A99Q0151 - Controlled Flight into Terrain - Régionnair Inc. - Raytheon Beech 1900D C-FLIH - Sept-Îles, Quebec - 12 August 1999
Synopsis
The Régionnair Inc. Raytheon Beech 1900D, serial number UE-347, operating as Flight GIO347, was on a scheduled flight from Port-Menier to Sept-Îles, Quebec, with two pilots and two passengers on board. The aircraft departed Port-Menier for Sept-Îles Airport at 2334 eastern daylight time (EDT). The aircraft crashed at 2357 EDT while on approach to the airport, one nautical mile short of the runway, in reported weather conditions of 200-foot ceiling and one-quarter statute mile visibility. A post-crash fire destroyed the wings, the engines, and the right midside of the fuselage. The captain was fatally injured. The first officer was seriously injured, and the two passengers received minor injuries.
Safety Action Taken (as presented in the TSB Report)
Transport Canada
On 13 August 1999, Transport Canada (TC) conducted a post-occurrence audit of Régionnair Inc. The findings of this inspection, primarily regarding training shortcomings and the lack of qualified management personnel, resulted in the suspension of the company's air operator certificate effective that date. The company's response to the identified shortcomings resulted in the reinstatement of the air operator certificate on 18 August 1999.
TC, Safety Systems, gave three crew resource management courses specifically for the company in March, August, and December 1999. Twenty-four Régionnair pilots were trained and qualified. An additional course was offered to all pilots on 15 January 2000.
Subsequent to the TSB's safety recommendation (A96-11) in 1996 to raise commercial operators' awareness of the risks associated with flight operations in marginal visual flight conditions, many of TC's national aviation safety promotional efforts, safety awareness programs, and regional education programs have focused on the issue of weather.
A combined TC/industry study group is reviewing the safety data and the issues surrounding approaches in poor weather. Regulatory recommendations concerning approach bans, in the form of a notice of proposed amendment, were submitted to the General Operating and Flight Rules Technical Committee of TC in December 1999.
TC has issued special aviation notices and aeronautical information circulars and made entries in Aeronautical Information Publication concerning global positioning system (GPS) use. TC has also published a number of articles in the Aviation Safety Letter and Aviation Safety Vortex newsletters addressing the operating limitations and safe use of GPS. Aviation Safety Letter, issue 4/2000, contains an article titled "Dangers of Flying Home-made GPS Approaches". The author warns pilots that this practice "is like playing Russian roulette with the lives of all on board".
TC, Commercial and Business Aviation, is drafting a commercial and business aviation advisory circular (CBAAC) to emphasize to operators the importance of maintaining records of pilot flight duty hours and flight hours. The CBAAC will emphasize the importance and various parties' responsibilities regarding the recording of duty and flight hours of pilots who fly for more than one operator.
Régionnair
Since the occurrence, Régionnair appointed a new director of flight operations and established a safety program. The newly selected safety officer attended a safety officers' course in October 2000. Both persons met the TC requirements for the positions.
Nav Canada
The Nav Canada Sat Nav office is working with TC and the US Federal Aviation Administration to phase in full use of GPS for all phases of flight in Canada. The Safety of Air Taxi Operations (SATOPS) Final Report recommends that TC continue to publish articles in the Aviation Safety Letter and Aviation Safety Vortex newsletters about the safe, proper use of GPS and the hazards associated with its misuse.
Safety Action Required
(as presented in the TSB Report)
Low Visibility and Low Ceiling Approaches
The Board believes that there will continue to be inadequate defences against the risks associated with pilots descending below the decision height/minimum decent altitude in an attempt to land in visibility conditions that are unsafe because of a delay in the timely implementation of an approach ban. Therefore the Board has recommended that:
The Department of Transport expedite the approach ban regulations prohibiting pilots from conducting approaches in visibility conditions that are not adequate for the approach to be conducted safely. (A02-01)
Transport Canada's response:
Transport Canada has prepared sixteen (16) Notices of Proposed Amendments (NPA 2000- 001, 002, 006, 007, 008, 009, 010, 011, 012, 106, 107, 108, 116, 117, 194, and 195 attached) to address the TSB Recommendation A02-01 concerning approach ban regulations.
These NPAs are currently under review at the Department of Justice and it is expected that the final product will be published in the June 2002 issue of the Canada Gazette. The TSB will be sent a copy of the approved version once available.
Safety Action Taken(as presented in the TSB Report)
Joint Pilot/Cabin Crew Emergency Training
Northwest Airlines has indicated that, beginning in January 1995, joint training for pilots and flight attendants will be conducted during annual recurrent training. The training will focus on communications between the flight deck and cabin, and will include in-flight fire scenarios.
