RFT 521: Pan Am Flight 214
From Wikipedia:
Pan Am Flight 214 was a scheduled flight of Pan American World Airways from San Juan, Puerto Rico, to Baltimore, Maryland, and Philadelphia, Pennsylvania. On December 8, 1963, the Boeing 707 serving the flight crashed near Elkton, Maryland, while flying from Baltimore to Philadelphia, after being hit by lightning. All 81 occupants of the plane were killed. The crash was Pan Am's first fatal accident with the 707, which it had introduced to its fleet five years earlier.
An investigation by the Civil Aeronautics Board concluded that the cause of the crash was a lightning strike that had ignited fuel vapors in one of the aircraft's fuel tanks, causing an explosion that destroyed one of the wings. The exact manner of ignition was never determined, but the investigation yielded information about how lightning can damage aircraft, leading to new safety regulations. The crash also spawned research into the safety of various types of aviation fuel and into methods of reducing dangerous fuel-tank vapors.
Pan American Flight 214 was a regularly scheduled flight from Isla Verde International Airport in San Juan, Puerto Rico, to Philadelphia International Airport with a scheduled stopover at Baltimore's Friendship Airport. It operated three times a week as the counterpart to Flight 213, which flew from Philadelphia to San Juan via Baltimore earlier the same day. Flight 214 left San Juan at 4:10 p.m. Eastern time with 140 passengers and eight crew members, and arrived in Baltimore at 7:10 p.m. The crew did not report any maintenance issues or problems during the flight. After 67 passengers disembarked in Baltimore, the aircraft departed at 8:24 p.m. with its remaining 73 passengers for the final leg to Philadelphia International Airport.
As the flight approached Philadelphia, the pilots established contact with air traffic control near Philadelphia at 8:42 p.m. The controller informed the pilots that the airport was experiencing a line of thunderstorms in the vicinity, accompanied by strong winds and turbulence. The controller asked whether the pilots wanted to proceed directly to the airport or to enter a holding pattern to wait for the storm to pass. The crew elected to remain at 5,000 feet in a holding pattern with five other aircraft. The controller told the pilots that the delay would last approximately 30 minutes. There was heavy rain in the holding area, with frequent lightning and gusts of wind up to 50 miles per hour (80 km/h).
At 8:58 p.m., the aircraft exploded. The pilots were able to transmit a final message: "MAYDAY MAYDAY MAYDAY. Clipper 214 out of control. Here we go." Seconds later, the first officer of National Airlines Flight 16, holding 1,000 feet higher in the same holding pattern, radioed, "Clipper 214 is going down in flames." The aircraft crashed at 8:59 p.m. in a corn field east of Elkton, Maryland, near the Delaware Turnpike, setting the rain-soaked field on fire. The aircraft was completely destroyed, and all of the occupants were killed.
The aircraft was the first Pan American jet to crash in the five years since the company had introduced their jet fleet.
A Maryland state trooper who had been patrolling on Route 213 radioed an alert as he drove toward the crash site, east of Elkton near the state line. The trooper was first to arrive at the crash site and later stated that "It wasn’t a large fire. It was several smaller fires. A fuselage with about 8 or 10 window frames was about the only large recognizable piece I could see when I pulled up. It was just a debris field. It didn’t resemble an airplane. The engines were buried in the ground 10- to 15-feet from the force of the impact."
It was soon obvious to firefighters and police officers that little could be done other than to extinguish the fires and to begin collecting bodies. The wreckage was engulfed in intense fires that burned for more than four hours. First responders and police from across the county, along with men from the United States Naval Training Center Bainbridge, assisted with the recovery. They patrolled the area with railroad flares and set up searchlights to define the accident scene and to ensure that the debris and human remains were undisturbed by curious spectators.
Remains of the victims were brought to the National Guard Armory in Philadelphia, where a temporary morgue was created. Relatives came to the armory, but officials ruled out the possibility of visually identifying the victims. It took the state medical examiner nine days to identify all of the victims, using fingerprints, dental records and nearby personal effects. In some cases, the team reconstructed the victims' faces to the extent possible using mannequins.
The main impact crater contained most of the aircraft's fuselage, the left inner wing, the left main gear and the nose gear. Portions of the plane's right wing and fuselage, right main landing gear, horizontal and vertical tail surfaces and two of the engines were found within 360 feet (110 m) of the crater. A trail of debris from the plane extended as far as four miles (6 km) from the point of impact. The complete left-wing tip was found nearly two miles (3 km) from the crash site. Parts of the wreckage ripped a 40-foot-wide (12 m) hole in a country road, shattered windows in a nearby home and spread burning jet fuel across a wide area.
