Convair 340-71 N8277Q

Before departing on the flight that preceded the accident flight, the flight crew performed an engine-run, including a magneto check, during which they noted backfiring from the left engine. The captain first attributed the issue to water contamination of the fuel but then attributed it to fouled spark plugs. An additional engine run resulted in no further backfiring, and the captain decided to depart on the cargo flight; no maintenance was requested or performed on the left engine before departure. When the airplane was near the destination airport, the left engine backfired once again. The flight continued to the destination airport where the airplane landed uneventfully and the cargo was off loaded; again, no maintenance was performed or requested for the left engine. For the accident flight, the first officer was the pilot flying and the captain was the pilot monitoring. During the takeoff, the local controller noted black smoke trailing the left engine and advised the flight crew; however, the captain attributed the smoke to normal operation for the airplane type and decided to continue the flight. Meanwhile, air traffic control communications for the flight were transferred to San Juan Combined En Route Approach Control (San Juan CERAP). The local controller who noted the black smoke continued to watch the airplane’s departure. When the airplane was about 1 mile west of the runway, the controller observed bright orange then red flames from behind the left engine and immediately informed the San Juan CERAP controller, who in turn immediately notified the flight crew. The captain assumed control of the airplane and directed the first officer to go to the cabin to visually inspect the left engine. The first officer returned to the cockpit and informed the captain that he observed fire, and they immediately executed the fire checklist and shut down the left engine. However, the fire continued because it was located in an area where fire suppression bottles could not reach. The pilots returned to the airport; fire rescue vehicles were pre-positioned along various portions of the runway. The airplane touched down on the runway centerline. Because the fire had damaged the left brake line, braking was asymmetrical, and the airplane departed the right side of the runway and came to rest adjacent to the airport perimeter fence. Postaccident examination of the left engine revealed a discrepancy of two cylinders in which the pistons did not move during rotation of the engine. This discrepancy could result in unburned fuel or oil entering the exhaust system and igniting in the exhaust or augmentor tubes. Examination of the airframe found that the augmentor tubes had been removed after the accident. Although they were not available for examination, the location of the fire suggests that there was a leak in the vicinity of the augmentor tubes and muffler junction, causing the fire to burn through the nacelle rather than exit out the aft end of the muffler. The left engine was installed on the accident airplane in September 2009. At the time of the accident, it had accumulated about 1,004 hours since the last known major overhaul in 1975. Copies of the maintenance records for the left engine were requested but not provided; therefore, how often or whether the engine was maintained during the 34 years between the known last overhaul and when it was installed on the accident airplane could not be determined. A service check of the engines, including compression check of the cylinders, was last performed 5 days before the accident. The captain twice decided to depart without reporting or requesting maintenance for the backfiring of the left engine. If maintenance had been accomplished, it is likely that the lack of movement of the two cylinder pistons would have been detected and repaired, thereby preventing the engine fire. Because of the airplane’s distance from the airport at the time the flight crew received the local controller’s report about black smoke, it is unknown whether fire damage to the brake line would have been mitigated if the captain had decided to return to the airport immediately. However, the captain demonstrated poor judgment in deciding to continue the flight rather than immediately follow up on the report.

Quoted verbatim from the NTSB record.