Should an aircraft's registration match with its tail number? What are the requirements for an aircraft's tail number to match the registration?

What happens if an aircraft changes its number? Is it grounded until the new number can be painted on?

The registration number painted on the aircraft is required to match the aircraft's registration certificate (and airworthiness certificate). If the numbers don't match the aircraft's paperwork isn't in order, and it can't legally be flown.

There is a procedure for changing your N number which is usually used to put a "special" (reserved) number on an aircraft:

Send the FAA a letter requesting an N number change.
(It probably helps to have a good reason - like say United Airlines buying a used jet and wanting to re-register it with a N___UA tail number from their reserved block).
Wait for the FAA to send you paperwork authorizing the N number change.
You will get 3 copies of form 8050-64 - two for the FAA, one for you.
Put the new N number on the plane.
Usually you'd do this by repainting the aircraft (or the portion of the tail where the number is), but you could also do vinyl stickers or something similar)

  One of the copies of form 8050-64 becomes your temporary registration certificate at this time, and you must carry that along with your original registration certificate showing the old registraton number.
  Within 5 days of applying the new N number return one of the copies of form 8050-64 to the FAA to obtain a new registration certificate with the new N number.
  Within 10 days of applying the new N number return the other copy of form 8050-64 to the FAA to obtain a new airworthiness certificate with the new N number.

  I expected to find something stating how long you have between the time the FAA grants the request to change registration numbers and when you must apply the new one to the plane, but as far as I can tell you can take your time doing this: there doesn't seem to be an expiration on the authorization to change N numbers.

As long as you comply with the requirements for the registration number change the aircraft is only "grounded" for as long as it takes to apply the new registration number (if you're repainting this could take a while ; if you apply a large sticker with the new number on it it could be done in less than a day).


How long is a winds and temperatures aloft forecast valid for? How long is a winds and temperatures aloft forecast valid for and how often is it published?

Also, is there anywhere which says the times of publication and valid through times for all of the aviation weather charts? My google fu isn't helping.

Advisory circular 00-45 "Aviation Weather Services" documents the winds and temperature aloft (FB) product on page 7-39.  Table 7-11 lists the standard forecast periods for these products.

From this table you can see that the 6-hour forecasts are usable from the time they are issued until 3 hours after the valid time.  The 12 hour forecasts are usable from -3 to +6 hours of the valid time and 24 hour forecasts are usable from -6 to +6 hours of the valid time. The products are issued 4 times daily.

While these are standard times, you should consult the specific information available in the product header that has this information.  For example:

DATA BASED ON 010000Z
VALID 010600Z FOR USE 0500-0900Z. TEMPS NEG ABV 24000
FT 3000 6000 9000 12000 18000 24000 30000 34000 39000
MKC 9900 1709+06 2018+00 2130-06 2242-18 2361-30 247242 258848 550252

This says the product is valid at 06Z and for use from 05Z to 09Z and the data is based upon the 00Z forecast model run.


"Cancel altitude restriction." Under ICAO rules, does it cancel all altitude restrictions on a SID or STAR chart? Let's say there are altitude restrictions at 5000ft, 11000ft, 15000ft, 18000ft on a SID chart. While you were following the SID (under ICAO rules), the Departure tells you "Climb 12000ft, cancel altitude restriction." Does this instruction cancel all altitude restrictions on the chart or only restrictions below 12000ft?

'CANCEL LEVEL RESTRICTION(S)' cancels all the vertical restrictions above and below the new assigned level. From ICAO Doc 4444 16th edition (2016):

6.3.2.4 CLEARANCES ON A SID
CLIMB UNRESTRICTED TO (level) or CLIMB TO (level), CANCEL LEVEL AND SPEED RESTRICTION(S):
i) climb to the cleared level; published level restrictions are cancelled;
ii) follow the lateral profile of the SID; and
iii) published speed restrictions and ATC-issued speed control instructions are cancelled.

The same is true for clearances on a STAR (6.5.2.4).
The proper way to cancel specific restriction(s) and leave the rest is to specify the affected point(s).

CLIMB VIA SID TO (level), CANCEL LEVEL RESTRICTION(S) AT (point(s)):

A shortcut within the SID does not cancel the restrictions after the shortcut waypoint:

6.3.2.4.4 When a departing aircraft is cleared to proceed direct to a published waypoint on the SID, the speed and level restrictions associated with the bypassed waypoints are cancelled. All remaining published speed and level restrictions shall remain applicable.


How do I determine the maximum thrust that a Tesla powertrain (P100D for example) could produce if attached to a single propeller? I am theorizing a drone helicopter from a tesla powertrain (P100D).
Lets assume the system is theoretically maximized with an optimum propeller (this is what I am currently stuck on).  How much thrust could a Tesla powertrain produce (I understand the thrust would decrease as the battery drains and voltage decreases, just wanting to get an idea of theoretical optimal thrust)?

For a propeller/rotor, net consumed power = torque * rpm. For an electric drivetrain, net power delivered = current * voltage, with current equating to torque and voltage to rpm. Tesla should have really good data analyses on the power delivery as a function of demand over time, with wheel torque and wheel rpm as parameters.

Then you only have to replace the propellant medium: slippery air instead of the stony fixed world. Torque is a measure of drag of the rotor blade, thrust is a measure of lift. Both are a function of rpm as well, usually the rpm is limited by the tip speed approaching the speed os sound and is chosen to be as close as possible to it.

So a design process might be:

Determine payload.
Determine approximate disk load by comparing with existing designs, resulting in the disk area and the blade radius.
Compute rpm so that tip speed is about Mach 0.8
Compute power, torque and thrust from data available for comparable comfigurations.

Two books that contain chapters on pre-design of helicopters are Helicopter Performance, Stability and Control by Raymond Prouty, and Helicopter Aerodynamics by J. Gordon Leishman.

But the area that will give you most headache won't be computing the thrust etc, it will be figuring out how to control the flight path. Do you plan to use a swash plate?


What is the difference between an aeroscraft and an airship? I stumbled across this site when I was searching for info about airships. They have main three products - aerocraft aeroscraft, airship and aerostat. Aerostat is clear for me somehow. But what is the key difference between aerocraft aeroscraft and airship?

Aeroscraft is their brand name. It does not mean anything generally.

The general terms are:

"Aircraft" (but not "aerocraft") means any machine capable of sustained flight in the atmosphere.

"Aerostat" is a lighter-then-air aircraft. That is it has large shell filled with gas with lower density than air and uses buoyant force on that for lift. This includes balloons, hot-air or gas filled, tethered balloons and airships.

"Airship", or "dirigible" is an aerostat equipped with propulsion that allows it to move on it's own (as opposed to balloons that are tethered or carried by wind).


Which prop location creates more lift? Leading edge or blown flap? Which prop creates more lift? Leading edge or blown flap?

In distributed propulsion there seem to be 3 prop locations: leading edge (NASA X57, blackfly), blown flap (Lillium), and pusher prop (Kittyhawk).

Which would create more lift, leading edge or blown flap?

Leading edge: The entire wing chord sees about 50% of prop exit speed (turbulent though), the prop pushing 50% of the air under the wing (although it would create lift by hitting the flap (assume 45-90 deg flap position)
Blown Flap: wing sees 100% of prop exit speed but only on about 45% of the of the chord ( assuming 50% chord flap), but the first 45% of the wing sees non turbulent air. Blown flap has the advantage of providing vertical thrust.

See pictures below.

Lillium - blown flap ( assume props, not the actual electric turbines it uses)

Kittyhawk - pusher prop

Nasa X57 - leading edge/tractor prop

Below are 3 Cp plots from xflr.

First plot has no flap, but has a roughly 30 deg angle in (-) pressure drop.

Adding a 50% chord flap, increases the suction at 0% chord???

Was surprised to a spike in negative pressure at 0% chord from
a 50% chord, 45 deg flap!!! Would have thought there would be a negative pressure spike at 50-60% chord....

What would the shape of the pressure plot be when distributed propulsion is added to the flap? See plot below.

The X-57 should show the highest gain in lift from the props. They will wrap the full wing in accelerated flow. XFLR is not capable of capturing this effect, since the pressure distribution should be similar to the case without props, only the reference dynamic pressure is higher than that of the prop-less wing. Of course, swirl effects will add a spanwise pressure variation that is missing without the props.

Next best is the pusher arrangement of Kitty Hawk. Here the props can swivel, so maximum lift is less of a concern. The prop arrangement has been chosen to minimize noise from the prop blades cutting through the wing wake; that should explain the considerable distance between props and wing. At that distance the suction of the prop will affect the flow over the wing much less that what the X-57 should be capable of. In a pressure plot the main effect should be a delayed flow separation: The wing will tolerate a slightly higher angle of attack.

Worst of all is Lilium: Here the inefficient, small-diameter props sit in ducts which all have their own boundary layer and losses. Next, any accelerated flow only affects the upper side of the wing, so half of the effect will be lost. This arrangement, however, will make the plane sound much louder and powerful than Kitty Hawk's. Judge for yourself whether that is a worthwhile achievement.


What are these engine gauges in the Comet 4 for? What are these gauges on the Comet 4's engine-gauge panel (between the captain's and first officer's instruments, above the throttle levers), marked "POWER LOSS INDICATOR", for?  (Sorry for the blurry image.)

(Image cropped and annotated by me; original by Geni at Wikimedia Commons)

I'm assuming they're engine gauges of some sort, since there're four of them and they're located immediately below the engine RPM and EGT gauges (and above the throttle levers); could they be for monitoring engine performance during hot-and-high takeoffs?

They are apparently not present in the Comet 1, which instead has engine oil temperature/pressure gauges in this area (see pages 59-60 of this PDF, marked as pages 58-59).

They were used on takeoff to monitor engine performance. Takeoff power should result in the needles moving to the vertical marker and all engines should be registering the same reading.

The indicators monitor the pressure in the exhaust cone of each engine and will give a warning of failure which might in certain cases only become apparent by watching a combination of other instruments.


