What happened
During the landing phase of a flight, the aircraft's take-off/go-around (TOGA) mode activated without a clear command. This uncommanded activation had a direct impact on the aircraft's deceleration systems, as it caused the lift dumpers to remain disarmed, preventing them from deploying automatically upon touchdown.
Furthermore, the aircraft experienced an intermittent weight on wheels signal throughout the landing roll. Even after all landing gear components had made contact with the runway, the sensors did not provide a continuous ground signal. This intermittent sensing prevented the deployment of reverse thrust and hindered the manual extension of the lift dumpers.
The investigation
Investigators examined the possibility that the flight crew had inadvertently triggered the TOGA mode by pulling the thrust reverser triggers. However, based on the physical hand movements required and the crew's account of the event, the ATSB determined that the First Officer's hands were likely in the process of reaching for the thrust reverser levers rather than pulling the triggers.
Technical inspections of the aircraft revealed no mechanical or system faults, and the absence of any subsequent incidents suggested there was no persistent hardware failure. Consequently, the specific reason for the uncommanded TOGA mode activation could not be determined.
Regarding the weight on wheels sensors, the investigation found that the intermittent signal was likely a result of an exceptionally soft landing. Because the lift dumpers failed to deploy automatically, the aircraft's weight did not settle sufficiently to maintain a steady ground signal. The sensors eventually reached a stable ground state, and no further sensor issues were reported.