911 Communications During Airport Emergency Responses
Subsequent to this occurrence, the Centre d'Urgence established a new method of operation. Specifically, 911 operators have received directions on the amount and type of information to be collected prior to initiating emergency responses to local airports.
Unilingual Evacuation Instructions
Although not required by regulation, most Canadian air carriers endeavour to provide safety briefings in both official languages. Also, some foreign carriers routinely ensure that bilingual flight attendants are on aircraft serving Quebec airports to provide bilingual safety briefings during these flights.
In July 1994, the TSB forwarded an Aviation Safety Advisory to Transport Canada (TC) highlighting the potential for delayed and/or adverse reactions to unilingual emergency instructions by passengers who do not comprehend the language of instruction. In its response, TC indicated that, with the rewriting of the Canadian Aviation Regulations, safety briefings in both official languages will become a requirement under specified circumstances. Also, since the International Civil Aviation Organization (ICAO) has no established standard regarding the language of safety announcements, TC will address this issue with ICAO.
Safety Action Required
(as presented in the TSB Report)
Passenger Service Blanket Flammability
Passenger service blankets are carried on most large air carrier aircraft and are usually stored in the overhead bins in the cabin. In addition to using the blankets for passenger comfort, several Canadian air carrier Flight Attendant Manuals instruct flight attendants to use the blankets for smothering flames on a person's clothing or seat. As demonstrated by this incident and in TSB tests, some passenger service blankets have adverse flammability characteristics even though the blanket material passed the flammability test prescribed for cabin interior materials.
In May 1994, the TSB forwarded an Aviation Safety Advisory to TC and the Cabin Safety Standards section of the FAA indicating that passenger service blankets should meet an appropriate flammability standard and that TC might wish to advise Canadian air carriers that passenger service blankets may present a fire hazard. In July 1994, using TSB information from this occurrence, the National Transportation Safety Board (NTSB) recommended that the FAA develop a fire performance test method and performance criteria (standard) for blankets supplied to commercial operators, then require those operators to use only those blankets that meet the standard (NTSB-A-94-131). At the same time, the NTSB also recommended that the Air Transport Association of America (ATA) warn association members about the flammability of blankets used for passenger comfort and urge members to replace these blankets with blankets containing more fire-resistant materials (NTSB-A-94-132).
In August 1994, the ATA response to the NTSB recommendation indicated that ATA had advised its members about the flammability of passenger service blankets. In January 1995, in response to the TSB Advisory, TC indicated that they would be reviewing the issue of blanket and pillow flammability with the FAA via an international working group and that it would be premature to advise carriers of the potential fire hazard prior to the completion of the working group's activities.
The Board understands that the international working group is considering issues such as types of fabric and flammability protection processes, effects of in-service use, and appropriateness of flammability standards. It is recognized that it may not be practical to disseminate information on these issues until discussed by the working group. However, considering how easily the folded blankets ignited and developed a molten polyester pool fire in both the occurrence and post-incident test, Canadian air carriers may wish to take interim measures based on their assessment of the hazard. Therefore, the Board recommends that:
- The Department of Transport immediately advise Canadian air carriers about the potential flammability of some passenger service blankets. (A95-14)
Transport Canada's Response:
Transport Canada Aviation has developed an Air Carrier Advisory Circular (ACAC) which advises all commercial air carriers of the potential flammability of service blankets. The ACAC will be distributed to all commercial air carriers once finalized.
A98Q0087 - In-flight fire - Landing gear well - Propair Inc. - Swearingen SA226-TC C-GQAL - Mirabel / Montréal International Airport, Quebec - 18 June 1998
Synopsis
The aircraft, a Fairchild-Swearingen Metro II (SA226-TC), registration C-GQAL, serial number TC 233, took off as Propair 420 from Dorval / Montréal International Airport, Quebec, around 0701 eastern daylight time bound for Peterborough Airport, Ontario. On board were nine passengers and two pilots. About 12 minutes after take-off, at an altitude of 12 500 feet above sea level (asl), the crew advised air traffic control (ATC) that they had a hydraulic problem and requested clearance to return to Dorval. ATC granted this request. Around 0719, at 8600 feet asl, the crew advised ATC that the left engine had been shut down because it was on fire. Around 0720, the crew decided to proceed to Mirabel / Montréal International Airport, Quebec. At 0723, the crew advised ATC that the engine fire was out. On final for Runway 24, the crew advised ATC that the left engine was again on fire. The landing gear was extended on short final, and when the aircraft was over the runway, the left wing broke upwards. The fuselage pivoted more than 90º to the left around the longitudinal axis of the aircraft and struck the ground. All 11 occupants were fatally injured.
