAMs for each airport. For example, the Masters Golf Tournament referenced in the NOTAM above has a section in the NTAP, affecting airports AGS, AIK, DNL, and HQU. The information includes preferred IFR arrival routings, potential for holds and VFR arrival delays, departure procedures, preferred IFR departure routes, IFR overflights, and VFR arrivals/departures to/from DNL. There is also a special schedule for the tower at AGS, and a temporary tower at DNL.


What is the relation between aircraft altitude and ADS-B coverage? While reading the description of ADS-B given on the FR24 website (ADS-B How it works), I came across this sentence:

  The farther away from the receiver an aircraft is flying, the higher it must fly to be covered by the receiver.

What is the relation between height and coverage in this case?

The ADS-B signal used by FR24 is transmitted on 1090 MHz. Signals at that frequency do not follow the curvature of the earth very well. They work best in line of sight. Aircraft far away from the receiver must be at high altitude to be above the horizon.

At 1000ft, the horizon is about 33 nautical mile away. Aircraft further away will be shielded below the horizon. For 40000ft, the horizon is about 220 nautical mile away.

Due to a slight refraction of the signal the practical range is about 15% further.


How are multi vs single engine helicopters categorized? When looking at the FAA category, class, type list, you have airplane single-engine land, multi-engine land, etc. but just rotorcraft helicopter, gyrocopter, etc.

How do I specify a multi vs single engine helicopter? Does the FAA differentiate, or are you able to fly a multi engine helicopter the day you get your helicopter certificate?

For context, I'm making a web form where an operator can add their aircraft, and I want to be able to sort by single or multi engine helicopters because sometimes people request a multi engine helicopter.

I ended up just doing this:

For the FAA, rotorcraft powered by more than one powerplant are not separately classified.

A random N-number search for a random twin-engine helicopter—AgustaWestland AW109—using the FAA registry yielded the type as: Rotorcraft.

However for a Boeing 707, the type came back as: Fixed Wing Multi-Engine.

I couldn't find a place where the different classes are listed on the FAA website, whether for fixed-wing or rotorcraft.


What are these "pimples" on the jet engine for? When looking into the General Electric CJ 805-23B jet engine, I have discovered that all forward section of the compressor is covered by a number of near identically looking "pimples". What are these tiny devices for, what are they doing? And why only front section of the compressor has them?

They are the roots of the variable stator vanes that control the direction of the airstream as it enters each compressor stage to manage and optimize the angle of attack of the compressor blades in each stage.  The vanes are connected to the ring shaped gang bar and somewhere around the circumference there is an hydraulic actuator, or a series of them, that drives the gang bar rings to move all the vanes connected to it at the same time.  The hydraulic actuator is usually powered with pressurized fuel and is operated by the fuel control system to keep the vanes at the optimal rotational position.

This video (thanks, @Mackk) shows how the vanes operate:


How to determine the traffic avoidance manuver? Scenario A: I started the takeoff roll and then noticed another aircraft is crossing the runway in front of me, how could I determine what is the best avoidance maneuver, like full braking to abort the takeoff? Or proceed take off and leave the ground before the collision? Or change the aircraft heading just like a car driver to avoid the traffic, in which my aircraft could probably rushed out of the runway?

Scenario B: I am holding on the runway and ready for takeoff and another aircraft is on the final to land, should I initiated takeoff ASAP or exited the runway? If I initiated the takeoff and the landing aircraft also take avoidance action and do a go around, will things getting worse since we may collide in air?

In Scenario A there is no obvious answer. You take whatever action is necessary to avoid a collision. If this were a controlled airfield there would be questions raised to the ground controller. If not, similar questions would be directed at the pilot entering a runway without notifying anyone. Even at a completely deserted airfield without any form of station any pilot entering a runway would announce it on a radio beforehand just in case!

Scenario B can be a little more specific, and is a situation that occurs reasonably often at small airfields - less so at large controlled airports. Assuming you've not just busted onto the runway, ignoring traffic on final approach you probably have priority over the approaching aircraft. But if you're a large airliner and/or at a controlled airfield its hugely unlikely you've been cleared to enter the runway to line up if something is on final approach.

If this does happen:

an airliner would follow a missed approach procedure, which would take them well out of the way of the departing aircraft
a light aircraft would perform a similar manoeuvre but commonly known as a "go around". This involves positioning so that the pilot can keep eyes on the departing aircraft, for example flying just to the right of the runway at circuit height.


