What benefit is provided by an MCA that is not already provided by an MEA? I continue to read definitions of MEA as the minimum altitude across the entire segment to ensure obstacle clearance and navigation/comm signal reception. It also states that this is the lowest altitude across the entire segment.

The way I interpret this is that as I fly towards the segment I must be at or above the MEA when I enter the segment to ensure that minimum across the entire segment. Given this why is there a need for MCA (minimum crossing altitude)? The MCA definition requires that minimum altitude at the segment boundary. Why would the MEA not be sufficient?

MCA is for the fix and specifies the minimal altitude at which a normal climb can clear all obstacles.

MEA is the for between fixes and assures acceptable navigation signal coverage.

source wikipedia.

The MCA can be lower than the MEA of the adjoining route so MEA is required so you won't crash into the next mountain and MEA can also be lower than MCA so it's required so that the pilot can know to climb before reaching the fix so he knows he can get over the next obstacle safely without needing to circle or zigzag to buy time for the climb.


What type of jack is the flight interphone on transport category aircraft? Recently became an A&P and part of my job is to be on the ground communicating to the pilots during push backs. Started shopping for a headset and have seen various ones with different adapters and jacks. What size jack would work on the flight interphone  on e.g. a B777?

The jack on every commercial airliner from Boeing and Airbus is a single plug U/174 type (aka helicopter).

That holds true as long as we speak of the external jacks used for the flight interphone and service interphone. In the cockpit this is a different beast. You'll find a lot of variation:

classic two-plug
U/174 (aka helicopter, impedance must be matched, no power to headset)
XLR-5 (passes power to headset, often found in Boeing aircraft)
NeutriCON (passes power to headset, often found in Airbus aircraft)
LEMO (passes power to headset, used mainly by Bose)

What you'll find in the cockpit mainly depends on what the buyer ordered. Boeing standard in their newer aircraft is the classic two-plug and a XLR-5 side by side (e.g. B747-8, B787, not sure about the B777). As an example, the company AvtechTyee supplies their 5775 series jack panel for the B787 First Officers side.


How much of the landing runway is mine? If I am cleared to land a couple of miles on final, may I use the entire runway to the departure end, or do I have to comply with "taxi instructions" the tower controller might give me like "turn right at taxiway foxtrot," while I am still concentrating on safely completing the landing? If he gives such a clearance, and I don't acknowledge for safety reasons, do I still have to comply? If I do acknowledge and do not comply, have I committed a clearance deviation? It's great to "help the guy behind me on final" but is this type of clearance even supposed to be given? If I slide off into the grass trying to comply with a clearance that has no relation to my landing calculations, who goofed up?

Everything in Dave's answer is entirely correct.  To add to it, AIM 4-3-20 says:

  The following procedures must be followed after landing and reaching taxi speed. Exit the runway without delay at the first available taxiway or on a taxiway as instructed by ATC.

(emphasis mine)

Controllers are not supposed to give pilots a turn off the runway until they've already reached taxi speed, but at busy airports, I've seen that rule stretched. You don't have to comply with any ATC instruction that you deem unsafe, but if you do and you slide off into the grass, it's your fault.


Who is legally responsible for tiedown ropes? When an airport has tie downs listed on their official FAA record, who is responsible for the ropes/chains. Is there any federal regulation or legal precedent for this or is it a case-by-case determination based on the FBO policy?

I read this as "there is a place to park your plane for a while and tie it down if you are so inclined."  I do not expect the airport to provide the chains or ropes.  Some will, but small town or village airports are barely maintained and nobody is thinking about how to make life better for transient airplane owners.  If you intend to park and leave the plane for any length of time you should be carrying your own means of physically securing the airplane to the ground.
It's the pilot's responsibility to ensure the plane is safe.


How does the Learjet cabin pressurisation system work? In one of the MAYDAY Air Crash Investigation episodes (about the Payne Stewart crash), the flight's emergency manual had the following information under the cabin pressurisation section:

  NOTE: At 10,000 (± 500) Feet Cabin Altitude, control pressure to the
  outflow valve is trapped. This deactivates the Automatic Mode and
  stops cabin altitude from rising higher if the failure is in the
  automatic control system.

What does it actually mean? As the NTSB investigators mentioned, it sure does sound confusing.

If the pilots know the system, it isn't confusing at all.  It simply states that a solenoid valve closes causing the cabin pressurization system to go into manual mode and the pressurization controller cannot control the cabin pressure.

It is a feature of Learjets to prevent cabin pressurization issues in case the controller is faulty.

Since you reference the Payne Stewart accident you should also know there were other issues at play that did not cause the pressurization controller to fail.  It was one of the early Learjet 35's without an emergency pressurization system.


What kind of material should I use for rudder skins? I’ve done some research on this topic for awhile now, but I’m not exactly sure how to go about it. I’ve heard and read that on some World War Two aircraft had fabric covered fuselages, such as the Hawker Hurricane. The Mosquito aircraft was made of plywood and covered with fabric entirely. My primary concern is how the fabric will hold up and interfere with the yaw compared to metal, and I’m also occupied with costs, repair, and maintenance. This question might seem vague to some, but control surfaces are essential to performing maneuvers and controling pitch, yaw, and roll.

The aircraft speeds expected from the V8 engine are a top cruise speed of 193 knots and an economy speed of 170 knots. The rudder situation is an H-tail configuration, single engine powering a four bladed propeller. The aircraft wing is elliptical, in which the wing extends straight out for six ribs, then slants upwards at an angle of 15 degrees. Landing gear is retractable, taildragger configuration. Flaps are plain with a deflection full deflection of 45.

Some aircrafts have had fabric tails over the years that held up just fine. The Mooney Mite (M18) comes to mind. It topped out around 140Kts but flew just fine with a fabric covered empennage. The Vought F4U Corsair also had a full fabric empennage and operated well in excess of your quoted speeds so there is no problem using fabric for speeds you speak of. The FAA has a decent resource on fabric covering here thats worth reading through.

The problem is less about interfering with yaw and perhaps interfering with everything else. Fabric is not as widely used anymore now that we have engine power to compensate for heavier airframes as well as the ability to work with metals consistently and accurately. Fabric also requires routine maintenance as well as periodic replacement. Fabric has a habit of ripping and needing repairs as well as simply sagging over time causing it to require a potentially full replacement. Since a great deal of aircraft are metal skinned now the people left to work on fabric coverings are slowly dwindling as well.


What are the slides that ATCs use for tracking departures and arrivals? I've seen ATCs use little slides with flight numbers for tracking arrivals and departures - is there a term for them and are they still used today with modern ATC terminals?

Yes they are called flight progress strips or simply strips. They are still in use, though they tend to be replaced more and more by the electronic strip or e-strip.

They are also used by en-route controllers (not only terminal as you mentioned). From my experience from Athens ACC, PALLAS supports e-strips, but there is also a printer that prints them in some intervals (I don't remember what triggers the print). Note that some time ago, during the procedural control era, those were manually completed by the ATCOs. I guess they are still manually completed in TMAs and ACCs that use procedural control as primary method and lack RADAR service.


How are Cd and Cl calculated from Cp data? Given pressure coefficient data for corresponding x/c (position along chord) values on a wing, I am looking to calculate coefficients of drag and lift. Here's what I have: b, MAC, S, sweep angles at LE & c/4, and Cp vs. x/c data for 6 different stations (span position given). Angle of attack is 0 degrees.

I understand that to calculate Cl, I can numerically integrate Cp with respect to x/c from 0 to 1. (ignoring skin friction [which, I know, is not best practice])

To calculate Cd (again ignoring skin friction), I believe I need to perform the same integration but with the Cp values being first multiplied by dz/dx inside the integrand, where z corresponds with the airfoil thickness.

My problem is that I do not have any information on the airfoil thickness. Any thoughts on approaching this? Is this problem possible? If it matters, I'm sourcing my equations from Anderson's Fundamentals of Flight, Ch. 1.

Without the local inclination of the airfoil surface you will not be able to achieve exact results for drag. You need to integrate just the component orthogonal to the flow direction at infinity for the lift coefficient (because it is defined that way) and parallel to that direction for the pressure part of the drag coefficient.

While it is OK to neglect friction for lift, it does contribute about half of total drag when the flow is attached, so it should not be neglected for calculating total drag.

To illustrate how important the local inclination is, here the c$_{\text p}$ plot of the Eppler 502 at a moderate angle of attack (3°):

And now the same thing, plotted with vectors. Arrows pointing away from the surface denote suction and vice versa.

Since the c$_{\text p}$ plot should use the projected length along the X-axis, this inclination effect is already considered when you integrate the pressure coefficient over chord. Treat chord length as a dimensionless number that runs from 0 to 1. Since the angle of attack is 0°, you need no other correction and the net surface under the c$_{\text p}$ plot is your lift coefficient. Use the results at the six known span positions and interpolate between them.

In principle, the same applies to the drag coefficient, but now you would need a plot which projects the pressure coefficient on a coordinate which runs orthogonal to the flow direction. In inviscid flow, the pressure differences equal out, so it is only the friction-induced changes in the pressure distribution between inviscid and viscous flow which cause drag.

My best advice is to find airfoils with the same pressure distribution and use their drag coefficient values. Make sure you know the Reynolds and Mach numbers, because both have a higher effect on drag than on lift. Some quirks in the pressure distribution can give them away, like the location of the laminar separation bubble on the lower side of the c$_{\text p}$ plot above or the magnitude of the stagnation point pressure coefficient. Regarding the relative thickness of the airfoil: The amount of suction on both sides of an airfoil grows with its relative thickness.


Are VOR frequencies static? I am a brand new student pilot pursuing my private cert.  I don't need to know this for a while, but I'm trying to learn about VOR navigation to enjoy my sim flights more, in the meantime.

My question is this: is the VOR frequency for a given station static/permanent?  If you're looking at a chart from ten years ago (which, granted, I'm sure you're not supposed to be doing) and it shows a freq for a given station of 116.20, is that frequency likely to still be 116.20 for that station today?

