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. Probable Cause: “The NTSC determines that the probable causes of the accident were the combination of 1) The aircraft had entered severe hail and rain during weather avoidance which subsequently caused both engines flame out; 2) Two attempts of engine-relight failed because the aircraft was still in the precipitation beyond the engines’ certified capabilities; and 3) During the second attempt relight, the aircraft suffered run-out electrical power.”