Is there any rule in commercial aviation, that two pilots in a plane cannot be a married couple? Is there any rule followed or imposed by commercial airlines that the pilots of a particular plane may not be a married couple? My thinking comes from common workplace rules, where generally HR does not allow a couple to work in the same department, for obvious hierarchical issues.

The Air Force, at least when I was flying there, had strict rules forbidding a husband and wife flying as crewmembers in the same aircraft.  Generally, airlines in the US don't have to have any similar policy, and there are plenty of examples of married couples (either pilot-pilot, pilot-flight attendant, or flight attendant-flight attendant) working a flight together.

An individual airline might be able to create such a policy themselves (although I have no idea if there would be legal grounds for a married couple to challenge the rule), but at least in the US there's no legal requirement that prohibits it.


Is it possible to increase available take-off distance for a seaplane by turning? In the video below an A5 had an accident after takeoff. The final cause of the accident seems to be a sharp increase of AOA above stall.

Do sea planes have an alternate technique for takeoff from tight spaces. Let me draw what I mean:

So in case 1 take distance available for T/O is not enough. Is there a procedure such as in case 2, where you use one side of the lake to accelerate to some speed and then turn to main leg to complete the takeoff?

Yes when I was bush flying in Northern Ontario (C-185 on straight floats) I used turning takeoff runs from time to time when loaded and with limited space.  You start the turn once on the step.  Step turns are a normal skill on floats although it's not a good idea to do it on choppy water in high winds.
The guy in the video had insufficient space to take off even with the turning takeoff run and it looks like he couldn't be bother to head farther down the lake to get a better into wind run.  I wouldn't have done a turning takeoff like that in that sort of windy chop.  I would've started right at the far shoreline as far as I could go, and determined a go-no-go point using a landmark that was about 2/3rds of the total run.  If you're not airborne fairly quickly (by water takeoff standards) in that kind of wind and waves, something is really wrong or your airplane is grossly underpowered.  I suspect that guy was overweight.


What is the difference between Turn Coordinator and Artificial Horizon? I was reading this question about Turn Coordinator and Artificial Horizon, and now I want to understand the differences between those two components.

What is the main difference between Turn Coordinator and Artificial Horizon?

Turn Coordinator:

Artificial Horizon:

Attitude Indicator
It shows your attitude (nose up / down, bank left / right) relative to a horizontal surface. Basically, it tells you the orientation of the plane if someone were to take a photo of the plane from the outside at this very moment.
It does not tell you which way you are going (e.g. you can be nose up but descending).
Turn coordinator
This is actually two instruments in one: the white plane and the little ball.
The white plane tells you which way you are yawing (rotation about the normal (vertical) axis)). If you are yawing to the right (e.g. N -> NE -> E), the right wing of the little plane is lower. If you are yawing to the left (e.g. N -> NW -> W), the left wing is lower.
If you are yawing at the standard rate (3 degrees per second), the wing of the little plane will align with the white mark.
Combining the two
Suppose that you manage to yaw the plane to the right while keeping it horizontal, like a spinning top:

You will get:


Why do we have a booking code and a ticket number? As per subject why is this done? Doesn't it make operations more confuseing as we have to references for every single passenger? A ticket number seems to be unique so why is this not used for all passenger references?

Part of it is a hold-over to historical systems (where airlines ran their own booking systems). Now that most airlines use a global system like Amadeus this is less of an issue.

The ticket number (PNR) and booking number (record locator) do have slightly different purposes though. The former contains the details needed for the actual flight (your name, contacts details, flight numbers, etc) while the record locator can also contain other information not directly related to the flight.
In short: The record locator contains a reference to the PNR but can also contain additional information that is not contained in the PNR.


How can static pressure be obtained over a range of airspeeds? Multiple instruments rely on static air pressure, i.e. pressure unaffected by airspeed.
To my understanding, no such air should exist around an aircraft. Air in motion exhibits a lower pressure measured laterally, and a higher pressure measured head-on (ram air).
Switching to an in-cabin alternate static source usually decreases measured pressure, as the cabin altitude is above outside altitude, due to its equalizing with accelerated outside air.
The only solution I could think of was to measure pressure at an angle, where both effects (Bernoulli and ram, so to speak) cancel out. Now such an angle would be airspeed-dependent. How can a reliable pressure be obtained, without computational aid, over a range of airspeeds?

I used to have that misconception too.
It turns out, to get that pressure drop, you need to accelerate the air. On aircraft, this is done by changing its direction and causing it to flow around convex curvature. This occurs at the tail, on top of the wings, and often at subsonic speeds, on the nose just past the tip high pressure point, and beneath the wings. (Yes, subsonic flow is weird)
Freestream air flowing undisturbed past a flat surface will have the same static pressure - relative to the surface or absolute -, regardless of airspeed.


How can I calculate which runway to use for landing, based on the wind? I have a project where the user enters the name of the airport. We fetch the wind direction (degrees) for that airport. Then we use the wind direction and the data about the runways at that airport to calculate which runways the planes will land at. What is the best way to do that?

My approach:

Find the compass direction, for instance 90 degrees is equivalent to east. Then, if the direction of the wind is east, the plane will land from the west (to land against the wind).

My question:

How do I calculate which runway the plane will use to land? There are multiple runways at some airports. Do we use runway heading, or runway longitude/latitude, assuming wind is the only factor affecting landing? Is there a mathematical way to calculate which runway the plane will use? I am asking because I will have to do some calculation to accurately give that answer to the user.

Any expert/aviation help would be greatly appreciated.

Also, I am using the airports and runways table from ourairports.com/data.

Also, what do HE and LE mean in the context of runways?

The name of a runway is a number indicating its direction in tens of degrees.1 For example, to land west-to-east, use runway 09.

Generally, each runway paving may be used in either direction, and the physical paving actually contains two logical runways, running in opposite directions. Only one of these logical runways is allowed to be in use an any time.2

The two logical runways on a paving have names that differ by 18. Thus a paving aligned due east-west will contain logical runway 09 and logical runway 27.

The information you will need about each airport is simply a list of the available runways and their lengths. You will also need the minimum runway length required for your aircraft to land.

To determine the best runway to land on, divide by the wind direction by ten and use the runway that is long enough whose name is closest to the result.

Example: An airport has runways 04 (1200'), 09 (5000'), 15 (5000'), 22 (1200'), 27 (5000'), and 33 (5000').3 Your airplane needs 3500' to land. The wind direction is from 232 deg.4

So, 232 divided by ten is 23. Runways that are long enough for your aircraft are 09, 15, 27, and 33. Of these, the one closest to 23 is 27. You would request and expect landing runway 27.5

This is a rough outline of the steps a math project would take to guess the landing runway. Most pilots have no trouble hearing the weather advisory, glancing at the Jepp chart, and just knowing which runway should be in use.

Often two digits are used, i.e. runway 9 is called 09.
If a tower controller is present, he will identify and grant access to the runway in use. Your project will calculate the most likely expected runway. With no controller, the pilot should co-ordinate with any present traffic before using your project result.
Notice that reciprocal runways occupy the same paving and perforce have the same length.
Your project must be told whether the reported wind direction is from or toward. When the reported wind direction is toward, as it might be from a non-navigational source such as a local news broadcast, you must calculate the reciprocal from direction.
If you had a plane that could stop in 1200' you would use runway 22.


What is the relation of stall speed to the position of the center of pressure with respect to the centre of gravity? Would the centre of pressure being aft or forward of the centre of gravity (CG), reduce or increase the stall speed in straight and level flight?  I know it is a weird question, I just cannot figure out if a centre of pressure being ahead of the CG (rare) would increase or decrease the stall speed, or even change it at all.

The comment written by wbeard52 is correct however this does still not explain exactly why the stall speed is increased. As an airframe stalls at an angle of attack, which will result in CLmax.

If the CG is moved to a more forward position, more downward force will be required on the horizontal stabilator to counteract the higher moment of the lift generated by the wings. This will increase the apparent weight. As (apparent) weight is increased stall speed will increase. All other parameters are fixed, in this situation.

Stall speed formula : V = √( 2 W g / ρ S CLmax )


Is it possible to get the QNH value in Austria using a web service? I got a altimeter sensor which can be connected to a computer and can be adjusted by the QNH!

I need the QNH for Austria, I figured out that the current QNH of the airports are streamed via radio.

Are QNH provided as text format or even better web service, so I can fetch mine automatically for transparent altimeter setting?

The current QNH at an airport is included in METARs so you can grab it form there. There are a few online services to retrieve the METAR automatically, such as this one (using Vienna airport as an example).

The latest METAR when I wrote this answer was:

LOWW 281050Z 14010KT 9999 FEW040 SCT065 BKN300 04/M03 Q1012 NOSIG

which shows a QNH of 1012.

Note that depending on the country the format may vary slightly, but in Austria (and European countries) you should always find a Qxxx value in the report.


Can a commercial pilot transport friends for free? Is there anything in the FARs that would prohibit a commercial pilot from doing multiple trips to ferry friends to an event in his/her personal aircraft assuming that the friends did not provide any compensation?

According to this interpretation that seems to match your scenario very closely, as long as you're also attending the event then a single trip is fine but multiple trips are not. And you would be acting as a private pilot, not a commercial pilot.

The interpretation was about an ATP who ferried fellow club members to an event (in nine flights!) and did receive money to cover costs, but the main points would apply to a CPL in your scenario too. In summary:

Flight time is compensation, therefore you're being compensated for the flights even if no money changes hands (the ATP argued that flight time in a C172 was worthless to him, but the FAA said they don't analyze individual cases)
Acting as a private pilot you can receive compensation only if a "bona fide common purpose" exists

If you aren't attending the event yourself, there's no common purpose
If you are attending the event, only the first flights there and back have a common purpose; subsequent flights to bring more people to the event do not

Acting as a commercial pilot you can receive compensation for transporting people only if you have an air carrier certificate (per 14 CFR 119.1)

You didn't give many details about your scenario, but if you're attending the event yourself then you should be fine for one flight each way under your private privileges. Any more than that and there's no common purpose.

