‘Sleep Will Not be Denied’
ASHBURN, Va. – Factors used to examine the role of human fatigue in accident investigations might also provide a useful scheduling template to help avoid fatigue-related crashes.
Biological needs can be translated into scheduling factors. “The goal is to make sure that fatigue does not contribute to risk,” asserted Dr. David Dinges, a noted sleep researcher at the University of Pennsylvania School of Medicine.
Hewing to certain rules of thumb can support this goal:
- An employee’s awake period within 24 hours should not exceed 17 hours, especially when involving night shift work. Within that maximum 17 hours of wakefulness, the duration of time at work should not exceed 12 hours. “All the curves [of declining performance] are exponential right at 12 hours. They break and go up,” Dinges said. Accidents have resulted when pilot duty times exceed the 17 hour limit. As an example, the captain and first officer of a DC-8 freight that crashed on final approach at Guantanamo Bay, Cuba, in 1993 had been awake for 23.5 hours and 19 hours respectively at the time of the accident.
- An employee’s rest period in which sleep is taken should be 10 or more hours. Since people do not and cannot sleep for an entire rest period, an eight-hour rest period implies six or less hours of sleep. “If we can get rest periods to 10 hours, there’s a better chance people will get enough sleep,” Dinges said. Presently, pilots on domestic flights are scheduled under the eight-hour look-back rule. That is, there must be eight hours of rest at the end of a 24-hour period. A pilot may not take off if, at the end of the flight, there will not be eight hours of rest in the 24 hour period ending with that flight.
- Circadian timing is important. Daytime and early evening are the periods of greatest wakefulness. After midnight and late in the afternoon are considered circadian “lows.” Above all, Dinges said, “Shift rotations are disruptive to sleep and waking.”
- To minimize the accumulation of sleep debt, at least one in seven days should involve a full 24-hour cycle free from work. If a person has accumulated a sleep debt of more than eight hours, it can take up to two nights’ sleep to recover, pointed out Dr. Mark Rosekind, founder and president of Calif.-based Alertness Solutions, a fatigue consultancy.
These scheduling factors were presented at a recent fatigue factors symposium hosted here by the National Transportation Safety Board‘s (NTSB) new Training Academy. The goal of the March 10-11 course was to outline the means by which operator fatigue can be examined during the course of an accident investigation.
“Almost every accident investigating body in the world underestimates the role of fatigue in accidents,” Rosekind declared.
There is no straightforward “blood test” for fatigue, he said, and persons involved in an accident usually are highly subjective when assessing their state of fatigue. However, Rosekind and co-presenter David Dinges suggest there are ways to tie fatigue to human performance in an accident investigation. Conversely, the same overall indices can be used to rule out fatigue.
Dinges was adamant about what is known, even with the imperfect state of science and knowledge, about human sleep. “The homeostatic drive for sleep eventually crushes alertness and performance,” he said. The drive for equilibrium (homeostasis) means simply, Dinges said, “Sleep will not be denied.”
The role of fatigue, and its impact on safety, can be divided into four major areas of interest. These are: sleep loss, continuous hours of wakefulness, the circadian time of day, and sleep disorders, plus some related considerations, Rosekind said.
First, a brief recapitulation of what can confidently be said about fatigue, sleeplessness, and the impact on workplace performance. As fatigue accumulates, performance degrades. But how so? Dinges ticked off the indicators. Involuntary “microsleeps” begin to occur (anyone who has caught himself dozing off driving at night has probably experienced a microsleep). Attention lapses occur, and working memory errors increase (i.e., what one can recall instantly when rested become difficult to recall when tired). Problem-solving skills erode, nonessential activities start to be neglected and vigilance tasks become increasingly difficult to perform. The relevance to aviation safety is clear.
The consequences of fatigue play out in the form of increasingly varied and unreliable workplace performance. Activities judged to be of lower priority tend to become more neglected, situational awareness suffers and the risk of errors and accidents increases. The neglect of activities judged “non-essential” is especially pernicious, “a much bigger risk to safety than checklist skips,” Dinges said. Indeed, just about all of the key points emphasized by Dinges and Rosekind are documented in the case of a fatal 2001 nighttime crash of a Falcon 20 non-scheduled cargo flight on approach in Greenland.
Well-known factors adversely affect performance. “There is nothing magic here,” Dinges said. He ticked off three major items: “Long shifts, bad. Night shifts, risky. No days off, real bad.”
To flesh out Dinges’ overall observations, after millions of years of evolution on a planet with a 24-hour rotation cycle, “humans are built for 16 hours of wakefulness,” Dinges said. Moreover, their body clocks are synchronized by light, and people have evolved to be most alert during daylight. Technology has changed all that. The invention of electric light, and work shifts scheduled around the clock, have put the body under stresses unknown to humankind’s ancestors.
If people are working at night, or if they rise before 5 a.m. to go to work, performance degrades. “What’s the difference between night work and jet lag? There’s hope of adjusting to jet lag,” Dinges quipped.
While individual sleep needs vary, most people need 6-8 hours of sleep every 24 hours. As a general statement, less than seven hours sleep and less than eight hours time in bed can lead to acute impairment.
