National Transportation Safety Board

Volume I contains the Safety Board's responses to a number of recommendations made by the aviation industry during the Safety Board's Aviation Accident Investigation Symposium held at Tyson's Corner, Virginia, from March 29 through 31, 1994. Volume II contains presentations made by symposium participants. The symposium provided a forum for the aviation industry to discuss and critique Safety Board programs and practices, as well as procedures used during aviation accident investigations. Participants included representative from U>S. air carriers, airframe and engine manufacturers, aviation associations and unions, government officials and interested parties, as well as foreign investigative and manufacturers.

Keith E. Crouch

The Navy and the Air Force recognized the need for improved test procedures for evaluating the lightning protection design of aircraft fuel systems. Under their sponsorship, a program to develop adjustable, standard ignition sources which could be used to calibrate techniques for detecting ignition sources during lightning testing was established. The minimum ignition levels of voltage sparks and hot spots were established under the program before it was terminated due to funding problems.

The present program, under FAA sponsorship, is a continuation of the original program. The Standard Voltage Spark Ignition Source and the Standard Hot Spot Ignition Source were completed and documented. The most promising approach for developing a Standard Thermal Spark Ignition Source was determined and is presented.

.Photographic detection techniques were investigated and the limitations determined. The presence of light on a photographic film indicated the possibility of an ignition source but can not confirm the ignition probability (if any).

Hydrogen mixtures appear to provide the ability to have adjustable ignition probabilities and low energy (low over-pressure) ignitions.

Richard M. Johnson

A series of 150 comparative tests were run by four currently operating laboratories using heat release apparatuses compliant with present FAA/JAR standards and the ATI-Russian Institute of Aviation Materials (VIAM) designed heat release apparatus. The evaluation of data showed little or no correlation between the subject apparatus and the four compliant apparatuses.

Joseph L. Scheffey, Joseph A. Wright

Foam agent quantities and application rates for FAA certified airports are based on large-scale fire test data of Aqueous Film-Forming Foam (AFFF) and " protein-based foams. The philosophy is to control aircraft fuel fires in sixty seconds. Foam agents which are used for aviation applications should demonstrate this level of performance, including a safety factor which assures adequate performance under less than optimum conditions.

A review of standard test methods and performance criteria indicates a wide range of requirements. The U. S. Military Specification (MIL SPEC) for AFFF, on which the original agent criteria was developed, is the most stringent in terms of extinguishment application density. However, no direct correlation has been demonstrated between many of the required physical/chemical properties tests and fire extinguishment/burnback performance.

It was demonstrated, using comparative data from numerous small- and large-scale fire tests, that the small-scale MIL SPEC fire tests correlate with large-scale test results. MIL SPEC agents, which provide a safety factor over minimum FAA requirements, also are formulated to have proportioning, storage, stability, and shelf-life attributes appropriate for crash rescue firefighting applications. Adoption of the MIL SPEC for AFFF agents is recommended. Future work related to foam testing should focus on the use of first principles to establish fundamental foam extinguishment mechanisms.

P. Laing, S.N.B. Murthy

In a continuing effort to establish perfonnance changes due to water ingestion into an aircraft gas turbine engine and possible design improvements, an experimental investigation was perfonned with a model gas turbine prediffuser-combustor sector utilizing a number of mixture and flow conditions in a tunnel operating with a two-phase, air-liquid film-droplet mixture. For given entry conditions into the prediffuser (which can be related to the exit conditions of the core compressor in a bypass engine, and, therefore, also to ingestion conditions at the engine face) the two main issues are (1) the amount of water entering the primary zone of the combustOr, and (2) the local reduction in temperature, flame-water interactions, and the vitiation caused by the vaporizing of water. Flow,visualization and estimates of water flow and droplet size in the primary zone have been undertaken under cold flow conditions. The amount of water entering the primary zone has been found to be a complex function of (1) the air-water mixture conditions at entry to the prediffuser, and (2) the effects of gravity on the flowfield for given geometry of the prediffuser-combustor, and the flow split between the primary and the coolant streams in the combustor. Combustion tests have been carried out to establish the effects on perfonnance. occurrence of flameout, and recoverability of combustor exit temperature by enhancement of one or both of the fuel equivalence ratio and the oxygen content of air. It was tentatively concluded that the observed effects of the presence of water are a result of the interactive effe.cts of heat transfer to water, vitiation by water vapor on combustion, and the total heat release in the primary zone. The latter being the dominant factor in stabilizing the flame with a large increase in combustor exit temperature, as found in the tests with the addition of both fuel and oxygen to a given burning mixture.