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AF 447 Thread No. 11

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AF 447 Thread No. 11

Old 19th Nov 2013, 17:15
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Chris
It is Entree Level Training/Jet Familiarisation/Multi Crew Cooperation. It can be consolidated during Refresher training and online but unless you know the symptoms and the correct procrdure of UAS you may not handle it competently and safely. Let us say a pilot is competent in hand flying but does not remember correct procedure of TCAS he can mess it up.
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Old 19th Nov 2013, 21:34
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I'll try different approach this time

Originally Posted by Gums
Glad to see a few that "believe" in a decent AoA indication that could have the "limit" AoA clearly marked for the pilot.
What limit?

Originally Posted by rudderrudderrat
The pitots don't measure the angle of attack!
What do they measure?

Originally Posted by BOAC
Indeed, 100kts TAS is well enough to register an AoA on a balanced probe
100 kt in which direction?

Originally Posted by RetiredF4
why besides the AoA a speed indication is needed to determin wether you are in a full stall.
Really, why?

Originally Posted by rudderrudderrat
Why keep the 60 kt logic when airborne?
Really, why?

Originally Posted by RetiredF4
At the moment we are discussing the inconsistency of the stall warning, right?
What inconsistency?

Originally Posted by retiredF4
Due to an airspeed, which was inconsistent in itself?
And therefore rendered an available AOA indication as unreliable?
What occurrence are you discussing here?

Originally Posted by RetiredF4
And you think, that is a logic system in itself and not worth improving?
Improved in what way?

Originally Posted by BOAC
That sounds suitably over-complicated.
How would you simplify it?

Originally Posted by RetiredF4
I can understand that some input like speeds are necessary to compute the exact angle of attack.
Why is it so?

Originally Posted by RetiredF4
Why not implement a logic, where an AOA value above the highest stall onset AOA bypasses the above logic and thus keeps the stall warning active?
Really, why not?

Originally Posted by BOAC
no - the lack of stall warning when the Captain arrived in the cockpit was non-'trivial'.
What occurrence are you referring to here?

Originally Posted by gums
I do not understand the "HUD resistance" here by several heavy pilots that seem to tolerate MFD's that are crowded with data and tapes and....
What MFDs are crowded with data and tapes? How do you propose to reduce crowding?

Originally Posted by ventus45
We all now know, definitively, that (a) the AoA resolver outputs were available, and (b) that they were valid. Discarding them is unforgivable.
Why every aeronautical power that be does not see that?

Originally Posted by ventus45
The “below 60kias” is a classic case of such an arbitrary false premise “knock out filter”.
How many medium and heavy jets vent below 60 kias while airborne, ever?

Originally Posted by ventus45
That allows the aeroplane to tell a pilot, “Everything else, air-data wise, is tits up guys, but I still have valid AoA, any use to you ?
TWA843

Cheap provocation, eh? Think again, gentlemen. All of these questions are answered many times during the course of 11 threads we had on subject yet same old opinions resurface again and again. Please put some effort in answering these, I would really like to know what you didn't understand last time and time before that and before that...


Originally Posted by gums
I never worried about ":floors" or "protect" or any of that.
You were not supposed to return it to earth unscathed if everything went southward so not much point in having backup FCS modes. No ACES in passenger jets.

Originally Posted by Turbine D
As I understand it, the idea is for the PF to look through the center of the HUD and fly the flight path symbol, but incorporate the side displays in his periphery vision as to how they maybe changing.
Well... might be idea but it doesn't work out this way. I'd estimate the display to be 2 - 2.5 times wider than PFD and display being monochromatic aggravate the complete scan. It excels at visual approaches where any change in flightpath is immediately recognized as conformal flight path vector jumps around and that's the only thing you need to know besides speed. It is excellent for CAT3a approaches where there is not much scan anyway - you just make perfect doughnut with aeroplane symbol and guidance cue, shorten the speed error tape as much as possible, keep energy caret aligned with wing symbol using throttles (all of the symbols are concentrated in the middle of the HUD so you just stare straight ahead) and rely on F/O scanning classic PFD and HGS annunciator panel to shout "GUIDANCE" if things go pear-shaped.

Originally Posted by Chris Scott
My suggestion of an initial "knee-jerk" reaction implies, by definition, an absence of rationality. Explanation is not justification.
It's not kneejerkiness I don't agree with, it's idea that pull-up-no-matter-what came initially from attempt to return couple of hundred feet lost on altimeters when speed correction went missing.

