Bell 407 N175PA

Summary

On 27 March 2003 at about 22:36 local time, a Bell 407 registered N175PA, operated by Fema, Usfs, TFS, was involved in an accident near Broadus, Texas, United States. 5 people were on board and 2 died, 3 were seriously injured. The aircraft was destroyed. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

27 March 2003 at 22:36

Classification

Accident

Location

Broadus, Texas, United States

Coordinates

31.0538, -97.5633

Aircraft

Bell 407

Registration

N175PA

Category

Helicopter

Engines

1

Operator

Fema, Usfs, TFS

Operating rule

Part 91: General Aviation

Purpose of flight

Public Use

Phase of flight

Not recorded

Route

Lufkin → Unknown

Aircraft damage

Destroyed

Weather

VMC

Light

Day

NTSB number

FTW03FA118

2 people died.

The partial loss of engine power due to erratic fuel flow metering to the engine resulting from the single point failure of the PLA potentiometer in the hydro-mechanical fuel control unit. A contributing factor was the lack of suitable terrain to execute a forced landing.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

While establishing a 125-foot out of ground effect hover during a search and recovery mission of Columbia Space Shuttle debris, the helicopter lost power without warning, descended rapidly into a forest with 80-foot tall trees, and impacted the ground. There were no reported radio communications or distress calls. During post accident component examinations, while performing the rigging procedure for the Hydro-Mechanical Unit (HMU) during an engine test cell run, anomalies were noted with the actual position of the throttle Position Lever Angle (PLA) and the readings obtained from the Electronic Control Unit (ECU). During the test cell run, the Full Authority Digital Electronic Control System (FADEC) controlled engine operated erratically in the Auto mode when rigged with its original Electronic Control Unit (ECU) and (HMU). The engine control was then changed from Auto to Manual mode, and the engine responded to throttle input as required; however, the ECU readings were erratic. After a slave ECU was installed, the engine operated with similar erratic readings. A slave HMU was installed, and the engine operated normally without erratic readings. The ECU's nonvolatile memory was downloaded, and revealed no faults on the accident flight. Extensive electrical and mechanical testing of the HMU revealed severe signal fallout on the PLA signal, which was found to be random in location, bi-directional, and present during both rotational and stationary operation of the PLA input of the HMU. The source of the fallout was traced to the HMU potentiometer. The PLA potentiometer examinations consisted of mechanical measurements, electrical testing, inspection of the conductive epoxy joints, and microscopic examination of the three lead wire connections to the potentiometer elements. The PLA potentiometer was found faulty due to insulation breakdown between the rotor and shaft, resulting in a single-point failure that induced erratic fuel metering to the engine. As a result of the findings from this investigation, the Safety Board issued four safety recommendations (A-03-18 through A-03-21), on May 27, 2003, to the FAA that addressed the PLA potentiometer deficiencies.

Quoted verbatim from the NTSB record.