What happened
On 24 August 2012, a Piper Chieftain PA-31-350, registration PK-IWH, was conducting an aero-magnetic survey near Bontang, East Kalimantan. The flight, operated by PT. Intan Angkasa Airservice, was carrying four occupants: the pilot, a security officer, and two surveyors. The mission involved flying at low altitudes, with a flight plan specifying 500 feet above ground level (AGL) during the survey portion of the mission.
After departing Temindung Airport, the pilot communicated with air traffic services, reporting an altitude of 300 feet AGL at 0005 UTC. Shortly thereafter, the aircraft's flight-following system ceased receiving data. Following the aircraft's failure to arrive within its expected timeframe and exceeding its fuel endurance, authorities declared an uncertainty phase, followed by alert and distress phases.
Two days later, a ground search team located the wreckage on a ridge of Mayang Hill at approximately 1,200 feet AMSL. The impact was severe, and a post-impact fire occurred. All four fatalities were confirmed, as the accident was not survivable.
The investigation
The investigation focused on the flight path, aircraft condition, and environmental factors. Examination of the wreckage and propellers revealed that the engines were still operating at the moment of impact. Analysis of the airspeed indicator suggested an impact speed of approximately 130 knots.
Investigators also examined the flight path through the treetops, which indicated the aircraft was in a climbing maneuver prior to hitting the ridge. While the aircraft was found to be airworthy and properly maintained, the investigation noted that the operator lacked specific standard operating procedures for aero-magnetic survey operations. Additionally, the aircraft was not equipped with a flight data recorder or cockpit voice recorder.
Findings
- The aircraft was in an airworthy condition and properly maintained at the time of dispatch.
- The pilot was flying at 300 feet AGL, which was lower than the planned 500 feet AGL.
- The engines were functioning at the time of the crash, as evidenced by the condition of the propeller blades.
- Low visibility due to cloud cover prevented the pilot from effectively observing the terrain ahead.
- The accident was a classic case of Controlled Flight Into Terrain (CFIT), where low-altitude visual flight rules (VFR) operations were conducted in an environment with restricted visibility.
Safety action
Following the accident, PT. Intan Angkasa Airservice updated its Company Operation Manual to include specific procedures for aerial survey operations. The NTSC issued recommendations to the operator to enhance training for special operations and to ensure pilot proficiency, as well as recommendations to the Directorate General of Civil Aviation to review operational specifications for specialized flight services.