Accident Flight
On the morning of 20 September 2014, a DHC-6 Twin Otter aircraft was returning from Woitape, Central Province, to Jacksons Airport in Port Moresby on a charter flight under instrument flight rules (IFR). The aircraft was cleared by air traffic control to descend while maintaining visual separation from terrain and to track to a left base position for runway 14R at Jacksons Airport. The crew accepted the clearance.
Weather and Clearance
Weather at Woitape was reported clear, but Port Moresby reported low cloud and rain. Witnesses stated that the summit of Mt Lawes, at 1,700 ft above mean sea level, was covered in cloud all morning. When the aircraft was 36 nautical miles from Port Moresby, the descent clearance was given. Later, at about 9.5 nautical miles from the airport, the pilot in command (PIC) contacted the tower, reporting that they were “running into a bit of cloud” and suggested they “might as well pick up the ILS if it’s OK.” However, the flight crew could not have conducted an ILS approach from that position. They could have discontinued the visual approach and requested radar vectoring for an ILS approach but did not.
Approach Challenges
The Port Moresby Aerodrome Terminal Information Service (ATIS) current during the approach required arriving aircraft to conduct an ILS approach. The PIC’s last ILS proficiency check was nearly 11 months prior, while PNG Civil Aviation Rule 61.807 mandates a 3-monthly currency for a particular instrument approach. It is likely that the PIC did not request clearance to intercept the ILS from 30 nautical miles because he lacked the required currency and was therefore not authorized to fly an ILS approach. During the descent, the PIC told the copilot, “we know where we are, keep it coming down,” but recorded data showed his position assessment was incorrect and the descent should not have continued. Both pilots appeared to have lost situational awareness.
Impact and Injuries
The aircraft impacted terrain near the summit of Mt Lawes. The impact forces caused substantial damage. Both pilots and one passenger were fatally injured in the impact; one passenger died the following day from injuries sustained in the accident. Of the five surviving passengers, three were seriously injured and two received minor injuries. One of the fatally injured passengers was not wearing a seat belt.
Probable Cause
The following contributing factors were identified:
- The flight crew continued the descent in instrument meteorological conditions without confirming their position.
- The flight crew’s assessment of their position was incorrect and they had lost situational awareness.
- The flight crew deprived themselves of the “Caution” and “Warning” alerts that would have sounded about 20 seconds and about 10 seconds respectively before the collision, by not deactivating the EGPWS Terrain Inhibit prior to departure from Woitape.