Does holding a medical certificate mean you automatically have a student pilot certificate? If you have a 1st, 2nd, or 3rd class medical certificate and a private balloon certificate (as an example) does that mean you have a student pilot certificate if you now want to get a private pilot certificate? Would you have to go back to a medical examiner, DPE, or FSDO to get a student pilot certificate?

This answer reflects rulemaking effective 1 April 2016
Regarding the question in the title, no, holding a medical does not mean you have a student pilot certificate.  New regulations going into effect 1 April 2016 separate the student pilot certificate from the combination medical+student pilot certificate.  Students will need to apply for a student pilot certificate with their CFI or with the FSDO (or their part 141 flight school) through IACRA.  The new student pilot certificate is plastic just like a normal pilot certificate and do not expire.
This part is true with or without the rulemaking changes
Regarding the question in the body of your post, you are already a certificated pilot with a balloon rating.  You are not a student pilot, you are a private pilot.  The regulations you are subject to are to add an airplane category rating are in 14 CFR 61.63.

§61.63   Additional aircraft ratings (other than for ratings at the airline transport pilot certification level).
(a) General. For an additional aircraft rating on a pilot certificate, other than for an airline transport pilot certificate, a person must meet the requirements of this section appropriate to the additional aircraft rating sought.
(b) Additional aircraft category rating. A person who applies to add a category rating to a pilot certificate:
(1) Must complete the training and have the applicable aeronautical experience.
(2) Must have a logbook or training record endorsement from an authorized instructor attesting that the person was found competent in the appropriate aeronautical knowledge areas and proficient in the appropriate areas of operation.
(3) Must pass the practical test.
(4) Need not take an additional knowledge test, provided the applicant holds an airplane, rotorcraft, powered-lift, weight-shift-control aircraft, powered parachute, or airship rating at that pilot certificate level.

As a balloon pilot seeking the airplane category rating with the single-engine land class you

must meet the aeronautical experience requirements in 61.109(a)
must be endorsed and found competent in aeronautical knowledge of 61.105(b), 61.107(b)(1)
must complete a private pilot airplane written exam

and then you will be able to take the practical examination and have airplane single-engine land added to your existing private pilot certificate.


How to determine if pilots in crashes flew again? I checked this post on Airliners.net , but the formatting is hard to read, and the information or hearsay may not be trustworthy. Also, I'm hoping for a more efficient, efficacious method, rather than researching each accident separately.

I'd wanted to be advised if pilots, suspected of (provable, veritable) pilot error, were still flying: Qantas Flight 1, American Airlines Flight 1420

Yet I'd be heartened and inspired by heroic or esteemed pilots, like those for United Airlines Flight 232.

How can I determine if a driver who was involved in an automobile accident is still driving?
The answer is "They probably are."

Broadly, unless the pilot died or the FAA (or equivalent authority) revoked their license as a result of their actions there is no reason the pilot wouldn't still be flying unless they decide to hang up their wings for personal reasons.
They may not be flying for the same airline, and certainly will have had some sort of remedial training (particularly if they were involved in an incident where pilot error was the cause), but damaging an aircraft is usually not a career-killing move unless one makes a habit of it.

If you want to know for certain about a particular flight crew you would need to research each accident separately (locate the pilots' information - name or certificate number - and check something like the FAA airman records branch to see if the pilot still holds a valid certificate and medical.


Does a high "wing loading" require a high approach speed or does it cause a high approach speed? Raymer says:

  Landing distance is largely determined by wing loading. Wing loading affects the approach speed, which must be a certain multiple of stall speed (1.3 for civil aircraft, 1.2 for military aircraft). Approach speed determines the touchdown speed, which in turn defines the kinetic energy which must be dissipated to bring the aircraft to a halt. The kinetic energy, and hence the stopping distance, varies as the square of the touchdown speed.

My question is : In which manner does wing loading affect approach speed?

I'll explain my question better:

The first option:
Higher wing loading implies less wing surface. Therefore, you have a higher value of stall speed (because, for the same lift needed and the same CL and the same density, with a small wing surface area, you have to increase speed to compensate for less surface), so you need a higher value of approach speed.
In this case : a higher wing loading REQUIRES a higher approach speed.
The second option:
Higher wing loading causes less wing surface. Therefore, you have less exposed surface, so you have less drag, so it’s easier to maintain a higher speed.
So if this last sentence is correct (I’m not sure), in this case it’s not only the required speed, but the CAUSED speed.

What do you think?

SOURCE:   DANIEL P: RAYMER “Aircraft Design: A Conceptual Approach”, Chapter 5 “THRUST-TO-WEIGHT RATIO AND WING LOADING”, Paragraph 5.3 WING LOADING, Subparagraph: “Landing distance”

It's the first of your options.

The effect of reduced drag with reduced wing area is dominant only at high speed, when friction drag is dominant. At low speed induced drag is the major source of drag, and with a given planform a smaller wing will create more drag at the same speed, not less.

Due to the possibility of wind shear or gusts you should keep some margin to your stall speed during approach, right down to the flare. Therefore, the safe approach speed dominates the landing distance, as Raymer writes.


How do pilots/controllers deal with overlapping transmissions on the radio? A disadvantage of the analogue radio1 used for communication is that it does not receive when it transmits. Everybody is trained to wait until the frequency is quiet before starting to talk, but it's still possible that two stations will start talking at the same time, in which case everybody else will hear an unintelligible mess but the two talking will not be aware of it. The station who talks longer won't be aware at all and if they talk for similar time, neither may be aware.

What I would like to know is how humans deal with the problem and whether there is any specific guideline for resolving these conflicts.
It seems like if the controller just says "calling centre, say again" the two may just both start talking past each other again.

1 Just like any other shared frequency radio, but digital systems seem to have more options to handle it, especially for the relatively low bandwidth requirement of voice communication.

Well in regard to "How are these situations resolved?" you've already answered your own question in a way: the intended recipient responds with something like "Blocked" or "Calling center, say again." (If they are expecting to hear from a specific aircraft they'll often respond with "N12345, say again.", and if the frequency congestion is really bad controllers may add "All other aircraft standby").
As kevin42 pointed out this is very similar to what digital CSMA/CD systems do - they detect a collision ("Blocked"), wait a while, and try their transmission again.

As a practical matter, two-way voice communication over the radio is possible, but difficult: for example a discrete "uplink" and "downlink" frequency as you have with some radio systems would be impractical in the sort of mesh topology that you have with aviation radio (you could implement it for a single air-to-ground pair trivially, but aviation radios are also used for air-to-air communication, and it's important that pilots hear what's going on as this enables them to build a mental picture of the airspace, as well as ensure that they're not blocking other pilot's transmissions).

Regarding analog-vs-digital, the traditional AM radio used in aircraft has one major advantage over its digital counterparts: when two digital signals overlap the result is garbage -- you can't recover any of the information. When two analog AM signals overlap you get heterodyning (the two signals mix, and your receiver pipes that mix into your ears).
The resulting mixed signal sounds AWFUL, there's an ear-bleeding squeal from the out-of-phase carriers and the voice modulations combine to a garbled mess much of the time, but with experience you can usually pick out one of the communications (particularly if you're close to one of the transmitters, where it will overpower the more distant signal).

The ability to step on a transmission as described above this can be useful: Instructions have been issued over a "stuck mic" before to get other aircraft off the frequency.

In a similar vein, if you have an emergency you probably aren't going to listen before you talk - you're going to key the mic with your mayday and even if the controller misses half of what you're saying under the heterodyne noise they'll know there's an emergency when they hear the other half of your transmission and tell everyone else to standby while they talk to you.

In both of those situations a digital system implementing CSMA/CD would detect that the frequency was in use and not transmit (and if were a digital system and transmitted anyway both digital signals would be garbled and unusable).


How is the moment due to pressure distribution calculated? Consider the airfoil shown, with a co-ordinate system set up from the leading edge $O$:

I want to find the moment of force about point $O$ due to pressure on an infinitesimal piece of the airfoil at point Q.

A text book I'm referring to(Fundamentals of Aerodynamics by John D Anderson) says that the moment is:
$$ dM= (p dS) cos \theta ~ x_Q $$ (where $x_Q$ is the x co-ordinate of Q)

Is this expression an approximation that assumes thickness of the airfoil to be negligible compared to the chord length?

Because, the moment should be length $OQ$ multiplied by component of $pdS$ perpendicular to $ \vec{OQ}$ ... or have I made a mistake with the physics?

If you calculate "component of pdS perpendicular to OQ" you get

$$ dM= (p dS) (cos \theta ~ x_Q + sin \theta ~ y_Q) $$
The pressure times the surface (gives you a force), splited in the two perpendicular forces(along axis) and applied at the $x_Q$ and $y_Q$ distances. Set $y_Q$ to 0 (negligible thickness) and you get the book formula.


Pitot tube pressure question I have this question is the pressure measured in the entry of the pitot tube the same  when the plane is flying headwind  or  turning a 360 degree turn while maintaining the same indicated airspeed?

Easiest thing is to imagine you're in a motorboat on a river, with a current, driving in circles at a constant water speed, indicated by a water speedometer that measures the dynamic pressure of the water more or less the same way as an airspeed.

Your path relative to the bottom of the river will be a spiral and your speed over the bottom will be faster or slower as you move with or against the current, as you make a perfect circle in the water, but your indicated speed through the water will be constant.

Airplanes are exactly the same.  The air is a big river.  You're just in it instead of floating on top.


How does a pilot board a B-2 Spirit? I haven't noticed any sort of plug door, so how do pilots board the B-2?

There is a hatch and a ladder in the bottom of the front fuselage, through which the pilots enter the bomber, as seen here:


Is GPS considered to be a navigational facility for the purposes of Ops Spec C055? For 14 CFR 119 certificate holders, Alternate Airport IFR Weather Minimums are prescribed by Operations Specification (Ops Spec) C055, specifically Table 1 of that specification.

Below is a generic example of Table 1:

The wording in this table is understandable in the context of a traditional, ground-based navigational facilities such as NDB, VOR, or ILS providing an approach. For a simple example, if an airport has an operational VOR navigational facility providing an approach, that satisfies the requirements of the first row with the result that the 400 ft ceiling and 1 sm visibility minimums might apply.