Of course, the caveat here is that every situation is different and perhaps there's something about your case that would result in a different FAA interpretation. However, the basic points about compensation and common purpose are very consistent across interpretations.

(Apologies for not quoting the interpretation directly, but the FAA seems determined to make it as difficult as possible to copy and paste from their documents.)


Why didn't Boeing make the Sky Interior for the Boeing 777? Generally, Boeing has attempted to make the interiors of their aircraft as similar as possible, with one "unified" interior across different aircraft (i.e. based on a single "look and feel" for you UX enthusiasts), such as the older (but still fairly new) "Signature Interior" (debuted with the Boeing 777) and the newer "Sky Interior" (debuted on the Boeing 787).
When a new interior style was created, it seems like Boeing generally tries to copy that same interior to other aircraft. For instance, the Signature Interior was also used on earlier 737 NG and later 747-400 and 767 aircraft (with a retrofit offered), and the Sky Interior was used on later 737 NG (conflicting information about retrofits), 737 MAX, and 747-8.
While it seems from the above that Boeing is pushing new interiors onto older aircraft, including the 737, 747, and 767, this doesn't seem to be the case for the 777; even those coming off the assembly line today still have the original Signature Interior. Why didn't Boeing make a Sky Interior for their 777?
To make it clear what I'm talking about, here are some images and descriptions of each interior:
Signature Interior

Source: Airliners.net
Notes:

Middle section overhead bins and passenger service units appear integrated with the ceiling.
Side passenger service units are angled.
Overhead bin open handles can only be pulled one way.
The interior fittings are beige.

Sky Interior

Source: Lufthansa Magazin
Notes:

Middle section overhead bins and passenger service units appear attached to, rather than integrated with, the ceiling.
Side passenger service units are almost completely horizontal.
Overhead bins have open handles that can be pulled either way.
The interior fittings are white.

Keep these mind's answer points to a Ukraine International Airlines marketing material that advertises the "Sky Interior" for their 777s. However, clicking through the link shows a picture of their 777, but it has the same Signature Interior as above.

I don't know if it is an exception, but Ukraine International Airlines seems to claim that they have a Sky Interior in their 777. User gparyani comments that this claim may be mistaken. I'll leave this answer here in case somebody else independently comes up with the same thing.

  Welcome on board modern Boeing 777-200ER airliner! The aircraft’s quiet and cosy cabins are equipped with comfortable reclining seats, contemporary Sky Interior [...]

https://www.flyuia.com/ua/en/services/long-haul-b777


Why didn't we see many VTOL aircraft in the history of aircraft development? US aircraft carriers mostly use F/A-18 Hornet.
French aircraft carriers mostly use Rafale-M.
Indian aircraft carriers mostly use Mig-29K.
Chinese use Shenyang J-15.
...

None of them are VTOL aircraft.

Why didn't VTOL aircraft achieve much popularity with aircraft carriers?

Why didn't we see many VTOL aircraft in the history of aircraft development?

VTOL (and STOVL) are concepts which were conceived as a result of not having large aircraft carriers or the space for a long runway. The primary feature of these aircraft is to enable them to take off and land using a minimum of runway distance, but in order to achieve this compromises have been made with the designs. This affects several aspects of the aircraft; complexity goes up as it requires at minimum additional controls for low-speed maneuvers where traditional control surfaces are inefficient and some way to distribute the thrust or add thrust to balance when flying vertically.

This tends to add weight and occupy internal volume which could otherwise be used for other things, such as fuel. It drives complexity when flying the aircraft and also in terms of maintenance, and thus cost.

Take the F-35 as an example. There are three models of a single design, where the A-model is designed to operate from regular air bases on land, the B-model for VTOL operations on amphibious attack ships or forward air bases, and the C-model for regular aircraft carriers. Compared to the other two models, the B-model has less internal fuel and a lower max takeoff weight. Because of this it will be required to refuel more often and/or carry less payload, which in turn will drive the complexity of operating the aircraft due to the logistics.

Another issue with VTOL airplanes, is that they (as far as I can tell) haven't been designed to takeoff vertically with a full fuel load and carrying a full payload. I could not find any numbers for the F-35, but for the AV-8B+ Harrier the max vertical take-off weight is around 9,5 tons, while a rolling take-off increases this to 14 tons. ([Wikipedia])1 This is quite a difference, and it shows how much you sacrifice to be able to do a vertical takeoff.

While having the option of VTOL is nice, cost is generally what drives decisions (even in the military). An AV-8 cost around \$19.000 USD to operate per hour, according to DefenceIssues. While older than eg. a JAS-39 Gripen (age tends to drive costs upwards), the Gripen which is of a similar size and empty weight has a longer range and only cost $4.700 USD per hour to operate. And according to the source that number is high, as labor costs more in Europe than in the US.

Use on aircraft carriers

While some VTOL aircraft have been developed, the reason for why they aren't used more is related to everything above. Many of the non-VTOL carrier aircraft used today have a basis in aircraft originally designed to operate from land-bases using regular runways. If you decide to use VTOL aircraft on an aircraft carrier, the carrier can generally be smaller than a carrier operating STOL or catapult-launched aircraft, but this will also affect how you can use the carrier.


What's the relation between cabin pressure and altitude? Usually, cabin pressure of an airliner is kept at a value corresponding to an altitude of not more than about 2000m.

Now, I heard that before takeoff, the pressure is already increased a little for higher stability of the fuselage. Maybe, this is wrong, but I had another experience:

I was in a 737-800 flying at 11500m. While the aircraft sank on approach for landing, I felt that typical pressure on my ears several times though we still were above 7000m. So, the cabin pressure already changed at that high altitude.

So, how is cabin pressure related to outside pressure during the entire flight?

Here is a plot of cabin pressure on one flight. You can see a small increase in pressure right before takeoff. The decrease and increase in pressure is fairly constant during climb and descent. The pressure will change based on the aircraft's altitude, and will not reach a minimum limit until closer to the aircraft's service ceiling. This keeps pressure changes as slow as possible while giving a lower cabin altitude when below the service ceiling.

Source


Why are propeller engines uncommon on airliners? My experience in aviation is essentially zero, but looking at Wikipedia it seems like the Tu-95 Bear offers high subsonic speed and extreme range.

I assume that turboprop engines are more fuel efficient than jet engines. If all the above are true then why we do not get to see more rotary engine planes in commercial airline flights?

Is it a noise concern? I see that the TU-95 is apparently the "noisiest military aircraft on Earth".

Well, first let's clear up a few terms:
When you say "rotary" engine I'm assuming you're referring to radial engines, a type of piston engine that used to be pretty common on aircraft. (These days opposed piston engines are what you typically find on piston-powered aircraft, rotary engines are yet another design, but their usage died out around the end of World War I.)

The TU-95 is not actually a piston-powered aircraft.  It's a turboprop – basically a turbine engine similar to what you'd find in a jet, only rigged up to turn a propeller rather than produce "jet thrust" directly.

From an efficiency standpoint, turbine engines are usually more fuel efficient than their piston counterparts, and jet fuel is denser and less refined than aviation gasoline and is consequently cheaper for operators to procure. Turbine engines also offer more reliability than piston engines, and the maintenance on a turboprop engine is also largely similar to a jet engine with a few extra components, which is an advantage for a company operating a fleet of jet and propeller driven aircraft.

The differences in operating efficiency and reliability are the major reason why gasoline-powered piston engines have basically disappeared from scheduled airline service.

So why don't we see more turboprops? Actually we see a lot of them, if you look in the right places.

Jets and Turboprops are good at different things: broadly simplifying, a turboprop is more efficient at lower altitudes and airspeeds while a jet engine is more efficient at higher altitudes and airspeeds.

As a result we see turboprop aircraft like ATR 72s in use for short-haul "commuter" service, but for trans-continental or trans-oceanic flights where they spend a long time cruising at high altitude jets dominate the sky.

Since most people are flying to go relatively long distances there are comparatively more jets in scheduled airline service than turboprops.

Noise is probably also a factor: fast turboprops like the Bear are LOUD not due to the engine, but due to the propeller.  The tips of the spinning propeller on a TU-95 can approach supersonic speeds, which causes quite a bit of noise. The TU-95's contra-rotating propellers (which help produce thrust more efficiently) also contribute to a louder noise footprint.  In the case of the TU-95 this doesn't matter – it's a military plane, and the Russian air force doesn't care if people complain as the aircraft has a mission to complete and that's more important than a few noise complaints.  If United Airlines were to operate a TU-95 out of Kennedy departing over people's houses I suspect they would quickly reconsider their choice of equipment when the noise complaints started coming in....


Do contra-rotating propellers have the same RPM? Image source

Here is a contra-rotating propeller. The front propeller rotates counterclockwise while the back propeller rotates clockwise. My questions are:

Do they rotate at the same speed (RPM)?
If not, which one is rotate faster, and why?

Most if not all contra-rotating propeller systems are geared together so that both sections turn at the same speed.  This is done so that as well as allowing effective conversion of very high power into thrust, torque and P-factor are cancelled, making the aircraft easier to fly (especially in a single-engine or two-into-one installation).

This is why you see the same diameter propeller in front as in the rear -- if they were turning at different rates, the slower one could be larger diameter (a limitation on diameter is transonic conditions at the tips) -- but you always see the same diameter on front and rear.


Why did the early versions of the Me-109 use a braced stabilizer? The Messerschmitt Bf-109 had struts holding the stabilizer in place up and including the E version. I marked it with a red circle in the picture below of the 109 E-3 of the Flying Heritage Collection.

Bf-109 E-3 in flight (picture source)

Given that Willy Messerschmitt was fanatical about reducing drag, and contemporaries like the Hawker Hurricane, the Supermarine Spitfire, the Curtiss P-40, the Heinkel 112 or the Dewoitine 520 had cantilevered stabilizers, why would he tolerate a strut on the tail of his new fighter aircraft?

To understand that particular design decision, some background may be necessary.

In the 1920s, Willy Messerschmitt had started a small aircraft factory in Bamberg with limited economical success. When he requested financial help from the Bavarian state, he was forced to merge with another aircraft factory in Augsburg, into Bayerische Flugzeugwerke. Since few of his designs enjoyed commercial success, he was forced to accept the production of other designs under license to keep the workforce of the combined companies occupied.

