Investigation Update Into the Fire on Board Air Canada Flight 116 Boeing 767-300, 13 May 2002 On completion of the work of its investigators, the Board will produce its draft report which will be sent on a confidential basis to designated reviewers who, in the opinion of the Board, have a direct interest in the findings. MAY 24, 2002 - 14:30 EDT "The electrical failure of the heater tape ignited the covering of the insulation blankets installed below the open cargo floor and some debris found in the area." TSB: Investigation Update Into the Fire on Board Air Canada Flight 116 Boeing 767-300, 13 May 2002 - TSB Investigation # A02O0123 TORONTO, ONTARIO-- On 13 May 2002, Air Canada flight 116, a Boeing 767-300 with 8 crew members and 177 passengers on board, was arriving at Toronto Lester B. Pearson International Airport (LBPIA) on a flight from Vancouver, B.C. At about 1737 EDT on final approach approximately 10 miles from the airport, the flight crew received an aft cargo bay fire warning. The flight crew followed checklist procedures, activated the cargo bay fire extinguishers and declared an emergency. The fire indication went out some 20 to 30 seconds after activation of the fire extinguishers, but a slight smell of smoke was noticed by the cabin crew and flight crew. Flight 116 landed and stopped on the runway to allow airport firefighters to inspect the aircraft for fire. Firefighters, using infrared sensing equipment, did not detect any sign of fire. The flight crew taxied the aircraft to the terminal but stopped approximately 40 feet back from the gate to allow firefighters to open the aft cargo compartment for a detailed inspection. When the cargo door was opened, a significant amount of smoke was observed. Firefighters entered the cargo compartment and confirmed that the fire had been extinguished. During this time the flight crew had prepared the aircraft for emergency evacuation should that be deemed necessary. However, the situation was secured and passengers were deplaned using normal portable stairs. The aircraft was taken to a hangar for further inspection and company maintenance personnel discovered substantial soot and fire damage on the floor of the cargo bay. The Transportation Safety Board of Canada (TSB) was notified and investigators from the Ontario regional office were deployed on the morning of May 14 to investigate. Investigation Progress to Date TSB investigators discovered that an intense but relatively small fire had occurred, causing significant structural damage in the floor area of the aft cargo compartment. The damage included burned insulation blanket material and two areas where holes had burned through an aluminium structural web resulting in significant heat distortion of the floor beam. There was no reported damage to any of the cargo and only minor smoke damage to two cargo containers. Before it was extinguished, the fire had progressed approximately 18 inches up the right side wall of the aircraft, outside the aft cargo compartment. The cargo bay fire-extinguishing system, a Halon-based system, effectively suppressed the fire before it could spread further. The fire appears to have been a direct result of an electrical failure of a heater tape used to prevent water lines from freezing. The electrical failure of the heater tape ignited the covering of the insulation blankets installed below the open cargo floor and some debris found in the area. During the inspection of this and other aircraft, additional examples of overheated and burned heater tapes were discovered. None of these additional failed heater tapes resulted in an aircraft fire, although burned insulation wrap was discovered. The TSB contacted Boeing, the US National Transportation Safety Board (NTSB), the US Federal Aviation Administration (FAA) and Transport Canada to advise them of the occurrence and invite them to participate in the investigation. Boeing deployed a technical specialist to assist in the investigation. The FAA and Transport Canada also attended the on-scene investigation in order to gain first-hand knowledge of the nature and severity of the fire.

The following matters of potential significance have been identified and are being addressed in the investigation:

*  failure mechanisms and consequences of ribbon heater tape failure

*  maintainability of ribbon heater tapes

*  flammability of insulation blanket materials and debris in cargo bays

*  effect of age, condition and contamination on the flammability of insulation blankets

*  potential for fires in inaccessible areas of an aircraft where there is a lack of fire-fighting capability /T/ Action Air Canada has taken immediate steps to inspect aircraft and deactivate affected systems and the TSB continues to investigate.

A recent belly hold fire once again raises the specter of aircraft vulnerability to conflagrations in areas not accessible by flight crews armed with portable fire extinguishing equipment. In this case, the fire was suppressed by Halon, and the incident aircraft was just 10 miles from its destination airport and emergency firefighting support upon landing.