The Civil Aeronautics Board was notified of the accident and was dispatched from Washington, D.C. to conduct an investigation. Witnesses of the crash described hearing the explosion and seeing the plane in flames as it descended. Of the 140 witnesses interviewed, 99 reported seeing an aircraft or a flaming object in the sky. Seven witnesses stated that they had seen lightning strike the aircraft. Seventy-two witnesses said that the ball of fire occurred at the same time as, or immediately after, the lightning strike. Twenty-three witnesses reported that the aircraft exploded after they had seen it ablaze.
The aircraft was a Boeing 707-121 registered with tail number N709PA. Named the Clipper Tradewind, it was the oldest aircraft in the U.S. commercial jet fleet at the time of the crash. It had been delivered to Pan Am on October 27, 1958 and had flown a total of 14,609 hours. It was powered by four Pratt & Whitney JT3C-6 turbojet engines and its estimated value was $3,400,000 (equivalent to $28,700,000 in 2020).
In 1959, the aircraft had been involved in an incident in which the right outboard engine was torn from the wing during a training flight in France. The plane entered a sudden spin during a demonstration of the aircraft's minimum control speed, and the aerodynamic forces caused the engine to break away. The pilot regained control of the aircraft and landed safely in London using the remaining three engines. The detached engine fell into a field on a farm southwest of Paris, where the flight had originated, with no injuries.
The plane carried 73 passengers, who all died in the crash. All the passengers were residents of the United States.
The pilot was George F. Knuth, 45, of Long Island. He had flown for Pan Am for 22 years and had accumulated 17,049 hours of flying experience, including 2,890 in the Boeing 707. He had been involved in another incident in 1949, when as pilot of Pan Am Flight 100, a Lockheed Constellation in flight over Port Washington, New York, a Cessna 140 single-engine airplane crashed into his plane. The two occupants of the Cessna were killed, but Captain Knuth was able to land safely with no injuries to his crew or passengers.
The first officer was John R. Dale, 48, also of Long Island. He had a total of 13,963 hours of flying time, of which 2,681 were in the Boeing 707. The second officer was Paul L. Orringer, age 42, of New Rochelle, New York. He had 10,008 hours of flying experience, including 2,808 in Boeing 707 aircraft. The flight engineer was John R. Kantlehner of Long Island. He had a total flying time of 6,066 hours, including 76 hours in the Boeing 707.
The Civil Aeronautics Board (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 American World Airways, the Air Line Pilots Association, Pratt & Whitney, the Federal Bureau of Investigation and the Federal Aviation Agency. The costs of the CAB's investigations rarely exceeded $10,000, but the agency would spend about $125,000 investigating this crash (equivalent to $1,060,000 in 2020), in addition to the money spent by Boeing, the Federal Aviation Administration (FAA), Pratt & Whitney, and other aircraft-part suppliers during additional investigations.
Initial theories of the cause of the crash focused on the possibility that the plane had experienced severe turbulence in flight that caused a fuel tank or fuel line to rupture, leading to an in-flight fire from leaking fuel. U.S. House Representative Samuel S. Stratton of Schenectady, New York sent a telegram to the FAA urging them to restrict jet operations in turbulent weather, but the FAA responded that it saw no pattern that suggested the need for such restrictions, and Boeing concurred. Other theories included sabotage or lightning, but by nightfall after the first day, investigators had not found evidence of either. There was also some speculation that metal fatigue as a result of the aircraft's 1959 incident could be a factor, but the aircraft had undergone four separate maintenance overhauls since the accident without any issues having been detected.
Investigators rapidly located the flight data recorder, but it was badly damaged in the crash. Built to withstand an impact 100 times as strong as the force of gravity, it had been subjected to a force of 200 times the force of gravity, and its tape appeared to be hopelessly damaged. CAB chairman Alan S. Boyd told reporters shortly after the accident, "It was so compacted there is no way to tell at this time whether we can derive any useful information from it." Eventually, investigators were able to extract data from 95 percent of the tape that had been in the recorder.
The recovery of the wreckage took place over a period of 12 days, and 16 truckloads of the debris were taken to Bolling Air Force Base in Washington, D.C. for investigators to examine and reassemble. Investigators revealed that there was evidence of a fire that had occurred in flight, and one commented that it was nearly certain that there had been an in-flight explosion of some kind. Eyewitness testimony later confirmed that the plane had been burning on its way down to the crash site.
