R.G.W. Cherry & Associates Limited

This report describes the methodology and results of a study undertaken for the Federal Aviation Administration into the characteristics of Fuselage Breaks and their effects on occupant survival in ground pool fire Accidents. For those accidents where the fuselage remains largely intact, a determination has been made of the nature of any Fuselage Ruptures resulting from the accident sequence. An assessment has also been made as to whether the probability of occurrence of ground pool fires is different for Aircraft with Wing Mounted Engines than for Aircraft without Wing Mounted Engines. The Cabin Safety Research Technical Group Aircraft Accident Database was used to select Survivable Accidents that occurred during the period 1967 to 2000, to Passenger carrying western world turbojet aircraft. Where appropriate to the study these accidents were analyzed in depth using Accident Reports and other data published by National Airworthiness and Investigating Authorities.

The results of the study suggest that further data would be needed to determine any significant difference that might exist between the probabilities of occurrence of a ground pool fire accident for Aircraft with Wing Mounted Engines and for Aircraft without Wing Mounted Engines. All that can be determined, within the constraints of the size of the existing data set, is that any difference that might exist is unlikely to be large. Whilst it is likely that the majority of ground pool fire accidents in which the aircraft remains largely intact sustain Fuselage Ruptures, there are insufficient data available to establish the size of any such ruptures.

For the Fuselage Break accidents studied the majority involved at least two breaks. Whilst the number of Fuselage Breaks does not appear to be influenced by the intensity of the impact the probability of a Fuselage Break tends to increase as the impact becomes more severe. Although no firm conclusions can be made, it is considered likely that approximately half of the Fuselage Breaks occur at a point of structural discontinuity. The occurrence of a Fuselage Break in ground pool fire accidents seems to result in a more severe fire threat to the occupants. However, it is evident that for the majority of ground pool fire accidents studied, involving a Fuselage Break, the occupants used the breaks as an escape route. In order to ascertain the net effects of Fuselage Breaks on occupant survival a Monte Carlo simulation model was developed. The primary value of the model was an assessment of the effects on occupant survival of changes in the probability of occurrence of Fuselage Breaks. Based on the results derived from the model it is considered that Fuselage Breaks have a net adverse effect on occupant survival. The change in the number of Fatal Injuries, F, with changes in the probability of a Fuselage Break ΔB for an aircraft with N occupants may be reasonably well represented by the following equation:

R.G.W. Cherry & Associates Limited

As part of a project commissioned by the Federal Aviation Administration data have been gathered on the relative proportion of accidents that involve Ground Pool Fires and statistical data on the following:

• Time to initiate an evacuation
• Time to complete an evacuation
• Time to arrival of fire-fighters
• Time for fire-fighters to establish control in a Ground Pool Fire accident

The data was extracted from accident reports and other information published by Investigating and Airworthiness Authorities using the Cabin Safety Research Technical Group Aircraft Accident Database as the search facility.

Robert I. Ochs

A new and improved burner was developed to test the fire penetration resistance of thermal acoustic insulation in accordance with Title 14 Code of Federal Regulations (CFR) Part 25.856 (b). This next-generation (NexGen) burner was developed mainly to provide industry with an alternative to the currently accepted burner apparatus manufactured by Park Electric Motors of Atlantic City, NJ. Title 14 CFR 25.856 was written based on the use of the Park DPL 3400 burner; however, the company stopped production of this apparatus shortly after the new test method became final in 2003. The NexGen burner can be considered a direct replacement to the Park-manufactured burner, with several key improvements.

The NexGen burner is based on the same operating principle as the Park DPL 3400, using the same, or very similar, internal components to avoid drastically changing the overall character of the flame. The main difference is the elimination of the electric motor, which provided power to the fuel pump and blower fan in the Park-manufactured burner. In the NexGen burner, these functions have been replaced with regulated and conditioned compressed air and a pressurized fuel delivery system. Compressed air, when metered with a sonic orifice and conditioned to remove heat and moisture, proves to be more consistent over extended periods of time than to using a shaft-driven blower and laboratory air for the burner, thus increasing the repeatability of the NexGen burner. NexGen fuel delivery is provided by applying a head pressure of nitrogen gas on liquid fuel contained in a pressure vessel. This new method eliminates any fluctuations that were previously experienced with the electric motor and shaft-driven fuel pump typical of the Park-manufactured burner.

