The National Transportation Safety Board has confirmed an initial finding that the captain and first officer of a go! airlines flight that overflew its destination in Hawai'i inadvertently fell asleep while the plane was on autopilot.

The NTSB yesterday issued its final report in the case of a 2008 go! airlines flight from Honolulu that overflew Hilo International Airport by 30 miles.

Flight 1002, with 43 people aboard, passed over Hilo International Airport at 21,000 feet and continued straight on over open ocean before Captain Scott Oltman and First Officer Dillon Shepley awoke and landed the plane safely.

A contributing factor was Oltman's previously undiagnosed severe obstructive sleep apnea, a condition that likely caused him to experience chronic daytime fatigue and contributed to his falling asleep during the Feb. 13, 2008, flight, the NTSB said.

Oltman also told NTSB investigators that he would intentionally take naps about once a week during his flights for go!, and that his naps usually lasted about 20 minutes.

Another contributing factor was the flight crew's work schedules, which included several consecutive days of early morning start times, it said.

The day of the incident "was the third consecutive day that both pilots started duty at 0540," or 5:40 a.m., the final report said. "This likely caused the pilots to receive less daily sleep than is needed to sustain optimal alertness and resulted in an accumulation of sleep debt and increased levels of daytime fatigue."

The NTSB cited a 1998 NASA report which concluded that "requiring early report times makes it more difficult for crew members to obtain adequate sleep."

The NTSB also cited a 1998 report published by North Atlantic Treaty Organization Research and Technology Organization that concluded "pilots reporting before 0600 (6 a.m.) had a significantly shorter total sleep time, impaired sleep quality, and impaired performance both preflight and at top of descent."

Go! fired both Oltman and Shepley in April 2008.

The Federal Aviation Administration suspended the licenses of both pilots. Their suspensions ended Sept. 9, 2008.

Oltman served a 60-day suspension after the FAA cited him for careless and reckless operation of an aircraft and for failing to maintain radio communications. Shepley served a 45-day suspension for careless and reckless operation of an aircraft.