Ultra Long Haul (ULH) flights are classified as non-stop flights by aircraft with no refueling stops during a flight route distance of approximately more than 12,000 kilometres (7,500 miles) and flight time of more than 14 hours between the departure point of origin and arrival destination.
The world’s longest scheduled passenger flight is Singapore Airlines’ Flight SQ21 between Newark-Liberty Airport, New Jersey, United States of America and Singapore Changi Airport, which is operated with an Airbus A340-500. The great circle flight route distance is 15,345 kilometres (9,535 miles/ 8,285 nautical miles). The flight time of SQ21 is approximately 18 hours 30 minutes3.
Human Factors Concerns
1) Health Concerns
Health issues can range from Deep Vein Thrombosis (DVT) due to limited body movements over a long period of time, spreading of contagious diseases within a confined space, food poisoning due to poor food hygiene for the food supplied onboard a well as long period of inhalation of hazardous cabin vapours from sources such as engine oil leakages or dysfunctional air conditioning units4.
2) Psychological Stress
The need to dedicate concentration onto then maintenance of good situational awareness and monitoring of flight deck instruments can be mentally taxing when required to do so for long periods of time 4.
3) Pilot Fatigue (Physiological Stress)
The numbers of hours as well as the quality of the sleep that the flight crew involved in ULH flights, obtained during the flight period is a crucial element towards upholding high level of operational safety. This is in addition to assuring that flight crew has sufficient quality rest prior to a flight operation. This is especially so during critical flight phases such as the approach and landing. The US Federal Aviation Administration (FAA) and Flight Safety Foundation accident statistics unveiled that the approach and landing phases of a flight are the most accident-prone. It is therefore essential to highlight and assure that these ULH flight crews are able to execute and complete these demanding flight tasks safely after being on duty for more than 14 hours4.
- Report issued in May 2003
- Involved 21 volunteer pilots
- Executed during Boeing B777-200ER delivery flights of duration of 15.5 hours from Seattle, Washington, USA to client air carrier bases in Singapore and Kuala Lumpur, Malaysia.
- Two sets of two flight crews each
- One early (30 minutes after departure and definite waking 7 hours 30 minutes before arrival) and one late (7 hours 30 minutes after departure and definite waking an hour before arrival) sleep opportunity of 7 hours period
- Flight crew slept with sleep research polysomnographic measurement technology electrodes attached to their head scalp and face
- Flight crew layover sleep is recorded as baseline reference.
- Flight crew slept in dedicated crew rest module compartment with higher level of humidity for comfort during the flight.
Main Research Finding:
Flight crew members who have their sleep later in the flight (more than seven hours later) are able to show greater level of alertness (and situational awareness) during the last 50 minutes of their duty period. This is due to the ability of the flight crew with the second sleep opportunity to have longer sleep period of higher quality than the flight crew with the first sleep opportunity.
In the case of two sets of two flight crew members, the flight crew members with the late second sleep opportunity (7 hours 30 minutes after departure and definite waking an hour before arrival) should be the set of crew to execute the approach and landing phases of the flight as they are more alert than the other flight crew members with the early flight sleep opportunity.
1) Each ULH flight should have at least two sets of two flight crew members.
2) The utilisation of a sleep scheduling tool could aim at allowing flight crew to maintain alertness at different desirable phases of the flight.
3) Since the approach and landing phases are the most crucial flight phases after the flight departure, the emphasis should focus on ensuring that the landing crew is at its highest level of alertness.
Other Useful Research Findings:
1) As compared to layover sleep (89% sleep efficiency) prior to departure, sleeping in the dedicated crew rest module compartment (70% sleep efficiency) was not as efficient.
2) Flight crew sleep duration and quality in the dedicated crew rest module compartment was not directly related to the flight crew layover sleep duration prior to flight departure.
3) Flight crew members of older age received a lower amount of sleep than flight crew members of younger age. This is, however, in consistent with human circadian rhythm changes observed in population at the start of the age of 50 years old.
1) Studies were carried out on delivery flights and thus not subjected to the presence of noises (meal services and passenger activities) on regular scheduled passenger flights that could affect the ability of the resting crew members to sleep properly.
2) Varying circadian rhythm could have different impact on the flight crew sleep pattern.
An early afternoon departure from the airline hub could make it difficult for the flight crew taking the first sleep opportunity to have efficient sleep period as they are used to being physically or mentally active during that particular point of the day.
3) The Boeing study only includes flight crew and does not extend to cabin crew.
It is also essential that cabin crew have a high level of alertness at all times as emergencies can occur anytime (e.g. medical, sudden mid-air turbulence).