However, some §119 certificate holders are authorized to conduct GPS approaches and to use GPS approaches in determining alternate airport weather minimums. For these operators, the table needs further clarification as it does not provide a framework to derive alternate airport weather minimums based on the GPS approaches that are otherwise authorized to be used for that purpose.

No such clarification seems to be given anywhere else in C055 or elsewhere in the Ops Specs.

How do GPS approaches fit into table 1? Does the Global Positioning System (GPS) constitute a navigational "facility" for the purposes of Table 1? If so, does it constitute a single navigational facility, thereby satisfying the requirements of the first row, just as if a single VOR provided an instrument approach?

Is there guidance provided elsewhere on this?

Yes, a GPS approach can satisfy the criteria of a navigational facility for the purposes of Table 1 in Ops Spec C055.

The FAA gives the following guidance in Notice 8900.218, Alternate Airport IFR Weather Minimums:

  G. 5) Planning for use of GPS-based IAP must be based on a single navigational
  facility when determining the approach facility configuration in Table 1, even if there are two or more RNAV (GPS) approaches to different suitable runways.

This guidance doesn't go to the length of explicitly including GPS in the definition of "navigational facility". However, it does mean that GPS-based IAP can be understood to substitute for a single navigational facility, thereby satisfying the criteria of the first row of Table 1.


How can ATC distinguish planes that are stacked up in a holding pattern from each other? If I understand holding patterns correctly, several planes stack up vertically, each circulating at its assigned altitude until given permission to exit the pattern and enter an approach for landing.
My question is, don't the vertically stacked airplanes appear to be superimposed on the ATC radar? I am wondering how the ATC can keep them sufficiently separated on the screen so they can track them individually.

Sometimes we can't.
While having two radar targets presented directly on top of each other is not really an issue (most radar presentation systems lets you move the data label around freely, so you can prevent overlap), the radar system itself can sometimes confuse two targets that are very close. A radar will search for aircraft by sending out a signal and waiting for the aircraft transponder to respond. When two aircraft are very close, they will receive the request from the radar almost at the same time, so their responses will be at the same time as well. The radar will receive the two replies on top of each other, which can result in garbling (see this related question).
In some situations, the radar software can also confuse two close targets, swapping the label between them, so aircraft A is presented to the controller as aircraft B and vice versa. We also sometimes see this close to an airport, where a departing aircraft can "steal" the label from an aircraft on short final, making it look like the departing aircraft is actually the one just about to land.
As a result of these issues, we are not allowed to use normal radar separation to individual aircraft in a holding stack. Instead, radar separation will be provided to a defined holding area, which is a geographical area established around a holding stack, large enough to ensure that anyone holding will remain within. Inside a holding stack, as you correctly noted, only vertical separation is used.
Mind you, most of the time, aircraft in a holding pattern are not flying directly on top of each other. That would require them to enter the holding at exactly the same time, fly at the exact same speed and turn at the exact same rate, which just doesn't happen. So the issues described above are not a problem most of the time, but they are common enough that we have specific procedures to mitigate the risks imposed.


NASA's flying telescope SOFIA — How to find flight plans and real time location? SOFIA, NASA's Stratospheric Observatory for Infrared Astronomy:

  SOFIA is based on a Boeing 747SP wide-body aircraft that has been modified to include a large door in the aft fuselage that can be opened in flight to allow a 2.5 m (8.2 ft) diameter reflecting telescope access to the sky. This telescope is designed for infrared astronomy observations in the stratosphere at altitudes of about 12 kilometres (41,000 ft). SOFIA's flight capability allows it to rise above almost all of the water vapor in the Earth's atmosphere, which blocks some infrared wavelengths from reaching the ground. At the aircraft's cruising altitude, 85% of the full infrared range will be available. The aircraft can also travel to almost any point on the Earth's surface, allowing observation from the northern and southern hemispheres.

has arrived in Christchurch New Zealand for a period of airborne observations; 1, 2. More about SOFIA can be found at SOFIA Science Center official website.

I know that there were plans to try to observe a rare occultation event, where the asteroid 2014 MU69 around 17-July 2017 will pass in front of a faint star and block out its light. There are predictions (data and maps) shown below, and a cryptic list of SOFIA flight plans can be found here.

You can read more about what's happening in this interesting answer as well as in the original question there. This is important because 2014 MU69 is the next target for the New Horizons spacecraft after its Pluto flyby in July of 2015.

QUESTION: If I wanted to look for official flight plans, and watch for any possibility of near real-time data (even if intermittent) on FR24, how and where could I look up the SOFIA aircraft?

above: predictions from here.

below x2: images from Space.com's Photos from SOFIA, NASA's Flying Telescope (Gallery); click them for full size images.

I don't know where to find flight plans, but according to Wikipedia, the aircraft is a Boeing 747SP with registration NASA747.

"747SP" set as aircraft type filter in flightradar24 was enough to find SOPHIA right now :


What's the name for the structure that helps stop the nose wheel in Boeing 747-400? From my understanding the nose wheel of a Boeing 747 does not have brakes, and as such when it is retracted it is still spinning. However, there are two "plates" that make contact with the wheels and slow them down, eventually stopping them.

I am curious as to whether someone could provide some more information about this structure, especially the name.

See the image below:

Thank you!

They are called Snubbers or scuff plates. Spinning tires rub against them on retraction.


What are the advantages and disadvantages of having landing gear doors? To make comparison easy, let us take the example of B737 and A320, both similar aircrafts with retractable landing gear.

As seen on the photo below, the B737 doesn't have gear doors for the wheels,

but the A320 does

Obviously, Boeing and Airbus made different choices for the same feature and both seem reasonable. Both aircraft models are well accepted by the airlines.

What are the advantages and disadvantages of both designs?

EDIT: I put links to other images where both aircraft are retracting landing gear after take off. The difference is obvious as we can see the landing gear doors operated for the A320 and no doors for the B737's wheel.

Benefits of gear doors

With gear doors, there are fewer constraints on the retracted gear position. This is especially important in larger aircraft with larger and more complex landing gear. It doesn't need to be flush with fuselage or streamlined (737 also uses hubcaps).
The gear doors provide a good aerodynamic surface
Opening to gear bay can be larger and easier to access

Drawbacks of gear doors

Extra weight for the door and the mechanisms
Extra complexity of opening another door (possibility for things to go wrong)


How can I know if a landing exceeds the hard landing threshold for a Cessna 172S? How does a pilot determine the difference between a firm landing, and one that needs to be written up for a hard landing inspection in a Cessna 172S?

Was it uncomfortable or did it hurt?

If it hurt you, it probably hurt the plane. That 500 pound engine is hanging a foot and a half from the firewall by four bolts. It's not hard to cause some damage.

Anyway, if you think it needs to be checked, just say something to the mechanic. It's not that time consuming, and it's better to be safe than sorry.


Why are fighter jets equipped with dorsal fin? I don't really get whats the purpose of dorsal fins and what they do with the flow over the vertical stabilizer. I noticed on most single tail configured aircrafts are equipped with a dorsal fin like the f 16.

There are two features that you may be referring to.

A) Is an antenna that is shaped to provide low drag. Not all F16 have this.

B) The true dorsal "fin":

increases structural strength
decreases drag by providing a fillet for the vertical stabilizer,
improves stability about the vertical axis,
and specifically in the case of the f16 (when installed)
     aerodynamically blends the drag chute pack (box at base of Rudder)
many aircraft use this as a convenient air intake for
     equipment or auxiliary cooling.

source


What is the temperature of intake air at several speed of sound intervals from 1x to 10x? I watched a YouTube movie about Reaction Engines development of the Sabre engine which main feature is cooling intake air. However, I cannot find an overview of the temperature of intake air at different airspeed levels. I am looking for an overview based on speed of sound levels and the increase on intake air temperatures.

Thermodynamics is your friend here. Compression in a ram intake is ideally isentropic (meaning entropy stays constant, so the whole process is reversible). In reality, some viscous losses cannot be avoided but are in the low percentage range in a well designed intake.

The temperature $T$ in isentropic compression from a state 1 to a state 2 can be calculated from the pressure $p$ and the ratio of specific heats $\kappa$:
$$T_2 = T_1\cdot\left(\frac{p_2}{p_1}\right)^{\frac{\kappa-1}{\kappa}}$$

$\kappa$ is 1.4 for air, so if the saber engine flies in air 250 K cold (-23.15°C) and a pressure of 500 mbar, and the intake compresses this air by a factor of 10 to 5,000 mbar, the temperature will ideally rise to 483 K (210°C). In reality, this might well be 220°C or 230°C due to viscous heating of the air in the process.

How the temperature ratio depends on flight Mach number $Ma$ (again, ideally) can be seen from this plot, based on this way to calculate the pressure rise:


Would ground effect and FOD ingestion be factors at high speeds close to the ground? How could flight 77 into the pentagon overcome the compression lift of the ground effect at 460 KIAS that close to the ground? Also wouldn't the engines ingest FOD at that power setting that close to the ground on the approach?

The amount of time a plane in a dive spends close enough to the ground to ingest foreign objects and thereby damage its engines is of order ~fractions of a second.

For a plane that is about to strike a building on the ground, the idea of FOD damage to its engines is not even relevant.


What trajectory do I fly if bearing angle is constant? Let's suppose I am flying at constant bearing (initial and final heading are equal and constant) relative to the geographical north pole; what kind of trajectory would I be flying?

The term bearing is not so clear, as the link to another answer in the comment shows.

But let's say bearing means the angle between the track (over ground) of an aircraft and a fixed location. This position usually is the magnetic or (true) geographic north, but within the context of this question, it could also be any location on earth.

If the bearing is 90° or 270° (perpendicular to fixed location), the aircraft just flies circles, in case of using the geographic north, it flies along a line of constant latitude.

If the aircraft is flying at a different angle, the trajectory is a spiral, more precisely a Rhumb line, with curls around that location and the location at the opposite side of the earth:

  (Source)

BUT due to the magnetic deviation, the magnetic field doesn't point to the (magnetic) north pole everywhere on earth.

I simulated the trajectory for a quite similar question here. The red arrows indicate where the needle of a compass points to. The black line is the trajectory for an aircraft flying a 90°-track with respect to the local magnetic field. It is just a deformed circle.

