NTSB Factual Report

On November 25, 2008, about 1245 mountain standard time, a Hughes 369HS helicopter, N9154F, sustained substantial damage during a forced landing following a loss of engine power in cruise flight near Fillmore, Utah. The commercial pilot, the sole occupant, was not injured. Skyhawk Helicopter Service, Inc., Spanish Fork, Utah, was the registered owner and operator of the helicopter. Visual meteorological conditions prevailed, and no flight plan was filed for the cross-country flight conducted under 14 Code of Federal Regulations Part 91. The helicopter departed Richfield, Utah, about 1230, and was en route to Spanish Fork.

According to the pilot, during cruise flight, the engine started to surge, then lost power, and within seconds regained power. The engine again started to surge and lost power. The pilot entered an autorotation. The helicopter was over mountainous/hilly terrain and there was no open place to land. The pilot selected a spot on a steep hill covered with 20- to 30-foot-tall oak trees. Upon touchdown, the helicopter began to roll, but was stopped by the vegetation. The tailboom incurred structural damage during the landing.

A post-accident examination of the helicopter was conducted under the supervision of a Federal Aviation Administration (FAA) inspector by representatives from the airframe and engine manufacturers. During this examination, it was noted that the fuel pump filter bowl's upper drain plug had been replaced with a non-standard fitting and cap. This cap was found with zero torque (loose) and partially backed off its seat. Less than two threads retained the cap on its fitting. According to the pump manufacturer's (Sundstrand Corporation) Overhaul and Maintenance Manual (IPL Appendix C, pgs 4-5), both the upper and lower drain ports on the fuel pump filter bowl should be sealed with identical AN814-4DL plugs and MS29512-04 O-rings. On the subject engine, the upper drain plug had been replaced with a threaded nipple fitting with a threaded cap.

The loose cap and its respective fitting had broken torque paint that was white in color and appeared weathered and dirty. Other fittings on the engine had torque paint that was blue or orange and was clean and bright in color. In standard configuration, the upper and lower drain plugs are lock-wired to each other, thus ensuring both fittings remain properly torqued. On the accident engine, the lower drain plug was lock-wired to the upper drain's threaded nipple fitting. However, the cap on this fitting was not lockwired. It was this cap that was found loose.

The fuel spray nozzle's fuel supply line was disconnected to measure the amount of fuel remaining. The line was found to be devoid of any residual fuel. (This line would typically have about 1 to 1.5 teaspoons of fuel following a normal engine shutdown.) No preimpact discrepancies, other than the loose cap, were noted to the airframe or engine. The engine was removed from the airframe and shipped to the facilities of the engine manufacturer in Indianapolis, Indiana, for a test run.

On January 15, 2009, FAA and Rolls-Royce representatives gathered at the Rolls-Royce facility in Indianapolis to test run the subject engine. Since the test cell uses a positive-pressure fuel system (unlike the helicopter's fuel system), the suspect loose cap was gently tightened with a wrench in order to prevent a fuel leak inside the test cell. The engine was then run in the test cell and met all test cell parameters for new engine production.

According to Rolls-Royce personnel, since the fuel pump filter bowl operates at a negative pressure during operation, a compromise at this point in the fuel system would not result in a fuel leak, but would rather result in an air induction into the fuel system. Induction of air into the fuel system interupts fuel to the fuel spray nozzle. The lack of fuel in the fuel supply line to the fuel spray nozzle is consistent with fuel starvation.

NTSB Probable Cause

The loss of engine power due to fuel starvation as a result of a loose fuel filter upper drain cap, which was not properly secured by maintenance personnel.