The only Messerschmitt design which had been accepted by Lufthansa was the M.20, and a close friend of a Lufthansa director was killed in a test flight of the M.20. When that director was promoted to the German air ministry and became responsible for selecting aircraft for building up the new Luftwaffe, he made it clear to Messerschmitt that he would avoid purchasing his designs because he disapproved of his reaction to that fatal accident of the M.20.

Messerschmitt M.20 (picture source)

The most successful type of Messerschmitt's designs was the M.23, a two seater sports plane. It had suffered two accidents in which the tailplane broke off in flight, so struts for the tailplane were added while initially produced aircraft had an unbraced tail.

Early Messerschmitt M.23a with ABC Scorpion engine (picture source)

Messerschmitt had gained a reputation for aerodynamically clean and very lightweight designs, and accidents of the M.20 and M.23 in which the tail section failed made pilots wary of the structural soundness of his designs. Nevertheless, his aircraft achieved surprising performance with very limited engine power, so he was unofficially asked to contribute a design when a competition for a new standard fighter was announced in 1934. As an outsider, he had to make sure that his design would be accepted by his critics, so he played it safe and braced the tail, as he had done on the M.37 (which was to become the Bf-108 and was in many ways the dress rehearsal to the Bf-109).

That is the real reason for the struts: Messerschmitt had to play it safe to not threaten his chances as an outsider for a very lucrative contract.


Which way should I rotate the propeller of a C172? During pre-flight which direction should I be rotating the propeller of a Cessna 172 if I need to reach the alternator belt?  I thought I was told "In the direction it rotates during flight"; however I feel there was some misunderstanding. Isn't there the possibility of accidentally hand propping if I do it that way on a warm engine? Today I rotated it clockwise in the direction of the blade and it kicked over and popped me in the knee (leg shouldn't have been there - lesson learned!) Please help me clarify!

Almost everyone in the industry has opinions about this, sometimes with good reason. I know knowledgeable people with good arguments for why you should only turn the prop backwards, never turn the prop backwards, or why it doesn't matter either way.

In any case, the issues of concern are primarily:

The engine firing and rotating the propeller, or
The dry vacuum pump sustaining damage.

Those who say "you should never turn a prop forwards," will typically argue that:

Rotating the prop in the firing direction can cause the engine to fire, if:

A magneto (with an impulse coupling) is live (faulty ground or actually switched on), and
The cylinder still has a burnable fuel/air mixture (particularly if recently not properly shut-down).

Rotating the prop backwards eliminates the possibility of the impulse coupling catching and sending a spark to any cylinder.

Those who say "you should never turn a prop backwards," will typically argue that:

Dry vacuum pumps are fragile and only meant to be turned in one direction (with normal engine rotation), and
Rotating the prop backwards introduces the possibility of damaging the vacuum pump's (relatively) delicate carbon vanes leading to pump failure.

Those who hold that either direction is potentially dangerous but can be done with caution will typically argue that:

Backward movement of the prop—especially small, gentle, cautious movement—introduces little likelihood of damage to the vacuum pump vanes;
Good engine shutdown and magneto switch policing will very nearly eliminate the possibility of an inadvertent cylinder firing, and
Carefully moving the prop forward while treating the engine as live will give you a good margin of safety.

One may present a variation on the above, but I think those three perspectives capture the essence of any argument on this topic. Inadvertent engine firing can indeed be very dangerous, and a piston prop should be treated as live and dangerous. Dry vacuum pumps are indeed built with carbon or composite vanes which are far more brittle and delicate than steel parts. However, there are differing takes on just how delicate these are.

"Healthy dry air pump, left, showing graphite vanes angled in carbon rotor. When an air pump fails, its rotor and vanes often shatter" — Photo and caption as seen in Aviation Consumer

The Australian Civil Aviation Safety Authority (CASA) states that:

  Simply pulling the propeller backwards to “test” cylinder compressions may fail the pump by forcing the vanes to rotate in a direction opposite to their intended design. In order to prevent the vacuum pumps from being operated in reverse, never turn the propeller backwards.

However, Aviation Consumer states in this article that:

  One of aviation’s old wives’ tales is that you’ll wreck your vacuum pump if you move the prop backward. Fortunately, that’s not true. While most vacuum pumps are unidirectional—they either turn clockwise or counterclockwise in service based on the direction of rotation of the accessory shaft on the engine (and have CC or CW as a suffice to their model number)—it takes more than a few turns in the wrong direction to cause damage.

Mike Berry, whose opinion on such matters I respect, seems to think that turning the prop backwards will not hurt it, as seen in this quote from his May 2002 article in Light Plane Maintenance, reprinted by AvWeb.com:

  By the way, pulling a prop through backwards will not hurt a dry pump.

I know people that operate and maintain several Cessnas with dry vacuum pumps and are not very gentle when they move the prop either forward or backward they don't seem to have issues either with the engine firing or with low vacuum pump replacement intervals. The vacuum pumps replacements that I have done were typically brought about by normal long-term wear, as far as I can tell.

My take is: firstly, know your aircraft and it's systems. Secondly, be careful; respect the prop. Personally, I turn the prop either direction, but not usually a lot, and I do so gently and cautiously.


How often is the name painted on fighters? This question is restricted to US Air Force fighters, as I don't know if other air forces paint the pilot's name on the fighter.
This question pops into my mind because of 2 reasons:

this comment reminds me a fact I saw on a comic strip long time ago: the name of the pilot is written on the fighter cockpit, at least in the US Air Force and perhaps in the US navy.
in this video (smarter everyday, episode235) there is one scheduled flight with the videographer. For this single flight they took the time to write the videographer's name on the fighter (see at 6min17s).

How often is this name (re)painted?

is it updated for every scheduled flight if needed?
is it updated for a single flight flown by another pilot of the same squadron?
is it updated when the fighter is operating on an external theater?
if no update is needed, is it repainted more often than the rest of the airframe?
does this answer varies from squadrons to squadrons?

Bonus question: is it actually painted (I may have made a false assumption, in which case I should substitute "painted" by another more suited word in the whole question)?

I cannot answer for the USAF, but Navy and Marine Corps squadrons have also done this for years.  In addition to the pilot, if there is more than one seat the Weapon System Officers name(s) will also be painted, in addition to the Plane Captain.  It is an honor to have your name on a plane, and it is done for morale reasons.  It does not mean that that airplane is assigned to you alone.
Names are painted based on seniority in the squadron.  Typically there are more crews in a squadron than airplanes, so the junior most pilots will have to wait for some time to have their name on a plane.  It is a minor rite of passage when it happens.
For example, in the EA-6B squadrons I served in there were 4 airplanes, and typically 6 crews assigned.  The senior 4 pilots got their names painted, and if memory serves me correctly, the Naval Flight Officers, (NFOs, or WSOs...) who were assigned to their crews were also painted on the same plane.  So, while a junior pilot might need to wait a year or two, a brand new NFO assigned to the Commanding Officer's crew might get on right away.
They are painted on with a stencil whenever a change is called for.  It is low priority in the maintenance scheme of things, so when a senior pilot transfers out and someone moves up the rung it might take several weeks before the plane is moved into the hangar for some other maintenance interval, and the name is repainted then.


How to calculate flight time from time at full throttle? I'm building an electrically powered paraglider,  and I'm trying to reach one hour of flight time.  I've resolved to using 2 18-kilowatt motors. I could use one 35-kilowatt motor, but I'd wrather not kick out my spine on a hard start.

Anyway,  with 6 x 504Wh packs,  I'd get 6 minutes at full throttle.

But powered paragliders don't use full throttle the whole time. How can i calculate aproximate flight time from time that i can have full throttle?

You can assume that my glider has a forward rate of 9:2, and a climb rate of 9:4.

You say mention a 'forward rate' of 9:2. If I get you right, that means L/D = 4,5 The mass of your body, plus electric motor, battery and parachute is probably around 110 kg. Assuming you may glide with an airspeed of 15 m/s at L/D = 4,5, the vertical component of the airspeed is 15/4,5 = 3,33 m/s, and the 'gravitational power' involved is 110 x 9,8 x 3,33 = 3600 W. The conversion efficiency of motor + propeller is probably 0,5, so the electric power needed to fly level at L/D = 4,5 and 15 m/s would be 7200 W. If the capacity of your batteries is 6 x 504 Wh = 3024 WH, then your flight time would be 3024/7200 = 0,42 hours = 25 minutes...

More or less...


How does handover between Air Traffic Controllers work? I have a questions about air traffic control.
I understand how the controllers monitor and direct aircraft on their intended routes while maintaining clearance distances to other aircraft and obviously recognizing and avoiding collision courses, or at least I think I do.
My question is about hand-offs and range.
Presumably traffic is handed over to the next area controller when it approaches or reaches the limit of the controllers radar scope. However, how can the controller know that there is not another aircraft approaching out of scope range that is on a collision course with the aircraft leaving or approaching or traversing the boundary of his scope range?
Wiki says...

As an aircraft reaches the boundary of a center's control area it is "handed off" or "handed over" to the next area control center. In some cases this "hand-off" process involves a transfer of identification and details between controllers so that air traffic control services can be provided in a seamless manner; in other cases local agreements may allow "silent handovers" such that the receiving center does not require any co-ordination if traffic is presented in an agreed manner. After the hand-off, the aircraft is given a frequency change and begins talking to the next controller. This process continues until the aircraft is handed off to a terminal controller ("approach").

From that I guess is some centres the controller is expecting an aircraft to appear from a particular bearing, though even then, the variance would be wide at radar ranges.
I also realize that aircraft normally follow set lanes and altitudes depending on direct etc, but an aircraft in transition could appear pretty much anywhere. No?
That got me thinking that there must be an overlap on the visible range and that an aircraft is, for some period of time, visible from both centers. I guess that would work, but then it got me wondering how each centre knows who has control over the aircraft and if situations could occur where nobody is...?
That all brought up another question. I have to assume there is more than one human at busier control centers all working together. How is that managed? Who controls what?

