July 26, 2021 | Susan Napier-Sewell

What Happens When a Flight Crew Faces a Non-Normal Situation?

non-normal situation

Uncommanded TOGA mode activation shows how flight crews can be faced with non-normal situations.

The unplanned activation of TOGA (take-off/go-around) mode during the landing of a Fokker F100 highlights that flight crews can be faced with non-normal situations that require good judgement and expertise to safely manage, according to an Australian Transport Safety Bureau (ATSB) investigation into the incident.

On September 1, 2020, Virgin Australia Regional Airlines Fokker F100 VH-FNR was landing at West Angelas aerodrome in Western Australia’s Pilbara region, on a scheduled passenger service from Perth — faced with a non-normal situation.

Just prior to touching down, the aircraft’s take-off/go-around mode activated, preventing automatic deployment of the lift dumpers to slow the landing roll.

The flight crew reported that, after touching down right wheel first, they selected the engine thrust reverser levers to the idle position

However, they did not deploy. The thrust reversers were selected a second time, but again they did not deploy.

The first officer then moved the levers beyond reverse idle and applied manual braking, at which point both thrust reversers and lift dumpers deployed. The landing then proceeded as normal.

After the landing, the captain observed on the primary flight display that the go-around (GA) flight mode was active. The multi-function display unit also indicated the TOGA thrust mode.

The ATSB’s investigation into the event concluded that the TOGA mode activated for an unexplained reason, preventing automatic activation of the lift dumpers

In addition, the weight on wheels sensors gave an intermittent signal during landing. This was most likely due to a softer than typical landing, combined with the lift-dumpers not automatically deploying due to the TOGA mode being activated.

The intermittent weight on wheels signal delayed the manual activation of the lift dumpers and deployment of reverse thrust.

“Despite the high reliability of modern flight control systems, this event highlights that flight crews can still be faced with non-normal situations that require their combined judgement and expertise to safely manage,” said ATSB Director Transport Safety Dr. Stuart Godley.

“Delayed deployment of reverse thrust, lift dumpers, or a combination of the two, has contributed to runway overruns in the past.”

Under normal operation, the F100’s TOGA mode is selected by pulling two triggers located on the thrust levers. The flight crew reported the motion to actuate the triggers would be an intentional one, and they did not believe it could happen accidentally.

After the incident, maintenance engineers tested the TOGA switches, weight on wheels sensors, lift dumpers, thrust reversers, flight computers and auto-throttle systems. No anomaly or unserviceability was found.

The aircraft was then returned to service, and at the time of publication there had been no reoccurrences of inadvertent TOGA mode activations.

This Lesson Learned is from an Australian Transport Safety Bureau investigation report release. Read the final ATSB report.

Do you have a story to share about the failure of critical equipment?

We’d like to hear from you about what happened. What was the response? The sequence of actions? Feel free to comment on this blog post. 

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Accidents, Equipment Reliability / Equifactor®
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