What happened
On 18 June 2018, a Cessna 208B, registration PK-FSL, was performing an unscheduled passenger flight from Bilorai to Nabire, Papua. The aircraft was carrying two crew members and 11 passengers. During the descent toward Nabire, the pilot encountered developing cloud cover and chose to deviate from the GPS route to avoid the clouds.
As the aircraft descended to approximately 2,500 feet, it entered another layer of clouds, obscuring the pilot's visual reference to the ground. While attempting to regain visual contact with the terrain, the crew noticed obstacles ahead. The second in command alerted the pilot to the terrain, prompting an immediate climb. During this maneuver, the left side of the aircraft struck the tops of trees, causing substantial damage to the left wing tip, aileron, and horizontal stabilizer. The aircraft subsequently stabilized at 3,000 feet and landed safely at Nabire with no injuries.
The investigation
The KNKT investigation focused on the pilot's decision-making during the descent and the effectiveness of onboard warning systems. Investigators examined the aircraft's GPS and Ground Proximity Warning System (GPWS) data, noting that while the GPS displayed symbols indicating potential impact points, the crew was primarily waiting for an aural alert or visual terrain confirmation. The investigation also reviewed the operator's operational manuals, noting discrepancies between the company's internal flight guidance and the official Aeronautical Information Publication (AIP) regarding altitude restrictions for VFR routes.
Findings
- The pilot failed to maintain the required VFR weather minimums, which prevented a clear view of the surrounding environment.
- The crew ignored GPS terrain alerts and continued the descent while flying in clouds, relying instead on visual contact or the GPWS aural alert.
- There were inconsistencies in altitude limit information between the operator's internal charts and official aeronautical publications.
- Operational oversight within the airline was insufficient to ensure all manual procedures were being strictly implemented.
Safety action
Following the incident, the operator, FlyingSAS, issued new notices regarding stabilized approach checklists for mountainous terrain and emphasized the importance of Crew Resource Management (CRM) to prevent overconfidence. Additionally, AirNav Indonesia and the Directorate General of Civil Aviation worked to correct coordinate errors for navigation aids in the AIP and developed better arrival guidance for airports lacking instrument approach procedures.