Why has the IO-390 not replaced the IO-360? Having looked at the IO-390 vs IO-360, one can not help but notice that very few STCs have been done, and even fewer OEMs have fitted this engine in place of the IO-360 used in many airframes.  180 or 200 gross HP vs. 210 guaranteed net for the extra weight of dynamic crank counterweights - to me that would be a no brainer.

Why is this engine having such a struggle for acceptance?

Short answer: OEMs don't see a big enough return on investment (ROI) to justify the change.

Long answer:  Getting an STC is not a simple or cheap process. It costs a lot of money. The recovery off that cost has to be factored into the sales price of the updated aircraft. And there are additional costs associated with supporting a new model of an aircraft -- supply chain, spare parts, warranty, maintenance documentation, flight manuals, etc.

Marketing has to figure how many they can sell at what price. Will it generate new sales in addition to the existing aircraft? Will it cannibalize existing a/c sales? How long will it take to recoup the cost of the change? How much will it add to the bottom line over each of the next 10 years?

Ultimately; what's the ROI? And; is there a better place to allocate our capital for a better ROI?

I'm guessing most OEMs found a better place to spend their development dollars.


Why tail wheel rather than tricycle? I'm working towards my tail wheel rating and enjoying it greatly. But, people ask me why some planes have a conventional landing gear (tail wheel).

Why indeed? I understand perhaps why they had them originally, but is it just historical reasons? Seems like maybe it can have slightly lighter gear and perhaps simpler design, but I'm wondering if there are deeper reasons.

Ratchet freak gives already most of the reasons. I might add that on a grass field the taildragger is easier to handle. The relatively high drag and long lever arm of the tailwheel or skid will help to pull the aircraft straight at low speeds when rudder control power is low. On a hard surface, however, the tricycle gear is easier to handle. Also, not only the weight, but also the drag of two wheels is less than that of three.

If you look at modern airplane designs, those where weight must be kept low (like aerobatic planes) still have a taildragger gear. It is also used in gliders and motor gliders, because they will operate mostly from grass strips and do not want to include internal space to accommodate three retractable wheels.

Big taildragger designs from the early days vanished with the emergence of concrete runways from the 1930s on and the need to brake more during rollout when wing loadings and landing speeds went up. On concrete runways, the tricycle gear handles better and gives much better visibility. Without the ability to brake hard, the rollout lengths of  taildraggers would prohibit todays wing loadings. With retractable gears the drag disadvantage is no more, and the increased weight can be tolerated.


Why were the cabin lights turned on during the flight? I was on a flight last night that the Captain came on and said in three minutes we all had to be in seats and buckled due to severe storms we had to fly through. After about five minutes and until we landed-approximately 20 minutes the interior lights were turned on.  This has never happened on a flight I have been on. Was it so we could not see what was going on outside?  There was tons of lightning and clouds.

Most likely to keep the passengers awake and alert in the even to severe air turbulence, unusual attitudes, or even a mishap which might be encountered during the passage through those areas of storms.  Awake and alert passengers can better react and avoid injuring themselves and/or others.

It's the nice form of the captain coming on the intercom and saying:

"Good evening ladies and gentlemen.  We are about to pass through an area containing several red cells, possibly hail, and severe turbulence.  If you don't feel like having your head put through an overhead bin, wake up and get those seat belts fastened - NOW!"


What is a minimal step angle deflection for flight control surfaces? If the flight control surfaces (ailerons, elevators, rudder) are controlled digitally by servo motors, yet disregarding the way how the input to the servo motors get generated (manually or autopilot), what is the suggested minimal single step deflection of the control surface to be of practical value for a large UAV or piloted airplane?

By "practical" I mean not a ridiculously small angle that slows down the servo with unnecessary many steps, yet sensitive enough to allow for a smallest practically useful deflection or ensure the precision of a small input.

If the minimal step of deflection is not the same between them, then please suggest your answer for each control. Please give answer in degrees within 360 circle.

There are several phenomena that may affect the asked resolution. The easier one is the static (steady case), and the dynamic case which requires several more analyses.

Statically, the resolution of any surface will determine the moments that that particular surface can generate. Consider the elevator, the resolution will determine which aoa and which speeds the aircraft will be able to fly (with a given weight and a given thrust configuration).

Dynamically, the stability of the plane will derive the required resolution. Consider the elevator, and suppose your resolution is 1 degrees. The inputs will generate short period and long period (phugoid) modes simultaneously and your controller will become a bang-bang controller, because you can only command increments (decrements) of 1.

