TSB # A 15/2000
INTERIM AVIATION SAFETY RECOMMENDATIONS IN-FLIGHT FIREFIGHTING OCCURRENCE NUMBER A98H0003
(Halifax, Nova Scotia, 04 December 2000) - The Transportation Safety Board of Canada (TSB) today released five Aviation Safety Recommendations dealing with in-flight firefighting measures. The recommendations are the result of the continuing investigation into the crash of Swissair flight 111 (SR 111).
The safety investigation has raised concerns with the overall approach taken by the aviation community in addressing the ways that are available for aircraft crews to systematically detect, locate, assess, control, and suppress an in-flight fire within some areas of the fuselage of transport category aircraft.
To date, the SR 111 investigation has identified extensive fire damage in an area above the ceiling sometimes referred to as the "attic", in the front section of the aircraft within an area extending about 1.5 metres forward and 5 metres aft of the cockpit wall. Although the origin of the fire has not been determined, the Board believes that shortcomings in design and equipment, and crew training, awareness, procedures, and checklists may have deterred prompt detection and suppression of this in-flight fire.
In the course of this investigation, investigators assessed fire-fighting measures within the aviation industry, including procedures and equipment intended to prevent, control, or eliminate fires in aircraft. Material flammability, accessibility to areas within the aircraft, smoke/fire protection and suppression equipment, emergency procedures, and training were among the areas studied.
The TSB has identified safety deficiencies in several aspects of the current government requirements and industry standards involving in-flight firefighting. Each of these deficiencies has the potential to increase the time it takes for an aircraft crew to gain control of what could be a rapidly deteriorating situation. Time is a prime consideration in the successful identification and control of an in-flight fire.
In the case of SR 111, approximately 20 minutes elapsed from the time the crew detected an unusual odour until the aircraft crashed, and about 11 minutes elapsed between the time the presence of smoke was confirmed by the crew and the time that the fire is known to have begun to adversely affect aircraft systems. The TSB reviewed a number of databases to look for fire events that had similarities to the scenario of SR 111. Fifteen such events were identified, the earliest of which occurred in 1967. For these events, the time from when fire was first detected until the aircraft crashed ranged from 5 to 35 minutes. Each of these accidents had the same characteristic: the in-flight fire spread rapidly and became uncontrollable.
The Board believes that the five Safety Recommendations released today describe initiatives that can be taken to reduce the risks that have been identified.
As the investigation proceeds, should the Board identify additional safety deficiencies in need of urgent attention, it will make further aviation safety recommendations.
The Transportation Safety Board of Canada is an independent agency operating under its own Act of Parliament. Its sole aim is the advancement of transportation safety. It is not the function of the Board to assign fault or determine civil or criminal liability.
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Backgrounder: Five TSB Interim Aviation Safety Recommendations
Integrated Firefighting Measures
During the course of the Swissair flight 111 investigation, the TSB has necessarily looked beyond the specific circumstances of this single occurrence to examine industry standards in the area of in-flight firefighting. The Board believes that industry efforts have fallen short in this area, and that the industry should look at fire prevention, detection and suppression as being the components of a coordinated and comprehensive approach. Such an approach would consider and include all aspects of firefighting, such as:
The Board is concerned that the present approach to in-flight firefighting, both in design and implementation, is inadequate. More needs to be done to develop an effective firefighting system, and to ensure that all of the elements of such a system are fully integrated, compatible, and supported by all the other elements.
The regulatory authorities and the aviation industry must ensure that aircraft crews are provided with an appropriate integrated system to successfully detect and suppress any in-flight fire. The TSB's Swissair Flight 111 investigation has revealed that there are a number of safety deficiencies that could reduce the chances of an in-flight fire being detected and extinguished in time, such as:
In general, these deficiencies highlight weaknesses in the approach to preparing for the eventuality of an in-flight fire.
Smoke/Fire Detection and Suppression
At present, built-in smoke/fire detection and suppression systems in transport category aircraft are required only in "designated fire zones," which are areas that are not readily accessible and that contain recognized ignition and fuel sources. These areas include: powerplants, auxiliary power units (APU), lavatories, and cargo areas.
This recommendation addresses safety deficiencies associated with fire detection and suppression systems within the pressurized portion of the fuselage (known as the "pressure vessel") of transport category aircraft that are not now designated as fire zones.
Most transport category aircraft contain many kilometres of electrical wiring and a multitude of electrical components that have the potential, under certain conditions of failure, to produce heat that could ignite flammable materials.
