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Thu Dec 31, 2020, 08:49 AM

48 Years Ago Today; Roberto Clemente dies in mercy mission air crash


A DC-7CF similar to the accident aircraft

The 1972 Puerto Rico DC-7 crash was an aviation accident that occurred on December 31, 1972, in Carolina, Puerto Rico. It is most notable for killing Pittsburgh Pirates star Roberto Clemente. As a result of inadequate maintenance, the aircraft's No. 2 engine failed after takeoff. After initiating a turn to return to the airport, the aircraft eventually descended into, or attempted to ditch into, the ocean a mile offshore. All five people on board died.

Roberto Clemente was a baseball star for the Pittsburgh Pirates, with whom he had won two World Series championships. On September 30, 1972, in his final at-bat, he had become only the 11th player in Major League Baseball history to collect 3,000 hits.

In October 1972, Clemente traveled to Managua, Nicaragua to coach the Puerto Rico national baseball team in the Baseball World Cup. On December 23, a 6.3-magnitude earthquake struck Managua, devastating the city and killing approximately 5,000 people. 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. Clemente had also been convinced to become involved by local television show host, reporter and celebrity Luis Vigoreaux.

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. Suspecting profiteering by the military, he chartered a fourth plane so that he could visit Nicaragua and directly confront the military leader, believing that as a celebrity he could not be harmed.

The accident caused the deaths of all five people on board, including Clemente. The airplane crashed immediately after takeoff from Isla Verde International Airport, flying into the ocean at the adjacent area known as Piñones.

Cargo carrier
Clemente and a relief committee had leased the aircraft for $4,000 from a local airline, American Air Express Leasing Company, which was owned by a 27-year-old Puerto Rican named Arthur J. Rivera.

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. This accident damaged the No. 2 and No. 3 propeller blades and the No. 3 engine cooler scoop. Advised to replace one of the engines, Rivera pressed his mechanics to do what they could to inspect the engine and keep it in service, but after inspecting the engines, the mechanics could not find a reason to justify replacing one. The standard procedure after the sudden stop of piston engine is to disassemble the engine to magnaflux its parts for cracks, but this was not done. An FAA maintenance inspector inspected the propeller shaft limits after the sudden stoppage repairs and found them within tolerances, though a later report said that he merely witnessed the inspection.

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. Rivera had just regained his FAA clearance to operate a cargo plane, claiming that it was his only livelihood. Struggling to keep American Air Express Leasing afloat against a tide of change in the airline industry, he began to cut corners.

Bad omens
Clemente's father, his wife Vera and son Roberto, Jr. warned him that they had bad feelings and premonitions about the flight, and just a few days before the flight, Clemente had a dream about overlooking his own funeral. However, Clemente insisted on conducting the planned relief mission and taking off on December 31 as planned, despite bad weather having hit the area near Isla Verde International Airport.

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. Rivera may not have understood the added complexity of the DC-7’s Wright R-3350 Duplex-Cyclone engine, which was nearly twice the size and power. Fransisco Matias, a fill-in mechanic employed by another airline who was moonlighting with several other mechanics for cargo carriers at the same airport, sat in the flight engineer's seat because Rivera and Hill had made several unsuccessful attempts to secure a flight engineer.

Hill, a well-qualified, seasoned pilot, was in command. He had been found by chance several days earlier while watching the plane being loaded. After another pilot had failed to show from a waitlist of itinerant pilots, Hill flew back from Miami on short notice. He sat in the plane for the first time the previous morning of the flight, and slept all day in a crew bunk to rest for the flight.

This was the aircraft's first flight since Rivera had purchased it several months earlier, and it was the first time that the pilot had flown with either Rivera or Francisco. Clemente boarded with associate Angel Lozano around the same time as the aircraft's crew.


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. By then the weather had cleared and visibility was at 10 miles, with only a few clouds visible.

After engine run-up by the crew, the flight was cleared for takeoff at 9:20:30 p.m. for the four-hour flight to Nicaragua. The aircraft took an exceptionally long takeoff roll and gained very little altitude. 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." To land safely, the aircraft would have first needed to dump 32,000 pounds of fuel; as a typical dump rate is one to two tons of fuel per minute, this process would have taken between 16 and 32 minutes.

At or soon after the time of the last radio transmission, the plane experienced a catastrophic failure of engine No. 2. It is possible that engine No. 3 was also lost. Engines 2 and 3 are closest to the fuselage and contain the hydraulic pumps. If both were lost, the pilot would be forced to rely on a controls reversion system. 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. In this scenario, the aircraft was essentially unflyable.

