Eurocopter Deutschland Gmbh MBB-BK 117 C-1 N271NE incident near Boston, Massachusetts

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 analysis

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.

Text from the NTSB. Open the NTSB docket for ERA11IA091 for the full record.