“No days off are tantamount to disaster,” Dinges said. Many people accumulate a “sleep debt” during their workweek and “make up” for it with more sleep on their time off. “The reasons for this weekend ‘sleep saturation’ and its benefits are not totally understood,” Dinges said. To assess or rule out the role of fatigue in accident investigations, Rosekind offered a checklist, simplified here, with the thresholds to watch for. The greater the number and severity of these factors, the more likely fatigue is a contributing element in an accident inquiry.
While there are enormous productivity, liability and operational factors involved in operator fatigue, it is evident that fatigue’s contributing role in an accident can be assessed, factored in or ruled out. Additionally, scheduling that recognizes the very human need for sleep can minimize the impact of fatigue on flight and maintenance operations. When fatigue is minimized, risk is minimized. >> Rosekind, e-mail [email protected]; Dinges, e-mail [email protected] <<
|
Fatigue in Accident Investigation – Factors to consider
|
||
|
Items
|
Details to Consider
|
Threshold of Concern
|
| 1. Sleep loss | Two major areas of concern: (1) acute sleep loss, or the total sleep in the last 24 hours and the timing of the sleep (e.g., day, night, interrupted, continuous, naps, etc.), and (2) cumulative sleep debt. | (1) Less than 6 hours of sleep in previous 24. (2) A total of 8 hours insufficient sleep over previous few days. |
| 2. Hours of wakefulness | Time continuously awake in previous 24 hours. | 17 hours or more should be a concern. More than 12 hours of duty time should be a concern. |
| 3. Circadian time of day | Accident time of day. Impaired function during circadian low. Variability of duty times. Time zone vs. local time. | General rules of thumb: sleep at night, good. Daytime sleep, bad. |
| 4. Sleep disorders | Are any sleep disorders known, diagnosed and treated (e.g., apnea)? | An estimated 70 percent of people with sleep disorders do not seek medical help. |
| 5. Other consider-ations | Working environment (e.g., sitting down, or standing up, which can mask sleepiness). Medical history (e.g., seizures, other?) Personal alertness strategies (e.g., use of stimulants) | Watch for factors that can mask sleepiness and fatigue, or aggravate same. |
| Source: Rosekind, Dinges | ||
Classic Fatigue –> CFIT Accident
CFIT: Controlled flight into terrain
On final approach to runway 07, Narsarsuaq, Greenland, Aug. 5, 2001
Dassault Falcon 20 destroyed on impact, two pilots and pilot passenger killed.
The aircraft impacted mountainous terrain 4.5 nautical miles SW of the aerodrome.
From the Danish Air Accident Investigation Board (AAIB) report (numbers correspond to sections in report):
1.1 With reference to the CVR [cockpit voice recorder] readout, there were no audible flight crew call outs concerning the use of checklists, altitude checks and standard operating procedures (SOP) during the descent, the initial and final approach phase.
2.3.3 The accident occurred at 0443 hours, where the body with reference to circadian physiology is programmed to sleep (peak fatigue). On the assumption that the flight crew got up at 0700 hours on August 4, 2001, the fight crew had been awake for approximately 22 hours at the time of the accident. It is in the opinion of the Danish AAIB that the exceeding of the flight duty time in combination with the above mentioned physiological elements resulted in fatigue and thereby degraded the performance and the alertness of the flight crew. It is possible that an underestimation by the flight crew of their fatigue contributed to improper decision-making, lack of situational awareness and thereby to their failure to properly execute the approach.
2.3.4 In combination with fatigue, another contributing element to the accident might have been stress, since the flight was chartered to deliver cargo in KSDF [Louisville, Ky.] at 0900 hours on August 5, 2001. When leaving EPGD [Gdansk, Poland], the flight was more than two hours late. The handling agent in BIKF [Keflavik, Iceland] stated that the commander seemed stressed.
3.1 Findings
3.1.12 The pre-flight planning did not fulfill the requirements of JAR-OPS 1 and the operator’s procedures.
3.1.14 The commander was the pilot flying.
3.1.15 The commander was not properly fastened.
3.1.21 The flight crew made a procedural decision error by planning a visual approach.
3.1.27 The flight crew were not aware of their proximity to terrain.
3.1.29 During the final approach, the flight crew did not comply with the operator’s SOPs.
3.1.31 CRM [crew resource management] techniques were not evident in the flight crew’s performance.
3.1.33 The planned flight duty time for the flight crew was limited to 14 hours.
3.1.34 At the time of the accident the flight crew had been on duty for 16 hours 56 minutes.
3.1.35 The flight duty time was exceeded by 2 hours 56 minutes.
3.1.36 The rest period for the flight crew should have begun at BIKF [Keflavik].
3.1.37 Regard[ing] flight duty time, the planned flight could not be a non-rest flight to KSDF [Louisville].
3.1.38 At the time of the accident, the flight crew had been awake for approximately 22 hours.
3.1.39 The flight crew [was] exposed to peak fatigue, which … performance and alertness.
3.1.40 Fatigue in combination with stress contributed to improper decision-making, lack of situational awareness and thereby to the failure to properly execute the approach.
3.1.47 The GPWS [ground proximity warning system] was inoperative.