After initiating a turn to return to the airport, the aircraft eventually descended into, or attempted to ditch into, the ocean a mile offshore.

[citation needed] In October 1972, Clemente traveled to Managua, Nicaragua to coach the Puerto Rico national baseball team at the 1972 Amateur World Series.

Many countries sent aid to Nicaragua, inspiring Clemente to contribute to the relief effort with his own money and to personally supervise the delivery of goods.

[5] Clemente had previously sent three cargo planes and a ship to help the Nicaraguans, but heard reports that the military had seized the goods intended for the earthquake victims.

The airplane crashed immediately after takeoff from Isla Verde International Airport, flying into the ocean at the adjacent area known as Piñones.

[12] Unknown to Clemente or to the pilot, the four-engine Douglas DC-7 had suffered a non-fatal taxiway accident just 29 days before the fateful flight took place.

[11] The post-war era in which cargo carriers operated surplus piston-driven prop planes was at its end, as high maintenance costs restricted the ability to keep up with newer aircraft technology.

Struggling to keep American Air Express Leasing afloat against a tide of change in the airline industry, he began to cut corners.

[citation needed] After volunteers spent most of the afternoon loading the aircraft, pilot Jerry Hill boarded the plane as the sole member of the flight crew.

Owner Rivera sat in the co-pilot's seat, though he was only certified to fly the twin-engine Douglas DC-3, which had Pratt & Whitney Twin Wasp engines.

[citation needed] National Transportation Safety Board (NTSB) investigators later estimated that the aircraft's gross weight at takeoff was 148,943 pounds (67,559 kg), based on a fuel receipt and customs declaration.

With a one-way fuel load, the pilot would have to divert to somewhere such as San José, Costa Rica or Panama City to refuel for the return leg.

However, the 1972 investigation was limited, because at the time, the effect of temperature on fuel density and weight was not well understood by the airline industry.

Puerto Rico has a hot climate, with the December temperature usually above 80 °F (27 °C), so the fuel would have actually weighed on the low side.

Regardless, Hill would not have known the concepts of fuel density, zero-fuel weight or air buoyancy adjustment, though by experience he should have become familiar with the engine performance change.

[13] The court ruled that because the FAA had not inspected planes at that airport previously, it was not liable, despite its knowledge of the aircraft's condition and its failure to act.

[20] On the dark, moonless night of December 31, 1972, at 9:11 p.m. local time, after the previously aborted takeoff and additional mechanical work, the plane taxied around the airport's runway 7.

[21] A left turn was commenced towards the north, and at 9:23:15 p.m., the San Juan tower received the following transmission: "N500AE coming back around."

With reduced control and possibly loss of electrical power, the pilot was then faced with the challenge of ditching the aircraft into the sea while maintaining a relation to the horizon over water on a moonless night.

Delgado Cintrón, a mechanic who witnessed the takeoff from the ground at the airport, testified that the engines sounded even and normal.

After the aircraft was out of sight behind trees, the engines sounded fine and then, a few seconds later, Cintrón heard three backfires and a large explosion, which he thought was the impact with the ocean, followed by silence.

In post-war civilian use, those problems continued, and aircraft with this engine were less favored for commercial flights and often were converted to cargo planes.

Clemente would have had no reason to have known the history of the R-3350, but Captain Hill would have had a good understanding from over 12,000 flight hours piloting multi-row, piston-powered, radial-engine aircraft over his nearly 30-year career, including the DC-4, DC-6, DC-7, C-46 and the USAF Globemaster.

A key concern was a lean air/fuel condition causing detonation because of the high supercharger boost on such engines, which by itself and with cooling issues was dangerous.

On or after January 7, divers from a naval ship reported that the aircraft wreckage was scattered throughout the bottom of the ocean at a depth of 100 to 130 feet (30 to 40 m), in an area of approximately 4 acres (1.6 ha).

The cockpit area forward of the main junction box was destroyed and the instrument panel and mechanical controls were missing.

The NTSB concluded that after a failure of one engine the plane had inadequate power to maintain altitude during a turn (suggesting that the pilot could not dump fuel fast enough to achieve a weight-to-power ratio that allowed level flight).

The lack of a horizon possibly prevented the pilot from realizing the altitude loss from only 100 feet (30 m) over the ocean, which would have indicated a need to prepare for a water landing with reduced engine power on splashdown (the engines appear to have been at full power, and fuselage damage indicated an aircraft at higher speed).

The prop wash dispersed the fuel, and given the low elevation, formed a thermobaric weapon that was ignited by the burning engine.

3) (presumably because of a lack of adequate power for three engines) Probable Cause: Factors: Remarks: The crash is referred to in the 2011 film The Ides of March.