Thirty-two helicopter pilots were studied before, during, and after 4- to 5-day trips providing support services from Aberdeen, Scotland, to rigs in the North Sea oil fields. Early on-duty times obliged subjects to wake up 1.5 hr. earlier on trip days than on pretrip days. Consequently, they slept nearly an hour less per night on trips. They reported more fatigue on posttrip days than on pretrip days, suggesting a cumulative effect of duty-related activities and sleep loss. Fatigue and negative affect were higher, and activation lower, by the end of trip days than by the end of pretrip days. The earlier a subject went on duty, the lower his activation by the end of the day. Caffeine consumption increased 42% on trip days. The incidence of headache increased twofold, of back pain twelvefold, and of burning eyes fourfold. In the aircraft studied, thermal discomfort and high vibration levels were common. The longer the time the pilots were on duty, the more negative their mood became. The most important environmental factor affecting subjective workload during preflight, taxi, climb, and cruise was the quality of the aircraft systems (as rated by the pilots on a 5-point scale from `perfect' to `useless'). During descent and approach, landing weather had the greatest effect. During landing, workload was most influenced by the quality of the landing site and air traffic control.

1.0 OPERATIONAL OVERVIEW

This report is the sixth in a series on the physiological and psychological effects of flight operations on flight crews, and on the operational significance of these effects. This section presents an overview of the major findings and their significance. The rest of the volume contains the complete scientific description of the work.

Thirty-two helicopter pilots (average age 34 yr.) were studied before, during, and after 4- to 5-day trips providing support services from Aberdeen, Scotland, to rigs in the North Sea oil fields. Duty days began and ended in Aberdeen. Half the trips studied took place in winter/spring, and the other half in summer/autumn. Heart rate, rectal temperature, and activity of the non-dominant wrist were monitored continuously by means of portable biomedical monitors. Subjects kept daily logs of sleep timing and quality, food and fluid intake, medications taken, and medical symptoms. They also rated their fatigue and mood every 2 hr. while awake. For every segment flown, they rated their workload (on a modified Bedford Scale) for each phase of flight, and the following five environmental factors assumed to influence workload: 1) functioning of the aircraft systems (rated on a 5-point scale from `perfect' to `useless'); 2) weather conditions for landing; 3) the landing site; 4) letdown aids; and 5) air traffic control (2-5 each rated on a 5-point scale from `very favorable' to `very unfavorable').

On trip mornings, subjects were required to wake up about 1.5 hr. earlier than on pretrip mornings (average on-duty time 0725 local time). Although they came off duty relatively early (average 1437 local time), they averaged only 6.4 hr. of sleep during layovers at home that averaged almost 17 hr. The inability to fall asleep earlier than the habitual bedtime is due to properties of the physiological mechanisms controlling sleep. Subjects were thus unable to compensate for the early wake-ups, and therefore averaged about 50 minutes less sleep per night on trips than pretrip. In the laboratory, 1 hr. per night of sleep restriction has been shown to accumulate and to progressively increase daytime sleepiness. Sleep was rated as better overall posttrip than on trip nights and deeper posttrip than pretrip, as is typical during recovery from sleep loss. Delaying the start of on-duty times (by 1.5-2 hr. on average) would be expected to produce a significant improvement in the amount of sleep pilots are able to obtain, and should be given serious consideration.

Pilots reported more fatigue on posttrip days than on pretrip days, suggesting a cumulative effect of duty-related activities and sleep loss. Fatigue and negative affect were higher, and activation lower, by the end of trip days than by the end of pretrip days. The inability to maintain subjective activation by the end of trip days was exacerbated by early on-duty times.

Pilots drank 42% more caffeine on trip days than on pretrip and posttrip days. More caffeine was consumed in the early morning, in association with the early wake-ups, and also around the time of the mid-afternoon peak in physiological sleepiness. The urge to fall asleep at this time would increase as the sleep debt accumulated across trip days.

There were twice as many complaints of headaches on trips as at home. Reports of back pain increased twelvefold, and reports of burning eyes increased fourfold. Helicopter pilots were three times more likely to report headaches, and five times more likely to report back pain than were pilots of fixed-wing aircraft on short-haul commercial flights. The physical environment on the helicopter flight deck was probably an important factor. Studies of the same operations, conducted in parallel, demonstrated that pilots often had skin temperatures outside the range of thermal comfort, and that vibration levels in all of the helicopters studied exceeded the `reduced comfort' boundary defined by the International Standards Organization (I.S.O. 263). The longer pilots remained on duty, the more negative their mood became. This situation could be improved with better seat design, including better isolation of the seat from floor vibration, and better flight-deck ventilation.

The predominant environmental factors affecting subjective workload assessments were different for different phases of flight. The quality of the aircraft systems had a significant effect during preflight, taxi, climb, and cruise. Paying particular attention to aircraft maintenance, thereby minimizing failures, might be one way of reducing workload during these phases of flight. Landing weather was the major factor influencing workload ratings during descent and approach. However, the effect of adverse weather on workload was reduced with better landing sites and better letdown aids. The quality of the landing site and air traffic control had a significant effect on workload ratings during landing. These findings confirm that improvements in landing sites, letdown aids, and air traffic control can reduce subjective workload during descent, approach, and landing.

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