How do I interpret electrical system indications in a G1000 C-182? I recently switched to a G1000 equipped aircraft C182 and trying to figure out the specifics of the G1000 and how it works in the 182.

One that I can't really figure out with the manual and the POH  is the Electrical System

I have the following Indication (in flight around 30 min after takeoff)

M        BUS      E
28.0     VOLTS    28.0

M        BATT     S
+1.5     AMPS     +0.3

Does this mean that the main and the backup battery delivery 28 Volts?

The + Amps mean that the alternator is charging the batteries ?

I noticed that the BATT Amps (M) never goes to 0 is that normal? I remember from the old analogue gauges that at some point they stay in the middle/0.

What are normal/acceptable values for BUS/BATT in a C182T?

You can find this in the C182T Operating Handbook. Section 3 has information about what values should be considered a malfunction:

  HIGH VOLTS ANNUNCIATOR COMES ON OR M BAT AMPS MORE THAN 40

It also says that the M bus should be at least 20 volts in normal operation:

  The Main Battery supplies electrical power to the Main and Essential
  Buses until M BUS VOLTS decreases below 20 volts. When M BUS VOLTS
  falls below 20 volts, the Standby Battery System will automatically
  supply electrical power to the Essential Bus for at least 30 minutes.

Section 4 has the expected values when starting the engine:

  BUS E Volts

  CHECK (Verify 24 VOLTS minimum shown)

  M BUS Volts

  CHECK (Verify
  1.5 VOLTS or less shown)

  BATT S Amps

  CHECK (Verify discharge shown (negative)

Section 7-54 describes the electrical system in detail, including wiring diagrams. It says:

  Normal bus voltages with the alternator operating shall be about 28
  volts.

And:

  Indicated voltages between
  24.5 and 28 volts may occur during low engine RPM conditions

As for the ammeter:

  A positive current value (shown in white) indicates that the battery
  is charging. A negative current value (shown in amber) indicates that
  the battery is discharging. In the event the alternator is not
  functioning or the electrical load exceeds the output of the
  alternator, the main battery ammeter indicates the main battery
  discharge rate. In the event that Standby battery discharge is
  required, normal steady state discharge should be less than 4 amps.

So long story short, all the information you need is in the POH and the best way to get all the details is to read it carefully. Your POH may be slightly different from the one I've quoted here, so if there are any differences then you should follow it, not this answer.


Do most flight schools and FBOs in the US prohibit student pilots from practicing stalls while flying solo? Do most flight schools and FBOs in the US prohibit student pilots from practicing stalls while flying solo?

This question is asked in the context of civilian flight training in single-engine land airplanes.

I've heard of this policy actually being in effect with at least one flight school.

"Most" means more than half. "Student pilot" is not meant to include anyone who holds a pilot's license for airplanes or for that matter for gliders.

The reference to FBOs means that they are renting an aircraft to the student pilot involved.

The question is asking about a blanket prohibition that would include a student who is close to being ready to take his or her checkride, not something only applied to (for example) the first few solo flights.

People who have had personal experience with a large number of flight schools and FBOs will be in the best position to answer this question.

The two flight schools I have used had this rule and all of the other local places I know of also have this rule. The FAA no longer recommends full break stalls during training anyway you merely need to bring it to the horn. Interestingly enough the data does not support the decision

  Student pilots are, by far, the least likely to suffer stall/spin
  accidents, as a proportion of in the pilot population. Pilots holding
  FAA Airline Transport Pilot (ATP) certificates are also less likely to
  stall/spin.

Although a case can likely be made that limits like this are what make student pilots least likely to stall/spin.


What is an acceptable phugoid oscillation duration? What is an acceptable settling time for the phugoid mode in a large aircraft?

As a more specific question, what is the settling time when the aircraft (say, a B747 or an A320) switches from Climb to Cruise phase at the top-of-climb?

Here is the response of a 180 passenger high-subsonic twin-jet simulator: the first period takes about 87 seconds.

Conditions:

  From the trimmed position, excite the phugoid mode by applying longitudinal control in one direction in order to change airspeed by approximately 10 kts, then release.

Initial conditions:

COG 0.2205 MAC
Pressure altitude 35,000 ft
Engine N1 rotor speed 87.47% (both engines)
Calibrated Airspeed 264.54 kts
Gross weight 66,360 kg

EDIT

To answer the additional question of when the resulting motion amplitude would be below 0.1 deg, I made a kind of a digital simulation according to this block diagram:

and then tuned spring stiffness C, inverse inertia 1/M, and damping constant K until the resulting response overlaid the original aircraft one. The resulting motion gets to a max. amplitude of 0.1 deg in about 1,600 sec - 27 minutes.


Is it permissible to log an instrument approach for purposes of IFR currency in a non-IFR certified aircraft? Assume you maintain VFR at all times and you have a qualified safety pilot on board. Can an IFR rated pilot fly practice approaches under the hood (view-limiting device) using an aircraft that is not IFR certified, and log these approaches for purposes of meeting his/her IFR currency?

Assume the aircraft has the required equipment for the approach (i.e. VOR for VOR approach, ILS for ILS, etc.).

As long as you remain VFR then the equipment requirements for the airplane and the flight are VFR.

§61.57 says “Within the 6 calendar months preceding the month of the flight, that person performed and logged at least the following tasks and iterations in an airplane, powered-lift, helicopter, or airship, as appropriate, for the instrument rating privileges to be maintained in actual weather conditions, or under simulated conditions using a view-limiting device…”.

It doesn’t say anything about having an IFR certified airplane or having a current pitot/static and altimeter check. If you are maintaining SEL IFR currency, then all you need is a SEL airplane. MEL IFR, then a multi-engine plane, etc. And if you are missing some of the 6-pack instruments, all the better for practicing partial panel.


Why are you not allowed to use power sockets in the seats during takeoff and landings? Is it because the extra strain on the electrical system reduces engine performance?

In case of emergencies.
If something unexpected happens during landing, you don't want people to trip over cables, look for their phone or whatever or start packing anything plugged into the socket. This is the same reason you are asked to stow away bags or any other loose items and so on as well.


What is the definition of load factor and how do you apply it? I'm a little confused about the definition of the load factor, n, as the definitions I found seem to contradict its application in force and moment balance analysis of an aircraft structure.

The definition given in my university script states that the load factor equals the ratio of all external forces acting on an aircraft minus its weight, to the magnitude of the aircraft's weight; this implies that the load factor is the ratio of all aerodynamic forces acting on an aircraft to the magnitude of its weight.

The Wikipedia definition of the load factor states that the load factor is the ratio of the sum total of all aerodynamic forces acting on an aircraft to its weight.

My script definition therefore tallies with the Wikipedia definition. All good so far.

Now, however, there is also a sentence in my script that states that the load factor is a means of including all inertial loads and gravity loads in observing the loading of an aircraft; this implies that weight is included in observing the loading of an aircraft: this makes better sense to me, since, when expressing the loading of an aircraft, it would be easier to say that the aircraft is now being loaded "this many times its weight", compared to this many newtons; this however, contradicts the definitions above.

And now to the force and moment balance analysis issue, I noticed that all components of an aircraft are expressed in terms of its load factor, which is fine, but then in performing the balance, the weight of the components are not considered. How can you ignore the weight force which is always acting on the aircraft when the load factor (per definition) excludes it? An added confusion is in that lift is considered in the moment balance, with all component's loading expressed in terms of load factor; how can you include lift, when it is already incorporated into the load factor of the components; this implies that the part is further loaded above its current loading.

I would appreciate if someone can straighten up what the load factor means, and how should it be applied in force and moment balance calculations.

The load factor is the total acceleration you feel, pointing downwards. In straight and level flight, the load factor is 1: you only feel the acceleration of gravity. So a load factor 1 equates to 9.81 m/s$^2$ (If gravity was higher, let's say 15 m/s$^2$. load factor 1 would equate to 15 m/s$^2$. But that's another story.)

Image source

Bank the aircraft 60° and fly a co-ordinated turn, and you'll experience a downward acceleration of 2g. This is a case that is easy to understand since it is a static situation with constant velocities. If we have a dynamic sine wave for instance, the load factor would be a function of where we are in the cycle, if the aircraft is accelerating up or down. The actual acceleration is added to the gravity vector.

Load factor does not ignore the weight of the aircraft:

In steady horizontal flight, load factor is 1 because it is the same weight that would show up on a scale on the surface of the earth.
All dynamic accelerations are added to 1. If the aircraft accelerates downward with -1g, the load factor is zero and everyone on board is weightless.
Forces are vector entities. For the load vector, we're only counting the resulting accelerations in the z-axis of the aircraft. After summing the forces in 3 degrees of freedom, the z-axis force F drives the airplane up/downwards with an acceleration of a = F/m.


Does being cleared for a visual approach supersede speed instructions from ATC? (FAA) Does being issued a visual approach clearance supersede speed instructions from ATC under FAA rules?

Here's an example. Let's assume an aircraft is being vectored for landing at a large class B airspace airport like KATL and has been instructed to maintain 210 knots. About 5 miles from the final approach fix on the ILS the aircraft is cleared for the visual approach. Does the visual approach clearance supersede the instruction to maintain 210 knots?

This is assuming the visual approach clearance didn't include an additional speed instruction along with it.

Please include the regulation or FAA-published guidance.

The AIM 4-4-12 says that an approach clearance cancels a speed restriction, but ATC can explicitly restate the restriction if needed:

  Approach clearances supersede any prior speed adjustment assignments,
  and pilots are expected to make their own speed adjustments as
  necessary to complete the approach. However, under certain
  circumstances, it may be necessary for ATC to issue further speed
  adjustments after approach clearance is issued to maintain separation
  between successive arrivals. Under such circumstances, previously
  issued speed adjustments will be restated if that speed is to be
  maintained or additional speed adjustments are requested. Speed
  adjustments should not be assigned inside the final approach fix on
  final or a point 5 miles from the runway, whichever is closer to the
  runway

The ATC orders 5-7-1 give the controller guidance:

  c. At the time approach clearance is issued, previously issued speed
  adjustments must be restated if required.

  d. Approach clearances cancel any previously assigned speed
  adjustment. Pilots are expected to make their own speed adjustments to
  complete the approach unless the adjustments are restated


Is a "GPS required" ILS (or other navaid-based) approach considered a "GPS approach" for alternate planning's sake when TSO-C129/196 gear is in use? If you have TSO-C129/TSO-C196 GPS gear (vs TSO-C145/146 WAAS/SBAS gear), you either have to have a non-GPS approach at your destination, or a non-GPS approach at your alternate.  If your choices are either conventional approaches or GPS-only approaches, this is simple to understand.

