Incident Overview
On Friday, 16 July 2004, two AN-28 aircraft operated by Rigas Aeroklubs Latvia were conducting parachute drops at the National Parachute Sport Centre, Østre Æra airstrip in Østerdalen. The company had nine years of experience with such operations in Norway and had brought their own licensed aircraft technicians. The weather was good when flights began.
Flight Sequence
The crew of aircraft YL-KAB, consisting of two experienced pilots, had rested normally. After six routine drop flights and refueling, they prepared for a seventh flight with 20 parachutists who would jump in two groups of 10. Departure occurred at 1305. The Commander requested and received ATC clearance to climb to flight level FL150 (15,000 ft). The parachutists were dropped from that altitude. The first group jumped on a southerly course above the airstrip; the aircraft continued briefly before turning 180° for a second drop on a northerly course. A large cumulonimbus cloud (CB) with precipitation had approached from the north. The aircraft flew close to the cloud to reach the drop zone. The aircraft was not equipped with weather radar. Video footage showed that the parachutists were covered in white ice within 2–3 seconds of leaving the aircraft, which thawed only at lower altitudes.
Engine Failure and Emergency Landing
After the parachutists jumped, the aircraft was positioned close to the CB cloud at low cruising speed and experienced moderate turbulence. The Commander (pilot flying) initiated a sudden 90° left turn while reducing engine power to flight idle to avoid the cloud and return to Østre Æra. The First Officer (pilot not flying) observed ice on the front windshield and switched on the anti-icing system without informing the Commander. A few seconds later, both engines stopped, and the propellers automatically feathered. No technical problems had been noted before the failure.
During descent, the First Officer attempted engine restarts using available checklists, but the engines would not start. The Commander prepared for an emergency landing at Østre Æra without engines. The runway was 600 m long and 10 m wide, surrounded by dense coniferous forest. Without hydraulic power, flaps could not be deployed, requiring a relatively high approach speed of 160–180 km/h. The final approach was complicated by the last 10 parachutists still in the air near the airstrip. The Commander positioned the aircraft on a downwind leg west of the airfield and turned left to final on runway 01. The landing occurred around halfway down the runway at approximately 160–170 km/h. The Commander applied wheel brakes but, realizing he could not stop, ceased braking. He used remaining speed to lift off and alter course slightly right to avoid a 2.5 m high embankment. The aircraft flew about 230 m in ground effect before landing on its heels in a flat marshy area north of the airfield. After about 60 m of roll-out, the nose wheel and nose struck a ditch, causing the aircraft to overturn lengthways, coming to rest upside down with its nose pointing toward the landing strip.
Probable Cause
The official investigation found that the Commander assessed the distance to the cumulonimbus cloud as sufficient for the drop, expecting a rapid exit from the exposed area. However, problems arose when the aircraft encountered turbulence and icing from the cloud. The AIBN believes that the limits of the engines' operational range were exceeded because the anti-icing system was switched on while engine power was low, combined with low airspeed, turbulence, and sudden maneuvering. Both engines stopped, and propellers automatically feathered. The engines would not restart because the Feathering Levers were not moved from forward to rear and forward again as required after automatic feathering. The investigation also noted that the crew lacked necessary training and suitable checklists, and that oxygen deficiency may have reduced their ability to assess the situation. Despite these factors, the crew executed a satisfactory emergency landing under demanding conditions.