The blue line is the trajectory of an aircraft flying a 93.6°-track. This is a deformed Rhumb line, and the aircraft coming from KLAX will circle around the magnetic pole at some point like a moth around a light. (at least mathematically)


What are the ANT and ADF modes on an NDB receiver? I am seeing this in a simulator, so I don't have a manual for it…
On the Bendix King KR87 NDB receiver, the leftmost button labelled “ADF” switches an indicator above it from “ANT”

to “ADF”

When pushed, the needle on the direction indicator indicates towards the NDB (if in range). When popped, it does not, at least for the NDB stations.
So I am wondering, what does this switch change and why it is needed?
(screenshots taken from FlightGear simulator by me)

ANT mode improves the audio reception when listening to a station's morse code identifier or whatever else is being broadcast.  Normally the directional needle gets parked at 3 o'clock when in ANT.  NDBs can also have other broadcasts besides station ident, like ATIS or AWOS weather data, etc., and in some cases use of ANT may make the difference between making out what is being said, or not.  It may also improve AM radio audio reception, but not sure.  I've used the ADF to listen to music back in the day, but never had to go to the trouble to switch to ANT to hear it.
Here's a link to a KR 87 manual.


Is an elevon (elevator + aileron) considered as an all-moving control surface? The delta wing on Concorde uses elevon as its control surface. Is the elevon considered as all-moving control surface?

An All-Moving control surface is a surface where the complete structure acts as a stabilizer. For example, in case of a horizontal tailplane which can be completely moved to work as an Elevator - instead of just the trailing edge of the horizontal tailplane moving to work as a control surface. In such cases, it is called a Stabilator (Stabilizer + Elevator). Elevon is a control surface which is part of the main wing, but the trailing edge of the wing is moved to get Yaw and Roll control. This makes Elevon a normal control surface and Not an all moving surface.


Could I use a powered parachute to fly around New York City? NYC traffic is so horrendous that it would be pretty convenient to be able to take off with a powered parachute (PPC) from the top of a building or from a park and be able to fly above all the traffic to your destination. I'm wondering if anyone has any insight into this.

I know the class B extends to the surface in upper Manhattan but how about downtown? Class B starts at 1100' (plenty of space for a PPC); could one fly around there without talking to anyone? Also, could one potentially get a class B clearance to fly around at low altitudes in upper Manhattan?

Finally, does anyone know how much space a PPC can take off in? Is there any way a STOL PPC could take off from an NYC rooftop (or more realistically an open space such as Central Park)?

Don't give this question too much thought, just something fun to consider. I think the real limitation would be regs here, even if you could go to the Great Lawn or something to take off.

Pretty simple, powered parachutes fall under the ultralight vehicle category, which is 14 CFR 103:

14 CFR 103.15 Operations over congested areas.:

  No person may operate an ultralight vehicle over any congested area of a city, town, or settlement, or over any open air assembly of persons.

And Also:

14 CFR 103.17 Operations in certain airspace.

  No person may operate an ultralight vehicle within Class A, Class B, Class C, or Class D airspace or within the lateral boundaries of the surface area of Class E airspace designated for an airport unless that person has prior authorization from the ATC facility having jurisdiction over that airspace.

It is highly unlikely that you would get a waiver to fly your PPC in the Manhattan Class-B, even if 103.15 didn't preclude it in the first place. You can fly in Class-B in certain areas, but you do need to be talking to ATC.


What is the ambient temperature used in RTCA/DO 160? I was going through RTCA/DO 160D for some work-related issue. I went through the whole document but nowhere does it define what the "ambient temperature" value is? In one place it defines +15 to +35 degrees Celsius as one of the parameters for ambient conditions. Does anyone know what is the value of ambient temperature, or it is generic room temperature of 20-25 degree C?

Ambient is the conditions in the test lab.  DO-160 defines it in sec 3.5:

  3.5 Ambient Conditions

  Unless otherwise specified, all tests shall be made within the
  following ambient conditions:

  a. Temperature: +15 to +35 degrees Celsius.

  b. Relative Humidity: Not greater than 85 percent.

  c. Ambient Pressure: 84 to 107 kPa (equivalent to +5,000 to -1,500 fi)
  (+1525 to -460 m).

  When tests are conducted at ambient conditions that differ from the
  above values, the actual conditions shall be recorded.

So anything within this range is acceptable and if it isn't within the range, just document what it is.

You'll also note that in each of the temperature profiles, the test starts at ambient at T0 and shifts to the first controlled test temp at T1. DO-160 includes the following Note as the time to transition from ambient to the test temp will vary:

  1) Temperature rate from T0 to T1 is not specified.

You have to remember that DO-160 is about testing extremes. If the equipment can't operate at any point in the ambient range, it's unlikely to operate at the extremes.

BTW, the latest version of DO-160 is rev G.  You should use it for new products.  Using rev D would only be appropriate for re-testing of a product originally developed to DO-160D.


How many active Cessna 172 aircraft (or any other make/model) are there in the United States? I define "active" in accordance with the FAA's definition: "An active aircraft is one that flies at least one hour during the year."
The Bureau of Transportation Statistics (BTS) provides a summary of aircraft registered based on aircraft configuration (fixed wing, rotorcraft, single/multi engine, turbo-prop, jet, etc.) and GAMA has a report on the annual shipments, but not the totals of active aircraft.
The FAA's downloadable aircraft registration database is cryptic to the point where I can't figure out what a specific entry means, and the online search interface returns data for one search at a time.
Is there a data source that provides the count of a given make and model across the active fleet of aircraft in the US?
(PS: If there is some trick to decrypting the FAA registration database that would be be great to know as well!)

The FAA database
In the zip-file you find a number of text files, and a PDF file called 'ardata.pdf'. This file is the key to the other documents.
The 'master.txt' file contains all aircraft records and 'ACFTREF.txt' contains all aircraft types and their id's in the register.
The third column in 'master.txt' is 'MFR MDL CODE', which corresponds to the first column in 'ACFTREF.txt' called 'CODE'.
By finding the right aircraft codes you can find the number of corresponding aircraft in the 'master.txt' file.
My procedure
I imported both text files in Excel and filtered the aircraft file to contain only the Reims and Cessna 172 variants. This resulted in a list of 54 variants.
Then I filtered the master file using the codes I found, resulting in 20,789 aircraft. This number is the total number of Cessna 172s that have a registration assigned to them in the United States.
However, not all aircraft with an assigned registration are actually active. For example, N-numbers can be assigned to reserve a registration while the aircraft is being transferred/imported or may be cancelled while the N-number still is assigned. This is also included in the 'master.txt' file as the 'STATUS' column.
I decided to only look for valid registrations (indicated by the letter 'V'), which returned 18,914 results. So there are 18,914 civil Cessna 172s with a valid registration in the United States. The actual number of Cessna 172s in the US will be lower, since US-registered aircraft may also be operated in other countries. And some of the aircraft with a valid registration may not be active, but I assume that number is low, so a guess of 18,000-19,000 active C172s will be accurate.


Is there a comprehensive list of IFR terms with definitions? Is there a comprehensive list of IFR terms with definitions easily available?  I am trying to make some flash cards for study

The FAA's Instrument Flying Handbook would be a good start, in particular the glossary.


Are carbon fiber/composite aircraft at greater risk from lightning? Modern jetliners are protected from lightning by their metal skin. When they are struck by lightning, the electricity almost invariably travels through the skin and out the other side without damaging the internals or passengers.

While carbon fiber is electrically conductive, I have not been able to find any resources with a direct comparison between it and aluminum. This forum post would seem to suggest that it is less conductive, mentioning that

  Although partially conductive, carbon fiber materials, and carbon fiber masts, are regarded as non-conductive (nonmetallic) for the purpose of this technical information report. For lightning protection, carbon fiber masts require the addition of an air terminal and primary conductor as described elsewhere in this technical information report.

Is carbon fiber as electrically conductive as aluminum, and if not, does this pose a problem in the event of a lightning strike?

From Boeing's AERO:

  Areas that have the greatest likelihood of a direct lightning attachment incorporate some type of lightning protection. Boeing performs testing that ensures the adequacy of lightning protection. Composite parts that are in lightning-strike prone areas must have appropriate lightning protection.

  Lightning protection on airplanes may include:

  Wire bundle shields.
  Ground straps.
  Composite structure expanded foils, wire mesh, aluminum flame spray coating, embedded metallic wire, metallic picture frames, diverter strips, metallic foil liners, coated glass fabric, and bonded aluminum foil.

That suggests for composite areas that are vulnerable to lightning strikes, extra measures are taken to enhance the conductivity.


Which refers to CFI renewal based on pass rate, "activities" or "duties and responsibilities"? It's that time again, gotta re-up my CFI.

I always forget when I'm filling out IACRA whether CFI renewals (in the United States) based on student pass rate percentage are considered "activites" or "duties and responsibilities".

Which of the two, "duties and responsibilites" or "activities" is the appropriate choice when submitting an IACRA application for a CFI renewal based on pass rate?

You want to check the Activities box.
The phrasing is a little weird, and it certainly doesn't line up with the regs (see 14 CFR §61.197), but that's what you want:

(2) Submitting a completed and signed application with the FAA and satisfactorily completing one of the following renewal requirements—
(i) A record of training students showing that, during the preceding 24 calendar months, the flight instructor has endorsed at least 5 students for a practical test for a certificate or rating and at least 80 percent of those students passed that test on the first attempt.
(ii) A record showing that, within the preceding 24 calendar months, the flight instructor has served as a company check pilot, chief flight instructor, company check airman, or flight instructor in a part 121 or part 135 operation, or in a position involving the regular evaluation of pilots.
[...]

So, best as I can tell, that means:

§61.197(2)(i) is activity - 80% pass rate on 5+ students in the preceding 24 calendar months.
§61.197(2)(ii) is duties and responsibilities - serving in a position that involves standardization flights or stage checks.

Disclaimer: unfortunately, all of the AOPA material on CFI renewal is designed to get you to buy their FIRC (eyeroll), and the unhelpful FAA IACRA document for instructors says squat as well. I'm having a hard time finding a reference that proves my interpretation, but I know it's correct!


