Aviation safety investigations & reports

Operational event involving Boeing 787, registered 9V-OJC, near Perth Airport, Western Australia on 4 December 2015

Investigation number:
Status: Completed
Investigation completed
Phase: Final report: Dissemination Read more information on this investigation phase

Final Report

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What happened

On 4 December 2015, a Scoot Boeing 787-9 aircraft, registered in Singapore as 9V-OJC (OJC) was operating a scheduled passenger flight from Changi International Airport, Singapore, to Perth International Airport, Western Australia. At about 1743 Western Standard time, OJC commenced an instrument landing system (ILS) approach to runway 21 at Perth.

During the approach, the aircraft’s autopilot flight director system (AFDS) entered a degraded mode, and presented the crew with information that they erroneously believed represented the glideslope. The crew followed the displayed information, which resulted in a descent below the designed approach path and the subsequent activation of the aircraft’s enhanced ground proximity warning system. The crew conducted a go-around, and completed an uneventful approach and landing.

What the ATSB found

During the approach, a disturbance of the ILS glideslope signal occurred, likely due to an aircraft taxiing for take‑off on runway 21, resulting in OJC capturing the ILS glideslope prematurely. Because of this, the AFDS entered a degraded mode, presenting the crew with information extrapolated from a previous position, rather than updated glideslope information.

While taking actions to reset the AFDS, the crew continued descending as per the presented information, without identifying cues that indicated the information was unreliable. This resulted in an abnormally high rate of descent, leading to a descent below the designed approach path, and activation of the aircraft’s enhanced ground proximity warning system.

The flight crew were likely experiencing higher than normal workload, due to a combination of the high speed approach and troubleshooting the unexpected glideslope indications. This reduced the effectiveness of cockpit communication and delayed correction of the aircraft’s low altitude.

What's been done as a result

The aircraft operator advised they communicated the essential elements of this event and associated AFDS implications (including primary flight display and head-up display indications) to the pilot group. Pilots have been reminded to monitor the basic flight instruments and relevant check heights during the approach, in addition to the aircraft calculated guidance.

Stabilised approach criteria and associated callouts and actions have also been emphasised. In addition, the importance of energy management and use of the HUD to monitor appropriate descent path information has been highlighted.

Safety message

Flight crew are reminded that when conducting an ILS approach in visual conditions, ILS signal paths are not protected by air traffic control, and may be subject to interference. The aircraft’s flight path needs to be constantly monitored to ensure that guidance presented to the flight crew is valid. Constant monitoring will also ensure that early action can be taken to correct any deviation from the approach path.

Download final report
[Download  PDF: 715KB]

The occurrence


Safety analysis


Safety issues and action

Sources and submissions

General details
Date: 04 December 2015   Investigation status: Completed  
Time: 1745 WST   Investigation level: Defined - click for an explanation of investigation levels  
Location   (show map): 13 km from Perth Airport   Investigation phase: Final report: Dissemination  
State: Western Australia   Occurrence type: Navigation - Other  
Release date: 26 June 2020   Occurrence category: Incident  
Report status: Final   Highest injury level: None  

Aircraft details

Aircraft details
Aircraft manufacturer The Boeing Company  
Aircraft model 787-9  
Aircraft registration 9V-OJC  
Serial number 37114  
Type of operation Air Transport High Capacity  
Sector Jet  
Damage to aircraft Nil  
Departure point Singapore  
Destination Perth, Western Australia  
Last update 26 June 2020