In-flight Firefighting-Swissair Flight III

Interim Aviation Safety Recommendations
In-flight Firefighting - Swissair Flight III

Background

The aircraft crashed into the ocean, and all fire damage occurred in flight. The investigation (A98H0003) has identified extensive fire damage above the ceiling in the forward section of the aircraft extending about 1.5 metres forward and 5 metres aft of the cockpit bulkhead. Although the origin of the fire has not been determined, the investigation has revealed safety deficiencies in design, equipment, and crew training, awareness, and procedures related to in-flight firefighting. The elimination of these safety deficiencies would reduce the loss of life by increasing the probability of the prompt detection and suppression of in-flight fires.

The TSB is concerned with the approach taken by the aviation community in minimizing the risk and in addressing the means that are available for an aircraft crew to consistently detect and suppress fires within the pressurized portion of the aircraft.(1)

When confronted with an in-flight fire, an aircraft crew must be prepared to rely solely on their experience and training, and on the aircraft equipment at hand. Therefore, effective in-flight firefighting measures should allow an aircraft crew to quickly detect, analyse and suppress any in-flight fire.(2) While it is difficult to predict how much time might be required to bring a particular in-flight fire under control, the earlier a fire is detected, the better.

Anecdotal information suggests that odour/fumes/smoke occurrences that do not develop into in-flight fires are not unusual but that, where an in-flight fire does develop, there is very little time available to gain control of the fire. The TSB reviewed a number of databases to validate this information. The review confirmed that there are numerous odour/fumes/smoke occurrences; however, occurrences leading to accidents as a result of uncontrolled fires similar to SR 111 are rare. Details of the TSB review of available data are included in Appendix A. This sample of in-flight fire accidents was compiled based on similarity to SR 111. These data indicate that, in situations where there is an in-flight fire that continues to develop, the time from detection until the aircraft crashed varied from 5 to 35 minutes.

Furthermore, the TSB looked at numerous in-flight fire events that, because of variances with the criteria established for the review, were not included in the validation process. Many of these events resulted in fatalities and each contains examples of where one or more components of the firefighting system failed to provide adequate protection. Appendix B contains a sample of these events.

Safety Deficiencies

The TSB has identified safety deficiencies in several aspects of the current government requirements and industry standards involving in-flight firefighting. These deficiencies increase the time required to assess and gain control of what could be a rapidly deteriorating situation. When viewed together, these deficiencies reflect a weakness in the efforts of governments and industry to recognize the need for dealing with in-flight fire in a systematic and effective way.

The Board's interim air safety recommendations address safety deficiencies in the following areas:

  • The lack of a coordinated and comprehensive approach to in-flight firefighting increases the overall risk.
  • Smoke/fire detection and suppression systems are insufficient.
  • The importance of making prompt preparations for a possible emergency landing is not recognized.
  • The time required to troubleshoot smoke/fire problems is excessive.
  • Access to critical areas within aircraft is inadequate.

Integrated Firefighting Measures

An important aspect of the Board's mandate to advance transportation safety is to look beyond the specific circumstances of any single occurrence and identify systemic safety deficiencies. Over the years, lessons learned from a number of accidents have resulted in modifications to aircraft, systems, and procedures as a direct response to specific failures.(3) However, aircraft and equipment design changes aimed at providing better firefighting measures have sometimes been made in isolation from each other. Although considerable efforts have been made to prepare and equip aircraft crews to handle in-flight fires, these efforts have fallen short of adequately preparing aircraft crews to detect, locate, access, assess, and suppress in-flight fires in a coherent and coordinated manner.

In-flight firefighting "systems" should include all procedures and equipment necessary to prevent, detect, control, and eliminate fires in aircraft. This systems approach would include material flammability standards, accessibility, smoke/fire detection and suppression equipment, emergency procedures and training. All of these components should be examined together and the inter-relationships between individual firefighting measures should be re-assessed with a view to developing improved, comprehensive firefighting measures. The Board believes that the most effective in-flight firefighting capability will exist when the various elements of the firefighting system are integrated and complementary; it therefore recommends:

Appropriate regulatory authorities, in conjunction with the aviation community, review the adequacy of in-flight firefighting as a whole, to ensure that aircraft crews are provided with a system whose elements are complementary and optimized to provide the maximum probability of detecting and suppressing any in-flight fire. (A00-16)

Smoke/Fire Detection and Suppression

Designated Fire Zones

Presently, the requirements for built-in smoke/fire detection and suppression systems are restricted to those areas that are not readily accessible, and in which a high degree of precaution must be taken.(4) Areas such as these, either inside or outside the pressurized portion of the aircraft, are designated as "fire zones" due to the presence of both ignition sources and flammable materials. Consequently, aircraft manufacturers must provide built-in detection and suppression systems in powerplants (including Auxiliary Power Unit (APU)), lavatories, and cargo and baggage compartments.(5) The built-in suppression features are either automatic, as in lavatories, or controlled from the cockpit, as in powerplants. In each case the extinguishing agent must consist of an amount and nature tailored to the types of fire most likely to occur in the area where the extinguisher is used.(6)

There are no requirements for built-in smoke/fire detection and suppression systems in the remaining areas of the pressurized portion of the aircraft. Detection and suppression in non-designated fire zones, such as the cockpit, cabin, galleys, electrical and electronic equipment (E&E) compartments, and attic spaces are, for the most part, dependant on human intervention.(7)