How do individually controlled feather like winglets work? I want to know how the individually controlled feather like winglets work on controlling and rolling by reducing drag.(concept of airbus bird's of prey)
I just need a detailed review of the aerodynamics and its mechanics and how it reduce drag and what are its effect on L/D ratio etc as i am a aeronautical student i wish to know more about it on the futuristic design so it can be helpful in my projects

The "Bird of Prey" is nothing more than an artist's conception at this point so there is nothing to review from a mechanical design standpoint.

Somebody thought it would be neat to make a plane that looked like a bird, but the methods by which birds achieve flight is far different than in modern aircraft.  I don't believe there are any practical advantages to having a control surface that looks like a feather, and "function follows form" isn't a design strategy that has been proven to work.

I doubt we will ever see one fly, but it would make a fanciful sculpture, like this:


Is it mandatory to go missed following full scale CDI deflection? In the USA, AIM 5-5-5 paragraph a1 specifies when a missed approach is required. I have also heard that a missed approach is required if the aircraft reaches full scale CDI deflection on a localizer course (this old CFI test standards doc from 2001 says it’s recommended in paragraph b).
Where is this requirement written? Is it true for all types of approaches, or only ILS and LOC?

The point being, once you've reached a full scale deviation in IMC, there's no telling how much beyond it the airplane has gone. Your USA AIM 5-5-5 is quoted here, and point 'b' is sufficient to conclude an immediate Missed Approach:

5-5-5. Missed Approach
a. Pilot.
1. Executes a missed approach when one of the following conditions exist:

(b) Determines that a safe approach or landing is not possible.

With a full scale deviation and the LOC beam narrowing as you approach the RWY, what is the pilot going to steer at low altitude and descending lower in IMC? What is the IFR reference that the pilot would use? A VOR course? An FMC course? A locator beacon (NDB)? Even if these existed, there would have to be an IFR procedure to continue to landing, including revised minimums.
Quoted below are the Elements of a Stabilised Approach, widely accepted as The Gospel by regulators and industry, All manufacturers have incorporated into their procedures, this concept from the Flight Safety Foundation's ALAR 'toolkit':
(ALAR = Approach and Landing Accident Reduction )
(notice too, the applicability to VMC conditions)

Most airlines and other aviation organisations specify minimum acceptable criteria for the continuation of an approach to land. These vary in detail but the following summary published by the Flight Safety Foundation is one view of the important considerations.

Their Approach-and-landing Accident Reduction (ALAR) Briefing Note 7-1 suggests that "all flights must be stabilised by 1000 feet above airport elevation in IMC and 500 feet above airport elevation in VMC. An approach is stabilised when all of the following criteria are met:

The aircraft is on the correct flight path
Only small changes in heading/pitch are necessary to maintain the correct flight path
The airspeed is not more than VREF + 20kts indicated speed and not less than VREF
The aircraft is in the correct landing configuration
Sink rate is no greater than 1000 feet/minute; if an approach requires a sink rate greater than 1000 feet/minute a special briefing should be conducted
Power setting is appropriate for the aircraft configuration and is not below the minimum power for the approach as defined by the operating manual
All briefings and checklists have been conducted
Specific types of approach are stabilized if they also fulfil the following:
ILS approaches must be flown within one dot of the glide-slope and localizer
a Category II or III approach must be flown within the expanded localizer band
during a circling approach wings should be level on final when the aircraft reaches 300 feet above airport elevation; and,
Unique approach conditions or abnormal conditions requiring a deviation from the above elements of a stabilized approach require a special briefing.

An approach that becomes unstabilised below 1000 feet above airport elevation in IMC or 500 feet above airport elevation in VMC requires an immediate go-around.


What frequency should be used for air-to-ground communication other than airport ground operation? On a VFR flight, what frequency should be used to talk to somebody on the ground in USA?

In another word, if I am overflying my house and I would like to talk to the people on the ground, what frequency should I be using? Is it even legal to do something like this?

Radio frequencies in the USA are assigned by the FCC, not the FAA. There's no 'private' air-to-ground frequency mentioned in the AIM but section 4-1-11 does say that the FCC has assigned 122.900 as a MULTICOM frequency for:

  Activities of a temporary, seasonal, emergency nature or search and
  rescue, as well as, airports with no tower, FSS, or UNICOM

Arguably your fly-by is "temporary activity", however the definition of MULTICOM is:

  A mobile service not open to public correspondence used to provide
  communications essential to  conduct the activities being performed by
  or directed from private aircraft

So if your fly-by is "essential" (and safe!) then I guess you could use 122.9. There are procedures for requesting temporary air-to-ground frequencies for air shows, but that's obviously a special case.

As for legality, it seems that you need an FCC license to use an aviation handheld radio on the ground:

  You may only use your hand-held aircraft VHF radio in your aircraft
  under the terms of your aircraft license. You are required to have a
  separate Ground Station license to operate your radio on the ground.

But because this is more about FCC regulations than FAA ones, I suggest that you ask on ham.SE; they'll probably know a lot more about how it all works.


How can I improve the reception of my coaxial collinear antenna (1090 MHz)? I've built a coaxial collinear antenna (16 arrays), according to this guide but having some issues picking up traffic from the West (?). I'm not very experienced in the area, so I've no idea where to start or why this is happening.

The antenna is located in my living room and is aprox. 2 meters.

If the antenna is located in your living room, then the incoming 1090 MHz signals will be blocked by your house. 1090MHz signals are more-or-less line of sight. They don't travel very far through concrete or wood and are severely attenuated by glass, especially is you have energy efficient windows.

I suspect you have a window towards the East or South East so that you have some signal reception from that direction. Try to put the antenna outside, preferably on top of your house to improve your signal reception.


Why does U.S. airspace revert to class E above flight level 600? According to Wikipedia, airspace defaults to class E below 18,000 feet AMSL (that is, all airspace below 18,000 feet AMSL is class E unless otherwise specified), whereas all airspace from 18,000 feet AMSL through FL600 is class A... but, above FL600, U.S. airspace reverts to class E.

Why does U.S. airspace revert to class E above FL600, instead of simply staying class A all the way up?

You ask why doesn't it go all the way up... but all the way up to where? It's somewhat of an arbitrary limit, but FL600 tends to generally be the top of the troposphere, so it seems like a good choice if we're picking numbers.

One reason could be that the FAA AIM (Airman’s Information
Manual) says that the top of the service volume for the high-altitude
VORs is 60,000 feet above the VOR facility, so it seemed like a good altitude to end the restriction of Class A, that all aircraft must be on an IFR flight plan.  If you're tooling around above FL600, perhaps you don't want/need to be on an IFR flight plan (think experimental planes, rocket launches, etc.)

It could also be that when they set up the airspace, there wasn't a whole lot going on above 60,000 feet, and given that survivability at that altitude without a space suit is low, so there weren't a lot of aircraft that high, plus the top of the troposphere is around that altitude, it just seemed to be a good number. Most commercial aircraft have a service ceiling well below FL600 (the Boeing 777 ceiling is FL431), and since Class A is positively controlled airspace with everyone having to be on an IFR flight plan, aircraft above FL600 are not as common, and so it didn't make sense to spend resources (at the time) to force things that high to go through some kind of waiver process, or put the effort in maintaining the services required to provide IFR separation services for aircraft that high.

However, as we look to the future, there is a great report from Embry-Riddle about Safe Operations Above FL600 that sheds some light on what goes on above FL600 and considerations that should be taken into account going forward as the airspace starts to get more crowded with drones, and planned spaceflight and supersonic transports.


How would a low-airspeed fixed-wing drone be designed to reduce effects from gusts and wind shear? In a story I am working on, the characters need a fixed-wing drone that can rendezvous with a blimp, where by "rendezvous" I mean "come within a very short distance at low relative airspeed".  The challenge is that the blimp will typically be flying through powerful gusts and abrupt wind shear—ideally hurricane-like conditions or worse.  The characters have the time and resources to design and build a custom drone for this purpose, and while I realize that I will probably have to stretch credulity at some point, I'd like the drone's design to at least seem plausible.  Hence my question: What would a drone custom-built for such missions look like?

Here's what I found so far (and which I hope is accurate):

Wing loading is the single largest factor in gust response.  If the only concern were dealing with the wind, the drone would have as much wing loading as could be managed.  However, I also need the rendezvous to happen at low (blimp-relative) airspeed.
A long wingspan is a liability in wind shear, increasing the chance for an asymmetric stall and upping the rolling moment even if there is no stall; the drone should probably have its wings tucked tight to its body.
Given the risk for sudden stalls, the wings should be designed with substantial washout.  They will probably not be swept (in either direction), both because drag reduction is not a driving consideration and because swept wings would tend to push the drone nose-up in a stall.
Anhedral wings, while less good for stability, would cause the drone to bank into crosswinds, which could be useful given the feedback delay the drone pilot has to deal with, and some of the stability could be made up by placing the wings high, creating a pendulum effect.  But maybe stability is the more important factor here.
An inverted tail will cause the drone to both roll and yaw into crosswinds.  I am not sure whether an inverted T or inverted V would make more sense.

I have also found some planes that are intentionally flown into hurricanes: the Lockheed WC-130, the Lockheed WP-3D Orion, the Gulfstream IV, the Douglas DC-8, NASA's ER-2 (a Lockheed U-2 derivative), and the AAI Aerosonde, the only drone on my list.  The last, at least, backs up some of the ideas I have above.

First, kudos for the well-researched question! You certainly did your homework before coming here.

As you realized yourself, your requirement is quite contradictory. I also wonder what blimp would be flown into hurricanes, but I leave that aside for the moment.

In order to reduce gust susceptibility, a variable configuration would be one option. However, just when you want steady flight in gusty conditions, you also will fly slowly, so variable wing sweep or elaborate wing flaps will not help. The next option which combines low flight speed and high wing loading would be some direct lift, like in the VTOL-designs of the 1960s. Since the direct lift is needed for a short time and when propulsive demands are low, an engine like the Rolls-Royce Pegasus would allow to add lift that is less affected by gusts than the wing.

Make sure your design will draw ample bleed air in order to feed the reaction control system, and maybe a gyro platform to control this system, and the contradiction can be resolved.