That's a bit exaggerated of a timeline, but another way to ask this question is this: how often do VOR frequencies change?  How recent does a chart have to be, for you to rely on a frequency as printed on that chart?

Charts are updated regularly by the FAA and expired charts should not be considered legal for navigation. Your chart must be current as per the date range printed on the cover for it to be considered reliable. That being said in my experience the VOR frequencies remain constant although I'm sure you can find instances in which they have changed over the years I have yet to see it happen.

FWIW the FAA is slowly shutting down the VOR system as GPS has become the prevalent navigation method.


What do you squawk when multiple conditions apply? There are three standard transponder codes for exceptional situations: 7500 (hijacking), 7600 (radio failure), and 7700 (general emergency).  Which code do you use if multiple situations apply?  For example, if a hijacker smashes your co-pilot's head into the radio, do you squawk 7500 for the hijacker, 7600 for the smashed radio, or 7700 for your co-pilot's head injury?

There is a trail of canceled AC's here that all say "only available within the FAA network" that might cover the topic if you can get ahold of them.

I found a brief mentions of it in this AC relating to ADS-B and its integration with transponders.

  Operational procedures regarding the transmission of the generic
  emergency code (i.e., 7700) in cases when the flightcrew actually
  selected a discrete emergency code (e.g., 7500, 7600);

According to that language you basically use 7700 unless its explicitly one of the other two cases. In your example I would say a hijacking supersedes all but as with many things its a case by case kind of things.

Ultimately the codes are there as somewhat of a backup to actual radio telephony and cover 3 important cases the way I see it. In an actual scenario you use the code that is most applicable to the situation as the pilot in command sees it.

  7500: The aircraft has been hijacked, they may not know what I (the pilot) is fiddling with so Im sending you this code since I cant say anything on the radio

  7600: My radios are down, I may not be able to send or receive transmissions. There may be nothing else wrong with the aircraft in which case radio out procedures prevail. The tower may need to get a light gun out. In IMC see this question.

  7700: Somethings going on this is how Im telling ATC for what ever reason chatting on the radio is insufficient. As to what the advantages are see this question.

This ICAO document on reply codes states that

  ATS authorities should establish the procedures for the allotment of SSR codes in conformity with Regional Air Navigation agreements, taking into account other users of the system.

  2.1.4.2 The following Mode A codes shall be reserved for special purposes

  2.1.4.2.1 Code 7700 ... {2}7600 ... {3}7500 ...

So what will happen when you use the code is somewhat up to local jurisdiction and you should know what will happen when you enter the code to help you (as the pilot in command) decide which one to use.


Is there any instrument similar to a compass but which I can electrically drive? I would like to build a home weather station with analog instruments showing for example temperature, wind speed and wind direction.

I would like to use a salvaged flight instrument to show the wind direction: I have a wind vane transducer that convert the wind direction in an electrical signal and I would like to use this signal to drive a suitable instrument.

The instrument I have in mind is like a magnetic compass but while the magnetic compass does not need an "input signal" I need to drive the needle.

I have a look at a heading indicator

but it seems to me that the "airplane needle" is fixed while the 0-360 graduation is moving. I need, like in a compass, a fixed graduation and a moving needle.

For example this seems fine to me but I have no idea what instrument is:

MASCO SERV. CORP.
DALLAS, TEXAS
PART NO. 503A
SER NO. 2500

Your best bet is to try and use an ADF readout, also known as a Fixed Card ADF (its most likely what you have pictured in your question). There are a few variants of the display out there and it will require some hacking to make it do what you need but it should suffice. As these units are generally considered "older" technology you may be able to get a read out for fairly cheap. On the even older side you can look for a Radio Compass/Radio Direction Finder which is quite similar.

Note: A heading indicator is NOT what you want. While you could pull one apart and install some kind of drive system to make it do what you want it is not, as it stands what you want.


Where can I find data sets on jet fuel prices, including futures and options? I understand that most airline companies buy jet fuel using hedging instruments such as futures and options. I have been searching on the internet data sets of having both jet fuel and option prices. Can someone give me a link or a research paper which has these data values?

Airnav.com lists current fuel prices at most airports (that they can get data for). Keep in mind that airlines may (and most likely do) get a bulk discount based on the volumes they buy in.You may want to take a look at this, and keep in mind they may also trade on kerosene futures as that is what jet fuel is made from.


Which CPUs and programming languages are used in new airliner flight control systems? Are the new systems of today built with the same CPUs and programming languages and development software as those of 20 or more years ago?

By new I mean that these systems are currently being designed for future airliners, or have seen service for the first time recently.

Any specific examples of new designs as used in a major latest-generation airliner (the A350 and 787 be the most obvious examples) would be better than general answers.

I'm interested in examples from any flight-essential systems (but not, for example, on-board entertainment).

As part of this question: does the industry tend to update its products through incremental updates to the microprocessors and programming languages it adopts, or does it tend to make once-in-a-generation shifts to new technologies? And, are there significant differences in the way airline manufacturers (as opposed to military/general aviation industries) approach this?

Note: I focused more on changes in aviation hardware and software than what's currently used since the question linked about programming languages is still current for "new" aircraft.  I do not wish to duplicate that question or its answers.  In my opinion C++, C#, and Ada will probably be the dominant programming languages for avionics for the next decade at least.

First, you've got to understand the life cycle of aircraft.  Many aircraft are in service for more than 30 years.  The avionics do get updates (whether adding new features, fixing bugs, or adding in compliance to meet mandates). However, the bulk of the work is done during initial development of the software and hardware.  The configuration is then mostly fixed until that generation of avionics is replaced by the manufacturer or retrofitted by another manufacturer.

So What's Changed in Practice?

If the avionics goes through a generational update (like CRT's to LCD screens), anything changed has to be worth the cost, so usually not much is changed.  Maybe the CPU, but definitely not the programming language. For example, the G1000 was out for 12 years before releasing another generation of hardware (although in the meantime they published numerous software updates for hardware compatibility and synthetic vision and such).

Similarly, Avidyne Entegra was out for five years and continuously adding major features like data link weather and LPV approach before it finally upgraded the hardware in release 9 in 2009.  Falcon jets like the Falcon 900 had a software and hardware update to their avionics in 2011, but that upgrade was based on Primus Epic family of hardware and software, whose first generation was already 9 years old.  I believe all the 900's were still running the old 1996 hardware before the 2011 upgrade.  On the other end of the spectrum from these slow upgrades, the military's JSF system is designed to be upgraded easily every few years (but they don't say just how often).

Why Not Make More Frequent Upgrades?

What drives value in avionics isn't usually exotic new features and definitely not computing performance.  Value is driven by reliability, compliance to mandates, and safety-compliance.  This requires features that are simple enough for the engineer and the pilot to understand and are robust enough to have hundreds of lives depend on it. So the new features being added generally require little extra performance, and there's little incentive for cutting-edge technology or the latest programming paradigms like cloud computing, machine learning, or object orientation.

An engineer at Rockwell Collins stated something that applies to all avionics "In the past, we struggled to fit everything we needed to do into the size of processor and speeds we had and how to get all those bits over the interfaces we had. With the processors we have now and fiber interfaces, that is no longer a concern... Now the problem is how to manage and design good, trouble-free software and test all the lines of code involved. So now that we have all the processing and bandwidth we need, we have to make sure we can use it and not design ourselves into a corner."

Verification is one of the biggest driving factors (and costs) in processor and programming language usage.  All hardware and software must have a safety level attached to it, with the most critical functions (like avionics for autoland) considered "Level A" meaning such a failure of the avionics could be catastrophic.  In order to achieve the stringent safety requirements for Level A software (which is often one such failure per 10^9 flight hours), the software and hardware need to be exhaustively tested to ensure nothing will ever go wrong.  That includes covering every condition on every line of code.  Most tools developed to work with your programming language and software architecture needs to be formally verified (usually called "qualified") as well. On top of that all, costly flight testing needs to be done to evaluate any changes.  This creates a lot of inertia and means a complete overhaul of an existing product or starting from scratch for a new product just to get a "faster system" is often not cost-effective.

What about support for new CPU features?

Virtualization (allowing different OS's to act like they're running by themselves but are actually running with a layer between themselves and the bare hardware) and multi-core processing is now supported by some real-time OS's for commercial off-the-shelf processors. These have to follow the standards in DO-332 and other materials.  According to my 2013 text, this is still in the investigatory phase and no avionics with these features have been certified.  The main issue is that multi-core processors don't just have more features, but they have more features that are not comprehensively documented or testable. For more information on issues with use of multi-core see the FAA's CAST 32 and this presentation.


How can an airplane fly with single propeller without rolling over? I have no knowledge about aviation or mechanics or something. Recently I started a computer game 'besiege', a kind of sandbox-like game with bunch of parts to make all kinds of machinery.

And I'm trying to make a single-propeller airplane. What I'm concerned about is that it might roll over. I made a simple helicopter once before, which rotated to the other direction of the way propeller(of course facing up) did when only one prop is attached. I know this is why another small prop is at the tail.

So, is my airplane going to stay in balance with single propeller? I considered putting one on another rotating to the opposite direction in the same speed too, but that isn't the way I am planning to. Thanks in advance.

When it is slow, the two or three wheels should keep it from flipping over.

Once it is fast enough to fly, the wing will provide what we engineers call roll damping: Any tendency to roll† will cause an opposing moment which will stop the motion quickly. The rest is done by a differential deflection of the ailerons, so the wing creates an equal and opposite rolling moment to that of the propeller.

What is roll damping: Once the wing starts to roll, one side will go up while the other goes down. This will cause a change in local angle of attack and, consequently, local lift. The down-moving wing will see a higher angle of attack and a local lift increase, and the opposite happens on the other side. Total lift will remain unchanged, but now the change in the spanwise lift distribution will lift the down-moving wing back up and vice versa. The movement stops before it could pick up any speed.

