Mcdonnell Douglas MD88 N924DL incident near Greer, South Carolina

Probable cause

The overheating and arcing of the DC Ground Service Relay and Block Diodes component for undetermined reasons.

NTSB analysis

While cruising at 30,000 feet, the captain and first officer initially smelled smoke in the cockpit, prompting them to initiate an unscheduled, precautionary landing at an airport along their route. While descending, the crew noticed that smoke was “pouring out” from underneath the first officer’s glare shield and instrument panel. No fire or flames were present. The captain declared an emergency and proceeded to depressurize the aircraft while descending through 10,000 feet in order to clear the smoke from the cockpit. Four tires on the left main gear burst on touchdown, and the aircraft came to rest on the runway. Ground personnel notified the crew that the right main brake system was on fire, and the crew and passengers made an emergency evacuation from the left side of the aircraft.

The DC Ground Service Tie Relay (R2-51) and Blocking Diode Assemblies (R7-50 and R7-51), located in the forward accessory compartment of the airplane, exhibited signs of overheating and smoke damage. A detailed examination of the components revealed internal damage consistent with arcing of the electrical contacts. However, due to the extent of the damage, the cause of the arcing could not be determined.

Text from the NTSB. Open the NTSB docket for DCA09IA018 for the full record.