Nevertheless, the May 13 incident involving an Air Canada B767-300 with 185 passengers and crew on board is under investigation by the Transportation Safety Board (TSB) of Canada. The case has many of the same earmarks that characterized the fatal 1998 crash of Swissair Flight 111, an MD-11, in which a runaway in-flight electrical fire in an overhead ceiling area doomed the aircraft. The TSB’s investigation of that case is in its final stages. This most recent case occurred below deck, but it is significant nonetheless as another case where electrical system safety, materials flammability, and the adequacy of fire detection and suppression are major issues.

According to a preliminary TSB account, the airplane was on descent to a landing at Toronto on a flight from Vancouver when the crew noted an aft cargo bay fire warning. They activated the built-in extinguishing system, declared an emergency, and the aircraft was met upon coming to a stop on the runway by airport firefighters. The firemen, using infrared sensing equipment, did not detect any sign of fire, so the aircraft taxied to a position just 40 feet short of the gate to allow firefighters to open the aft cargo compartment for a detailed inspection. Smoke billowed out when the door was opened. The firefighters crawled into the belly hold and discovered that the fire had been extinguished by the airplane’s Halon system.

Looking Forward Photo of the belly hold taken from the front looking aft into the same fire-damaged area. The fire was starting to spread forward, as evidenced by the distribution of burned/scorched material. There are two potable water lines shown in this photo. A metal line to fill the supply of potable water is shown running across the photo, making a right angle turn to disappear into the area where the fire started. The larger line below it, made of Teflon and wrapped in Nomex, makes a more gradual turn and is the potable water drain line. Both lines are warmed by the heater tape, which is under the gray protective tape shown spiraling around the water fill pipe above.

The charred evidence and metal structure distorted by exposure to heat suggested to TSB investigators that "an intense but relatively small fire occurred, causing significant structural damage," according to the TSB preliminary report.

The damage included two areas where the thermal/acoustic insulation blanketing was burned, an aluminum structural web had burned through completely, resulting in "significant heat distortion of the floor beam." The cargo bay does not have a floor, per se; rather, there is an aluminum webbing between the joists and rails supporting the cargo pallets. The fire consumed the aluminum web between these support members – not so much as a congealed bubble of melted aluminum was found (See photo)

"The fire was hot enough to consume aluminum, not just melt it," said TSB investigator Mike Stacey.

"They were fortunate the fire was detected early," Stacey added. The charred evidence suggests that the fire already was spreading. "It looks like the insulation blanketing provided fuel for the fire," Stacey said. Two types of insulation were installed. Metalized Tedlar was at the bottom of the cargo hold. Basically, this material lines the bottom of the pressurized hull. Non-metalized Mylar is used in areas above the bilge. Neither of these materials meets the latest radiant heat and direct flame test for insulation material flammability (see ASW, Oct. 16, 2000, p. 4).

The fire burned its way forward and also spread approximately 18 inches up the outer side of a fire liner placed in the cargo bay to contain a fire. The defense supposedly provided by that liner clearly was breached. Fortunately, the Halon was able to follow and suppress the fire, halting its increasingly dangerous spread.

The ignition source was traced to an electrical failure of a heater tape used to prevent water lines from freezing. "We believe the source of the fire was on the potable water drain line," Stacey said. Similar damage was found on other aircraft (e.g., burned insulation wrap), but they had not been significant enough to cause a fire. Air Canada took "immediate steps to inspect aircraft and deactivate affected systems," according to the TSB’s preliminary report. Investigators are looking closely at the kind of fluids and other contaminants that soiled the insulation blankets, reducing their fire resistance. The incident airplane was built in 1991; the metalized Tedlar was most likely installed after entry into service, as this material is more durable than the factory-installed insulation material, which tends not to hold up well, one source explained.

The latest case recalls the fires and damaged insulation involving heated static ports a couple of years ago on MD-80s operated by Delta Air Lines [DAL]. In those cases, too, the heat from failed electrical circuitry led to burned insulation material in the belly hold area.