The answer to your question heavily depends on jurisdiction which you don't specify. I will answer for Europe-Greece where I have some knowledge. The procedures might differ between the ANSPs and are subject to change.

how can the controller know that there is not another aircraft approaching out of scope range that is on a collision course with the aircraft leaving or approaching or traversing the boundary of his scope range?

There are several factors affecting that and I would say it's part of the job:
Training and personel
In Greece I know that controllers are specifically requested to setup their CWP in such a way that they can see at least 10 nautical miles from the border of the controlled area and definitely they should see the whole sector at all times. Also if some area is quite busy they have a secondary radar screen (imagine it like a PIP) that can focus in that area. That way they can have a good look of crowded areas without losing the full picture.
Also there is not one controller per sector, there are two. The RO (radar operator) and the planner. It's the planner's job (among others) to coordinate with the neighboring sectors for the trajectory of all incoming flights, and if there will be significant deviations they will notify RO.
Actual handover procedure
When a flight approaches the boundary (geographical or vertical both can happen and are valid) the RO initiates in their CWP the handout sequence. At the same time they switch the plane to the next sector's frequency. The other controller is not supposed to assume control of the flight until the plane calls them (yes there can be errors in frequency switching, that's why planes have the standby frequency on the comms panel). When the plane calls the next sector, the controller assumes control, finishes the handout sequence and the plane is officially theirs and doesn't belong to the previous controller anymore.
If the next controller doesn't accept the handout, the flight returns back to the previous sector controller. The details of that process changed after Helios 552 accident happened;(1) that's why I've said that the procedures might change at the ANSP's discretion.
There are exceptions and nothing is carved in stone:
A flight might have requests that the current controller cannot grant safely: Altitude, higher or lower. Direct to some point outside of the sector. Speed change like for example 250 knots speed restriction waiver for approach sectors. Then the controller currently controlling the flight might handout the flight earlier to the next sector with or without coordination with the next controller depending on the situation.
FIR Design
Also note that the FIR design (sectors, airways and points) is not done randomly but in such manner that there are no conflict points on the boundary of a sector but closer to it's core. So that the surprises on sector seams are minimized. See the appendix for a detailed example.
Finally, for sectors where the handover of climbing or descending flights is routine (TMAs for example), there are predefined altitudes for handover. For example a flight should be at FL210 when crossing the sector boundary. Again, nothing is carved in stone and there might be small deviations. If there are big deviations, the sectors coordinate as I've mentioned before.
Coordination between FIRs
All the above happen between control sectors in the same FIR. When handing over control to other FIRs that is a whole other story. Flights are coordinated via a communications channel, either manually (via telephone) or automatically (via protocols like OLDI). The boundary sector controller of the next FIR expects the flight on a specific point at a specific time. If the flight doesn't show up they start looking for it... They call at the expected frequency, they call at the emergency, they call the previous FIR (and not necessarily with that order).

how each centre knows who has control over the aircraft and if situations could occur where nobody is...?

There is no such thing as nobody is in control when we talk about en-route ATC. The flight is in the control of the sector (and FIR consequently) that "contains" the flight in the 3D space. The fact that you "see" the flight doesn't mean that you control it. It means that you know its presence which is a good thing.

I have to assume there is more than one human at busier control centers all working together. How is that managed? Who controls what?

Please see above the comment about RO and planner. There are also other very good answers on that specific question like this one where  you can see somewhere in the end, a

Typical sector radar team

consisting of two people, and from what I see, the left one is the RO equivalent and the right one is the planner equivalent.
Appendix I: Sector design importance explained
Here is an example from Milos sector (aka AC5) of Greece. To declutter the map, I've hidden the coastline, and displayed only the aerodromes. The sector is the black area and the rest of the FIR is in gray. Note that this is not the case in reality, I've just changed the color setup to highlight the area of interest.

To get a better idea of the area, here is what is displayed. Milos island is on the center.
Without getting into the details of the sector as this will be off topic, you can see that the conflict point I was talking about is where the red arrow is. That is MIL VOR-DME located in Milos island. There you have 10 airways(2) converging, being "fed" by Athens airport (LGAV) in the North and Heraklion airport (LGIR) in the South (green arrows). As I've mentioned, the conflict point is almost on the sector's center. It's right in the controller's eyes, away of the "ambiguity" of the sector border.
One might argue that there are 2 more points where airways converge, one in the North (KEA VOR-DME, name not shown) and one Northwest (DDM VOR-DME , name not shown) that are very close to the next sector border. Though this is true, the points are not as big conflict points as MIL VOR-DME because

KEA and DDM are major navaids for Athens TMA and it's expected to have that many airways converging towards them and
most of the flights that will cross these points over 250 (Athens TMA vertical limit) will usually be en-route, ergo no unexpected changes in heading and altitude

Also notice that Athens TMA (light coral line) overlaps will AC5. That means southbound departures from LGAV will be handed over to AC5 when they are way in the sector, away from the boundary.

Notes
(1) Many people ask how the Helios 552 accident can be related to the process. It's not related directly. Before Helios accident, the process was as follows: Propose the aircraft to next sector. Next sector accepts the proposal. Previous sector sees that and switches the frequency. That was reversed: the receiving sector is not accepting the handover unless the aircraft calls first. That way it's easier (and faster) to spot flights that for any reason did not call. As you can see, it's not directly related, but it was a change to keep the procedure on the safe side.
(2) For the record these are A10, A14, B26, B34, J56, R32, L617, M601, N134, P32
Acronyms
ANSP Air Navigation Services Provider
RO Radar Operator
CWP Controller Working Position
OLDI On-Line Data Interchange
TMA Terminal Maneuvering Area


Is constant air pressure maintained inside the fuselage? I just heard it somewhere but I'm not sure about it.   If it is, then why don't they build airtight fuselages?

For the purposes of air pressure inside aircraft, they are broken down into two broad categories:

Unpressurized - These aircraft are typically piston powered and can't go very high, so do not even attempt to regulate the air pressure inside the fuselage.
Pressurized - These aircraft do maintain pressurization in the fuselage, but it isn't constant beyond a certain point.

The category determines the answer to your question:

Unpressurized Aircraft

Unpressurized aircraft are not built air-tight for a couple of reasons:

It is very hard to make something as large as an airplane truly air-tight, and keep it that way.  Over time, seals will start to leak, fittings will loosen, etc.
The fuselage would have to be much stronger to withstand the pressure difference between the inside and the outside.  This would make them heavier and more expensive.
There isn't much need.  These airplanes don't fly high enough to really require a pressurized fuselage and a person can breathe more or less normally even though you aren't at sea level.  (Think of people that live on mountains.)

Pressurized Aircraft

Without going into the details of how an aircraft is pressurized (which isn't really relevant to your question), the air pressure inside the fuselage of a pressurized aircraft is usually maintained at sea level pressure up to a certain point.  However, the fuselage is designed to withstand a particular maximum differential air pressure, so in order to protect it (basically keep it from "popping" when the air pressure outside the airplane drops too low), the pressure is allowed to decrease when needed.

In typical jet airplanes, the pressure inside portions of the airplane (typically the passenger compartment, some of the cargo holds, and maybe an avionics bay) at cruising altitude is maintained at a pressure which corresponds to an outside air pressure at an altitude of about 5,000 - 8,000 feet (referred to as "cabin altitude"), depending on the cruising altitude and the design of the airplane.


Why does this calculation show Gustave Whitehead's propellers were more than 100% efficient? I have tried to calculate the efficiency of Gustave Whitehead's propellers using the information he provided to the American Inventor Magazine in 1902 (see the citation below).
Number of propellers = 2
Engine power per propeller, $P$ = 20 hp
Propeller diameter, $D$ = 6 ft
Static thrust per propeller, $T$ = 254 lbf
Propeller efficiency, $\eta_{prop}$
Gear efficiency, $\eta_{gears}$ < 100%
Air density, $\rho=1.2 \frac{kg}{m^3}$
Doing the calculations: $\eta_{prop} > \sqrt{\frac{T^3}{(P^2 \cdot \pi \cdot \eta_{gears} \cdot \frac{D^2}{2} \cdot \rho )}} = 101.4\%$ which is impossible.
Is there a mistake? If yes, where?
Note: I used the formula that relates static thrust to efficiency, power and propeller diameter.

The Whitehead Flying Machine
Has the End been Finally Attained, and is the Dirigible Balloon to Go?
Editor, American Inventor
Dear Sir: Replying to your recent letter, I take pleasure in sending you the following description of my flying machine No. 22, the latest that I have constructed:
This machine was built in four months with the aid of 14 skilled mechanics and cost about $1,700 to build. It is run by a 40 horse-power kerosene motor of my own design, especially constructed for strength, power and lightness, weighing but 120 pounds complete. It will run for a week at a time if required, without running hot, stopping, or in any possible manner troubling the operator. No electrical apparatus is required for ignition purposes. Ignition is accomplished by its own heat and compression; it runs about 800 revolutions per minute, has five cylinders and no fly-wheel is used. It requires a space 10 inches wide, 4 feet long and 10 inches high. ...
The propellers are 6 feet in diameter and have a projecting blade-surface of 4 square feet each. They are made of wood and are covered with very thin aluminum sheeting. The propellers run about 600 revolutions per minute under full power and turn in opposite directions. When running at full speed they will exert a thrust of 508 pounds. I measured this thrust by attaching the machine to a post by means of a dynamometer and running the engines at full speed. ...
I have no photographs taken yet of No. 22, but send you some of No. 21, as these machines are exactly alike, except the details mentioned. No. 21 has made four trips, the longest one and a half miles, on August 14, 1901.   The wings of both machines measure 30 feet from tip to tip, and the length of the entire machine is 32 feet.   It will run on the ground 50 miles an hour, and in air travel at about 70 miles.  I believe that if wanted it would fly 100 miles an hour. The power carried is considerably more than necessary. ...
Trusting this will interest your readers, I remain, Very truly yours,
GUSTAVE WHITEHEAD
Bridgeport, Conn.

Source: The American Inventor Magazine
, 1 April 1902
.

The equation you referenced shows prop diameter squared, divided by 2, not 4.

