On April 11, 1952, at 12:10 PM, Pan American World Airways’ Flight 526A, a Douglas DC-4 named 'Clipper Endeavour', took off from San Juan bound for New York. The plane, manufactured in 1945 with 20,835 hours of flight, was designed for medium and long-range passenger and cargo operations. Ten minutes after takeoff, the crew made an emergency landing 11 miles northwest of San Juan, 4.5 miles from the coast, due to engine failure.
The rear section of the fuselage separated, and the plane sank in three minutes. The Civil Aeronautics Board determined that inadequate maintenance caused the failure of engine No. 3, which had malfunctioned the day before. The captain attempted to ascend without using full power after the problem arose in engine No. 4, leading to loss of aerodynamic speed and altitude.
The investigation found that maintenance personnel in San Juan had detected metal shavings in the engine’s oil filter, indicating internal damage, but did not follow proper procedures to repair it. The plane was not airworthy at the time of departure, and the crew failed to inform passengers of the impending emergency landing.