An E190 airliner's approach became unstable after the flight crew inadvertently disengaged the desired approach mode, and then did not effectively monitor the aircraft's flight path.
On 9 May 2024, an Alliance Airlines-operated Embraer E190 was stabilised on the Brisbane runway 19L instrument landing system (ILS) approach, in darkness, with 2 flight crew and 29 passengers on board, an ATSB investigation report details.
The captain, who was pilot flying, disconnected the autopilot and enabled the flight path reference line on their primary flight display in order to assist with manually flying the approach.
The captain then asked the first officer, who was pilot monitoring, to adjust this reference line to the ILS glideslope angle for runway 19L.
"The first officer had a correct understanding of the situation, but inadvertently pushed the flight path angle button - a 'slip' type error, which unintentionally disengaged the ILS approach mode," ATSB Director Transport Safety Stuart Macleod explained.
Surprised by the mode change, over the next 10 seconds the flight crew focused on resolving it, rather than conducting a go-around.
"During this time, the pilots were not effectively monitoring the aircraft's flight path, and it exceeded the glideslope limit requirement of the operator's stabilised approach criteria," Mr Macleod observed.
Once the captain identified the aircraft was low, they began to increase pitch, but at this time, the enhanced ground proximity warning system (EGPWS) generated a glideslope warning, in response to which, as it was night, the operator's procedures required the flight crew to perform the operator's terrain avoidance manoeuvre.
Subsequently, the flight crew instead continued the approach and landing.
Mr Macleod said the incident highlights how quickly a disruption can result in an aircraft transitioning from a stable to unstable approach.
"When pilots are faced with unexpected events, effective crew resource management, with each crewmember performing their procedurally assigned roles of flying and monitoring, is essential to ensuring the continued safety of flight while the disruption is investigated and managed," he added.
"Early recognition of an unstable approach and prompt execution of a go around, rather than continuing the approach, significantly reduces the risk of approach and landing accidents.
"Further, flight crews must also execute the correct response to ground proximity warning systems alerts without hesitation to ensure obstacles or terrain are avoided."
In response to the incident, Alliance Airlines has amended its cyclic training program, issued a relevant Operational Notice, and conducted a thematic review of unstable approaches, analysing data for further review.
You can find here the report: Unstable approach involving Embraer 190, VH-UZI, about 4 km north-east of Brisbane Airport, Queensland, on 9 May 2024
