March 2009 Archives

Recently we have learned from studies by the NTSB and NASA that distractions in cockpits can be fatal, and certainly represent a considerable risk that has not been properly acknowledged.

The NTSB's senior human performance investigator Dr William Bramble finds that all the recent fatal airline accidents caused by pilot disorientation were preceded by crew distraction or fixation on an issue other than flying. This is most common when the distraction occurs just before or during a turn at night or in instrument meteorological conditions.

NASA is just beginning a programme to see if there is a better way of training pilots to recover from the upsets that can result from distraction-caused loss of control. But that is a strategy to cope with the results of a problem, not an attempt to eliminate the problem in the first place. In fact the previous blog addresses an aspect of this issue.

Now a NASA Ames study finds that cockpit operations are far more complex than pilots, airlines and the military acknowledge in their training and procedures. It's not just the "linear procedures" laid out in crew manuals and checklists that make up crew workload. That's an ideal world scarcely related to the real one. Distractions cause flapless take-offs as well as loss of control, NASA's study demonstrates, and they are more frequent than we thought, because crews sometimes get away with them.

Routine flights, from arriving at the aircraft to shutting down the engines, are packed with potential distractions as a part of doing business. The golden rule of flightcrew priorities is "aviate, navigate, communicate", but pilots are rarely left alone to do things in that order. Distractions, maybe interrupting checklists, take the form of air traffic control communications, calls from the cabin crew in the essential course of their duties, weather anomalies. The list is endless.

Talking of cabin crew, before the cockpit security door and associated procedures were adopted, flight attendants who had to deliver anything, from a message to a coffee or a meal, could enter discreetly, wait until the pilots were obviously between tasks, then deliver. The interphone does not give cabin crew the opportunity to judge when the time is right, and when the flightcrew are aware of an attempt to communicate it is a distraction if they are busy. That leads to a reluctance of the cabin crew to communicate, and sometimes that can be a risk in its own right.

The "sterile cockpit" concept adopted during descent to approach is about the only acknowledgement of the need to limit distractions. The rest of the time pilots have to cope with whatever  comes their way. NASA says they have to recognise distractions for what they are: potential dangers. And to recognise when the distractions are taking over from the  aviating.

Is NASA barking up the wrong tree with its "large transport aircraft upset recovery research programme?"

While I'm sure that the human factors, physiological and psychological results of testing pilots in centrifuges will be scientifically interesting, I'm not so sure they will be useful.

NASA is not the first organisation to do research on why pilots become disorientated. The NTSB's senior human performance investigator Dr William Bramble, having done lots of research on what happens in real cases, suggests the most useful solution is an education for pilots about the physiological and psychological causes of disorientation, including the fact that distractions from instrument flying are frequently a precursor to it. He points out that distractions during a turn at night or in instrument meteorological conditions were common to all the recent serious disorientation cases that actually caused fatal airline accidents.

Boeing also devised and ran a simple but ingenious test recently to determine whether appropriate upset recovery training  actually improves pilot performance. The result? It does.

The point I think NASA may be missing is this: when pilots look up at the instrument panel and see a picture that is totally different from what they expected to see - in fact it feels unbelievable because of preconceived notions about what is really going on - the SOP is to believe the instruments. Human sensory organs are so easily fooled that sensory misperceptions are a major part of the disorientation problem. So successful recovery from an upset entails blanking out any "seat-of-the-pants" physiological sensations and recovering the aircraft to straight and level flight (plus safe flying speed) purely according to what you see on the displays.

Doing tests that prove the human senses are easily fooled and that full flight simulators are no good at representing sustained accelerations is a waste of time because these are known truths.  

The prevailing situation:

The FedEx MD-11 was approaching runway 34L at Tokyo Narita, with fairly high gusting winds forecasted. Gusting winds always raise the spectre of potential windshear, and Narita is renowned for it.

The forecast wind (320deg at 26kt gusting to 40kt) would have provided a crosswind from the left that was some 20deg off the runway heading, although that may not have been what actually prevailed on landing.

So although it was not going to be particularly easy to land any aircraft type in an elegant way that day, the conditions were far from extreme and the visibility was excellent.

Now watch the video below, be ready to pause it from time to time to examine the very rapid transition from a relatively normal landing to a disastrous one, and then check the text below for my interpretation of what you are seeing at each point:

The landing sequence shown in the video tells us the following:

1. On the last part of short final approach the aircraft appears to be stable, if slightly low, with wings level and a normal pitch attitude for the circumstances (given that we don't know what the airspeed is);

2. the touchdown is very firm, but under gusty circumstances the pilots would naturally aim for a firm touchdown;

3. the nosewheel was lowered onto the runway at a high rate. Although the crew would want to put the nosewheel on the runway quickly to stop the aeroplane flying, the rate at which it was lowered might have threatened damage to the nose-gear - but it looks as if it survived the impact anyway.

