The Dutch are famous for being blunt about things, and the initial report by the Dutch Safety Board overnight about last Thursday’s crash of a Turkish Airlines Boeing 737-800 at Amsterdam’s Schiphol Airport is about as brief an accident summary as you could get.
The chairman of the Dutch Safety Board, Pieter van Vollenhoven, said that on final approach “the left radio altimeter suddenly showed a change in altitude from 1950 feet to minus 8 feet”.
This caused the computerised auto throttle controlling both engines to shut them down, as if the jet had already landed at Schiphol, which, like much of the Netherlands, is slightly below sea level.
The captain, who is among the nine dead, did not regain control from the immediate stall which caused the 737 to drop nose high on to the ground and break into three sections.
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While they are totally different in systems, size and design, the Turkish 737 accident has one thing in common with the very serious incidents which involved two Qantas Airbus A330s last year.
They all involved a sudden error in the data being fed to a critical and automated part of the control system — in the Qantas cases, the autopilot — causing an upset and loss of control.
In the first Qantas incident, a flight from Perth to Singapore, on 7 October, an emergency landing was made at Learmonth and 14 people were seriously injured by being flung against the ceiling and lockers.
This accident has already been traced to faulty data “spikes” being sent to the autopilot system, and is the subject of a continuing inquiry by the Australian Transport Safety Bureau.
The interim airworthiness directives arising from that inquiry may have helped another Qantas A330 crew quickly regain control in a near identical failure in their air data inertial reference unit on 27 December.
These incidents are focusing the attention of airlines on the flight data generating components of commonly used airliners that were previously treated as highly reliable, if not infallible.
There are part of a recent trend in which larger airliner crashes are being caused by pilots getting bad or incomplete data from their systems rather than errors that can be attributed to the human or catastrophic mechanical failures that characterised the earlier jet age.
However, in the case of the Turkish Airlines jet, the Dutch authorities have revealed that the airline had kept it in service with an altimeter it had known to be faulty.
That also makes the Schiphol crash look like it involves management failure in relation to the maintenance of standards and equipment.
The disclosure that the jet was dispatched with a suspect altimeter is a very serious reflection on Turkish Airlines, and on the habit of many airlines to defer work on faulty redundant items regarded as non-critical and which pilots can work around.
This habit wasn’t a factor in the two Qantas A330 incidents, although detailed causes in those events are being pursued by the ATSB with the help of its American and French counterparts.