How does early rotation increase the likelihood of a tail strike at take off? This question indicates that an early rotation can cause a tail strike. What are the (pre-)flight dynamics that would cause this to happen vs what happens when rotating at the proper time?

When preparing for a flight, pilots will calculate many things, including their rotation speed. This is the speed in their takeoff roll at which they will start to pitch up, and hopefully the plane lifts off the ground. The rotation speed is dependent on many things such as temperature, altitude, and aircraft weight.

My answer here discusses the lift calculations in relation to rotation. That question covered the importance of speed related to weight. More speed is needed to create the lift to take off with a higher weight.

When the airplane rotates, it increases the angle of attack of the wing, which increases the lift coefficient (if the wing does not stall). The pilots will pitch up at a certain rate, and they do not stop until they reach a climbout attitude higher than what is possible when the main gear is still on the ground (though this may depend on company policy). They count on the plane acheiving enough lift during rotation to leave the ground so that they pass that maximum pitch while in the air.

If pilots underestimate their weight, they will calculate a lower speed than is necessary to provide the lift for takeoff. This means that when they rotate, the plane doesn't have enough airspeed yet to create enough lift to take off. So instead of leaving the ground before fully pitching up, the tail strikes the runway.

It may seem like an easy mistake to make, but thousands of pilots do it every day without a problem.

Aerodynamics (the laws of physics) dictate that when a wing produces 'lift' it necessarily produces 'drag' too. It's not difficult to visualize that a force is produced when a wing moves through the air. Going a step further, the vertically upward component of this is lift, and the horizontal rearward component is drag.
Though these forces are active the moment there is forward motion through the air, the flight controls of large jet aircraft become aerodynamically effective around 60kts, the minimum acceptable inflight effectiveness of controls is deemed to be achieved at a minimum speed starting around 110 to 120 kts and above. (below that, it's still steering and brakes included!)
If the pilots erroneously use speeds based on a lower weight than the actual weight, the ability of the airplane to get the nose up using normally expected control forces is compromised as the airflow over the wings is not producing the required lift (yet), and elevator control effectiveness is also lower, nevertheless whatever lift is being produced does cause the nose to rise. Now the scenario is that, from a frontal viewpoint, far more wing area is being presented to the air because the airplane continues to roll on it's wheels rather than starting to get airborne. This results in a larger portion of the already low (due to low speed) aerodynamic force remaining in the direction of the drag component which naturally impedes acceleration thereby keeping it below the correct rotation speed for even longer.
The early rotation can be visualized as a wing mushing through the air and churning it up rather than flying through it in a streamlined manner with a relatively smooth airflow all around.
Now the angle of attack of the wing (~ pitch) has has to be increased still further to produce enough lift to counter the twin effects of insufficient lift due to lower speed, as well as higher drag component. The airplane runs the risk of getting airborne in a high angle of attack high drag configuration seeking even higher pitch - so all around there's a tendency for high pitch and the possibility of a tail strike.
In the earliest days of jetliners, many went off the end of the runway, getting caught out by the compounding of these 2 effects and engine thrust limitations. Those accidents signaled the need for clearcut requirements by the regulations, of take-off calculations based on performance requirements.
The performance calculations do have some inbuilt margins, so the chance of a tail strike if they've calculated the speeds for say 202tons rather than 220tons is less than if they've used speeds for 230tons instead of 320tons.
Be clear that there is no subjective element in take-off procedure and technique. To achieve the legally required take off performance the the thrust setting and speeds are calculated from approved published data and this is only valid provided the airplane is operated as described in the book.
Gross error such as wrong weights used can only be guarded against by doings checks and cross-checks at every stage.


How would flow angle change along the length of a propeller airfoil? Let's assume I have:

windspeed of 15 m/s
blade length of 10 m
rotational speed of one revolution per second

Can someone please help me calculating how the flow angle would change along the length of an airfoil? I have been trying to do the process for the last couple of days but I don't know how to do it.

In order to explain the situation, I have drawn a couple of pictures.
Consider a propeller rotating with the rotational velocity $\omega$ (in $\frac{rad}{s}$), which is flying at a velocity of $u$ (in $\frac{m}{s}$).

(Please excuse my crude drawing skills...). If we cut the propeller at four places along the radius $r$, we get the following velocity triangles (at the respective positions 1, 2, 3 and 4). Note that in the following we look at the propeller from the tip in direction of the hub:

Note that the tangential velocity at each crosssection rises, however the forward velocity stays the same!
The tangential velocity can be simply calculated by the factor $\omega \cdot r$.
Now everything which is left to do is to calculate the angle $\alpha$, which can be simply done by taking the $atan()$ function (btw, I believe that Fern got this point wrong)
$$\alpha = atan(\frac{u}{\omega \cdot r})$$
Therefore in your specific case with $n=1 \frac{rev}{s}$ we get:
$$\alpha = atan(\frac{15}{2\cdot \pi \cdot r})$$
with $r$ going from 0 to 10 meters (in order to remain practical from 0.1 to 10 meters)

$$ \arctan \left( 2 \pi \times n \times \frac{r}{v} \right) $$

n is the rotational speed in rps
v is the wind speed in m/s
r is the radius in m

The relative wind seen by the blade airfoil has 2 components:

on in the direction of the wind, which value is the actual wind speed $$ v $$
perpendicular to the wind due to the motion of the blade, which value is the lineal speed of the blade section: $$ \omega \times r$$

So, the angle along the blade will be the one with tangent
$$ \tan  \left( \frac{\omega \times r}{v} \right) $$


Does aircraft/ATC get any information directly from a weather balloon? We have been launching radiosonde (a meteorological instrument containing GPS and other sensors to measure meteorological variables attached to a balloon filled with Hydrogen) to obtain meteorological data of the atmosphere.
This radiosonde transmits the information to a ground station we have in a frequency close to 400 MHz (well, this is what we uses, not sure about others). We frequently update the vertical height, direction, bearing position etc to our nearest ATC.
I was told that ATC and aircraft get information from the radiosonde directly (I am not sure what sort of information they get) other than what we give to the ATC.
So, I want to know whether ATC/aircraft get information directly from a radiosonde and if they do, what sort of information do they get?
I am not concerned about the radiosonde's meteorological data going into the weather models for forecast products that is available to aviation industry. What I need to know is if ATC/aircraft can know the position of the balloon/radiosonde directly by the information the radiosonde transmits?
In essence, can ATC/aircraft track a radiosonde without inputs from the agency that launches/manages the radiosonde?

No, neither ATC nor aircraft receive any information directly from a radiosonde balloon. However, in many cases the meteorological agency operating the radiosondes does use them to produce forecasts that are made available to ATC and pilots.

Does your radiosonde have an ADS-B transponder in it?  If so, then ATC and aircraft can get location and speed information from it without any other communication links.


What are the hurdles to overcome before purely electric commercial aircraft can fly? What are currently the largest issues with purely electric commercial aircraft (large scale ones like the size of a Boeing 737)?

Are there any organizations right now that are trying to solve those issues?

The biggest problem with an all-electric-powered aircraft is the same as those plaguing all-electric cars; our current battery technology has nothing on the energy density of fossil fuels:

There's just no contest in being able to pack the energy needed to push a plane through the air into a volume and weight compatible with an airliner. Jet fuel is kerosene, which is pretty much right in between gasoline and diesel, while any battery technology we've developed can't even be accurately plotted on the scale of this graph.

I see commercially viable electric driven aircraft requiring major changes in several areas. Aircraft design is certainly one. It also requires changes in regulations and flight profiles. I'm convinced you could take a classic prop driven air frame, say a DC-3, and convert to electric. It was designed for relatively long flights but pulling out all of the fuel and power systems, replacing them with lithium batteries and electric driven composite props could yield shorter flights with less payload viably. Your flight profile would need to change. Climb high, glide down to extend your range. It's what the recent round the world solar powered flight did. What we need is a visionary like Musk, to depart from the linear thinking and designs that the major manufactures are stuck in. Technology is fast approaching a point where this could become a reality. We need someone to put multiple technologies together and challenge convention.


Why do police helicopters always fly in circles? Why do police helicopters always fly in circles while news helicopter hover in one spot? Is it to avoid criminals opening fire at them, or is it because there is a difference between the two types of helicopters?

Police helicopters don't always fly in circles. I've often seen my local police helicopter hovering. There are a few reasons you might have seen police helicopters flying in circles:-

Not all types of helicopter can hover out of ground effect. It might be that the police helicopters in your area can't hover at the heights they work at, with the weight of their usual equipment.
Helicopters are safer if they're moving forwards than hovering. In the event of an engine failure, they can autorotate to land safely, but they need to have some airspeed to be able to do this. The required airspeed depends on height (see the chart in the linked question), so if your news helicopters are usually operated higher up than police helicopters, they may be able to hover safely. (This is quite likely, as police aircraft are exempt from the 500 ft rule and the 1000 ft rule, while news helicopters are not.)
Police helicopters often circle to search an area for a fugitive or casualty using thermal imaging cameras. News helicopters tend to either follow a vehicle or hover to get a steady camera shot of a news event.

Police helicopters search, follow, and chase things. You need to be moving to do this.  News media don't do those things.


ETOPS 330 vs ETOPS 370 etc; how are the exact minute ratings derived? I am curious how the ETOPS minutes categories are arrived at. i.e. Say, ETOPS 330 vs 370.

What extra abilities would the 370 type have demonstrated that the 330 didn't have? Was it just that the test flight on single engine was longer? Or something else in the design limits the type to a 330 minute rating while on the drawing board? Is it the MTBF of a component? Or is the 330 minute time back calculated based on actual empirical testing and the associated failures?

On ground and maintainance procedures is there any substantial difference when dealing with a ETOPS 330 aircraft vs and ETOPS 370 aircraft?

Could there be (say) an ETOPS 430 in the future?

