Incident Details
On December 4, 2010, approximately 0900 eastern standard time, a Eurocopter Deutschland GMBH MBB-BK117-C1 (registration N271NE) sustained minor damage from an in-flight electrical fire while on approach to Brigham & Women's Hospital Heliport (MA39) in Boston, Massachusetts. The helicopter was operated by ERA Med LLC under Part 135 as an air ambulance flight for Boston MedFlight. The crew—an airline transport pilot, flight nurse, flight paramedic—and a patient were not injured. Visual meteorological conditions prevailed, and a company flight plan had been filed for the flight departing from Oak Bluffs, Massachusetts.
According to the flight nurse, the helicopter was on final approach when she noticed a smell, followed by smoke and flames from the suction control mounted on the left side of the cabin. She notified the pilot and discharged a fire extinguisher, which extinguished the fire. The pilot landed without further incident. Post-landing inspection revealed fire damage on the left cabin wall near the suction device control switch and the liquid oxygen gauge.
Post-Incident Examination
A Federal Aviation Administration (FAA) inspector examined the helicopter and found fire damage on the face of the overhead medical cabinet around the vacuum control switch. The cabinet, part of a medical interior installed under a supplemental type certificate (STC) in May 2003, housed a vacuum regulator, vacuum pump switch, liquid oxygen quantity indicator, and 120-volt AC electrical outlets. A sheathed wiring bundle for the 120-volt AC 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. An approximate 2-inch portion of composite material surrounding the switch was consumed by fire.
Further examination by an FAA inspector indicated that the wiring was installed without adequate clearance or support to prevent chafing on the switch housing. The electrical power to the outlets was supplied by a KGS Electronics SPS-1607A medical inverter system, installed under an STC in June 2003.
Maintenance and Inspection
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. The helicopter was maintained under an FAA-approved inspection program. Its most recent 300-hour/12-month inspection was performed on August 12, 2010, approximately 254 flight hours before the incident. Item 24 of the inspection checklist included visual inspection of the inverter and mounting for damage, security, and electrical connections, and testing the medical inverter for proper operation, referencing the KGS-SPS-1607A Removal/Installation Manual. However, the manual stated, "No regular periodic maintenance is required for this product. Service is required only when a malfunction is detected. Maintenance consists of removal and replacement."
Prior Incidents
An FAA check of service difficulty reports for the BK117 did not reveal any previous instances of fires associated with the medical cabinet installation.
Advisory Guidance
FAA Advisory Circular AC65-15A, Airframe and Powerplant Mechanics Airframe Handbook, Chapter 11, Aircraft Electrical Systems, Protection Against Chafing, states: "Wires and wire groups should be protected against chafing or abrasion in those locations where contact with sharp surfaces or other wires would damage the insulation. Damage to the insulation can cause short circuits, malfunction, or inadvertent operation of equipment."