With powerful engines, engine torque is a real problem and needs to be canceled with a few tricks:

Camber on the vertical tail: The vertical tail will create a side force and rolling moment which depends on the speed of the air flowing over the vertical. This helps to make the correction depend on the power setting of the engine. Just make sure that the vertical is in the slipstream of the propeller.
With contra-rotating propellers you can cancel the rolling moment of each propeller with that of the other. This needs a more complex gearbox, however.
In operation, apply power changes only slowly. With its narrow undercarriage, the Me-109 would become uncontrollable if the pilot went from idle to full power on the ground too quickly.
Watch the gyro forces of a spinning propeller: In taildraggers, the aircraft will yaw due to gyro forces once the tail is lifted during the ground run or the pitch attitude is changed in flight. Also, yawing (rotation around the vertical axis) will create a pitch moment (which acts around the spanwise axis).

† Roll: Movement around the longitudinal axis.


What does "OBJECTIONABLE" indicate on a VFR chart? On the Tulsa, Oklahoma VFR sectional the top of the outer Class C ring says "OBJECTIONABLE". Does this indicate some information on the chart is in dispute? I don't see anything in the VFR chart legend or side panels about the meaning.

It means that the airspace around the airport is still under review after a proposed change.

This article explains it in more detail: http://expertaviator.com/2012/07/31/what-is-an-objectionable-airport/

And here's the official text: Part 157

  §157.7   FAA determinations. (a) The FAA will conduct an aeronautical
  study of an airport proposal and, after consultations with interested
  persons, as appropriate, issue a determination to the proponent and
  advise those concerned of the FAA determination. The FAA will consider
  matters such as the effects the proposed action would have on existing
  or contemplated traffic patterns of neighboring airports; the effects
  the proposed action would have on the existing airspace structure and
  projected programs of the FAA; and the effects that existing or
  proposed manmade objects (on file with the FAA) and natural objects
  within the affected area would have on the airport proposal. While
  determinations consider the effects of the proposed action on the safe
  and efficient use of airspace by aircraft and the safety of persons
  and property on the ground, the determinations are only advisory.
  Except for an objectionable determination, each determination will
  contain a determination-void date to facilitate efficient planning of
  the use of the navigable airspace. A determination does not relieve
  the proponent of responsibility for compliance with any local law,
  ordinance or regulation, or state or other Federal regulation.
  Aeronautical studies and determinations will not consider
  environmental or land use compatibility impacts.

  (b) An airport determination issued under this part will be one of the
  following:

  (1) No objection.

  (2) Conditional. A conditional determination will identify the
  objectionable aspects of a project or action and specify the
  conditions which must be met and sustained to preclude an
  objectionable determination.

  (3) Objectionable. An objectionable determination will specify the
  FAA's reasons for issuing such a determination.

  (c) Determination void date. All work or action for which notice is
  required by this sub-part must be completed by the determination void
  date. Unless otherwise extended, revised, or terminated, an FAA
  determination becomes invalid on the day specified as the
  determination void date. Interested persons may, at least 15 days in
  advance of the determination void date, petition the FAA official who
  issued the determination to:

  (1) Revise the determination based on new facts that change the basis
  on which it was made; or

  (2) Extend the determination void date. Determinations will be
  furnished to the proponent, aviation officials of the state concerned,
  and, when appropriate, local political bodies and other interested
  persons.


Are flight schools required to verify citizenship of all students? Is the requirement to confirm citizenship and provide a logbook endorsement required for those who already hold a pilot certificate?

Does another instructor's prior endorsement that confirms citizenship was verified act as a substitution for subsequent instructors, or does each instructor need to check and make their own endorsement verifying citizenship no matter what? This is with the assumption that there are multiple freelance CFIs rather than a flight school employing many CFIs who take turns teaching the same student.

If no, would that not imply that each flight review with a new instructor would need a new citizenship verification or are currency checks exempt?

You are required to verify the identity of people undergoing initial Sport Pilot, Recreational Pilot, Private Pilot, Instrument, and Multi Engine training.  Any other kind of dual instruction does not require verification of US citizenship or TSA approval of resident aliens.  See 49 CFR 1552.3(h).

The CFI must inspect the original documents and verify they are authentic.  The CFI must endorse the CFI’s own logbook with an endorsement per AC 61-65 indicating they have done such and verify the student is a US Citizen.  These records must be kept for a minimum of 5 years.  If the CFI cannot validate the student as a citizen, be done, they must submit the student’s information and immigration documents to the TSA and with for their approval prior to beginning flight training.

https://www.aopa.org/advocacy/pilots/alien-flight-training-program/us-citizens-seeking-flight-training


What does it mean for a ATC to say a flight's callsign followed by "in disguise"? So I'm just a aviation fan without industrial background.

I'm listening to Kennedy Steve's ATC communication and he said more than once like "American 600 in disguise."

What does it mean "in disguise" in this context?

Thank you.

The controller was probably referring to an airplane in a different livery but operating under the American call sign.

A likely example is US Airways. After the two companies merged, from October 2015 all flights were operated under the American call sign, but re-painting the US Airways planes took at least a couple years.

This is not standard phraseology but "Kennedy Steve" is known for trying to inject some humor into his work. See also: What does Top 1% mentioned by ATC refer to?


Are seaplanes allowed to taxi in residential areas? There's a small pond/lake behind my house. A sea plane was just going around it. It was very loud and got like 10 feet from the shore. It's just going in circles and won't take off and leave.

This is at the tiny town of Elbow lake, MN. There's a small airport here, Elbow Lake Municipal (Y63). If you look at the links, you can see it's near a small lake, and there is a large peninsula on it that comes to a point.

It's so annoying. How can they do this, so close and in residential? Isn't there some regulation to prevent this?

Note: The town of Elbow Lake, MN should not be confused with the body of water, Elbow Lake located some 70 miles NNE. That lake does have a seaplane base (M49), but that area is entirely unrelated to this question.

A sea plane was just going around it. It was very loud and got like 10 feet from the shore. It's just going in circles and won't take off and leave.

As has been pointed out in other answers and comments, if the aircraft is taking off or landing, there are no regulations requiring distance from persons or structures, at least that I know of.

What you may be witnessing is an attempt to takeoff in less than optimal conditions. For example, if there is no wind and the surface of the water has no wave action, it can be very difficult to break away from the water sufficiently to get the aircraft "up on the step", in other words to get it going fast enough that it can plane along the front part of the floats (or the hull). Once the floats are "planing" on the water, with the lesser drag than if they are fully in the water, the aircraft may then be able to accelerate to takeoff speed.

The usual procedure if you're having trouble taking off from a wave-less water surface (often called glassy water), is to run back and forth at a high power setting with as much speed as you can get to generate waves. Then, at some point hopefully, as you run back across waves you've previously generated you'll be able to break free of the water because there's less drag running across waves, even small ones (ripples even) than glassy water.

I had to employ that procedure a few times back when I was flying floats, and I remember one instance when it took at least a half hour before I managed to get airborne.

  Are seaplanes allowed to fly in residential areas?

I can't speak to current practices and regulations as I retired in 1999. However, back in the 1970s and 1980s when I was flying floats, we often operated in residential areas. For example, go to Google Earth and bring up Eugene, Oregon. Look at the area on the Willamette River immediately adjacent to downtown Eugene. You'll notice two bridges. We often operated alongside residental areas upstream and downstream of the bridges. We also operated between the bridges. Depending on conditions that sometimes meant flying under one of them, not an uncommon practice for seaplanes, and perfectly legal, at least back then.

If you don't have Google Earth, you can use the Google Earth browser version or see it on Google Maps.


How long does it take on average for a control surface to deflect by one degree? I know this should vary quite a bit (because of aircraft size / use / build / actuation / control surface weight), but I was wondering if anyone here could ball-park some numbers on how long it would take a control surface (aileron/flap/vertical stabiliser) to deflect by one degree on average.

I am writing a small aircraft simulator, and would like to try and use realistic numbers if possible.

If these figures are too variable, I would love to know some ball-park figures for some example aircraft if possible.

With hydraulically actuated flight controls, the deflection speed is only limited by the maximum hydraulic fluid flow through the servo valve. I've taken some step responses of civil airliners in the past, and on-ground they can deflect full range in about 1-2 seconds.

For a mid-range passenger jet:

Elevator range = 42 deg, max no load deflection speed = 66 deg/sec
Aileron range = 40 deg, max no load deflection speed = 66 deg/sec
Rudder range = 48 deg, max no load deflection speed = 56 deg/sec

At higher airspeed the maximum deflection angle and speed become less due to aerodynamic blowback - by design, to limit the inertia forces on the airframe.


What is the difference between a P-51 Mustang and an A-36 Apache? Both were made by North American Aviation and the planes were almost twins - the A-36 having a ground attack role while the P-51 was a fighter. Are there any noticeable differences between the two?

They were largely the same aircraft but the first line of the A-36 wiki sums it up nicely

  the ground-attack/dive bomber version of the North American P-51
  Mustang, from which it could be distinguished by the presence of
  rectangular, slatted dive brakes above and below the wings

later in the article they go on to list some more features

  The contract for 500 A-36A aircraft fitted with bomb racks, dive
  brakes, and heavier-duty wing, was signed by Kelsey on 16 April
  1942,[6] even before the first flight of the first production P-51 in
  May 1942.

This website also lists the same mods as well as some other fun facts.

This website lists two other features noteably the vent window which is not mentioned elsewhere.

  ...and the installation of small vent windows in the windscreen side
  panels. In addition, two Browning M2 .50 caliber machine guns were
  mounted in each wing, and two more .50 cal. guns were mounted in the
  lower nose to fire through the propeller.


What is the relationship between the UH60 Blackhawk stabilator function lateral sideslip and pitch coupling? I'm having a hard time understanding the correlation between the wind gusts (where are they coming from, what are they affecting) and why, in a nose left situation,  the stabilator is driven down.