Although materials used in aircraft must conform to specific criteria for fire-resistance, some flammable materials, such as the metallized Mylar thermal acoustical covering material described in the TSB's interim Safety Recommendation A99-08, dated 11 August 1999, remain in some aircraft. The U.S. Federal Aviation Administration (FAA) has mandated the removal of this material from aircraft; however, the associated FAA Notice of Proposed Rulemaking indicated that there are other thermal insulation blanket covering materials that exhibit flame propagation properties similar to those of metallized Mylar. In addition, within transport category aircraft there are many spaces that are seldom inspected and that can become contaminated with dust and other combustible debris that could contribute to fire propagation.
The Board believes that there is the potential for a fire to ignite and propagate without detection in areas not designated as fire zones. Such areas include, but are not limited to:
The Board believes that the present detection and suppression capabilities in those non-designated fire-zones of the aircraft fuselage, are inadequate. Presently, they are for the most part dependant on human senses for smoke/fire detection. In most transport category aircraft the occupied areas are isolated from the inaccessible areas by highly efficient aircraft ventilation/filtering systems, which can effectively remove combustion products from small fires and impede the timely detection of smoke by human senses; therefore, small fires can continue to propagate, and remain undetected by cabin occupants. Furthermore, any attempt at smoke/fire suppression in these areas would require direct human intervention using hand-held fire extinguishers. As the SR 111 accident and other occurrences demonstrate, early detection and suppression are critical in controlling in-flight fire.
Prompt Preparation for Emergency Landing
Instances of various odours on board aircraft are relatively common; however, odour/smoke occurrences rarely develop into uncontrolled in-flight fires. The SR 111 accident raised awareness of the potential consequences of an odour/smoke situation, and the rate for flight diversions has increased as a result. Some airlines have modified their policies, procedures, checklists, and training programs to facilitate timely diversions and rapid preparations to land immediately if smoke from an unknown source appears and cannot be readily eliminated. Along with other initiatives, Swissair amended their MD-11 checklist for "Smoke/Fumes of Unknown Origin" to indicate "Land at the nearest emergency aerodrome" as the first action item. While such initiatives reduce the risk of an accident, the Board believes that more needs to be done, industry-wide.
Within the aviation industry, there is an experience-based expectation that the source of odours/smoke will be discovered quickly and that troubleshooting procedures will "fix the problem." Although in-flight fires like that aboard Swissair Flight 111 are rare, the TSB review shows that in a situation where an in-flight fire continues to develop, there is a limited amount of time to land the aircraft. In situations where odour/smoke from an unknown source occurs, the decision to initiate a diversion and prepare for a potential emergency landing must be made quickly.
Time Required to Troubleshoot in Odour/Smoke Situations
In circumstances where the source of odour/smoke is not readily apparent, flight crews are trained to follow troubleshooting procedures, contained in checklists, to eliminate the origin of the smoke/fumes. Some of these procedures involve turning off electrical power and/or isolating an environmental system. Completing such checklists takes time, increasing the chances that a specific heat source could ignite a fire.
The Board believes that smoke/fumes checklists must be designed so that the appropriate troubleshooting procedures are completed quickly and effectively. By design, an indeterminate amount of time is required to assess the impact of each action. It can take a long time to complete the checklist, including troubleshooting actions. For example, the MD-11 Smoke/Fumes of Unknown Origin Checklist can take up to 30 minutes to complete. There is no regulatory direction or industry standard specifying how much time it should take to complete these checklists.
Efficiency of Fire Suppression in the Pressurized Portions of the Aircraft
An uncontrollable in-flight fire constitutes a very serious and complicated emergency. A fire may originate from a variety of possible sources, may start slowly, and after a certain development time, can spread very rapidly. Response time is critical. Aircraft crews must not only be knowledgeable about the aircraft and its systems, they must be trained and equipped to combat any fire quickly and effectively in all areas within the pressurized section of an aircraft, including those areas that may not be readily accessible.
Current aviation requirements and standards stipulate that aircraft crews must be trained to fight in-flight fires; however, the TSB found that within the industry there is a lack of coordinated cabin and flight crew fire-fighting training and procedures to enable crews to quickly locate, assess, control, and suppress an in-flight fire within the fuselage of aircraft. The Board is also concerned that aircraft crews are not trained or equipped to have ready access to spaces within the fuselage where fires have the potential to ignite and spread. The Board believes that the lack of comprehensive in-flight firefighting procedures, and coordinated aircraft crew training to use those procedures, constitutes a safety deficiency.