May 2011 Archives

This is what the Air France A330's trajectory looked like during its last few minutes, starting when everything was still fine...

The BEA's simple three-page factual summary is here. It doesn't attempt to judge, it just reports facts. Conclusions will come with the final report.

From this point I will number the paragraphs so I can refer back to information already mentioned. The paragraph numbers are not intended to tally with those on the diagram - it has its own key directly below it. 

1. On page 1 the report sets the scene on the flight deck. The captain has gone for a rest, and has been replaced by a supernumerary First Officer. That is standard for long flights.

2. The aircraft is cruising at FL350 (35,000ft) and there are storm clouds in the area, as there always are in the inter-tropical convergence zone. The two copilots are aware of them. The pilot flying (PF) briefs the copilot who has just taken the captain's seat that they are in choppy air but cannot climb above it because the aircraft's weight and the relatively high outside air temperature means that they are about as high as the aircraft can safely go until it has used up more fuel.

3. A few minutes later the PF makes a sidestick control input which raises the nose and causes the aircraft to climb rapidly to 38,000ft. There was no reason to climb, the PF did not announce an intention to do it, and the aircraft was not cleared by ATC to do so. The natural result of climbing without an increase in power is a loss of speed. But we'll deal with that shortly.  

4. The problems for the pilots began when the autopilot(AP)/autothrottle (AT) disconnected. The disconnect occurred because there was a temporary disagreement between two independent airspeed sensors (pitot tubes) about what speed the aircraft was flying at. When there is a disagreement between two inputs to the flight control computers, the computers do not adjudicate, they abdicate control to the pilots.

5. The drill for pilots at that point, according to flight manuals for Airbuses and Boeings alike, is to leave the power where it is and to continue to fly straight and level. That way the aircraft's speed remains the same as it was, no matter what the airspeed indicators are showing. When the AP/AT trip out the aircraft is fully in trim and the power stays where it is.

6. The same logic that caused the autopilot disconnect also caused a change to the flight control law, taking it from "normal" to "alternate" law. This robs the pilots of the flight envelope protection that is automatic in "normal" law, but otherwise the aircraft flies in the same way. The main protection they lost was protection against stalling.

7. The PF verbally acknowledged the fact that the AP had tripped out and that alternate law was in force.

8. Meanwhile the BEA report says that the airspeed disparity that caused autopilot/authrottle disconnect, lasted for less than a minute.

9. The crucial moment in this flight came 11s after the autopilot had tripped out. Because of the light turbulence, the aircraft rolled slightly to the right when no longer controlled by the AP, and the PF naturally made a sidestick input to bring the right wing back up. The problem is that, simultaneously he pullled the stick back, pitching the nose up. There is no indication of why he should have done that (see paragraph 3), but a few minutes before this action he had stated that they should not climb (see paragraph 2). He said: "So we've lost the speeds", and then: "alternate law", so I suspect it was a slightly panicky reaction to the airspeed disparity and the AP/AT trip-out, but it was not a logical reaction.

10. The result of the PF's flight control input was a dramatic climb at 7,000ft/min and a similarly dramatic drop in the airspeed because of the climb. The aircraft reached 38,000ft, way beyond the height at which it could have sustained stable flight. Almost immediately upon applying the nose up demand the stall warning sounded twice.

11. When the stall warning first sounded the PF maintained nose-up pitch, but as the speed dropped with increasing height he applied a nose-down input and the rate of climb dropped from 7,000ft/min to 700ft/min. The aircraft reached a maximum height of about 38,000ft, and at that point the angle of attack was 16deg, which is well beyond the stall.

12. The stall warning sounded again when the aircraft began to descend, and the pilots selected maximum power on both engines (TOGA). At that height this would not have had the dramatic effect it would have had at a low altitude. But the PF still maintained nose-up inputs, and the trimmable horizontal stabiliser was gradually trimming further and further nose-up because those inputs were maintained.