However, some approaches have arisen that are hybrid approaches -- combining GPS intermediate guidance with a ground based navaid (usually an ILS) for the final approach course guidance.  An example of this can be found at Jackson Hole, WY, where the KJAC ILS Z or LOC/DME RWY 19 approach is listed as "GPS REQUIRED" on the approach plate due to the use of GPS to set up a curved feeder leg onto the ILS final, bypassing some terrain to the north of the airport and allowing much lower minimums as a result.

Are these "hybrid" approaches considered the same as a GPS-only approach for alternate planning if you are TSO-C129/TSO-C196 equipped?  Or are they considered as conventional approaches for alternate planning purposes?

This is an excellent question.

However, since the approach you reference, KJAC ILS Z or LOC/DME Rwy 19, "requires" GPS, I would interpret it the same as a GPS-only approach for planning purposes and subject to the appropriate restrictions. Those are: either the destination or alternate, but not both can be a GPS-only approach airport for TSO-C129/TSO-C196 [GPS-no WAAS] equipped aircraft.  Both destination and alternate can be a GPS-only approach airport if the aircraft is equipped per TSO-C145/146 [WAAS].


Can horizontal stabilizer trim be worked independently (each side)? I notice most jetliners have a big trim wheel on each side of the center console.  This wheel is black with white stripes, and notably turns on its own via the autopilot.

Two large trim wheels: And obviously, most jetliners have two horizontal stabilizers or stabilators.

Can each side be trimmed independently of each other?  That is, does each big wheel control one stabiliz/ator and can they be unlocked and operated in different directions if need be?

No.  Theoretically you could have the left and right stab move independently so there is still some trim authority if one jams, but would be structurally way more complex and quite heavy, your trim authority would still be cut in half, and there isn't really a strong need to do that from a risk perspective.  There may be aircraft out there that are like that, but most moving stabs are single surfaces usually operated by a big electric jack screw.

The required redundancy is provided by redundant control channels for the trim system, dual drive motors for the screw jack that drives the stab, and a dual load path design in the acme thread and the trunnion (the "nut" part of the jack), and in the attachments that connect the trunnion to the stab and the actuator assembly to the structure.  The only single point of failure would be for the hinge of the stab itself to completely seize, and the risk of that is low enough that it doesn't need to be accounted for in the system architecture.

Two independent stab surfaces would require an attachment to the fuselage or fin that allows independent movement of each surface while cantilevered off the root structure, which would require a pretty heavy and complex center structure for not a lot of gain safety wise.


EASA and National Aviation Authorities What are the boundaries of responsibility by the  National Aviation Authorities (Member States of EASA, e.g. France = DGAC) versus the responsibilities of EASA concerning aircraft operations? I know EASA has some responsibility for aircraft operations as noted in EC No 1592-2002, EC 216-2008 and EC 2018-1139. However the National Aviation Authorities (DGAC, ENCA, FOCA, etc.) surely still maintain some operational power or they would cease to exist?

Does anybody have a reference that can clarify whom is responsible for what areas of the "Air Operation" regulations (EASA calls Part 121 "Air Operation") for National Aviation Authorities versus EASA?

Let's continue with you example of France DGAC.

National body: DGAC

DGAC is in charge of French ATC, in airports and enroute, manages ATC education and training (ENAC, École Nationale de l’Aviation Civile), is the spokesperson for operators, crews and industrials.

DGAC in general is the operational safety people you can see at the airport, EASA is not present. They are reporting to French authorities (e.g. Ministère de la transition écologique) who are still responsible for overseeing aviation activities in France.

Regarding safety, the domain of EASA:

  DGAC is responsible for ensuring the safety and security of French air
  transport. On one hand it is a regulatory authority, but it also
  supervises security and safety [...]

  DSAC, The Civil Aviation Safety Directorate is the department of DGAC
  in charge of safety. Its task is to ensure safety for everyone
  involved in air transport. It is in charge of monitoring the
  application of the regulations, which are primarily developed by the
  European Aviation Safety Agency (EASA).

(Source)

STAC (Services Technique de l'Aviation Civile) is a branch of DGAC in charge of planning navaids and airports and designing airports systems.

EU body: EASA

The actual domain of EASA, as name implies, is safety. While EASA doesn't replace local authorities, it is the main regulatory body in EU for civil aviation.

DGAC (actually DSAC) on the other hand is participating to safety regulation preparation as do other national agencies in EU. Remember EASA was only 400 people a few years ago, maybe twice today.

EASA has issued a number of "regulations". Regulations don't have to be implemented locally contrary to "directives", they are binding per se. An analysis of the regulations structure is available here:

Some activities have logically shifted from DGAC to EASA, in particular the ICAO role to issue airworthiness directives for commercial aviation:

  From 15th February 2006, DGAC France stops issuing Consignes de
  Navigabilité (= Airworthiness Directives) on behalf of EASA

However ULMs or gliders topics (among other) are still under DGAC responsibility.

EASA vs FAA

Contrary to FAA which encompasses nearly every aspect of civil aviation in the US, EASA has a limited, though critical and expanding, role around security, safety and airworthiness.

Contrary to FAA, EASA is not an ANSP. Eurocontrol itself has not to be compared (yet) with FAA ANSP role, they actually cover only a very small part of the EU sky (Maastricht UAC), even if the long term idea is to standardize ANSP tools in EU and allow a true single sky ATM to cope with the increasing traffic. DGAC (DSNA branch) has still full authority for this aspect in France, and probably for some time since ATC means also coordinating with national air force.


Why did the Junkers Ju-52 have corrugated external surfaces? Every time I pass by Munich I have to pay a visit to the Deutsches museum, in particular to the aviation wing.

Among the other aircraft on display, there is a Junkers Ju-52. A different photo taken from a different website illustrates well what caught my attention:

Why are the external surfaces of both wing and fuselage corrugated?
Were the designers hoping to achieve some performance improvement through this choice? Are there any papers/documents about this?

It was largely a structural decision. The Ford Tri-Motor which was designed to mimic many things the Junkers plane designs included, including the corrugated metal.

  ...all of which were constructed of aluminum alloy, which was corrugated for added stiffness, although the resulting drag reduced its overall performance.

Corrugated metal is common for roof panels and ironically, hangars, these days. You can find some info on the strength and flex properties of it when related to those topics. Here is an interesting thread on increased drag (and load) on corrugated roofs.

As for the availability of the material vs sheet aluminum I would argue that it had little effect on the design choice. Keep in mind all corrugated aluminum starts out as sheet aluminum at some point in the line so its hard to say there is more than one or either material. On top of that it takes more corrugated material to cover a specific square area than flat sheet material which would drive the price up. At that time period in aviation a lot of experimenting was going on and anything that made a plane a bit stronger or a bit faster was considered quite an achievement. Keep in mind we are coming of the tails of the fabric plane era so a design like this would have seemed revolutionary. The Ju-52/3m (the one you have pictured) came out in 1932 (work began in '28), by that time other makers were already looking at and working on smooth aluminum body planes. There is of course a large social aspect to the availability of materials at this time in history especially in Germany. I will refrain form a full history lesson here but you can read up on Junkers history here and about the man him self Hugo Junkers here which include some of his political views and his involvement (and issues with) the Nazi party. His work in all metal designs is credited with inspiring many passenger planes in the post WW1 and WW2 eras of design.


What is a "natural flight loop"? I'm roughly (edit: very well) familiar with flight simulation, but recently I came across a new term. In this brochure (scroll to the second page) by Airbus about flight simulators, they talk about

  Natural Flight Loop models:

  GRM, Aerodynamics...

I've never heard that term before. What does "Natural Flight Loop" mean? Is it Airbus-specific?

(GRM is probably ground-reaction model, aerodynamics is obvious - but that doesn't really explain Natural flight loop, does it?)

EDIT: Ok, "roughly familiar" is a bit understated... I should have made clearer that I'm an aerospace engineer. Actually I have been working on flight dynamics models for simulators myself, so I understand very well, what it needs to develop an accurate flight simulator from a technical point of view (yup - natural flight loop seems to be what is required for FAA FTD Level 6 devices and FFS).

The issue that remains is that I'm curious what this natural flight loop contains in detail.

Is there someone out there who can tell me if this is...

executable code (like a .dll or whatsoever),
mathematical equations (with probably huge lookup-tables for the parameters),
something like Simulink models (or Modelica or ... )?
does it contain separate models for actuators, gear, aerodynamics, weight & balance,...?
does it contain just the open loop model or also the flight control system?

At Airbus, the Natural Flight Loop is the set of the models that simulate the Natural
Aircraft behaviour: kinematics, mass, fuel, center of gravity, inertia, thrust, ground handling, ground reaction, slat/flap, aerodynamics.

Let me know if you need more info.


Do noise abatement procedures have an impact on aircraft emissions? The ICAO has imposed Noise Abatement Departure Procedures (NADP1 and NADP2) in order to limit the noise impact of departing aircraft on communities living nearby airports. Could noise reduction lead to an increase in NOx/CO2 emissions (an aircraft needs more power to achieve faster climbing rates)? If so, why don't the ICAO (or local authorities) impose "Emission Reduction Procedures"?

Generally, it is most fuel efficient - when considering fuel for the whole flight as opposed to individual flight phases - to climb to cruise altitude as quickly as possible (i.e. using maximum thrust), since the aircraft flies much more efficiently at cruise altitude than at lower levels. This is in direct contradiction to anything to do with close-in noise reduction (i.e. around the airport), but it would reduce total flight emissions (other than noise).