Safety Action Taken
(as indicated in the TSB report)
On 26 October 1998, the TSB issued five recommendations covering several aspects of the investigation, as follows.
Overheating in Wheel Well and Wing
The Board believes that to help ensure the safety of the crew and the passengers on Fairchild/Swearingen SA226 and SA227 Metroliners, the definitive operating manual__the aircraft flight manual (AFM) for these aircraft__must be amended. Furthermore, both ab initio and recurrent training for aircrew on these aircraft should include instruction on the handling of overheated brakes and wheel well fires. In this vein, the Board believes that the AFM will require amendments to reflect the following, inter alia:
- the susceptibility of the brake system on Metroliners to overheating, the precautions to deal with or prevent overheating, the symptoms of potential problematic brake systems, and the fact that overheated brakes can cause wheel well fires
- that a L or R WING OVHT warning light may indicate a wheel well fire and that there are other key symptoms associated with the L or R WING OVHT light that are indicative of an on-board fire
- the actions to be followed in conjunction with the emergency procedure for wheel well and wing overheat warning light ON to effectively handle the possibility of a wheel well fire
The US Federal Aviation Administration (FAA), as the regulatory body in the State of the aircraft manufacturer, has primary responsibility for mandating and approving revisions to the AFM. On 26 October 1998, the US National Transportation Safety Board (NTSB), in coordination with the TSB, submitted six recommendations to the FAA in this regard. Transport Canada (TC) has communicated with the FAA concerning amendments to the AFM and to checklists. The Board recommended as a matter of urgency that:
Transport Canada consult with the Federal Aviation Administration regarding a timely amendment of the Aircraft Flight Manual for the Fairchild/Swearingen SA226 and SA227 Metroliner to have the Manual specify the risk of wheel well fires caused by overheated brakes, and include procedures both to mitigate this risk and address emergency situations of actual and potential wheel well fires. (A98-02)
Brake Overheat Detection and Wheel Well Vulnerability
The Fairchild/Swearingen SA226/SA227 Metroliners do not have a brake temperature monitoring or overheat detection system. Under current regulations, these systems are not required for certification. Such systems, especially in an aircraft with wheel brake systems that are susceptible to overheating, would allow aircrew to monitor the temperature of the wheel brakes and take appropriate precautions to prevent overheating or to preclude the inadvertent raising, into the wheel well, of main landing gear with overheated brakes.
As noted previously, post-accident examination of the occurrence aircraft determined that a pre-crash fire had occurred in the left main landing gear wheel well. This was shown by burned tires, melted aluminum hydraulic and fuel lines and fittings, and a fire-damaged rubber fuel crossover line. Additional damage to the wheel well, especially to the fuel and hydraulic lines, might have also resulted from bursting tires, since the wheels on the main landing gear of Fairchild/Swearingen SA226 aircraft do not incorporate fuse plugs (which melt when hot, giving a controlled release of tire pressure built up from the heat). If so, flammable fluids flowing from melted or damaged aluminum hydraulic and fuel lines, and the rubber fuel crossover line, would have further fuelled a fire.
TC issued Commercial and Business Aviation Advisory Circular (CBAAC) No. 0146, dated 16 September 1998, to alert Canadian flight crew and operators of these aircraft to the hazard associated with overheating of the brake system. CBAAC No. 0146 outlines the warnings and other possible abnormal aircraft indications associated with known Metroliner brake overheat / wheel well fires, explains the wheel well and wing overheat warning light system, specifies actions to be taken at the first indication of the wing overheat annunciator light, and highlights the susceptibility of the Metroliner brakes to overheating and the conditions for suspecting potential brake system overheating. The CBAAC also states that TC has communicated a recommendation to the aircraft manufacturer; in fact, TC communicated with the FAA regarding amendments to the AFM and to checklists.
The measures outlined in CBAAC No. 0146 and associated with the above recommendation focus on risk reduction through enhanced awareness of the hazard and improved operational practices to deal with possible or actual fires. However, the Board believes that additional preventive actions can be taken in the aircraft's systems to minimize the likelihood and severity of a fire in the wheel well. Therefore, the Board recommended that:
Transport Canada, in consultation with the Federal Aviation Administration and the aircraft manufacturer, explore options for the installation of a brake temperature or overheat detection system on Fairchild/Swearingen SA226 and SA227 aircraft; and (A98-03)
Transport Canada, in consultation with the Federal Aviation Administration and the aircraft manufacturer, explore means to protect or otherwise harden the hydraulic and fuel lines in wheel wells to minimize the damage to these lines in the event of bursting tires or wheel well fires. (A98-04)
Mixing of Hydraulic Fluids
Analysis of fluid from the accident aircraft's main and brake hydraulic systems revealed a mixture of MIL-H-83282 and MIL-H-5606 hydraulic fluids. These hydraulic fluids are nearly identical in colour and consistency. The mixture had a flashpoint of approximately 114ºC (239ºF).
