Columbia, MD, USA
N407HC
BELL 407
During a routine police patrol flight, while about 600 feet above the ground, the helicopter suddenly yawed to the left and the red "ENGINE OUT" warning light illuminated. The engine lost all power and the pilot performed an autorotation landing on a nearby football field. While avoiding obstacles, the helicopter landed hard, resulting in substantial damage to the airframe. A postaccident examination of the engine revealed no damage or obvious reason for the loss of power. The engine's electronic control unit (ECU) was removed and was shipped to the manufacturer's facility for evaluation and testing. The examination of the ECU revealed that the engine was operating normally until an unexpected activation of the full authority digital electronic control overspeed protection system fuel reduction solenoid, which is internal to the ECU, resulting in an uncommanded in-flight engine shutdown. A subsequent ECU functional review confirmed that a short circuit failure of a tantalum capacitor was the source of the ECU malfunction. After the accident, Bell Helicopter issued an Alert Service Bulletin and Rolls-Royce issued an accompanying Commercial Engine Bulletin that included the installation of an overspeed adapter to reduce the likelihood of a false overspeed activation.
On May 30, 2013, about 2307 eastern daylight time, a Bell 407, N407HC, was substantially damaged during an autorotation following a total loss of engine power at Columbia, Maryland. The commercial pilot and three crewmembers were not injured. The helicopter was registered to the State of Maryland and was operated by the Howard County Police Department as a public use flight. Night, visual meteorological conditions prevailed and no flight plan was filed. The local flight originated at Tipton Airport (FME), Fort Meade, Maryland, about 2210.According to the operator, the helicopter was on a routine patrol flight on a heading of 130 degrees and at a speed of 120 knots. About 600 feet above the ground, the helicopter suddenly yawed to the left and the red "ENGINE OUT" warning light illuminated. The pilot commenced an autorotation for landing on a nearby high school football field. To avoid trees and a goal post, the pilot extended the glide path by raising the collective control. The helicopter landed hard on the football field and came to rest in an upright position. The pilot secured the rotor blades and engine and the crew exited the helicopter without injuries. The wreckage was recovered and secured in a local hangar. The wreckage was examined on June 4 and 5, 2013, by Federal Aviation Administration inspectors and investigators from the airframe and engine manufacturers. The damage was determined to be substantial, including a severed tail boom and damaged main rotor blades. Damage to the landing gear also resulted. The on-scene examination of the engine revealed no damage or anomalies. The engine's electronic control unit (ECU) was removed and was shipped to the manufacturer's facility at West Hartford, Connecticut for further evaluation and testing. The examination of the ECU revealed that the engine was operating normally until an unexpected activation of the Full Authority Digital Electronic Control (FADEC) Overspeed Protection System (OSPS) fuel reduction solenoid, internal to the ECU, occurred, resulting in an uncommanded in-flight shutdown of the engine. The unit's non-volatile memory revealed evidence of an OSPS power supply malfunction shortly after the solenoid activated. An ECU functional review confirmed that a short circuit failure of component C49, a 22 uF tantalum capacitor, part number M39003/09-0254, was the source of the ECU malfunction. The ECU, Rolls-Royce part number 23080490, was affected by Rolls-Royce Commercial Engine Bulletin (CEB) 73-6052, dated December 3, 2012, which, if complied with, replaced the old ECU with an improved design (part number 23088856). The design change incorporated improvements to the OSPS. The compliance date per Rolls-Royce was March 31, 2015. Compliance was not mandatory through an FAA Airworthiness Directive (AD). For additional information regarding the engine and ECU examinations, refer to the excerpts of the Rolls-Royce Engine Investigations Report and the Triumph Group Investigation Report, located in the public docket for this accident investigation. On January 23, 2014, Bell Helicopter Alert Service Bulletin (ASB) 407-14-102 and Rolls-Royce Commercial Engine Bulletin (CEB) A-73-6059 were issued to (1) install an overspeed adapter to reduce the likelihood of a false overspeed activation as well as to introduce a recurring functional check of the overspeed protection circuits within the ECU; (2) provide instructions to apply Stabilant 22 to the connector and adapters required in the bulletin, and (3) introduce a recurring 50-hour requirement to functionally check the overspeed protection system by performing overspeed test shutdowns.
The short circuit failure of a tantalum capacitor, internal to the engine’s electronic control unit, resulting in an uncommanded shutdown of the engine in flight.
Source: NTSB Aviation Accident Database
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