Later In-Flight Sleep Produces More Alert Pilots for Landing

Scheduled sleep periods critical for safety of ultra-long haul flights

The amount and quality of sleep long-haul pilots obtain during flight is a critical factor in the safety of ultra-long range flight operations. A recent study suggests that a sleep period later in the flight results in a more alert crew on duty for the critical landing phase.

Ultra-long range (ULR) flights are defined as those non-stop flights of 16 hours duration or more covering 8,000 nautical miles (NM) or more. Flights of up to 20 hours are on the horizon, with duty periods for aircrews of up to 22 hours (ground and airborne activity combined). Modern aircraft entering service, such as the Boeing [NYSE: BA] B777-200ER (extended range) and the Airbus A340-500 are among the first aircraft capable of ULR operations, meeting passengers’ desire for direct point-to- point service. Emirates, for example, recently took delivery of an A340-500 capable of 17-hour flights, e.g., Dubai to San Francisco. Globe-girdling flights connecting city-pairs 9,000 NM apart are within the realm of current technology.

For such long flights, there is a risk that crews on continuous duty would end the flight with the degraded alertness of sleep-deprived zombies. As international airline Capt. Tim Crowch observed two years ago in this publication, “All these [fatigue-related] weaknesses come at the most critical point of the pilot’s working day – the approach and landing. How many senior business managers would consciously plan their most critical decisions to be made at the end of a hard working day?” (See ASW, July 30, 2001) In a Dec. 17 communication concerning the advent of ULR flights, Crowch updated his concerns. “I shudder at the thought of flying sectors of this length. The longest I have done is 13.5 hours,” Crowch declared. “This new increase in range produces a new mission requiring a new strategy, and I repeat my earlier statement that the most demanding tasks come at the end of the working day,” Crowch said. He pointed out that approach and landing accidents are at “the top of the Federal Aviation Administration and Flight Safety Foundation hit lists.”

“This new ULR challenges their commitment [to reduce these accidents] head-on,” Crowch cautioned. “A poorly-rested or exhausted crew will negate all other positive efforts to reduce and reverse current statistics,” he pointed out.

Some pilots have dubbed long-range flights as “iron butt” endurance challenges. It is widely recognized in the airline industry that aircrew fatigue is a factor in the safety equation, given the recognized potential for degraded alertness to contribute to the potential for human error. Indeed, upgraded hours of service regulations across all modes of transportation are on the National Transportation Safety Board‘s “Most Wanted” list of safety improvements (see ASW, May 12).

In a recent presentation, Curt Graeber, Boeing’s chief engineer for human factors, said, “If you take the current flight and duty time regulations and extrapolate them to ULR operations, they don’t make any sense.”

The regulations have their roots in an earlier era, when flights of such long duration as those routinely being flown today did not present nearly so demanding a challenge for aircrew endurance, and all of its implications for minimum crew complements, crew scheduling and fatigue management during the flight.

“In-flight sleep is much less than the opportunity provided,” Graeber said, adding, “This is important,” particularly for ULR flights.

Documentation for Graeber’s observation comes from a May 2003 report by Dr. Leigh Signal and colleagues with the Sleep/Wake Research Center at New Zealand’s Massey University. Boeing funded the study, in which 21 volunteer pilots participated in preflight and enroute sleep research. The trials were conducted as part of B777-200ER delivery flights from the Boeing plant at Seattle, Wash., to customer airlines in Singapore and Kuala Lumpur, Malaysia.

The six delivery flights, with four pilots assigned to alternate shifts in the two-pilot cockpits, averaged about 15 hours in duration while crossing nine time zones. Researchers were on board for these flights.

The seven-hour scheduled sleep periods in a designated crew rest compartment are the longest yet monitored. The study also utilized polysomnographic measuring technology, which Graebner described as the “gold standard” for sleep research. In this technology, electrodes attached to the face and scalp monitor brain activity, muscle tone and eye movement.

For one night during the volunteers’ layover before the delivery flights, their sleep was monitored for baseline purposes; this exercise also helped in getting them used to the attached electrodes.

The flights were scheduled with one early and one late seven-hour rest period. The first began at the top of climb, about 30 minutes after takeoff. After seven hours, the early crew was awakened if they were still asleep. They slept in a crew rest compartment installed in the aircraft. Although no passengers were on these delivery flights, with attendant noise from meal and other services, this compartment isolates the crew from the passenger compartment and provides a higher level of humidity. The higher humidity meant less irritation of the nasal cavities and a more conducive sleep environment.

Not men-tioned in the study are some other aspects of the crew rest module, which on some aircraft is located below the main deck. While it was not the purpose of the study, the crew rest facility might be designed to provide for more than just enhanced in-flight rest. Improved air filtration against micro-organisms might be a useful feature. Consider the case of a crew exposed to disease on an outbound flight and coming down with something a couple days later on the return flight? Additionally, should the crew rest facility be located between the fore and aft cargo compartments, it will have to be evacuated in the event of a belly hold fire alarm. In this event, airflow isolation valves will be closed. The compartment will have to be evacuated before the cockpit crew can activate the fire extinguishing bottles, as a precaution against agent seeping into the compartment.

