Narrative:Flight 421 departed Mataram around 15:00 and climbed to the cruising altitude of FL310. During the initial descent the crew decided to deviate from the planned route because of thunderstorms along their planned route. At 16:19 the flight encountered an area of severe turbulence and thunderstorm activity with extremely heavy precipitation and hail. The crew attempted to fly towards a gap between two storm cells. About 90 seconds after entering the thunderstorm, as the airplane descended through about FL180 at a flight idle power setting, both engines flamed out. The crew carried out three unsuccessful attempts to restart the engines followed by one unsuccessful attempt to start the auxiliary power unit (APU). The flight crew’s reported actions to restart the engines and APU however, were contrary to the procedures contained in the Boeing 737 Operations Manual. For instance, they waited only about 1 minute between each restart attempt instead of three minutes.
As the airplane descended below an overcast cloud layer at about 8,000 feet, the crew observed the Bengawan Solo River and decided to attempt to ditch the airplane into the river with flaps and landing gear in a shallow, 1 metre deep part of the river. One stewardess did not survive the crash.
Similar occurrences (Boeing 737-300 double engine flameout while descending in heavy precipitation with engines at flight idle) happened May 24, 1988 and July 26, 1988. Following these incidents OMB 88-5 and AD 6-14-88 were issued to require minimum rpm of 45% and to restrict the use of autothrust in moderate/heavy precipitation; engine modification was provided for increased capacity of water ingestion.
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This map shows the airport of departure and the intended destination of the flight. The line between the airports does not
display the exact flight path.
Distance from Mataram-Selaparang Airport to Yogyakarta-Adisutjipto Airport as the crow flies is 626 km (392 miles).
This information is not presented as the Flight Safety Foundation or the Aviation Safety Network’s opinion as to the cause of the accident. It is preliminary and is based on the facts as they are known at this time.