Originally Posted by Chriss Scott
So he handflew in the wrong way, but not because he was unable to handfly?
Exactly! He did not understand what happened despite uttering "We have no good display of speeds" so had no idea the best thing to do under the circumstances was...to do nothing. Pull was so consistent that it just couldn't be unintentional. Problem was within cognition.

Originally Posted by Chris Scott
He knew that he wanted to maintain altitude but felt it necessary to keep pulling back on the stick to achieve such?
No. He didn't know anything. He wanted to pull-pull-pull for reasons he never verbalized. If he was afraid of overspeed and tried to trade speed for altitude, why going to TOGA? As soon as the AP dropped out, all the thinking on the FD stopped for good.

Originally Posted by Chris Scott
All that needed to be done in AF447 was to keep the wings level
Done.

and MAINTAIN a suitable pitch attitude and thrust for high-altitude cruise.
Yes but this is all very well when you either know what happened or maintain presence of mind not to do harm when you are not sure what exactly you should be doing.

Originally Posted by Chris Scott
Firstly, you will not learn the very gentleness of any corrections that need to be made on the side-stick if you unexpectedly find yourself without the AP at high altitude.
You suggest that A330 is sensitive beast that has to be treated gently. I say that it is exaggeration and you can throw her around hamfistedly at cruise altitude, in alternate law for 4 minutes with normal acceleration varying between +1.96 and -0.26G with end result being no worse than just utter mess in cabin and galleys.

How are we going to resolve this?

Originally Posted by Chris Scott
Well, I agree that the three main L.O.C. cases we have been discussing the last few months have involved different pilot reactions to problems in the cruise, but all have been seriously deficient:
Why are we not discussing some other LOCs like Birgenair? 20 000 hrs could not prepare the skipper for simple recognition that rejecting the takeoff when airspeed is not working is a must or just to crosscheck the three ASIs. Or close call at EHAM where the guy who taught others how to perform V1 cut just couldn't make it properly when it happened for real? That's what AF447 is about: the crew that just couldn't perform when it needed to. It's very ugly picture and I understand the need to try to overpaint it with unrealistic theories about FBW or instrumentation.

Originally Posted by vilas
Pilots without jet experience have to undergo ELT MCC as part of Airbus type rating where Absolute raw data flying without ATHR, AP, FD, FPV is taught.It includes executing SIDs,Arrivals,Approach and landings. Out of eight sessions 6 are to be flown manually. So 447 pilots were not strangers to raw data flying.
Depends on what local CAA will allow, operator demand and training organization provide. In my case it was all spiced up by flying in direct law. It was piece of cake but then it was sim, not a real aeroplane over Atlantic at 4AM.

OK I'll give up quoting for a bit but when making sweeping statements about general flying capabilities of modern pilots, bear in mind that more than 30 other crews passed through same ordeal without a scratch and at least four of them were Air France.
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Old 19th Nov 2013, 23:54
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Originally Posted by Clandestino
You suggest that A330 is sensitive beast that has to be treated gently. I say that it is exaggeration and you can throw her around hamfistedly at cruise altitude, in alternate law for 4 minutes with normal acceleration varying between +1.96 and -0.26G with end result being no worse than just utter mess in cabin and galleys.
Do that in roll direct and I suspect you will learn gentleness, and there might even be an additional mess in the cockpit.

Alternate1 and Alternate2 laws might work similarly in pitch, but they bear no resemblance in roll.
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Old 20th Nov 2013, 03:31
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In response to Cland, the three points where I was called out .....

a) Seems to be confusion here, even amongst the 'bus drivers about the various "alpha" limits or protections or whatever. And when one is the actual FCS limit. So if the FCS doesn't have an absolute AoA limit, then at least show the pilot the stall AoA.

My system had AoA limits depending upon A2A loadout, heavy iron on the wings or in landing configuration. We could only select the A2A or A2G limits, not the gear down limits.

b) Looking at my HUD video you will see what most considered the minimum displayed data for a safe and precise approach. The ILS cross bars are easy to understand. AoA bracket shows where you are and when aligned with the flight path marker( FPM), where you should be. Heading, altitude ( AGL or baro) and speed.