The SA226 and SA227 specification originally called for MIL-H-5606, with a minimum flashpoint of 82ºC, to be used in the aircraft's main and brake hydraulic systems. However, after two Swearingen SA226-TC Metroliner II cockpit fire accidents in which the MIL-H-5606 hydraulic fluid was involved, the FAA issued Airworthiness Directive (AD) 83-19-02, applicable to certain Swearingen SA226 airplanes, including the Mirabel accident airplane. The AD required that operators drain and purge the main hydraulic and brake system reservoirs, refill them with MIL-H-83282 hydraulic fluid with a minimum flashpoint of 205ºC, and change the placards on both reservoirs to specify the MIL-H-83282 fluid. The accident aircraft was placarded in accordance with AD 83-19-02.
Current maintenance instructions state that MIL-H-83282 is to be used in the main and brake hydraulic systems of the aircraft. However, there is no reference to indicate that MIL-H-83282 is used because of the higher temperature at which its vapours will ignite or that a mixture of MIL-H-83282 and MIL-H-5606 can have a significantly lower flashpoint than the 205ºC flashpoint for pure MIL-H-83282. Given that MIL-H-5606 was the original specified fluid for SA226 and SA227 aircraft, that MIL-H-5606 and MIL-H-83282 are similar in appearance and most properties, and that there are no cautions about the consequences of using a mixture of the two fluids, the Board believes that MIL-H-5606 is being mistakenly used by some air operators and aircraft maintenance engineers as an alternative hydraulic fluid in systems requiring MIL-H-83282. Therefore, in view of the increased risk of fire occurring on Fairchild/Swearingen SA226 and SA227 aircraft resulting from the incorrect use of MIL-H-5606 hydraulic fluid, the Board recommended that:
- Transport Canada, as a matter of urgency, notify all Canadian operators of Fairchild/Swearingen SA226 and SA227 aircraft of the importance of, and requirement for, using only MIL-H-83282 hydraulic fluid in the main and brake hydraulic systems of these aircraft; and (A98-05)
- Transport Canada, in consultation with the Federal Aviation Administration and the aircraft manufacturer, review the adequacy of existing aircraft standards, procedures, manuals and maintenance practices for the Fairchild/Swearingen SA226 and SA227 aircraft with an aim to ensuring that only MIL-H-83282 hydraulic fluid is used in the main and brake hydraulic systems of these aircraft. (A98-06)
Responses to Recommendations
(as indicated in the TSB report)
General
TC concurred with recommendations A98-02, A98-03, and A98-04. TC's Aircraft Certification Branch requested an AFM amendment from the FAA to provide more direction and information on wheel well fires. TC also issued a CBAAC to all Metroliner operators in Canada. The CBAAC effectively provides information and guidance to pilots on wheel well fires.
In addition, the NTSB issued recommendations to the FAA similar to the TSB's recommendations A98-02, A98-03, and A98-04. TC forwarded the TSB recommendations to the FAA for review, comment, and action, in conjunction with review of the NTSB recommendations. The FAA's responses to these TSB recommendations are outlined below.
Response to Recommendation A98-02 (NTSB A-98-115)
Fairchild has released FAA-approved airplane flight manual changes that expand the "Wheel well and Wing overheat light on" material in Section 3, "Emergency Procedures", for the SA226 and SA227 aircraft. Subsequently, TC mandated these revisions for Canadian-registered aircraft. TC considers this recommendation closed.
Response to Recommendation A98-03 (NTSB A-98-116)
The FAA has investigated and evaluated a temperature monitoring or overheat system on the SA226 and SA227 aircraft and concluded that such an installation would be cost prohibitive.
Although this recommendation was not adopted, other action has been taken to reduce the probability of overheated brakes occurring during take-off. FAA AD 2000-17-01 was released on the 22 August 2000, with an effective date of 06 October 2000. This AD mandates compliance with Fairchild service bulletins (SBs) 227-32-017 and 226-32-049 to modify the parking brake system and with BFGoodrich SB 1498 to revise the inspection brake wear and clearance limits. Additionally, the FAA released AD 2001-20-14, which mandates Fairchild SBs 226-26-003 and 227-26-002. Effective after 21 November 2001, this AD is designed to correct potential brake shuttle valve problems, which could cause the brake assembly to drag and overheat. These actions are intended to prevent brake overheating, not to detect brake overheating. TC has mandated these ADs for Canadian-registered aircraft and considers this recommendation closed.