Stalls should now be less of a concern, too. Much of how much lift is lost in a stall depends on the choice of airfoils, and if you use one with benign stall characteristics, stalls can be tolerated.

Anhedral is a poor idea, however, especially if you use unswept wings. Only if you have a high wing on a large fuselage can anhedral be justified. Examples are the Harrier jump jet and the F-104 Starfighter, where the large T-tail made wing anhedral necessary. You want moderate dihedral in order to make the aircraft roll in a sideslip. This rolling motion will tilt the lift vector sideways and pull the aircraft away from the sideslip condition.

Also, please reconsider whether there really is such a thing as a pendulum effect.

Regarding the tail: The best one is as symmetrical as practical.


How many commercial passenger aircraft suffer tail strikes in a given year? This is inspired by a lengthy set of comments on this question (for reference).

I've been searching the internet high and low for reliable information on how many tail strikes occur per year for commercial passenger aviation, and I can't seem to turn up anything reliable.  Articles I've read range from saying they happen maybe once a year to several times a year, but none of them show hard numbers or list all incidents (here, here and here for a sampling.)

If anyone has verifiable hard numbers on this, I would love to see them...

A preliminary answer might be the results of searching incident reports at AVHerald

Accident    Ryanair B738 at London on Jul 29th 2014, tail strike on landing
Incident    Ryanair B738 at Alicante on Mar 27th 2013, tail scrape on takeoff
Report      Jazz DH8C at Gaspe on Sep 10th 2012, hard landing and tailstrike
Incident    Smartlynx Estonia A320 at Tallinn on Jul 31st 2014, tail strike on landing
Accident    Swiss A321 at Geneva on Mar 9th 2014, tail strike on landing
Incident    ANA B763 at Tokyo on Mar 13th 2014, suspected tailstrike on departure
Accident    TAROM B733 at Bucharest on Apr 4th 2011, tail strike
Accident    Lufthansa A333 at Chicago on Mar 5th 2013, undetected tailstrike on takeoff
Incident    Transavia B738 at Amsterdam on Apr 29th 2013, suspected tailstrike
Accident    Aeromexico B762 at Madrid on Apr 16th 2013, tail strike on takeoff
Accident    Titan B733 at Chambery on Apr 14th 2012, tail strike
Accident    Sata A313 at Ponta Delgada on Mar 2nd 2013, tail strike on landing
Report      Jetstar A320 at Sydney on Feb 6th 2012, thrust lever asymmetry during takeoff and early rotation
Accident    China Cargo B772 at Copenhagen on Apr 17th 2011, tail strike on go-around
Accident    Austrian A321 at Manchester on Dec 23rd 2011, tail strike during go-around
Incident    Air Atlanta A306 at East Midlands on Jan 10th 2011, tailstrike on landing, go-around with open thrust reverser
Incident    Air Atlanta A306 at East Midlands on Jan 10th 2011, tailstrike on landing, go-around with open thrust reverser
Accident    Emirates A345 at Melbourne on Mar 20th 2009, tail strike and overrun on takeoff
Accident    Gol B738 at Porto Alegre on Nov 16th 2011, tail strike on landing
Report      Lufthansa MD11 at Mumbai on Jun 11th 2011, tailstrike on landing
Accident    China Cargo B772 at Copenhagen on Apr 17th 2011, tail strike on go-around
Report      Kam Air DC86 at Manston on Aug 11th 2010, tail strike on takeoff
Accident    TUIFly B738 at Tenerife on Mar 27th 2011, rejected takeoff due to tailstrike
Report      Tunisair B736 at Paris on Oct 10th 2008, rejected takeoff after rotation
Accident    United Airlines B744 at Sydney on May 7th 2010, tail strike on takeoff
Accident    Northwest A320 at Denver on May 4th 2009, tail strike on landing
Incident    Austrian B763 at Beijing on Jan 29th 2010, tailscrape on takeoff
Accident    Northwest A320 at Denver on May 4th 2009, tail strike on landing
Report      Ryanair B738 at Dublin on Sep 11th 2008, tailstrike on takeoff
Crash       Avient Aviation MD11 at Shanghai on Nov 28th 2009, overran runway on takeoff
Report      Thomas Cook A332 at Montego Bay on Oct 28th 2008, mislaid manual leads to wrong takeoff speeds
Report      Thomson Airways B763 at Manchester on Dec 13th 2008, tail strike
Incident    PIA B743 at Lahore on Jun 23rd 2009, suspected tail strike leads to discovery of tail strike
Incident    Australian Air Express B463 at Brisbane on Oct 23rd 2008, tail strike on hard landing
Accident    Emirates A345 at Melbourne on Mar 20th 2009, tail strike and overrun on takeoff
Accident    Emirates A345 at Melbourne on Mar 20th 2009, tail strike and overrun on takeoff
Report      Aigle Azur A321 at Algiers on Jan 8th 2008, tailstrike during landing
Incident    Pegasus B738 at Cologne on Dec 20th 2008, tailstrike on takeoff
Report      Flybe DH8D at Paris on May 28th 2008, tailstrike
Report      My Travel A320 at Kos on Jul 5th 2007, very hard landing
Incident    Cargo B B742 at Brussels on Oct 27th 2008, tail strike on takeoff
Incident    Ryanair B738 at Dublin on Sep 11th 2008, tail strike on takeoff
Accident    Swiss RJ100 at London City on Aug 18th 2007, tailstrike on landing
Incident    Comair (SA) B732 at Cape Town on May 3rd 2008, tail strike
Incident    Ryan Int B738 at Milwaukee on Mar 14th 2008, tailstrike on takeoff
Accident    RyanAir B738 at Stansted on Feb 18th 2008, tailstrike on takeoff
Accident    RyanAir B738 at Stansted on Feb 18th 2008, tailstrike on takeoff
Incident    Delta B767 at Moscow on Jan 26th 2008, tailstrike on takeoff
Accident    Swiss RJ100 at London City on Aug 18th 2007, tailstrike on landing
Incident    LaudaAir B738 at Linz on Oct 2nd 2007, tailstrike at about taxi speed
Accident    Swiss RJ100 at London City on Aug 18th 2007, tailstrike on landing
Accident    Swiss RJ100 at London City on Aug 18th 2007, tailstrike on landing
Accident    Swiss RJ100 at London City on Aug 18th 2007, tailstrike on landing
Accident    Swiss RJ100 at London City on Aug 18th 2007, tailstrike on landing
Incident    RyanAir B738 at Dublin on Mar 20th 2007, tailstrike during takeoff

You need to check some of these, some of them mention tailstrike where none occurred (e.g. inapppropriate pilot action due to fear of tailstrike)

You may need to define tailstrike, maybe a controlled flight into terrain sometimes involves a tailstrike but wouldn't be categorised as such.


Do solo night time and “towered” landings total separately toward the solo night requirements in FAR 61.129? FAR 61.129(a)(4)(ii) reads as follows for an applicant for commercial airplane single-engine, and makes similar provisions for other categories and classes.

(4) Ten hours of solo flight time … that include -
…
    (ii) 5 hours in night VFR conditions with 10 takeoffs and 10 landings (with each landing involving a flight in the traffic pattern) at an airport with an operating control tower.

Must a solo flight be conducted at night and involve at least one landing at an airport with an operating control tower to count, or do night time and “towered” landings total separately? Given a pilot with five hundred solo night hours all to pilot-controlled airports who goes up at night to fly ten laps around the patch at a nearby Class C, where does that pilot stand with respect to the requirement above?

501 solo night hours and 10 towered landings, or
1 solo night hour and 10 towered landings

Night time does not need to include a landing at a controlled airport to count.  You just must have at least 10 solo night landings at a controlled tower, as well as 10 hours of solo night time, they don't have to happen together (though whatever time it takes you to get those landings counts toward the 10 hours too).

The pilot in your question would have 501 solo night hours and 10 towered landings.


Was NextGen simulated/tested against alternatives? Researchers in aviation usually test systems in simulated environments to find out the pros, cons, challenges, etc. Now ADS-B is a key component of NextGen and its European counterpart. And I've seen papers/researches on applications than utilize ADS-B.
For the US, even shortly before the current pandemic, the Office of Inspector General was not too thrilled with NextGen, with the latest in a series of audits being announced in Oct of 2019. Based on earlier audits, the benefits will not be realized before 2025, and that was before the pandemic, and the latest audit is currently questioning the benefits:

Given concerns over the progress and benefits of NextGen, the FAA Reauthorization Act of 2018 mandated that our office study the potential impacts of a significantly delayed, diminished, or completely failed delivery of FAA's NextGen initiative.

Two years ago I asked, What benefits does Automatic Dependent Surveillance bring to continental ATC over Mode S? Of the pros noted, there were these two relevant to my question here:

ADS-B updates faster
ADS-B is cheaper

Since one of NextGen's big aims is boosting the traffic capacity, which is mostly limited by separation in the terminal environment, were alternatives tested? For example:

Sector limited radars (one per approach end) that would provide the faster update rates. (Radars that don't make complete revolutions.)
Its relative cost, i.e. equipping thousands of planes versus tens of super busy airports.

If no, were there [then-valid] reasons?

