Accident Overview
A Cessna 208B Grand Caravan I (registration not specified in source) was destroyed when it crashed in the Yahukimo District, Indonesia. Both crew members were killed. The aircraft was being operated on a non-scheduled cargo flight from Wamena Airport to Kenyam Aerodrome in Papua, Indonesia, under visual flight rules (VFR). The pilot reported to ATC a planned altitude of 9,500 feet.
Loading and Weight Issues
On board were two pilots, a manifested load of diesel drums and grocery items, and a non-manifested load of 25 bags of rice weighing 827 lb (375 kg). The investigation estimated the takeoff weight at 9,681 lb (4,391 kg), which was 619 lb (281 kg) above the certificated maximum takeoff weight. Additionally, the aircraft's center of gravity (C of G) was outside the certificated envelope.
Flight Progression
The aircraft took off from Wamena runway 15 at 12:17 local time and flew a track toward Kenyam consistent with the route used by other company pilots and previously flown by the pilot in command. The additional loading contributed to a reduced rate of climb, resulting in the aircraft being below 10,000 ft as it approached high terrain. This altitude was 1,500 ft lower than specified in the operator's route guide for operations between Wamena and Kenyam, and lower than altitudes flown by other company pilots on the day of the accident, who overflew the high terrain between 11,200 and 12,500 ft.
Sequence of Events
At 12:29:43, as the aircraft approached high terrain at 9,538 ft, airspeed began decreasing, accompanied by an average rate of climb increasing to about 390 fpm. It is probable that the pilots recognized the terrain proximity and attempted to improve climb angle by decelerating toward the best angle of climb speed of 72 kts. Recorded data showed engine power varied 31 seconds later, with maximum torque of 1,675 ft/lb at 12:30:30, consistent with a higher power setting selection likely to improve terrain clearance. Subsequently, the aircraft entered a descending right turn for about 6 seconds, descending from 9,865 ft to 9,728 ft at an average rate of about 2,000 fpm. This turn was likely initiated to avoid cloud or improve terrain clearance.
At 12:30:35, the aircraft began rolling left for 14 seconds, likely to avoid cloud or terrain. During this left turn, the angle of bank reached a maximum of 46°, and the aircraft descended from 9,728 ft to 9,045 ft at a high rate. Airspeed increased from 92 kts to 122 kts. Engine power was reduced to idle soon after descent began, most likely due to the handling pilot attempting to recover. Three EGPWS alerts activated during the descent. The aircraft stopped descending at 12:30:50 and began climbing with a reducing left bank when it impacted terrain at an elevation of 9,100 ft.
Probable Cause
Factors that contributed to the accident are as follows: a. The aircraft was loaded to a weight in excess of the maximum certificated takeoff weight. b. The aircraft climb performance was adversely affected by the aircraft being operated above the certificated maximum takeoff weight. c. The aircraft approached high terrain along the proposed route at an altitude which was below that specified in the operator's route guide. d. The aircraft entered a high rate of descent during a terrain avoidance maneuver. e. Recovery from the abnormal flight path was not achieved before the aircraft collided with terrain.