Final Report

Summary

What happened

On 12 June 2015, the crew of a Boeing B737-300, registered VH-NLK, were conducting a non-directional beacon/distance measuring equipment (NDB/DME) approach into Kosrae Airport in the Federated States of Micronesia. The flight was the inaugural regular public transport (RPT) flight for Nauru Airlines into Kosrae. During the approach, at night and in instrument meteorological conditions, the aircraft descended below the minimum descent altitude and three enhanced ground proximity warning system (EGPWS) ‘too low terrain’ alerts were triggered. A go-around was performed prior to the aircraft reaching the missed approach point. During the go-around, the airspeed decayed and required the pilot to use full thrust. The flight crew identified and corrected the barometric pressure setting and the subsequent approach and landing into Kosrae were uneventful.

What the ATSB found

The flight crew did not complete the approach checklist before commencing the non-precision NDB approach into Kosrae, resulting in the barometric pressure setting on the altimeters not being set to the local barometric pressure. This resulted in the aircraft’s altitude being lower than what the pressure altimeter was indicating to the pilots. The aircraft descended below the EGPWS terrain clearance floor profile for the Kosrae runway, resulting in three separate EGPWS alerts.

Terrain clearance assurance was eroded further after receiving the first two EGPWS alerts by the flight crew not correcting the flight profile. The crew's belief that the EGPWS alerts were due to a decreased navigational performance and not terrain proximity led to the crew’s decision to inhibit the first EGPWS alert and not correct the flight path.

The flight crew initiated a missed approach when they lost visual contact with the runway. The captain was experiencing fatigue and the flight crew had an increased workload and stress due to the inaugural RPT flight into Kosrae at night in rapidly deteriorating weather. As a result, the crew’s decision making and task execution on the missed approach were affected, and the aircraft state, airspeed and attitude were not effectively monitored by either crew member.

The ATSB also found that there were established risk factors associated with Kosrae at the time the operator commenced regular public transport operations into Kosrae. The only instrument approach available for use was an offset procedure based on a non-precision navigation aid. The risk associated with this type of approach was amplified due to the need to use a 'dive and drive' style technique instead of a stable approach path, and that it required low level circling manoeuvring from the instrument approach to align the aircraft with the runway. Furthermore, there was very high terrain in close proximity to the runway and the airport did not have a manned air traffic control tower.

What's been done as a result

Following this occurrence, the operator has reviewed and changed procedures relating to:

  • increased time for flight crew on non-standard/non-routine activities during their cyclic training program
  • reviewed and included control column checklists, which includes the descent and approach checklist, with tactile indicators
  • included two-engine go-arounds in simulator sessions
  • reviewed and improved awareness of QNH setting procedures and human factors aspects of briefings and line checks.

Safety message

This occurrence highlights the importance of flight crews declaring any instances of acute fatigue and stress-inducing circumstances that may have an impact on their flying performance. Operators also need to remind flight crew of the importance of their decisions with regards to their fitness to fly. For flight crews, the importance of completing approach checklists and monitoring the approach at safety critical times is emphasised. For operators, the occurrence highlights the importance of incorporating dual-engine go-arounds into simulator training sessions.

The occurrence

Context

Safety analysis

Findings

Safety issues and actions

Sources and submissions