If there is a formula currently used to generate an ETOPS time, no regulatory agency has made it public that I can tell. ETOPS originally grew out of a "60-minute rule" that was the result of earlier distance-based rules (see this report for a thorough history). My guess is that 60 minutes was a case of  "well, that sounds good" rather than the result of any rigorous analysis. From there, it's mostly been manufacturers slowly pushing and getting approved for longer and longer extensions (usually just a percentage increase that results in round-ish numbers—again, this is policymaking, not engineering).

However, take a look at the formulas on pages 9–11 of this report. I hesitate to declare them the way to generate an ETOPS number because the report is thirty years old and a lot of it is critical of the methodology, so the regulators may have changed their approach between then and now. In fact, the report does not explicitly state that the formulas within were in use at the time, either. Nevertheless, if there is a formula in modern use, it likely uses a similar approach of quantifying the probabilities of failure and using a factor to convert them into a do-not-exceed diversion time.

The difference between certification at 330 minutes (777) and 370 minutes (A350) may be due to FAA vs. EASA methodologies and/or decreases in inherent failure probabilities as technology matures. With that, I doubt there is much difference in maintenance of a 777 vs. an A350 (at least as far as ETOPS goes—obviously their construction necessitates very different maintenance programs), as that 40-minute increase for the A350 was approved without any in-service maintenance data. It may be different for the 787, which was not initially certified at 330 minutes.

Going forward, I have no doubt we'll see ETOPS 430 and above. Airbus already toyed with 420 minutes for the A350, and perhaps we'll see that after some time in service. At 420 minutes, there are only a few non-compliant routes; I expect that, eventually, any new twin will be able to fly unrestricted between any two points within its endurance.

The answer ETOPS minutes categorised arrived from the Engine failure diversion range and the time is calculated based on OEI (One ENgine Inoperative) max range distance or other speed selected by applicant.
I do agree with previous answer there is no point to go to 300+ minutes.  see image.

The north and south pole concern is more critical and additionally there is Polar certification where the operator have to prepare the polar survival suit for crew member and additionally passenger arrangement incase they divert to this remote airport in advance (such as food, clothing, accommodation, etc)


Which airports have the highest fuel upload? Which airports consume the most fuel for aircraft refueling, and how much fuel do they use?   I was able to find that "Heathrow uses about 20m litres of fuel a day", but it isn't easy to find figures for other airports.

The best data I could find is in this paper about biofuels, which has data for US airports in 2014. Based on my reading of the chart on page 14 and some conversion:

Airport  Millions of barrels per year
KLAX     48.6
KJFK     43.5
KATL     30.8
KORD     30.5
KSFO     28.3
KMIA     26.0
KDFW     25.4
PANC     19.0

Comparing this to the top US airports in 2013, it is interesting to note that LAX and JFK use significantly more fuel than KATL, despite passenger traffic figures ranked the other way. Also notable is Anchorage showing up here right after DFW, while MIA and ANC are the only ones not in the top 10 by passengers, showing up at 11th and 58th, respectively.

Figures for other countries have been harder to find. This article from 2004 estimates the Dubai International usage at 24.2 million barrels that year, which has certainly grown since then. The 2012-2013 environmental report from Emirates Group lists their consumption at 73.9 million barrels, and half of this figure would be in line with the other numbers available.

I found a similar figure for Heathrow, listing it at 20-25 million liters per day, depending on season, which gives a range of 61.2 to 76.5 million barrels per year, well ahead of the US airports.

Becoming even fuzzier, the pipeline to Narita Airport in Tokyo transported 130 billion liters in its first 30 years of operation, which averages out to 36.3 million barrels per year.

Easiest way is just to look at the busiest airports in the world, they have the most planes flying in and out, therefore, they have to fuel more.


Why do some multi-engine aircraft have accelerate-go distance in their performance charts and some don’t? I'm curious about why some airplanes have accelerate-stop distance (ASD) and accelerate-go distance (AGD) in their performance charts and some don’t include that. Does anyone know why?

It depends on the aircraft in question.  This isn’t required for the certification of a light twin and is solely up to the OEM’s discretion to publish said information.


Can the ILS glideslope be intercepted from above? Is it recommended to intercept the ILS glideslope from above? Are there any special considerations like unstable approaches or GPWS warnings?

Assuming that you're asking about intercepting the glideslope from above rather than the localizer, the answer is that it is definitely NOT recommended.

There are at least two significant problems if you do this. First, is the fact that at high vertical angles there can be false glideslopes. Looking at the diagram below, if you're coming at the glideslope from above and the needle starts to move, are you intercepting the real 3° glideslope or the false 9 ° glideslope?

The diagram above is the best I could find, but it has one error. It shows a "Flag no signal" at 6°. Actually what you'll have there is another false glideslope, but one which has reverse sensing.

You can, of course, do a reasonability check if you know your distance from the runway, or you could compare your vertical speed if following it with what you know your vertical speed should be, or on the 6° line a command to go up when you know you should go down would be a hint, but it's unwise in my opinion to put yourself in a situation that increases your work load that much during an instrument approach.

You asked about GPWS warnings. None of the aircraft I flew that had GPWS would sound a GPWS warning just from receiving a false glide slope. However, all of them would have sounded the GPWS if you followed a false glideslope and were close to the ground because doing so would give you an excessive sink rate.

A second problem with approaching from above is that the vertical angular width of the glideslope as measured from needle full down to needle full up is very small. As I remember only about one degree. Whatever it is, though, the point is that if you descend into the glideslope with a vertical speed of only a few hundred feet per minute greater than the glideslope itself is descending, the needle is going to go from full down to full up very quickly. Without working it out, I'd guess that if you're inside the outer marker you might well miss its movement if your instrument scan had you away from the needle more than a second.

In the late 1970s a friend of mine was flying a charter in a Cessna 310. He unwisely decided to intercept the glideslope at Salem, Oregon from above. The aircraft hit the ground in the vicinity of the outer marker, killing all aboard. During the accident investigation, the NTSB found from radar data that he had a descent rate greater than 1,000 fpm going through the glideslope.

There's never a reason to do this.  Proper Planning.  If too high at the FAF request vectors back around and set it up correctly.


How do aircraft window size compare to each other? What are some possible improvements on them? I'd like to see a comparison about the window sizes of various commercial aircraft, maybe to give evidence of eventual progress in it over the generations.
For example, I surely know that the B-787 has the biggest ones but it seems strange to me that A350XWB has smaller ones in comparison, considering that it, too, is made with composite materials. Why this difference?
In addition, Boeing increase their window sizes between different iterations of the same model (for example, the first 747s had smaller windows than the later generations, and 777X has larger windows than the original 777), but Airbus seems to not have this approach (neo versions are equal to ceo ones).
Finally, I heard about Boeing Skyview, a very big single windows in Business variants but... is already delivered as solution? Any similar solution from Airbus?
P.s: I found only a link with similar topic but is more general and not specific to a comparison chart between models and/or difference B787 and A350 construction design related to window size

How aircraft windows compare:

  Aircraft windows can be made bigger by improving the materials of the window or fuselage or reducing the amount of Gs the window frames get by changing the exterior shape and design of the fuselage. Another way is making the window surfaces smoother (to reduce surface friction) or changing the shape of the window itself.


What is the purpose of having contra-rotating props on an aircraft? Why do planes, like the famous XF-11 and the Tu-95, have contra-rotating props? What is their purpose?

Image credit: Mike Freer / Touchdown-Aviation / Wikimedia

According to my experience, you have two problems with props:

Torque
Exhaust Speed

If you use contra-rotating propellers, you eliminate the torque reaction problem because you now have two contra-rotating propellers each cancelling out the opposite's torque.

Also you increase the speed of air accelerated by the propellers, thus the aircraft’s efficiency at relatively high travelling speeds is increased.

Normally, the propeller can only be operated effectively at low Mach numbers and increasing the RPM above a certain point will only cause the air behind the propeller to compress but not accelerate. Using a second propeller with higher pitch angles can generate high enough airspeed without the problem of compression because the second propeller is rotating inside the airstream generated by the first propeller.

Correction
However, having a different speed and pitch WILL induce a torque effect.

Regarding noise of propellers at speeds close to sound barrier, you may have a look at the F-84 'Thunderstreak', propeller version video in YouTube, https://youtu.be/UFhSzReWTgs it has contra-rotating propellers, and is probably one of the fastest airplanes with this arrangement ever, the video discusses the development and findings of a contra-rotating propeller in a fighter flying close to Mach 1; at any speed, the aim of having contra-rotating propellers I guess is reducing the effect of torque that will tend to make the airplane turn in the opposite direction as the propeller, along the propellers axis, in a centrally placed, single engine airplane, a propeller rotating in a clockwise direction, looking from behind, will indice a force making the fuselage turning in the opposite direction, also the vortex and other changes in air column induced by the propeller may have an influence on control elements, such as the rudder


Has anyone built an aircraft with a flat ring wing? When I try to search for circular wing aircraft, everything I find has the wing loop up over the top of the craft.
What I want to see, however, is basically an Aerobie Flying Ring, but with a motorized propeller, etc.
I'd be equally happy to see a "real" plane, or an RC one.
Also, while I would expect the wing to be attached to the fuselage via cables, I'd be equally interested in learning about alternatives (e.g. blended wing).

George Kitchen patented a design and half-built a biplane. It was completed by Cedric Lee and Tilghman Richards in 1911 but failed to fly. Richards went on to develop a series of increasingly successful Lee-Richards annular monoplanes before the outbreak of WWI.
This was a serious and promising design, having been wind-tunnel tested by the National Physics Laboratory in the UK during development. Kitchen and Richards understood that the strange shape would create vortices which trailed back over the rear part of the wing, and they used these to help impart stability. The monoplanes were indeed all safe and stable in flight (although the first was tail-heavy), a rare characteristic in those days. Pilots included Gordon England, Gordon Bell and NS Percival.