Hope these give some clues to understand the physics. For more details, control theory will be useful.


Why is the nosewheel of the MiG-29 placed in front of the engine intakes? Why do MiG-29 have a front-wheel of landing gear placed in front of an intake? would not it throw water or stones into the intake as mentioned in Raymer?

I am designing an aircraft based on the reference aircraft MiG-29.
I have used an RD33 twin-engines with twin intakes placed in chin position beneath the fuselage. Which design configurations should be kept in mind?
The intake I have selected is a ramp intake.

The MiG-29 series of aircraft are designed to operate from poor quality airfields, and for this reason, they feature separate air intakes for use while moving on the ground.

See this article, including pictures of the aircraft:
https://www.airforce-technology.com/projects/mig29/

Notice the additional louvre-shaped intakes on top of the aircraft's leading edge extensions.

Quote from the article:

  The MiG-29 is the world’s first aircraft fitted with dual-mode air
  intakes. During flight, the open air intakes feed air to the engines.

  While moving on the ground, the air intakes are closed and air is fed
  through the louvres on the upper surface of the wing root to prevent
  ingestion of foreign objects from the runway. This is particularly
  important when operating from poorly prepared airfields.

In general, aircraft designers will have to consider factors such as the aircraft's weight distribution and center of gravity when choosing a position for the landing gear.
If you compare with other fighter aircraft of similar layout and configuration, such as the F-15 or the F-18, you will notice that most aircraft have the landing gear approximately in line or in front of the air intakes, mostly because either changing the landing gear position or the length of the air intakes only to move the landing gear behind the air intakes would likely create other problems, such as undesirable taxi characteristics, unstable takeoff/landing roll or undesirable aerodynamics in flight.
The configuration where the landing gear is approximately in line or in front of the air intakes, on the other hand, has been used successfully on many existing types, so it can be assumed that there are no major problems that would be solved by moving the landing gear further back.

As it can be seen on the MiG-29, there are also other ways to avoid specifically dirt or foreign objects ending up in the air intakes during takeoff and landing.


Why, until recently, were smooth nose sections not popular? Why, until recently, were smooth nose sections not popular? By smooth I mean without a break between the nose and windshield. (The question focuses on airliners.)

Seeing the Starliner (left) and DC-7 (middle), which were vying for the transatlantic market, with their almost perpendicular windshields, I wonder if they were more slanted and followed the nose -- like the Commando (right), for example, which proves it was possible -- enough drag reduction would have helped their payloads on windy days.

The Commando style windshields only made a comeback with the 787 and A350 -- the 747 gets close, but like the 75/76/777, there is still a break.

Manufacturing difficulty:
I don't think that's the reason (unless proven otherwise), because the noses are already smooth. The nose could start from the top surface of the fuselage, and cut-outs to be made where the windshield panels would go.

Windshield materials:
Plexiglas was used early on and on wartime aircraft with complex curvatures.

Image sources:
- https://imgur.com/iA7tbFV
- https://airandspace.si.edu/multimedia-gallery/dc-7jpg
- http://www.historynet.com/going-commando.htm

Because it's bloody difficult to make the curved shapes out of the materials used until recently, with the technology available at the time.

The few aircraft that had it in the past generally were very expensive and labour intensive to build, compared to competitors, and therefore not economically successful.
Now, with improved manufacturing techniques and materials, plus the rising cost of fuel, it's becoming ever more viable and more such are appearing.


How is paint embrittlement countered in high altitude aircraft? There are cases of aircraft that are not designed for high altitudes that can still fly there and as a result the paint on these aircraft "falls off".
Although most aircraft have paint that is chosen to work up to their maximum flight altitude (that is mainly limited by the engine and by aerodynamics), sailplanes are an example of aircraft that do not have a fixed maximum flight altitude. As long as thermals push these aircraft higher, there are few limiting factors for their maximum altitude, as the necessary lift and thus velocity at high altitudes is not as significant as other aircraft since they have a large wing area and low wing loading.

My question thus is not centered around the aerodynamic limits and answers such as "it is selected to work up to its maximum flight altitude" but rather around the process of the selection of compatible paints. It may include design and selection considerations for civil aircraft at 10.000m AGL and for high altitude military fighters. Does the paint over the aircraft surface change due to additional influences e.g. front edge heating?

If necessary, an overview of the different paint types used (at certain altidudes) would be appreciated.

