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Concorde Safety

Cosmic radiation is always present in the atmosphere and is encountered in subsonic and supersonic flight. Cosmic radiation rates vary with altitude. At the cruise altitudes of SSTs, the rate were found to be approximately double those at subsonic aircraft cruise altitudes. However, since SST flight times are approximately half of those of subsonic aircraft, the total dose per flight is about the same for SST passengers and subsonic aircraft passengers. The total dose is the significant factor in determining the impact on passengers. This dose is approximately the same as the impact on subsonic passengers traveling the same distance and is concluded, as for subsonic passengers, to be harmful.

A potential radiation hazard at SST altitudes is caused by solar flare radiation. On rare, unpredictable occasions -- there have been three since 1956 -- the radiation at SST altitudes from a solar flare may reach levels considered sufficiently high to warrant reducing the flight altitude in order to increase shielding by the atmosphere. It is expected that SSTs will carry radiation monitoring devices that measure the radiation rate and warn the pilot during a solar proton event which precedes a solar radiation increase from a solar flare, although such devices are not presently required. When this warning occurs, the pilot can descend to flight levels that assure safety.

During the SST review in the 1960s, it was noted that certain pressurization system failures, whether considered by themselves or in combination with the use of hot ram air for emergency pressurization, could lead to cabin temperatures exceeding human tolerance. The FAA therefore concluded that any failure or combination of failures that could lead to temperature exposures that would cause undue discomfort must be shown to be improbable.

The risk of fire and explosion in aircraft fuel tanks in the Concorde SST due to uncontained failure of the Olympus 593 engine was initially recognized in a British Aerospace report by J.C. Wallin in 1976. The probability of ignition for Jet-A was estimated, based on judgment, to vary from 0.05 to 0.8 depending on fragment trajectory and fuel temperature (starting at -50C, well below the flash point). Wallin of British Aerospace developed a methodology to assess catastrophic risks resulting from uncontained failures of turbine engine rotors. This work was undertaken as part of the Concorde SST certification program, using an engine failure model for the Olympus 593. It is summarized in this section because it is the only study we found that recognized the potential hazards of in-tank fire and explosion from uncontained engine failures in commercial aircraft. Wallin began by establishing a hazard tree, evaluating debris size for each engine stage, and determining potential risk items for each stage. A statistical analysis of earlier tests and actual failures provided data for the distribution of risk through each flight stage. A mean catastrophic risk across a typical flight mission was established by summing the overlapping risks using success theory.

Wallin established a hazard tree for engine rotor failure that included the effects of damage to structure and essential systems, loss of thrust, disturbance of operation, and fires and explosions. The risk assessment included the effects of 1/3 disk pieces and disk rim pieces of 1/2 radius. Such a failure model was adapted from the British Civil Airworthiness Requirements and Olympus 593 failure models that are based on experimental test data and statistics. By examining the structure of the Concorde, Wallin determined the fragment fly-off zone in plan view and established the risk angle associated with each engine stage. In this manner the at-risk items were identified and an overall risk was obtained for each flight phase.

During the 20-month period from July 1979 through February 1981, there were four occasions in which an Air France Concorde operating from Dulles International Airport or Kennedy International Airport was involved in a potentidly catastrophic incident resulting from blown tires during takeoff. The repetitive nature of these incidents and, in particular, crew response in the more recent incidents is of serious concern to the National Transportation Safety Board.

On June 14, 1979, an Air France Concorde experienced blowouts of the Nos. 5 and 6 tires on the left main landing gear on takeoff from Dulles International Airport, Washington, D.C. Tire debris and wheel shrapnel resulted in damage to the No. 2 engine, puncture of three fuel tanks, and severance of several hydraulic lines and electxical wires. Additionally, a large hole was torn in the top wing skin which covers the wheel well area. As a result of the Safety Board's findings in the ensuing investigation of that incident, several mechanical and operational recommendations were being considered; however, prior to a final decision on their issuance, a second blown tire incident occurred on July 21, 1979, involving a takeoff from Dulles. The similarities between the two incidents led to immediate voluntary corrective action by the appropriate authorities. An Airworthiness Directive, issued by the Director Generale de 1'Aviation Civile, and a Technical Information Update, issued by Air France, revised procedures.

Although there was general agreement as to the validity of the corrective action among the various parties involved in the investigations, operational experience since that time casts serious doubt on the effectiveness of the corrective action. Despite the requirement for increased tire inspections and monitoring, there were two additional incidents in U.S. operations of the Concorde involving blowouts during takeoff.

In October 1979 F-BVFD had a tire failure during takeoff from Kennedy International Airport. On this occasion the Nos. 7 and Nos. 8 tires failed. Despite the extent recommended practice to the contraty, the gear was retracted and the flight continued to Paris. No investigation was conducted by either the Safety Board or the French Bureau Enquetes Accidents at the time of the incident.

In February 1981 - F-BTSD incurred blown tires during takeoff from D International Airport following a stop on a Mexico City to Paris flight. On this occasion the crew also disregarded the Tech Update and raised the lending gear. Engine problems resulting from damage forced the crew to land at New York. Preliminary informetion indicates that there was no preparation of the passengers for a possible emergency landing end evacuation. Additionally, the cockpit voice recorder (CVR) on the aircraft was inoperative end had been for several flights, including a layover at Paris.

On October 8, 1998, a British Airways Concorde experienced a partial separation of the lower rudder while in cruise flight over the North Atlantic. On August 26, 1999, two Concordes passed within 800 feet vertically and 0.7 mile horizontally of each other near John F. Kennedy Airport in New York. There were no injuries in either incident.



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