Even then, the calculation shows that marketing is to experimentation as about 2:1 :)


Does the FAA always require a neuropsychological assessment battery for applicants with a history of ADD? I'm in the middle of a medical struggle with the FAA. I'm applying for a 3rd class medical certificate but was hit with a deferral letter due to a childhood ADD diagnosis. Currently the FAA is only asking for:

"A personal statement regarding my ADD history and medication use."
"All treatment records and evaluation from the physician who prescribed the ADD medications in the past."

My question is this - does the FAA require a neuropsychological battery test for all applicants with an ADD history, or is their requesting a testing battery contingent upon what I say in my personal statement and the included treatment records / evaluations?
My treatment records and physician evaluation conclude that I no longer have ADD symptoms. In addition, I've flown intensively with a United Airlines check airman (pilot responsible for evaluating the flight ability of other United Airline pilots) and he has written a letter stating he's seen no evidence of ADD and, in his professional opinion, I am qualified to pilot an airplane.
Do you think, after submitting this documents in my favor, I will be able to avoid undergoing the testing battery?

If you have ever in your life been diagnosed with any mental health condition, such as ADD/ADHD, then the FAA presumes you to be mentally defective until proven otherwise to their satisfaction, by their own experts at your expense. They do not care what your personal doctor says, or what other pilots say.
You will need to get evaluations from a HIMS Psychiatrist and/or HIMS Neuropsychologist, which will likely take you months to arrange since there are only a few in the entire country. Then you will need a HIMS AME to process the paperwork and send it to OKC, which will spend a few months reviewing it to make sure the file is complete. Then your file will be sent to DC, where it will sit on the Federal Air Surgeon’s desk for several more months before he reviews your file. If all goes well, he will issue a Special Issuance medical, conditional on renewing the above evaluations every 6 or 12 months until he is eventually convinced you are mentally stable enough for a regular medical certificate. That may take up to 10 years, depending on your exact condition.
If your AME is not a HIMS AME, they will have no idea how this process works or what paperwork is required, so switch now and save yourself months of wasted time and money.


Why turn mobile phones off on take off and landing? Why do commercial airlines insist on turning phones to airplane mode? Does it really interfere with the planes dedicated frequencies?

It is unlikely that phones and other personal electronics could interfere in a way that would significantly impact communications, navigation or other systems. But, the possibility is still there, and that possibility forces the FAA to impose regulation. In most cases, device-use regulations are passed down to the airlines, and it is the airline that sets rules for device use on their flight. It's quite possible they limit device use during critical flight phases like takeoff and landing to help ensure people pay attention to safety briefings.


How are condensation cones created by supersonic airplanes? There are many awesome pictures of this phenomenon such as this one:

What is the physical explanation of how this occurs? Does it occur only when the airplane crosses the sound barrier or does it continue throughout the whole supersonic regime if enough water vapour is present in the atmosphere? What factors does this condensation depend on?

It is important to note that the vehicle is not traveling at supersonic speed when condensation collars (rockets) or condensation cones (aircraft) occur. It is merely close to the speed of sound.

From the vehicle's viewpoint

Air is accelerated by the displacement effect of the vehicle - it pushes the air aside and around itself, causing the flow to accelerate and to become supersonic relative to the vehicle. This acceleration is directly connected with lower pressure (see this answer for a detailed explanation), and air with high relative humidity will be pushed beyond its dew point, causing the water vapor to condensate. Please note that the onset of condensation is slightly delayed, so the fog is not strictly indicating the region of lowest pressure. Also, the forward cone is not the same as the forward shock front of a lambda shock.

However, the rear boundary of the condensation is indeed caused by a shockwave. The low pressure area is instantly ended by a compression shock, when the supersonic flow around the aircraft is abruptly decelerated to subsonic speed by a compression shock. This raises the local air pressure back to around ambient pressure, so the capacity to absorb water is raised again and the fog evaporates. Again, this happens with a slight delay, so the end of the condensation area does not coincide with the compression shock but follows it.

From the viewpoint of the air

Since the low pressure area is caused by the aircraft, it travels with the aircraft, and so does the condensation effect. The air around the aircraft or rocket is accelerated towards the vehicle by its pressure field, which causes the condensation. Now the air is so fast relative to the vehicle that it is decelerated and recompressed by a straight shock, causing the condensation to disappear again.

Factors

A relatively blunt vehicle traveling at close to Mach 1 and humid, almost saturated air are the factors which help this effect to occur. Note that you can witness similar condensation effects over the wings of airliners in humid air during the landing phase, when flaps are fully deployed. Here, however, the condensation does not end abruptly, since no shock is involved. Also, the disturbances produced by the aircraft do not reach out so far at lower speed, so the condensation happens only close to the aircraft's surface. Bluntness helps: The cockpit causes its own small condensation area shortly past its maximum thickness, where suction due to displacement is highest.


What is the registration number of the 10,000th Airbus? Recently, Airbus delivered its 10,000th aircraft (an A350 to Singapore Airlines). What is its registration number?

I understand the registration number is specific to the airline, and has nothing to do with the manufacturer.

The answer you are looking for is: 9V-SMF.

Current registration number: 9V-SMF (source)

Let's try to add some related details.

Aircraft can have multiple ID during their life, at least a preliminary ID to be used by the manufacturer prior to delivery to the customer, and then at least a national registry ID.

Manufacturer pre-delivery ID

Airbus aircraft final assembly line for the A350 is in France at Blagnac, a small city near Toulouse, with parts coming from several countries. There are other final assembly lines, but none is for the A350.

The first test flights will therefore happen in France, well before delivery to the customer. The French registry delivers temporary IDs to Airbus, the same IDs being continuously reused on successive airframes. Airbus uses a lot of them.

In France temporary IDs start with letter W. This A350 has been registered F-WZFD until being delivered to Singapore Airlines:

The special 10,000th aircraft delivery logo on A350-900 MSN 54 with its temporary registration: F-WZFD (source)

This same number was previously used on other aircraft, e.g.this A350 c/n 9 and will be reused on next pre-production or pre-delivery aircraft.

Customer registration

Singapore Airlines then requested an ID which was delivered by the Singaporean registry. This ID is 9V-SMF:

This number was previously used for a B747 at Singapore Airlines.


How to define quarter-chord sweep angle for a cranked wing? I have the values for surface area, span, aspect ratio, and quarter chord sweep angle, etc., for a general trapezoidal planform. So, I changed my wing to a single cranked wing such that surface area and span doesn't change. Therefore, parameters like root chord, tip chord, etc., changed. Now, for the, cranked wing how to define quarter-chord or half-chord sweep angles?

I think you have to define the sweep angles for every section on the cranked wing. You can use the same definition for each segment as for a "normal" wing. So practically speaking: Root Segment quarter chord --> create line between quarter chord of root and quarter chord of kink. Then you can measure the sweep angle of the root segment. Continue with next segment. The quarter-chord sweep angle is the angle between the y axis and the quarter chord line.


When an alternate minimum applies, does it change MDA or DA? In US, the weather minimums for an alternate airport are typically 600-2 for precision approaches and 800-2 for non-precision approaches at ETA, unless otherwise specified at US Terminal Procedure Publication.

When it comes when we actually fly the approach,

a) Is the DA raised to 600 for precision approaches?
b) Is the MDA raised to 800 for non-precision approaches?
c) Is the visibility requirement raised to 2SM for approaches at an airport?

Do alternate minimums work similar to inoperative components, use of alternate altimeter settings, NOTAM to change the actual minimums we use to fly, or a purely preflight planning number for selecting alternate airport?

From the FAA Instrument Procedures Handbook, section 6-4: "The 600-2 and 800-2 rules, or any exceptions, only apply to flight planning purposes, while published landing minimums apply to the actual approach at the alternate."


What should I expect during a first class medical examination? About 57 months ago I got my first FAA medical, a second class certificate.  I am currently a sophomore in college.  I'm in AFROTC trying to become an Air Force pilot so I wanted to get a first class medical just to make sure that I can (I realize military aviation medicals are even more intense though).

What types of things do they do during an exam for a first class medical that aren't included in the exam for a second class?  Also, if I "fail" one of the tests while being examined for a first class - can I still get a second or third class medical to keep my private pilot privileges?

You can see the requirements for all FAA medicals in 14 CFR 67.

Specifically, Subpart C (67.2xx) deals with second class medicals and Subpart B (67.1xx) deals with first class medicals.

The only difference my cursory read of these regulations revealed is:

x.111 - Cardiovascular. A first class medical requires EKG after your 35th birthday and every year after age 40.

This leads me to believe any real differences are likely in the ME's guidelines for issuing the medical, and I am not familiar with those.

The only other differences relate to duration and requirement for the exercise of privileges.

On your second question, if you apply for a first class medical and for some reason could not qualify for one, you will be denied or deferred even if you could hold a lower class medical (this is also true of a second class application).  The only possibilities at the end of a medical exam are walking out with a medical of the class you applied for or walking out without a medical.  There is no fallthrough to a lower class.

If you have an issue that you believe would inhibit your ability to get a first class medical, an avenue to explore this is through AOPA where you can talk with a doctor and get advice on your ability to pass a medical and support in handling a deferred medical application.


What components of the Boeing 787 are made out of titanium? Inspired by the question, Why is the 787 tail cone made out of titanium?, I want to know what other parts of a Boeing 787 are made out of titanium.

We now know, the APU exhaust cone is made out of titanium, but what else?

The Boeing 787 is special due to its high count of composite parts. When aluminium comes in contact with graphite fiber, contact corrosion will damage the aluminium whereas titanium will be unaffected due to its higher position in the electrochemical series.

15% of the initial 787s empty weight consists of titanium, a fraction much higher than in other airliners and one of the reasons that Boeing lost 23 million USD on each of their 787s sold initially.

787 material breakdown (picture source). Dark grey is carbon fiber composites and light grey is glassfiber composites.

The linked Reuters article contains a few parts which Boeing made from titanium in the first 787s:

  Boeing has changed the cockpit window frame to aluminum from titanium, and has changed the frames of some doors to composite from titanium. Special coatings or materials are used to prevent aluminum corrosion, experts said. It wasn’t known how much Boeing saved by the change. Boeing declined to comment.

