Sunstate DH8D at Sydney on Jul 12th 2021, crew did not retract landing gear
Last Update: March 30, 2022 / 18:09:19 GMT/Zulu time
The aircraft remained on the ground in Sydney for about 16.5 hours before returning to service.
Australia's ATSB opened a short investigation rating the occurrence an incident.
The ATSB released their final report concluding the probable causes of the incident were:
- After take-off, the flight crew’s attention was heavily focused on maintaining the aircraft's speed and pitch, resulting in the omission of the ‘positive rate’ call. This removed a trigger for the ‘gear up ‘call, which neither pilot identified, and subsequently the landing gear was not retracted after take-off.
- Although the landing gear handle was in the down position and 3 green lights were illuminated, the pilot flying incorrectly called 'up, no lights' when conducting the after-take-off checklist. The pilot monitoring did not identify the error. It is likely that both pilots had a strong expectancy that the landing gear had been retracted after take-off when completing the checklist.
- The cabin crew observed that the landing gear remained extended longer than normal following take-off. They advised the flight crew, resulting in the landing gear being retracted.
The ATSB analysed:
Landing gear not retracted after take-off
After taking off from Sydney, the flight crew did not raise the landing gear. Ultimately the problem was not identified until the aircraft had reached 15,000 ft. No landing gear speed limits were exceeded. Although the 15,000 ft maximum altitude for operating with the landing gear extended was exceeded, this had no subsequent effect on the serviceability of the aircraft. Nevertheless, the occurrence was of some concern as the flight crew did not identify the incorrect configuration for an extended period of time.
Conducting a take-off is a specialised task that is acquired through comprehensive training and significant experience; it involves conducting routine, frequently-practiced tasks in a largely automatic manner with occasional conscious checks on performance. Errors, known as slips and lapses, will occasionally occur when conducting such skill-based tasks (Reason 1990). Omitting a step or an action is one of the most common forms of error (Reason 2002), and they are often associated with interruptions, distractions or attention being diverted to other tasks. Accordingly, occurrences where flight crew forget to raise the landing gear after take-off almost always involve some form of distraction or diverted attention.
In this case, both pilots were heavily focused on the aircraft’s speed soon during the initial climb. Additionally, the captain was focused on the aircraft’s pitch attitude, having previously observed other pilots pitch higher than the operator’s procedures stated in similar situations, and the workload of the first officer (FO) was increased while hand flying the aircraft.
The confirmation of positive rate and subsequent call was a frequently-practiced action for the crew and therefore one normally conducted automatically, with little conscious oversight. Their diverted focus of attention was probably sufficient to result in the omission of the positive-rate call and neither pilot identifying that it had not been made.
Not calling ‘positive rate’ removed the standard verbal cue for the FO to call ‘gear up’, increasing the likelihood that the gear-up call would not be made. At this time, both pilots were still focused on aircraft performance but also shifting their focus to the increasing workload of the standard instrument departure.
Misidentification of landing gear status
Errors of omission are often difficult to detect by the people who make them (Sarter and Harrison 2000), and the absence of something (such as an action) is harder to detect than the presence of something (Wickens and others 2013). Trying to recall from memory whether actions have already been completed is also vulnerable to source memory confusion, such that the current situation is confused with the memory of many previous occasions when the action was successfully done (Dismukes and others 2007). Accordingly checklists, like the challenge and response after-take-off checklist, perform a vital role in ensuring omissions in a flight crew’s procedural flow are captured (Barshi and others 2016).
When actioning the after-take-off checklist on this occasion, the ‘landing gear’ item was called by the captain (as pilot monitoring) but neither pilot identified the problem. The captain observed that the 3 green landing gear lights were illuminated, but did not identify it as being problematic for that stage of flight. Although the FO could not recall what they saw at that stage, they also recalled seeing the 3 green lights later in the flight and not thinking it was problematic.
Expectations strongly influence where a person will search for information and what they will search for (Wickens and McCarley 2008), and they also influence the perception of information (Wickens and others 2013). Pilots frequently conduct the task of raising the landing gear and, in almost all cases, it is done successfully. Consequently, the pilots on this occasion had a strong expectancy that the landing gear had been retracted, and they probably conducted the after-takeoff checklist with a high degree of automaticity, rather than consciously looking for what was required (that is, no green lights). Although the 3 green lights provided a clearly visible indication that the landing gear was still down, green lights are often associated with something being in a safe state; therefore this cue can be interpreted incorrectly in this phase of flight if the flight crew’s attention is not focussed on exactly what they are looking for.
This type of occurrence is very rare but, when it occurs, a flight crew’s further troubleshooting of symptoms associated with the landing gear still being down is often not effective. In this case, both pilots reported observing noise and vibration from the aircraft. After some discussion, the crew associated the noise and vibration with the propeller balance maintenance log entry. In an effort to reduce the noise and vibration, the crew reduced the climb speed. This reduced the abnormal indications and seemingly confirmed that the propeller balance was the source of the problem, consistent with the effects of confirmation bias.
Awareness displayed by cabin crew
The cabin crew displayed a high level of vigilance regarding the aircraft state. Their willingness to bring this to the attention of the flight crew allowed the flight crew to identify the problem and retract the landing gear as soon as possible and highlights the strength of timely communications between crew members.
Reduced flying activity
Skill decay or skill degradation refers to the loss of trained or acquired skills or knowledge following periods of non-use (Arthur and others 1998). Skill decay increases as the retention interval (or time since learning) increases, and it also increases depending on the quantity and quality of the initial and recurrent training and the amount of on-the-job exposure (Arthur and others 1998, Sanli and others 2018, Vlasblom and others 2020).
Procedural skills involving the retrieval and application of step-by-step actions are more sensitive to skill decay than many other types of activities (Goodwin 2006, Stothard and Nicholson 2001, Wisher and others 1999). As recently noted by the European Union Aviation Safety Agency (EASA 2021):
Procedural tasks that require specific procedural or declarative knowledge (e.g. checklists that require more items than prescribed on paper) may be more susceptible to skill decay than higher order cognitive tasks (e.g. decision making) or perceptual/psychomotor tasks. Cognitive shortcuts for procedures decay rapidly, requiring a significant increase in cognitive resources, in particular for procedures that are normally routine. By their prescriptive nature, procedures are easily subject to slips and lapses. Procedures must be viewed as highly sensitive to proficiency decay.
In this case, the FO had undertaken less than the operator’s normal amount of flying since March 2020. In particular, the FO had conducted less than one third of their normal amount of flying in the previous 90 days and had not conducted any flights for 11 days. However, the operator was aware of the potential issues associated with reduced flight recency and had introduced measures to mitigate the risk. Both flight crew had recently undertaken a proficiency check. Overall, there was insufficient evidence to conclude that the FO’s reduced flight recency contributed to the procedural errors made by the flight crew on this occasion.
Aircraft Registration Data
This article is published under license from Avherald.com. © of text by Avherald.com.
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