I doubt that, since it wouldn't make much sense.
The aerobie, like frisbie, is spin-stabilized, which is why it is round. But that does not allow controlling it. Controllable aircraft don't spin, so they don't get any advantage from being round.
On the other hand the shape would be very complex, because the profile would have to change depending on the local flow direction. Airfoils that work in both directions are not very good; see Is there an aerofoil that gives reasonably good lift for both air flow directions: forward and backward? That is good enough for aerobie, which at its size has much lower mass for surface area, but wouldn't work for a full-scale aircraft.
And even the complex shape wouldn't be very efficient, because the lift distribution would be far from the optimal elliptic with a lot of lift generated by the sides. The aerobie isn't designed to be efficient at flying at all.
The closest you can have were the experiments with full disk circular wing. Some full-scale prototypes were built, but they didn't show any useful advantage, so all the projects were stopped.


What can be logged as Total Time? The FAA regulates logging time in FAR 61.51. There are plenty of questions about logging PIC time, as well as SIC time. Another type remains: what can be logged as total time? It's only mentioned once:

  Total flight time or lesson time.

It is clear that any time logged as dual, PIC, or SIC can be logged as total time. Is total time merely the sum of those, minus any overlap, or is there a situation where total time can be logged but none of the others?

In particular, two situations arise:

I'm at the controls of an aircraft I'm not rated for (i.e. an ASEL pilot in the right seat of a multi-engine aircraft, where the other pilot is appropriately rated and not a CFI). I can't log PIC, SIC, or dual - but can I log total time?
In a plane I'm rated for, I pass the controls to a non-certificated passenger. I'm not a CFI. I cannot log PIC, SIC, or dual while my passenger is the sole manipulator of the controls, but I am acting as the PIC for this portion of the flight. Can I log this as total time?

"Total time" isn't an officially defined term as far as I know. Most people seem to use it to mean "total flight time", i.e. the total of their PIC, SIC and flight training time (excluding simulator training).

In general, you can log and count whatever you want in your logbook provided that you log at least the items required in 61.51(a):

  (a) Training time and aeronautical experience. Each person must
  document and record the following time in a manner acceptable to the
  Administrator:

  (1) Training and aeronautical experience used to meet the requirements
  for a certificate, rating, or flight review of this part.

  (2) The aeronautical experience required for meeting the recent flight
  experience requirements of this part.

So, the bottom line is that "total time" is whatever you want it to be, and if you want to log 'fun time' in aircraft that you aren't qualified to fly then go ahead; the time just won't count for anything as far as the FAA is concerned.

As for your two scenarios:

You can't log any 'FAA time' because you're not certified to fly the
aircraft as PIC or SIC, and you aren't receiving training. You might note it in your logbook for your own reasons but you can't count it towards anything for the FAA's purposes.
You can't log 'FAA time' here either, for the reasons you mentioned. You're acting PIC for the entire flight, of course, but acting as PIC doesn't automatically let you log PIC unless other conditions are met. 61.51(e) lists all the ways you can log PIC time, e.g. sole manipulator, acting as PIC when more than one crewmember is required.

The interpretation of "Total Time" I've always seen is the sum of all the other categories. That is, your "total time" should be the sum of your PIC/SIC/Instruction (not as PIC/SIC) time. That said, it's your logbook, you can log whatever you want as "total time" (e.g. if your airline co-pilot has the fish & you get called up to sit right seat you can log that as "total time" if you wish - just not as one of the categories that "counts" under the regs: PIC/SIC/Instruction Received etc.)

Note that your second example is a different situation:

  In a plane I'm rated for, I pass the controls to a non-certificated passenger. I'm not a CFI. I cannot log PIC, SIC, or dual while my passenger is the sole manipulator of the controls, but I am acting as the PIC for this portion of the flight. Can I log this as total time?

You are acting as PIC in this situation. Who is manipulating the controls is irrelevant: As your passenger is not rated to act as PIC of airplane carrying passengers you must be filling that role. You would therefore log PIC time in this case (you cannot however log it as "dual given", nor can your passenger log it as "dual received", because you are not a CFI).
This is also true if your passenger holds a student pilot certificate, or a certificate for a different category/class of aircraft (e.g. if they have a rotorcraft certificate they still can't be PIC of an airplane - they are not rated for that category of aircraft).


For aircraft with variable-sweep wings, how unstable is it to have each wing in a different position? Wikipedia presents this photograph of an F-14 Tomcat, with one variable-sweep wing swept forward and the other back:

I was surprised to see that this configuration was possible; much less feasible or safe to fly with. My idle assumption, not being an aviator of any kind, was that this would be extremely unstable and difficult to handle. I would have assumed, given the prior assumption that the aircraft would be unstable, that the wings would have interlocks requiring them to be swept symmetrically, as a safety feature.

Is this photograph of a maneuver that is manageable and safe enough to perform routinely, or would doing this with the wings be an exceptional event or done only for testing? What kind of impact would this have on the aircraft's handling, given a forewarned, experienced pilot?

This was an intentional test run by Grumman in response to US Navy concerns about asymmetric wing sweep.

From The story of F-14A, Aircraft No. 3, BuNo. 157982

  One of these [flight tests] was in response to concerns raised by the US Navy regarding asymmetrical wing sweep. No. 3 is best remembered for photo shown at right. A series of flight tests were conducted from December 19, 1985 to February 28, 1986. Grumman's Chief Test Pilot, Chuck Sewell, conducted several trials with the right wing locked in the forward position of 20 degrees, and positioned the left wing at 35, 50, 60 and 68 degrees of sweep in flight. 60 degrees was determined as the maximum for landing. In the event of an operational in-flight malfunction, Sewell found the aircraft to be acceptable for carrier landings in this configuration.

Evidently it was manageable, and safe enough that carrier landings were permitted with asymmetric sweep.  There's no control available for the pilot of the Tomcat to intentionally asymmetrically-sweep the wings in flight, though.

How the handling qualities change I haven't seen reported anywhere.  I agree with Robert DiGiovanni that you'd expect additional drag on the side with the extended wing, but the Tomcat has additional options on how to move spoilers and other control surfaces and it isn't clear to me if it can detect and respond to asymmetric sweep or if it's just up to the pilot to do so.

This appears to be a very fancy version of a side slip, which can be routinely performed with many aircraft.  Note the ailerons are set to roll left, with the outstretched right wing providing drag to yaw right.  It is doing the same job right rudder would do.

Slipping to the left would also be consistent with "raise the dead" thrust asymmetry technique if this was a twin with the right engine out.  Slipping to the left puts side force on the tail to counteract right yaw.

I would not do this particular maneuver too slow, particularly in that plane, where spin recovery would be more difficult.  But a well trained pilot would be in a safe enough envelope for a few photo shoot takes.


Why is the ISOLATION VAVLE switched to OPEN during ENGINE START on Boeing 737? As the SOP says in Preflight Procedure – First Officer:
"ISOLATION VALVE switch – OPEN"
In this way, when engine starts, the ISOLATION VALVE is OPEN not AUTO.
The PACK valve is switched to OFF, under AUTO can also make the ISOLATION VALVE open.
SO why is the ISOLATION VAVLE switched to OPEN instead of AUTO?

Position OPEN is guarantee correct work supply air bleed, AUTO is not. For safety.


Is it an acceptable practice to take off in a microburst? This video has been posted on Youtube:

Strong winds are blowing at the airfield, pilots are taking off aircraft to prevent them being damaged. However I noticed that gliders have been successfully kept on the ground.

Is that standard practice to take off and fly to try to escape a burst? Is that even allowed and/or sensible?

The airfield in the video is KAFF, the Air Force Academy air base. Everybody you see in the video are air force cadets or retired Air Force pilots (in the tows).

There is a credible thread about this over on Reddit where one commenter says:

  I'm very curious as to how you got this video, i was under the impression it never left the airfield.

  This happened in April 2014, this past year. The weather is absolute crap here, especially for soaring. Well... we get good weather sometimes. Anyway, it's not uncommon for those TG-16A's to go up with a 25 knot gust... But i digress.
  The cadets were pushing in because winds were out of limits and the weather was getting worse... and BAM! Microburst.

  This microburst hit right next to the airfield. The tower spotted it early, gave a verbal warning "look out..." and cadets are trained to do the following: grab a wing (glider) and turn broadside into the wind and put the spoilers out. The tows were not so easy... nor lucky. Their takeoff speed is about 50 knots, and none of them were powered up when they lifted off the ground, to give you an idea of how bad the wind was. Their only maneuver is to face into the wind and pray they dont actually take off. The tows that took off left for COS airport... it took another 30 minutes of holding gliders before the tower let the cadets start moving the gliders.

  As for taking off... 55 kt gusts are the highest the Academy has had in a long time. Considering there were a half-dozen other aircraft within 100 ft of the tows, along with people (i.e. cadets around/in the gliders) if he was moving too far from his position in the queue, the safest action is to get some altitude and try and leave the microburst. Or at the very least put some altitude and distance in between himself and the cadets and aircraft. You saw how slow the tows in the air were moving relative to the ground... those were HARSH winds.
  At about 0:20, you can see a cadet hanging onto the wing of a glider on the bottom of a screen. This wind was scary. I don't know if anyone was up at the time, but full tempo ops can be up to 5 tows and 8 gliders... on a standard afternoon training day 3 tows and 4 or 5 gliders is normal. It looks like they were already pushing the gliders to the hangar...

I believe the commenter is wrong in that the planes were not powered up, but everything else is accurate (relatively so, those Cub (?) tow planes can take off much less than 50kts).

From your question:

  Taking off against the wind seems impossible because where does it get its thrust? And with the wind also seems impossible because all the wind is traveling at the same speed as the airplane, which to me should make the airplane drop like a stone.

Taking off against (into) the wind is the most preferable way to get an airplane into the air. It reduces the amount of ground speed that you need in order to take off. Aircraft work according to the airflow over the wings, if the airflow is great enough and the angle of attack is right, then the aircraft flies.

Taking off with the wind is also possible, but it extends your ground roll since you need to get to the same relative speed with respect to the wind before the airplane will fly.

