Laura Samuel, a 49-year-old bank cashier from Carmarthen, was one of those who died. Her husband, Denis, suffered concussion and head injuries. The Dutch pilot also died along with a passenger believed to be from Singapore.
Pilot error, further mechanical problems and poor weather are all possible causes.
Ben Groenendijk, of the Netherland's independent Aircraft Accident Inquiry Board, told a news conference at Schiphol Airport: 'These aeroplanes are designed to be able to fly and land on one engine - otherwise they would not be allowed in the air.'
The aircraft, a twin-engine Saab turboprop, turned back 20 minutes into its afternoon flight to Cardiff after the pilot reported an engine fault.
'It was not really an emergency, more of a problem,' Mr Groenendijk said. 'Everything was going well on the return but then, at the very final point, things went wrong.'
The aircraft's flight recorders have been recovered and Mr Groenendijk said they would be opened today. But if that data provides no clues, British and American experts may be called.
The inquiry is expected to last two months, unless the flight recorders clear up the many questions raised, such as whether the undercarriage of the aircraft was down as it attempted to land or if the pilot was trying to regain altitude.
Yesterday the shattered fuselage was lifted by crane out of the muddy field where it broke up after its starboard wing touched the ground. The wreck will ne examined for clues.
Investigators have established that a fire-flash reported on impact came when fuel in the wing ignited. Had it not been detached in the crash the 30-second fireball could have engulfed the passengers.
The pilot gave no details to the control tower of the nature of his engine problem as he tried to bring the aircraft back. 'This is a very important thing. We will be studying carefully what the pilot did say,' Mr Groenendijk said.Reuse content