For noise further away from the airport, climbing with maximum thrust may actually be more beneficial, as there is another tradeoff between noise emitted at the aircraft and the altitude achieved at the noise sensitive area (quiet can mean passing with low thrust or at high altitude).

So, yes, by altering the climb profile, the emission profile for the flight is altered. The noise abatement procedures will often lead to higher emissions than could be achieved theoretically (not necessarily practically though).


Does lift generation create a vacuum over an airfoil? According to Bernoulli’s principle, airflow speeds up over an airfoil which decreases the pressure, and I read somewhere that when airflow speeds up over an airfoil, this creates a vacuum. Is this statement true?

How would a vacuum above an airfoil be different from airflow separation?

I think this is simply a terminology issue.

There is no vacuum in the physical sense on the upper surface of an airfoil. There is an area of low pressure, though, which in certain context is also called a vacuum.

A great example for this linguistic imprecision is my vacuum cleaner, inside of which there is no vacuum in its physical sense by far, but clearly it sports considerably lower pressure than the atmosphere in the rest of my living room.


How soon can I start my turn after reaching the missed approach point, when missed approach procedure calls for a climbing turn? If the missed approach procedure only calls for a climbing right hand turn, at what altitude after reaching the missed approach point (MAP) can I initiate the turn on a precision approach that takes me down to 200 AGL.

Some missed approach procedures say, for example, climb straight ahead to 1000 then climbing right turn to 3000, but some just say climbing right turn to 3000.

Is it documented anywhere that in this situation you can immediately start your climbing turn from the DH (or MDA on non-precision approach)?

Based on your question and the circumstances you indicate:

On an approach that takes you down to 200' HAT (height above touchdown) and specifies a climbing turn without a "climb straight ahead to [some altitude] then climbing right turn," you should climb to 400 feet AGL and then start your right climbing turn along the missed approach course track.

From FAA Order 8260.3C, Section 2-8 Missed Approach, paragraph 2-8-6 [pertinent portion]:

  "2-8-6. Turning Missed Approach Area. If a turn of more than 15 degrees from the FAC is required, a turning or combination straight
  and turning missed approach area must be constructed.

  Note: If the HAT or HAA value associated with the DA/MDA is less than 400 feet, construct a combination straight and turning missed
  approach (see paragraph 2-8-8) to accommodate climb to 400 feet above
  TDZE/airport elevation prior to turn."

========================================================================


Why does the spanwise flow along a swept wing not accelerate? I read this article explaining flow around a fixed-sweep swept wing, and it stated that the spanwise flow component does not accelerate, but the chordwise flow component does. What is so special about spanwise flow that it does not accelerate?

In chordwise direction there is a curvature that accelerates the flow. In spanwise direction there is no such curvature.
See this answer for a more elaborate description of the lift generation.


What is the difference between an RPL and a PPL licence? I am looking forward to starting my training to get my RPL license and I was wondering what the difference was because on the website it looked like you have to do 2 different pieces of training for each license. If I was to get my RPL in Australia what would the difference be between the two?

Thanks,

An RPL requires less training (i.e. money) but is more restricted in how far you can fly, how many passengers you can carry and how heavy the aircraft can be. You can get an endorsement to fly anywhere domestically; there is no endorsement available to fly internationally or for the other two restrictions, nor is an instrument rating available.

A PPL allows you to fly just about any small aircraft anywhere, and you can add an instrument rating as well if desired. There is still a weight limit, but it's high enough you wouldn't hit it without needing to get (at least) a commercial license anyway.

All of the training you take for an RPL will count toward a PPL, so if you start on the former and switch to the latter, you lose nothing. Or you might get an RPL first and, if you find the it too limiting, upgrade to a PPL later; the only thing you lose in that case is having to pay for twice as many tests.


Why don't pilots always use autoland? In aeroplanes that are equipped for autoland and landing at an airport with a working and adequate instrument landing system for the conditions, why would a pilot choose not to use autoland?

If I had to guess, I'd say it's due to some of the following:

Autoland is stressful and labour-intensive for pilots compared with flying the plane normally down to the ground in VMC.
Autoland produces less comfortable or otherwise "worse" quality landings.
Using autoland is less fun or enjoyable for the pilots.
The use of autoland is restricted by aviation regulations.

But I don't have any sources to back up these claims.

There are a number of reasons why pilot don't use autoland all the time, even if the airport and aircraft are equipped with the right equipment.

To name the two most important ones:

Pilots need to practise their flying technique. If they would always
fly autopilot, they would lose the skills to fly. Skills that they
need when the autopilot does fail. There are phases of flight where
it is better or even required to let the autopilot do its job, but
landing is one the things pilot are allowed to and need to be capable
of doing themselves. Of course autoland needs to be practised as well.
Auto land requires very accurate ILS guidance. Even if the airport is
equipped with calibrated ILS Cat IIIb equipment (required for
autoland), the signals will be degraded by traffic that is operating
near the ILS antennas. Under low visibility circumstances, when
pilots cannot land visually, traffic spacing is increased and ground
vehicles are not allowed anywhere near the ILS antennas to ensure the
best possible signal quality. This is a standard part of the Low
Visibility Procedures (LVP) of all airports. The downside of this is
that the capacity of the airport is reduced. If autoland would be
performed while there is no ILS signal protection, the effects can be
spectacular at best or fatal at worst.

Photo by BFU, incident report here


Can a company return an aircraft in leasing? regarding A380 I see that Singapore Airline and AirFrance return 2 and 5 respectively to their lessors, so I would like to know, how the give back operation works? Are there any penalty to pay?

I was wondering if Emirates too can give back its A380.

Thanks in advance

Yes there is a penalty to pay if you break the lease contract by returning it before the completion date. Same as a car.  It may be that they simply continue the lease payments to the end of the contract, or the contract may have some kind not-quite-so-bad penalty that was negotiated to sweeten the deal for the airline to get the deal in the first place.

The airline will do a business case and balance the penalty costs of breaking the lease early against the losses of continuing to run their unwanted behemoth to the end of the lease contract and proceed based on the cheaper option.  Even if they have to keep making lease payments to the end of the contract, it still may be worthwhile to return the aircraft and escape from maintenance and insurance costs, if the aircraft was killing them financially, which is what this sort of thing suggests.


Is a cIearance only valid once it's accepted? I've read somewhere that "a clearance is not valid until read back correctly," but I can't remember where or find a specific rule saying that.

I understand some clearances can be accepted with "Wilco" or similar in lieu of a full readback, but assume this isn't one of those cases.

For example, is it technically a violation to cross the runway hold bars before you finish reading back a takeoff or crossing clearance?

Interesting question - although not FAA, I hoped the UK's CAP 413 would hold some insight as it tends to follow ICAO rules:

https://publicapps.caa.co.uk/docs/33/CAP413%20MAY16.2.pdf

Page 25 is the relevant chapter, and while it doesn't outright say the clearance is not valid it is very strong in its readback requirements. The following language applies to runway entry/take off/landing:

  The stringency of the read back requirement is directly related to the
  possible seriousness of a misunderstanding in the transmission and
  receipt of ATC clearance and instructions. ATC route clearances shall
  always be read back unless otherwise authorised by the appropriate
  ATS authority

  The ATS messages listed below are to be read back in full by the pilot/
  driver. If a readback is not received the pilot/driver will be asked to do
  so. Similarly, the pilot/ driver is expected to request that instructions are
  repeated or clarified if any are not fully understood.

  [Lists the relevant activies, including runway entry]

It also points to ICAO Doc 4444:

https://ops.group/blog/wp-content/uploads/2017/03/ICAO-Doc4444-Pans-Atm-16thEdition-2016-OPSGROUP.pdf

With similarly direct wording:

  The flight crew shall read back to the air traffic controller safety-related parts of ATC clearances and
  instructions which are transmitted by voice. The following items shall always be read back:

  a) ATC route clearances;

  b) clearances and instructions to enter, land on, take off from, hold short of, cross, taxi and backtrack on any
  runway; and

  c) runway-in-use, altimeter settings, SSR codes, level instructions, heading and speed instructions and, whether
  issued by the controller or contained in automatic terminal information service (ATIS) broadcasts, transition
  levels.

It seems clear to me that ICAO, EASA and CAA standpoint is that readbacks are completely mandatory, and the clearance has not been fully delivered until the readback is completed. The readback is a controller final opportunity to correct a potentially critical misunderstanding or communication and it seems to me that proceeding without reading back, and waiting for any call of "Negative" is negligent.


Is there a list of aircraft which squawked 7700? Is there an accurate and updated list of aircraft which squawked 7700?

An ATC facility probably has a method of recording any aircraft they dealt with each day which declared an emergency, via the transponder code or otherwise.  One is probably safe in assuming that this information is passed along up the food chain for some sort of collection at a national level, although such an aggregated list may not be immediately available to the general public.  My first guess is that a FOIA request might be able to get what you're looking for, although if the requested scope is "every emergency aircraft at every facility in the US over the last two decades," you may be out of luck.  (That would be a huge volume of data anyway.)

Understand a couple of things about declaring an emergency:

Most aren't accompanied by actually squawking 7700.  Of the (relatively few) emergencies that I've declared in a couple decades of military + civilian flying, I can't think of any that required us to change the transponder code -- we declared the emergency with ATC on the radio, kept our assigned squawk, and did what we needed to do.
Many aren't related to the aircraft at all.  I had occasion about a year ago to ask our airline safety department what the most common cause was for declared emergencies in our operation, and was told that far & away, sick passengers (medical emergencies) were #1 by a huge margin, and everything else (which includes all the aircraft-related events) was far down in the weeds in comparison. Given that, seeing that aircraft 123XY declared an emergency 5 times last year doesn't necessarily mean that it has had more mechanical issues than its fleetmate 234XY that only did so once; it may just mean that 123 got more than its share of sick passengers.

In fact, in airline operations at least, mechanical issues are almost always caught on the ground, so an aircraft with "gremlins" will usually manifest them in terms of maintenance delays and cancellations, rather than in-flight emergencies.


