On December 4, 2010, about 0900 eastern standard time, a Eurocopter Deutschland GMBH, MBB-BK117-C1, N271NE, sustained minor damage when it experienced an in-flight electrical fire, while on approach to the Brigham & Women's Hospital Heliport (MA39), Boston, Massachusetts. The helicopter was owned by New England Life Flight, doing business as Boston MedFlight, and operated by ERA Med LLC, as an air ambulance flight conducted under the provisions of 14 Code of Federal Regulations Part 135. The airline transport pilot, flight nurse, flight paramedic, and patient were not injured. Visual meteorological conditions prevailed and a company flight plan had been filed for the flight that departed from Oak Bluffs, Massachusetts. According to the flight nurse, the helicopter was on final approach to land, when she noticed "a smell" followed by smoke and flames emanating 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 the helicopter without further incident. He subsequently noted obvious fire damage on the left cabin wall near the suction device control switch and the liquid oxygen gauge. Post incident inspection by a Federal Aviation Administration (FAA) inspector revealed fire damage on the face of the overhead medical cabinet around the vacuum control switch. The cabinet was part of a medical interior that was installed per a supplemental type certificate (STC) during May 2003, and housed a vacuum regulator, vacuum pump switch, liquid oxygen quantity indicator and 120-volt alternating current (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 arching consistent with rubbing on the metal housing for the vacuum control switch. In addition, an approximate 2-inch portion of composite material, which surrounded the switch, was consumed by fire. Additional examination was performed by an FAA inspector, who reported that the wiring was installed without adequate clearance or support to prevent it from chafing on the switch housing. The electrical power to the outlets was supplied by a KGS Electronics SPS-1607A medical inverter system, which was installed per an STC during June 2003. 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 and had been operated for approximately 254 hours since its most recent 300 hour/12 month inspection, which was performed on August 12, 2010. Item 24 on the inspection checklist included: "Visually inspect inverter and mounting for damage, security and electrical connections" and "Test medical inverter for proper operation," with a reference to the KGS-SPS-1607A Removal/Installation Manual. Review of the KGS-SPS-1607A Removal/Installation Manual revealed instructions for removal and installation. Under instructions for maintenance, 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." An FAA check of service difficulty reports for the BK117 did not reveal any previous instances of fires associated with the medical cabinet installation. FAA Advisory Circular AC65-15A, Airframe and Powerplant Mechanics Airframe Handbook, Chapter 11, Aircraft Electrical Systems, Protection Against Chafing, stated in part: "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…."