NextGen is an FAA programme that strives to modernise America's air transportation system to make flying  safer, more efficient, and more predictable.
NextGen is not one technology, product, or goal. As such, you can't test NextGen against an alternative.
Also the major benefit of ADS-B is not that it providing faster updates or that it is cheaper. It allows for a paradigm shift in ATC.
Separation minima in the TMA are not primarily driven by surveillance performance. They are driven by the latency in the chain from surveillance -> interpretation of situation by controller -> deciding resolution of situation by controller -> communicating instructions to affected aircraft -> pilots implementing the instructions -> aircraft reacting to pilot commands. Wake turbulence is another driving factor. Surveillance update rate is a minor factor in all of this.
The more aircraft there are in an area, the more the controller needs to monitor and to communicate, the more critical the separation becomes. We are reaching a fundamental barrier which can't be solved by adding more air traffic controllers. The only way to break that barrier is to automate some of the functions the air traffic controller performs in the Air Traffic Control System, or to offload them to the cockpit. ADS-B is an enabler for that.
ADS-B allows for the development of a Cockpit Display of Traffic Information (CDTI), increasing the situation awareness in the cockpit and thereby improving safety.
ADS-B enables applications like Cockpit based Interval Management, where the pilot receives speed and heading instructions from a system based on ADS-B in order to achieve a spacing distance or spacing time with respect to another aircraft, taking workload of the air traffic controller while achieving a higher arrival throughput.
ADS-B enables CDTI Assisted Visual Separation (CAVS), which will allow airport to achieve visual arrival rates in marginal visual meteorological conditions.
ADS-B allows for new types of TCAS, reducing the RF overload on the radar frequencies that are congested in some area. (Your suggestion of just adding radars on every runway end is probably achieving the opposite of what you want. It causes transponder overload and a very poor update rate as a result)
ADS-B allows for space based surveillance, providing global coverage and thereby improving safety and efficiency on oceanic flights.
I am sure alternatives were discussed. Some applications did not make it through the whole process, others did. But ADS-B, conceptually, is fundamental to the many of the changes in NextGen. That is not to say that ADS-B is perfect, or even good. On the technology level it could be a lot better and for example a lot more secure. But it would have costed a lot more too.


Has fuel boiling ever been an issue for high altitude aircraft? Are special measures being taken to prevent fuel from boiling inside the fuel systems at high altitudes? If so, when (with what aircraft) did this practice start?
(question is pertaining to air-breathing, hydrocarbon fueled engine powered aircraft)

Yes, e.g. U2

  Both planes, equipped with the older -37 engines, landed at Kirkland Air Force Base Albuquerque, New Mexico. After each development flight, a careful accounting is made of fuel consumption. A special fuel, dubbed lighter fluid, was developed by Shell Oil Company specifically for the Angel, and the finished product was shipped to Nevada in tank cars labeled LF 1A. This blend will not boil at the low pressures encountered at altitude, yet will still give adequate air starts. It is so involatile that fire seldom follows a mishap.

  A simple 100 gallon-slipper tank has been developed to fit each wing for extremely long flights. These pressurized tanks contain enough fuel to carry the Angel to cruising altitude where they have no significant effect on speed or range. Even after the addition of an external drag chute, three times the normal oxygen supply, improved breaking and an autopilot, the final all-up weight was within ten pounds of the original proposal.

https://www.cia.gov/library/video-center/video-transcripts/u2-developments.html


Can a barrel roll really be executed at a constant 1G? I see this stated from time to time, for example in an answer to Can large airliners do aerobatics such as loops?

  A barrel roll is one thing; they can be performed at constant load factor of 1 G (assuming sufficient control authority).

In a properly executed barrel roll, however, I do not think there is any point in the trajectory where the vertical velocity is constant. In particular, the entry and exit of the maneuver require transitions from level to ascending, and from descending to level trajectories, respectively. In these two cases, at least, I cannot see how a load factor greater than 1 can be avoided.

This IAC guide states a maximum in the range 2.5 - 3 (and a minimum of about 0.5), though it is probably not intended to be a minimum feasible value.

You are absolutely right, a load factor of greater than 1 is impossible to avoid in a proper barrel roll. The barrel part of its name comes from the spiral path the aircraft needs to perform in order to add a centrifugal acceleration which is greater than gravitational acceleration at the top of the roll. This is the condition to ensure a still positive normal load factor in the reference system of the aircraft through the whole roll. Therefore, at the bottom of the roll the normal acceleration needs to be greater than 2 g.

I took the liberty to edit the wrong answer. Given that it has received 14 upvotes at this time, it should teach everyone around here a lesson how much to rely on the number of votes to assess the correctness of an answer ;-).


What is the thick, dashed, magenta line on a sectional chart? In the attached area of the sectional chart we see restricted areas R-2101 and R-2102. Also covering that general area is a circular, thick, dashed magenta line. There's a notice there that I assume corresponds to it, but I wasn't familiar with this marking before I saw it. I glanced at the Aeronautical Chart User's Guide but didn't see a reference. Anyone know what's happening here?

The Atlanta sectional near KANB, KASN, and KPLR gives a hint:

FOR REASONS OF NATIONAL SECURITY
PILOTS ARE REQUESTED TO AVOID FLIGHT
AT AND BELOW 5000’ AGL IN THIS AREA

It is called a National Security Area, which FAA’s training ALC-42: Airspace, Special Use Airspace and TFRs describes as follows.

National Security Areas
National Security Areas consist of airspace of defined vertical and lateral dimensions established at locations where there is a requirement for increased security and safety of ground facilities. Pilots are requested to voluntarily avoid flying through the depicted NSA. When it is necessary to provide a greater level of security and safety, flight in NSAs may be temporarily prohibited by regulation under the provisions of 14 CFR Section 99.7. Regulatory prohibitions will be issued by System Operations, System Operations Airspace and AIM Office, Airspace and Rules, and disseminated via NOTAM. Inquiries about NSAs Inquiries should be directed to Airspace and Rules.
Example — National Security Area near Pueblo, Co. and request to avoid flight at and below 3000’ AGL.

Wikipedia gives a brief description.

In United States aviation, a National Security Area is a designated airspace through which flight is discouraged for reasons of national security.
Flight through NSAs is not prohibited and no special advance clearance or authorization need be obtained to enter them. However, pilots of aircraft are strongly encouraged to either stay clear of NSAs or obtain prior authorization to pass through them in order to reassure the controlling agency that no threat to national security exists.
NSAs are a compromise between normal airspace and restricted or prohibited airspace. NSAs can be temporarily converted into restricted airspace by NOTAMs.
On VFR sectional charts, NSAs are delimited by a heavy dashed magenta border and a special notation.


Shouldn't the instructor in this scenario try to avoid a deadstick landing? In the Netflix drama "The Crown" (season 1, episode 4) Prince Philip has flight lessons with Group Captain Townsend (below is an image of that scene, I was unable to identify the plane).

After Prince Philip complains about the noise of the engine, Group Captain Townsend deliberately turns it off, and they both enjoy the silence for a while. After some chat, Prince Philip notices the ground getting closer:

Prince Philip: "Shouldn't we get her started now? The ground seems terribly close."
Group Captain Townsend: "No, it's too low to restart, sir. We'll do a dead-stick landing."

And they land safely.
My question is: if that was a real event, shouldn't Group Captain Townsend (as the instructor) interrupt the relaxing gliding with a warning? Something along the lines of "excuse me, sir, we're losing altitude, if you want me to restart the engine we have to do it now", or even "I'm restarting the engine now". I mean, shouldn't he be checking the limit altitude for restarting the engine?
I'll not ask why Group Captain Townsend didn't do that, it would be off topic, opinion-based and, despite the Group Captain being a real person, that scene is fictional anyway (The Crown is not 100% historically accurate). I'm just curious about the most probable behaviour of a real instructor in a situation like that.

if that was a real event, shouldn't Captain Townsend (as the instructor) interrupt the relaxing gliding with a warning? Something along the lines of "excuse me, sir, we're losing altitude, if you want me to restart the engine we have to do it now", or even "I'm restarting the engine now". I mean, shouldn't he be checking the limit altitude for restarting the engine?

This question appears to be predicated on the idea that the instructor had no plans to land the plane with the engine turned off. Having watched the scene, I'm far less convinced that this is the case. In fact, it's not until Philip remarks that the ground is coming up that the Captain tells him they'll be landing deadstick.
In the series, this instructor featured is a renowned flying ace with huge amounts of combat flying experience including a number of forced landings and ditchings.
Bob Hoover (who you could argue with cut from a similar cloth) regularly displayed and demonstrated with the engines turned off, up to and including landing in that configuration.* On the basis that turning the engine off was deliberate and not an emergency, I don't think the scene after that point is particularly unrealistic. They appear to be making a straight in approach and land on an airfield - it's entirely plausible the Captain made a deliberate decision to land with no engine from the very start.
*Example:


What is the weight saving of windowless fuselage for cargo aircraft? What is the weight saving of a windowless fuselage for cargo aircraft?
Does anyone have a rough estimation?

Let's take a Boeing 737 as a generic example, and spitball some numbers.
I'll make the post community wiki so someone can come along and plug in more accurate numbers.

Aluminum has a density of 2.7 g/cm3
(For our purposes let's assume the skin alloy is "close enough to pure aluminum" because I'm too lazy to look up the proper alloy density).

Plexiglass (just picking a random variety) has a density of 1.18 g/cm3.

The aluminum skin on a 737 is about 0.038 inches (or 0.1cm) thick.
We know a window on a 737 is thicker than the skin. I couldn't find the number but let's go with 0.25" (0.6cm).

If we have a hypothetical one-foot square window (about 930 cm2), the aluminum skin occupying that area would weigh about 251 grams. The Plexiglass equivalent would weigh about 658 grams (407 grams heavier, little more than 2.5 times as heavy).

Figure there are about 70 side windows on a 737 (quick count from a photo of a Southwest plane, not including exit door windows), so that's 28,490 grams or about 64 pounds, just for the plexiglass.

In addition to the plexiglass there's also supporting structure that needs to be added around the window to hold it in place, sealants to seal it against the skin, etc. - these add additional weight. I've no idea what these components weigh, but let's assume it weighs twice as much as the plexiglass, that's about 1.5 pounds per window of additional structure, or 105 pounds, bringing the total weight savings to just under 170 pounds.

170 pounds is not a lot of weight (in passenger terms it's not even one person), but it is that much more cargo you can carry. Also when combined with the fact that you no longer have to maintain the windows (fix pressure leaks in the seals, replace cracked plexiglass, etc.) the savings can add up over the life of an airframe.

Some more spitballing here... please feel free to correct my numbers:

On the subject of the cost savings: a 737 can carry about 27000 lbs payload, and burns about 5500 lbs of fuel / hour during cruise, and about 3000 lbs for a 15 minute climb. Assuming an average flight of 4 hours you get about 25000 lbs of fuel burnt, or almost 1 per pound of weight. This means that the fuel cost of 170 pounds of weight is about 170 pounds of fuel, which today costs (at around \$4 / gallon, and 6.5 lbs/gallon) around \$100.  Note that the cost of fuel varies a lot with location, so this is very approximate.

