Prior Sleep, Prior Wake, and Crew Performance
In order to test the hypothesis that restricted prior sleep or excessive prior wake would degrade threat and error detection and mitigation among flight crews conducting commercial flight operations, Thomas and Ferguson conducted a 2010 study using data obtained inflight during scheduled short haul airline operations. A total of 302 sectors were flown.
884 threats and 841 errors were observed. This was considered typical for the type of operations conducted and no correlation between threats and errors encountered and prior sleep/wake were obvious.
Captains averaged 7.04 (SD 5 1.18) hours and First Officers averaged 7.11 (SD 5 1.43) hours sleep in the prior 24 hours.
Captains averaged 14.37 (SD 5 1.81) hours and First Officer averaged 14.27 (SD 5 1.99) hours sleep in the prior 48 hours.
Captains averaged 6.99 (SD 52.77) hours and First Officers averaged 7.00 (SD 5 2.70) hours prior wake at the time of the data collection.
Captains had obtained less than 6 h sleep in the prior 24 h on 8.0% ( N 523) and First Officers on 11.8% ( N 5 30) of flights.
Captains had obtained less than 12 h sleep in the prior 48 h on 6.0% ( N 5 17) of flights and First Officers on 6.2% ( N 5
18) of flights.
Restricted sleep in both the 24 and 48 hour periods before the flight sectors resulted in less threats being effectively managed by flight crews However, no serious consequences were observed.
42% of errors were committed by the Captain and 48.2% by the First Officer. The remainder were committed by both crew members together.
Captains detected 30.9% of errors and First Officers detected 16.2%.
Generally, significantly more errors were associated with restricted sleep with both Captains and First Officers committing similar types of errors. However, effective management of error was not affected by restricted sleep.
Flight crew communication, situation awareness, task management, or decision making were not affected by either prior sleep or prior wake.
The study adopts a behaviourist and cognitive approach in that it examines the effect of fatigue on the mental processes of crew behaviour. In this context, the detection and management of threats and errors.
A biological element is also present due to the physiological effects of fatigue on human behaviour.
Flight crews consisting of a Captain and First Officer were observed and questioned to obtain the study data. Captains averaged 15.8 (SD 58.3) years flying experience and First Officers 8.3 (SD 5 6.8) years flying experience.The number of individuals involved in the study was not disclosed but it seems likely that some data volunteered on separate flights came from a previously sampled crew member.
53.9% of the crews had flown together in the past and the remaining 46.1% of the crews were flying together for the first time. This suggests that having a structured set of airline standard operating procedures (SOP's) is an effective tool in threat and error management given that no serious threats or errors were left unmanaged.
The study took place over a six week period and all data collectors were trained expert observers who had attended a four day training course in preparation for the study. The observers took detailed notes over the duration of the study in accordance with Line Operations Safety Audit process. All data was checked and cleansed to ensure accuracy. This is evidence of thorough preparation and procedure on the part of the study designers.
Previous studies have established that critical values of 5 and 6 hours sleep in the previous 24 hours are linked with degraded performance. The authors created variables that represented when: 1) neither crew; 2) only the captain; 3)
only the first officer; or 4) both crewmembers exceeded a critical prior sleep-wake threshold value. The crews provided this information to the observers. The crews were also rated on their performance in communication, situation awareness, task management, and decision making.
302 typical flight sectors were flown and crew members were observed from the beginning of the pre flight process through to end of the sector. Flight times ranged from 30 minutes to 5 hours in duration and occurred during he day and at night. Sleep - wake data was collected from the crews during the cruise as this was the only realistic time to do so.
Analysis of variance (ANOVA) procedures were performed using SPSS 16.0 on the Macintosh platform to allocate individual crew members into groups according to their reported prior sleep-wake. This data was then subjected to the least significant difference (LSD) procedure to obtain the effects of prior sleep or wake and normalised using an arcsine function.
The results are moderately useful as they confirm the results of previous studies showing less effective performance as a result of restricted sleep and fatigue. The results will be useful if distributed to the pilot community as they reinforce the importance of adequate rest before commencing duty.
THOMAS Matthew J W & Sally A FERGUSON (2010). Prior sleep, prior wake, and crew performance during normal flight operations. Aviation, Space, and Environmental Medicine, Volume 81, Number 7, July 2010, page 667.
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