The article goes on to mention a part in the wing-fuselage connection which is milled from a solid block of titanium. 97.5% of the block is lost when it is machined - very similar to the Tornado center wing box!

Another use of titanium is in the hi-lok fasteners which are used to bolt metallic or graphite parts together. I would expect that those are the biggest use of titanium in regular aluminium airliners, because using titanium hi-loks instead of steel results in weight savings.


Should I contact ATC if I don't have a transponder? The flight school I usually rent from is under the shelf of class C airspace. If you're going out to a practice area, the standard procedure is to contact approach control and get a squawk code, so they can better coordinate traffic. However, it's not required, since the practice areas are outside the class C.

At the moment, none of the school's planes have transponders*. One of the instructors said not to contact approach for now, because without a transponder, they wouldn't be able to do anything anyway and it'd just annoy them. On the other hand, during my last practice flight, I heard** them vector an aircraft around some unknown other aircraft. I suspect the unknown aircraft was me, which made me think that it would be better to talk to them after all. That way, I could (for instance) tell them my altitude, and they wouldn't have to vector an aircraft that was (say) 5,000 feet above me. But, back on the first hand, if I'm just a primary contact, they have no way of knowing which blip is talking to them, so maybe they'd have to vector the traffic anyway.

So, in that situation, is it better to contact ATC or not?

* Since this came so soon after the switch to ADS-B, and since it affects all aircraft at the flight school, I rather strongly suspect that they just got a bad batch of ADS-B transponders and had to send them back. That's just my theory, though, I don't know for sure one way or the other.

** I tuned in the approach frequency, even though I didn't contact them.

Every US controller I've ever heard from says they'd prefer to be talking to every aircraft in their airspace, period. This lets them know your intentions and allows them to move you around if needed, which saves them far more time than it costs giving you traffic advisories.

If you don't have a transponder, they can still tag your primary target with your tail number. Since you can't squawk or ident, they'll need a turn and/or an exact position for positive identification before they're allowed to do that. Once you're tagged, though, you look the same to them as someone with mode A only.

If you're practicing maneuvers, I suggest letting them know what to expect with something like "maneuvering at or below 3500 ft." That's a good idea even if you have mode C, but it's critical without it.


How to artificially increase the Reynolds number in a wind tunnel? I'm currently scaling down a model 64 times for a wind tunnel analysis, where I'm measuring drag force (for drag coefficient) and lift force (for lift coefficient). However, I read that scaling down 64 times means that wind velocity must be scaled up by 64 times to keep the Reynolds number constant. I read that using trip strips are a viable solution. How do I calculate the location, size, and number and strips of the slips required to increase the Reynolds number by 64 times so I can get accurate results?

Trip strips will approximate a higher Reynolds number in the sense that you get turbulent flow at a lower Reynolds number, but they will not increase the Reynolds number themselves. You will have different pressure and density gradients in the boundary layer, as though you were operating at a higher Reynolds number, but the number itself has no way of accounting for a trip.

The equation for the Reynolds number is $$\frac{\rho v d}{\mu}.$$ These are the only parameters you have to work with if you're going to be using the Reynolds number as your similarity parameter. If you absolutely have to use a wind tunnel, then increasing the model size or increasing the velocity are your only options (theoretically you could pressurize the wind tunnel to increase density if it were sealed, or you could change the temperature of the flow within the tunnel, but these have not been realistic options for any wind tunnel I've worked with). If you don't have to use a wind tunnel, a water tunnel is a viable alternative.

See An Assessment of the Usefulness of Water Tunnels for Aerodynamic Investigations for more details on water tunnels.


What is special about the ICAO Caribbean region for VFR climb/descent? In the FAA JO 7110.65 that provides rules for air traffic control, the following limitations are listed for VFR climb and descent:

  8−8−5. VFR CLIMB AND DESCENT

  a. In the Houston, Miami, and San Juan
  CTAs, IFR flights may be cleared to climb and descend in VFR
  conditions only:
  1. When requested by the pilot; and
  2. Between sunrise and sunset.

The key part here seems to be the second condition, as section 7-1-2 just lists the first one.

  7−1−2. VFR CONDITIONS

  a. You may clear aircraft to maintain “VFR
  conditions” if one of the following conditions exists:
  1. The pilot of an aircraft on an IFR flight plan requests a VFR climb/descent.

So what makes the Houston, Miami, and San Juan areas special that VFR climb/descent must be during the day? Section 8 is the Caribbean ICAO region, which seems to only include the oceanic sections of Houston and Miami. But this rule doesn't specify "oceanic" and none of the other oceanic areas seem to have this rule.

It looks like by default, night VFR isn't allowed in oceanic airspace. The 8-8-5 text you quoted appears to be an exception that does allow night VFR in certain specific Control Areas (CTAs) that are in US airspace.

This is from the US AIP 7.1:

  1. IFR/VFR Operations
  1.1 Flights in oceanic airspace must be conducted under Instrument Flight Rule (IFR) procedures when operating:
  1.1.1 Between sunset and sunrise.
  1.1.2 At or above Flight Level (FL) 055 when operating within the New York, Oakland, and Anchorage Oceanic Flight Information Regions
  (FIRs).
  1.1.3 Above FL180 when operating within the Miami and Houston FIRs and in the San Juan Control Area. Flights between the east coast of
  the U.S., and Bermuda or Caribbean terminals, and traversing the New
  York FIR at or above 5,500 feel MSL should be especially aware of this
  requirement.

1.1.1 essentially says "no night VFR"; 1.1.2 and 1.1.3 say "except in US airspace".

As to why, many countries don't allow night VFR at all and I suspect that it's generally not allowed in oceanic regions to simplify international operations and/or comply with ICAO requirements. Trying to remember which countries allow night VFR as you fly along an international route is probably impractical, especially in the Caribbean. But, since the US does allow night VFR, a VFR climb/descent is possible if the specific airspace in question is US airspace.

(I couldn't find any source on why these rules exist so this is all just my own explanation based on what I could piece together. Someone else may come up with something better.)


Why do some aircraft (e.g. Avro RJ85) have rear-mounted air brakes? I recently saw an Avro RJ100 on approach and I wondered why the Avro RJ100 and also the RJ85 have the air brakes at the rear of the aircraft, and not on top of the wings like most airliners?

(photobucket.com)

What is the advantage you get from this, and/or what made it impossible to mount the air brakes on top of the main wings?

Location choice

Note: the BAe 146 / Avro does have wing spoilers.

Air brakes are in most cases mounted directly on the fuselage. Forward mounted air brakes would disrupt the airflow to the wings and engines, so the designers are left with three choices: above, under, or at the rear / on the sides.

Under, like on the Aero L-39, works well1 if the air brakes aren't big. Above is usually if all else fails, like on the F/A-18 Hornet and F-15.

Rear-mounted—inline with the center-of-mass—is the most convenient, aerodynamically and for maintenance. Like the Avro, F-16, or F-86.

Now, as to why the Avro—as most military jet aircraft and few jetliners—has it:

Lack of thrust reversal and steep approaches

The Avro RJ lacks thrust reversers "due to their perceived reduced effectiveness in anticipated conditions." The reduced effectiveness is because of the low landing speed and the closeness of the engines to each other on each side. Using reverse at low speed risks FOD ingestion and stalling of the nearby engine.

  It reasoned that since the
  146 would have a touchdown speed
  of only 90 kt, and because reversers
  are not normally used below about
  60 kt, their effectiveness would be
  limited. Reverse thrust also would
  have subjected each engine to an
  extra cycle/flight.

  Maximum descent rate achievable
  with the airbrakes is 7,000 ft/min and
  at speeds of less than 250 kt and below 10,000 ft, there is still 4,000 ft/min available. By comparison, a
  typical airliner descent rate on the
  approach is around 2,000 ft/min. BAe
  146 operators may also use airbrakes
  during the landing roll.

  (Flight, 1981)

One advantage that came out of having air brakes is the ability to fly steep approaches into airports like London City.

  [For] several years the BAe 146 was the only conventional jet aircraft capable of flying from London City Airport.

Thrust-to-weight ratio

Because of the Avro's high thrust-to-weight ratio, having air brakes deployed on approach makes it easier to control the speed. The thrust-to-weight ratio for the RJ100 is 0.28:1, compared to 0.16:1 for the comparable Boeing 717. It's even higher for the smaller RJ's.

Having a high thrust-to-weight ratio also allows operations from short runways and runways within cities, as the airplane can climb more steeply, thereby reducing the noise impact and also allows high payload.

(flickr.com)

Spoilers

  Air brakes differ from spoilers in that air brakes are designed to increase drag while making little change to lift, whereas spoilers reduce the lift-to-drag ratio and require a higher angle of attack to maintain lift, resulting in a higher stall speed.

The Avro still sports wing spoilers as shown above, those also help in braking as they transfer more weight to the wheels, and help reduce the likelihood of a bounced landing.

1 Belly-mounted air brakes on the L-39 help the pilot configure the plane for landing. Half-flaps + air brakes require the same trim/power as full-flaps and landing gear down (hence the under positioning). The pilot would use the air brakes to slow down, put down half the flaps, and trim the aircraft. The pilot can then on final approach put down the landing gear and full flaps, retract the air brakes, all without having to re-trim or change the engine power setting (which is narrow-ranged on the L-39).

Related: Why does this regional jet have its air brakes wide open before touchdown?


How to measure wind speed in a wind tunnel I'm currently building a wind tunnel that moves air at hundreds of meters per second. How do I cheaply measure the wind speed?

A simple pitot tube attached to a fluid level balance can do this, if you can develop a pressure differential vs airspeed reference for it.


How to calculate pressure distribution over an airfoil from its coordinates? I need to compute the pressure distribution over an airfoil (I have the coordinates, but any will do) with the streamline curvature method. Unfortunately, I cannot find much on the web.

Can someone point me in the right direction or walk me through it? I understand it qualitatively (the concepts) but have a hard time quantifying it (actually solving the flow field).