I keep thinking it would make sense for it to go up (e.g. left pedal, more tail rotor torque, tail up, nose down.

  sideslip to pitch coupling to reduce susceptibility to gusts.    When the helicopter is out of trim in a slip or skid, pitch excursions > are also induced as a result of the canted tail rotor and downwash on the stabilator.

  Lateral accelerometers sense this out of trim condition and signal the stabilator amplifiers to compensate for the pitch attitude change (called lateral to sideslip to pitch coupling).

  Nose left (right slip) results in the trailing edge programming down.
  Nose right produces the opposite stabilator reaction.

If the stabilator drives down, this will make the nose go down further.

I know I'm missing something big here but can't put it together.

The sideslip to pitch coupling is a result of the canted tail rotor and the asymmetry of the main rotor downwash. The tail rotor thrust pushes the tail to the right and upward (pitch down). The main rotor downwash across the tail boom also generates a pitch up motion.  The 'static' position of the stabilator is set (stab range is 10 deg up to 45 deg down based on airspeed) to counter this pitch tendency.

A right sideslip condition will result in a reduction of tail rotor vertical thrust resulting in a pitch up motion. The stabilator is programmed downward to counter the pitch up. Conversely a left sideslip will result in increased tail rotor vertical thrust and a pitch down motion.  In this case the stabilator will be programmed up to counter the downward pitch.


What is the fuel/air ratio of the CFM56-5A1 engine (in the A320 model)? I could find the fan-bypass ratio, which was 6:1 (on some models 5:1) but I was unable to find the fuel to air ratio used in this engine. For reference, it is a high-bypass turbofan engine.

The ratio can be different for different phases of flight. It is easy to calculate for the Takeoff (TO) case because the required numbers are easily available:

TO Thrust: $ 25 \, 000 \, \text{lbs} $ [1]
TO TSFC (thrust specific fuel consumption): $ 0.3316 \, \text{lbs/h} $ per $ 1 \, \text{lbs} $ of thrust [2]
Airflow: $ 852 \, \text{lbs/h} $ [1]
bypass ratio: $ 6.0 : 1.0 $ [1]

The takeoff fuel flow $ \text{FF} $ is then given by

$$ \text{FF} = 25 \, 000 \times 0.3316 \, \text{lbs/h} \approx 8290 \, \text{lbs/h} \approx 2.30 \, \text{lbs/s} \approx 1.04 \, \text{kg/s} $$

and the airflow $ \text{AF} $ through the core is given by

$$ \text{AF} = \frac{1}{6 + 1} \times 852 \, \text{lbs/s} \approx 122 \, \text{lbs/s} \approx 55.2 \, \text{kg/s} $$

This results in a fuel/air ratio of

$$ \frac{\text{FF}}{\text{AF}} \approx \frac{1}{52.9} \approx 0.0189 $$

Sources:

[1]: www.cfm56.com
[2]: Wikipedia CFM56


What does the "D" symbol mean on this instrument approach chart? What does the "D" symbol mean on this approach plate in the airport diagram section (bottom left of plate)?

A [D] symbol is shown to indicate runway declared distance information available, see appropriate Chart Supplement for distance information.

That's from the FAA Aeronautical Chart User's Guide page 124. The wording was different in the 12th edition, it used the A/FD terminology:


What level of damage to an aircraft is acceptable to let it depart? Yesterday (28 June 2016), a Bombardier Q400 from EPGD to EPWA made an emergency landing because of a blown tire, spotted by a passenger. Everything went smoothly and the plane landed successfully assisted by fire trucks.

You can see the article and video here (in Polish).

In addition to the damaged tire, I've spotted that there is some damage to some parts of the plane:

Is it okay to fly with that?
I guess it isn't important for the safety of the flight (it looks like some landing gear cover or something), but what damage to the airplane is considered safe for flight?
Is it possible to force the airline to repair non-critical parts?
I know that loose parts of airplanes could do harm when they fall off, e.g. during takeoff, and stay on the runway (like in the Air France Flight 4590 Concorde crash).

Aircraft Maintenance Engineer here.

To evaluate if an aircraft is safe to fly we use three main reference documents:

1. MEL (minimum equipment list).

This document contains the list of elements that are allowed to be inoperative.

For example a pneumatic valve, a computer, a seat, etc...

All unserviceable elements will have to be fixed within a predetermined duration/limit.
(Usually 1, 3, 10 or 120 days)

If the failure is not fixed by the due date, the whole aircraft will not be released to fly. (No matter how small the fault is)

2. CDL (components deviation list).

This document contains the list of components that may be removed from the aircraft.

For example a damaged refueling service door can be removed, if the maintenance team is unable to fix it before departure.

These will usually be associated with performance penalties.

CDL defects will also come with a deadline.

3. SRM (structural repair manual).

This manual contains all information needed to evaluate structural damage such as dents, scratch, lightning strike.

This manual will also give you the information needed to evaluate if a damage is "no-go" (meaning the aircraft is not safe for flight) or if the damage is within tolerance.

If it is within tolerance you will also get time or aircraft cycles limitations (a cycle is a takeoff and landing)

Regarding your picture:

The plane will not be allowed to fly with a blown tyre. A blown/damaged/worn out tyre is a no-go.

However, airliners are designed to land safely with one blown tyre. Aircraft incorporate lots of redundancy so as to eliminate single points of failure — for example, most commercial jetliners are designed to be able to land safely even if they lose an engine. Efficiency, comfort, and ease of operation may be reduced but the situation can be kept under control and is still within the aircraft's design specifications.

I can see damage on the landing gear door. It is possible that an aircraft would be allowed to fly with the landing gear door removed if a fix cannot be performed before departure, however; the aircraft may experience increased drag. This would be covered in the CDL.

The aircraft should also receive extensive inspection before departure and after landing.


Who should design the nozzle of jet engines on aircraft? There is a question in my mind that which company should design the nozzle of jet engine - the aircraft designer or the engine designer?

If you watch this documentary:

BBC Documentary Rolls Royce How To Build A Jumbo Jet Engine

You will see that the engine is designed without the nozzle. e.g. You see something just like the following come out from the manufacturer (Trent 700).

But in fact you will see it on aircraft just like this (Trent 700 on A330).

Which company designs this duct/nozzle/intake? The aircraft designer (in this case Airbus) or the engine designer (in this case Rolls Royce)?

I suspect there will be some collaboration between the two (as the nozzle partly determines the performance of the engine), but this is primarily the domain of the aircraft designer. Only he/she knows the (aerodynamic) specifics of the integration of the power plant on the aircraft and is able to make a proper trade-off, for example regarding ground clearance.

A textbook example of that is the integration of the CFM56 on different aircraft. The Boeing 737 uses flattened nacelles, whereas the nacelles are circular  on the A320-family. The flattened ones are structurally less efficient, but at aircraft level, it was an easier/better option than increasing the landing gear height. (This problem, by the way, is still haunting the 737-series. A recent innovation featured on the 737 MAX-10 extends the landing gear using a new lever to prevent the tail from scraping the runway on rotation, another problem of a shorter landing gear.)


How can pilots differentiate runways and taxiways during landing? There have been many incidents where pilots landed or attempted to land the aircraft on a wrong surface (for example Continental 1883 and Air Canada 759). Are there any tips for pilots to avoid that? Especially during nights or low visibility scenarios.

During daytime and good visibility, it should be pretty obvious that runway markings are white and taxiway markings are yellow. Runways have the runway designator in big white numbers at the end and a dashed centerline, while taxiways have a narrow continuous yellow centerline.

During nighttime, you will notice that runway lights are white or yellowish while taxiway lights are green (center) end blue (edge). Additionally, many runways have approach lighting, which taxiways obviously do not.

During low visibility, you won't be trying to identify the runway visually, since you will be performing an instrument approach, which will usually take you all the way to the threshold. For non-precision approaches, where some visual maneuvering is required, the information above regarding markings and lights apply equally.
In addition, taxiways are generally narrower than runways. While many runways do have parallel taxiways that run for the full length of the runway, in many cases the taxiways will have a few bends or be at a slight angle, whereas the runway will be completely straight and wider.
You should always study aerodrome charts and familiarize yourself with the airport layout before attempting to land at an airport. When doing so, pay attention to the airport layout, and try to notice any areas where confusion is likely (such as long straight taxiways that run parallel to a runway). If you come prepared, and pay attention to the details mentioned above, you should be home safe.


Wind vs high altitude cruise Yesterday I flew back from Tokyo down south against great head wind around 150kt at 34000’, the original flight plan was to cruise at FL240 for a while then climb up, but the captain decided to get up early, which resulted in a longer cruising time.

It became a bit confusing to me in this case,
One, The higher you go the stronger the winds, at the same time the fuel consumption is more efficient, but at what point do you say the wind factors wins over the fuel factors, ex. Take us longer to get to the destination resulting in more fuel burn.

And what are some rule of thumbs to help me develop a decison wether to cruise high or low in terms of fuel saving.

I found a wind altitude trade off in my A321 FCOM, but not too sure if the chart fits my situation, and I’m almost sure the captain didn’t take out the chart to form his decision.

Thank you for your answers on advances. Any input is appreciated.
Best regards,

Simply a matter of fuel burn rate per time in air.  Generally you want to go as fast and as high as practically possible against the wind. (Indicated Airspeed - headwind) x Altitude factor = groundspeed (temperature, atmospheric pressure, humidity may be factored in too)

Trip Time hours = Trip Distance miles/Ground Speed miles/hour

Fuel consumption = Trip Time hours x gallons/hour fuel burn rate at given power setting

The pilot may have thought the headwind would be just as bad at FL 240 as at FL 340.
Weather prediction is not perfect, but apparently they did take enough fuel along to make it.

I would give them credit for that.


Why do glider licences have fewer restrictions than powered aircraft? Under FAA rules a license for gliders doesn't require a medical certification and you can get your license at 16 rather than 17 for powered aircraft. You can get your student license two years sooner at age 14.

It appears to me that gliding would require MORE skill and experience than a powered aircraft. It looks very unforgiving. You only have one shot at landing, there is no go-around. If you lose too much altitude you could end up not being able to reach the airport. You have to know how to find thermals, etc to gain altitude. While being towed you will be flying in closer proximity to another aircraft than you normally would in a powered airplane.