Why did Concorde not have horizontal stabilizers? The Concorde did not have horizontal stabilizers or elevators. As a result, the pilots have to move fuel around the aircraft to trim it up or down, as sluggish and hazardous move.

Why did the design team chose not to use a horizontal stabilizer? Was it because of the understanding of supersonic aerodynamics and/or technology of the time? Or, was it due to some aerodynamic principles? If someone were to design the Concorde today, would they still use the fuel transfer method to balance the CG?

(Source: concordesst.com)

It does have elevators in the form of elevons at the trailing edge.  A delta is effectively a tailless flying wing with a really long chord.  Like any flying wing, pitch stability is achieved by down force generated at the local trailing edge by a control surface that does the same job as a regular elevator/stab, by applying down force to balance the forward pitching moment of the CG ahead of the centre of pressure (an airplane is really just a teeter totter with the C of G at one end and the elevator at the other).

Fuel transfer is used to keep the C of G in a sweet spot range to minimize trim drag, which is the penalty taken in generating the down force at the rear, so that the down force can be no more than necessary for adequate pitch stability.

As for why they didn't use a horizontal stabilizer, the reason is that the delta plan form with elevons provides the required stability and control in pitch and allowed the designers to dispense with a separate tail surface, greatly reducing the drag of a separate tail (not eliminating, because there is still a drag penalty from the elevons generating down force).  Same reason anybody goes with a flying wing.  Plus, you need lots of sweep for low supersonic drag and lots of wing area for high altitude efficiency, so a tailless delta fits the bill.

A limitation of this is a narrower CG range (a more limited forward CG than with a regular tail that is farther aft and has more leverage) because the elevons have a short moment arm, a limitation of all flying wings.  The ability to transfer fuel to adjust CG would help with this and I think Concorde's modest passenger loading didn't cause the CG range issues that a normal airliner would have to deal with.


How does the MiG-23 fuel system work? In what order are the fuel tanks on the MiG-23 used? In other words, which tank is used first, then second etc.?

These guys could probably answer this question.

It'll cost you $20, but you can obtain a MiG-23 POH here which should have a systems description in it for the jet's fuel system.

http://www.flight-manuals-on-cd.com/MIG23.html


Why does obstacle clearance area splay outward instead of being a rectangle? I am having trouble figuring out the logic behind the way that obstacle clearance areas are constructed. Take, for example, a departure procedure where Initial Climb Area is defined in TERPS (section 14-1-6) as a trapezoid:

Even as far as subsequent segments are concerned, their respective obstacle clearance areas seem to follow the same pattern, like this example from TERPS:

Why is this happening? Is there a reason that at the beginning of each segment the obstacle clearance area "shrinks" and then splays outward? Especially when one considers SIDs with really lengthy segments, where near their end the aircraft's perpendicular distance from OCA's borders is huge. It would seem more reasonable to me if the obstacle clearance area was a rectangular region, as it is the case with STARs:

Could someone point me in the right direction?

Because the navigational beacons and the indicator instruments in the cockpit are such that the system is less precise at longer distances. Second the plane must find the initial fix or intersection while flying blind under IMC before becoming aligned and so the area acts like a funnel. In some areas the terrain may limit the radio beacon signal so a wedge is all that is available.

A rectangle isn't needed because planes can't make use of the inner corners and it would be both a wasted area and a hazard as a plane may be able to get in but not out. Directly over a VOR the signal is not useable and the turns in a route must be wide enough for a large-radius turn not a sharp angle precisely over the beacon. The political types like to minimize the zone of low flying aircraft noise and building restrictions on the ground dwelling tax paying voters.
STARS are higher altitude and so the design is more forgiving and can be of simple rectangles.


Is the F-16 cockpit pressurized? Is the F-16's cockpit pressurized? If so, why does the pilot receive oxygen from the mask (please state the correct terminology for this)? Is it due to redundancy in case cabin pressurization fails?

Yes, the cockpit of the F-16 is pressurized. However, there are two types of cabin pressurization:

Isobaric Pressurisation: The system maintains a constant cabin pressure (usually between 2000 and 8000 ft) as the atmospheric pressure decreases. This is used in commercial aircraft.
Hypobaric Pressurisation: In such a system the pressurisation commences at a
given altitude and cabin altitude is maintained at this value until a preset pressure differential is reached. With continued ascent the pressure
differential is maintained. This is used in military aircraft including the F-16, as the weight penalty of the Isobaric system would seriously affect the range.

Provision of supplemental oxygen in the aircraft ensures that the occupant receives increasing quantity of oxygen in the inspired air. The aircraft oxygen system (regulator assembly) ensures that the correct percentage of oxygen is added from the on-board Oxygen reserve to the inspired air in order to maintain lung pO₂ at 103 mm Hg.


What is the difference between EGT and TIT? In a gas turbine engine, what is the difference between Exhaust Gas Temperature (EGT) and Turbine Inlet Temperature (TIT)? I assume EGT is the temperature after the gas has transferred power to the turbine. Does that significantly change the temperature? Are they both proportional to engine power output?

EGT is just that - the temperature of the gas leaving the gas core at the jet pipe.  TIT is the temperature of the gas in the gas generator as it exits the combustors and enters the first high pressure turbine stage.  EGT will be significantly cooler - sometimes by as much as 1500°F! - than the TIT, as the enthalpy or internal and kinetic energy of the working gas is converted into mechanical work by the turbine, reducing the pressure and temperature of the gas flow as it exits each stage of the turbine.  See the Brayton Cycle model for these kinds of heat engines.

Usually the power output for a turboprop or turboshaft is measured as the torque on the power shaft turning either the propeller or rotor transmission.  Thrust on jet engines is usually gauged by the flight crew as N1, or the ratio of the current speed of the fan/LPC/LPT spool to its maximum speed.  This is a bit misleading as the actual thrust the engine generates does not vary linearly with fan speed, but that is the benchmark.

EGT and TIT are not monitored for power output reasons so much as making sure the engine does not exceed its thermodynamic limits.  Too hot a temperature in parts of the gas core will cause serious damage to the engine, requiring major overhaul and/or replacement of the entire engine or subsections.  These temperature limits can exercise limitations on power or thrust settings for the gas turbine during operation to prevent overheating.  On a free turbine turboprop, for instance, your power settings are bounded by both the torque limits of the propeller gearbox and another kind of hot section temperature called the Inter Turbine Temperature (ITT) which is the gas temperature between the high pressure gas generator turbine and the low pressure power turbine.  These limitations cannot be exceeded in order to prevent engine damage and may restrict maximum power settings at both low and high altitudes.


How does compressibility affect the critical angle of attack? Why does the critical angle of attack reduce with increasing mach number or What is the effect of compressibility on critical angle of attack?

First, I have to define what the critical angle of attack is:

When an aerodynamicist speaks of critical conditions, he or she means the condition when the speed of sound is reached locally. The critical Mach number is the speed, measured in multiples of the speed of sound, when the top local speed in a flow field equals the speed of sound.

The critical angle of attack is the one when the local flow speed first reaches the speed of sound. Since it depends on the initial flow speed, it is only valid for a given flight speed.

Two parameters are responsible for the local increase in speed: Thickness and angle of attack. A body needs to displace air, so the air will squeeze around it, speeding up in the process (or slowing down in fully supersonic flow).

When the angle of attack is increased, the stagnation point moves below the airfoil nose so the air flowing over the top of the wing needs to negotiate its leading edge first. This speeds it up and leads to a suction peak. Another view of the same phenomenon is that increasing suction on the upper side of the airfoil will accelerate the air flowing towards it.

With a higher flight speed, less local flow acceleration can be tolerated before the critical conditions are reached. There is even a maximum speed in that suction region of high local curvature that will not be exceeded in subsonic flight and which limits the maximum possible lift coefficient. Higher flight speed leaves less margin, so the angle of attack for maximum lift is reduced with increasing flight speed.

If by critical angle of attack you mean the one where maximum lift is reached (conventionally called stall angle of attack), please read here how it can be influenced. Depending on the flight Mach number, flight speed should be increased or decreased to maximize it.


Why would a plane perform 360° turns to balance fuel on the ground? Why would a plane need to do a couple of 360’ turns on the taxi way/run-up area. The crew were given clearance to taxi and hold. They told the tower they needed to turn the plane 360’ and were cleared. When they asked for a second 360  they said they were trying to resolve a fuel imbalance issue. I think this was a Gulfstream. What was going on with this.

They probably had a fuel imbalance that was marginally outside the limit for takeoff, and perhaps the powered fuel transfer system was unserviceable and was deferred.  Typically there is a gravity transfer capability by just opening a transfer valve and letting fuel run across on its own with the imbalance present, or by skidding slightly.

If they were say 50 or 100lbs above the max lateral imbalance for departure, a spin around on the ramp a couple times with the gravity transfer valve open so that some fuel "sloshes" through the gravity transfer line to the opposite tank, due to the centrifugal force of the turn, may have been enough to get the value in limits.


Are requests for an emergency landing ever refused? Under what circumstances might it happen that a pilot's request to make an emergency landing is refused?

Is such a thing known to have occurred?

I can imagine a couple of reasons why ATC could tell the pilots to please land somewhere else even if they have an emergency

All runways are closed, e.g. they are repaving the runway surface or when the snow trucks haven't yet cleared a thick layer of snow or the instrument landing system is inop and the visual conditions are not good enough, runway flooded after hurricane,...
Another emergency in progress, e.g. passengers freely running around on the airport after an evacuation, not safe to land
Political reasons with hijacked plane (e.g. Lufthansa Flight 181 Landshut was refused to land even when they declared an emergency with low fuel) https://en.wikipedia.org/wiki/Lufthansa_Flight_181
Presidential no-fly zone when other airports are available close by.
Virus infected people on board to avoid contamination of those on the ground (zombie apocalypse)


Are transport gliders used by modern armies? Famous WW2 operations involved transport gliders, for troops landing and vehicles transportation behind front lines. Gliders were cheap and quiet aircraft. The advantage over individual parachutes were landings grouped in a smaller area, allowing troops to be quickly operational.

