AMSTERDAM - Turkish Airlines on Friday released the names of four crew members who died in the crash that killed nine people in the Netherlands, while investigators at the scene mapped the exact location of each piece of mangled debris.

As 40 investigators swarmed the crash site Friday, the plane's flight data and cockpit voice recordings were being analyzed in Paris. Sandra Groenendal, spokeswoman for the Dutch Safety Authority, said a first assessment of what went wrong according to the black box data would likely be released by Wednesday.

Five Turks and four Americans were killed when the Boeing 737-800 plunged into a farmer's field Wednesday morning, smashing into three pieces.

Turkish Airlines said the dead included pilots Hasan Tahsin Arisan, Olgay Ozgur and Murat Sezer and flight attendant Ulvi Murat Eskin.

Boeing said two of the dead Americans were employees, another American employee was in critical condition and the status of a fourth was not yet certain.

Boeing was flying their relatives to the Netherlands if they wanted to go, spokesman Andrew Davis said Friday, but he gave no details of their movements.

No new information was released Friday about the injured. On Thursday, 63 survivors remained hospitalized, including six in critical condition.

Flight TK1951 was coming in from Istanbul with 135 passengers and crew when it crashed about 1.5 kilometres short of the runway at Amsterdam's Schiphol Airport.

One survivor, Henk Heijloo, said the last message he heard from the captain was for flight crew to take their seats. He said it took him a while to realize the landing had gone wrong.

"We were coming in at an odd angle, and I felt the pilot give the plane more gas," he said. He thought the pilot might have been trying to abort the landing, because the nose came up.

Mayor Theo Weterings of Haarlemmermeer said the relatives of the people who died had been informed but not all the bodies had been officially identified. Once that is done, families will be able to bring the bodies home.

Pieter van Vollenhoven, head of the Dutch agency investigating the crash, said Thursday that the plane had fallen almost directly from the sky, which pointed toward its engines having stopped. He said a reason for that had not yet been established.

Groenendal said engine failure was still only "one of the possible scenarios" for the crash. Other possible causes range from weather-related factors to insufficient fuel, loss of fuel, navigational errors, pilot fatigue or bird strikes.

"(It) just fell straight down and then you heard the engines at full power as if it was trying to go forwards," survivor Fred Gimpel told the Dutch NOS news.

Survivor Kerem Uzel, a student, told Turkey's NTV television that he didn't realize anything was wrong until the plane was skidding through the muddy field.

Witnesses on the ground said the plane dropped from about 90 metres.

Several crash survivors returned to Istanbul on Thursday -- including a young man with a bandaged wrist in a wheelchair.

Turkish Airlines chief Temel Kotil said Arisan, the plane's captain, was an experienced former air force pilot.

The airline also denied reports that the plane, which was built in 2002, had had technical problems in the days before the accident. The plane underwent routine maintenance Feb. 19, and had to delay a flight Feb. 23 -- the day before the crash -- to replace a faulty caution light.