Back to the study. Once the early rest crew took over operation of the aircraft, the late crew began its seven-hour rest opportunity. This period ended an hour and ten minutes prior to landing. The late crew was awakened and returned to duty in the cockpit. It might be worthy of mention the newly refreshed crew that would be taking stations for landing could be inheriting fuel, equipment and terminal weather-related decisions made by the crew just relieved. In other words, some options may already have been foreclosed.

Results in brief

Crewmembers who slept later in the flight were more alert during their final 50 minutes of duty. The policy implication is evident: the landing crew should have the second sleep opportunity. Since the amount and quality of sleep pilots are able to obtain on board is an important aspect of safe ULR flights, the study’s ancillary findings are important:

• Sleep in a bunk during flight was not as efficient as layover sleep. The efficiency of the predeparture sleep was judged some 89 percent, as measured by the time actually asleep in comparison to the time spent trying to sleep. Bunk sleep during flight was judged about 70 percent efficient. Volunteer crewmembers averaged seven hours of layover sleep. Although crewmembers were asked to spend as much of their in-flight rest period as possible trying to sleep, no one spent seven hours trying to sleep. On average, the test pilots spent 4.69 hours trying to sleep, in which an average of 3.27 hours was scored as sleep.
• Sleep later in the flight was longer and of higher quality than early in the flight. Even after controlling for age and the individual’s “sleep deficit” before the flight, those scheduled for rest later in the flight got more sleep. As measured by awakenings longer than 60 seconds, the pilots from the second rest period also slept more soundly (although variations in rapid eye movement, or REM, and other measures of sleep “quality” were not statistically significant).
• Pilots who slept later in the flight were more alert than those who slept earlier.
• The amount and quality of sleep in the bunk was unrelated to the amount of layover sleep before the flight. This finding suggests that purposely restricting predeparture sleep to improve sleep on board is not advisable.
• Older crewmembers got less sleep than younger crewmembers, which is consistent with changes in human sleep patterns that start to appear at about 50 years of age. In fact, the subject’s age was the most dominant factor affecting bunk sleep.

Some study limitations

The findings need to be couched in terms of the study’s limitations. Notably, the test subjects were all male pilots.

The sleep trials were conducted during delivery flights, not on regular revenue flights, which would be part of a more complex sequence of back-to-back flights, and where varying noises associated with meal service and passenger activity could impair the resting crewmember’s ability to sleep.

The study examined only one of two possible approaches to fatigue management. For instance, sleep scheduling could aim for maintaining the highest possible alertness across all phases of flight, which might result in a less alert crew for landing. Alternatively, the focus could be placed on ensuring that the landing crew is as alert as possible. That is where this study provides insight.

Leigh added, “The findings [in the report] apply to flights with similar departure times. As explained in the [report] introduction, our body clock is important in determining when we can sleep most easily. The flights [we studied] departed Seattle around midday local time, and this will have an impact on sleep quantity and quality in flight.”

The study did not address in-flight sleep for cabin staff. As one flight attendant remarked, “I wonder what an emergency evacuation would look like after cabin crew has been on duty for 20.5 hours?” One carrier recently proposed this duty time for its ULR flights. (ASW note: Dr. Signal relates that the Massey University Sleep/Wake Research Center study is not yet available on the Internet, but interested persons can e-mail [email protected] for a pdf copy.) >> Signal, e-mail [email protected] <<

Fatigue – ‘Use what we already know’

Observations on the ULR sleep study by Dr. Mark Rosekind, president of Alertness Solutions:

It is critical that we use what we already know scientifically about fatigue. For example, that it represents a significant safety risk, that all types of flight operations create fatigue (i.e., short haul, long haul, overnight cargo, on-demand), and that there are alertness strategies that have been scientifically validated. Regarding this study, it is important to consider the context that the National Aeronautics and Space Administration (NASA) nap study showed even a brief in-flight rest of only 40 minutes resulted in a 34 percent performance boost and increased alertness 54 percent. In another NASA study of bunk sleep, it was found that the sleep obtained in the bunk was not as efficient as home sleep but did result in pilots maintaining their performance throughout long flights.

It is equally critical as technology and operations evolve that we continually increase our knowledge about what is actually happening to alertness, performance, and safety. Hence, the importance of this study. It builds on a scientific knowledge that exists, and expands to new challenges associated with ULR operations. The findings and messages are important: in-flight sleep periods improve alertness and performance, they should be planned/scheduled, the landing pilot will receive more benefit from a later rest period that boosts alertness and performance closer to the time when a critical phase of operation is undertaken. And, scientific studies can provide important basic information about what is going on in real operations and provide practical guidance that can have real-world effects on safety. And it is good that Boeing recognizes the challenges posed by its airplanes and supports activities that will make their use safer. >> Rosekind, e-mail [email protected] <<