Response to Recommendation A98-04 (NTSB A-98-118)
TC advises that the FAA has responded by issuing ADs 2000-14-01 and 2001-20-14. These ADs incorporate modifications to the parking brake system, establish brake wear and clearance limits, replace the brake shuttle valve, replace a rubber fuel hose with a metal device, and install a shield over the hydraulic lines. TC mandated the ADs for Canadian-registered aircraft.
Response to Recommendation A98-05
TC concurred with recommendation A98-05 and issued an airworthiness notice titled "Hazards of Incorrectly Identifying or Mixing Aircraft Fluids" to the aviation industry.
Response to Recommendation A98-06
TC concurred with recommendation A98-06 and consulted with the FAA regarding the adequacy of existing aircraft standards, procedures, manuals, and maintenance practices for the Fairchild/Swearingen SA226 and SA227 aircraft. The aim of this review was to ensure that only the specified hydraulic fluid (MIL-H-83282), where usage of this fluid type applies, is used in the hydraulic systems of these aircraft.
TC confirms that Fairchild, in coordination with the FAA, has amended the SA226 and SA227 maintenance manuals to include warnings that reinforce the prohibition of fluid mixing.
The FAA had earlier issued AD 83-19-02, which required purging lower flashpoint hydraulic fluid from the aircraft's hydraulic systems and substituting higher flashpoint MIL-H-83282 hydraulic fluid. The AD also required installation of a placard specifying that only MIL-H-83282 fluid be used
Safety Action Required
(as indicated in the TSB report)
Brake System Pressure Warning Indicator
The Propair crew took off unaware that residual brake pressure remained on the left brake system during the taxi and the take-off roll. During the take-off roll, the heat generated by the friction of the left dragging brake increased exponentially. This extreme heat resulted in brake seal failure, brake fluid leak on the hot brake components, and ignition and fire in the wheel well, eventually causing failure of the wing structure in flight.
From 1983 to present, a large number of incidents and a few accidents involving landing gear failures, tire failures, flat tires, wheel fires, and loss of control on ground have been reported for these types of aircraft. Of this number, 62 incidents and 3 accidents involving circumstances similar to those found in this accident have been reported. Some of the incidents and accidents had the potential to result in a catastrophe similar to this accident.
For the most part, the Board's recommendations resulting from this occurrence were directed at minimizing the consequences of such an occurrence and at providing better information to the crews about recognizing the symptoms of a wheel well fire. However, one recommendation dealt with the installation of a brake temperature system to provide timely overheat information to the crew. This recommendation was negatively received as being too costly to implement in view of the expected remaining life of the aircraft.
In spite of the risk controls implemented to date, flight crews are still not provided with an unambiguous alert of a dragging brake condition caused by residual hydraulic pressure in the brake system. Failure to identify and warn the crew about a dragging brake in a timely manner will result in a continued high risk of fire with possible ensuing loss of life and property. The brake system manufacturer has indicated that a brake pressure cockpit indicator for each wheel brake system is feasible.
Therefore, the Board recommends that:
- Transport Canada, the United States Federal Aviation Administration, and Fairchild explore options for SA226 and SA227 aircraft to be equipped with a brake pressure warning indicator for each main wheel brake system. (A02-03)
Transport Canada's Response:
During the course of investigating solutions in response to the TSB Interim Recommendation A98-03 regarding brake overheat detection issued on October 26, 1998, the brake system manufacturer indicated that a brake pressure indicator for each wheel brake system installed in the cockpit would be feasible. This system would alert the crew that, due to the residual hydraulic pressure in the brake system, a dragging brake condition might exist.
The Federal Aviation Administration (FAA) did not implement recommendation A98-03, however, the FAA initiated another course of action, which was to reduce the probability of overheated brakes occurring during aircraft takeoff. Transport Canada also believes that the most effective safety actions can be achieved by providing safety barriers to preclude the occurrence of brake overheating rather than a system to detect break overheat conditions. Attached are updates to actions taken in response to TSB Interim Recommendations A98-03 and A98-04.
Given the TSB position that the flight crew should be provided with the unambiguous warning of a dragging brake condition, and considering the vendor’s opinion that the cockpit brake pressure indicator is feasible, Transport Canada has requested the FAA to contact the aircraft manufacturer and the brake vendor to investigate the feasibility of installing a brake pressure warning indication system in the Fairchild SA226 and SA227 airplanes as recommended by the TSB.
