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What happened

On 24 April 2015, a Bombardier DHC-8 aircraft, registered VH-TQM, was operating QantasLink flight QF2274 from Port Lincoln to Adelaide, South Australia.

During the approach to runway 30, in instrument meteorological conditions and with vertical navigation (VNAV) flight director mode engaged, the airspeed reduced. As the flight crew responded, an uncommanded disengagement of the aircraft’s flight director occurred. The flight crew re‑engaged the flight director and selected vertical speed mode. That mode resulted in the aircraft descending below the approach profile and 100 ft below a segment minimum safe altitude.

As the aircraft drew nearer to the runway, the flight crew received an obstacle proximity warning, since their projected approach path would bring them too close to a tower. In response, the crew conducted a missed approach and instead landed the aircraft on runway 05. No damage or injuries were sustained.

What the ATSB found

Flight director dropouts had occurred previously – including on that aircraft and on that day. On those occasions the flight director had automatically re-engaged in the same mode it had dropped out in. As the flight crew expected this would happen again, they continued the approach. The reason for the uncommanded disengagement of the aircraft's flight director was not established. The previous flight director dropouts had not been reported by company flight crew, affecting the operator's ability to resolve the issue and to educate flight crew about it.

The manual re-engagement of the flight director was done during a period of high workload and focus on other tasks and the flight crew did not identify the incorrect active mode. The captured vertical speed resulted in the aircraft descending too fast for the approach profile. Without the protection provided by VNAV mode, the aircraft descended below a segment minimum safe altitude. The altitude and vertical speed resulted in the activation of an obstacle proximity warning.

The elevation of the tower was incorrect on the published approach chart and in the terrain database, and there had been previous occurrences of obstacle warnings on that approach. There were also deficiencies in the induction and route information provided to flight crew about the instrument approach.

What has been done as a result

Following this occurrence, QantasLink immediately prohibited use of the GNSS RWY 30 approach and has since undertaken a range of education, training and operational safety actions.

Airservices Australia amended the approach chart with the correct height of the tower. While safe obstacle clearance existed on the approach profile, they also amended the approach procedure to increase the clearance above the obstacle, with the aim of eliminating proximity alerts to aircraft on the approach profile.

Safety message

This incident highlights the importance of auto-flight system mode awareness and the adverse effects of flight crew expectation and high workload. It also demonstrates the value of operators conducting a thorough risk assessment and making flight crew aware of hazards associated with airport approaches.

Reporting of technical faults, even those that occur momentarily and resolve quickly, is important as it enables the operator to resolve the issue and educate flight crew.

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The occurrence

Safety analysis

Findings

Safety issues and actions

Sources and submissions

 
General details
Date: 24 April 2015 Investigation status: Completed 
Time: 19:54 CST  
Location   (show map):near Adelaide Airport Investigation type: Occurrence Investigation 
State: South Australia Occurrence type: Control - Other 
Release date: 05 February 2018 Occurrence class: Operational 
Report status: Final Occurrence category: Incident 
 Highest injury level: None 
 
Aircraft details
Aircraft manufacturer: Bombardier Inc 
Aircraft model: DHC-8-315 
Aircraft registration: VH-TQM 
Serial number: 604 
Operator: QantasLink 
Type of operation: Air Transport High Capacity 
Sector: Turboprop 
Damage to aircraft: Nil 
Departure point:Port Lincoln, SA
Destination:Adelaide, SA
 
 
 
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Last update 05 February 2018