XCG-16 assault glider, source: Retro-Mechanix

Browsing online seems to show an absence of gliders in the modern era. Are there any military (transport/troop) gliders in use in modern armies?

No, there are no modern military glider forces, the Soviets kept an active glider force up until the early 60's before they retired them. All other military forces retired them before that because they really are not an effective delivery platform; they were inaccurate, often landing many miles off target, and had high rate of loss.

Gliders also tie up a large number of tow airplanes. Helicopters are much more capable, you can land troops on the tops of buildings or small clearings and are re-usable as well - gliders are generally non-recoverable as even if they are intact after landing they are often in inaccessible areas. Transport airplanes like C130s can land on very short, unprepared strips, or use the Low Altitude Parachute Extraction to deliver supplies without landing.


Why does Schiphol Airport have such a long taxi? I recently flew into Schiphol and experienced a very long taxi time (about 20 minutes) from landing to pulling into the pier at the terminal. Given that the flight was only 90 minutes from closing air plane doors to opening air plane doors. I feel that over 20% of flight time is a little excessive for taxiing at the destination airport.

I landed in the early evening. Around 19:30 local time with KLM.

Looking at a map I think I landed at Polderbaan runway as we crossed a main highway. Possibly the A5.

My question is: Why does Schiphol build a runway so remote when there is clearly available land nearer to the main airport terminal? And should this runway be used by short haul flights. Should it not be kept for long haul as it is the widest and longest runway at Schiphol?

Schiphol indeed seems to have enough space to build a runway close to the terminal. However it is more the lack of airspace and laws preventing excessive sound levels that made it necessary to create the "polderbaan". It is also one of the two primary runways for nightflights (link in Dutch (sorry). Found a reference in the English wikipedia:

  Newest runway, opened 2003.
  Located to reduce the noise impact on the surrounding population; aircraft have a lengthy 15-minute taxi to and from the Terminal.


Why do I never see fighter jets on sites like FlighRadar24 and ADBSExchange.com On ADS-B Exchange they even have a filter option for military aircraft, and it will show all kinds of transport, mid-air refuelers, helicopters, and even training aircraft like the Texan, but I don't think I ever see fighter jets on there. Even when I see some F/A-18s fly overhead IRL I still never see them show up on any websites. Or like right now I noticed that Air Force 1 was flying out of Palm Beach I think it was but I didn't see any fighter escorts show up. Are fighters allowed to just turn off their transponders in civilian airspace?

Because they don't want to be seen.

  Are fighters allowed to just turn off their transponders in civilian airspace?

FR24 and ADS-B Ex are not based on normal transponders (that would require access to actual RADAR data) but rather ADS-B and mode-S transponders. The military can simply choose not to operate with this equipment. This does not make the fighters invisible on normal ATC radars, since ATC obviously still needs to be able to see them.


In case of a drone strike with an airplane below 400 feet, who is at fault? If a plane is flying VFR (see and avoid) below 400 ft, and the pilot collides with a drone due to not seeing the drone until it's too late to take evasive action, then would the pilot be at-fault for insurance purposes? Would the drone operator (or the pilot) have violated any federal regulations for not keeping clear of the other craft?

Conditions:-

Class E or G airspace
out of the 5nm radius of an airport
sparsely populated area
operator of drone is not within 500 ft of where the collision occurred (i.e. for the purposes of FAR 91.119 (c)).
I have a smaller piston engine plane in mind, but I'm assuming that the outcome would be the same for faster jet aircraft too

The FAA has some rules pending about this, you can read them here but for drones under 55 LBS one of the proposed rules is,

  Must yield right-of-way to other aircraft, manned or unmanned.

and since you bring up class E it should be noted that

  Operations in Class B, C, D and E airspace are
  allowed with the required ATC permission.

if/when this goes through it looks like its the drone operators fault since the plane had the right of way

According to the FAA's website in relation to model aircraft they state that,

  (4) the aircraft is operated in a manner that does not interfere with and gives way to any manned aircraft;

this is pretty much a blanket statement that maned aircraft have the right of way but the FAA handles most things on a case by cases basis so in the end of the day it could go either way.


How airlines are calculating crew member's payroll? What methods are used by the airlines to calculate the payroll of a commercial airline crew member?
Does it always depend on the number of flight hours in the period, the number of duty days, or some other metric?

As mentioned in the comments, this is different per airline. I'll list some of the options used, though there may be airlines out there with their own unique system not included in this list. Note that I use Flight Attendants as examples, as their payroll information and training requirements is a bit more "open source", but these pay methods carry over to anyone working in the aircraft.

Hourly:

This is by far the system of choice for the larger airlines, as they are more easily able to track performance and efficiency statistics (hours worked v hours needed v pay per hour), as well as the fact that it often ends up being cheaper. Flight Attendants have seen remarkable raises in recent years for most companies, and can make anywhere from $25-60/hr, depending on how long they have been working with that particular airline, or in that particular occupation. This provides an incentive for sticking with your current employer.

Static Salary:

A static salary is similar to what you would find in a regular job. You have a minimum number of hours expected of you, and you get paid a flat rate. In the interest of keeping your job, you would be expected to work many more hours than the minimum, as cabin crew understandably work different amounts each month.

Dynamic Salary:

A dynamic salary is a mix of the above two, and is more of a European method. This type of pay expands or shrinks depending on your hours. There is a maximum number of hours you can work, but a relatively low minimum. If you hit the maximum number of hours, or more, you will receive 100% of your salary. If you work half the number of hours, you receive 50% of your salary, and so on. These salaries are typically much higher than a static salary, but it averages out to about the same as a static salary.

Trips for Pay:

TFP is not the easiest way to do it, but gives the airlines a way to pay the lowest wages! You get paid "per trip", as long as the trip hits the minimum distance to count as a trip. If not, you earn a fraction of "per trip" pay. Depending on the airline, a standard trip is typically between 200-300 miles. If the trip is longer, you get paid an additional rate per mile. This system also tracks time that is blocked off for your duties, so you will still get paid if you are waiting for your next aircraft to arrive, but it is a much lower rate.

Extra Pay:
On top of all those methods of pay, nearly all airlines provide some form of additional pay that is added either per trip, or per month. This can be for special skills or training that a flight attendant has received, or for working through holidays or red-eye flights.

That said, I spoke with an old 747 pilot in my family, and he mentioned that holiday pay is not all it's cracked up to be. He was used to them calling in  pilots to work every Christmas Eve, so he ensured when he got out of work on the 23rd, he would take a swig of brandy as soon as possible so that they couldn't legally force him to work extra hours!


Do I have any authority over airspace above my land? With all this talk about drones flying around and delivering parcels for the merchant websites, I'm wondering from a "landlubber's" perspective, how much say I have over the airspace of my private land.

Now I know this question is a bit broad and quite difficult because it might differ from country to country and also depend on the size of the land, for instance a farm vs. a house in the city. It might also be interesting to know how it affects a piece of private land with a private runway.

But since it is sadly the norm these days for every country to follow Europe's lead eventually on these kind of privacy issues, Europe's might be the most relevant in the end. Any general insight from you all on this would be very informative.

In the US you have, effectively, zero rights over the airspace above your land by default: Control of airspace is entirely delegated to the FAA, and they're super serious about it.

If you designate your land as an airport you can certainly establish a control tower and request an airspace designation from the FAA - whether or not they approve your plan depends on the existing airspace around you though: If your airport would create a problem for an existing airport you'd probably not be able to get an airspace designation for it, and it may even be classified as an objectionable airport.


Why do naval jet aircraft need to have strengthened undercarriages? I've read several times that the navy versions of jet aircraft need to have a strengthened undercarriage. Here is one example, and another.

I've always just automatically assumed this was needed because aircraft landings are "rough". That is, the aircraft smacks down hard on the carrier deck (or so went my assumption).

Now I find myself questioning this. Naval jets land by catching a wire that brakes them hard. They may also takeoff with a catapult, which is some running device that pulls the nose gear forward at high g's.

So, what is the real reason that naval versions of jets need a strengthened undercarriage?

The landing on carrier is indeed hard. The reason is not the deceleration (which is handled by the hook), but the touch-down. Since the deck is short, the wires can't be spaced very far apart, so the aircraft must touch down very precisely. Since the precision is better at steeper angle, the aircraft landing on carrier do not flare. At all. So they hit the deck at more than twice the vertical speed compared to typical landing on decent runway.


Feasibility of using secondary props to generate power on an electric model aircraft Beginning with the aeroplane itself, it is a small, fixed wing model aeroplane, reminiscent design-wise to a Cessna 172. It is completely battery powered and has a primary prop attached to a motor housed in the nose of the aeroplane.

I was wondering how feasible it would be to attach two props behind the wings of the aircraft, one on each wing, connected to a generator which would then connect to the main battery, so as to recharge the battery while the aircraft is airborne.

I haven't been able to find much information regarding this, so any ideas would be greatly appreciated.

It seems to me to be somewhat pointless - your extra 2 props will create more drag, thus the main drive motor will need to work harder for the same result as without them. They're effectively cancelling each other out, and the laws of thermodynamics tell us that energy will be lost from the overall system.

It's much like connecting a solar panel to a lightbulb; physics just doesn't allow for a 100% efficient system, so it can't work.


Why can’t the F28 be deiced with one or both engines running? Recently, I was contemplating Air Ontario Flight 1363, which, despite heavy, wet snowfall while it was on the ground at CYHD, could not be deiced before takeoff, as it arrived bearing an inoperative APU, necessitating (as CYHD, at the time, had no ground-starting equipment available) that one of its engines be kept running the whole time the aircraft was on the ground, and hot-deicing an F28 (deicing it while one or more engines are running) is forbidden.  The aircraft eventually took off, and, predictably, crashed almost immediately due to snow and ice accumulation on its wings.