If you want some kinda "magenta line" to helpsteering , fine, but that can be a symbol that you keep aligned with the FPM. Had that on my A-7D, but no autopilot connection to anything. Viper was pure manual, as seen in the video.

c) We had one important backup mode - Standby Gains, which is extremely relevant to our discussions here the last three years. If air data was deemed unreliable the FCS used a fixed value for "gains". One with gear up, and the other gear down. Sure, if way off of the Q that the system used, it got touchy or sloppy. but very easy to fly, much like the "old days" when we didn't have all that stuff.

We did not worry about a myriad of alpha stuff, as we had one with gear up and the other gear down. Both limited the jet to stall AoA ( roughly). You could not command above those limits as the AF447 folks did. Could still run outta energy in a steep climb and momentum would allow the jet to exceed the limts because the flight controls could not react quickly enough ( very hard for our jet, and even more so for the heavies, IMHO).

Having an ACES II seat was very comfortable, and several of my friends are true believers. One, and main reason I never wanted to fly the heavies after getting out was the responsibility of many SLF behind me. If I screwed up, or the jet screwed up, so it was just me. Ain't gonna talk about that anymore.

.....and I assume Cland and maybe one or two others have bothered to look at my HUD tape of the emergency landing. Otherwise, much of my views could be misunderstood.
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Old 20th Nov 2013, 08:17
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Chris Scott - I have just found your post #800 buried in the grass at the bottom of a page (missed it previously). Your point about 'trigonometry' is irrelevant when we were talking AoA signals and is only relevant in terms of IAS which only enters the fray due to some software code. Therefore it would not matter if the jet was flying backwards or upside down - an airflow of that magnitude would, I suggest, generate a 'useable' AoA signal. Whether the designers choose to ignore that signal is another matter. That was one of the errors of design.

Clandestino said
Originally Posted by post #850
How many medium and heavy jets vent below 60 kias while airborne, ever?
- not sure what 'vent' means here, but it does appear that the designers forgot this very important 'trigonometry' and that a jet in a fully developed stall can and did, in fact ?'vent'? below 60kts (IAS).
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Old 20th Nov 2013, 09:34
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@BOAC

Firstly let me say that I am NOT arguing that the A330 design does not need any change - on the contrary I think the stall warning logic should be altered. However the discussion relating to validity or otherwise of the AoA signal does, I think, ignore some relevant facts:

Your point about 'trigonometry' is irrelevant when we were talking AoA signals and is only relevant in terms of IAS which only enters the fray due to some software code. Therefore it would not matter if the jet was flying backwards or upside down - an airflow of that magnitude would, I suggest, generate a 'useable' AoA signal. Whether the designers choose to ignore that signal is another matter. That was one of the errors of design.
I doubt very much whether usable AoA signals would be generated if the aircraft were flying backwards or upside down, but I imagine you wrote that tongue in cheek ...
More to the point, if an equipment manufacturer declares in his formal paperwork that his equipment will work to specification only inside a given range of ambient parameters then the aircraft designer has no option but to conform to those limits. It is not a case of design error but one of a fully auditable certification trail.
The problem comes of course when the system sees input conditions which say that the operating limits of the equipment have been transgressed, but the measurement of those ambient parameters is itself false. To that extent Chris Scott's comment on trigonometry is relevant - the input data, in this case airspeed, was rendered false by the angle at which the airflow entered the pitots. Was it then a design error to fail to consider this case?

- not sure what 'vent' means here, but it does appear that the designers forgot this very important 'trigonometry' and that a jet in a fully developed stall can and did, in fact ?'vent'? below 60kts (IAS).
I doubt very much that the designers "forgot" that an AoA in excess of 40 deg would give stupid speed signals, but they did of course fail to believe that a trained pilot would allow the aircraft to get into that state. Be fair, would you have believed it before publication of the AF447 final report? In which regard I would refer you an earlier posting, from PJ2 I think, that designers work on an assumption that the aircraft will be flown to a given set of rules, allowing for some sensible variations thereto, but not to any extreme one cares to dream up.

So what of their treatment of the stall warning which is, when you go back to basics, the reason for all this discussion?

With hindsight the logic is faulty, but I don't see any need to alter the logic governing validity of AoA signals which might well bring on other problems we know nothing of. Instead I would propose a change of stall warning logic so that if triggered by a valid AoA signal it should stay latched on until it received another valid AoA signal that stall conditions were a thing of the past. That would have avoided the confusion found in the AF447 cockpit for a minimal change to the aircraft systems. It would also, incidentally, bring the aircraft into line with the latest EASA requirements on the subject.
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Old 20th Nov 2013, 12:22
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Indeed "tongue in cheek".