Now multiply this by the typical life of the aircraft - three flights per day, 7 days per week, for 30 years? That would be over \$3M of savings. And all because your parcels can't look out of the window.


On an ADS-B In display, do the pilots see the squawk code or call sign for other aircraft? If I understand correctly, with a ADS-B In equipment or TCAS equipment on board, the pilots could see the surrounding traffic with its assigned squawk code like "4653", is that right? But could the pilots know the aircraft identification like "UA858"?

ADS-B is part of a system that compromises a number of different things. ADS-B (In) means that your aircraft is capable of receiving the ADS-B data, FIS-B and TIS-B as well. FIS-B broadcasts information such as weather. TIS-B is a traffic broadcast system.

ADS-B includes a number of messages (about 27 different messages), including:

Aircraft Identification
Surface Position
Airborne Position (Barometric)
Airborne Velocity
Airborne Position (GNSS)
Aircraft Status
Target State/Status
Aircraft Operation Status

Each message packet holds 56-bits of data. The aircraft identification message includes the aircraft type, category, and callsign.

Now, to a pilot, here is basically what you would see:

Source: NexAirAvionics.com

You can see that some targets include the flight number (JBU1075) and clicking on a target (this is in Garmin Pilot) will give a little more information on the target:

Source: Garmin.com

What the pilots don't see is the squawk code, this information is not useful to pilots because they don't really care about that for other aircraft. The only real use of ADS-B target information is to understand where other aircraft are. If a pilot needed to call up another pilot, they would do so by tail number or flight number. ATC Controllers and other pilots will never call a pilot by squawk code.

Why? Because the squawk code changes potentially many times during a flight. Let's take for example a simple flight from KGRB to KMNM (a flight I'm familiar with):

On the ground at KGRB, when telling ATC about my destination they will assign me a squawk code, for example 2044. After departing they will call me up "1205C turn on course, altitude your discretion" and I will acknowledge. About 30 miles out (if I didn't get flight following) they will say "1205C squawk VFR, frequency change approved". Now my squawk code changes to 1200. I might then pick up Minneapolis Center if I want to change my destination and they will assign me a different squawk code.

The one thing that remains constant there is my tail number. I know to listen for (and have mentally trained a "listen up" trigger when I hear) "1205-charlie" or "05-charlie" on the radio. ATC has been talking to specific aircraft using the tail number/flight number since the ATC system was born. Squawk codes match aircraft with targets on the radar (because before ADS-B all that was transmitted was the squawk code). This information is only useful to ATC and not other pilots.

Now if I'm cruising around and I see a target on my ADS-B that is headed in the same general direction I am, and I'm not talking to ATC, I can try calling that target using the tail number/flight number directly (this is done on the air-to-air band or a local frequency, don't broadcast on 121.5 or you'll hear "guaaaaarrrrrrd" from some obnoxious pilot).

Either way ADS-B is useful for traffic avoidance. I don't really need to know where that airplane is going, why it's going there, etc. I just need to know what it is (big jets can cause wake turbulence issues for smaller aircraft), which way it's heading, and how fast it's going there.


Are modern fighter jets allowed to fly with an inoperative ejection seat? I'm wondering if a modern fighter jet (Eurofighter, JAS Gripen, F-35 etc.) is allowed to fly when the ejection seats are known not to be in working order.

Summary
If the ejection seat is inoperable on a US military aircraft, the aircraft will be grounded 100% of the time.  I'm sure you could come up with some weird hypothetical "end-of-the-world" scenario where you'd still take off, but that isn't reality today.
F/A 18 E/F Checklist Procedures
Interior Checklist
After strapping into the jet, the ejection seat is the first thing you check:

Leads, leg restraints, and harness - SECURE/ADJUST
Ejection control handle - CLEAR
Ejection control handle pin - VERIFY REMOVED

There's no point in removing the pin and checking the handle if you do not intend to arm the seats.  This is further confirmed later in the checklist.
Before Takeoff Checklist

[...]
Harness - ATTACHED 8 POINTS
[...]
Seats - ARMED IN THE FRONT
(2 seater) EJECT SEL - ARMED, AFT INITIATE

If the seats aren't armed, then the jet is never leaving the ground.  It is potentially suicidal for fighter aircraft to takeoff without ejection seats.  Fighters don't glide well (they fly to the scene of the crash), they can't fly in a total electrical failure, some can't fly without computer guidance, they can't fly with hydraulic failures, and they fly in very adverse flight conditions.  There are a lot of things, that if totally failed, would turn a fighter into a flying coffin, sans ejection seat.  Fortunately these systems are very redundant, but its usually not worth staking your life on it.


When should cross country flights occur in flight training Question about 141 flight schools.  I'm 52 hours into flight training and my 141 flight school wants me to do my cross country work prior to a maneuvering stage check, landing stage check and solo endorsement.

Is this a red flag, meaning the school is milking me for my money?

My understanding is there are two 50 NM flights and 150 NM flight that occurs with instructor and then need to be completed individually.

Monetarily  I want to know that I'm endorsed to fly solo before spending the money on the dual cross country.

My school is unwilling to endorse Solo flight until I have fulfilled cross wind landings with winds at 15 knots.

Thank you

There is no prescribed threshold to cross that indicates when XC training should start.

I generally wait until after a student's first solo to start talking about cross country work.  The first solo is a massive psychological barrier and once the student realizes that they really can fly a plane by themselves, it gives them confidence to learn new stuff.

That said, you are at a 141 school.  They need to follow their approved training schedule.


How can I find a final approach fix (FAF)? I have a problem understanding FAF - how can I find FAf on a precision approach without the lightning bolt/zigzag symbol. I know the Maltese cross means FAF for a non-precision approach.

According to the Jeppesen airway manual,

  by the glide slope/path intercept point on precision approaches

Which means that wherever I intercept the GS, I can say that point is FAF?

I added a chart. (In case you cannot see the picture I will explain the chart) FAF (Maltese cross) is positioned at DME 5.1 and 1700ft on a 3 degree glide path.

At the moment I pass the Maltese cross at 1700 ft, the GS indicator will be below because from 5.1DME on a 3 degree glide path, altitude will be about 1620ft so I need to descend at a steeper rate to intercept the GS. Then I will intercept the GS after FAF of a non-precision approach. In this case the FAF for the precision approach is positioned after the Maltese cross?

Is the FAF of aprecision approach not fixed at a specific position?

Until now, I have regarded the Maltese cross as the FAF for precision approach because there was no lightning bolt symbol.

Please correct my misunderstanding...

For precision approaches, the Final Approach Fix (FAF) is defined as one of three points:

A lightning bolt symbol on FAA government approach plates
The (published) glide slope/path intercept point on Jeppesen approach. The glide slope/path symbol depiction starts at the FAF on these plates.
Or, it is the resultant actual point of the glideslope/path intercept when ATC directs a lower-than-published glideslope/path intercept altitude

Since FAA government (NACO) charts answer your question with the depiction of the lightning bolt symbol, your question applies primarily to Jeppesen charts (other chart vendors perhaps as well). Jeppesen charts include the glide slope intercept altitude in the briefing strip near the top of the plate. So, the FAF for precision approaches is the location at which glideslope intercept is to occur when at the lower of either the published or ATC directed altitude.

See the following excerpt from the FAA's Pilot/Controller Glossary:

  FINAL APPROACH FIX− The fix from which the final approach (IFR) to an airport is executed and which identifies the beginning of the final approach segment. It is designated on Government charts by the Maltese Cross symbol for nonprecision approaches and the lightning bolt symbol for precision approaches; or when ATC directs a lower-than-published glideslope/path intercept altitude, it is the resultant actual point of the glideslope/path intercept.

See the following excerpt from Jeppesen's Airway Manual:

  FINAL APPROACH FIX (FAF) — The fix from which the final approach (IFR) to an airport is executed and which identifies the beginning of the final approach segment. It is designated in the profile view of Jeppesen Terminal charts by the Maltese Cross symbol for non-precision approaches and by the glide slope/path intercept point on precision approaches. The glide slope/path symbol starts at the FAF. When ATC directs a lower-than-published Glide Slope/Path Intercept Altitude, it is the resultant actual point of the glide slope/path intercept.


How significant is the lift induced drag contribution to total drag of aircraft at cruise speed? How significant is the lift induced drag contribution to total drag of aircraft at cruise speed? From what I've learned so far it seems to be around 10 to 15 percent of total drag. I suspect the ratio doesn't vary too much between aircraft provided they're within the same speed range. Therefore, let's focus on airliners and other high subsonic jets.

According to an article on leehamnews.com, the drag breakdown for an A320 at FL 370 and Mach 0.78 is:

  The 7,900 lbf of drag is composed of 4,700 lbf of Parasitic drag or drag independent of lift and 3,200 lbf of Induced drag or drag caused by lift.

With the induced drag being ~40% of the total drag.

Related:

Why would maximum fly-time (endurance) not coincide with max L/D operating point?
Why is the thrust/drag increase much lower at a lower FL with weight the only variable?


Can a closed Airworthines directive get reopened by a new revision? There is an Airworthiness Directive that has been closed by accomplishing its terminating action. But there's a new revision that changes the terminating action. Do I have to comply with the new terminating action to close the AD?

ADs aren't 'closed', they are 'complied with'. If the AD has been revised and the new compliance criteria are not met, then you would need to perform whatever measures are required by the revised AD.

There are a number of reasons that the AD may have been revised but in the example that you allude to, the proposed action does not appear to be sufficient to remedy the problem. Therefore a new or revised AD has been issued.

If the revision is mostly a clarification or change in affected aircraft, the identifier usually remains the same e.g. 2018-03-03 R1

If the revision makes a substantial change to the method of compliance, they usually rescind the original AD and issue a new one. e.g.

  SUMMARY: We are rescinding an airworthiness directive (AD) for Lycoming Engines model TIO- 540-A series reciprocating engines. The existing AD, AD 71-13-01, was prompted by a report of a failed fuel injector tube assembly. Since we issued AD 71-13-01, we became aware that Lycoming Engines no longer supports Service Bulletin (SB) No. 335A, which was incorporated by reference in AD 71-13-01. The intent of the requirements of that SB is now in Lycoming Engines Mandatory SB No. 342F, which we have incorporated by reference into AD 2008-14-07. The FAA determined, therefore, that this requirement is duplicated by another AD.