What helped me was the book "Theoretical and Computational Aerodynamics" by Jack Moran (ISBN 0-471-87491-4). That was 30 years ago, but the physics haven't changed since then. And it is still available.

An online source would not go deep enough to cover all what you need. My advice is to get the book and work through the exercises. It worked for me, and if even I could code a 2D potential code after having read this book, you should have no problems.

There is one trick: At one point you will end up with n equations for n+1 unknowns. Bummer! What you need to do is to prescribe flow direction at the trailing edge, and then you will have n+1 matching conditions for those n+1 unknowns, n being the number of panels you divide the airfoil surface into. Google "Kutta condition" for an explanation.

EDIT

Now you have quite a different question:

  by CFD i meant RANS. how does it compare to RANS methods in term of stall prediction and pressure distribution

@toshiba: The comparison is like between a Volkswagen Beetle and a Mercedes. A potential code is simple, robust and gets you there, like the Beetle. Pressure distribution is good until separation starts. Compressibility can be modelled until locally the speed of sound is reached. Stall prediction is a bit tricky, but with a bit of experience and an added boundary layer calculation you will get good results.

RANS is a simplified Navier-Stokes algorithm which is used for modelling turbulent flows. Like the Mercedes, it needs much more effort to code and run (and computing power - it requires a mesh where the potential code only needs panels on the airfoil surface) but also produces better predictions if the mesh is laid out well. Drag and stall approximation is included while potential flow needs some extra effort for boundary layer modelling. A Navier-Stokes code can also be used for transsonic flow.

If you want to build your own, assume you get the parts only and have to assemble the cars. No plans included. The VW Beetle heap is much smaller and you can figure out quite quickly how it fits together (did that once with a Beetle engine that someone else had disassembled and left behind). When you are finished, the car will run and require little maintenance.

With the Mercedes, there are many more parts, more complicated looking and requiring special tooling. It takes much longer to get assembled and in the end you will have some parts left over and others in the wrong place if nobody experienced guides you along. Maybe the car runs, but it will break down quickly unless you put much effort into maintaining it.

In other words: Start with a potential code. MUCH easier.


Why do passenger jet manufacturers design their planes with stall prevention systems? I understand why passenger jets use software that overrides pilot inputs that might cause the jet to exceed the flight envelope.  But why do passenger jet manufacturers design their planes with stall prevention systems?  Shouldn't professional pilots be well aware that a stall is possible when the airspeed is too low, or the angle of attack is too high?

Why do car manufacturers install seat belts? Shouldn't licensed drivers be well aware that they should slow down when it's raining or snowing and that they shouldn't run through red lights or stop signs?

A better analogy:

Why do car manufacturers install anti-lock break systems? Shouldn't drivers know that when their brakes lock up they should release brake pressure and/or pump the brakes quickly to slow the car down?*

*To be fair, I don't think this is actually taught in driver's education (at least in the US) anymore - my kids learned this from me, but never reported being taught and/or practicing when they took driver's ed. One of the many reasons flying is safer than driving.

Because accidents happen.
Because pilots are human and make mistakes.
Because when you're flying in the clouds with no visual references, it's easy to get confused.
Because even with stall warning & prevention systems in place, confused pilots will fight the system. AF 447


When has a pilot legally accepted an ATC clearance or instruction? At what point is a pilot considered to have accepted an clearance or instruction? Upon simple acknowledgement (e.g., Roger or Wilco), any readback, correct readback, or something else?

I would try to not over complicate this issue.  There are three conditions a clearance/instruction can have:

Transmitted/Received
Accepted
Rejected

If ATC provides a clearance/instruction, but has not yet received a response, the clearance/instruction has not been accepted or rejected.

If the pilot acknowledges the clearance/instruction with a read-back or affirmation of understanding, then it is accepted.

If the pilot responds with the term "unable" to any element of the clearance/instruction, then the entire clearance/instruction set is rejected, which may prompt ATC to inquire as to why the clearance/instruction is being rejected or to provide a different clearance/instruction.

Per 91.3 the pilot-in-command reserves the right to act as the final authority as to the operation of the aircraft, but once a clearance/instruction is accepted, it is an indication that the pilot-in-command is agreeing, as the authority of operation, to operate by that clearance/instruction until released from it or forced to deviate due to an emergency or TCAS alert.

One note for safety: to be clear, one cannot simply reject one element of a clearance/instruction without rejecting the entire clearance/instruction.  For example, if ATC issues a turn and a climb, but the pilot's aircraft cannot or may not climb higher for whatever reason, the pilot should not read back the new heading and say, "unable climb," and then turn to the heading and wait for more instructions.  What if the climb is to avoid obstructions that exist on the new heading?


Were Airbus planes always fly-by-wire? So, as most of you know, Airbus has adopted fly-by-wire (fbw) technology. Pretty much every single plane made by Airbus is a fbw plane. So I was wondering, before computers were everywhere, did Airbus implement fbw systems?

As Ron notes in the comments the A300 did not have it and neither did the A310 however the A300-600 and A310 did have electronically augmented controls according to the airbus site.

  One of the A300-600 and A310’s notable innovations had been the
  introduction of electrical signalling on secondary flight controls,
  replacing the web of cables and pulleys tradionally used. Béteille
  wanted to take this evolution further with the next Airbus aircraft –
  to computer-driven digital “fly-by-wire”, in which the deflections of
  the flying control surfaces on the wing and tail are no longer driven
  directly by the pilots’ controls, but by a computer which calculates
  exactly which control surface deflections are needed to make the
  aircraft respond as the pilot wishes.

The A320 on had Fly-By-Wire

There is a nice little video on the same page that has some facts abut Fly-By-Wire tech over the years. A quick history note is applicable here: what we know of today as Airbus had heavy ties to the Concorde program which implemented the first commercially used analog fly by wire system and depending on how you look at it Airbus' first Fly-By-Wire system as well. These engineers who would later go on to work at what is now Airbus and drive the mentality into the designs which is why they have largely chosen it on all their airframes.


Does joystick position control bank angle in some Airbus aircraft? And what happens when the pilot deflects the joystick when wheels are on ground? Does joystick position control bank angle rather than directly controlling aileron/spoileron deflection in some Airbus aircraft?

Also, what happens when the pilot deflects the joystick when the all wheels are on the ground and the bank angle (or roll rate) cannot change substantially?

Also, if the pilot is landing and the left main undercarriage assemblies are not extended for some reason, when the wheels on the right main undercarriage assemblies touch the ground, will maintaining a strong right control input on the joystick help delay the left wingtip (or engine nacelle) from contacting the runway, or not?

Does joystick position control bank angle rather than directly controlling aileron/spoileron deflection in some Airbus aircraft?

To complement @Bianfable's answer, in Normal Law Flight Mode, Airbus FBW families (including A220) command roll rate via lateral stick position up to the artificial spiral stability limit of 33 deg bank (for A220 it's 30 deg). Below 33 deg bank, the aircraft exhibits neutral spiral stability; beyond 33 deg bank, it exhibits positive spiral stability, and lateral stick position commands a steady-state bank angle up to the roll limit of 66 deg (for A220 it's 80 deg).

  Also, what happens when the pilot deflects the joystick when the all wheels are on the ground and the bank angle (or roll rate) cannot change substantially?

Upon landing, the Normal Law transitions to Ground Mode, whereby the stick inputs command direct control surface movements. For A320, the lateral control transitions from Flight Mode to Ground Mode in 0.5 sec on ground detection is met, as shown below:

  Also, if the pilot is landing and the left main undercarriage assemblies are not extended for some reason, when the wheels on the right main undercarriage assemblies touch the ground, will maintaining a strong right control input on the joystick help delay the left wingtip (or engine nacelle) from contacting the runway, or not?

From this German accident report, in the case of an asymmetric gear deployment, ground signal is generated if "both LGCIUs (Landing Gear Control Interface Unit) detect that one landing gear has been lowered and is under load, and the radio altimeter measures the height above ground as less than 50 ft".

Therefore, immediately upon touchdown, you can expect the FBW to partially resist roll motion; but after 0.5 sec, you will have to use lateral stick to hold the aircraft level until the airspeed is too low to do so.


Vertical autorotation with passive rotor Let's say we have a simple hollow cube(chosen for simplicity) with outside side length=10cm, thickness=5mm (or another arbitrary shape with arbitrary dimensions).

Clarification: I am NOT talking about a helicopter. It has no tail rotor, no forward speed, no controllers etc.

It has a passive rotor(no power, no engine) on top of it with 4 blades(total diameter of rotor l=30cm) (with arbitrary foil shape). We drop it from height of H.

What would be free-body diagram on this rotor-cube system?
I am imagining that there would be 3 forces. First one is downward and the other two is upward. Both velocities are descent velocities, the area S in both of them is $\frac{\pi l^2}{4}$, l being diameter of circle created by rotating blades.

Weight Force $W=mg$
Lift force $L=½ρv²SC_l$
Drag force $F_d=½ρv²SC_d$

Is this correct?  Also please post your source, whether the name of the book from or site link which you learned how to find free-body diagram of these kinds of aviation systems.

Also will all kinds of foils work in this scenario? What is the important parameter in foils that will make it start spinning and descent with constant speed?

There's some info on autorotation, including some references, in this answer. And also a pertinent question on Physics SE. Free body diagrams included.

In short:

Autorotation only works in a satisfactory way if the vehicle has forward velocity: in a vertical descent, in optimal circumstances, autorotation works as well as a leaky parachute does.
Getting the rotor to actually rotate from standstill is a hair raising kettle of fish, the first thing about autorotation that helicopter pilots learn is that they must maintain rotor rotation from when it was driven by an engine. During any time of rotor standstill the aircraft is simply falling, with no real means of aligning the rotor with the airflow.
Autogyro's start their flight by starting the rotor to rotate. Can be done on ground by driving fast and making use of the horizontal velocity, or by a flywheel mechanism attached to the propeller engine. Again, the first thing to do is to rotate the rotor.

