The Federal Aviation Administration has opened an investigation into whether two go! airlines pilots fell asleep during a flight from Honolulu to Hilo last Wednesday.

go! Flight 1002 was headed for Hilo Airport around 10 a.m. but overshot the airport by 15 miles before returning to land safely.

FAA spokesman Ian Gregor said yesterday the agency has opened an investigation.

"We're investigating whether the pilot and co-pilot of a Feb. 13 go! airlines flight fell asleep while the plane was in the air between Honolulu and Hilo," Gregor said.

Joe Bock, a spokesman for go!, said the company is conducting its own investigation.

Gregor said the FAA plans to interview the pilots of the 214-mile flight. Under FAA rules, they could be subject to a warning, suspension or license revocation depending on the findings.

A radar track of the flight provided by the Web site www.flightaware.com shows the plane remained at 21,000 feet as it flew past Hilo before returning to the airport.

Air traffic controllers, which had been tracking the plane by radar, were unable to reach the plane for 25 minutes, according to a report by KGMB-TV.

Complaints of pilot fatigue are not new to go!'s parent company, Phoenix-based Mesa Air Group.

In 2006, Dallas television station WFAA-TV reported that pilot schedules at Mesa Mainland operations were so tight that many pilots were flying exhausted and some were forced to camp in their aircraft.

Last year, the Mesa unit of the Air Line Pilots Association complained that staff shortages on the Mainland hurt morale and affected operations.

go!, which began flying in Hawai'i in June 2006, is the state's fourth largest carrier. The company flies 50-seat Bombardier CRJ-200 aircraft.

Local pilots say that most commercial flights between Honolulu and Hilo have an autopilot function that can set the plane's route, altitude and speed. The autopilot also controls the aircraft's descent when it approaches an airport.

But toward the end of the flight, the pilot needs to manually set a lower altitude for landing. Failure to do this would mean that the plane would continue past its landing point, which may have occurred on Flight 1002, the local pilots said.

FAA officials could not recall the last time they investigated an off-course airliner in Hawai'i.

In 1988, the FAA investigated a Hawaiian Airlines flight from Los Angeles to Honolulu that strayed 200 miles off course.

The DC-8 aircraft corrected its course and landed safely. Hawaiian said at the time that pilots had informed radio air traffic controllers that they were having navigational problems. No one was hurt.