13. The horizontal stabiliser eventually stopped at a 13deg nose-up setting, and the report says it stayed in this position for the remainder of the flight. At about the same time the airspeed disparity that had caused the confusion resolved itself, and the airspeed on both ASIs increased to 185kt in response to the high power.

14. The captain re-entered the flightdeck 1min 40s after the AP/AT disconnect, and about that time the stall warning stopped because the recorded speeds become invalid. The BEA explains that this occurs because, when the indicated airspeed drops below 60kt, the angle of attack measurements become unreliable and are rejected.

15. The aircraft by this time was descending through 35,000ft with an angle of attack exceeding 40deg, a nose-up attitude of 15deg or less, and a rate of descent of about 10,000ft/min, and the aircraft was oscillating in roll up to 40deg each way. The pilot's response, says the report, was to pull back the stick to the stops (full nose-up demand) combined with full left roll demand for about 30s.

16. At some point the pilots had taken the throttles out of the TOGA detent and set them to idle thust. The PF declared he had no valid instrument indications. The BEA does not explain this, but it may have been caused by the very high angle of attack.

17. Then the PF made some nose-down inputs, the angle of attack decreased, and the airspeed readings became valid again, causing the stall warning to recur.

18. The BEA observes that whenever the angle of attack readings were valid, they exceeded 35deg, so the aircraft was deeply stalled during its entire descent.

19. The aircraft, at impact with the water, had a nose-up attitude of 16.2deg, it was 5.3deg left wing low, and had a vertical speed of 10,912ft/min.

If you struggle to understand how professional pilots can become so confused, I admit I do too, but history shows it happens sometimes. Read this to understand where today's pilot training might be going wrong.

And if you put the key word 447 into the search window for this blog, you will find that I have listed some examples of previous accidents that contained many of the factors this one does.

Learning the Boeing 787 starts here.

It doesn't matter whether you are a mechanic or a pilot, when you're learning about aircraft systems the manuals are in an identical laptop/tablet/EFB, and are based on the same software. So you learn to use the manuals which can, in virtual reality, walk you through the process of system diagnostics, faulty LRU identification and the removal and replacement process.

If you were a pilot on diversion because of a faulty box, you could diagnose which one it was, and if a replacement could be delivered, you could fit and test it.

The same software extends to the flight training device... 

... where pilots can familiarise themselves with the flight deck equipment, and and become adept at systems manipulation, but at a fraction of the cost of learning in a full flight simulator. In this picture the head-up displays are superimposed on the external visual screens.

The FFS comes next.

All these training systems were created as a total system for Boeing by Thales, which is why they are integrated and complementary

Today I "flew" the 787 simulator for the first time at Boeing UK Training and Flight Services near Gatwick. Capt Patrick Garrigan, lead flight instructor Boeing 787 training and flight services, was in the right hand seat doing the detailed work while I got to grips with the handling and the HUD.

The 787 is a dream to fly if this simulator is anything to go by. And the simulator's fully electric six-axis motion system is about as good as motion systems get - much less lurchy and upsetting than traditional electro-hydraulic ones.

The 787 feels civilised, predictable, stable, intuitive. And those head up displays: HUDs have never really grabbed me before because I haven't used them much, but these did. Soon we'll wonder why we ever flew without them. 

Aerodynamics, even at its most primitive, conspires to make aeroplanes art. If they aren't art, they don't fly. Engineering and art share a spectrum, even if some manifestations of each are at opposite ends.

TAG Aviation, not satisfied with having created the world's coolest terminal and sexiest hangar (above) at Britain's oldest aerodrome (Farnborough), expects it to be the venue for an exhibition of world class contemporary art sometime soon.

TAG is the acronym for Techniques d'Avant Garde. As Michael Caine allegedly says, "not a lot of people know that."

Anyway, the art/aviation connection was established when Tatiana Ojjeh, grand-niece of TAG Group founder Akram Ojjeh, proposed to take her forbear at his word and mount a contemporary art exhibition at a TAG base.  Her uncle, TAG Group president Mansour Ojjeh was delighted with the idea.