The exit air velocity and the fuel flow rate of the NexGen burner were matched to that of the Park DPL 3400 burner specifications to produce a flame of similar temperature and heat flux. Initial comparison tests indicated that the NexGen burner provides burnthrough results similar to that of the Park burner when comparing identical materials. Multiple NexGen burners were produced, and all were proven to provide the same results. NexGen burners were shipped to participating laboratories, tested with identical materials, and proven to be reproducible at different locations. This work has shown that an equivalent burner can be fabricated from readily available materials and can be used to test materials according 14 CFR 25.856 (b).

R.G.W. Cherry & Associates Limited

The National Transportation Safety Board has recommended that fire suppression systems be installed in the cargo compartments of all cargo airplanes operating under 14 CFR Part 121. Currently, Class E cargo compartments, which are the primary cargo compartment type used in US cargo airplanes, do not require fire suppression systems. In response to this recommendation, FAA has requested that a cost/benefit analysis be carried out relating to the installation of on-board fire detection and extinguishment systems in cargo airplanes. This report contains the results of this analysis and a description of the methodology used.

The analysis assessed whether fire suppression systems, fitted to the cargo bays of cargo airplanes, type certificated to FAR Part 25 and operating under FAR Part 121, are likely to be cost beneficial. Potential benefits will result from a reduction in Injuries (Fatal and Serious) to personnel, a reduction in the damage incurred to the aircraft and its cargo, and a reduction in the damage that might be incurred to property on the ground. Potential costs are those that might be incurred from the installation and operation of fire suppression systems.

A mathematical model has been developed to assess the benefit. The model utilizes statistical distributions derived from data on in-service airplanes and accident information. Cost assessments were made for modifying cargo aircraft to the new Type F Cargo Compartment being considered for combi aircraft. These cost assessments were based on the installation of a Halon type fire suppression system together with suitable cargo compartment liners. The data used in the cost assessment was based on that contained in the ARAC document relating to main deck class B cargo compartments.

The results of the study suggest that crew injuries (Fatal and Serious combined) and the loss of the aircraft and cargo in freighter fire accidents are likely to be a significant factor in the prediction of benefit. Collateral ground damage does not appear to contribute significantly to the prediction of benefit. It is concluded that Halon fire suppression systems, or alternatives that are likely to be developed for below floor cargo compartments, are unlikely to be cost beneficial for the cargo compartments of cargo aircraft. Fire suppression systems, of the kind currently being considered for the cargo compartments of combi aircraft, may prove to be cost beneficial, particularly on larger cargo aircraft.

John W. Reinhardt and Robert Penman, III

This research was conducted to determine if a combination of Halon 1301 and nitrogen gas would prevent an aerosol can explosion. The aerosol can explosion simulation tests were conducted in the Pressure Fire Modeling Facility, at the Federal Aviation Administration William J. Hughes Technical Center, Atlantic City International Airport, New Jersey. The aerosol can explosion simulator, used for the Aircraft Cargo Compartment Minimum Performance Standard, was mounted inside the instrumented pressure vessel that was located in this facility. The Halon 1301 and nitrogen were introduced to the pressure vessel using two different commercial off-the-shelf systems. The Halon 1301 gas was dispensed using a typical 20-pound fire bottle connected to a single nozzle via a 0.5-inch pipe. The nitrogen, used to reduce the oxygen volumetric concentration, was introduced to the pressure vessel via a hose connected to a ground-based inert gas generator. The aerosol can explosion simulator was activated once the desired concentrations of Halon 1301 and oxygen were reached, and it was pressurized at its designed (failure) value. The results showed that a clear benefit existed when Halon 1301 and nitrogen were combined below their inerting concentrations, thus preventing an aerosol can explosion.