Pan Am Flight 214

Investigation

The CAB assigned more than a dozen investigators within an hour of the crash. The CAB team was assisted by investigators from the Boeing Company, Pan Am, the Air Line Pilots Association, Pratt & Whitney, the Federal Bureau of Investigation, and the Federal Aviation Agency (FAA). The costs of the CAB's investigations rarely exceeded $10,000, but the agency spent about $125,000 investigating this crash, not including the money spent by Boeing, the FAA, Pratt & Whitney, and other aircraft-part suppliers during further investigations.

Initial theories included that severe turbulence had caused a fuel tank or fuel line to rupture, causing a fire from leaking fuel. U.S. House Representative Samuel S. Stratton of Schenectady, New York, contacted the FAA urging them to restrict jet operations in turbulent weather, but the FAA said it saw no need for such restrictions and Boeing concurred. Investigators also considered sabotage or lightning, but by nightfall after the first day they had not found evidence of either. Airline spokesmen discounted speculation that metal fatigue as a result of the aircraft's 1959 incident could have been a factor, saying the aircraft had been overhauled four times since the accident without any problems being found.

Investigators rapidly located the flight data recorder. Built to survive the impact of a crash, it had nevertheless been badly damaged. CAB chairman Alan S. Boyd said, "It was so compacted there is no way to tell at this time whether we can derive any useful information from it." Eventually, investigators extracted data from 95 percent of the tape in the recorder.

The recovery of the wreckage took 12 days, and 16 truckloads of debris were taken to Bolling Air Force Base in Washington, D.C., for investigators to examine and reassemble. One investigator said it was nearly certain that an in-flight explosion of some kind had occurred.

Within days, investigators said the crash had apparently been caused by an explosion that had blown off one of the wing tips. The left wing tip had been found a few miles from the crash site with burn marks and bulging from what looked like an internal explosion. Remnants of 9 ft of the wing tip had been found at several points along the flight path short of the impact crater. Investigators said rough turbulence was unlikely to have caused the crash because the crews of other aircraft that had been circling in the area reported that the air was relatively smooth at the time. They also said the plane would have had to dive a considerable distance before it would break up and explode, but the aircraft had apparently caught fire close to its cruising altitude of 5,000 ft.

Before this flight, lightning had not been known to cause a plane to crash, despite many instances of planes being struck. In normal operations, an airplane is typically struck by lightning once or twice a year without causing any problems. Experts and airline industry representatives disputed the early theory that lightning could have caused the aircraft to explode, calling it improbable. The only similar event involving a mid-air fuel explosion caused by the weather occurred on June 26, 1959, when TWA Flight 891, a Lockheed L-1649 Starliner, crashed near Milan, Italy, as a result of static electricity igniting fuel vapor emanating from the fuel vents. Investigators examining Flight 214 found multiple lightning strike marks on the left wing tip and a large area of damage that extended along the rear edge of the wing, leading them to conclude that lightning was indeed the cause. The CAB launched an urgent research program in an attempt to identify conditions in which fuel vapor in the wing tanks could have been ignited by lightning. Within a week of the crash, the FAA issued an order requiring the installation of static electricity dischargers on the approximately 100 Boeing jet airliners that had not already been so equipped. Aviation industry representatives criticized the order, stating that there was no evidence that the dischargers would have had any beneficial effect since they were not designed to handle the effects of lightning. They said that the order would only serve to create a false impression that the risk of lightning strikes had been resolved with little actual benefit.

The CAB conducted a public hearing in Philadelphia in February 1964 as part of its investigation. Experts had still not proven that lightning had caused the accident, but they were looking into ways that lightning could have triggered the explosion. The FAA also said that it would conduct research to determine the relative safety of the two types of jet fuel used in the United States, both of which were present in the fuel tanks of Flight 214. Criticism of the JP-4 or Jet B jet fuel that was in some of the tanks was related to the fact that its vapor can be easily ignited at the low temperatures encountered in flight. Advocates of Jet B countered that the fuel was as safe, or safer than, Jet A, the other fuel used in turbine engines which was also present in Flight 214's fuel tanks.

In a test flight designed to simulate moderate to rough turbulence in flight, Pan Am tested a Boeing 707 to find out whether fuel could leak from the tank-venting system during such conditions. The test did not reveal any fuel discharge, but it did show that some fuel had entered the vent system, collected in the surge tanks, and returned to the tanks. Pan Am said that it would test a new system to inject inert gas into the air spaces in the fuel tanks in aircraft, hoping to reduce the risk of ignition of the hazardous fuel-air mixtures in those spaces.

On March 3, 1965, the CAB released its final accident report. The investigators concluded that a lightning strike had ignited the fuel-air mixture in the number-one reserve fuel tank, which had caused an explosive disintegration of the outer part of the left wing, leading to a loss of control. Despite one of the most intensive research efforts in its history, the agency could not identify the exact mechanics of the fuel ignition, concluding that lightning had ignited fuel vapor through an as-yet-unknown pathway. The board said, "It is felt that the current state of the art does not permit an extension of test results to unqualified conclusions of all aspects of natural lightning effects. The need for additional research is recognized and additional programming is planned."