A continued unstable approach into Darwin by an Embraer E190 has resulted in Alliance Airlines clarifying its stabilised approach criteria and amending the applicable stabilisation height, an ATSB investigation final report notes.
The aircraft, with 2 flight crew, 2 cabin crew and 49 passengers on board, was approaching Darwin at the conclusion of a scheduled flight from Cairns on 12 February 2025, the report details.
Passing the initial approach fix for the ILS (instrument landing system) approach to runway 29, the aircraft's auto‑flight system approach mode unexpectedly disarmed and reverted to basic flight director (roll and flight path angle) modes, due either to a system synchronisation issue or the pilot flying inadvertently disarming the approach mode.
"Following this unexpected change, the pilot flying did not re-engage approach mode, or disconnect the autopilot, and the aircraft deviated right and then left of the ILS course, before intercepting the lateral course again at about the final approach fix," ATSB Director Transport Safety Stuart Macleod said.
The deviation took the aircraft outside the required lateral tolerance of the approach below the minimum safe altitude, while in instrument meteorological conditions.
Additionally, as the aircraft descended through 1,000 ft, it was above the glideslope, at a high rate of descent and a high airspeed.
"The flight crew did not discontinue the approach at this time, because they had become visual, and incorrectly assessed they could therefore continue to 500 ft with multiple stabilised approach criteria unmet," Mr Macleod said.
As the aircraft continued through 500 ft, the flight crew incorrectly assessed they were now stable, although still too fast. They were also unaware that the pilot monitoring had inadvertently selected an incorrect flap setting.
The pilot monitoring subsequently identified that the flaps were not in the landing configuration and selected the correct position. The flight crew continued the approach and conducted an uneventful landing.
Mr Macleod noted data showing more than 97% of unstable approaches in large air transport operations are continued, and the vast majority result in an uneventful landing.
"This reinforces bad practice, given the highest risk factor for a runway excursion is an unstable approach," he said.
The ATSB's investigation identified Alliance's standard operating procedures were unclear about the criteria for continuing an unstable instrument approach to 500 ft when the aircraft entered visual conditions.
In response, Alliance issued an operations notice intended to improve clarity and compliance with the stabilised approach criteria. As detailed in the notice, Alliance also amended its stabilisation height to 1,000 ft (above aerodrome altitude) for 3‑dimensional and 2‑dimensional instrument approaches and straight‑in visual approaches, and the 500 ft stabilisation height applied only to a visual circuit or circling manoeuvre approaches. The notice also reiterated the operator's 'non punitive go‑around policy', and the requirement for all unstable approaches to be reported.
Mr Macleod said the incident also demonstrated how important continuous attention to automatic flight system modes on the primary flight display is to the maintenance of situation awareness.
"It also illustrates the need for effective flight crew monitoring, which can be improved by standard operating procedures, increased emphasis, and practice," he concluded.
You can find here the final report: Unstable approach involving Embraer E190, VH-UYO, near Darwin Airport, Northern Territory, on 12 February 2025
