Incident Overview
On Saturday, July 9, 2016, an Airbus A320-232, registered JA04JJ, operated by Jetstar Japan Co., Ltd., was operating as a regularly scheduled flight 502 from Fukuoka Airport to Narita International Airport. At 09:38 Japan Standard Time, while cruising at an altitude of 37,000 ft approximately 96 km south-southeast of Chubu Centrair International Airport, the airspeed indications on both the captain's and co-pilot's sides temporarily failed. The aircraft subsequently descended to 25,000 ft and continued its flight, landing at Narita International Airport at 10:26.
Flight History
The flight departed Fukuoka at 08:50 with 156 persons on board: the captain, five other crewmembers, and 150 passengers. No injuries were reported, and the aircraft sustained no damage. During the flight, the crew requested multiple course deviations to avoid adverse weather conditions, including a 25 nm northward deviation around 09:14 and later a 25 nm southward deviation at 09:33. At 09:36, the aircraft reported its position at FL370 above ISEBI waypoint. Shortly after, at 09:37, Tokyo Control inquired about a direct flight to BUNGU waypoint.
Investigation Findings
The Japan Transport Safety Board conducted an investigation. The flight data recorder and cockpit voice recorder, along with weather radar data, were analyzed. The investigation determined that the temporary failure of airspeed indications was due to icing in the Pitot tube. The aircraft's Pitot tubes were examined, and maintenance records were reviewed. Meteorological data indicated the presence of an ice crystal area in the vicinity of a cumulonimbus cloud that had grown to a high altitude.
Probable Cause
The JTSB concluded that it is probable that this serious incident occurred because icing formed in the Pitot tube when the aircraft was flying at an altitude of 37,000 ft, leading to the temporary failure of airspeed indication on both the captain's and co-pilot's sides. It is somewhat likely that the icing occurred because the aircraft flew in an ice crystal area that existed in the vicinity of a cumulonimbus that grew to a high altitude.