Non-Designated Fire Zones

Detection of smoke and fire in non-designated fire zones depends on the eyes, ears and noses of the crew and passengers. However, while some areas of an aircraft are almost certain to have a human presence during much of a flight, other areas, such as E&E compartments and attic areas, are more remote. A fire may ignite and propagate in these areas well out of the range of any human detection. The United States National Transportation Safety Board (NTSB) report on an Air Canada DC-9 in-flight fire that occurred near Cincinnati on 02 June 1983 suggests that the crew first detected smoke approximately 11 minutes after the related circuit breakers tripped.(8) Compounding this problem, 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. These systems can allow small fires to burn undetected by cabin occupants.(9)

Some areas not designated as fire zones have been treated as "benign", from a fire potential perspective. They have not been assessed by the aviation industry as needing built-in fire detection or suppression equipment. Furthermore, there has not been a recognized need either to train aircraft crews for firefighting in all of the non-designated fire zones, or to design aircraft so as to allow quick and easy access to these areas for firefighting purposes.

Aircraft materials must conform to fire-related standards. These requirements necessitate that materials used in compartment interiors, and in cargo and baggage compartments, meet the applicable test criteria.(10) In interim Air Safety Recommendation A99-08, dated 11 August 1999, the TSB identified limitations in these test criteria which allowed flammable material, used as a covering on thermal-acoustical insulation blankets, to be certified for use in aircraft. The Federal Aviation Administration (FAA) is actively pursuing a replacement program for a specific insulation cover material (metallized Mylar), which it deems to pose the greatest risk. Additionally, a more effective test is in development. The FAA's applicable Notices of Proposed Rulemaking (NPRMs) indicate that there are other insulation blanket cover materials that exhibit flame propagation properties similar to those of metallized Mylar.(11) Therefore, even with the FAA's metallized Mylar replacement initiatives, many inaccessible areas containing combustible materials will remain in aircraft remote from smoke/fire detection systems. Additionally, such materials, located in inaccessible areas, are prone to surface contamination which may provide fuel for flame propagation.

There are many spaces, including some large areas, within transport category aircraft that are seldom inspected and that can become contaminated with dust, debris and metal shavings. Inspections conducted under the auspices of the FAA's Aging Transport Non-Structural Systems Plan identified surface contamination on wiring bundles as a hazard.(12) The SR 111 investigation team has observed, in a variety of aircraft, similar contamination on insulation blanket material and on wire bundles. While the extent of the overall contamination problem has yet to be determined, over time debris such as metal shavings may damage wire insulation, which could lead to short-circuiting and, potentially arcing of wires. Additionally, dust and combustible debris would provide fuel and would contribute to fire propagation. Well-designed and well-executed maintenance programs may limit such contamination, but it is unlikely that contamination can be completely eliminated.

In recent years, there have been changes in requirements regarding detection and suppression in areas not previously designated as fire zones. For instance, the inclusion of lavatories as fire zones was largely a result of the lessons learned from the DC-9 accident near Cincinnati. The SR 111 accident, and other occurrences, clearly demonstrate that early detection and suppression are critical in controlling an in-flight fire. The present situation is inadequate, and more needs to be done to improve detection and suppression capabilities in some of the pressurized areas of aircraft. There are significant areas within the pressurized portion of the aircraft, not now deemed to be fire zones, that are virtually inaccessible and in which ignition sources and combustible materials may both be present.

The Board believes that the risk to the travelling public can be reduced by re-examining fire zone designations in order to determine which additional areas of the aircraft ought to be provided with enhanced smoke/fire detection and suppression systems. Therefore, the Board recommends:

  • Appropriate regulatory authorities, together with the aviation community, review the methodology for establishing designated fire zones within the pressurized portion of the aircraft, with a view to providing improved detection and suppression capability. (A00-17)

FOOTNOTES

1.  For the purposes of this discussion, the pressurized portion of the aircraft, or pressure vessel, includes cockpit, cabin, avionic compartments, cargo compartments, etc.

2.  For the purposes of this discussion, the term in-flight firefighting includes all procedures and equipment intended to prevent, detect, control, or eliminate fires in aircraft. These include, but are not limited to material flammability standards, accessibility, smoke/fire detection and suppression equipment, emergency procedures, and training.

3.  Specific improvements were made to fire detection and suppression in lavatory and cargo areas following the Air Canada accident near Cincinnati, Ohio, and the ValuJet accident in Florida.

4.  Each Civil Aviation Authority establishes its own requirements pertaining to in-flight firefighting. Since the MD-11 was certified in the United States, the Federal Aviation Regulations (FARs) are referenced in this document.

5.  See FARs 25.854, 25.855, 25.858, 25.1181, 25.1195, 25.1197, 25.1199, 25.1201, 25.1203, 121.308.

6.  See FAR 25.851(a).

7.  For the purposes of this discussion, the attic is defined as that area between the crown of the aircraft and the drop-down ceiling.

8.  See National Transportation Safety Board report DCA83AA028 concerning the 02 June 1983 accident involving an Air Canada DC-9 near Cincinnati, Ohio.

9.  Development and Growth of Inaccessible Aircraft Fires Under Inflight Airflow Conditions (DOT/FAA/CT-91/2, dated February 1991).

10.  See FARs 25.853, 25.855, and Part I of Appendix F of Part 25.

11.  See NPRMs A99-NM-161-AD and A99-NM-162-AD.

12.  FAA Aging Transport Non-Structural Systems Plan, dated July 1998.

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