Sunstate DH8D at Horn Island on Jun 26th 2024, wrong flap setting for departure

Last Update: January 21, 2025 / 12:28:05 GMT/Zulu time

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Photo of Sunstate Airlines VH-QOI, De Havilland Dash 8 (400) — Sunstate Airlines VH-QOI, De Havilland Dash 8 (400) (Photo credit: Alec BHX/KKC / Flickr / License: CC by-sa)

Incident Facts

Date of incident
Jun 26, 2024

Classification
Report

Airline
Sunstate Airlines

Flight number
QF-2489

Departure
Horn Island, Australia

Destination
Cairns, Australia

Aircraft Registration
VH-QOI

Aircraft Type
De Havilland Dash 8 (400)

ICAO Type Designator
DH8D

A Sunstate Airlines de Havilland Dash 8-400 on behalf of Qantas, registration VH-QOI performing flight QF-2489 from Horn Island,QL to Cairns,QL (Australia) with 67 passengers and 4 crew, was preparing for departure when the crew considering runway length and load of the aircraft briefed to depart with flaps at 15 degrees and bleed air off. However, inadvertently the aircraft departed with flaps set to 5 degrees. The pilot flying needed to apply more pressure at the control column than normal, the aircraft rotated about 5 knots past the determined Vr. The aircraft did not climb according to expectations prompting the pilot monitoring to check trim and speeds, while the pilot flying identified the flaps had been set to 5 instead of 15 degrees. The aircraft subsequently climbed out and continued to Cairns for a safe landing.

The ATSB released their final report concluding the probable causes of the incident were:

Contributing factors

- The FO mistakenly set flaps to 5° for take-off at Horn Island when pre-flight planning identified flaps 15° should have been set.

- Standard pre-flight checks and crosschecks were conducted, however the flight crew failed to identify the incorrect flap setting before take-off at Horn Island. This was likely due to automatic behaviour by the crew registering flap 5° to be the usual setting at take-off.

- The incorrect configuration of the aircraft reduced the climb performance and potential obstacle clearance on departure from Horn Island.

The ATSB released this safety message:

The preparation, taxi and take-off phases of flight involve high workload and demand heightened attention to ensure correct settings are selected as unintentional slips can easily occur without. To minimise the risk of slips going unnoticed, flight crews must carefully verify and methodically complete checks and checklists. Maintaining focus and staying mindful of potential deviations to usual settings is essential during periods of high workload for safe operations.

The ATSB analysed:

The inadvertent selection of the flaps to 5° instead of 15° by the FO was likely influenced by habitual behaviour driven by prior experience. A flap setting of 5° had been used for the previous two sectors flown by the flight crew and was, in their experience, the most common setting for take-off at most of the airports in the operator’s network. It is likely therefore, that the FO developed an unconscious habit for a flap setting of 5°, and the setting of 5° was a result of a slip.

A slip is a form of human error defined to be the performance of an action that was not intended (Reason, 1990). Slips often occur during the largely automatic performance of routine tasks, usually in familiar surroundings, and characteristically involve an incorrect implementation of an intention (Mylopoulos, 2022). If other factors are also present, such as distraction, then the chance of such errors occurring increases. This type of slip cannot be eliminated by training alone, however, improvements in system design can reduce the likelihood of occurrence and provide a more error tolerant environment, which is why checks of the flap setting are built into the pre-flight processes (the after start checklist).

The flight crew reported adhering to the procedures for the pre-departure checks which provided 4 occasions to potentially identify or rectify the incorrect flap setting. Flight crews are particularly vulnerable to checklist errors during the pre-flight sequence in the time-compressed phase of pre-departure (Loukopoulos, and others, 2001). Under normal pre-flight procedures workload is usually at a high level and for this flight the extra calculations for weight, weather and performance limitations elevated the crew workload. When workload is high, automaticity can be amplified as the mind seeks to conserve energy by relying on well learned routines (Bermúdez and others, 2021). This can be detrimental when a situation requires mindful engagement. The flight crew likely conducted the after start checklist with a high degree of automaticity, rather than consciously verifying the flap setting against the Aerodata or TOLD card. In this case there was a breakdown of this normal layer of defence, which emphasises how safety measures can be degraded if crews are not consciously focused on the task. It was possible that the crew had diminished sensitivity for error detection due to completing the checklist without carefully ensuring the confirmation of each of the steps.

As a result, the crew performed the take-off with the flaps inadvertently at 5° instead of 15°. The incorrect configuration reduced the intended performance envelope of the aircraft. The FO’s continued back pressure to the controls during the take-off run resulted in the aircraft successfully becoming airborne slightly after the expected rotation speed. The FO’s actions to reduce pitch during the take-off increased the airspeed and the aircraft maintained a positive climb.