Incident Overview
On July 7, 2021, about 1450 Pacific daylight time, a Bell 212 helicopter, registration N911KW, was substantially damaged in an accident near Weed, California. The pilot was not injured. The flight was conducted under Title 14 Code of Federal Regulations Part 133 as an external load operation, supporting a US Forest Service contract for water drop operations.
Sequence of Events
The pilot reported approaching a lake to retrieve water with a 100-ft long line and bucket. At about 400 ft above ground level, an instrument scan showed no anomalies; the radar altimeter was set to 200 ft agl. While crossing the shoreline, the pilot noted the bucket was not yet visible and still behind the helicopter. Shortly after, a sudden vibration described as a once-per-minute rotation began. An inspector explained that this term indicates an imbalance in the main rotor head or blades. The pilot saw no annunciator lights or engine power loss indications but then realized the helicopter had descended.
The pilot aborted water retrieval, applied forward cyclic and raised the collective, but descent continued. Determining the descent could not be stopped, and wanting to avoid engine or transmission overspeed, the pilot performed a forced landing on water. After leveling and touching down, a last takeoff attempt failed. The pilot reduced throttles to idle, applied right cyclic as rotor speed slowed, and the helicopter rolled right, causing main rotor blades to strike water; the helicopter then sank. Controls responded normally, and no significant yaw occurred. The pilot did not jettison the long line and bucket, believing he could fly away.
Data and Examination Findings
Automatic dependent surveillance-broadcast data showed the bucket about 35 ft above water at the last data point, with a descent rate of about 768 ft per minute. Substantial damage affected the fuselage, main and tail rotor blades, and drive systems.
Postaccident examination of the bucket and engine powerpack found no preimpact mechanical malfunctions or failures. Pylon corner mounts and dampers were hydraulically tested and showed normal operational performance except for rod end bearings tolerances: right aft damper bearing play 0.006 inch and left aft 0.016 inch, exceeding the Bell 212 manual’s 0.004-inch limit. Bell Textron noted that excessive radial clearance reduces damper stroking. A separate event also traced a vibration to excessive pylon damper rod end bearing wear.
Performance Information
The 240-gallon bucket was configured for 90% capacity, adding about 1,966 pounds, increasing gross weight to about 10,116 pounds. According to the rotorcraft external load manual using Bell charts, at 35°C and other conditions, OGE takeoff power gross weight limitation was about 10,250 pounds. At a gross weight of about 10,116 pounds, the helicopter had OGE takeoff power limitation at pressure altitude of about 3,700 ft and maximum continuous power limitation of 9,300 pounds.
Pilot Training
The pilot completed six recurrent long-line training flights from May 3 to 29, 2021, and on May 31, 2021, passed a US Forest Service helicopter pilot evaluation checkride, clearing him for solo external-load water bucket operations.