A Boeing 737 departing London Stansted airport flew for 6 miles at 500 feet (150 meters) above ground only, before climing to a safer altitude. This incident occured on 16th of October 2006, and the report has been published last week.

Shortly said, the crew misinterpreted a note meaning “don’t turn below 500 feet” and thought it was “stop climb at 500 feet”. A summarized report always sounds silly… this is why media always do it !

This incident report left me with a mixed feeling… It was the second flight of the day for this crew, so they were not tired. They were may be not familiar with this particular departure route, but with many other English departures (which have some specific points, just as in any country).

The plane worked well, even if the auto-pilot had to be disconnected, but this was because of the extemely low level-off altitude selected by the crew. Disengaging it was a correct decision from the captain, based on an incorrect assumption of initial climb altitude.

Weather was favorable, the crew was in sight of ground all the time, and this even helped them to realise something was wrong with their altitude. They even mentionned the fact that they were flying below the local minimum safe altitude.

The procedure design and publication has been questionned by the crew, but they also said to investigators that this initial altitude seemed unusual to them. The question is why they did not ask for clarification before departure.

An hypothesis is that they both thought that as the other one was not asking, everything was ok. A simple breakdown in crew collaboration lead to this strange airline incident, and this is why my feeling is quite mixed… the whole theory of safety says that “Human”, “Procedure” and “Equipment” contain all risks, but also all mitigations. Apparently nothing here was mitigating this bad interpretation.

Ok, ATC did correct the situation and the crew itself was on the way to take action, and if the terrain had been more “problematic” the Ground Proximity Warning System (GPWS) would have issued “Climb” warnings, to which the crew would certainly have reacted properly…

But still… what was missing here was not even airmanship as the crew reaction was quite good in the end. The missing part is what safety studies frequently disregard… what management does not considers as an important part of the system… and what I personally consider of paramount importance, even if it can not be measured nor evaluated: common sense !

This crew has been silly for a few seconds, and this is the proof that this can happens ! Luckily no other factor aggravated the situation, and the whole system reacted properly, avoiding the worst.

Best of all for the end: the investigators recognised this as a “double brain’s fart”, and resisted the temptation to issue complex, costly and useless recommendation. Kudos to the UK Air Accident Investigation Branch for this !

The report from the Air Accident Investigation Branch is available here.