Note: up until this point the aircraft's landing performance and behaviour has been well within the normal range. But then:

4. immediately following nosewheel touchdown the aircraft pitched up dramatically and the aircraft ballooned into the air again.

Note: the rate at which the nosewheel was lowered may have been a part of the cause of  the pitch-up following nose oleo compression, and that pitch-up might also have been exacerbated by the automatic extension of the spoilers which, in this type, are renowned for producing a pitch-up moment;

5. Now the aircraft is airborne again. This ballooning following first touchdown might have been made worse by a sudden gust of wind, momentarily raising the airspeed. But if that were true, the spoilers would have been simultaneously destroying a lot of the lift, and producing considerable drag; so, as the gust died (if it did) the aircraft might have been at or below stalling speed;

6. then - and this is what leads to disaster - the nose drops and stays low until the nosewheel's impact with the runway. This happens either because of lack of elevator authority, or because the pilot flying was tempted into a classic pilot induced oscillation.

Note: there are no circumstances under which a pilot of any type should deliberately select a nose-down attitude at that point - if, indeed, pilot selection of the nose-down attitude is what actually happened. During ballooning following touchdown the nose MUST be held up (if the elevator authority allows it) and appropriate power applied, whether the crew are trying for a successful second touchdown or for a go-around.

7. finally the nosewheel hits the ground extremely hard and the nose instantly rebounds upward, the main gear touching the surface momentarily a fraction of a second later. Almost simultaneously, the aircraft begins its fatal bank to the left, from which recovery was impossible once the left wingtip had hit the ground.

Note: banking to the left is not what the forecast crosswind would have been expected to produce. Normally, especially in a swept-wing aircraft like this one, the upwind wing has a tendency to lift, but in this case it didn't. So the crosswind does not appear to be the critical factor here, although windshear is very likely to be one of the causal factors.

For all those with different interpretations (or even to agree), please feel free to file your comments,

Last year's safety figures confirmed a trend that was becoming established over the last five years: airline safety has stopped improving, something it never did before since the Wright Brothers.

This year's serious occurrences show no sign that this is changing for the better.

Another unwelcome fact is that more accidents are happening to aircraft registered in a country that has, on average over the decades, the world's best safety rates: the USA. That country has now suffered four serious accidents this year so far, three of them fatal. The non-fatal accident - the US Airways Hudson River ditching - can be statistically ignored in this argument because birdstrikes that cause total power loss are not only rare, but they are what insurers would call "acts of God" - there is no protection against them and they could happen to anyone. But three fatal airline accidents in less than three months is not good for US carriers by today's expected standards.

In February we saw the Colgan Air Bombardier Dash 8 Q400 crash on approach to Buffalo; and now in the last two days we have seen a chartered Pilatus PC-12 come down just short of Butte, Montana killing all on board; and finally at Tokyo Narita a FedEx Boeing MD-11F has killed both its pilots - the only people on board, in a horrific crash in which crosswind and windshear seem likely to have played a major part. My colleague Kieran Daly has listed the numerous chillingly similar occurrences that have affected MD-11s and its predecessor the DC-10 series in his blog Unusual Attitude.

Only a couple of years ago it was possible to say that serious airline accidents nowadays are happening only to second- or third-tier airlines in countries whose safety record had never been particularly good. It is no longer possible to make that claim.

There is nothing new under the sun.

In the 1950s a Boeing B52 strategic bomber was lost during a long duration, high level sortie, and it was believed this was caused by fuel system icing. Of course it will never be proven because ice melts before you can check it out, but that was deemed the probable cause.

Following the January 2008 British Airways 777 accident on final approach to Heathrow when the engines failed to respond to demands for higher power after a long descent at low power, it has come as a relief that the UK Air Accident Investigation Branch has been able to issue a clarification of how icing can form in the plumbing of engine fuel systems, and how that can intermittently affect power delivery..

It's a relief because - now the AAIB has been able to replicate the phenomenon in tests with Boeing and Rolls-Royce - we have more knowledge about the issue than we had before. What's more we understand enough about it to be able make a recurrence much less likely by employing one of several straightforward procedures while we await system modification to make the accumulation of ice in fuel supply tubing a harmless phenomenon. Ice accumulation in the plumbing has probably always happened, and almost certainly in many different aeroplane engine types, but it has hardly ever caused a problem until recently.

The difference between existing fuel systems and the modified ones has to be that, when (not if) ice forms in them, it will never prevent the demanded power from being delivered.

Today's long-haul aeroplanes are longer haul than they ever were before, so the cold-soaking of fuel has never been more thorough. At the same time engines, especially in the big twins, cruise at a smaller fraction of their potential power output than they ever did, with lower fuel flow rates lasting for longer. These are the basic combinations of circumstances that make modern aircraft more vulnerable than earlier ones to the accumulation of fuel/water ice slush in the plumbing.

The AAIB has made it quite clear in its latest interim statement that this is a generic problem that we have been able to ignore until now.

But although we have begun to understand its nature, we still don't know what we don't know. So we have to find out what we don't know. The job has only just begun.