Investigators with the US National Transportation Safety Board (NTSB) today said both an undiagnosed sleep apena condition for the captain and crew work schedules were factors in two pilots falling asleep during a flight operated by Mesa's Hawaii interisland subsidiary go! in February 2008.
The crew was operating a Bombardier CRJ200 on a 40min flight from Honolulu to Hilo. But the aircraft flew 26nm beyond Hilo at cruising altitude. Both the captain and first officer later reported falling asleep during the flight to Mesa management.
"The fact that both pilots fell asleep during the midmorning hours, a time of day normally associated with wakefulness and rising alertness, indicates that both pilots were fatigued," NTSB says.
In its final report issued today NTSB not surprisingly states the probable cause for the aircraft veering off course was the captain and first officer inadvertently falling asleep during the cruise phase of flight.
After the incident, the go! captain was diagnosed with severe obstructive sleep apnea. But the board also states that symptoms such as snoring and risk factors of obesity were present prior to the flight.
"This condition likely caused him to experience chronic daytime fatigue and contributed to his falling asleep during the incident flight," the board explains.
In an interview during the NTSB's investigation of the incident the captain stated: ""Working as hard as we had, we tend to relax. I just kind of closed my eyes for a minute, enjoying the warm sunshine, and dozed off."
The board also stresses the day of the flight was the third in a row that both pilots started duty at 0540, which caused the crew to get less sleep than needed and increased daytime fatigue.
NTSB estimates the first officer accumulated a sleep debt of 1hr 15min to 2hr 45min in the 72 hours prior to the incident. The board cites a 1998 NASA study that concluded early report times make it more difficult for crews to obtain adequate sleep.
Another study conducted that same year by the North Atlantic Treaty Organization Research and Technology Organization highlighted by the board concluded that pilots reporting before 0600 had a significant shorter total sleep time, impaired sleep quality and impaired performance both pre-flight and top of descent.
Proposed legislation recently introduced by the US House of Representatives would require FAA to update and implement new flight and duty time rules for pilots, and for airlines to create fatigue risk management systems.