Linea Aeropostal Venezolana Flight 253 (June 1956)

Investigation and aftermath

The debris and remains recovered the night of the crash provided no clues as to the origin of the sudden fire; initial speculation was that fuel vapor may have come into contact with hot exhaust gases from one or more engines. Locating the main wreckage proved difficult due to the relatively wide dispersion of the debris- Hancox had observed the airliner shed flaming parts during its descent, and the final impact and explosion were described as violent, strewing debris over a considerable area. U.S. Navy salvage teams dragged grappling lines across the site for several days without success. Finally, a June 30 sonar search provided tentative identification of the main wreckage, which the Navy estimated would require "days or weeks" to raise. Minimal progress was made over the ensuing week, largely due to bad weather; On July 6, the Venezuelan government requested that recovery operations be halted.

The investigation spent considerable time analyzing the events of the fuel dump in order to identify the likeliest source of the ignition. Hancox reported that as soon as Captain Plata commenced dumping fuel, Hancox observed sparks and flame in the vicinity of the #3 engine, the inboard engine on the starboard (right) wing, opposite the engine with the propeller problem. The investigative board concluded that the vibration induced by the runaway #2 propeller had caused internal structural damage to the starboard wing behind the #3 engine, between the fuel tank and fuel dump chute, as this area would have been the symmetrical point of the vibration. The board considered this the most probable cause, but stated that it was unable to determine this with certainty.

Ruth Noel, widow of passenger Marshal L. Noel, subsequently sought damages from both the airline and United Aircraft (owners of Hamilton Standard, the manufacturer of the failed propeller). In the course of the litigation, evidence was introduced that within moments of the fuel dump commencing, the faulty #2 propeller broke free of its mountings and slashed into the fuselage. The double seat in the area of the impact was apparently ejected from the aircraft at this time, as it was found some distance from the spot where YV-C-AMS crashed; it had been cut in half from top to bottom by a heavy object. The bodies of its two occupants were among the few recovered from the scene; both had suffered leg amputations. Expert testimony provided two possible scenarios for ignition of the jettisoning fuel:

When the #2 propeller separated, the airstream blew sparks from its broken hub or shaft backwards into the plume of fuel;

When the #2 propeller slashed downward through the fuselage, it sliced through the cabin floor into the #5 fuel tank (center tank), immediately igniting the fuel within. The flames blew out of the fuselage into the fuel plume.

In May 1959, propeller pitch-lock mechanisms, designed to arrest the pitch of the blades and prevent them from opening further when an overspeed is imminent, became mandatory on U.S. piston-engined transport aircraft.