There are 3 critical areas one may wish to address with paint:  the formulation of the paint, how it is attached to the substrate, and the properties of the substrate.

The substrate may expand, contract, bend or twist with heating, cooling, or stress.

The attachment of the paint to the substrate is crucial to durability.  Surface preparation includes cleaning, deposition of a chemical coating such as chromate, or primer.  This is a make or break step that should not be ignored.

Finally the paint itself.  Bare bones paint formula is solvent, pigment, and resin. The solvent evaporates, leaving the pigment (color or shade) and the resin, which is essentially the coating.

Factors such as temperature, flexability, hardness, weather and UV resistance must be considered.  The closer the properties of the paint are to the substrate the better.

I would find out what the airliners use.


Can the measured thrust of a propeller be greater than the max thrust predicted by Froude's theory? Can the measured thrust of a propeller be greater than the maximum possible thrust predicted by Froude's Propeller Theory?

Is Froude's theory reliable in practice regarding the upper limit of the thrust delivered by a propeller of diameter, d, turned by an engine that absorbs the power, P?

I get the measured thrust of a 26 inch, 2 blades propeller, higher than what Froude's theory predicts.

No.

The actuator disc theory for Propellers uses some simplifications, which are grouped into a propeller efficiency factor which normally is between 0.7 and 0.9. This accounts for friction and swirl losses, which are both neglected but very real. Also, the theory assumes equal speed over the stream tube and an infinitesimally small hub, both of which increases efficiency over that of real propellers.

If the propeller uses a large duct, Froude's actuator disc theory would be insufficient to explain all thrust. You might want to explain your measurements in more detail to get a better answer.


Using aluminium busbar/cables in an aircraft instead of copper I have just found out Airbus uses aluminium wiring in the A380 to save weight. However, I didn't see anything about whether all the wiring is aluminium, or if copper wiring is also used. What is the logic behind this, and do other aircraft manufacturers do the same? Does Airbus use aluminium wiring in aircraft produced since the A380 was introduced? Are there any risks associated with using aluminium wiring on aircraft?

While it is true that copper is 1.6 times more conductive than aluminum per volume,

  Conductivity in $\frac{\mathrm{MS}}{\mathrm{m}} = \frac{\mathrm{10^6}}{Ω\,\mathrm{m}}$:

  copper:    56
  aluminium: 36
  $$\frac{56}{36} = 1.56$$

aluminium is 2.1 times more conductive than copper per weight.

  Density in $\frac{\mathrm{g}}{\mathrm{cm^3}}$:

  copper:    8.96
  aluminium: 2.7
  $$\frac{36 \cdot 8.96}{56 \cdot 2.7} = 2.13$$

Another important metric concerns the cost. The conductivity per cost is 7.1 times higher for aluminium.

  Base metal price in $\frac{\mathrm{US$}}{\mathrm{lb}}$ (as of today):

  copper:    2.71
  aluminium: 0.81
  $$\frac{36 \cdot 8.96 \cdot 2.71}{56 \cdot 2.7 \cdot 0.81} = 7.14$$

Aluminium wiring is safe if it is sized and terminated correctly. In comparison with copper, aluminium is softer, shows more creep, and has 30% stronger thermal expansion.


How can you identify an Airbus and or Boeing from the inside based on features of the interior? I already asked a very similar question, but the answer wasn't was I was expecting. Hence this time I am more specific.

How can you recognize a plane from the inside, when you are already sitting as passenger?

In particular, is there a way to understand if you are inside a Boeing or an Airbus based on interior features of the aircraft?

The question is specifically related to the differences in interior features between aircraft built by the two companies. I am not looking for answers such as "check on your ticket", "ask the flight attendant" or "read the evacuation pamphlet".

You can't, unfortunately, airlines (of same type) choose different seat manufacturers, etc.

It's like asking how to identify a building's architecture from one room.

We can discuss wing shapes, or a tail camera's feed on the IFE if there's one, but what if you're stuck on the middle seat of the middle column on a wide-body without a tail camera and no wing view?


Do thrust reversers only have idle and full modes or are there intermediate settings? Are there any intermediate thrust reverser settings?

If so, how often do pilots use these intermediate settings?

My experience is on the CRJs but most airliners are similar.  Normally you can work reverse thrust variably between idle and max reverse.  The reverser levers will have a stowed and locked position (all the way down), and there will be a latching device you operate with your fingers to pull them up from stowed.