Wikipedia claims that the prohibition against hot-deicing an F28 is to prevent vapours from ingested deicing fluid from entering the cabin ventilation system via the engine bleed air used to heat and pressurise the cabin, but the engine bleeds can easily be turned off before deicing the aircraft, and any residual deicing fluid left in the engine after deicing can be dealt with by letting the engine run for a few minutes to flush out its passages before turning the bleeds back on (and, if necessary, one could start the engine on the side not being deiced at the moment, and route bleed air from there into the other engine to blow out any deicing fluid, or vapours therefrom, that did somehow make it into the bleed-air passages).

What gives?

The Fokker F28 can be de-iced with engines running, but this was not permitted by the Air Ontario manuals.

The Wikipedia article does not list a source for their claim:

  the Fokker F28 aircraft is never supposed to be de-iced while the engines are running because of a risk of toxic fumes entering the cabin of the aircraft

One can however find all details in the final report, which shows an excerpt from a memorandum distributed by Air Ontario's director of maintenance:

This memorandum was not known to all Air Ontario pilots:

  The body of evidence on this point does not support a conclusive
  finding, one way or the other, as to whether Captain Morwood and/or
  First Officer Mills received the Fokker cold-weather operation publication
  or the Mauracher memorandum, which contained, among other
  important information, the crucial proviso, "NEVER: Spray while main
  aircraft engine's are running!!!" (Exhibit 317, p.3). What is clear is that
  a specific pilot bulletin was never disseminated on this point, and there
  is strong doubt, based on the above-mentioned evidence of Air Ontario
  pilots, as to whether pilots Morwood and Mills had received the Fokker
  cold-weather operation publication.

  Air Ontario pilots Hansen, Wilcox, Stoger, and Monty Allan testified
  that they were not aware of specific restrictions against spraying the F-28
  for the purpose of de-icing while one engine was running. Only Captain
  Maybury, who had received the Fokker publications, was aware of such
  restrictions. In the absence of specific instruction or a company policy on
  this point, Air Ontario pilots who were questioned in this regard (in
  particular, pilots Hansen, Wilcox, and Allan) testified that they considered
  the practice of de-icing with a main engine running unsafe,
  because of the risk of ingesting glycol into the engine and the danger of
  having a person in a de-icing bucket in close proximity to a running
  engine. However, the evidence of experts in the fields of aircraft ground
  de-icing, aircraft engines, and cold-weather operations indicated that
  aircraft ground de-icing is routinely performed in Europe and the United
  States with engines running. Clearly, an operational matter of such
  importance requires a standard company policy that is made explicitly
  known to all pilots and operational personnel.

(final report, p. 658f., emphasis mine)

This implies that de-icing with engines running is possible, but without
proper guidance or procedures most Air Ontario pilots would advise against
it. The report summarizes its finding on this matter:

The report does not say however, why the original Fokker publication prohibits
de-icing with engines running.


Does “trimmed for current speed” mean that the plane will do whatever to maintain the current airspeed? If I understand right, when you are trimmed for current speed, let’s say 290 KTAS, does that mean if airspeed increases to 295, the plane will pitch up to slow it back down? And vice versa for the speed falling below 290. The plane would essentially dive on it, to get the speed back? Or am I way off?

The pitch trim setting is based on the angle of attack.  The angle of attack is affected by indicated airspeed, center of gravity and any unbalanced forces.

In a steady state aircraft where the airplanes forces are all balanced then we are left with airspeed and center of gravity.  Under normal operations where fuel is not being transferred from an aft tank to the wing tanks or vice versa, center of gravity for a certain period of time remains relatively constant.  This leaves airspeed as the primary change in angle of attack.

Your analysis would be correct.  If you are trimmed for 290 KIAS (not KTAS like you stated) and you increase thrust the following sequence will occur.

Airplane will begin to accelerate
The lift formula comes into play and additional lift is created on the wings causing the airplane to pitch up and start to climb.
The airplane experiences an increase in induced drag which opposed thrust.
The airplane will now begin to decelerate while still climbing.
The decreased airspeed causes lift and induced drag to decrease.
The aircraft will pitch down and start to descend.
Aircraft will begin to accelerate as it descends.
The cycle continues until the phugoid oscillation dissipates (provided the airplane demonstrates positive dynamic stability)
In the end, the airplane will be at a higher pitch attitude (in relation to the horizon), climbing, and at 290 KIAS.

The same type of analysis can be accomplished if airspeed is reduced.  The airplane, at the end of the phugoid oscillation, will be at a lower pitch attitude and the same airspeed.


What is this hole on the tail of an MD-88? There's a little hole on the leading edge of the vertical stabilizer of this plane:

What is that? What is its purpose?
Thanks
Source: Airliners.net

That is the ram air intake for the air conditioning packs.


How can you fly your own military jet in terms of altitude and acrobatics? So I know that you can legally buy and fly a military jet like the Mig-29 and the SU-27 https://www.wired.com/2010/01/own-the-coolest-jet-on-your-block/ and https://www.thedrive.com/the-war-zone/29292/you-can-buy-paul-allens-mig-29-fulcrum-jet-fighter. But practically can you fly it? I mean how high can you climb? How fast can you go (I know no supersonic flights are allowed above land, but what about sea)? Can you do barrel rolls and pull Gs? Also, can you use it to fly internationally (assuming that you can attach external fuel tanks in the first place)? Can you actually have fun with it lol?
Assume that money is no issue.

But practically can you fly it?

Sure.

I mean how high can you climb?

As high as you want, assuming you have an oxygen delivery system (14 CFR 91.211, note that "civil aircraft" means "any aircraft not a public aircraft" means "any aircraft not owned by the government," so you can't get out of it that way) and assuming both you and the plane are certified for IFR flight (14 CFR 91.135).

How fast can you go (I know no supersonic flights are allowed above land, but what about sea)?

Below 10,000 MSL no faster than 250 KT, and below a Bravo shelf or near a Charlie/Delta airport no faster than 200 KT, unless the minimum safe airspeed for the aircraft is higher than that (14 CFR 91.117). For supersonic flight see 14 CFR 91.817, 91.819, 91.821.

Can you do barrel rolls and pull Gs?

Assuming the aircraft is certified for aerobatic flight (or perhaps if it has an experimental certification), yes, as long as you comply with the restrictions in 14 CFR 91.303; or failing that, submit an application for a waiver of Part 91 rules (FAA Form 7711-2) (see also) and get such a waiver.

Also, can you use it to fly internationally (assuming that you can attach external fuel tanks in the first place)?

Yes, if you comply with each country's respective airspace/border entry rules.

Can you actually have fun with it lol? Assume that money is no issue.

Depends what you think is fun.
Basically there are no special rules for ex-military aircraft; if you can legally get your hands on one, and if you can legally fly it, you can do whatever any other aircraft is allowed to do as long as you follow the rules any other aircraft has to follow.


Do LED lights work well for CAT III B operations? Does any airport equipped with LED lights for all the CATIII B Components? If so, is there any history that it caused difficulty in aircraft operations?

We are planning to install our new runway with CAT III B lighting with LED fitments.

I don't know if you can do Cat IIIB with a HUD (I'd have said that you're limited to Cat IIIA with one, but somebody may have a capability I'm not aware of) but no, LED lights generally don't wash out a HUD any worse than other lights do.  If your HUD brightness is sufficiently dim, then bright enough lights of any sort can wash it out, but that just requires you to turn the brightness up a bit.

I've never heard of or seen any "Sea of Blue" effect from LED lights, and I don't think LED lights have particularly worse glare (or any other) characteristics when used as runway lighting.  They're somewhat distinctive, but not particularly worse.

If LED lights have regulatory approval for what you want to do, I'd say that right there is the answer to your questions.  And if they don't, well, then that's also an answer.


Are there any models for planning aircraft placement in hangars? I work alone at night doing line operations (fueling, tugging/towing, etc.) and emergency services (police, fire and EMS) at my airport. When a pilot/customer comes in and wants to know if we have hangar space available for their aircraft, it would be nice when planning aircraft placement in those hangars to have figures to scale of various aircraft. That way you can see whether or not a specific aircraft can indeed fit, and in what configuration, before trying as I rarely (if ever) have a "spotter" or a wing-walker.

Or perhaps even software or a computer program. Put in the hangar dimensions and which aircraft are to be placed.

I’ve not heard of software programs to do this, but the Navy has made use of a relatively low tech solution to address this problem for decades aboard their aircraft carriers.

Known simply as the Ouija Board, the aircraft handler and his crew utilize a scaled physical map of both the carrier flight deck and hangar deck along with appropriately scaled footprint models of aircraft in order to track and plan aircraft movements.

I’d guess a similar scheme could be employed to solve your problems.


How many AOA sensors does the 737 MAX have? How many AOA sensors does the 737 MAX have?

Given that it's reported in the media, that one faulty AOA probe activated the MCAS on the Lion Air flight, I was wondering if anybody also knows how an input consensus is reached for the AOA value that gets send to the MCAS system.

The Boeing 737 MAX has 2 AoA sensors.

However, MCAS only takes input from 1 AoA sensor at a time.

Sources:

The black box flight recorder data for Lion Air JT610 shows the data from 2 AoA sensors, labeled "Left" and "Right".

Also, if you look at the nose of the 737 MAX, you will see a left and right AoA vane. (The sensors with the red tags are pitot tubes).

"[Boeing] said it will change the MCAS software to give the system input from more than one AOA sensor."


What is the standard rate of turn for heavy aircraft? I have heard and read many times that for "heavy aircraft", they use a standard rate of turn which is 1.5° per second (4 minute turn), but I have never found an official source which addresses this. Although... I'm actually not even sure where the normal 3° per second (2 minute) standard rate turn is defined either.

The wikipedia entry on ROT (Aviation) says:

  Light aircraft are equipped with 2-minute turn indicators while heavy aircraft are equipped with 4-minute turn indicators.

I don't see why "heavy" would have anything to with turning rate, but airspeed certainly does.
So, I'm wondering if this is true, or just something they think is true because airplanes often use half-rate turns at airspeeds above 250 knots and bank limiting prevents them from making a standard rate turn at airspeeds above ≈ 200 knots?