I had my A&P comply with a fuel selector AD 2018-02-05 so it was noted as complied with in my logbook. The AD was superseded by AD 2018-07-03 which allows a pilot to comply with the AD, so I made an entry in the logbook to indicate that I had complied with the new AD. This example is the same as the one in your question, though in my case the only additional action required was a logbook entry.

  SUMMARY: We are superseding Airworthiness Directive (AD) 2018-02-05 for certain Piper Aircraft, Inc. Models PA-28-140, PA-28-150, PA-28-151, PA-28-160, PA-28-161, PA-28-180, PA- 28-181, PA-28-236, PA-28-201T, PA-28R-180, PA-28R-200, PA-28R-201, PA-28R-201T, PA- 28RT-201, and PA-28RT-201T airplanes. AD 2018-02-05 required inspecting the fuel tank selector cover to verify the left and right fuel tank selector placards are located at the proper positions and replacing those that are improperly located with new placards. This AD addresses the same unsafe condition and requires the same actions as AD 2018-02-05, but changes the inspection of the fuel tank selector cover to a preflight check and allows for various fuel selector clocking configurations. This AD was prompted by our determination to allow the owner/operator (pilot) holding at least a private pilot certificate to perform the preflight check. We are issuing this AD to allow the pilot to do a preflight check of the fuel selector placards.


Are there any contemporary advantages in favor of wing warping? The early Wright Flyer famously used wing warping for its roll control surfaces. This technology was soon abandoned in favor of ailerons and by the end of the biplane era, was not used anymore. I assume a good part of this was the greater amount of control that rigid control surfaces allowed.

There appear to be some experimental supersonic aircraft that are using wing warping (or wing morphing) technology. What is the perceived advantage of this new generation of wing warping technology, what are barriers to its adoption, and how practicable is it for it to trickle down to general aviation?

All wings warp. The extent of warping is one restriction which limits the fast side of the flight envelope.

Once aircraft designers realized that thick wings have less drag, they tried to build their wings as stiff as possible. Stiff wings allow to use airfoils with rear loading, will have higher flutter frequencies and keep their shape even when operating at high dynamic pressure.

Since the center of pressure moves chordwise on cambered airfoils depending on the angle of attack, any cambered wing will suffer from pitching moments around its axis of elasticity. This moment will twist the wing and change the incidence of the outer wing sections. A stiff wing will suffer less twisting and stay closer to its ideal aerodynamic shape. Add an aileron, and another twisting moment is added on top. Now the wing twists opposite to the aileron deflection! This can become so bad that most of the aileron's effectiveness is lost as the wing is warped in a way which counteracts the lift change of the aileron.

The X-53 research aircraft uses this effect with an array of leading and trailing edge devices to actively warp the wing in the desired direction. Using computer-controlled deflections of small but very effective control surfaces, it creates a desired deformation of the wing for roll control.

This can be compared to the effect a Flettner tab has on an aileron. The Flettner tab is a small control surface at the trailing edge of a larger control surface and is deflected by the pilot such that it moves the big control surface in opposite direction. It slightly reduces the effectiveness of the big control surface, but needs only a fraction of the stick force, thus helping to manually control big aircraft.

Since the active wing warping of the X-53 depends on the proper functioning of the FCS and an array of movable devices, each with its own failure mode, I would hesitate to see this as a clear advantage. It allows, however, to control the aircraft at high dynamic pressure with minimal drag penalties.


How is combustion flame maintained in the combustion chamber after igniters are switched off? During start phase of a jet engine, igniters in the combustion chamber create sparks to initiate combustion.  As far I know, when the engine reaches self sustaining speed, igniters get turned off (this might be different (takes longer) in an Airliner due to FAA regulations during take off).

My question is how do flames in the combustion chamber (or canisters) get sustained (like a candle) without igniters support?

How does a candles flame sustain itself after you have lit it?  It stays lit by continually burning fuel.  The jet engine works the same way.  Once the fire is lit (by the ignitors) it is constantly burning.  Air is constantly being supplied by the compressor and fuel is constantly being supplied by pumps.

This is fundamentally different to a traditional combustion engine you might be trying to reconcile this idea against.  In a 4-stroke internal combustion engine, for example, you have intake, compression, power and exhaust happening separately and you need spark plugs (or glow plugs) to ignite the fuel each cycle.  In a jet engine, however, instead of 4 independent cycles you have a constant flow of air through the engine.  Air comes in the front, is compressed by the N2 stage and fed continually into the hot section where the fire is constantly burning and then exhausts through the back of the engine.

Look at it like a propane barbecue grill or a gas stovetop -- you only need the ignitor to start the fire. Once the fire is burning it stays that way until you turn off the flow of gas.


Why is mist abbreviated BR on METARs and TAFs? The abbreviation for a condition of mist is BR on METAR and TAF reports. How did mist end up getting abbreviated as BR?

According to a CFI's lesson plan on the internet, it comes from the French word for mist, brume.


Is QNE pressure altitude? In trying to understand pressure altitude better, am I wrong or right when I say this?
I am at an airfield. The pressure altitude at that airfield is 200 ft a.m.s.l.
If I set subscale 1013 mb on my altimeter, the altimeter should, theoretically, indicate 200 ft a.m.s.l.
Am I wrong or right when I say this? And am I right in thinking along these lines in trying to understand pressure altitude better?

That is not correct. There are three different altitude systems:

True altitude is the height above Mean Sea Level (MSL). This is what you get when you set your altimeter to QNH. Using this, your altimeter should read 200ft when you are on the runway if the airport elevation is listed as 200ft MSL.

Absolute altitude is the height Above Ground Level (AGL). This is what you get when you set your altimeter to QFE.  Using this, your altimeter should read 0ft when you are on the runway.

Pressure altitude has no relation to the ground or sea level. This is what you get when you set your altimeter to QNE (always 1013 or 29.92). You never use this near the surface of the Earth, only when up high enough that terrain or obstacles clearance isn't a concern. Pressure altitudes are expressed as Flight Levels (FL), with the last two digits omitted.


Private Pilot Compensation I am a new private pilot. My parents want me to take them flying. I do work and have a bit of my own money, but compared to the cost of flying it is not much. My parents paid for most of my training. I am still in high school, so I live with them and they pay for most of my existence. Obviously I cannot be compensated for flying them, but I wonder if there is any legal way for this to happen. The same question can be extended to when I take friends flying. Would it be as simple as me using a card that draws from one of their accounts? Me paying but with their money. Any knowledge/advice is appreciated, I would rather not break FAA regulation on my first flight as a private pilot.

The short answer is that in practice the FAA doesn’t care about “compensation” between family and bona fide friends.
The long answer is that the FAA’s mission is to protect the general public from pilots. (If they also happen to protect pilots, that is a side effect at most.) Your parents and bona fide friends are not the “general public”.
As a practical matter, the FAA could never prove beyond a reasonable doubt in court that any particular dollar that your parents or bona fide friends gave you was for flying vs a gift or for something unrelated, especially when it is likely they would be uncooperative with any investigation or charges against you. If they give you money, and you happen to use some of it to take them flying to a place of your choice, so be it. It’s just not worth the FAA’s time to look too closely at that, so they consciously turn a blind eye.
Where you will get into trouble is flying strangers or acquaintances to a place of their choice. The exact path the money takes is irrelevant; if you accept compensation from the “general public”, then you are operating an illegal charter, and the FAA will hit you like a ton of bricks for that.


What is the impact of thermal Anti-Ice on descent performance? I am just another one of the passionate flight simmers trying to understand more about Anti-ice system mechanics. I am talking about the Boeing 737-800 here if it makes a difference.

What bothers me is: Why is turning on TAI systems having negative impact on descent performance? Given a constant speed that we want to keep a shallower descents can be experienced.

Let's imagine a descent with thrust levers in IDLE position. From my research about aircraft systems and jet engines I would assume that turning on TAI would (in that order):

get more bleed air -> less air to burn -> turbine turning slower -> decreased N1

But from what I can experience and read on the web N1 is actually increased instead. I can guess the aircraft it trying to compensate something - but what is it if we're in idle descent? Also, I am assuming the decreased vertical speed comes from somehow increased thrust, which I would also suspect to be lower (or at least kept on the same level as before TAI) not higher than originally.

I understand this is a complex system and each part has impact on each other but maybe you can point me in the right direction ;)

When turning on the Anti-Ice, the demand for bleed air increases and the EEC (Electronic Engine Control) will increase the target N1 to provide enough pressure by injecting more fuel. From the Boeing 737 NG FCOMv2 (7.20.5 Engines, APU - Engine System Description, emphasis mine):

  In the normal mode, the EEC uses sensed flight conditions and bleed air demand
  to calculate N1 thrust ratings. The EEC compares commanded N1 to actual N1
  and adjusts fuel flow to achieve the commanded N1.

This impacts the descent performance as explained in the Boeing 737 NG FCTM (4.24 Climb, Cruise, Descent and Holding):

  The use of anti-ice and the increased thrust required increases the descent
  distance. Therefore, proper descent planning is necessary to arrive at the initial
  approach fix at the correct altitude, speed, and configuration. The anticipated
  anti-ice use altitude should be entered on the DESCENT FORECAST page to
  assist the FMC in computing a more accurate descent profile.

Note: the above quote is for the 737 NG models. The older 737 classic series does not increase thrust:

  Since all engines have been manufactured or modified to use a single idle speed
  in flight, the use of TAI does not increase thrust as it does in other models.


What would be the drawbacks of using a rotating engine as thrust reverser on airliners? What are the drawbacks for having engines mounted on an aircraft such that their direction can be hydraulically controlled for best performance and efficiency? The idea would be to turn the engine 180 degrees at landing so it can operate as a thrust reverser, even on jumbos like the Airbus A380 and the Boeing 747.  That would be some serious thrust reversing power.

I wouldn't worry to much about the mass of the engine. That's actually not the biggest problem. Instead, I'd be scared far more by the angular momentum. That turbine has a large moment of inertia and also a higher angular velocity.To flip it, you have to reverse the angular velocity. It's essentially flipping a gyroscope, but this is a gyroscope weighing several tons.