The May 13 case is likely to provide added grist to the TSB’s earlier expressed concern about the need to remove flammable materials from aircraft. TSB officials maintain that if combustible materials were prohibited from use, in-flight fires would not occur (see ASW, Sept. 10, 2001, p. 1). Indeed, TSB officials attach considerable significance to the Air Canada in-flight fire. They perceive a number of major issues:

b Consequences of ribbon heater tape failures.

b The maintainability of ribbon heater tapes.

b The flammability of insulation blanket materials and the flammability of debris in cargo bays.

b The degrading effects of age, condition and contamination on the flammability of insulation blankets (i.e., making them more prone to accelerate rather than retard an in-flight fire).

b The potential for fires in inaccessible areas of an aircraft, where there is a lack of fire-fighting capability, to spread with lethal consequences. This case doubtless will help to beef up the TSB’s forthcoming report on the Swissair Flight 111 disaster and the hazard of an unmonitorable fire in inaccessible areas.

Actually, one might go further in terms of implications. Terrorists may quickly perceive the vulnerability of belly holds to caustic chemicals and flammable materials, placed in baggage as well as freight containers, the deadly combination activated by a barometric timer. The terrorist threat provides an added impetus for improving the fire protection of airliner belly holds.

The Air Canada jet was saved by the Halon, injected into the cargo bay under the pressure of inert nitrogen gas. Engines and auxiliary power units (APUs) normally feature the option of combating a fire with a second Halon injection from another engine’s bottle, should that be necessary. The absence of a second dousing shot of extinguishing Halon for belly holds may be a significant oversight. In the B767-300, three Halon bottles are plumbed to combat a fire in either the forward or the aft belly hold. Bottle 1 is supposed to extinguish the fire. After a 30-minute delay in flight, the Halon stored in Bottles 2 and 2A is metered to provide 195 minutes of ongoing fire "suppression" with a three-percent  (only)  concentration of Halon. This feature is necessary should a fire warning occur during extended twin-engine operations (ETOPS).

Burned Beam Photo taken from the rear of the incident aircraft looking forward to the damaged area. In the center of the picture, note the significant heat distortion of the aluminum floor beam in the center. The white mechanism at right is the electric power unit that moves the cargo pallets. Investigators believe the fire started in the dark area below this assembly. The burned insulation material in the lower area is metalized Tedlar. Non-metalized Mylar is the insulation blanketing used in areas above the floor, as in the material at top of the photo with the numbers scrawled on it.

However, Bottle 1 is supposed to "knock down" the fire. In the case of the B767-300, Bottles 2 and 2A not only  long-term sprinkle-supplement the Number 1 bottle during  the remainder of the flight, they are rigged to  wholly discharge  immediately upon landing, regardless of the time delay. This design feature may have had a significant impact in the Air Canada case, as the fire received the equivalent of a second "knockdown" of Halon just minutes after Bottle 1 discharged.

If the fire had broken out earlier in the flight, would the 195 minutes of suppression have been of any use if the outer skin had been pierced and the hold open to the airflow? In addition to a second-shot option, pilots might also benefit from closed circuit television (CCTV), enabling them to physically see the course of events when fire strikes in an inaccessible area. Smoke detectors, once initiated, are useless in a smoke-filled environment. A CCTV would provide pilots the ability to ensure that the fire is out. To be sure, infrared cameras would be needed for the CCTV to provide the pilots with the best capability to locate the heat of flames concealed visually by smoke. Infrared cameras are being installed in Swissair’s surviving MD-11s as part of the carrier’s "Modification Plus" program (see ASW, July 30, 2001, p. 1).

Moreover, water-misting or  galley/lavatory-water diversion, if available, would give pilots the option to "flood" the hold. Not least, simultaneously getting the power entirely off the  hold's  electrical circuits certainly would aid in killing an electrical fire. Many is the electrical fire that can get a second breath after having been doused with fire suppressant the first time. Another question is whether it would be worth the cost of the extra plumbing to build in the capability to divert engine and APU fire-bottle output into the cargo holds.

In addition, if nitrogen enriched air (NEA) is available to inert the flammable vapors in fuel tanks, the capability could also be employed to use the same NEA to dampen a belly hold fire – or a fire in virtually any remote space in the airplane.

In the Air Canada case, the stark evidence of the fire’s brief but rapacious appetite was plainly laid out, unlike the Swissair jet, which was shattered into thousands of pieces. "Fortunately, no one was killed" in the Air Canada fire, Stacey said. With the evidence so obviously at hand, he declared, "We have an opportunity to fix things." Q

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