Tuesday, May 10, 2011

Shifting the Burden

Pitot tube
This post emanates from the ongoing investigations of the crash of Air France flight 447 from Rio de Janeiro to Paris.  In some respects it is a follow-up to our January 27, 2011 post on Air France’s safety culture.  An article in the New York Times Sunday Magazine* explores some of the mysteries surrounding the loss of the plane in mid-Atlantic.  One of the possible theories for the crash involves the pitot tubes used on the Airbus plane.  Pitot tubes are instruments used on aircraft to measure air speed.  The pitot tube measures the difference between total (stagnation) and static pressure to determine dynamic pressure and therefore velocity of the air stream.  Care must be taken to assure that the pitot tubes do not become clogged with ice or other foreign matter as it would interrupt or corrupt the airspeed signal provided to the pilots and the auto-pilot system. 

On the flight 447 aircraft, three Thales AA model pitot tubes were in use.  They are produced by a French company and cost approximately $3500 each.  The Times article goes on to explain:

"...by the summer of 2009, the problem of icing on the Thales AA was known to be especially common….Between 2003 and 2008, there were at least 17 cases in which the Thales AA had problems on the Airbus A330 and its sister plane, the A340.  In September 2007, Airbus issued a ‘service bulletin’ suggesting that airlines replace the AA pitots with a newer model, the BA, which was said to work better in ice.”

Air France’s response to the service bulletin established a policy to replace the AA tubes “only when a failure occurred”.  A year later Air France then asked Airbus for “proof” that the model BA tubes worked better in ice.  It took Airbus another 6-7 months to perform tests that demonstrated the superior performance of the BA tubes, following which Air France proceeded with implementing the recommended change for its A330 aircraft.  Unfortunately the new probes had not yet been installed at the time of flight 447.

Much is still unknown about whether in fact the pitot tubes played a role in the crash of flight 447 and of the details of Air France’s consideration of deploying replacements.  But there is a sufficient framework to pose some interesting questions regarding how safety considerations were balanced in the process, and what might be inferred about the Air France safety culture.  Most clearly it highlights how fundamental the decision making process is to safety culture.

What is clear is that Air France’s approach to this problem “shifted the burden” from assuring that something was safe to proving that it was unsafe.  In legal usage this involves transferring the obligation to prove a fact in controversy from one party to another.  Or in systems thinking (which you may have noticed we strongly espouse) it denotes a classic dynamic archetype - a problem arises, it can be ameliorated through either a short term, symptom based response or a fundamental solution that may take additional time and/or resources to implement.  Choosing the short term fix provides relief and reinforces the belief in the efficacy of the response.  Meanwhile the underlying problem goes unaddressed.  For Air France, the service bulletin created a problem.  Air France could have immediately replaced the pitot tubes or undertaken its own assessment of pitot tubes with replacement to follow.  This would have taken time and resources.  Nor did Air France appear to try to address the threshold question of whether the existing AA model instruments were adequate - in nuclear industry terms, were they “operable” and able to perform their safety function?  Air France apparently did not even implement interim measures such as retraining to improve pilot’s recognition and response to pitot tube failures or incorrect readings.  Instead, Air France shifted the burden back to Airbus to “prove” their recommendation.  The difference between showing that something is not safe versus that it is safe is as wide as, well, the Atlantic Ocean.

What we find particularly interesting about shifting the burden is that it is just another side of the complacency coin.  Most people engaged in safety culture science recognize that complacency is a potential contributor to the decay and loss of effectiveness of safety culture.  Everything appears to be going OK so there is less need to pursue issues, particularly those lacking safety impact clarity.  Not pursuing root causes, not verifying corrective action efficacy, loss of questioning attitude and lack of resources could all be telltale signs of complacency.  The interesting thing about shifting the burden is that it yields much the same result - but with the appearance that action is being taken. 

The footnote to the story is the response of Air Caraibes to similar circumstances in this time frame.  The Times article indicates Air Caraibes experienced two “near misses” with Thales AA pitot tubes on A330 aircraft.  They immediately replaced the parts and notified regulators.


*  W.S. Hylton, "What Happened to Air France Flight 447?" New York Times Magazine (May 4, 2011).

1 comment:

  1. still feel too linear think re safty. Air France toronto downed in thunder storm, polish airliner, all weather related not enough briefs,shut down airports computer models data base. Strom over equator from ground up some base , tops 50,000 plus depth of storms also. One might forget electrical failure.Some concerns over composite materials and lighting strikes the statistics probability. Can't find placements of pitot tube designs on different aircrafts seem rather low on nose for diesel towing vehicles also can be sabotaged .Some new insites into lighting strikes leader lighting ,the aircraft need have electrical problems. Swss air over Canada also had electrical shut down went down over maritimes. Model very very poor cinsudering night flight and deadly depths and heights of t-cells. Computer also reflects concern pilot have over system programs envelopes. Much fault findings can shut airport ,delay flights, upgard computer model weather systems from 447 data base model.lights out .too much generalisation with statistics without the concerns lighting strike scattering diagram 3d. 'e' natural exponential constant 'i' imaginary numbers square root of -1. updraft downdraft t-cells sorry general and special relativity.did have electrical power failure see those shots lighting strike burn the bark of the trees can do a better model with winds also.3d ABC XYZ

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