Within days, investigators reported that the crash had apparently been caused by an explosion that had blown off one of the wing tips. The wing tip had been found about three miles (5 km) from the crash site bearing burn marks and bulging from an apparent internal explosive force. Remnants of nine feet (3 m) of the wing tip had been found at various points along the flight path short of the impact crater. Investigators revealed that it was unlikely that rough turbulence had 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 that the plane would have had to dive a considerable distance before aerodynamic forces would have caused it to break up and explode, but it was apparent that the aircraft had caught fire near its cruising altitude of 5,000 feet.
Before this flight, there had been no other known case of lightning causing a plane to crash despite many instances of planes being struck. Investigators found that on average, each airplane is struck by lightning once or twice a year. Scientists and airline-industry representatives vigorously disputed the theory that lightning could have caused the aircraft to explode, calling it improbable. The closest example of such an instance occurred near Milan, Italy in June 1959 when a Lockheed L-1049 Super Constellation crashed as a result of static electricity igniting fuel vapor emanating from the fuel vents. Despite the opposition, investigators 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 investigators to believe that lightning was indeed the cause. The CAB launched an urgent research program in an attempt to identify conditions in which fuel vapors in the wings 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 were critical of the order, claiming that there was no evidence that the dischargers would have any beneficial effect, as they were not designed to handle the effects of lightning, and they said that the order would create a false impression that the risk of lightning strikes had been resolved.
The CAB conducted a public hearing in Philadelphia in February 1964 as part of its investigation. Experts had still not concluded that lightning had caused the accident, but they were investigating how lightning could have triggered the explosion. The FAA 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 jet fuel that was in the tanks centered around the fact that its vapors can be easily ignited at the low temperatures encountered in flight. JP-4 advocates countered that the fuel was as safe, or safer than, kerosene, the other fuel used in jets at the time.
Pan American conducted a flight test in a Boeing 707 to investigate whether fuel could leak from the tank-venting system during a test flight that attempted to simulate moderate to rough turbulence in flight. The test did not reveal any fuel discharge, but there was evidence that fuel had entered the vent system, collected in the surge tanks and returned to the tanks.[1](p9) Pan American said that it would test a new system to inject inert gas into the air spaces above the fuel tanks in aircraft in an attempt to reduce the risk of hazardous fuel-air mixtures that could ignite.
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 1 reserve fuel tank, which had caused an explosive disintegration of the left outer 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 vapors 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."
The following recommendations for your consideration are submitted:
- Install static discharge wicks on those turbine powered aircraft not so equipped.
- Reevaluate problems associated with incorporation of flame arrestors in fuel tank vent outlets. We believe positive protection against fuel tank explosion from static discharge ignited fuel/air mixtures at fuel tank vent outlets can be provided by flame arrestors having sufficient depth.
- A possible alternative to No. 2 that may be considered is to render the mixture emitting from the vent outlet non-ignitable by the introduction of air into the vent tube.
- We believe the surge tanks located just outboard of the reserve tanks, by virtue of their location near the wing tip, are vulnerable with respect to lightning strikes. Burn marks on the skin in the tip area of N709PA substantiates this belief. This being the case, it is believed a measure of protection will be attained if the wing skin is not utilized as part of the surge tank walls. This could be accomplished by providing an inner wall with an air gap between it and the wing skin to form the surge tank. It is recommended that this concept be considered. Another alternative appears to provide sufficient thickness of the skin in this area to prevent burning through by lightning strikes.
- Suggested for consideration is the requirement that only Jet A fuel be used commercially. Vapor flammability temperature charts provided by Esso show that much less of the operations would occur with the vapor in the flammability range while using Jet A fuel as compared with Jet B fuel.
- Finally, it is recommended that every effort be expanded to arrive at a practical means by which flammable air/vapor mixtures are eliminated from the fuel tanks. There appears to be at least two approaches to accomplish this act. There is the possibility of inerting the space above the fuel by introduction of an inert gas. An alternate approach is to introduce sufficient air circulation into the tanks to maintain a fuel/air ratio too lean for combustion. There may well be other approaches to attain this goal; if so, they should be explored. Other problems of like complexity have been resolved and we feel the resolution of this problem is likewise attainable at a cost commensurate with the benefits. We recommend that FAA/CAB solicit the aid of the aviation and petroleum industry as well as government and defense agencies to provide a solution to this problem that is applicable to aircraft in service as well as new aircraft.
More information on lightning and aircraft.