Look at it this way, lets say you have the wind at your back and you take off on a bike. As you gain speed there is a point at which there will feel like there is no wind since you have the same speed as the wind at your back. As you keep going faster you'll start to feel like the wind is blowing at you, but slower. The amount of wind blowing at you is your air speed, the speed you are actually going is your ground speed.

Airplanes work the same way, taking off down wind requires the aircraft to get a greater ground speed (but the same air speed) to take off. After the airplane starts moving the only thing that really matters is the speed of the relative air flowing over the wings. When somebody says they need 50 kts to take off, they mean 50kts of airspeed, or 50kts of air flowing over the wings.

Now, a little commentary. There are two aircraft that take off in the video, one goes to the left which is up wind and the other goes to the right which is down wind. The upwind pilot has a much easier time controlling the aircraft since they don't need as much ground speed to keep it in control.

The downwind pilot almost bought the farm, and I'm pretty sure when he got back on the ground he needed a change of pants and a new aircraft seat. He's having a lot more difficulty controlling the aircraft because of the low airspeed. It doesn't look like he had much of a choice to go in that direction though, so I'd buy that man a beer if I ever met him just to hear the story.

The thing to take away from this is those pilots are retired Air Force pilots with thousands of hours of experience in high performance aircraft. The average pilot would be a stain on the tarmac in similar conditions.

To answer your edited question:

  Is that standard practice to take off and fly to try to escape a burst? Is that even allowed and/or sensible?

No, it is not standard practice. Larger aircraft would probably not have this issue but the aircraft in the video all weigh less than 1000lbs, a little more with the pilots and fuel probably but not much. Pilots are trained specifically to avoid microbursts if possible because they are very dangerous things. A search of the NTSB accident database for the keyword "microburst" provides 73 accident reports with that mentioned, 21 with fatalities.

Is it allowed? No, airports will halt operations when low level wind shear is detected, however its not to say an aircraft isn't already in its takeoff run when the shear is detected. The highest priority is to stay on the ground. The aircraft in the video however don't have a choice, the wind speed they encountered is greater than their take-off speed, they were probably going to fly or tumbleweed.

CFR 91.3(b) gives a pilot full authority to deviate from any ATC instruction or rule in an emergency. An emergency does not need to be declared first, a pilots responsibility is Aviate, Navigate, Communicate. If all your attention is on flying (or keeping from flying) you can be in an emergency without telling ATC. I'm sure these pilots did not face any disciplinary or regulatory actions as the result of taking off from the parking ramp.

Taking off against the wind seems impossible

Taking off (and landing) "against the wind" (head-wind) is actually easier, is a daily practice and manufacturers recommend it over taking off "with the wind" (tail-wind) or with a cross-wind.

Aircraft care about their airspeed, not their ground speed. Generally speaking, the greater the airspeed, the greater the lift the aircraft's wings can produce (speed plays the major part of the lift equation, as it is squared).

Counter intuitively, as the head wind speed is going up, the takeoff distance actually shortens. Small aircraft can literally takeoff and land "on the spot" if there is a strong enough head wind:


Why is landing on a carrier not handled by a computer? Landing on a carrier seems like a difficult and risky task for military pilots, especially at night when the carrier should keep low profile and is practically unlit.

It seems exactly like a problem which can better be performed by a computer rather than a human being. A machine can take in account exactly the motion of the carrier and other parameters and land the aircraft precisely where it should. The fact that there should be no enemy aircraft nearby also means that the initiative of a pilot is not needed.

The system can:

Either be exclusively inside the aircraft (doing image recognition of a carrier and trying to determine where to land; not sure how easy and reliable this can get),
Or be presented as a subsystem within the carrier which sends the encrypted information to the authenticated aircraft about the exact position of given points of the carrier and a second subsystem inside the aircraft which relies on this information to make the controlled landing.

Why isn't it handled (yet) by a computer? Are there projects of implementing such system?

Computers can, in fact, control the approach of a Super Hornet all the way to touchdown.  However, there are limits to the sea state. Gross deviations in glide path resulting from a pitching deck would make a coupled approach impractical.

However, the most compelling reason to hand fly all our approaches is that we fly a $60 million jet. Murphy's Law tells us that the most junior guy, with the least experience behind the boat, is going to get an engine fire, at night, in rough seas.  If our fictional JO wasn't proficient hand flying the ball behind the boat this could result in catastrophic consequences including both the loss of aircrew and aircraft. As often as possible, we prepare for the 1 percentile, not the 99th percentile, so when we do get that engine fire at night we get the upgrade OK, and not the cut pass/ ejection.

Plus, its just plain eerie letting the jet fly itself to the boat, and the current system isn't reliable enough that most guys would feel comfortable letting it fly itself on a regular basis.

Edit:  Heck, new guys aren't even allowed to perform auto approaches (auto throttle) to the boat for the same reason.

There are three main reasons: reaction time, sensor inadequacy, and predictive intelligence. Taking them in order...

For certain types of stimulus-response activities a human can respond faster and has a better reaction time than a computer. For example, imagine it takes 50 milliseconds to sense something completely, 100 milliseconds to transmit that information to the computer, and 100 milliseconds for the computer to figure out the right action, and 80 milliseconds to transmit the response to an actuator. That's a total of 330 milliseconds. A human can respond to an event in 200 milliseconds. Note that for some types of actions the computer's sense-and-respond loop could be much slower than the numbers I have given. For example, most artificial intelligence algorithms are complicated and take a lot longer than 100 milliseconds to complete. Some types of optimization algorithms, like dynamic programming have unpredictable running time, so they might finish in say 50 milliseconds with one set of inputs and 1000 milliseconds in another.

The next big problem is that the human eye, which is wired in parallel directly to the brain, is a far better sensor than anything available to an aircraft. It has a wider field of view, higher bandwidth and better focusing and movement ability than any man-made optical system. Currently the sensors on planes are things like inertial measurement units, GPS and flight instruments (altimeter etc). These sensors are not enough to reliably land a plane on flight deck except in very calm conditions.

Finally, landing on a moving flight deck requires predictive intelligence. You basically have to guess where the deck is going to be in the future, combine that with estimated wind gusts, and then calculate in the future motion of the aircraft given a range of factors. Putting all this together is currently way beyond the ability of artificial intelligence systems.

There are actually a lot of things MUCH simpler than landing on a flight deck that we cannot do. For example, if the Air Force could just land UAVs in heavy cross winds that would be a huge win for the military. Currently, if the cross wind component is above a certain amount we cannot even land UAVs because they would crash. This is because the UAV cannot react fast enough to a wind gust the way a real pilot can. We lose hundreds of millions of dollars in UAVs every year because of simple stuff like this, and remember these are manned system that are only semi-automated. Fully automated aircraft don't even exist, because they would crash so much as to be much more costly and dangerous than useful.


Is it legal to compensate a CFI for more than 8 hours of his services per day? A CFI can only log 8hrs of in-flight dual given in a 24hr period (FAR 61.195).  In my scenario, a CFI is required to be aboard a plane to satisfy insurance requirements.  This CFI will put in a 17hr day, all of it in a plane that a non-student customer is flying as PIC.  The customer has a valid medical, is current, and is appropriately rated in category and class.

The CFI might (or might not, he doesn't need the time) log a few hours of dual given to complete a checkout with this customer but then just sit there for the next ~15hrs staring out the window as the ground slides by and the customer racks up the hours he needs.

At the end of a very long day the CFI hands the customer a bill for 17hrs and is rewarded about as handsomely as a CFI can be rewarded.  The CFI walks away with a fat stack of $20s and maybe 3hrs in the logbook.

Has the CFI broken a rule?

In my scenario, a CFI is required to be aboard a plane to satisfy
  insurance requirements.

This is the important line and you need to reference the policy for the exact wording. I happen to have some quotes from when I was shopping for an M20C about a year ago and here is the exact wording from my aircraft owner policy,

  Named Pilots and Additional Pilot Requirements

  You are to receive a minimum of 5 hours dual flight instruction in the
  make/model by a CFI who meets all the requirements of the policy and
  receive a written endorsement in your logbook from the CFI prior to
  solo; then 5 hours solo in the make/model prior to carrying
  passengers.

In this case it clearly states that the time is all flight instruction and not simply "CFI present" time if your policy is written this way then its pretty clear the FAR would be broken in your scenario. I think its safe to assume most policies are written this way although if the policy simply states CFI on board then its tough, although I agree with Ron's comment its going to be hard to explain as a CFI that you just "sat there".

Well it depends.  First off the CFI could only bill him for a minimum or eight hours of instruction time per §§61.195, so a bill for 17 hours of flight instruction is illegal under law.

Now if it happened that the pilot undergoing training hired via his own solicitation, the CFI as a commercial pilot could fly him under Part 91 Regs for the 17 hours.  This would have to be understood in advance or through a binding contract, and flight instruction could not take place for more than eight (8) hours during the trip.

While technically legal, this kind of flight is highly inadvisable as the CFI would be severely fatigued after such a long flight, whether he spent it as PIC or not.  There are reasons that Part 121 and Part 135 operations limit their flight time to eight (8) hours in a 24 hour period.


Why are airships not more popular? There is this question but I am hoping for more general answers to why airships are not more commonplace.

The previous question does bring up the cost of production (mainly because of hi-tech fibers used in body construction) and the high capital costs for constructing hangars for these airships.

However, civilization did operate fleets of these before and I'm just not certain why they have not 'come back' in a meaningful way. For instance, here are just a few uses that I can think of off-hand:

For tourism! Instead of a water-bourne cruise tourists can literally sail all over (I'd pay for that!)...
As the previous question implied, they can be used to carry cargo vast distances (although I am unsure if there is any real economic advantage here).

I know we use them in a small way for various things (military, sports, etc) but why are they not more commonplace?

I imagine the answer is mere economics but at the same time I feel there should be a market if for nothing else than tourism.

No one has really touched on the possibility of a cruise ship style airship. We have mentioned brief aerial tours but I'm talking about a semi-luxury week long trip in one of these things over very remote areas such as Alaska or the Siberia or even a desert... I realise there would not be room for all the luxuries of a cruise ship (pool, casino, etc) but I image about the same luxuries as a small yacht...