I don't think I have ever argued that AB was partly 'responsible' for the accident due to the Stall warning 'logic', but just that it was significantly contributory. I agree people would not 'expect' the crew to take an airliner to these realms. However, why WoW was 'abandoned' I do not know - I thought it was a well-proven input? Surely the point is, Owain, that as far as we know there was a 'useable' AoA input available, probably throughout the episode, and indicating a stalled wing. The fact that 'trigonometry' rendered the USE of this signal impossible due to the IAS constraint is indeed relevant, but I cannot see why posters are going on about 'non-swivelling pitot tubes' etc etc. Surely we all understand why the IAS reading was invalid?

I agree with your last paragraph and if that is also the EASA thinking, then good, although as with all ever-increasing complexity of systems there may well be a hidden pitfall in that approach.
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Old 20th Nov 2013, 12:28
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BOAC,

The post of mine that you refer to was merely an attempt to explain to you and rudderrudderrat that you were misunderstanding Clandestino's cryptic remark about trigonometry, and taking seriously his reference to "no swivelling pitots". It was not a statement of my own opinion, merely an attempt to help you understand his point in his absence (for which, predictably, he has offered me not a word of thanks).

It's well known that Clandestino's style of response sometimes invites irritable misunderstanding by the passing objects of his contempt, myself included. Did my polite, but non-didactic, explanation go over your head? Should I have tried the long version?

(Ah, I see OG has done a far better job!)
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Old 20th Nov 2013, 13:25
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....and I hope you understood my t-i-c remark about there always being a reading from an AoA probe (given enough wind to 'swivel' - that's for real) regardless of 'trig'?
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Old 20th Nov 2013, 13:41
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Affirm, BOAC
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Old 20th Nov 2013, 13:59
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BOAC

I don't think I implied that you were arguing about responsibility - if I gave that impression then my apologies. Nobody is going to contradict a statement about the S/W anomalies being a contributory cause though.

So far as WOW is concerned I don't think I have ever seen anything from Airbus on the subject - mostly the argument about it being 'abandoned' seems to emanate from PPRuNers speculating - but I stand to be corrected. What I would say is that leaving aside the AF447 affair, the existing logic functioned without complaint for several decades; why take the head off if it is working?

Now if your objective is to supply an AoA signal pure and simple and which is not going to be used as an input into some more flight critical system then I would agree there may be no need to complicate life by making that signal contingent on some other input - it being tacitly assumed that the aircraft will not be flying at a real 60 kts indicated or otherwise. Implicitly here I am taking the view that since airline pilots have been flying without AoA information since the year dot such information cannot really be classed as flight critical no matter how useful it might be in certain circumstances. [pace gums!]

I entirely agree your point about non-swivelling pitots etc.

To be clear, my remark about EASA requirements simply reflects the latest stall warning requirement CS25 207 (c) which, as I have said before, differs from the requirement applicable at the time the A330 requirements were frozen.

Last edited by Owain Glyndwr; 20th Nov 2013 at 14:07. Reason: grammar
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Old 20th Nov 2013, 14:57
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Good thots, OG.

To be honest, I don't know when the Viper FCS ignored AoA or didn't. Best I have in documents is that it was used as long as we had WoW switch decompressed. When I did a tail slide one day all the warning lights came on ( AoA sensors at limits, calibrated speed below 120 knots) and without resetting them, I had complete control once the nose fell thru. Reset the FCS panel and fight was still on, heh heh.

OTOH, the A-7D and other jets displayed the AoA whether the plane had a FBW system or not. Viper didn't, as some folks the braket was a nuisance symbol in the HUD.

I learned in planes that had very clear warnings you were approaching a stall. In later planes, we had buffet and wing-rocking and such to let us know we were reaching the edge of the envelope. It was a different feel than when nearing critical mach, which usually exhibited stuff like aileron reversal, nose tuck and a pronounced "buzz" in the airframe as the shock waves formed.