The first location, working with Geneva's Opera Gallery, was at the TAG chalet at the 2011 European Business Aviation Conference and Exhibition at Geneva (see below)...

 Tatiana Ojjeh with Tempetes Inconnues by Georges Mathieu, exhibited at the TAG Chalet, EBACE 2011. Photography Steve Eastell

Originals exhibited at EBACE included works by Joan Miró, Pablo Picasso and Damien Hirst among many. The value of the works on view was about $40 million, and all were for sale.

Mansour Ojjeh with Tatiana in front of Damien Hirst's 5-AMINOURACIL at EBACE 2011

Tatiana Ojjeh said her new Artliner venture "explores ways of marrying art and aviation" as a way of enriching the business aviation travel experience. She expects to stage an exhibition at TAG Farnborough in due course.

TAG Farnborough's tower 

The UK Government, through the 2000 House of Lords Inquiry into contaminated cabin air, called for research "to refute the 'common allegations' and give public confidence with regard to cabin air quality".

No call for a genuine inquiry to find out whether the air actually does get contaminated, then? Apparently not.

Anyway, the result of that call for refutation has been the Cranfield University report (see the immediately preceding blog), which said that the highly neurotoxic chemical tricresyl phosphate was detected in cabin air, but at levels that are legally acceptable.

Apparently these neurotoxins are politically acceptable as well, because Transport Minister Theresa Villiers has welcomed the report. 

Dr Susan Michaelis, just back from the Aerospace Medical Association's annual meeting in Anchorage, where she presented her PhD "Health and Flight Safety Implications from Exposure to Contaminated Air in Aircraft" , has this to say about the Cranfield report:  

"The study is completely contradictory as it clearly identified the  organophosphate TCP - from the engine oil additives - at concerning levels in the cabin air, but dismissed this as all satisfactory.

"It is anything but OK. By dismissing the significance of the findings [of TCP in the cabin air], the government can follow its public position that they do not need to study the health of the people who have been exposed to contaminated air.

"TCP was clearly identified as neurotoxic in the 1930's and again in the 1950's, so they have long known how toxic the substances found are, but this report has just ignored all  the science. The government considers it acceptable to expose people to TCP, but following my PhD studies I can assure you it is not.

"This report confirms that, in normal aircraft flight, people are being exposed to TCP, the organophosphate from the engine oil."

Incidentally, there were 103 UK mandatory occurrence reports about airborne fume events during airline flights in the nine months to March this year. 

Cranfield ran tests on 100 flights and, if its definition of reportable events has any credibility, there were no "reportable level" fume events during its trial. What use was it, then?

You can almost hear the UK authorities breathing a collective sigh of relief at the publication of Cranfield University's report on a series of flights in which cabin air samples were analysed. Apparently crews and passengers don't need to worry because the quantity of pernicious neurotoxins collected were at a legal level.

Whew! What a relief that the legal thresholds are such that we can continue doing what we were doing before.

But wait a minute, those legal thresholds don't apply to aircraft cabins, or to exposure at altitude in a confined space, do they? Never mind! 

Now here's our pilot (pictured above), a member of the British Airline Pilots Association, walking out to his aeroplane: "Oh well, what the hell, let's go and do the preflight checks and hope we don't get a real fume event this time. And I hope that multiple exposure to low levels of tri-cresyl phosphate isomers does not cause a build-up of organophosphates in my body that screws up my brain and nervous system so I lose my licence like some of my mates have done. Besides, BALPA thinks it's a risk worth taking."  

The best test tubes that Cranfield could have used in a valid sampling trial would have been pilots and cabin crew, especially those who had just returned from flights in normal airlines in which reportable fume events took place. But Cranfield's terms of reference did not include taking blood samples from crew.

But let's step out into the sunshine and hear the message from UK Transport Secretary Theresa Villiers: "The main conclusion of Cranfield's research was that there was no evidence of pollutants occurring in cabin air at levels exceeding available health and safety standards and guidelines." So that's alright then.