I imagine there are a lot of issues with long trips but can airships make unimproved 'port calls'? IE can they just set down for a few hours to let the passengers stretch their legs?

Airships are much more susceptible to bad weather. With an airplane you can pretty much count on it taking off on time and arriving within a couple of minutes of the scheduled time. This allows operators to employ their aircraft with a reliability which an airship will never be capable of. This means that the investment made into an airliner will lead to a predictable stream of revenue and (hopefully) profit, whereas the airship might need to wait several days until it can take off again, or headwind  might delay it by more than a day on a long trip. In this time, it will accumulate interest and fixed cost, but no additional revenue.

Scheduled air services were indeed first done with airships, but as soon as dependable aircraft were available, only a few niches like transatlantic travel were operated with airships. As soon as airplane performance covered those niches, airships became obsolete.

Today the most credible use of airships would be transportation of heavy equipment into remote areas. Tourism could be a second use, but the number of airships needed to cover this market is small. Airships do have some benefits:

no need to build roads or runways
carrying of outsize cargo is no problem
if the airship is big enough, payload can be immense
destinations can be anywhere, not only on a coast or a big river (where regular ships cover this niche more than adequately)

The few cases where the airship could be employed gainfully would not cover the expense of developing and building one. Development cost alone would be similar to the development cost of a new airliner!

But if we look back in history, even at a time when airships were available, big transportation tasks were done by aircraft. Papua has impenetrable jungles, and to transport dredging equipment and personnel to the Morobe goldfield from 1932 on, aircraft were used rather than airships. The huge dredges were dismantled for air transport and flown into Bulolo, where they were re-assembled and put to work. With a Zeppelin, less dismantling would have been needed, but just the complication of keeping the airship balanced when the load is released made this option less attractive.

For the history buffs: To transport very long items like the dredge shafts, a single-engined Junkers Ju-52 (Ju-52/1m) was used. It had a detachable rear fuselage with  automatic couplings for the control rods. Spherical collar screws ensured precise positioning of the two fuselage sections.

Has anyone mentioned the large ground crews required in launching and docking an aircraft? When labor was plentiful and cheap, this wasn't a problem.

Remember, the Hindenburg fire caused many casualties, most of them among the ground crew.


Can you land IFR at sea? I've heard that some seaplane bases have IFR approaches, but what about landing at sea?

If you flew out into international airspace, could you land at sea and then taxi back into US waters without being subject to US regulations? You wouldn't have to know where the "runway" is because it's everywhere.

(FYI, I'm a SEL pilot, so I'm not considering actually trying this!)

Well there is at least one case where this is true and it's used by the military - A Case 3 instrument approach to an aircraft carrier.

The approach is essentially equivalent to a terrestrial military TACAN approach coupled with a precision microwave landing system on final approach.  See the basic plate below.  Both IMC and night VFR conditions require a Case 3 approach per NATOPS.

As to civilian seaplane bases, the answer is actually, yes, some do.  One example is the GPS RNAV approach into Greenville Seaport (52B) in Greenville, Maine.

As for an instrument approach to land a seaplane at a arbitrary point in the middle of the ocean, no, I am not aware of anything like that.  Maybe one day an advanced version of GPS or some similar satellite based navigation system coupled with an advanced INS could allow a pilot to arbitrarily pick a point then create a custom approach which provided lateral and vertical guidance to the landing site.  Even if you could do this, you still face unknown hazards like surface winds and waves (seaplanes were never made to brave rough open ocean swells).  It would be virtually impossible to safely land on a moonless night.

it is not possible to land to sea in IFR condition. You need to see and you have to land your plane parallel to waves.


At what angle of deflections do rudders become inefficient? This article (picture) says rudders for ships can deflect 35° max,so at what aoa does an airplane rudder lose its efficiency,at what " angle of deflection " does it start to stall ?

The only time you should be using full rudder is when doing a side slip - such as turning the yoke for a left turn but pressing right rudder, so you are descending and looking to your left as the plane goes forward tracking down the runway direction.  Normal coordinated turns, you would not use anywhere near that much rudder while turning.

I just found a NASA Test Report on my plane, a Cessna Cardinal, that lists control deflection amounts as a reference for a light general aviation airplane:

Angle of attack,           -4° - +20° ± 0.5°

Sideslip,                 -15° - +15° ± 0.5°

Pitch angle,              -15° - +15° ± 0.5°

Roll angle,               -75° - +75° ± 0.5°

Rudder deflection,        -24° - +24° ± 0.5°

Stabilator deflection,    -20° - + 5° ± 0.5°

Right aileron deflection, -20° - +20° ± 0.5°

Left aileron deflection,  -20° - +20° ± 0.5°


Tailplane/Equilibrium conditions In regards to achieving equilibrium conditions, what is the relation between airspeed and the tailplane?

To be statically stable in pitch, the tail has to generate a downforce that opposes a continuous nose down pitching moment.  Everything else being the same, more speed increases downforce, less speed decreases it.  The equilibrium state is when the opposing forces are in balance in steady state flight, hands off the controls, and the airplane is said to be "in trim".  This is achieved at a given airspeed for a given set of "configuration of forces" you might say (pitching moments, thrust lines, C of G positions etc) and is called "trim speed".

Trim speed is the speed at which tail downforce balances the nose down pitching moments to achieve equilibrium (not accelerating or decelerating) for a given set of physical conditions.  FAR 25 static stability requirements require the plane to positively seek this speed by pitching uphill or downhill when disturbed from that speed in an attempt to regain equilibrium.

So the relation to the tailplane is that speed in excess of trim speed causes the nose to pitch up due to excessive downforce, which makes it go uphill and slow down, trying to get back to that equilibrium state.  Vice versa when speed is less than trim speed; it pitches down trying to get to the equilibrium state.  In an actual airplane it overshoots its equilibrium point several times trying to get there and eventually zeros in (the Phugoid oscillation).

Some other configuration change, a power change, a C of G change, a dragging item change, a flap sticking down, or elevator incidence change, will alter the speed at which equilibrium is achieved or trim speed. Once stabilized at a new trim speed, it will now seek the revised trim speed as before, if disturbed, as the tail responds to downforce changes with airspeed as described.


How high can I fly a model aircraft under 14 CFR 101 rules? For a UAS operated recreationally, may altitude exceed 400 AGL?  AMA rules state in several places that flight above 400 AGL should be avoided. And close to airports there is a more firmly worded restriction. But away from an airport, and presumably in Class G, what are the altitude restrictions?

This question presumes 14 CFR 101 applies.

Addendum to question: FAA appears to be attempting to impose a 400AGL restriction on 101 operations, without regulation. See the amended AC: https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_91-57A_Ch_1.pdf, stating: Model aircraft operators should follow best practices including limiting operations to 400 feet above ground level (AGL).

There's no specific altitude restriction for model aircraft anywhere in part 101 (that I can see). Even within 5 miles of an airport you only have to inform the tower, per 101.41(e):

  When flown within 5 miles of an airport, the operator of the aircraft
  provides the airport operator and the airport air traffic control
  tower (when an air traffic facility is located at the airport) with
  prior notice of the operation.

However, practically speaking there is an indirect altitude restriction in 101.1:

  For purposes of this part, a model aircraft is an unmanned aircraft
  that is:

  [...]

  (ii) Flown within visual line of sight of the person operating the
  aircraft

In other words, you have to be able to see the model aircraft and that limits the altitude and distance you can fly it at. It's also worth noting that 101.43 is very broadly written:

  §101.43   Endangering the safety of the National Airspace System.

  No person may operate model aircraft so as to endanger the safety of
  the national airspace system.

Arguably, that also implies you shouldn't fly any higher than you really need to.

There are no specific altitude restrictions.

The reason for the 400 foot guidance is that powered aircraft are supposed to stay at least 500 feet above the ground or any structure on the ground. So, if you stay under 400 feet then you minimize chance of collision with a full-size aircraft.

The main exceptions would be crop dusters and flight paths into landing zones, such as airports, heliports, helipads and sea plane bases where aircraft will descend below 500 feet above the ground objects.


How can L/D Max be both Best Glide speed and Max Range speed? According to the book "Aerodynamics for Naval Aviators", best glide speed AND max range speed for propeller aircraft both occur at L/D max.
This is a little confusing because in an A36 Bonanza Vbg is 110 KIAS and Vmax range has been experimentally calculated by several sources to be about 125 KIAS.
So my explanation for how both of these are L/D Max is that L/D Max is a specific AOA, not a speed.
However, this brings me to my question.  Obviously Vbg is power off and Vmax range is power on. Assuming that L/D max is around 6 degrees AOA, with no power the airplane is descending at about 700-1200fpm (depending on prop pitch and other configuration items) at a speed of 110 KIAS.  At max range speed the airplane is level at 125 KIAS and presumably also at an AOA of approx 6 degrees.
Something seems off here.  Here is what I’m having a hard time correlating:  I teach that trim controls AOA, not speed.   If the airplane is trimmed for an AOA of 6 degrees, adding or removing power should only change the rate of climb/descent, not the airspeed.  Adding power gradually from the power off glide config at 110KIAS will eventually result in
level flight AT 110 KIAS.  If we wanted 125 KIAS we would have to add power while trimming down (lowering AOA) which means we are not at the same L/D Max AOA at Vmaxxrange that we were at Vbg.
I feel like I’m missing something here, so either one of my assumptions is incorrect, or there is another puzzle piece I’m missing that explains this. If we have to retrim for 125 KIAS level with added power, how can we be at the same l/D max AOA?