I'm only able to find the following about bank angles, which specifically refers to turns while in a holding pattern:

AIM 5-3-86.(b):

  (b) Make all turns during entry and while holding at:

  (1) 3 degrees per second; or

  (2) 30 degree bank angle; or

  (3) 25 degree bank provided a flight director system is used.

  NOTE-
  Use whichever requires the least bank angle.

This is also in the Instrument Procedures Handbook which under *High Performance Holding on page 3-25 says that a flight director has a bank angle limit of 25 degrees.

If we use the above guidelines, then a flight director will use 3 degrees per second or 25 degrees of bank, whichever is less.  My calculations give us the following bank angles and associated rate of turns1:

        Standard Rate      Actual        Rate
TAS      Bank Angle      Bank Angle     of turn
80         13.17           13.17         3.00
120        19.34           19.34         3.00
160        25.08           25.00         2.99
200        30.33           25.00         2.39
240        35.07           25.00         1.99
280        39.31           25.00         1.71
320        43.10           25.00         1.49
360        46.48           25.00         1.33
400        49.48           25.00         1.20
440        52.15           25.00         1.09
480        54.54           25.00         1.00

As you can see, a jet travelling at 480 Knots TAS (not uncommon at altitude) would require almost a 55 degree bank angle to make a standard rate turn, which would be an amount considered by almost anyone as excessive.

When limited to 25 degrees of bank, this would result in a rate of turn of 1 degree per second (or a 6 minute turn).  Anything over 160 Knots TAS would be less than a standard rate turn, and once past 320 Knots TAS it  wouldn't even be a 1/2 standard rate turn.

As far as the 1/2 Standard Rate, they often use the 1/2 BANK autopilot mode at high altitudes.  This would result in a rate of turn approximately halved, so a 360 degree turn would take 12 minute at the same 480 Knots TAS.  ATC expects the normal bank in the terminal environment though, so it isn't used at lower altitudes.

As others have said, transport category jets don't even have a rate of turn indicator (it isn't required by 14 CFR 25 if you have a third attitude indicator) and they simply fly bank angles.  Normal hand flying is limited to 30 degrees, which would allow a standard rate turn at a slightly higher airspeed, but then starts to taper off just the same.

That being said, the Instrument Flying Handbook does include this little tidbit in the section on turn indicators on page 5-21:

  The dial of these instruments is marked “2 MIN TURN.”  Some
  turn-and-slip indicators used in faster aircraft are  marked “4 MIN
  TURN.” In either instrument, a standard  rate turn is being made
  whenever the needle aligns with a  doghouse. A standard rate turn is
  3° per second. In a 2 minute  instrument, if the needle is one needle
  width either side of  the center alignment mark, the turn is 3° per
  second and the  turn takes 2 minutes to execute a 360° turn. In a 4
  minute  instrument, the same turn takes two widths deflection of the
  needle to achieve 3° per second.

So maybe at some point in the past it was more common (or maybe faster but-not-quite-as-fast-as-todays-jets) but you just don't see that anymore.  (It could be where all of the references to 1/2 standard rate turns come from though.)

1 Math adapted from the formulas here.


What are the names of the antennas which I have marked in this picture of a Boeing 737? I have taken the picture from PMDG 737NGX Microsoft flight simulator X. I am really curious to know what this antennas are. These antennas are behind the nose gear.

ATC, Altimeter Transmitters and Receivers, and DME-1


Why doesn't the air force order more F-22's? I've come across several articles touting the F-22 as the most formidable air-to-air killing machine to date, such as this one:

https://nationalinterest.org/blog/buzz/f-22-nearly-unstoppable-air-force-has-too-few-them-32152

However, this article and others are also quick to point out there are too few of them.

It is not clear to me what the problem with restarting F-22 production is. The cited article appears to state that the USAF will focus on the sixth generation of aircraft, and integrate the F-22 into that.

Doesn't this seem like a huge gamble? When will sixth generation aircraft be ready in massive numbers?

There are new F-15's and F-16's being built, even today, and they still comprise the bulk of the entire USAF inventory. I don't buy the argument that they can simply "skip" the fifth generation in terms of air superiority fighters and wait for the sixth generation.

With the F-35 being in full production, is it really that hard to restart F-22 production as well? I'm aware that probably nothing at all on the F-35 can be just bolted on to an F-22 airframe -- but shouldn't advances in avionics on the F-35 (if any) only compliment a restarted F-22 production?

It seems at least plausible that the personnel and facilities involved in making F-35 would be able to be adapted to build new F-22's.

However, I'm sure it isn't as plausible as I imagine, and I'm just curious what are the reasons.

Aside from Juan's point about the F-22 being fairly outdated by now (it's an 80's era design), it is also not possible to just restart production of it.

First, it would cost ~$10Bn to simply get to a place where you can produce the an F-22 again. That doesn't include the actual cost of a single plane, just the money required to re-equip factories, train workers, produce a new engine since the old one is end-of-life, etc. Source

This estimate is assuming that the project was left off in the state Lockheed claimed it was. There is reason to believe that some of the tooling for the F-22 no longer exists at all. Source

Finally, the F-35 program has, in my opinion, shown that there is not so much to be saved by re-using components if the overall process is not efficient.


Can I do an IFR checkride in an airplane that isn't certified for IMC? Related to Can a plane be IFR certified, but not allowed in IMC? and Are there any LSA aircraft that can be flown IFR in IMC? .  I understand the distinction between IFR and IMC.  I can train for IFR in such an airplane in non-IMC conditions, but I cannot fly in actual IMC.

Does this mean that I can take my IFR checkride in such an airplane, too?

Legally, you can take your instrument rating checkride (not "IFR checkride") in an airplane that is not equipped for flight under instrument flight rules. That is because you will fly your check ride under VFR. As I did. The examiner will act as "safety pilot," a require crew member, while you are the sole manipulator of the controls under SIMULATED IMC via the view limiting device. The examiner will ask you to do the required tasks, and you will coordinate the tasks needing ATC assistance with ATC, who will remind you to "remain VFR" while you are on practice instrument approaches and so on. You cannot fly the checkride under instrument flight rules because you don't have an instrument rating. The examiner won't (or at least most won't) file an IFR flight plan as PIC using his/her rating.

But that's legal. In practical terms, at least in my opinion, any examiner is going to be reluctant, or at least suspicious, of a request for an applicant to complete the instrument rating checkride in an airplane not fully equipped for instrument flight. In particular, he or she is going to insist that the airplane be equipped for several different types of instrument approaches. My understanding is that it's up to the examiner, so check in advance if your examiner is comfortable using the airplane that you propose to use.


Why do turbofan jets fly faster in cold weather? Why do turbofan jets fly faster in cold weather at high altitudes?

I read somewhere that prop planes do it due to cold weather means air is more dense, and the prop therefore produce more power.

But what about jet aircraft at say 36000 feet? I looked at performance chart of a jet fighter, and at ISA-15 it could fly 0.17 mach faster than ISA.

Do not misunderstand I am NOT asking why it flies faster higher up. I am asking why it flies faster at winter than in summer at same (optimal for speed) altitude.

They don't. They fly slower.

Most aerodynamic effects depend on dynamic pressure. More precisely, lift is proportional to dynamic pressure and drag has parasitic component, which is proportional to dynamic pressure, and induced component, which is inversely proportional.
Therefore there is an optimal dynamic pressure at which the aircraft flies most efficiently, and minimal dynamic pressure needed to maintain flight.

Now dynamic pressure is (half of) air density times velocity squared ($q = ½\varrho v^2$) and due to its significance the “indicated airspeed” shown in cockpit actually corresponds to dynamic pressure expressed as equivalent airspeed. All the desired speeds for various phases of flight are referenced to that.

Since cold air is denser, the same dynamic pressure will occur at lower velocity, and because the pilot will maintain the same indicated airspeed, they will actually fly slower.

One more thing: the maximum speed is one of the few exceptions that is not dependent on the dynamic pressure. There are three effects that may limit maximum speed:

Aeroelastic flutter depends on true airspeed (velocity), so the temperature does not, actually, have an effect on it. However because true airspeed is not usually indicated in cockpit, the pilots will use tabulated indicated airspeed values and since these are only tabulated for altitude, they will actually fly slower.
Mach tuck i.e. loss of lift, accompanied with undesirable change in trim, due to exceeding critical Mach number. Since speed of sound increases with temperature, critical Mach number corresponds to lower true airspeed (velocity) in colder weather, so they'll fly slower again.
Engine power. Engines are able to produce more power in colder weather due to being able to achieve higher mass flow with the higher density air. However, engine power is limiting factor mainly for smaller general aviation aircraft, which have low power engines, or fighters at the other end of the performance spectrum, which are designed to fly supersonic and resist flutter. But transport category aircraft generally hit the other two limits first.

Original answer for the version before the reason they fly at higher altitude was explicitly excluded from the question:

There are two, distinct, effects:

Aircraft fly faster at high altitude due to the lower air density. This is because both lift and drag are proportional to air density. So at higher altitude, the plane both have to fly faster to generate enough lift, and can do it because the drag is lower.

More precisely, lift is proportional to dynamic pressure and drag has parasitic component, which is proportional to dynamic pressure, and induced component, which is inversely proportional.

Therefore there is optimal value of dynamic pressure where the drag is lowest. The optimal cruise speed is slightly above this point. Since dynamic pressure is proportional to density and square of speed, the same dynamic pressure corresponds to higher true airspeed at higher altitude.

Dynamic pressure is usually expressed as equivalent airspeed, which is the speed to which current dynamic pressure would correspond at sea level. The indicated airspeed shown on the instruments is approximation of this value.
Heat engines are more efficient at lower temperatures. This is because efficiency of a heat engine (applies equally to both piston and turbine engines and both internal combustion and external combustion (steam) ones) depends on the ratio of temperature, but the combustion increases the temperature by the same (approximately) difference. So if the starting temperature is lower, the ratio is higher and the engines produce slightly more power for the same fuel flow.

Additionally, the maximum temperature is often limited by what the materials can withstand, so at higher altitude the engine can be operated at higher power (well, not really; the power is also proportional to the density, but the engine will again run more efficiently).