A02O0123 - Air Safety Recommendations - In-Flight Fire Aboard Air Canada 767-300 - 13 May 2002
Background
On 13 May 2002, Air Canada Flight 116, a Boeing 767-300, registration C-GHML, with eight crew members and 177 passengers on board, was arriving at Toronto Lester B. Pearson International Airport on a flight from Vancouver, British Columbia. At about 1732 EDT, while on final approach, 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. Although the fire indication went out approximately 50 seconds after activation of the fire extinguishers, a slight smell of smoke continued to be noticed by the cabin crew and flight crew. Flight 116 landed and stopped on the runway to allow a preliminary examination of the aircraft by airport firefighters. Firefighters, using infrared sensing equipment, did not detect any sign of heat from the fire. The aircraft was taxied 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. The emergency situation was secured and passengers were deplaned using portable stairs. A Transportation Safety Board of Canada (TSB) investigation (A02O0123) is ongoing.
To date, the investigation has determined that an Electrofilm ® brand heater ribbon, used to prevent the potable water drain/supply line from freezing, failed and exhibited signs of overheating and arcing in the vicinity of station 1395. The heater ribbon, which was spiral wrapped around the water line, burned through both the protective tape used to hold the heater ribbon in place and the Rubatex ® foam thermal insulation material wrapped on top of the protective tape, igniting the non-metalized Polyethylene Teraphthalate (PET)-covering (Mylar®)of the thermal acoustic insulation blanket mounted on the vertical web of the floor beam.
Floor beam damage.
The fire then spread to the PET insulation blanket covering on the bottom of the pressurized hull and ignited debris in the non-fully enclosed floor area of the aft cargo compartment. The fire became self-propagating, burning its way forward, inboard and outboard, spreading approximately 46 centimetres (18 inches) up the right side wall of the aircraft before it was extinguished by halon from the fire extinguishing system. Heat from the fire was intense enough to burn holes through the aluminum web of a floor beam and significantly distort the top cap (chord) of the beam structure.
Heater ribbons are used on the Boeing 767 and other aircraft to prevent water lines from freezing. They generally consist of a number of heating elements encased in an insulating material such as vinyl, rubber (Ethylene Propylene Diene Terpolymer, EPDM) or silicone rubber. Typically, a heater ribbon system is thermostatically controlled with power being applied, both on the ground and in the air, when the water temperature in the line approaches freezing. In C-GHML, the aft cargo compartment ribbon heater control thermostat was located 85 inches aft of station 1395, below the bulk cargo floor. The thermostat was set to turn the ribbon heaters on when the ambient air temperature reached 50 F and off at 60 F. Although the exact failure mechanism of the heater ribbon on the occurrence aircraft is still under investigation, examination of other failed heater ribbons suggests that an internal short or arcing event between two of the elements occurred.
Discolouration, consistent with overheating while in service, was observed on some intact heater ribbons on C-GHML and on numerous other aircraft examined by investigators and Air Canada maintenance personnel. Overheating can cause the heater ribbon insulating material to degrade. This degradation may contribute, in some instances, to an internal short or arcing event between two of the heating elements, which can cause the insulating material between the elements to carbonise and/or burn. A reduction of material separating the elements could allow them to migrate towards each other and arc again.
Heater Ribbon Installation
TSB has identified safety deficiencies related to the potential for heater ribbon installations to start a fire, and the potential for contaminated thermal acoustic insulation blankets and debris in the vicinity of heater ribbons to propagate a fire
Failed Heater Ribbon
Potential for Water Line Ribbon Heater
Installation Failures to Start a Fire
In addition to the fire damage associated with the occurrence flight, TSB investigators found burned Cox and Company heater ribbon, protective tape and Rubatex ® foam insulation behind the aft wall of the aft cargo area on the occurrence aircraft. Although a self-propagating fire had not occurred, the area had become hot enough to burn through the insulation wrap and a nearby plastic clamp.
Another Air Canada Boeing 767-300 was examined by TSB investigators, and burned Cox and Company heater ribbon was found in the vicinity of station 1395. In this case, the water line was wrapped in a "jacket" that consisted of an insulation blanket covered on one side with PET and on the other side with Bradley BF-6620, a polymer coated fabric. The "jacket" was held in place with a "hook and loop" fastener system similar to Velcro ®. The failure had burned a hole through the "jacket". Further examination of the same aircraft revealed another overheated Cox and Company heater ribbon behind a side wall panel in the aft cargo compartment.
