Serious Incident Involving McDonnell Douglas MD-82 I-SMEB at Turin Airport

Event Overview and Immediate Response On 3 January 2010, at 14:50 UTC (15:50 local time), a serious incident occurred at Turin Airport involving a McDonnell Douglas MD-82 registered I-SMEB, operated by Meridiana SpA for public passenger transport. During boarding, cabin crew reported a strong acrid smell from the rear of the aircraft. With the Auxiliary Power Unit (APU) running, the commander informed ground technicians, who inspected the APU compartment and observed smoke and sparks from the APU starter. The technicians extinguished the initial fire using extinguishers on the apron, while the commander ordered the APU shut down and the cabin crew to evacuate the aircraft. The aircraft was subsequently returned to service in accordance with Minimum Equipment List (MEL) limitations. ## Aircraft and APU Details The aircraft was a twin-engine McDonnell Douglas MD-82 powered by two Pratt & Whitney JT8D217 engines. The APU, a GTCP 85-98 (P/N 381276-1, S/N P-996), had 26,260 hours and 25,404 cycles since new and was installed on 28 September 2009. The APU starter (P/N 3605812-17, S/N P34419C) had been installed on 19 October 2009 after a previous unit failed due to a structural fault. The APU starter relay R2-63 (P/N A-770WA-2, S/N CJ-62951) was factory-installed and had accumulated 48,000 cycles against a design life of 50,000 cycles. ## Investigation and Technical Findings Post-incident inspection revealed significant damage to the APU starter's positive power cables, likely caused by overheating, along with paint charring and melted cable clamps. The relay R2-63 was sent to the U.S. National Transportation Safety Board (NTSB) for non-destructive testing. NTSB continuity tests indicated the relay contacts were open, meaning the APU starter should not have been energized. X-ray examinations confirmed the open contact position but could not verify the integrity of the return spring. Subsequent disassembly at NTSB laboratories in Washington, D.C., in the presence of Boeing and Hartman representatives, was conducted to examine the contacts and spring under a microscope. The source notes that contact A1 appeared soft, but the provided text is truncated before stating the final conclusion or probable cause.