Turkish 737 crash investigation focuses on crew actions

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Dutch investigators, who will present their initial findings later today, have found no serious faults with the Turkish Airlines Boeing 737-800 that crashed at Amsterdam last week.

Sources familiar with the investigation tell ATI that physical and recorded evidence so far also shows no evidence of bird-strike, icing, windshear, or wake turbulence. They say the CFM International CFM56 engines and aircraft controls responded "normally" to the pilots' inputs.

The only fault so far discovered on the aircraft was in the left-hand radio altimeter which read negative 7ft altitude throughout, although the right-hand radio altimeter functioned correctly. It is not immediately clear whether that could have played a significant role in the accident.

One airline source says that the aircraft was initially "fast and high on the glideslope" but that it subsequently descended below the glideslope, and an eventual attempt to climb away was too late to prevent the aircraft hitting the ground.

Boeing is today expected to issue a safety information bulletin to operators and the source says the bulletin will describe how the aircraft was flying under autopilot and autothrottle control. At about 2,000ft (610m) above ground, while fast and high, the throttles were "pulled" to idle thrust and the autothrottle reverted to 'retard' mode.

The throttles remained at idle for about 100s during which time the aircraft slowed to 40kt (75km/h) below reference speed and the aircraft descended through the glideslope. During this period the captain was "coaching" the first officer in conducting the before-landing checklist.

At about 400ft above ground the stick-shaker activated and the first officer advanced the throttles. The captain took control and the first officer released the throttles, which then moved to idle as the autothrottle was still in retard mode.

About six seconds later the throttles were once more advanced and the engines responded but too late to prevent the aircraft striking the ground in a nose-high attitude.

The source says the Boeing bulletin will remind pilots of the importance of monitoring airspeed and altitude and give guidance on troubleshooting radio altimeter discrepancies.

Boeing declines to comment pending a press conference by the investigation board in Amsterdam today.