Why are the restrictions less for a glider?

First of all, gliders fly slowly. Everything happens more slowly than in other aircraft, and this helps to make flying them less challenging than you might think. Flying them well is a different matter - this requires a lot of skill and good physical health.
Historically, the early age limits were introduced in Nazi Germany when the Deutscher Luftstportverband (DLSV) and later the NSFK organized groups of adolescents to let them build and fly gliders. Flight training started at the age of 14, mostly in very simple, bungee-launched gliders like the Zögling or SG-38 which were flown in summer and built or repaired in Winter. Since bungee launching is a very labor-intensive process and flights last only a few seconds, this was less about pilot training than keeping the young occupied and under the influence of the Nazi party.

Bungee launch of a Zögling glider (picture source)
And it worked. Accidents did happen, but were almost never fatal since all operations happened at low speed and altitude. Therefore, these age limits were exported together with the idea of flying unpowered aircraft.
Note that in Europe the same health certificate is required for glider flying as for flying GA aircraft.
Now to your concerns about the demanding nature of gliding:

Glider flying is done from airfields which are suitable for GA aircraft (or the gliders could not be aerotowed) or winch launching. 800 meters is about the minimum, and this leaves plenty of space to land a glider.
Flight training is done initially only in the direct vicinity of the airfield, and students are supposed to stay within a cone which allows them to reach the airfield at any moment. Flying cross-country comes much later, when the students have made more than a hundred landings and know how to get the plane down in a certain spot. Again, the slow speed helps to make such landings simple if the pilot is prepared.
Today, training is initially in two-seaters, so there is an experienced pilot around for the first landings and the first cross-country flights.
Aerotowing is also quite simple, and altitude management while in tow is more challenging than keeping the right distance from the towplane. Again, this is done initially in two-seaters, and all the glider pilot has to do is to fly with the same bank angle as and slightly above the towplane. The rope takes care of the rest.


Does a stopper (chock) really prevent the plane from moving? In Crime-Thriller movie American Made (2017), Barry put this stopper in front and in the back of the plane's front wheel. Do wheel chocks really prevent an airplane from moving?

Wheel chocks are used to prevent accidental movement, generally on airplanes. They are placed in addition to setting the brakes, if present.

On smaller planes, chocks are used to prevent the airplane to roll, and tie downs are used to prevent the airplane to stay on the ground and not take off on its own. Using both the chocks and tie downs will ensure that airplane is secured and will not move, under normal conditions of course. Other safety measures are discussed in this answer.


FAA test question about load factor The following question is from the FAA PAR (Private Pilot, Airplane) exam :

The load factor on an airplane increases with :
(A) Any moderate change in pitch attitude, increase in weight, and steep turns.
(B) Increase in weight, an increase in power, and any moderate pitch changes.
(C) Increase in weight, steep turns, and abrupt changes in airplane attitude.

The correct answer is supposed to be (C).
All of the answers say that load factor increases with an increase in weight. However, load factor is inversely proportional to weight by definition.
What am I misunderstanding?
Edit: I think it is supposed to say "load" instead of "load factor" but it was not written that way.

I agree that this can be confusing.

The load factor is indeed inversely proportional to weight, unlike the load factor on an aeroplane, which might be thought of as the lift required divided by the certified MTOW for the category of operation (g limit).  If the aircraft is in a steady 1 g flight at MTOW, the load factor to achieve this is one.  Start turning in a steep bank and the load factor becomes two in relation to the design load factor of the aeroplane's structure. If you then reduce the weight of the aircraft to, say, half the MTOW, the load factor in 1 g flight is a half of the load factor the aircraft was designed for.

The load factor on an aeroplane differs from the abstract concept of load factor as it relates to the load imposed on the aircraft compared to the load imposed on the aircraft when operating at gross weight at 1 g.

I hope this helps.


Where can I find the number of commercial jets that a country or airline purchases annually? Is there any authoritative source from where we can find out the number of commercial jets that a country or airline purchases annually?

planespotters.net lists, for many commercial airlines, all their airplanes along with their delivery dates.

As for an authoritative source, you would have to look at the IATA or any other paying site such as airfleets.net.


How does a student pilot learn the process of pre-flighting a Robinson R22? I've watched a few youtube videos on pre-flighting a Robinson R22 helicopter, and I'm always impressed by the way the pilot methodically does the external checks and the internal pre-start, start-up and warm up.

For me, there's a big gap: knowing what to check (because the checklist says so), and being able to identify it (put your finger on it / point to it), and knowing how to check it.

How does a student pilot learn the process?
How long does it take to master the process?

Assuming being able to pre-flight is a pre-requisite for flying solo, and a private pilot has one lesson per week, and there are say 20 1-hour lessons before solo is even considered, then 20 opportunities to learn such a complex set of processes does not seem enough repetition and re-enforcement somehow, and the risk of stuffing it all up seems very high.

I have never flown the R-22 but I am rated in RH and ASEL. I can answer specifically about the Schweizer (Sikorski) 300C/ CB/ CBi helicopter.

1) How does one learn the preflight? From your instructor. During each lesson the first part of touching the aircraft should be the preflight. Legally speaking, that is after touching the log books/ registration/ weight and balance/ etc. to make sure that it is potentially airworthy in the first place. First you watch them do the inspection, then you do it under supervision, then they watch you from a distance, then the instructor finishes up whatever they are working on last while you preflight it solo (with the best instructors doing the preflight themselves before you even start).

2) How long does it take? For the Schweizer it took me probably the first 10-12 lessons since I was initially not able to fly frequently enough to remember most of what I learned the last lesson and I was working 80+ hours per week at the time. Going 1-2 months between lessons is very bad for retaining new information. Had I worked less and flown more it probably would have taken half of that for me to get comfortable doing the preflight myself.

The items on the checklist are really not that hard when you understand the function of the parts you are checking. When you check control rod integrity you know what they do. You follow them from the cyclic and collective through the cabin, up the mast, through the mixer arms, and to the swash plate. You check the swash plate. You follow up the mast to the control rods attaching from the swash plate to the rotor blades themselves. Other than the climbing around the aircraft it probably took me longer to type that than to actually do it for a preflight.


Knots vs MPH, is there some standard for when to use which unit? In looking at all the sources of aviation data, including POH's, instrument dials, instructional materials, FAA publications, METAR's, flying magazine stories, YouTube videos, etc., I see no standard usage of either knots (nautical miles per hour), or mph (statute miles per hour).  It seems many people use them not interchangeably, but mix them up seemingly randomly.

Is there any kind of agreed upon standard about when to use which system of units?  It's easy enough to convert one to the other (well actually a lot easier to convert knots to mph), but it seems this is just a latent trap for mistakes in navigating and, more importantly, in airspeed errors.

According to the FAA Flight Navigators Handbook (the Flight Navigator Cert is rarely issued any more to my understanding but none the less).

  The standard unit of distance for navigation is the nautical mile
  (NM). The NM can be defined as either 6,076 feet or 1 minute of
  latitude

It goes on to talk about speed

  Closely related to the concept of distance is speed, which determines
  the rate of change of position. Speed is usually expressed in miles
  per hour (mph), this being either SM per hour or NM per hour. If the
  measure of distance is NM, it is customary to speak of speed in terms
  of knots. Thus, a speed of 200 knots and a speed of 200 NM per hour
  are the same thing. It is incorrect to say 200 knots per hour unless
  referring to acceleration.

It seems it comes down to what you measure distance in, then simply report the appropriate speed units.

Most pilots will calculate (and talk in units) based on the instrumentation in their plane. Some airspeed indicators contain both knots and MPH however its not uncommon for them to contain only a single unit (generally older GA planes is where I have seen MPH instruments). POH's will generally contain what ever unit the air speed indicators in the original build of the plane contained (some POHs will contain both units). Just to show some examples, Mooney reported speeds in MPH in their older POH's while say a Piper from that era shows Kts in its POH. For example this indicator contains both units.

(source)

In the end of the day its most important that the units are not mixed up and or used interchangeably.

As for the errors in airspeeds this is one of the reasons that air speed indicators have color queues to indicate things like stall range, flap extend range and smooth air operating range. This way if a pilot does accidentally confuse units there are other things to rely on. (Side note there are some important speeds that do NOT appear on airspeed indicators that should always be noted).

-Edit-
To answer the comments below.

I report distance in NM since thats what foreflight uses on its ruler function as well as its ring function (at least the way I have it set up). Most plotters I have seen are in NM so even if I had a paper map I would be reporting NM as well.

Im not sure the FAA has official declared that Knots are the only acceptable unit. MPH airspeed indicators are still considered air worthy so they must at least accept it on that level. There have been pushes to standardize instrumentation after the issues caused by the eastern vs. western attitude indicators but with the advent of glass cockpits most of these things can now be configurable in software and changed by a simple setting. The FAR's (such as 91.117) report speed in both KTS and MPH and that is the letter of the law from the FAA.


Why did the backup landing gear deployment fail on LOT 16? LOT 16 was a 767 which experienced a hydraulic leak, resulting in the failure of the landing gears and the proceeding belly landing shown below:

Why did the backup system(s) fail? I was under the impression that a gravity/freefall backup is mandatory.

Gravity/freefall backup (or more precisely some backup) is mandatory, but in large aircraft running pulley from cockpit to the wheel wells to release the uplock (the thing that keeps the gear retracted) mechanically would be too complicated or the force required to operate it too large, so the uplock still needs to be released electrically.

Unfortunately the circuit breaker that protects the circuit responsible for releasing the uplock was "popped" (open), so the uplocks didn't release and the gear didn't fall down.

The crew was trying to troubleshoot the issue for 80 minutes and consulted maintenance over radio, but because the checklists for either central hydraulic system (which does the normal gear extension) failure or alternate gear extension did not mention the circuit breaker (C829) neither crew nor maintenance thought of checking it.