Air Canada conducted an inspection of its fleet of fifty-five Boeing 767-200 and 767-300 aircraft. Numerous occurrences of overheated / burned heater ribbons were found in both visually accessible areas and "hidden" areas, such as behind wall and floor panels. Thirty of the aircraft were found to have defective heater ribbons (including both Cox and Company and Electrofilm ® brand), resulting in 66 ribbons being either removed or de-activated.
Between June 1985 and June 2002, operators of Boeing aircraft made a total of 67 reports to Boeing of heater ribbon failures where thermal degradation was evident. Charred insulation material was identified in many of the reports. Structural damage from fire had occurred in at least two cases. In some instances, water had leaked from melted water lines which, in one case, led to failure of an engine indication and crew alerting system (EICAS) computer.
Service Difficulty Reports USA 1999042300717, USA 1988040800197, AUS 19990967, and AUS 19991248 all report burned heater ribbons. Two of the reports involved Boeing 767s and two involved Boeing 747s. There have been no previous TSB safety communications concerning heater ribbons, and heater ribbons have not been addressed in TSB occurrence reports or in the TSB occurrence database.
The above information concerning heater ribbon failures supports the existence of an unsafe condition relating to the potential for water line heater ribbon installations to provide a source of ignition, combined with the availability of flammable materials in sufficiently close proximity to the ignition source to ignite.
Heater ribbons are used extensively in transport category aircraft, including Boeing 707, 727, 737, 747, 757 and 767 series and Boeing (Douglas) DC-9, DC-10, and MD-11 aircraft. In-line water heaters and water lines that contain integral heating elements are more prevalent on newer generation aircraft. Although historical data is limited, the possible failure modes of in-line and integral water heaters are considered to present a much lower threat of ignition than those associated with external heater ribbons.
Ribbon heaters manufactured for use in aircraft must comply with the requirements of US Federal Aviation Regulations (FAR) 25.853 and Appendix F to Part 25. These FARs specify the flammability characteristics of materials used in transport category aircraft. The ribbon heaters installed in C-GHML met these requirements; however, the FAR requirements may not adequately address the issue of fires associated with failures within specific heater ribbon installations.
The heater ribbon was protected by a circuit breaker (CB); however, the CB did not open. Not all electrical fault situations will cause a CB to open. The CB is designed to protect the circuit when the temperature and time duration characteristics of the over-current condition exceed the CB's design limits. Subsequent to the cargo bay fire, Air Canada took immediate action to reduce the risk of heater ribbon fires. An inspection of specified areas of the 767 aircraft fleet was conducted and defective heater ribbons in these areas were removed or de-activated. However, not all of the heater ribbons in the 767 aircraft were examined, nor were any heater ribbons examined on other aircraft types in Air Canada's fleet.
Air Canada amended their Boeing 767 Service Check (96 hour maximum interval) to include a requirement to remove all debris found below the floor level of both the forward and aft cargo compartments. They also enhanced their zonal General Visual Inspection (GVI) to ensure inspection of ribbon heaters during the scheduled 24-month "M" checks.
As a result of the fire on aircraft C-GHML, Boeing released Alert Service Bulletin (ASB) 767-30A0037 on 28 May 2002 to provide instructions and corrective action necessary to avoid a possible fire in the forward and aft cargo areas. The bulletin is applicable to all 767-200, 300 and 300F aircraft with non-fully enclosed cargo floors in the lower cargo areas. The bulletin called for operators to take the following actions with respect to visually accessible potable water and drain lines located under the cargo floor in the forward and aft cargo areas:
- Remove all foreign object debris (FOD) found on, near or around the potable water and drain line.
- Inspect all heater ribbons on the potable water and drain lines for excessive heat damage.
- Inspect all heater ribbons on the potable water and drain lines for damaged or missing protective tape.
- Replace heater ribbon and add protective tape, if necessary.
On 07 June 2002, the Federal Aviation Administration (FAA) issued Airworthiness Directive (AD) 2002-11-11 which reflected Boeing's ASB. The AD indicated that action associated with the AD is considered interim action until final action is identified, at which time the FAA may consider further rule-making. Action taken in accordance with the ASB and the AD should reduce the risk of fires associated with heater ribbons, but they do not adequately defend against risk in a number of areas:
- They provide for a one time inspection only. Unsafe conditions that occur in the future could go undetected.
- Action is not required to identify and remove damaged or failed heater ribbons that do not show signs of excessive heat damage. Consequently, the risk of these heater ribbons starting a fire will not be addressed by the ASB and AD. Similarly, the ASB and AD do not address the risks associated with heater ribbons that do not appear heat damaged but fail to pass a continuity check.