With an engine lost, the airplane slowly descended and about 10 to 30 seconds later crashed into the Atlantic Ocean at a point approximately 1​1⁄2 miles offshore, and 2​1⁄2 miles on the 040-degree radial from the western end of Runway 25. In that time, 500 to 2,000 pounds of fuel would have dumped. In the last seconds of flight, ground effect would have kept the plane aloft, skimming the wave tops.

Delgado Cintrón, a mechanic who witnessed the takeoff from the ground at the airport, testified that the engines sounded even and normal. However, the plane was too low at 25 feet off the ground. Other witnesses estimated that the plane gained altitude to 100 feet. 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.

Issues with engine design
That a DC-7 had lost an engine on takeoff was not unexpected. During World War II, twice as many aircraft were lost because of problems with the same type of engine (in aircraft such as the Boeing B-29 Superfortress) as were lost to enemy fire.

The Wright R-3350 engine that powered the DC-7 had started as a problematic multi-row radial design that was rushed into wartime production. 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.

An issue related to the cooling of additional rows of radial cylinders in multi-row radial engines was understood and well known. 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. Problems with cooling had plagued the engine since its use in the hot Pacific climate during World War II, prompting the military to add an air scoop to the top of the engine cowling that directed air to cool the back cylinders. Those problems only added to the engine's sensitivity to detonation, particularly on takeoff.


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). After a few miles, the plane flew into the ocean on a moonless night. The lack of a horizon possibly prevented the pilot from realizing the altitude loss from only 100 feet 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).

An unexplored scenario is that, following an engine loss, the pilot began fuel dumping to lighten the aircraft. The prop wash dispersed the fuel, and given the low elevation, formed a thermobaric weapon that was ignited by the burning engine. The resulting air burst destroyed the aircraft. The DC-7 contained fuel-dumping facilities. A hazard of fuel dumping is ignition of the fuel, and precautions are taken to eliminate all sources of ignition, and also to prevent turbulence that mixes the fuel with air. Aircraft do not typically explode on impact, and in this case the plane would have been more or less in level controlled flight into the water. An air burst explains the explosion heard after an engine fire was seen, as well as the heavy destruction of the fuselage.

A scenario considered by investigators but later dismissed involved a load shift on turning, which careened the plane into a wing strike with water, cartwheeling the plane along the surface. Two engines were found several hundred feet directly ahead of the wing, indicating a level entry into the water.

The cause of the crash could not be determined precisely because of the difficulties encountered while attempting to recover the wreckage. Probable causes were attributed to lean detonation, poor maintenance, excessive wear in engine components, engine damage from a previous taxiing accident that was not repaired, an uncertified co-pilot, an uncertified flight engineer, a 4,000-pound fuel overload and inadequate crew preparation in correcting these issues.


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Reply 48 Years Ago Today; Roberto Clemente dies in mercy mission air crash (Original post)
Dennis Donovan Dec 31 OP
LeftInTX Dec 31 #1
ProfessorGAC Dec 31 #2
Demovictory9 Dec 31 #3
DeminPennswoods Dec 31 #4
Bradshaw3 Dec 31 #5
Sinistrous Dec 31 #6

Response to Dennis Donovan (Original post)

Thu Dec 31, 2020, 08:53 AM

1. You and Mahatma Jeeves always have these interesting articles

I didn't read much news back in the day. I certainly didn't watch it! Thank you for enlightening us!

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Response to Dennis Donovan (Original post)

Thu Dec 31, 2020, 09:09 AM

2. My Dad's Favorite Non-Cub

We went to Wrigley to see Cubs play the Pirates at least a half-dozen times when i was a kid.
My dad just had to see Roberto in petson!

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Response to Dennis Donovan (Original post)

Thu Dec 31, 2020, 09:41 AM

3. thx for the history lesson

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Response to Dennis Donovan (Original post)

Thu Dec 31, 2020, 09:58 AM

4. One of the worst days of my life

as a western Pennsylvanian. Just shocking. I can still hear Curt Gowdy annoucing it on whatever bowl game he was calling.

David Mariness' bio of Clemente is terrific and spells out all the failures that lead to the plane crash.

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Response to Dennis Donovan (Original post)

Thu Dec 31, 2020, 10:16 AM

5. A great player and even better human being

Just one of the all-time greats in sports, on the field and off.

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Response to Dennis Donovan (Original post)

Thu Dec 31, 2020, 11:41 AM

6. My wife and I had just moved to Pittsburgh and were moving into our new apartment

and looking forward to getting seats in the right field stands in Three Rivers stadium that summer when we heard the news of Roberto's tragic death. We didn't get much more done that day.

I still feel like somebody punches me in the stomach whenever I think about the loss.

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