International pilot representatives are dismayed over the arrest of a Garuda Indonesia captain on manslaughter charges, following a fatal Boeing 737-400 crash last year, insisting that the investigation into the accident failed to address fully the reasons for the crew's actions.

Investigators concluded that the pilot failed to fly a stabilised approach into Yogyakarta Airport on March 7, 2007. The aircraft had been too high during the initial approach and the pilot put the 737 into a steep descent, generating an excessive increase in airspeed.

Despite several ground-proximity warning alerts and calls from the co-pilot for a go-around, the pilot did not abandon the approach. The 737 touched down at 221kt, far above the required speed, and the jet overran the runway, killing 20 passengers and a flight attendant.

"The [captain] did not follow company procedures that required him to fly a stabilised approach and he did not abort the landing and go around when the approach was not stabilised," said the Indonesian National Transportation Safety Committee in its final report into the accident.

"His attention was fixated or channelised on landing the aircraft on the runway and he either did not hear, or disregarded, the [ground-proximity] alerts and warnings and calls from the co-pilot to go around."

Even after touchdown the co-pilot had urged the execution of a go-around. The investigation criticised him for failing to take control of the aircraft from the captain when he realised the warnings were being ignored.

But the International Federation of Air Line Pilots Associations (IFALPA) says that the investigation has not examined thoroughly the reasons for the captain's behaviour. It says the final report leaves "many serious questions" about the circumstances of the crash.

"We believe the explanations proffered by the report do not square with the collective experience of our members," says the federation.

"We have continually maintained that the report, while final, is in fact incomplete and that additional investigation into the underlying pathology of the crew actions is required to make certain that the factors contributing to the observed actions are fully identified.

"Unless this is done there is little possibility that aviation safety in the area of crew performance can be improved by the lessons of this accident. Clearly a criminal prosecution at this time may well foreclose further investigation for safety purposes."

IFALPA says it is "saddened" by the arrest of the Garuda captain and reiterates its stance that criminalisation of individuals involved in accidents "does little" to improve air transport safety.