I'm going to answer with the caveat that I don't have as deep of an understanding of this as I would like, and someone smarter than me may be able to correct or expound on my response.
Best Glide is a purely aerodynamic concept. There is no powerplant involved, so you're simply converting potential energy (altitude) into forward motion, at a rate and L/D ratio that is driven by the angle of attack. It's a simpler concept.
When you add a powerplant into the equation, it gets a lot more complicated. The powerplant itself has modes where it's more efficiently converting fuel energy into thrust, and modes where it's less efficiently doing so. Max Range, therefore, depends not only on aerodynamics, but also how efficient the powerplant is. When you add powerplant dynamics into the equation, you might settle on a best range speed that is different than the purely aerodynamic best glide range speed.
Simply put...

Best Glide is where L/Dmax occurs.
Max Range occurs when (FuelBurn / GroundSpeed) is the lowest.

On a related, but slightly different, note: Piston airplanes and Turbo(fans/jets) behave differently when it comes to producing power at different airspeeds. It's why we generally measure turbofan engines in thrust, and piston engines in horsepower. This difference is why Max Range and Maximum Endurance speeds correlate with Best Climb Angle and Best Glide speeds differently, when you compare pistons to jets.
I hope this helps.

The general "textbook" formula to show calculate the max range speed (at least the one I was taught), goes more or less as follows:
For a piston engine, fuel consumption is roughly proportional to engine power:
[1] fuel_consumption_per_hour = constant * power

Hence
fuel_consumption_per_mile = constant * power / ground_speed

Assuming no wind, gs = tas, power is thrust * tas. In steady level flight, we get power = drag * tas.
Plugging it back:
fuel_consumption_per_mile = constant * drag

Which is minimum for lowest drag. For a given weight, assuming lift = weight, we can get:
D = (D/L) * W

So in order to minimize the fuel consumption per mile, we need to maximize the L/D ratio.
All of this hinges around the assumption [1], which works for an ideal piston engine with perfect efficiency.
Furthermore, as you pointed out, the relationship between angle of attack (and airspeed), and L/D ratio normally is affected by the engine RPM because of aerodynamic interference. (Also in certain aircrafts, thrust vectoring effect will significantly affect the tail lift, making the entire relationship even more complicated).
Conceptually, one would have to:

Select optimal L/D ratio
Compute AOA and Airspeed (weight dependent) that results in the selected L/D ratio
Compute engine power required for steady flight
Re-enter at 2 with new engine power setting, and repeat.

In practice an approximate answer is always fine. In your case an error of 15 kts doesn't seem to terrible.


Has a flight data recorder or cockpit voice recorder ever failed in an accident? Has there been a time either during an aviation accident or during normal flight where the flight data recorder or the cockpit voice recorder devices failed or the data was significantly corrupted?

As mentioned in the comment above, there is lot of aviation accidents with unrecovered flight recorders. List from wikipedia:
https://en.wikipedia.org/wiki/List_of_unrecovered_flight_recorders


Could an airliner be as efficient lower and slower? Could an airliner ever be as efficient at 15 or so meters using ground effect as it is at 50,000 km even if it has to go slower and be shaped differently?

It's important to note that an airliner cruising at 50000 ft (I assume that's what you meant, and that's actually business aircraft territory; airliners are generally below the low 40s).  Is going pretty slow from an indicated airspeed perspective.  At 50000 ft an airplane is going roughly twice its indicated airspeed (it's actual speed through 3D space is twice the dynamic air pressure acting on it - if you stick your hand out, you'll feel the force of a 200 kts acting on your hand, even though you're actually going 400 kt).  So, such an airplane is actually optimized to only fly at 240 kts anyway, if it's cruising at a true airspeed of 480 kts.

What it means is, however you want to optimize for sea level flight, the higher you go the faster you can go in reality for a given fuel burn, whatever the configuration, burning far less fuel per unit of distance in the process.

Could an airliner ever be as efficient at 15 or so meters using ground
  effect as it is at 50,000 km even if it has to go slower and be shaped
  differently?

Yes it can.  The most efficient shape for an airliner is no shape at all, so that the passengers have to get out and walk.  (On 15-meter-tall stilts of course.)

Alternatively, consider attaching electric motors to the wheels, so that the airliner could taxi to its destination along established roadways. 15-meter-tall landing gear could be used to maintain the prescribed altitude. "Stub" wings could be retained, so that the aircraft could be claimed to be "using ground effect" to some infinitesmal degree.  This mode of transportation would surely be more efficient, in terms of energy expended per unit mass transported per mile, than climbing to 50,000 km, at least for any total distance equal to less than one half of a complete orbit of the planet.

Unless, of course, the airliner is assumed to be magically transported to 50,000 km before we begin the calculations to establish efficiency.  If this is the case, the airliner can follow a ballistic trajectory toward its destination and then, upon entering the atmosphere, transition to gliding flight.  In this particular case, flying between the same two geographic points while maintaining an altitude of 15 meters AGL would likely represent a greater expenditure of energy than following the ballistic/ gliding profile described above.


What happens when a takeoff clearance is cancelled by the ATC? Let's say an commercial passenger jet is accelerating down the runway, taking off. The ATC receives some signal that he/she should cancel all takeoff clearances.

Exactly what happens in the control room?
What does the ATC do and how does he/she make sure pilots understand the cancellation?
How do the pilots in the aircraft taking off respond? Are they trained for this scenario?
Is a takeoff cancelled even after V1?

What happens in the control room?

Aborting a take-off at high speed is dangerous, even if the aircraft is travelling below V1. If the aircraft is already rolling, the controller will make a quick decision whether the situation justifies an aborted take-off. For example, if there is traffic infringing the runway and a crash is imminent the controller would attempt to stop the aircraft. If an aircraft is attempting to take-off from a taxiway in snowy conditions it might be safer to just let him take-off unless there is other traffic on the taxiway.

If the aircraft hasn't started rolling the decision is of course easily made.

  What does the ATC do and how does he/she make sure pilots understand
  the cancellation?

Using standard phraseology is the best way of making sure the message comes across, especially in international aviation.

If the aircraft is not yet rolling, the proper ICAO phraseology is:

  Tower: Big Jet 345 hold position, Cancel take
  - off, I say again cancel take
  - off (due to vehicle on the runway)

  Big Jet: Holding, Big Jet 345

If the aircraft already started rolling the controller would say:

  Tower: Big Jet 345 stop immediately, (Big Jet 345 stop immediately )!

  Big Jet: Stopping, Big Jet 345

No immediate verbal reply is to be expected as the flight crew have other things to care about at that moment. The effect of their actions should be clearly visible from the tower.

  How do the pilots in the aircraft taking off respond? Are they trained for this scenario?

The crew will assess whether they can stop safely. Below V1, they will probably abort the take-off, above probably not. The final judgement is made by the captain. He might reason that it is safer to get airborne and pass the infringing traffic overhead than running into it at full brakes. They are trained for aborted take-offs, but since there are so many non-standard situations the final decision is made on the basis of a mix of training and expert judgement.

  Is a takeoff cancelled even after V1?

Since ATC does not know when the aircraft passes V1, a controller might attempt to cancel the takeoff after V1. The flight crew will only attempt to cancel the take-off after V1 if it is clear that there is no way the aircraft can become - and stay - airborne safely. In such a case it becomes damage control rather than damage prevention.

A takeoff clearance cannot be revoked. Once you issue a clearance the aircraft is CLEARED for takeoff.

If the tower realizes that something that will obstruct or threaten an aircraft taking off is present, all they can do is inform the PIC of the situation. At that point it is up to the PIC to figure out what to do. They might try to abort the takeoff or perform an evasive maneuver.

To clarify you this for you: a tower cannot tell an aircraft to abort a takeoff because they are not qualified to make that determination. The guy in the tower neither is qualified nor can see the instruments of the aircraft so they have absolutely no idea whether it is safe to abort a takeoff or not. Therefore, they will never tell a pilot to abort a takeoff once it is underway. All they can do is cancel the clearance (See Section 9. Departure Procedures and Separation in FAA ATC guidelines). The phraseology is:

  [Call sign] Cancel Takeoff Clearance [state reason]

Of course, if the aircraft has reached V1 it will not abort.

In situations I have been in where something bad has happened is that the tower will just tell the pilot what to do. Like if some plane tries to land the wrong way on a runway when you are taking off, the tower will say "[call sign] Bear right immediately, traffic dead ahead!" So, you basically try to veer to the right to avoid the head on collision.

To answer your specific questions:

Exactly what happens in the control room?

In a crisis scenario, the tower guy will say whatever he/she thinks is necessary to avoid a collision. Once I had a near collision because another guy was not where he supposed to be, but I was the one with comm, so she moved me by screaming "TURN LEFT RIGHT NOW !!!" Phraseology goes out the window when you are 0.5 seconds away from a huge fireball with multiple fatalities.

What does the ATC do and how does he/she make sure pilots understand the cancellation?

(I gave the phraseology above.)

How do the pilots in the aircraft taking off respond? Are they trained for this scenario?

If you can safely abort, you abort and slam on the brakes. If not, you keep going and try to maneuver around whatever it is, moose, truck, whatever. Pilots are trained to never abort when they reach V1. Other than that it is experience and nerves that count, no more training.

Is a takeoff cancelled even after V1?

Cancelling is what the tower does. Aborting is what the pilot does. The tower cannot "cancel after V1" because they have no way of knowing if the plane is at V1 or not. A pilot will almost never abort after V1 because the consequences of going 100 miles an hour off the runway are almost always worse than the consequences of going 100 mph in the air. If an unavoidable obstruction occurs, like a plane rolls onto the runway in front of you, and you are at V1 you still takeoff, you just try to do it sooner.


Can you broadcast a very low power nav vor signal in air? Are there any FCC restrictions on broadcasting a test nav signal on 108.0 in the air? Or perhaps on other nav frequencies that can be received within the navigation band?

The use of radio transmitters is strictly controlled almost everywhere in the world. FCC would be the authority in charge if you are asking for the USA.

The International Telecommunications Union (ITU) is in charge of allocating frequency bands for different applications in the radio spectrum. You are only allowed to transmit if you have a frequency assignment, if your equipment is certified, and you are holding the required radio license.

