EUROCOPTER DEUTSCHLAND GMBH MBB-BK 117 C-1 near Boston, MA — 2010-12-04

Probable cause

Improper installation of wiring associated with a medical cabinet interior, which resulted in chafing and a subsequent in-flight fire. Contributing to the incident was inadequate maintenance procedures for continued airworthiness.

NTSB narrative

During the air ambulance flight, the helicopter was on final approach to land when smoke and flames were observed emanating from the suction control mounted on the left side of the cabin. The fire was subsequently extinguished, and the pilot landed the helicopter without further incident. Postincident examination revealed fire damage on the face of an overhead medical cabinet that was part of a medical interior installed about 7.5 years prior to the incident per a supplemental type certificate. A sheathed wiring bundle for a 120-volt alternating current power outlet mounted in the aft end of the cabinet displayed chafing damage and arcing consistent with rubbing on the metal housing for the vacuum control switch. The wiring was installed without adequate clearance or support to prevent it from chafing on the switch housing. The helicopter was maintained under an approved inspection program; however, review of the instructions for continued airworthiness associated with the medical cabinet installation did not reveal any required inspections of the associated wiring harnesses for general condition or chafing.

Analysis

Primary failure mode

Mechanical failure

First missed decision gate

Inspection of wiring harnesses for chafing could have prevented the fire.

NTSB coding

• Fire/smoke (non-impact) · Approach
• Maintenance

Evidence available

• Photos
• 13 docket documents

Docket documents13

• Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 and Crew Statementsform
• FAA FSDO Inspector Statementinterview
• ERA 300 Hour/12 Month Inspection Checklistother
• FAA AC 43.13-1B – Chapter 11 Aircraft Electrical Systems (excerpts)other
• FAA AC 65-15A – Airframe and Powerplant Mechanics Handbook (excerpts)other
• Helicopter Accident/Incident Checklist Supplementother
• Supplemental Type Certificate and FAA Maintenance Records (excerpts)other
• Photograph # 1 – View of fire damage on installed medical cabinet (Courtesy of the Operator)photos
• Photograph # 2 – View of front on side of medical cabinet assembly after removal. (Courtesy of the FAA)photos
• Photograph # 3 – View of wires installed within the medical cabinet (Courtesy of the FAA)photos
• Photograph # 4 – View of chafed wire (Courtesy of the FAA)photos
• Photograph # 5 – View of aircraft sidewall after medical cabinet was removed. (Courtesy of the FAA)photos
• Company Service Difficulty Report (SDR)report

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