ERA22LA145 · Airbus Helicopters MBB-BK 117 C-2

The helicopter pilot had just completed a night public-use medical flight to a hospital and was returning to the base airport along with two flight paramedics. The pilot initiated the takeoff and increased power to enter a hover, at which time he observed (via engine instrumentation) an uncommanded surge (increase) in power, which he also heard. The pilot continued the liftoff into a low hover and found that, despite the momentary power surge, all engine parameters and flight controls appeared normal, so the flight continued to its operational base. The pilot arrived at the base without any en-route anomalies and maneuvered the helicopter in the ramp area to align with a landing dolly connected to a tractor. The maneuver required the pilot to complete a right sidestep over the dolly. When visual alignment was attained, the maneuver required the pilot to reduce power to allow the skids to settle on the dolly. During the sidestep maneuver, the pilot felt a skid touch down momentarily; however, he heard an engine surge that was similar to what he experienced during takeoff. Simultaneously, the helicopter abruptly entered a steep nose-low attitude and right bank and began rotating to the right 180° opposite of the direction of landing. The pilot lowered the collective and pulled the cyclic aft, and the helicopter impacted terrain about 50 ft east of the dolly’s original location. (During the accident sequence, the dolly had been lifted and rotated from its original orientation and position.) Neither flight paramedic reported hearing or feeling an anomaly with the engines at any point during the flight. Postaccident examination of the helicopter and its engines revealed no evidence of preimpact mechanical malfunction or failure. The flight and throttle controls operated normally during postaccident testing. Both engines were removed from the helicopter and operated in an engine test cell. The engines produced normal power, and an uncommanded engine surge could not be duplicated when the engines were operated at various power settings. Several witness marks were observed on the left edge, right top, and underside of the dolly, portions of which were painted yellow. Examination of the helicopter’s skids revealed evidence of yellow paint transfer on the inboard forward area of the left skid. Additional yellow paint transfer was observed on the right skid forward area and rearward top portions. The forward portion of the right skid had sheared off; yellow paint transfer and an indentation were observed within that portion. Available evidence suggests that the helicopter skids were misaligned during the attempted landing on the dolly, and the right skid likely fell into the dolly’s 3.5-ft-wide center gap, which resulted in a rapid loss of helicopter control. This likelihood is consistent with the pilot’s report that the helicopter abruptly entered a noselow attitude and right bank. The helicopter likely dragged the dolly and tractor during the bank to the right before breaking free of the dolly and impacting terrain. The dolly and its design is no longer sold by the manufacturer without a center plate that covers the gap. The pilot had been awake for more than 17 hours and on duty for about 16 hours, and he was completing his fifth flight of the day as part of the operator’s standard 24.3-hour shift. The length of the shift was based on the number of qualified pilots on staff and the need to maintain continuous operational coverage. The standard shift started at 0800 and ended at 0820 on the next day. The landing maneuver required precision from the pilot under normal circumstances; however, he was attempting the landing at night (a time when limited lighting would be available) and at the end of a long duty day. In addition, the accident occurred about midnight, a time when the pilot likely would have been experiencing fatigue based on his sleep schedule. Although the pilot reported that he was not fatigued, research has shown that performance decrements can occur after 17 hours of continuous wakefulness. Further, flying multiple flight segments can be more fatiguing than flying a single, longer segment. Therefore, the pilot was likely fatigued at the time of the accident due to his time since awakening, the time of day, and the multiple flight segments that he flew on the day of the accident. The operator’s 24.3 hour shift practices did account for total task time limitations, however, other than a pilot self-reporting that they were fatigued, there were no limitations preventing pilots from initiating flights after being awake for total durations, or times during the night, when fatigue is commonly experienced. Several factors contributed to the pilot’s misalignment of the helicopter skids: the pilot’s fatigue, the operator’s scheduling practices, and the dolly’s design with a center gap. Following the accident, the operator reduced the standard scheduled shifts from 24.3 hours to a maximum of 16 hours and 12 hours where staffing permits. In addition, the operator no longer utilizes landing dollies that possess a center gap.

Verbatim NTSB analysis and probable cause from the NTSB dataset