LAX00LA018

While the aircraft was shutting down, the flight engineer exited the aircraft, and gave the pilots the signal that the droop stops had engaged. He then climbed up on a stepladder next to the tail boom as the main rotor continued to coast down to a stop. A minute or so later, the two remaining crewmembers heard a 'thump.' The pilot-in-command (PIC) asked the copilot to go outside and find the source of the noise. When he walked toward the rear of the aircraft he found the flight engineer laying across the top of tail boom with a massive head injury. The main rotor of the Ch-54A is fully articulated. The rotor system employs a series of main rotor blade droop stops. As the rotor rpm slows, centripetal force is reduced and the droop stop springs pull the stops back into ground stop position. During spool down it can take 20 seconds or more for the first through sixth stop to move into the ground stop position. The visual strobe effect, caused by the turning rotor head, can make it appear that all the stops are in place when one or more stops still have not yet been fully repositioned. Winds were gusting up to 14 knots at the time of the shutdown. Gusting winds during shutdown can cause a slow turning rotor blade to suddenly flap down independently of the remaining blades.

On October 16, 1999, at 1410 hours Pacific daylight time, a Sikorsky CH-54A, N9125M, was shutting down at Elko, Nevada, when the flight engineer was struck by a main rotor blade. The aircraft was not damaged. The airline transport pilot or his copilot was not injured; however, the flight engineer received fatal injuries. The aircraft was being operated as a positioning flight by Siller Brothers, Inc., under 14 CFR Part 91 when the accident occurred. The flight originated in Tooele, Utah, at 1230, and was en route to Yuba City, California, with a planned fuel stop in Elko. Visual meteorological conditions prevailed at the time and a company flight plan was filed.

According to the Bureau of Land Management (BLM) State Aviation Manager for the state of Nevada, while the aircraft was being shutdown the flight engineer exited the aircraft. He then gave the pilots the signal that the droop stops had engaged, and then climbed up on a stepladder next to the tail boom. A minute or so later, the two remaining crewmembers heard a "thump." The pilot-in-command (PIC) asked the copilot to go outside and find the source of the noise. When he walked toward the rear of the aircraft, he found the flight engineer lying across the top of tail boom with a massive head injury. He returned to the cockpit and informed the PIC that the flight engineer was injured. The PIC called the tower, requesting immediate emergency medical aid. Emergency medical personnel who responded concluded that the flight engineer had been struck in the back of the head by a main rotor blade.

The main rotor head of the CH-54A is fully articulated with each blade being free to flap independently of the remaining blades. The rotor system employs a series of main rotor blade droop stops. As the rotor rpm slows, centripetal force is reduced and the droop stop springs pull the stops back into ground stop position. Manufacturer's representatives stated that during spool down it can take 20 seconds or more for the first through sixth stop to move into the ground stop position. The visual strobe effect, caused by the turning rotor head, can make it appear that all the stops are in place when one or more stops still have not yet been fully repositioned.

A postaccident inspection of the static main rotor system found all six droop stops fully in the ground stop position.

Winds were gusting up to 14 knots at the time of the shutdown.

The aircraft was on a repositioning flight to its home station in Yuba City, after being released from a Call-When-Needed exclusive use contract with the U.S. Forest Service earlier that day. The stop in Elko was for fuel.

No autopsy was performed. A toxicological study was conducted on samples from the flight engineer by the Washoe County Sheriff's Forensic Science Division. The results were negative for alcohol and all screened drug substances.