From there you end up at an idle reverse position (which may have a physical detent you can feel), and there is a range of movement above idle reverse going up to maximum reverse.  You can vary the reverse thrust between idle and max as you wish, although most pilots will just go from stowed to idle to max, then back to idle then stowed on a landing.

One technique issue on using reversers is if you slam the reverser levers back down to fully stowed really quickly, the reverser devices on the engine stow while the fan is still running at high rpm and on some engines you will get a little shot of forward thrust at the end of the landing roll.  It feels like you let off the brakes at bit for a couple seconds.  Once you get a bit of experience, you learn to ease them off to idle reverse and wait at idle a few seconds before stowing.

Reverse thrust is not taken credit for in landing distance calculations, so their use is optional by the landing pilot.  Some airlines may prefer a bit faster brake and tire wear to wear and tear on the reverser system, based on a relative cost analysis, and encourage crews to avoid reverser use unless they need them.

Some pilots will plan not to use reverse but will want it ready just in case, so they will unstow on landing but keep the reverser levers at idle.  This practice is frowned upon by the maintenance types because it counts as an operating cycle of the reverser system (impacting long term maintenance) even though reverse wasn't used to help slow down.


What are the rules for "see and be seen" when you suspect a potential conflict in class G airspace? The airfield I learned to fly helicopters at is in uncontrolled airspace and has an air/ground radio service only.  It has a main runway, 07/25 and a secondary runway only used in high x-winds, 13/31.

All fixed wing circuits are to the North so fixed wings will fly right hand circuits when operating Westerly and left hand circuits when operating on the Easterlies.  Helicopter circuits are always to the South so the reverse is true.  This works well and keeps fixed wing traffic separated from helicopters.

Therefore, there is no "dead side" since the Southern leg is the downwind for rotary and the Northern leg is downwind for fixed wing.

Once, when preparing for take off from runway 25, I heard a call from a fixed wing announcing they were about 7 miles to the East and would "join dead side".  The A/G operator reminded the pilot, who clearly wasn't one for reading the relevant publications, that there is no dead side and advised them to make a standard overhead join.  We were operating to the West so my circuit would be left hand to the South.

The next call I heard from them was on the downwind leg when the pilot announced "descending dead side".  The operator reminded them that there was no dead side and more insistently instructed an overhead join.

I am now at 1,000 feet on my downwind with an aircraft I suspect is in front of me heading towards me and descending!  Referring to the plate, I am heading roughly East to the South of the road marked "A303" at the bottom of the plate.

I took 3 actions;  I made a position call of "downwind South", increased my height to 1,200 (I figured they were likely to have joined at 1,000 feet) and switched on the landing light.

I can't find any rules of the air or rules of thumb to help in this situation.  Are there any?  Is there anything else I should have done to help to avoid a conflict?

I never did see the other aircraft and I knew from the pilots actions and their lousy use of the radio that they were inexperienced or incompetent and I didn't go looking for them when I was back on the ground to "share a little wisdom" with them.

In the USA, RW aircraft are supposed to avoid the flow of FW traffic and FW traffic have the right of way for landing.

So I would have descended to 500ft instead of climbing. Slight differences in altimeters make 1,200 and 1,000ft too close for comfort. But  500ft AGL (noise abatement be damned in a safety situation) is a perfectly acceptable altitude in a heli.

Also, I would have adjusted my downwind so that I was fairly close to the runway where airplanes are rarely found.

So now I have both vertical and horizontal separation, and I am in a continuous position to land, at my convenience.


What is this 4-propeller plane? My dad noticed it flying quite low today, sadly we do not have a better photo.

4-propellers and uniquely shaped tail assembly.

Plane was spotted in northern Poland, around 9.30AM, near border with Russia/Kaliningrad.

The fuselage extension at the back of the empennage is similar to that of a Lockheed P-3 Orion


Who logs the flight hours for airline pilots? Airline pilots' flight hours vary a lot depending on the airline, type of operation etc. Who actually does the job of logging their flight hours? Do the pilots do that themselves after each flight or there is a system that does it for them?

At my outfit, both.

Pilots log their own hours in the logbooks and keep a rough mental track of hours flown to ensure compliance with Flight Time Limitation rules.

The airline will also log pilot hours to stay in accordance with FTL and compare rosters to actual hours flown. This also serves to create a legal record of who was flying the aircraft should that be required at a later date.

Many - including myself - use an electronic logbook that pulls the data from the airline, so no writing needs to be done.