It is not possible to find why and when the breaker popped. They tested the alternate extension afterwards and it worked, but the breaker covers several other circuits and there could have been transient problem somewhere or it could have been maintenance error or some other reasons.

You can read excerpt from the report on The Aviation Herald.


Why aren't bird radars placed on the front of commercial aircraft? Unfortunately, my skills and understanding of radar and the like are very limited, but if somebody could enlighten me why there is no such thing as a dual bird/weather radar to switch to?

I've understood there there have been some (successful) attempts with ground station. It would add weight, but i'd guess that perhaps would be offset for some time by a single ruined engine.

There really is no such thing as "bird radar".  Radar comes in a few frequency bands that have certain advantages depending on the distance, resolution and attenuation you need out of it.  The band isn't the only factor here as the band will dictate what size dish you need and your aircraft nosecone will but a distinct upper limit on that.  Weather radar is geared toward detecting rain drops and anything bigger than rain (hail, bugs, birds, etc) with reasonable distance and attenuation features (you want to penetrate into a storm).  Birds will show up on this radar, though depending on smoothing and processing algorithms you may need a flock of them before they get drawn on the radar, at which point they'll look like some rain.  A radar optimized to detect bird sized objects would probably use a wavelength that did not let you see things as small as rain drops and small hail.
Some other things to keep in mind are that the radar is not always on, and it should be off on the ground except during takeoff when needed.  The reason for this is that you do not want to be putting radar energy into people, and they tend to be in the way on the ground.  We only turned the radar on for takeoff when there was significant weather around the field and wanted to be prepared for requesting diversions.  Aircraft radar tilt can also be adjusted, so we wouldn't be looking at birds in front of us, but clouds above and in front of us.
Wit that said, our SOP on fields with known heavy bird activity was to takeoff with the radar on and pointed forward because someone had the idea that the birds didn't like being in the radar beam.  I have no sources to back that idea up, but it was written into our FOM.
Now assume you can takeoff and see a flock of birds on the radar.  Do you have enough time to do anything about it?  If so, what do you do, some maneuver away from them or do you turn into them in hops they take the evasive action?
Now back to the title question: Why aren't bird radars in the nose cone?

The weather radar can see birds, it would be redundant.
A bird radar (optimized for birds) would not be good at seeing weather, so where would the weather radar be placed?
In a real situation, what would a bird radar enable you to do with a positive detection with the time you have to react to it?  Probably not much.
Weather is a much more common threat than flocks of birds, so if you can only have 1 radar system, you want the weather radar.


Is 3 crew cockpit safer than 2 crew? Today, commercial aircraft cockpit is manned by 2 pilots, previously  it was 3 to 5. Is safety compromised in any way?

No aircraft ever had more than two pilots (on duty at the same time).

The additional flight crew members were flight engineer, navigator and radio operator.

Dedicated radio operators were only needed in the early days when the radio was primitive and required some care and experience to tune properly. As it improved, operating radio was merged into navigator or flight engineer job and eventually became simple enough for pilots to do themselves.
Navigators were used on long-distance flights especially over water. They kept track of the progress on the map and corrected the position using celestial navigation and some landmarks where available. With advent of inertial navigation systems and long range radio this simplified enough that dedicated crew member was not needed any more.
Flight engineer was most common and remained longest. Engines had many gauges that needed monitoring and controls that had to be correctly set to start them and adjusted to keep them running efficiently. And while turbine engines are simpler to manage than piston ones, the addition of more electric and hydraulic system meant that there was still a lot to set up and monitor. But now this job is done by a computer that monitors all the parameters and displays specific messages when something fails including instructions what needs to be checked and done for each problem.

In the meantime, the improvements in autoflight systems freed more time for the pilots in which they can now handle, with help of the electronics, the tasks that before needed a dedicated crew member.

Due to these technological advances allowing for the removal of these crew members, overall flight safety has not been compromised. It is likely that safety has actually improved by reducing the probability of human error.


How do you write 'to', 'then', or 'via' in IFR clearances shorthand symbols? Although there are NO restrictions about the usage of shorthand symbols, still it would be useful when I fly with another person together, so I studied those symbols and got some doubt points.

If someone wants to write 'N123 is cleared to AAA airport'
I assume it would be 'N 123 C AAA A', so shall I exclude 'to' in this sentence?

How about 'via B departure then as filed'?
It seems that I can write 'via' as 'VIA', But I can't replace 'then' with '>' or '→', since each of those means 'before' and 'cruise'.

I referred to the site below, about symbols :
https://nova.aero/repository/IFR/IFR%20Clearance%20Shorthand%20Symbols.pdf

Do what works for you, and omit what you can. For example, "N123 is cleared to KABC" can be condensed to "ABC"... assuming the clearance is for you, why copy your own tail #? You're copying a clearance, so "is cleared to" is, to me, entirely implied by the fact that there is something written.

"Climb & maintain 7,000" is for me an "M" with a horizontal line through it, and "7". If it was 5,500 I'd either write it as 55 or 5.5, since neither 550' nor 55,000' would make any sense. "Expect FL210 in 10 minutes" is "x 210 / 10" -- or "x21/10" -- because I know that I won't be cruising at 2,100', "21" isn't ambiguous.

"As filed" is AF, "climb via the (filed) SID is "via". Direct is a "D" with a horizontal line through it. (Or an arrow, but omitting the arrowhead saves writing & is equally clear that this is a symbol with specific meaning, rather than a letter.) Some people use "DCT" for direct, which is fine, although the D symbol will never be confused for being a navid I need to locate. "Right" and "Left" are circled R and L, if needed.

"Squawk 1234" is "sq 1234" and "departure on 126.55" is copied as just the frequency, unless there are several - then "dep 126.55 mtr 121.65 5 pr" would record the need to also call Metering 5 prior to start. If it's Ground or Clearance I need to call 5 prior, I'd probably just abbreviate those as G or CD, without the frequency unless there are more than one -- I have all of those on my EFB so "Gnd 121.9" is no more info for me than just "G".

For me, the recorded clearance isn't a document I need to refer back to months from now so I can recite verbatim what the controller read to me; it's a memory aid so that for the next hour or two I can know the pertinent elements without having to remember them. So numbers like squawks, frequencies, headings, and altitudes are vital. Fixes and procedure names likewise, which is easier with a printed copy of the filed route handy, where I can underline those elements I was given.

For example, if the filed route for KABC to KXYZ is to the ABC VOR, then to AFFIX then to BBFIX then V123 to DEF then the WHOZT1 arrival, the clearance might be "on departure fly heading 150, radar vectors to BBFIX then as filed," so I'd write "H 150 RV" then underline BBFIX, and below that I'd write "AF". After I'm done reading that back, I'd line out the ABC VOR and AFFIX (that weren't part of the issued clearance).

Your instructor may have a different way that's preferred, and in that case go with what you're being taught. But over time, this is what I've found works well for me. Less writing, no need to scramble, what I need & no excess when I come back to look at it later.


When may passengers board the aircraft and who makes the decision? Who decides when the passengers may board the aircraft? Is this a pilot or cabin crew decision, and what are the prerequisites / conditions (cabin checks completed, flight plan filed, ...?) for this decision?

It is a joint decision of the entire flight crew (flight crew consists of pilots and cabin crew).

It is mostly a decision by the most senior flight attendant because it is mostly a cabin issue. The prerequisite is, obviously, the cabin has to be cleaned and prepared. There are "cabin checks" to be carried out when the plane is empty. Typically, each flight attendant will be assigned an area. When everyone reports they're ready, then boarding can begin.

But there are factors from the cockpit that can delay the boarding process too. For example, ATC informs them that takeoff will be delayed for 2 hours. Or a maintenance is being carried out. So, the pilots would always been informed before boarding begins, but in most cases there'd be no objection.


For a small flying wing, can two motors with different speeds replace the ailerons? I was thinking about a way to get rid of the aileron, and I was wondering if:

I install two motors on the wing, and make the right one spin faster than the left one, will my wing roll to the left ?

First thing first:
I think you mean yaw not roll. See Yaw definition

If you actually mean roll, then the answer is no.

If you mean yaw; then the answer is yes.
However it is impractical for two reasons:

1) Engines, especially jets but also propellers have a latency when speeding up and down. This will make it impractical, and might create pilote induced oscillations.
Electrics motors are more reactive, but so far they have yet to be commonly used in aviation.

2) Redundancy. If one engine fail.... you have to shut down the second engine, and you lost yaw control.


Is it possible to own an F-14 Tomcat? Ok, I'm a wartime aviation enthusiast who loves, in particular, 3rd-5th generation fighters. I have held an avid interest in them for years, but I've always wondered whether or not I could own one myself. Obviously, it would cost a lot of money to own a fighter aircraft, and the aircraft would come with a lot of restrictions. But, my question is this: Is it possible to own the F-14 Tomcat (demilitarized/used) as an airliner/civilian pilot?
Although I am young right now, I plan to become an airliner pilot and eventually purchase a small plane (single engine turboprop) for myself. After all that, which I assume will take anywhere between 30-40 years, I would like to know if it would be possible to purchase and own an F-14. It is my all time favorite fighter for many reasons, the main one being its variable sweep wings. Assuming that I can acquire the proper training and equipment to utilize its true speed and maneuverability, would it be possible (in roughly 30-40 years) to purchase and fly an F-14 at its full potential, disregarding the costs to own and maintain it.

