What happened
On December 18, 2007, a SAAB 340B, registration JA001C, operated by Japan Air Commuter Co., Ltd., was performing a scheduled flight from Osaka International Airport to Izumo Airport. During the landing roll on Runway 25, the aircraft veered toward the right side of the runway, eventually exiting the paved surface and traveling onto the apron.
As the aircraft approached touchdown, the crew adjusted the power levers. Shortly after contact with the runway, the left propeller speed dropped sharply, and a master warning chime sounded. The aircraft began to deviate significantly from the centerline. Despite attempts by the pilot to use nose wheel steering and differential braking, the aircraft continued to veer right, eventually striking a ditch that caused the nose gear to break. There were no injuries among the 37 people on board, though the aircraft sustained minor damage.
The investigation
The JTSB investigation examined the flight data recorder (DFDR) and cockpit voice recorder (CVR), as well as the aircraft's mechanical systems and the runway environment. Investigators analyzed the movement of the power levers, the behavior of the autocoarsen system, and the effectiveness of the nose wheel steering. The investigation also included simulator verification to test the crew's ability to maintain directional control under similar conditions and an examination of the engine and propeller components.
Findings
- The primary cause of the deviation was an asymmetric thrust condition created when the left propeller pitch was increased to a coarse setting almost simultaneously with touchdown.
- This change was likely triggered by the specific manner in which the power levers were operated during the final approach and touchdown, which activated the autocoaster system.
- The crew failed to implement necessary procedures to counteract the veering, such as exiting the reverse thrust setting or using forward power to straighten the aircraft.
- The nose gear failure was caused by the aircraft striking a ditch located parallel to the runway during the excursion.
- While the pilot attempted to use the nose wheel steering, the investigation suggests the steering input was insufficient to recover the centerline.