The Mystery of the Lost Clipper
The Civil Aeronautics Board and the FBI abandoned the case 47 years ago, but two amateur detectives are still searching for the cause of the crash of Pan Am 944.
- By Gregg Herken with Ken Fortenberry
- Air & Space magazine, September 2004
NASM (SI Neg. #00129509)
(Page 5 of 7)
Boeing’s 377s had a history of problems with propellers. The airline had initially adopted seven-foot-long Hamilton-Standard Hydromatic propellers with hollow-core steel blades. But centrifugal force tended to push the neoprene in the cores (the blades weren’t truly hollow) toward the tips of the blades, creating an imbalance and, in at least a few instances, causing pieces of blades to fly off. When the wreckage of a Pan Am Stratocruiser that disappeared over the Brazilian jungle in 1952 was finally found, investigators discovered that the airplane had literally shaken itself to pieces after losing first a propeller and then an engine.
Pan Am and Hamilton-Standard sought to solve the problem by nickel-plating the blades. But when another Stratocruiser—with newly plated blades—was forced to ditch off the Oregon coast in 1955 because of a runaway propeller, the airline realized that hollow-core props weren’t the 377’s only problem.
A runaway, or “over-speeding,” propeller was a nightmare for any flight crew. If the variable-pitch propeller could not be feathered—its blade pitch changed to point the leading edges in the direction of flight—centrifugal force wrenched the blades to the lowest pitch stop. The resulting drag was equivalent to that produced by a solid disk the diameter of the propeller in front of the wing. At that pitch, even if the prop simply windmilled, there was a danger that it would fly apart and pieces would penetrate the fuselage.
Equally terrifying was the fact that a runaway could occur virtually without warning, and left the pilots only seconds to react. Often the first indication of a problem was a sudden change in propeller noise, from the normal dull throbbing to a rapidly ascending, blood-curdling whine. One Pan Am pilot likened the sound to “the cry of a thousand banshees.”
A year earlier, an over-speeding propeller and engine failure had forced 944’s sister ship, PAA-943, Clipper Sovereign of the Skies, down on its way from Hawaii to San Francisco at nearly the same spot Romance of the Skies crashed. After circling until daylight, Sovereign ditched next to the Pontchartrain. All 31 passengers and crew were able to evacuate the airplane before it sank.
Curiously, the final CAB report on 944 paid little attention to earlier Stratocruiser over-speeds and claimed that Romance of the Skies never had an over-speeding incident. But a telephone call from one of our Pan Am veteran contacts, a gruff-voiced, 90-year-old Irishman and former B-377 pilot named Clancy Mead, contradicted that claim.
Mead recounted that he had been at the controls of Romance of the Skies when the airplane experienced a runaway propeller on a flight to Hawaii in June 1957, barely six months before its fatal plunge into the sea. Unable to feather the prop on the no. 3 engine, and losing altitude at a rate of 100 feet per minute—even with the remaining engines at rated power—Mead turned 944 around and headed back to San Francisco. He estimated that Romance cleared the mountains along the coast by only 500 feet. Luckily, he was able to set the airplane down safely at the airport.
What may be the last pieces of the puzzle came to Ken and me from two more veterans, Frank Garcia and Tony Vasko, who contacted us when word of our search got around on aviation-related Web sites. For decades, Garcia, the flight engineer on Sovereign when it ditched in 1956, has suspected that the cause of Sovereign’s runaway prop was a small part in the engine nose case needed to move oil to the prop dome (see illustration, opposite). A failure of the oil transfer tube or the bearing connecting it to the dome would make it impossible to feather the blades on that propeller. But conclusive proof of Garcia’s theory remains inaccessible on the ocean floor. Tony Vasko was the director of overhaul at Eastern Airlines until he retired in 1990. An expert on aircraft engines and propellers, Vasko is a frequent contributer to technical journals and aviation magazines. He found evidence that Pan Am, the manufacturers, and the Federal Aviation Administration had recognized, by the time of 944’s accident, that the transfer tube—which was brazed, rather than bolted in place—represented a potentially fatal flaw on the 377. Thus, an emergency “AD”—Airworthiness Directive—issued by the FAA in early 1957 warned: “As a result of propeller shaft oil transfer bearing failures, several cases of loss of propeller control occurred which make it impossible to feather the affected propellers.” The directive ordered that the brazed joint be inspected on every engine and either replaced or repaired “not later than May 31, 1957.”