I’ve chatted with a few F-14 pilots who are members of the Tomcat Association, aviation museum curators, as well as former NFWS Topgun instructor Dave “Bio” Baranak about the possibility of getting one or two F-14 airframes flying again.  The depressing conclusion we have all come to is that it is almost impossible for this to happen.  Multiple F-14 pilots, RIOs and maintainers have approached the DOD about doing so, to no avail.
Virtually all Tomcats which did not get donated to museums were cut up and melted down into beer cans, more or less.  The Navy destroyed nearly all of its Tomcat fleet to prevent spare parts from winding up in Iran, the last known Tomcat operator.  As of 2018, the DoD did maintain at least 11 flyable F-14 airframes in long term storage at AMARC and they are not parting with them.  Period.  The exact reason the DOD keeps these aircraft is unclear, though I suspect they are retained for limited purposes such as RedAir aggressor aircraft, flight test and research, or similar role that the type is deemed suitable for.  F-14s which were donated to museums or for public display as “gate guards” still remain the property of the DoD and the airframes have been mutilated to permanently prevent them from carrying flight loads.
The only other potential source of flyable Tomcats remains Iran and it’s believed that all or nearly all are out of commission due to lack of spare parts.  If somebody could purchase an F-14 airframe from Iran, then take it back to the states, it might be possible. However this would almost certainly be seized and confiscated by customs.
And even if you could get the aircraft back into the United States legally, plus find the enormous funding required for this enterprise, you’re still faced with the prospect of finding spare parts for it.  It will be very difficult to get anything from the manufacturer i.e. Northrop Grumman as the assembly lines have long since closed, there are ITAR and national security restrictions, and all existing spare parts, aside from those needed for the last AMARC F-14s, have been destroyed.
It’s a great dream, but it looks like if you ever want to see an F-14 fly again, the closest you will get is watching a DVD of Top Gun or Final Countdown.


In a piston aircraft engine, how much heat must be removed by the oil cooler? It is pretty straightforward to compute the heat and power generated by the combustion process, given the displacement, RPM and fuel mass flow rate. Similarly, the power exhausted can be computed with knowledge of EGT and conservation of mass.  The difference is dissipated as heat, from air cooling of cylinders and oil cooler.  I'm looking for a rough ratio between oil cooler and cylinder heat dissipation.

According to Fundamentals of Powerplants for Aircraft, quoted in Mike Busch on Engines (chapter 2), "Other thermal losses" account for 12.2% of fuel energy:

Conduction to air: 7.2%
Conduction to oil: 1.6%
Radiation and misc: 3.4%

The other two areas of loss are exhaust (51.6%) and mechanical (36.2%).

I don't know how "cylinder heat dissipation" would fit into this classification (some combination of air conduction and friction losses?), but looking only at conduction losses gives a ratio of air to oil of 4.5:1.


When can I log PIC time in a new category of aircraft? I am currently a Private Pilot Rotorcraft and I am doing an addon for ASEL. When can I log PIC time?

I've been told it's only when you're the solo occupant but after some reading I'm not so sure. 14 CFR 61.63(d.2) says:

  Have received training required by this part that is appropriate to
  the pilot certification level, aircraft category, class, and type
  rating (if a class or type rating is required) for the aircraft to be
  flown, and have received an endorsement for solo flight in that
  aircraft from an authorized instructor.

Do you have to have your license in category to log pic time? Or is it after you have received your instructor's endorsement to fly solo per 61.63?

When I showed this to my instructor and we did the endorsement in my logbook we received some backlash from the flight school saying that PIC time is only accrued after you have your PPL in the applicable category of aircraft. During my flight lessons I was always operating the aircraft for the entire duration of the flight after I had received my solo endorsement which satisfies the requirements for PIC time per 61.51(e.IV).

Am I misinterpreting the rules? Can someone point out to me why I wouldn't be able to log PIC time even though it's in a different Category? Thanks for the input!

Short answer: you can log ASEL PIC time only while flying solo, not while flying with an instructor.

You seem to be mixing up a few regulations: you quoted 61.63 but the text is actually from 61.31. However, since neither of those regulations are about logging time anyway, they aren't directly relevant.

The rules on logging PIC time are in 61.51:

  (e) Logging pilot-in-command flight time. (1) A sport, recreational,
  private, commercial, or airline transport pilot may log pilot in
  command flight time for flights-

  (i) When the pilot is the sole manipulator of the controls of an
  aircraft for which the pilot is rated, or has sport pilot privileges
  for that category and class of aircraft, if the aircraft class rating
  is appropriate;

  (ii) When the pilot is the sole occupant in the aircraft;

  [...]

(e)(i) says that you can log PIC time as sole manipulator only if you're rated in the aircraft. In your case, you aren't rated for ASEL (yet!) so you can't log ASEL PIC time while flying with an instructor, even if only you touch the controls. This is probably what the school is referring to.

However, (e)(ii) says that a private pilot who is the only person on board the aircraft may log PIC time, without any additional requirements (although other regulations do require an endorsement in order to solo, as you said).

That means, you can log solo ASEL time as PIC, but not training time with an instructor.


Are sun's UV rays more harmful on an airplane at high altitude? Most airplanes fly at >30k feet, way into the stratosphere / mesosphere where sun's UV rays aren't filtered by lower atmosphere layers.

If the windows of the plane are open and the sun is shinning right on a passenger, will the UV rays be more harmful than those on the earth's surface?
Are there any long term effects if a passenger is exposed frequently?

Hmmm, opening the window at 30.000ft, where the air temperature is about -40°C/-40°F, air speed is extreme, you can't survive without oxygen, and you want to put your arm outside???

Well, if you really do, you'll get a sunburn quite fast. I got a sun burn within an hour in an altitude of 3500m / 12000ft, though I was tanned due to two weeks at the beach.

The ozone did already absorb a large fraction of the UV-C radiation, but as most of the air mass is already below you, the rest of the sun light will not have been filtered so much.

So, let's close the window.

To my knowledge, side windows and canopies are made of some kind of polycarbonate like or Plexiglass.

CERN measured the transmission of light through a 2mm sheet of plexigas and came to the result that no light below ~350nm, passes this sheet. Depending on source, the UV region starts below 380-400nm.

Source: https://cds.cern.ch

Keep in mind that the windows are usually thicker, which makes this step in the diagram much steeper.

So, there isn't much UV left which can cause a sun burn, but let's take the data from rredc.nrel.gov to calculate how much light you get and compare it to the light at ground. I found a function describing the data from CERN quite well, and applied it to the sun spectrum data (without atmosphere) twice, to get a Plexiglass window of 4mm thickness. So, this is the worst-case, with no air above the aircraft pre-filtering the sunlight.

Here is the result, which shows that sunlight is much more intense, and its color is heavily shifted to blue. But the intensity drops to zero, just where the UV-A range starts. Even, if you put the beginning of the UV-A range to 400nm, the intensity is still lower than at the ground.

Wind shields of larger aircraft are usually a quite thick composite material of glass and some plastics, which should absorb UV the same way as polycarbonate does, if not better.

So, I don't see any evidence that you get more UV light in an aircraft than on ground.

However, you should not underestimate cosmic radiation, which is absorbed by our atmosphere quite well on the ground, but not at high altitude. A transatlantic flight is equal to an X-ray photography of your chest. Flying staff is an occupation group exposed to much higher radiation doses than any other group and it's dose usually is supervised.

EDIT:

As @PeterKämpf pointed out, Plexiglass is only one material used, and it is not a polycarbonate, which I didn't notice. But polycarbonates don't differ much concerning UV transmission, as the following diagram shows. However, I also read that polycarbonates - in contrast to plexiglass - are not UV hard and need an UV blocking coating when used outside.

Source: www.plasticgenius.com


How close can separation be during a landing clearance? How close can separation between two aircraft be during landing? during visual landing clearance?

Specifically, I refer to this Aviation Herald Report where:

  When the Boeing 777-300 was about 2.1nm before touch down a BAe Avro
  began its takeoff run on runway 08R. The Boeing 777 was subsequently
  cleared to land on runway 08R, winds from 130 degrees at 7 knots.

  When the Boeing 777-300 crossed the runway threshold, the Jumbolino
  was climbing out still short of the runway end.

(Source: www.avherald.com - Singapore B773 at Munich on Nov 3rd 2011, runway excursion)

Is it typical for two aircraft to be so close during landing? i.e. Essentially both landing & departing aircraft are simultaneously overflying the same runway but at opposite ends.

How much closer would cause the landing aircraft to abort? Would one proceed with landing even if when one crossed the threshold the other craft was just rotating?

There's other things that went wrong in that incident,  but I'm only asking about the close separation in the landing clearance visual clearance aspect.

PS. I've edited the question to remove a confusing misunderstanding. It was apparently not a visual clearance.

According to the avherald article, the airport was operating below visual minima, thus no visual approach would have been possible. Unfortuntely, the ATC communication transcript is not available, so we will will not know whether the CAT III AutoLand approach by the B773 was communicated to ATC, which would not allow the Avro to enter the runway protected area during the B773's approach or whether this was a decision by the B773 crew only.

Since the airport was operating under CAT I procedures, the B773 is likely to have been cleared for a CAT I ILS approach. The Avro will have been cleared for departure before the B773 was cleared to land, ATC has most likely used a non-withheld landing clearance.

  321.5 Landing clearance need not be withheld until prescribed separation exists if there is reasonable assurance that the appropriate separation will exist when the aircraft crosses the runway threshold. However, do not clear an aircraft to land before a preceding landing aircraft has crossed the runway threshold.

The runway is considered no longer occupied if the preceding departing aircraft has reached Vr and has rotated, although still being over the runway. If ATC can be reasonably sure that this will be the case when the landing aircraft crosses the threshold, the landing clearance can be issued.

The BFU bulletin reads:

  The B777 crossed the runway threshold of 08R at 12:09:09 in 40ft. Six seconds later, the BAe Avro crossed the opposite runway threshold at approx. 380ft.

(Source: BFU Bulletin NOV 2011 - Translation: Own Work)

Is it typical for aircraft to be so close during approach and departure? Yes, aircraft can be close during these phases, depending on procedures in use and meteorological conditions. Aircraft can be asked to maintain visual separation to preceding traffic in VMC, however without the full transcript of the ATC communication, this will not be answerable in regards to your scenario in Munich.


If I own land, can I create a private runway on my property for my own use? In the United States, if I own land that has an area suitable for landing a small general aviation airplane, can I just create a private runway, or do I have to officially be registered with the FAA or some government agency?

