An undiagnosed sleep disorder and an early morning schedule were contributing factors in a captain and first officer falling asleep and flying 40 passengers 30 miles past their destination in Hilo, the National Transportation Safety Board said.

The board said yesterday that the 53-year-old captain flying go! Flight 1002 suffered from undiagnosed obstructive sleep apnea and that consecutive early morning start times contributed to his and a 23-year-old first officer's falling asleep on Feb. 13, 2008.

Sleep apnea causes an individual to have small awakenings during sleep due to breathing difficulties, disrupting rest and causing fatigue.

“;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,”; the board said.

The captain and first officer were suspended and did not return to work, an airline spokesman said.

The board's findings come as the Federal Aviation Administration is planning to rewrite rules for pilot flight and duty time.

FAA Administrator Randy Babbitt said his agency is looking at changing the rules based on recent scientific research.

The captain said that before Feb. 13, 2008, he had flown eight legs on Feb. 11 and 12, for a little more than nine hours each day, the board said.

The duration is within federal guidelines limiting two pilots to fly no more than 10 hours during regional flights.

But the captain, who had applied for temporary assignment in Hawaii in search of relief, said he found the work no easier because he had to fly eight legs per day with few breaks, the board said.

He said the eight-leg schedule reduced his ability to obtain coffee, eat and smoke cigarettes, the board said.

The board noted that according to a 1998 report, pilots who reported for work before 6 a.m. had “;significantly shorter total sleep time, impaired sleep quality, and impaired performance.”;

The flight left Honolulu at 9:16 a.m. for Hilo. When an air traffic controller instructed the flight to change radio frequencies at 9:40 a.m., there was no response, the board said.

The controller continued to try to contact the flight crew more than once but received no reply even after the Bombardier Inc. CL-600 flew past Hilo at 9:55 a.m., it said.

The board said that at 9:58 a.m., when the flight was about 30 miles southeast of Hilo, the captain called the controller, and the controller asked whether the flight crew was experiencing an emergency.

“;No, we must have missed a handoff or missed a call or something,”; the pilot said.

The board said the captain had undiagnosed severe obstructive sleep apnea, discovered during a medical evaluation shortly after the incident.

“;This condition likely caused him to experience chronic daytime fatigue and contributed to his falling asleep during the incident flight,”; the board said.

The board said in addition, Feb. 13 was the third consecutive day that both pilots started duty at 5:40 a.m.

“;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 board said.

A Hawaii spokesman for go! referred questions to parent company Mesa Air Group in Arizona, which did not return phone calls.