A Japanese pilot dozed off twice at the controls during an hour-long internal flight last month, All Nippon Airways (ANA) has admitted.
ANA said the passengers were never at risk
The airline issued an apology on Friday after the 50-year-old captain was revealed to have napped while flying 184 passengers and crew on auto-pilot.
The pilot has been suspended and is currently undergoing medical tests.
Last year, a bullet train driver fell asleep at the controls. He was later found to be suffering from sleep apnea.
The ANA pilot started snoozing about 20 minutes after take-off, after the Boeing 767-300 jumbo jet had levelled off to 12,000 metres (36,000 feet).
He was woken by his co-pilot, but fell asleep again before landing.
"He was asleep for two or three minutes," an ANA spokesman said.
The incident was reported by an examiner from the Transport Ministry, who happened to check on the cockpit at the time.
The captain told the airline that he had slept for seven hours the night before, and had reported no sleeping problems at a medical five days earlier.
"The sun was coming in from the front, and I nodded off," he reportedly told the airline.
Last February, a bullet train driver with 800 passengers on board travelled about 26km at almost 300 kilometres (186 miles) an hour while asleep.
He was discovered to be suffering from sleep apnea syndrome, a breathing difficulty which disrupts sufferers' sleep and therefore often causes them to feel drowsy during the daytime.