There are use cases where non-certified equipment may be used (e.g. amateur aka HAM radio), or no license is required (e.g. wireless consumer devices like cell phones, remote controls, etc).

108.0 MHz is at the upper edge of the frequency band allocated to FM radio broadcasting, and the lower edge of civil aviation frequencies. Therefore 108.0 MHz is not available for experimental navigation signals. Your usage would be illegal. The same will be the case for any other frequency that can be used with certified navigation receivers.

The answer is yes with the caveat that there are limits. The hard part in dealing with aviation radio systems is that there are multiple agencies with some overlapping regulatory authority.

As bogl points out, the ITU is the international forum for radio spectrum. The NTIA is the US agency that is the US representative to the ITU. The NTIA has general oversight of radio spectrum. Actual management of radio spectrum is delegated to various government organizations.

The FCC is the primary US manager of spectrum, but not the only one. The FAA and the military both have significant pieces of spectrum that they manage. For the FAA, these include the aeronautical radio navigation bands and the aeronautical radio communication bands. The VOR/ILS are within the VHF radio-navigation band of 108.00 to 117.95 MHz.

The FAA controls transmitting of navigation signals. They do allow for low power transmissions for the purpose of testing avionics. But you just can't build your own transmitter unless you're willing to go through a ridiculously lengthy approval process that includes both the FAA and the FCC. The FCC is involved because any transmitter has to comply with Part 15 for non-interference.

So, if you are using an approved piece test equipment you can use it for short periods of time to test avionics. The use of nav/comm ramp testers such as the IFR-4000 is quite common.


Can noise from the passenger cabin be picked up by the cockpit voice recorder? How sensitive is the cockpit voice recorder?  Can it pick up sounds from the passenger cabin?

It depends a bit. One of the microphones for the cockpit voice recorder is an "area microphone," which is designed to record whatever someone standing in the cockpit would hear (the others record from crew headsets and possibly the PA system). This area mic is continuously recording; it does not just turn on when there's more than some threshold of noise. If the noise in the cabin is loud enough to have been heard in the cockpit, it will be heard on that mic. If not, it won't.

I only have experience with general aviation (GA) aircraft, that being said, I bet the intercom in a commercial airliner is similar.

There is something in GA called "squelch" which is like a minimum volume limit for the microphone to turn on.  This makes it so background noise (such as the engine) doesn't make it into the intercom system.  If commercial airlines use this same technology it is very likely that any background noise from passengers is not going to get picked up by the intercom system, and it will not be recorded.

That being said, a commercial airline is much quieter than most GA aircraft, so they might not use squelch.  However, the microphones are still going to be pressed up against the pilot's lip, and any sound from the cabin that makes its way through the air, and cockpit door is going to be so quiet that it will be indistinguishable by the time it gets to the pilot's microphone.


"Airplane mode" does not disable GPS... is it safe to use GPS in flight? I noticed that even when my phone is in "airplane mode", I can still use the GPS.

Theoretically a GPS receiver just receives data, so I guess it would not jam anything.

On the contrary, on the iPhone airplane mode disables GPS, so it means that at least a few engineers at Apple are worried about people using GPS in flight.

Is it really OK to use my phone's GPS in plane, as a passenger of a typical commercial flight?
(when use of electronic device in airplane mode is allowed, obviously)

theoretically? GPS IS receive only. There's no way to talk to the GPS satellite network except using the big antennas of the network owners (the US DoD) and the communications are no doubt heavily encrypted.

Now, does that mean it's "safe" for aircraft electronics. Any receiving antenna does have an EM field around it, so if you believe the myth that those electronics are so sensitive and easy to jam that any EM field at all causes them to malfunction the answer is an obvious NO.
But that myth is just that, a myth. If they were so sensitive, that old walkman you were using in the 1980s during flights would have brought down that aircraft. Because not only do antennas have EM fields around them, any electrical device that's turned on has one (in fact any electrical cable with a current flowing through it has one, including the headphone cord for the in flight entertainment system).
And that GPS system in your cellphone uses a lot less power than that walkman, has a far weaker field surrounding it.

Of course it's theoretically possible that a strong enough EM field might interfere with the electronics in an aircraft, but then to you'd need just the right signal. Which would indicate you need intent (or incredible bad luck)!

Effectively the GPS in your cellphone is a lower powered version of the GPS receiver in the belly of the aircraft, which has its own antenna (which no doubt has a similar field around it, but of higher strength).

I would have added a comment to @JamesHam's answer but I don't have the rep.

Long story short, Your GPS on your phone is receive only. Yes your antenna will generate some field but I doubt it is much stronger when the phone is on than when it off. (However, antenna and interference were not my area of expertise.)

GPS signals travel at the speed of light. Even plane at top speed is still very close to stationary by comparison to the speed of light. Any issues you have with regards to GPS at speed have to do with your phone's hardware/software.

As far as the safety issue is concerned... It is a myth. Period.

While this is not my area of expertise a little simple logic goes a long way. Consider that your plane is awash in signals at a lot of frequencies while it is on the ground and at landing and takeoff (the most dangerous times). Signals from cell towers, FM and AM radio stations, GPS, DirecTv, lightning, etc. All of these sources bathe the airplane in EM waves across a slew of frequencies. Most bathe airplane with much more power than your phone can. Additionally, every wire with electricity in the airplane puts out an EM signal as well.

Another logic argument, there are approx 200+ people on every major flight in the US. If only 1% forget to turn off our phone that means there are at least 2 people on every flight with their phone's on the entire flight. EM interference happens over the course of less than a second so every hr of flight time represents at least 3600 discrete opportunities for EM interference per operational phone. How many flights crash every day?

Any modern aircraft is digital not analog. So interference due to EM can really only cause a flipped bit or a few. As far as a sweet spot in frequencies is concerned the most likely culprit for interference will come from other aircraft systems that sample and process data at the same frequency as the system being interfered with.

But so what? Every sensor man has ever created will create the occasional bad data point. Planes, satellites, etc all have to be robust to a few bad data points. So every computer that consumes sensor data on airplane has filters built in to it specifically to deal with a short series of bad data points.

Specifically the navigation system is usually blamed when the FAA or someone says EM interference brought that plane down. They then go about telling you how impossible it would be to prove it. So ... why do we believe them?

The navigation system in particular is built in such a way as to cope with missing and bad data. Typically the nav system uses some combination of multiple attitude, acceleration, velocity, and position sensors operating at different update frequencies. GPS is often only updated once a second while gyros and accelerators are updated sometimes 1000s of times a second. Then there is a propagator (or estimator) that calculates the aircraft's position, velocity, and attitude in between GPS updates using the faster sensor data. All of that sensor data is filtered so that the occasional garbage data point (which every sensor ever built generates) doesn't cause the aircraft to behave wildly, unpredictably, and sometimes fatally.

The nav system is often blamed because it is all software and sensors. The engine can't spin up or slow down fast enough for a few spurious data points to cause issues. Neither could the controls surfaces (flaps, ailerons, etc). A spurious blip in the radio or radar by themselves doesn't cause an aircraft to go down. So by deduction it can only be the nav system becoming confused by bad data. Except every modern nav system is inherently robust to noise on the sensor data and the larger the error is in the spurious noisy data the easier it gets filtered out.

Oh, and every single computer system on an aircraft is shielded against EM interference.

EM interference is a boogey man the FAA uses when they don't have an answer. It is reproduce-able in a lab in just the right setting. But the aircraft would never have gotten off the ground if it were sensitive enough to crash due to your cell phone or even 200 cell phones simultaneously in use on board.


Why cruise at 7000' in an A319? I was on a flight from Philadelphia (KPHL) to Boston (KBOS), after some delay and some change of route due to weather, the captain announced that we will be cruising at 7000' due to delays in the area.

The history of the flight is here: https://flightaware.com/live/flight/AAL2606/history/20190618/2235Z/KPHL/KBOS

My question is two fold:

Why cruise so low with such an aircraft (A319)?
What is the impact on fuel consumption, knowing that we were also slower?

The only reason for your flight to operate at such low altitude is because it is cheaper for them to do so.

As you said it is due to weather, other route/altitude may not be available. They can cancel the flight but that is likely to be costly. They may have to find accomodation for you and crew until they can put you to the next flight. Sub-optimal flight maybe better than no flight in this case.
They may need that aircraft at that location the next day. If they choose to cancel your flight today, they will have to find a way to have this aircraft or another aircraft to fill in for the required flight the next day. They might as well fly a slightly more expensive flight at lower altitude rather than fly an empty plane to Boston.
It is possible for them to wait for weather to improve but there is an issue of crew working hour. A pilot cannot work more than 8 hours in a day without provision for additional crew. They may approach that limit and the wait for weather to improve might means the airline has to provide another crew for the flight and might mess up crew schedule for the next few days.

So for the airline, in this case, flying lower and slower maybe a better option for them. Hence higher fuel comsumption is better than no flight.

Possibly, the flight was too dangerous at a high altitude due to complications in weather, and therefore they decided to fly lower and slower. Flying at 7000' is very fuel-consuming, but they could do it since Philadelphia and Boston are fairly close together.


What kind of damage would low-level supersonic flight inflict? I was watching a video about "The Big Stick" aka Project Pluto, a nuclear powered SLAM. In the video (I couldn't find the exact video) it said that after deploying its weapon payload a SLAM could fly over its target country as a "vengeance weapon", causing destruction with it's sonic boom for weeks and an altitude of just a few hundred feet.

What kind of damage would a mach 3 flyby at 200 feet cause?

I'm interested in both building damage and possible human injury.

The video is highly inaccurate in that area.

The actual damage the missile would have caused would have been largely radiological, from ejected radioactive material in its exhaust plume.

While windows and weak structures may receive damage from extremely low flying Mach 3 bodies, this would probably be limited to say some broken glass.

The plan was also never really considered. What was considered is having the weapon, now without its warheads, fly to a final target area and do a high speed dive into the ground, the kinetic energy alone combined with the spread of radioactive material from the rupturing nuclear reactor causing the damage there.