So my thot is that a display should be available and right in front of the pilot whether the FCS or Otto is using it.
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Old 20th Nov 2013, 15:13
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Originally Posted by Owain Glyndwr
So far as WOW is concerned I don't think I have ever seen anything from Airbus on the subject - mostly the argument about it being 'abandoned' seems to emanate from PPRuNers speculating...
I'm wondering if that speculation stems from the 1993 LH A320 accident at Warsaw, where the WoW timing was not sufficient to allow deployment of spoilers:

Lufthansa Flight 2904 - Wikipedia, the free encyclopedia

In response to that, Airbus reduced the required pressure on the WoW sensors, but they never abandoned it as a systems input.

OG, I'm almost certain you're correct in that the <60kts AoA NCD flag has nothing to do with determining air/ground mode - it's purely an attempt to enforce the AoA vane manufacturer's specified limitation of minimum 60kts airspeed for valid data, and prevent junk data from being used in FCS calculations.

Last edited by DozyWannabe; 20th Nov 2013 at 16:30.
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Old 20th Nov 2013, 15:56
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Just a reminder - the Final Report para. 1.6.11 says it thus:
If the CAS measurements for the three ADR are lower than 60 kt, the angle of attack values of the three ADR are invalid and the stall warning is then inoperative. This results from a logic stating that the airflow must be sufficient to ensure a valid measurement by the angle of attack sensors, especially to prevent spurious warnings.
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Old 20th Nov 2013, 16:16
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...and should read
If the CAS measurements for the three ADR are lower than 60 kt, the angle of attack values of the three ADR are considered to be invalid and the stall warning is then rendered inoperative.
and hopefully re-thought, having seen vanes moving on walk-rounds in a stiff breeze! I'm sure the intention was well-founded, but hindsight tells us the application was not, and WoW would have been far better.
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Old 20th Nov 2013, 16:32
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Originally Posted by BOAC
...and should read and hopefully re-thought, having seen vanes moving on walk-rounds in a stiff breeze!
With all due respect, there's a difference between "moving" and "providing valid data".

I'm sure the intention was well-founded, but hindsight tells us the application was not, and WoW would have been far better.
See above - I'd be surprised if WoW was not an input *in addition* to the <60kts IAS check, as opposed to "instead of". This is purely a way of preventing duff data from getting into the flight control systems calculations - entirely separate from air/ground mode determination.
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Old 20th Nov 2013, 16:43
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Dozy
I'm wondering if that speculation stems from the 1993 LH A320 accident at Warsaw, where the WoW timing was not sufficient to allow deployment of spoilers:

In response to that, Airbus reduced the required pressure on the WoW sensors, but they never abandoned it as a systems input.
That of course is a totally different application. For the record (I don't want to introduce another thread drift) it wasn't that WOW timing was adrift.Rather it was that the aircraft touched down so fast that even when derotated there was so much residual lift with full flaps that there was not enough weight on the wheels to overcome the breakout friction and allow the WOW microswitches to 'make' AI did introduce a software modification as a result but I cannot remember the details.
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Old 20th Nov 2013, 16:47
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@OG - check the Wiki link.

Originally Posted by Wiki
The spoilers [were] only activated if at least one of the following two conditions is true:

- there must be weight of at least 6.3 tons on each main landing gear strut
- the wheels of the plane must be turning faster than 72 knots (133 km/h)
Followed up with:

Originally Posted by Wiki
As a result of the accident, Airbus Industrie changed the required compression value from 6.3 tons to just 2 tons per main landing gear.
I remember the timing issue because the left gear touched down 9s after the right - it was the delay in the left gear getting the required compression value that caused the delay in spoiler deployment.

[EDIT : I'm aware that it's a totally different application, I was simply trying to distinguish the air/ground mode criteria, which are not relevant to AF447, from the AoA vane maker's specified NCD threshold of 60kts, which is. ]
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Old 20th Nov 2013, 16:56
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Would anyone like to know how much ADR/CAS independent AOA the digital portion of the display seen in Turbine Ds HUD U-tube link will indicate?

Probably not.
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Old 20th Nov 2013, 17:03
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Originally Posted by OK465
Would anyone like to know how much ADR/CAS independent AOA the digital portion of the display seen in Turbine Ds HUD U-tube link will indicate?
I, for one, would!

In fact I'd be exceedingly interested to see how the interoperations between flight control systems (both traditional and FBW), warning/alert systems and AoA sensing equipment pan out on every type in passenger service when exposed to values as extreme as AF447.

I don't think it's a shortage of people wanting to know - I think it's more a shortage of willing volunteer pilots* to fly the profile!

* - Because most pilots don't have a death wish...
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