In short: Yes, you can. The FAA doesn't really care, as long as you're not going to interrupt class B or C operations. And honestly as long as you're not hosting a dozen other aircraft, how are they going to tell the difference between a field and an airstrip? If you want it on a chart or you are near special airspace, you need to contact the FSDO and talk to them about it (it's good to do that anyway). They will send someone out to survey it and talk with you, and hopefully approve it.

It's the local authorities that usually ends up being troublesome. Your state/county/city might have laws that apply, and you'll need to find that out on your own. A friend of mine spent just a few days talking/meeting with the FAA on his strip, but spent weeks dealing with the state transportation department and a local ban on new grass strips which he sat right on the border of (as in it was a ban in a 50 mile radius and his house was on mile 50).

Persistence is key, good luck!


What exactly is a UK IMC rating? In chat, falstro mentioned the "UK IMC rating" and described it as "a lighter version of an instrument rating, allows enroute IFR, but no approaches or departures" (although to be fair he also said that he isn't familiar with the exact definition).

The name "IMC rating" implies that it allows flight in IMC, not just filing IFR in VMC for procedural reasons. But if so, and if approaches are not included, then it seems like it would allow a pilot to fly into IMC with no safe way out again if an emergency required an instrument approach.

So what exactly is a UK IMC rating, what does it not allow that a full instrument rating does, and what is the advantage of having it?

This is also know in Europe as an Enroute Instrument Rating or EIR, which allows flights under Instrument Flight Rules in the cruise phase, but not for departure or approach. It is based on EASA FCL 825

  FCL.825 En-route Instrument Rating (EIR)

  (a) Privileges and conditions.

  (1) The privileges of the holder of an en-route instrument rating (EIR) are to
  conduct flights by day under IFR or in IMC in the en-route phase of flight, with
  any aeroplane for which a class or type rating is held.

The curriculum to obtain an EIR is lower than for a full Instrument Rating (IR), especially the number of hours for theoretical and practical instructions have been lowered:

  (2) instrument flight instruction.
  (i) The instrument flight instruction for a single-engine EIR shall include at
  least 15 hours of flight time by reference to instruments.

As GdD has pointed out in his answer, this is not the same as the UK CAA IMC Rating. See his answer for more information on this.


Is it OK to greet ATC? My instructor told me that courtesies are forbidden in radio communication, however, we usually start conversation as "Turany Ground, OK-ABC, good morning, (... request)".

I find it natural. Is that acceptable violation of the rules, or could it cause some troubles?

It is not part of the standard phraseology by any means, but it is fairly common, as is a very quick pleasantry when changing frequency.

  [station name], Good morning, G-ABCD, [request]

and

  G-ABCD, changing to [other station] thanks for your service.

The thing to remember is to not choke up a busy station with overuse of non-standard comms, and therefore to remember when it might be inappropriate to stray from the standards.


Is the freestream dynamic pressure higher during cruise or during landing/takeoff? I was trying to calculate the forces generated by an uncommanded flap deployment during cruising flight ($M_\infty=0.85, Alt.=36kft$) in comparison to the forces say, during landing. Assuming similar geometries, the forces will be proportional to the freestream dynamic pressure. If $q_\infty=\frac{\gamma}{2}p_\infty {M_\infty}^2$, the Mach number will be higher at cruise but the static pressure will be lower due to altitude. Thus, it is not immediately obvious to me which flight condition has the higher dynamic pressure. Does anyone have reasonable numbers for $q_\infty [lbf/ft^2]$ at landing vs cruise for a modern commercial airliner so that I can compare?

Here is what I am getting:

Static pressure:
Sea level: 101300 Pa
30,000 feet: 30100 Pa

Mach:
Sea level1 (150 kt): 0.22
Cruise2: 0.85

Ratio of specific heats: 1.4

Using the equation:
Landing: $3432.044 Pa = 73.68 lbf/ft^2$
Cruise: $15223.075 Pa = 317.94 lbf/ft^2$

So the high Mach in cruise more than compensates for the lower static pressure. This calculator agrees.

1Landing speeds for large jets are generally between 120-150 knots (Mach 0.18-0.22). Smaller planes around 60 knots (Mach 0.091). You can convert to Mach by hand or using a calculator like here.

2Cruise speeds are generally between 240-280 kias (knots indicated airspeed) for large jets, which translates to around 450-500 knots ground speed and Mach 0.75-0.85 (depending on altitude and conditions).


Airplanes in static display at Whiteman AFB After reading the post about B-2 sizing, I spend a couple of minutes on Google Maps looking at airplanes on the Whiteman AFB.

On runways, I think there are one B-2 Spirit, 3 T-38 Talon, and one AH-64 Apache.

On static display, I have spotted an F-111, one B-52 (north of the base), one A-10, one T-38, one B-47, and one B-29 at the south gate.

But there are also 3 more fighters at this location.

Center one seems to be an F-22 Raptor.

What are the two other ones? And is there any more static airplanes spread over this base?

F-100, F-15, and F-4.  There is no F-22. The thing that looks like a brown nose cone on the F-100 appears to actually be the long, nose-mounted pitot boom, painted a light color, with its shadow visible just above it in the photo, all blurred together to give the impression of a much wider object.  It's clear from the shadow of the fuselage that the fuselage truncates abruptly in front, as per the air intake of an F-100.

All these three types were used by the US Air Force.

According to Wikipedia the F-100 on display at this base is a D model, number 55-3667.

Aerial Visuals has information about it, the neighboring aircraft, and other aircraft on display on the base.

This facebook page  describes these three aircraft being moved to their current location, with closer photos of the F-100.

This webpage of military aircraft on display in Missouri also has photos of these 3 aircraft before they were moved to Whiteman AFB (see the "St. Louis, Lambert Field" section), as well as other aircraft on display at Whiteman AFB.

These three types were all flown by the Missouri Air National Guard 131st Fighter Wing, now the 131st Bomb Wing- a unit currently based at Whiteman AFB.  Read more about it on this Wikipedia page.


What airframe designer/manufacturer is credited with the first retractable landing gear system? A quick follow-up to Why do planes always land on rear wheels instead of the nose wheels?

What airframe designer/manufacturer is credited with the first retractable landing gear system? I ran past the article on retractable gear over in Wikipedia without really finding an answer

It looks like the first plane that actually flew and had at least a partially-retractable undercarriage was a German racing plane, the Wiencziers Renneindecker, from 1911:

You can see the undercarriage designed to collapse to the rear, using a hand crank in the cockpit to lift the gear. Not a great idea by today's standards as the gear would be prone to collapse on landing, but it apparently worked well enough at the time.

There are plans for retractable landing gear dating back to the late 1800s, before powered flight in such a craft was ever achieved, but they didn't become common on planes until just after WWI. Even then, for relatively slow planes (<200mph) it remains common even today to keep the gear fixed and wrap the wheels in a cowl, as for only a ~4% increase in drag over a full retractable setup, you save a lot of weight and mechanical complexity. Notable fixed-gear craft in military service through WWII include the German Ju87 Stuka and the Nakajima Ki-27 "Nate". Though most of the American wartime air fleet had retractable gear as of just after the start of WWII, practically every WWII air corps draftee trained on either a BT-11 or one of the biplane trainers like the PT-13/17/18. Today, plenty of civvie small craft have fixed gear, such as the Cessna 150, 172 and variants, Piper Cubs and Cherokees, some Beechcraft Musketeers, etc etc.


Why do most biplanes have their top wing slightly forward of the lower wing? In most of the biplanes, the top wing is located a little forward of the lower wing. What is the use of this? Also, how does this affect stability of the aircraft.

Placing the top wing ahead of the bottom wing in biplanes is called (positive) stagger. It is mostly used in small biplanes and improves pilot vision.

In order to accommodate a variation of pilot weights and to reduce accelerations in maneuvers, it is advisable to place the pilot very close to the center of gravity. If the upper wing were in the same lengthwise location, it would obstruct the forward and upward vision of the pilot.

Why is upward vision so important? Because of the bank angle, in turns you need to look up in order to see what is ahead. A high mounted wing right at the center of gravity would rob the pilot of forward vision in turns.

Therefore, in small biplanes the top wing is moved forward while the bottom wing is moved back correspondingly, so lift is created close to the center of gravity, but the top wing is out of the way.

Large biplanes do not need this arrangement because the pilot sits ahead of the wing. The Antonov 2 below is an example (source):

In many designs, the center wing has a cutout at the rear in order to give the pilot a better field of view. Even more interesting is what had to be done to improve pilot vision in parasol monoplanes. The Focke-Wulf 56 used slight wing sweep in combination with a reduced root chord in order to reduce the obstruction to the pilot's field of view of the rear wing center (picture source).


Do I need to be 'current' or hold a medical to become a Basic Ground Instructor? I want to become an aviation ground instructor BGI.
I hold a commercial, multi, instrument and F/E pilot certificate but haven’t flown in a long time.

Do I need to be “ current” to become a BGI?
Do I need an FAA medical?

You do not need a medical certificate.  It also does not matter that you have not flown in a long time.  You will need to study and take two separate tests to get you ground instructor certificate.

Fundamentals of Instruction (FOI) Test
Ground Instructor Test

The FOI information is covered extensively in the Aviation Instructor Handbook and is 50 questions (at least it once was).
The Flight Instructor test question bank is also used for the BGI (Basic Ground Instructor) and AGI (Advanced Ground Instructor) tests.  If I remember correctly, the BGI test is 80 questions and the AGI test is 100 questions.  The information on the test is covered in multiple FAA handbooks (not all inclusive):

Pilots Handbook of Aeronautical Knowledge
Airplane Flying Handbook
Rotorcraft Flying Handbook
Balloon Flying Handbook
Aviation Weather Services

One thing to notice is that the ground instructor test covers all aircraft and not just the "airplane category" as you can teach and sign off written tests for all aircraft.  Since the BGI and the AGI are the same test, I would suggest getting an AGI as you will be able to sign off all written tests and not just tests for sport, recreational or private pilots.