What happened
On February 27, 2019, a Bell 505 helicopter, registered JA184A, was conducting training maneuvers at Sendai Airport, Japan. The aircraft, operated by the Japan Coast Guard School Miyagi Branch, was carrying an instructor and two trainees. The flight involved a series of touch-and-go training sessions, including power recovery autorotations.
During the flight, the instructor decided to perform a demonstration of a "Full Landing" autorotation. The goal was to touch down on the paved area of the west helipad. As the helicopter descended, the instructor intended to begin deceleration at 150 feet above ground level (AGle). However, the deceleration maneuver was delayed, only commencing at approximately 100 feet AGL.
In an attempt to avoid touching down short of the paved area, the instructor maintained a moderate flare rather than a more aggressive one. This resulted in the helicopter touching down with an excessive descent rate of 840 fpm. The impact caused the aircraft to slide and resulted in significant damage to the airframe, including a deformed skid cross tube and a damaged antenna mounting.
The investigation
The Japan Transport Safety Board (JTSB) examined the flight data from the aircraft's Garmin G1000H integrated instruments, as well as monitor camera footage from the airport apron. The investigation reviewed the instructor's training history, the specific procedures for "Full Landing" versus "Power Recovery" autorotations, and the technical differences between the Bell 505 and the older Bell 206 models used by the school.
Investigators analyzed the descent profile, noting that while the rotor RPM (Nr) remained near 100% at touchdown, the collective pitch control (CPL) remained in a low position. The investigation also looked into the instructor's decision-making process regarding the delayed deceleration and the prioritization of touchdown position over descent rate mitigation.
Findings
- The instructor delayed the start of the deceleration maneuver, beginning it at 100 feet AGL instead of the planned 150 feet AGL.
- The instructor chose to prioritize landing within the paved area over effectively reducing the descent rate, leading to an insufficiently elevated flare.
- The descent rate at touchdown was 840 fpm, which is considered excessive for an autorotation landing.
- There was insufficient time to raise the collective pitch control to mitigate the impact because the aircraft touched down immediately after the flare maneuver was ended.
- The instructor continued the Full Landing maneuver despite recognizing that the prescribed deceleration altitude had been missed.