Accident Overview
On 13 April 2016, a Pilatus Britten Norman Turbine Islander (BN-2T), registration P2-SBC, operated by Sunbird Aviation Ltd, departed from Tekin, West Sepik Province, for Kiunga, Western Province, as a charter flight under visual flight rules. The aircraft carried the pilot-in-command and 11 passengers (eight adults and three children), along with vegetables. The pilot had originally flight-planned from Kiunga to Oksapmin and back to Kiunga, but without advising Air Traffic Services (ATS), the pilot flew from Oksapmin to Tekin. Upon departure from Tekin, the pilot transmitted departure details to ATS, stating departure from Oksapmin. Recorded High Frequency radio transmissions were significantly affected by static and hash.
Approach and Impact
Weather at Kiunga was reported fine. As the aircraft entered the Kiunga circuit area, the pilot cancelled SARWATCH with ATS without reporting an emergency. Witnesses observed that during its final approach, the aircraft suddenly pitched up almost to the vertical, the right wing dropped, and the aircraft rolled inverted before rapidly falling to the ground. It impacted terrain about 1,200 metres west of the threshold of runway 07. The impact was vertical with almost no forward motion. The aircraft was destroyed, and all occupants were fatally injured.
Probable Cause
The aircraft's centre of gravity was significantly aft of the aft limit. When landing flap was set, full nose-down elevator and elevator trim likely had no effect in lowering the nose. Unless the flaps were retracted immediately, the nose-up pitch may have resulted in tail plane stall, exacerbating the pitch up. The wings stalled, followed immediately by the right wing dropping. Recovery from the stall at such a low height was not considered possible.
Other Factors
Other identified safety deficiencies include: a) Following the reweighing of P2-SBC, the operator did not adjust for the shift of the moment arm, specifically reducing the allowable maximum weight in the baggage compartment. b) The pilot, although signing flight manifests attesting that the aircraft was loaded within centre of gravity limits, had not computed the centre of gravity. No documentation was available to confirm that the pilot had computed it for the accident flight or any recent flights. c) All High Frequency radio transmissions between ATS and the aircraft were significantly affected by static interference and hash, making reception difficult and many transmissions unclear. This presents a safety concern for ensuring vital operational radio transmissions are not missed.