A Mohawk Airlines, Inc., BAC 1-11., Nlll6J, operating as Flight 40, crashed approximately one mile east of the town of Blossburg, Pennsylvania, on June 23, 1967, at approximately 1447 EDT. The aircraft was destroyed by impact and fire. The two flight crewmembers, two stewardesses, and 30 passengers aboard the aircraft all received fatal injuries.
Following takeoff from Elmire at 1439 EDT, Flight 40 estiablished radio contact with the New York Air Route Traffic Control Center at 1442 EDT, the flight was cleared direct to Harrisburg, PA. Acknowledegment of this clearance was the last communication received from the aircraft. A subsequent clearance for Flight 40 to climb to 16,000 feet trasmitted by the New York Center at 1444 EDT was received by the flight but their attempted acknowledgement was not received by the Center. At about 447 EDT the New York Center controller observed the radar target of the aircraft appear to slov down, move laterally, and then disappear from his radar scope. The aircraft was observed in flight by a number of ground witnesses, who gave varying reports of smoke· coming from the tail end of the aircraft as it proceeded south from Mansfield, Pennsylvania, which is about 9 miles north of Blossburg. Two witnesses, located about two miles north of Blossburg, observed large sections of the tail separate from the aircraft in flight, after which fire and smoke emitted from the tail as the aircraft dove into the ground.
We determined that the probable cause of this accident was the loss of integrity of the empennage pitch control systems due to a destructive in-flight fire which originated in the airframe plenum chamber, and fueled by hydraulic fluid, progressed up into the vertical tail fin. The fire resulted from engine bleed air flowing back through a malfunctioning nonreturn valve and an open air delivery valve, through the auxiliary power unit in a reverse direction, and exiting into the plenum chamber at temperatures sufficiently high to cause the acoustics linings to ignite.
