Steven M. Summer

This report discusses experiments to determine the reduction in oxygen concentration required to prevent a fuel tank explosion. A simulated aircraft fuel tank containing JP-8 fuel of an amount equivalent to a mass loading of approximately 4.5 kg/m3 was used to determine the limiting oxygen concentration (LOC) at pressures corresponding to altitudes ranging from 0 to 38 kft. In addition, the peak pressure rise was measured at various altitudes (pressures) due to ignition occurring at O2 levels approximately 1% to 1.5% above the LOC.

A wide range of ignition sources were used throughout the testing. An oil burner transformer connected to an analog timer provided a low power arc of both short (0.1 second) and long durations (1 second), a spark igniter taken from a J-57 engine provided a very short duration (175 µseconds) high powered spark, and a heated metal block was used as a hot surface ignition source. These varied capabilities allowed for an evaluation of the variation in the LOC due to a specific type of ignition source.

From these tests, it was determined that the LOC at sea level through 10 kft is approximately 12% O2, while exhibiting a linear increase from 12% at 10 kft to approximately 14.5% at 40 kft. Tests with various sparks/arcs as ignition sources at sea level showed little variation in results, with the LOC ranging from 12.0% to 12.8%. Also, a heated surface capable of igniting a fuel air mixture proved insufficient for ignition in a tank inerted to just 14%. Peak pressures resulting from ignition at oxygen concentrations 1% to 1.5% above LOC values decreased as the altitude was increased to 30 kft, while the duration to reach the peak pressure increased.

Michael Burns and William M. Cavage

The Federal Aviation Administration (FAA) is planning a series of ground and flight tests with Airbus to prove the concept of a simplified fuel tank inerting system, which has been developed by the FAA. The FAA has also developed an onboard oxygen analysis system to measure the oxygen concentration in the aircraft fuel tank during the testing. To help ensure smooth integration and the safety of the testing, the FAA has documented the system description, interfaces, operation, and has performed a failure mode effects criticality analysis. This analysis attempts to identify the failure modes of each system component and assess the effects of these failures on the component, system, and aircraft. The analysis also applies a hazard category to each hazard as well as some hazard probability when it was deemed necessary by the author. Hazard controls are also listed.

All relevant system information has been summarized to allow for the system to be properly integrated into the proposed flight test aircraft. The results of the analysis indicated that most failure modes had no effect on the aircraft or other secondary systems. The few hazards with potential aircraft effects have significant controls in place to reduce the likelihood of the hazard and mitigate any potential hazard exposure.

R G W Cherry & Associates Limited

A benefit analysis has been carried out to derive the life saving potential of a Cabin Water Spray system in conjunction with enhanced Fuselage Burnthrough Protection from large external pool fires. The effects of fire and evacuation related requirements that were introduced after the accident date have also been taken into account.

All benefits derived are based on the number of lives saved for the world fleet of western-built aircraft type certificated for more than 30 seats and are relative to the period 1967 to 1996.

Two configurations of Cabin Water Spray system have been considered in the benefit analysis - a Modular and a Singular system. It is assumed that a Modular system would consist of three separate water supplies located in the front, mid and rear sections of the fuselage and would be activated only in the areas affected by fire. A Singular system would have only one source of supply located in the centre section of the fuselage. It would provide benefit in this area should the nose and/or tail sections became detached in the accident.

Benefit has been determined for aircraft configurations having either enhanced Fuselage Burnthrough Protection or a Cabin Water Spray System. In addition, the study reassesses the benefit from Cabin Water Sprays on aircraft already configured with enhanced Fuselage Burnthrough Protection.

The analysis has been accomplished by analysing past accidents to western-built aircraft over the period 1967 to 1996. Two methodologies were used to determine the total assessed benefit for all accidents studied. The first was based on an assessment of the number of lives saved in each accident from which a determination was made of the average number of lives saved per year and its likely range. The second method was to determine the rate of occurrence per year of the number of accidents from which the improvements considered might yield benefit.

The merits of each method are discussed and it was considered that the best prediction of benefit is that derived from Method 2.

Enhanced Fuselage Burnthrough Protection has been reassessed and the life saving benefit increased from that previously estimated. The number of lives saved per year is estimated to be approximately 12.

The assessment for a Singular Cabin Water Spray system on aircraft that are configured without enhanced Fuselage Burnthrough Protection is approximately 27 lives per year.

The number of lives saved per year, by a Modular Cabin Water Spray system, on aircraft that are configured without enhanced Fuselage Burnthrough Protection is assessed to be approximately 34 lives per year.

The assessment for Singular Cabin Water Spray systems and enhanced Fuselage Burnthrough Protection combined is approximately 34 lives per year.

The number of lives saved per year by Modular Cabin Water Spray systems and enhanced Fuselage Burnthrough Protection combined is assessed to be approximately 46 lives per year.

For aircraft that are configured with enhanced Fuselage Burnthrough Protection, Cabin Water Spray systems would save a further 22 lives per year for a Singular system, and 34 lives per year for a Modular system.

David Blake

This report documents a series of tests to determine the amount of positive pressure differential between the flight deck and surrounding areas necessary to prevent smoke from penetrating into the flight deck. The testing also explored methods to demonstrate the effectiveness of those ventilation conditions. The tests were conducted on the ground in a Boeing 727-100 freighter and a 747SP aircraft. A thin plastic sheet covering the flight deck door opening and a theatrical smoke generator were successfully used to demonstrate a positive pressure differential that was effective at preventing the penetration of theatrical smoke into the flight deck of the B-727. The 747SP ventilation system was not capable of preventing smoke penetration during these ground tests.

John W. Reinhardt

This technical note presents the updated version of the minimum performance standards (MPS) that a Halon 1301 replacement or alternate system for aircraft cargo compartment must meet as part of the aircraft certification procedures. This standard considers gaseous and nongaseous fire suppression systems for full-scale fire testing. The Federal Aviation Administration developed this MPS in conjunction with the International Aircraft Fire Protection Systems Working Group (formerly know as the International Halon Replacement Working Group).