Incident Overview
On Saturday, March 13, 2021, a Honda Aircraft Model HA-420, registration JA01HJ, operated by Okayama Air Service Co., Ltd., ran off to the left side (south side) of Runway 27 at Kohnan Airport in Okayama Prefecture, Japan, after landing. The aircraft came to a stop in a grassy area and was unable to taxi. The incident occurred at about 17:26 Japan Standard Time (JST). The crew consisted of a captain and a trainee; neither was injured.
Aircraft and Crew Information
The aircraft, a Honda Aircraft Model HA-420 (serial number 42000133, manufactured November 20, 2018), was conducting training to acquire the captain qualification as per the company's Qualification Manual. The captain, aged 51, held a Commercial Pilot Certificate and a type rating for the HA-420, with a total flight time of approximately 5,950 hours. The trainee, aged 49, also held a Commercial Pilot Certificate and type rating, with about 5,150 hours of total flight time.
Flight History
After taking off from Kohnan Airport at about 16:13, the crew performed flight training around the airport, including six touch-and-go exercises at Takamatsu Airport. The aircraft then returned to Kohnan Airport. At approximately 17:25:30, the left main landing gear Weight-On-Wheel (WOW) sensor indicated touchdown, following the right main landing gear. At that time, the aircraft's heading was 274°, ground speed 101 knots, and roll angle right 0.4°. The captain's voice was recorded saying "Slowly," "Brake," "Brake."
By 17:25:33, the heading changed to 277°, roll angle left 3.5°, ground speed 96 knots, and lateral acceleration right 0.1 G. At 17:25:35, heading was 272°, roll angle right 1.4°, ground speed 90 knots. At 17:25:38, heading 283°, roll angle left 1.8°, ground speed 76 knots, lateral acceleration right 0.3 G. At 17:25:39, heading 282°, roll angle left 0.4°, ground speed 72 knots. At 17:25:41, heading 258°, roll angle left 3.5°, ground speed 60 knots, lateral acceleration left 0.6 G; the captain's voice indicated he sensed danger. At 17:25:44, heading 254°, roll angle left 3.5°, ground speed 48 knots. By 17:25:52, the aircraft stopped with heading 243°, roll angle left 2.1°, ground speed 0 knots. The captain later confirmed with the trainee that the left and right brake pedals were not symmetrically applied between brake application and the runway excursion.
Crew Statements
Both the captain and trainee reported that the training at Takamatsu Airport went well and the approach and touchdown at Kohnan Airport were stable. After touchdown, the aircraft's direction slightly veered left. The trainee attempted to maintain runway centerline using rudder pedals. Near the runway halfway marker, the trainee applied brakes to decelerate and corrected the left deviation using steering or braking, causing the nose to veer right sharply. The trainee then applied left rudder to correct, but the aircraft veered left abruptly. The captain, sensing a potential runway excursion, applied right rudder. He felt the load on the nose and main landing gear might not be fully placed. Both pilots tried to correct direction to the right, but the aircraft crossed the runway side stripe marking and entered the grassy area. The trainee reported trying to apply both brakes symmetrically from brake application until stop. No abnormal aircraft behavior or system warnings were noted from touchdown to stop.
Damage and Meteorological Conditions
The aircraft sustained minor damage, including scratch marks, paint peeling on the lower fuselage, impact marks on nose and main landing gear wheels, impact marks on the engine air intake, and partial damage to engine fan blades. The estimated weight at the time was 8,880.3 pounds and center of gravity 25.79% MAC, both within limits.
At 17:00, the weather observation reported wind from 290° at 9 knots, visibility 25 km, scattered cumulus clouds at 3,500 ft and 4,500 ft, broken altocumulus at 12,000 ft, temperature 12°C, dew point 5°C, and QNH 29.98 inHg.