The equations in OP are valid for fixed wing aeroplanes, and for the rotor blades. But since with rotor blades the velocity over the blade is a function of the blade radius, plus faster over the forward moving blade than over the retreating blade, they are not defined relative to airspeed V but to tip speed of the rotor blades $\Omega R$. Impulse theory using non dimensional coefficients, from Prouty Helicopter Performance, Stability and Control page 25:

$$ T = C_T \cdot \rho A (\Omega R)^2$$

with

T = rotor thrust
$\rho$ = air density
A = disk area
$\Omega R$ = tip speed

Note that Prouty uses the USA definition for $C_T$, which incorporates the factor ½ of the dynamic pressure $½ \rho V^2$ and is therefore twice as much as $C_T$ values used in Europe.

For the thrust to drive the rotor, analogous to aeroplane drag:

$$Q = C_Q \cdot \rho A (\Omega R)^2 R$$

And for the power:

$$P = C_P \cdot \rho A (\Omega R)^3$$

  Also will all kinds of foils work in this scenario? What is the important parameter in foils that will make it start spinning and descent with constant speed?

Airfoil shape is of much less importance than blade twist, solidity ratio and a whole lot more parameters, which would make the answer very broad. Best looked up in Prouty and Leishman.


Why is there a difference between aileron upwards and downwards deflection angles? I have noticed that on airliners the ailerons have different angles if deflecting upwards than deflecting downwards. When deflected at the maximum angle maximum angle downwards is lower than when deflected upwards. I suppose that this is due to the fact that when the wing has to be deflected upwards and consequently the aileron moves downwards, the force required is lower as there is already lift being produced by the wing whereas the opposite would happen when deflecting the wing downwards and more power is required.

Is this assumption true or are there any other technical reasons behind this deflection angle difference?

You're correct that the ailerons are deflected differently when they are deflected up or down. This is done in order to counter the adverse yaw effect which occurs when ailerons are deployed. Consider the situation when the ailerons are deployed.

Image from aerospaceweb.org

One aileron is deflected downward while the other is deflected upward. One the side with the downward-deflected aileron, lift increases as the deflection effectively increases the camber of that portion of the wing. The opposite happens in the other side.

However, the drag is also affected by aileron deflection- both induced and profile drags. For same deflection, the profile drag increase is same in both the wings. However, the induced drag on both sides are not equal, with a larger amount the wing with the down aileron (as the lift is more and induced drag is proportional to the square of lift).

One way of overcoming this is to deflect the ailerons differentially, i.e. deflect the down aileron by a lesser amount than the up aileron. The following table shows the aileron deflection in a number of aircraft, which shows the differential aileron deflection ($\delta_{A}$ is the aileron deflection, in degrees).

Table from Aircraft Design: A Systems Engineering Approach by Mohammad Sadraey

This adverse yaw can also be prevented by the use of,

Frise ailerons
Use of spoilers (in the wing up aileron)
Cross coupled controls (rudder and ailerons).

There is another reason to use a differential aileron- to prevent tip stall at high angles of attack (stall speeds). The rolling couple on the aircraft is always the difference in lift between the two wings. At or near stalling speeds, it is better to reduce the lift in up-going aileron than increase it in down moving one and risk stalling it.


Is it legal and safe to take off or land in zero visibility? Is it legal for planes to takeoff and land in zero visibility? Is it safe?

In the US, for general aviation flights, operating under Part 91 of the FARs, it is legal to take off with zero visibility (see page 2-2 of the IPH, PDF). In my opinion, it is not safe. If an emergency were to take place, you would be unable to return and land; under Part 91, it is not legal to land unless conditions are equal to or better than a runway's published approach minimums.

Unless you've got a great alternate nearby, conditions are improving rapidly, or you've got an extra engine or two, you probably shouldn't take off in conditions you couldn't land in.


How does the flap configuration affect the tailstrike limit on the A320 aircraft family? The configuration that provides the maximum FLEX temperature varies with the runway length.

On short runways, CONF 3 usually provides the highest FLEX temperature, and the tail clearance at lift off does not depends on the configuration.

On medium or long runways, the second segment limitation becomes the limiting factor, and CONF 2 or CONF 1+F becomes the optimum configuration, in term of FLEX temperature.

In these cases, the tail clearance at lift off depends on the configuration. The highest flap configuration gives the highest tailstrike margin.

How does the flap configuration affect the tailstrike limit?

A higher configuration number indicates that the flaps/slats are extended by an higher amount.

In turns this means that for the same angle of attack the wings will produce higher lift (and drag) in the higher configuration.

You achieve take-off when the lift is at least equal to the weight of the aircraft, and with higher flap/slat deflection you will have sufficient lift even when the nose is relatively low on the horizon, leaving plenty of margin against a tailstrike.

On the other hand, if you are using a low configuration, the flaps/slats will be mostly retracted, and you will need a higher AoA to produce sufficient lift, meaning that you have to raise the nose of the aircraft more, leaving less margin against a tailstrike.


Can Instrument Approaches be carried out when RVR is not given for the full runway length? (Approach Ban) Bristol Airport (EGGD) has the following NOTAM in place:

INSTRUMENTED RVR RWY 27 STOPEND OUT OF SERVICE

Would aircraft be allowed to continue approaches into Bristol? If so, would the touchdown and mid-point RVR values suffice to decide whether the approach is legal (see Approach Ban below).
For example, the listed RVR minima for the RNP Approach runway 27 is 1400m (LNAV) - if the touchdown point and mid point RVR values were above this, could someone legally proceed with the published approach.
The UK AIP describes the Approach Ban as follows.

AD 4.9  Approach Ban - All Aircraft
4.9.3 An aircraft may commence an instrument approach regardless of the reported RVR/Visibility but the approach shall not be continued
below 1,000 FT above the aerodrome if the relevant RVR/Visibility for
that runway is at the time less than the specified minimum for
landing.
...
4.9.6 The touchdown zone Runway Visual Range (RVR) shall always be controlling.

To perform an ILS CAT I approach, at least the touchdown zone RVR sensor must be operational. For CAT II, you need the touchdown zone and midfield sensors, and for CAT III you need all three. As per your NOTAM, if only the stopend RVR sensor is out of service, it should be possible to perform CAT I and CAT II approaches (assuming those are available for that runway in the first place).
There are procedures which allow aircrews to perform a CAT I ILS based on meteorological visiblity alone, using a special conversion table to estimate RVR values based on visiblity, but I believe those are company specific.
RVR can also be measured manually, but I am not sure this is actually allowed anymore. It would require someone to physically go to the end of the runway, and then count the number of runway lights visible from the end. Given there is a fixed distance between runway lights, you could then multiply the number of visible lights with the distance between them to get the RVR.
Not sure what the rules are for RNP approaches, but I would imagine they are similar to those regarding ILS.


Is it legal to fly the localizer approach when cleared for the ILS? Most ILS approaches include localizer minimums that can be used if the glideslope transmitter or receiver fails.  For example:

In this case, to fly the ILS you would intercept the glideslope just before PRAIZ and fly the 3 degree glideslope down to minimums.

If we were cleared for the ILS approach, but we instead wanted to ignore the glideslope and fly the LOC only approach1 (for whatever reason:  training, practice, etc.), could we do that without specific ATC approval since it is on the same chart and says "ILS or LOC"?

1 We could fly the LOC only approach by crossing PRAIZ at 2,200 ft. and then descend at an "optimum" rate until leveling off at the MDA of 520 ft.

The question really boils down to: "ATC clears me to fly an approach.  Is the approach clearance defined by what is on the approach plate, or is it specific to the type of navigation equipment used?"  It turns out that it is based on the approach plate.

The answer is found here:
https://www.faa.gov/air_traffic/publications/atpubs/aim/aim0504.html
Section 5-4-5.a.3(a)

  More than one navigational system separated by the word “or” indicates
  either type of equipment may be used to execute the final approach
  (e.g., VOR or GPS RWY 15).

When the chart is written as in your example, you are cleared for the approach, and you must use one of the approved types of navigational equipment to fly it.  There is no requirement in FAR/AIM to tell approach control which equipment you will be using (beyond the equipment code in your flight plan).

As further corroboration, section 5-4-7.d in the above document specifies that ATC is allowed to clear you for an approach even if the equipment required for some types of navigation systems is not available.  This actually is not that rare because NDB/GPS approaches are still used even if the NDB is not working.

The requirement to notify ATC in the event of navigation radio failure is separate.  Oddly, you don't have to tell ATC if you have a glideslope receiver at all, but you are supposed to tell them if one that you do have breaks.  If it happened while you were actually flying the approach, I would encourage you to execute a missed approach.  But if you just want to fly an ILS/LOC approach as localizer-only for practice, ATC doesn't care and you don't need to tell them.


I received a 1st Class medical certificate in May 2005. Do I qualify for BasicMed? One of the requirements for BasicMed is:

Comply with the general BasicMed requirements (possess a U.S. driver's license, have held a medical after July 14, 2006).

I received a 1st class medical certificate in May of 2005. I was under the age of 40, so it would have been valid for 12 months, expiring in May 2006 (i.e., just before the BasicMed cutoff).
That said, it would have still been valid for an additional 24 calendar months (i.e., until May 2008, well into the BasicMed era) as a 3rd class medical. Am I correct in my understanding that this qualifies me for BasicMed?
Thank you.

Your first-class medical certificate issued in May 2005 granted, since you were under 40 at the time:

First class privileges until May 31, 2006
Second class privileges until May 31, 2006
Third-class privileges until May 31, 2010

Since that last date is after July 14, 2006, then assuming it expired valid and you have not applied for another medical certificate since, you would qualify for BasicMed.


When do I have to hold during an instrument procedure? Trying to stay fresh on instrument regs, and I'm reviewing when you are able to bypass a procedure turn. I'm reading that if you perform a teardrop entry for a hold, you may. Does that mean you have to do the entire hold before proceeding the approach when you do a parallel entry?

I suspect you are thinking of AIM 5-4-8 (b)(2) [page 5-4-31], which states:

  When a teardrop procedure turn is depicted and a course reversal is required, this type turn must be executed.

If so, have a look at the Instrument Flying Handbook, page 7-31.  The teardrop procedure turn is not referring to the same thing as a teardrop entry into a hold-in-lieu-of-procedure turn, it's something different entirely.