Fatigue in trans-Atlantic airline operations: diaries and actigraphy for two- vs. three-pilot crews.
INTRODUCTION: The aim was to compare intercontinental flights with two-pilot and three-pilot crews with respect to fatigue/sleepiness and sleep, as there is considerable economic pressure on the airlines to use two-pilot crews. METHODS: Twenty pilots participated. Data were collected before, during, and after outbound and homebound flights using a sleep/wake diary (sleepiness ratings every 2-3 h) and wrist actigraphy. The duration of flights was approximately 8 h, and six time zones were crossed. The same pilots participated in both conditions. RESULTS: Napping during the outbound flight was 26 min for the two-pilot crew, and 48 min for the three-pilot crew. Napping during the homebound flight was 54 min and 1 h 6 min, respectively, and the difference was directly related to the time allotted for sleep. Subjective sleepiness was significantly higher for the two-pilot condition in both directions, peaking a few hours into the flight. Performance at top of descent for the two-pilot condition was rated as lower than the three-pilot condition. In the overall evaluation questionnaire there was a significant negative attitude toward two-crew operations. Sleep, sleepiness, subjective performance, boredom, mood, and layover sleep were assessed as having deteriorated in the two-pilot condition. The homebound flight was associated with considerably higher levels of sleepiness than the outbound flight. DISCUSSION: The study indicates that the reduction of crew size by one pilot is associated with moderately increased levels of sleepiness. It is also suggested that time allotted to sleep in the two-pilot condition might be somewhat extended to improve alertness.