Unfortunately for her this is not the end of the affair. Cranfield knows it, and so, I suspect, does she. 

This Tupolev Tu-154 is demonstrating a gyration known as dutch roll, but a rather more violent example than usual.

The sketchy details of what's going on where are here.

Before I explain why there are several things about this film that make me a bit sceptical about what's happening, I will describe how dutch roll develops.

If an aeroplane gets disturbed in yaw, for example by turbulence acting on the fin or by rudder input, the sideways movement of the tail makes the aircraft pivot around an imaginary vertical axis that passes through the aircraft somewhere near to where the wings meet the fuselage.

Consider a yaw to the right in this Tu-154. "Right yaw" means the tail has swung right, so the nose swings left. The aircraft is effectively beginning to "skid" to the right.

During that right yawing motion the right wing is moving forward relative to the oncoming air slightly faster than the aeroplane's airspeed, and the left wing's airspeed is slightly less than that of the aircraft, which creates a lift differential between the two wings, with greater lift generated by the faster (in this case the right) wing. That lift difference starts the aircraft rolling to the left.

Another factor exacerbating the roll to the left is the fact that, because the wings have a swept-back design, the advancing right wing is presenting a longer profile to the oncoming air than the retarding left wing, generating even more lift differential in the same sense.

(The Tu-154 has another wing design factor known as anhedral - wingtips slightly lower than wing root - which is intended to dampen a tendency to roll with yaw, but not to eliminate it. On the other hand, the fact that the Tu-154's three engines are mounted in the tail means the tail is heavy, so once a swinging motion begins, it takes more time to dampen it).

Back to that first yaw to the right: the swing of the tail to the right stops when the naturally stabilising force of the vertical fin, which tends to keep the aircraft flying straight with no yaw, equals whatever force caused the disturbance in yaw. That is the end of the first yaw/roll cycle.

If, at that point, the pilot applies right rudder, that will add to the fin's force, and the tail will start swinging back to the left, and the yaw/roll effects begin to reverse. If that swing takes the tail through the point of zero yaw, the aircraft is starting another yaw/roll cycle with the forces acting to create right roll instead of the previous left roll. So the aircraft is now dutch-rolling, and under certain circumstances the cycle will keep repeating.

These gyrations also have an effect on pitch, but that is less dramatic.

Now for the sceptic's questions.

The aircraft took off and made a fairly stable climb-out. The dutch-roll didn't start immediately. When the pilots made a final approach, the aircraft had become pretty stable shortly before it landed safely. How was this stability achieved on departure and again on approach when it could not be achieved during other phases of the flight?

If pilots, on a test flight, encounter a major handling problem, they maintain plenty of altitude while they sort it out, and do not attempt an approach until they have tested handling techniques and a configuration which provides the best stability they can achieve. But this aircraft continued dutch rolling until established on short finals.

Maybe gear-down was the stabilising factor? Maybe. The crew left the gear down a long time on departure. 

Why was this flight being filmed so assiduously? On the other hand, the film doesn't look like a professionally shot one.

Were they worried about getting this long-parked aircraft airborne again? What gave them cause to worry? Should they have gone ahead if they were worried?

Dutch roll as violent as that shown in the film was not the result of autopilot input or the pilots would (surely?) have tripped the autopilot out. The failure of the yaw damper system would not, alone, cause such dramatic dutch roll.

The investigators will look carefully at pilot input. Whatever force caused the first dutch roll cycle, if pilot input attempting to correct the yaw got out of phase with the swinging motion, the phenomenon known as pilot induced oscillation can set itself up, and this can take the form of dutch roll. It's like a driver attempting to correct a skid, overcorrecting and ending up in a skid the other way.

The best way of overcoming pilot induced oscillation, if there is enough altitude to be safe, is to take hands and feet off the controls and let the aircraft sort itself out.

Now let's see what the investigators say.