Mind that the damage (both physical and radiological) of the weapon flying overhead isn't clear. Different sources list different predictions.
Some way the damage would be minor, others that it would be severe.
But rest assured, the noise would shatter eardrums, the supersonic shockwave flatten crops and lightly constructed buildings, and the radioactive exhaust plume wouldn't have been healthy either.

I've always found this to be an excellent article on the project and the people surrounding it.

Edit: a very interesting article by the designer of the reactor about the problems inherent in the reactor design, and how he thought about the radiation hazard for people on the ground working with the missile:
Merkle public paper


Is an afterburner louder than the same jet engine without it? I would speculate that an afterburner increases the noise because it is nearer to the exhaust. But it certainly causes so many changes in the exhaust flow that it could be less loud as well. It may also depend on the shape of the nozzle.

That an afterburner increases the spacial volume of exhaust gases does not necessarily mean that the sound volume increases as well, because it strongly depends on the level of turbulence.

Does activating an afterburner make a jet engine louder? And why?

This PDF indicates an increase by ~10 dB for an F-8K in afterburner versus the same aircraft in 100% dry thrust.

This PDF indicates smaller increases:

+5 dB for an F-15
+4 dB for F-22 and F-35

If you are asking if the engine is louder, no it is not. The afterburner and the diversion of the exhaust is what makes it louder. Just like in a car motor running straight pipe to gain horsepower. You can take the same motor and put an exhaust system on it and it will give that motor a different tone.


Are you cleared to next altitude when you get "direct" while flying SID? Let's say you just took off from the TACOMA airport and were flying ATOME TWO DEP. ARRIE transition. The Seattle tower instructs you "direct to ZUMBI" and to contact Departure, and you contact Departure and report "Departure, N1234, passing 2000, direct ZUMBI." If departure just replies "N1234, Departure, Radar contact," are you cleared to the next altitude of KIMSH (at or above 10000ft) or should you maintain 9000 until Departure gives you higher?

As an example, say you receive an IFR clearance from clearance delivery prior to departure such as: "N1234 cleared to Los Angeles Airport, ATOME TWO DEPARTURE, ARRIE Transition, Q-One Forty-five, climb via SID, Squawk 2252, etc." Then, after passing 2000 ft. if the tower controller instructs you to "proceed direct ZUMBI" then he/she (controller) should issue you an altitude assignment because you are being taken off of the lateral path of the SID.  In the alternative the controller could assign an altitude by using the phraseology (or similar) "N1234 proceed direct to ZUMBI, climb via the ATOME TWO departure." The "climb via" verbiage in this sequence is the equivalent of assigning an altitude.

After switching frequencies to the radar controller he/she should instruct you (for example) "after ZUMBI climb via SID" (assuming that ATC wants you to meet the KIMSH restriction and climb to the published Top Altitude of 15000 ft).

Here is some information from the ATC Controller's Handbook 7110.65W, para. 2-6-4, g. 2 and the associated Note: (Air Traffic Controller's handbook, 7110.65W)

(Although the reference paragraph and note, as it is published in the controller's handbook, is an example when a deviation around weather is necessary, the principle underlying my explanation is the same (there is just not an example similar to the circumstances you describe in your question).

  When approving a weather deviation for an
  aircraft that had previously been issued a crossing
  altitude, including Climb Via or Descend Via
  clearances, issue an altitude to maintain along with
  the clearance to deviate. If you intend on clearing the
  aircraft to resume the procedure, advise the pilot.

  NOTE−

  After a Climb Via or Descend Via clearance has been
  issued, a vector/deviation off of a SID/STAR cancels the
  altitude restrictions on the procedure. The aircraft’s Flight
  Management System (FMS) may be unable to process
  crossing altitude restrictions once the aircraft leaves the
  SID/STAR lateral path. Without an assigned altitude, the
  aircraft’s FMS may revert to leveling off at the altitude set
  by the pilot, which may be the SID/STAR’s published top or
  bottom altitude.

Also, from the FAA's Pilot/Controllers Procedures & Systems Integration Workgroup FAQs regarding "Climb Via" procedures, here is an applicable Question and Answer (FAQs Climb Via):

  Q.
  I’m on a climb via clearance and the controller vectors me off the procedure.  Do I continue to “Climb Via?”

  A.  NO.  You are laterally and vertically off of the
  procedure.  The controller will issue an altitude to
  maintain and provide a further “expect” clearance.
  Note: Request an altitude to maintain if the
  controller does not provide one

The main point is that a clearance to fly a SID that contains a Top Altitude and verbiage that includes "Climb Via" assumes that you will fly the lateral route as published, thereby committing you to meet the altitude restrictions.  If you are taken off of the published lateral routing ("cleared direct" to a fix somewhere down-range on the SID) the controller needs to issue you an altitude assignment since you (while proceeding direct to ZUMBI) are no longer on the published SID lateral route. In the alternative the controller could assign an altitude by using the phraseology (or similar) "N1234 proceed direct to ZUMBI, climb via the ATOME TWO departure." The "climb via" verbiage in this sequence is the equivalent of assigning an altitude.

From the NBAA Access Committee briefing regarding "Climb Via" procedures:
(NBAA Climb Via Briefing) showing ATC Phraseology when being cleared direct to a fix on the SID.

Pictorial display from the NBAA briefing (see link above) of pilot/controller responsibilities and phraseology when being cleared direct to a (down-range) fix on the SID after departure:

If the controller did not issue me an altitude instruction ("maintain," "climb via," etc.) upon taking me off of the SID I would have asked for one.

Here is a link to the ATC Controller's Handbook (7110.65W) so you can review the reference noted above. Also, here is a link to a FAQ's publication regarding Climb Via Climb Via FAQs

Given the clarification in the comment, that the initial clearance was to Climb Via the SID...

You’re still cleared climb via, even with the turn direct, so not above 9 until past ZUMBI, but as soon as you are past that fix, climb up to 15, making sure you’re at or above 10 at KIMSH.

To address some things in the comments for the other answer:

When you're cleared OFF of a SID or STAR that you'd been climbing/descending via, you're in a no-man's-land of ambiguity: can I immediately climb/descend unrestricted to the top/bottom altitude as published, or does the controller need me to stop at something prior to that altitude -- perhaps to maintain separation with other traffic?

In the case of the OP's question, you still have the (only) hold-down point in front of you: ZUMBI at 9.  There was nothing before that would keep you from climbing straight up to 9, so why stop any sooner than that after the direct?  And, after ZUMBI you'll still be on the SID routing, which gives you a climb to 15, so nothing changed there either.

As for what the controllers ought to be doing, maybe they need to give you an altitude clearance with every shortcut no matter how inconsequential, but if they don't there is no ambiguity in what the pilot still needs to be doing here.

Getting vectored off the procedure (or, potentially, a shortcut that bypasses ZUMBI) is an entirely different story: you absolutely need to query the controller if he doesn't state an altitude clearance in that case. If he needs you to go no higher than 9 until past the line of arrivals that cross the departure path near ZUMBI, he should make that clear. Or if nobody is on that arrival path & you're good to climb unrestricted right now, he should tell you that as well.  But in the OP's question as stated, this isn't ambiguous. The shortcut mentioned doesn't bypass, nor introduce, any altitude restrictions.


Is the "glory" optical phenomenon frequently seen by aircraft pilots? A glory being this optical phenomenon:

(Source)

It reveals the presence of supercooled water, a hazard for an aircraft (see answers).
Due to the way it can materialize, the center of the rings indicates the position of the observer in the airliner. So this one was not shot from the cockpit.

Does it represent a specific icing hazard?
How frequent is it?

Short Answer:

Yes, pilots frequently see this phenomenon.
No, it does not necessarily present a specific icing hazard.
Yes, in some circumstances it can be in indication of an icing hazard.

Longer Answer:

Speaking for myself, yes, I often see this. I cannot speak for all pilots, but I think many pilots do also see this. The phenomenon depends on several conditions, the primary ones being angle of the aircraft relative to the sun, and the presence of liquid water droplets.

However, I would contest the assertion that it reveals the presence of supercooled water. I see the phenomenon most often in low level fog banks or mist. I do a lot of early morning flying when the conditions are right for the phenomenon. On many of these occasions the air temperature is well above freezing, and all other weather conditions would also indicate that the water droplets are not supercooled. See the following photos from the wikipedia page showing the phenomenon in low level (probably above 0°C) fog banks:

Since the water droplets connected with the phenomenon are not necessarily supercooled, the risk of icing will depend on other factors, primarily outside air temperature. Though the "glory" phenomenon does indicate visible liquid water droplets, it does not necessarily indicate an icing risk. A thorough pre-flight risk assessment for icing conditions should answer that question on a case by case basis.

Now, the conditions in which many airline passengers might see the phenomenon may well be at an altitude high enough that the liquid water droplets may very well be supercooled. In such cases the "glory" phenomenon indicates that the cloud in question is not formed of ice crystals (which pose little icing risk) but of liquid, and possibly supercooled liquid droplets.

Yes. It represents a potential icing hazard. As you noted, the glory (or pilot's halo or glory of the pilot) indicates the presence of liquid water in the cloud. If the temperature is in the freezing range and the aircraft descends into the cloud where glory is seen, icing can be expected.
From NavCanada manual:

The glory is one of the most common forms of halo visible in the sky. For the pilot it is a warning sign of potential icing because it is only visible when there are liquid water droplets in the cloud. If the air temperature at cloud level is below freezing, icing will occur in those clouds that produce a glory.
A glory can be seen by looking downwards and seeing it surround the shadow that your aircraft casts onto the cloud tops. They can also be seen by looking upwards towards the sun (or bright moon) through clouds made of liquid droplets. ... . Although ice crystals often produce other halos
and arcs, only water droplets form bullseyes.

Glory is quite common. In pre-airplane days, glories were quite rare and one good way to see them was to go up a mountain, a phenomenon called Brocken Spectre. However, with the advent of air travel, the phenomenon has become more common.