- Action is not required to inspect heater ribbon that is covered in Rubatex ® foam insulation or to inspect Rubatex ® foam insulation that is covered in protective tape. Consequently, heat damage in these uninspected areas will not be found and a damaged heater ribbon could start a fire. The TSB investigation has found numerous examples of heat damaged heater ribbon and Rubatex ® foam that were hidden from view.
- Action is not required for non-visually accessible areas that contain heater ribbons. The TSB investigation found burnt heater ribbons in these areas. Consequently, risks associated with heater ribbon fires starting in these areas will not be addressed.
- The required action is only applicable to 767-200, 300 and 300F aircraft. Because the unsafe condition exists on other types of aircraft, the risk of heater ribbon fires on these other types remains.
- The ASB and AD caution against having less than one inch (2.54 centimetres) between the heater ribbon and any fuselage insulation. Although Rubatex ® foam is commonly wrapped over the heater ribbons, there is no requirement to change existing heater ribbon installations. Consequently, the ASB and AD may not effectively reduce the risk of heater ribbon igniting Rubatex ® foam.
On 15 July 2002, Transport Canada (TC) sent a letter to the Manager, Seattle Aircraft Certification Office FAA, expressing concern regarding the AD. The letter states:
Transport Canada understands that heater tapes are used in numerous other areas of the aircraft and is concerned that the subject AD does not address those areas. In addition, we are also concerned that the one time inspection and replacement of defective heater tapes (with new parts that are the same) called for by the subject AD will not eliminate the known ignition source because replacement heater tapes could fail in the same manner.
While TC expressed concern, they have not yet taken any independent action.
Widespread use of heater ribbons on transport category aircraft exposes the travelling public to the risks associated with heater ribbon fires. Recent actions taken to reduce these risks are not comprehensive and do not address the risk in the long term. Consequently there remains inadequate defences against heater ribbon installations starting a fire, therefore the Board recommends that:
The Department of Transport take action to reduce the short term risk and eliminate the long term risk , of heater ribbon installation failures starting fires, and coordinate and encourage a similar response from other appropriate regulatory authorities. (A02-04)
General Response A02-04 and A02-05
In an effort to better understand the risks associated with the safety concerns underlying the TSB recommendations, and to identify any safety action required, Transport Canada (TC) is subjecting these concerns to a risk management process. The process is based on the Canadian Standards Association, Standard Q850. This six step process provides a guideline that will aid decision-makers in identifying, analyzing, evaluating and controlling all types of risks, including safety and health. A key part of the process is involving and consulting interested parties. Our preliminary assessment has determined that it is necessary to involve Transport Canada subject matter experts, as well as members from the TSB, Air Canada, United States Federal Aviation Administration (FAA) and Boeing.
This process is consistent with TC’s Civil Aviation philosophy of a “shared commitment to safety”.
The significant benefits to using this decision process to deal with risk issues include:
- Ensuring that all aspects of the risk problem are identified and considered when making decisions;
- Ensuring that the legitimate interests of all affected stakeholders are considered;
- Providing a comprehensive documentation of the decision process;
- Making decisions easier to explain;
- Providing a standardized set of terminology to describe risk issues and contribute to better communication about issues;
- Providing significant savings in time and money; and
- Explicitly identifying areas of uncertainty.
This assessment process has already started and is planned to be completed by mid 2003.
Transport Canada's Response to A02-04:
As an interim response, the FAA issued Airworthiness Directive 2002-11-11 requiring the performance of a one-time general visual inspection for Foreign Object Debris or contamination in visually accessible areas on or near potable water and drain lines and for discrepancies of potable water and drain lines located below the cargo floor in the non-fully enclosed forward and aft cargo compartments, in accordance with Boeing Alert Service Bulletin 767-30A0037, dated May 28, 2002.
Short Term Risk Action
TC’s Aircraft Certification Branch, Continuing Airworthiness Division is working closely with the FAA to determine if this interim action is required for other model types that use similar heater tapes.
On December 27, 2002 TC submitted a letter to the FAA and the manufacturer of the Boeing 767 aircraft requesting that a review of the initial development of Maintenance Significant Items, which preceded the B767 Maintenance Review Board analysis, be performed. Should this review be found inadequate in light of the incident on December 20, 2002 at Edmonton International Airport involving an Air Canada Boeing 767-200 aircraft, it was requested that a complete re-analysis of the system is done ensuring that all failure modes are included.
Boeing has been asked to take into consideration the overheating/arcing failure mode combined with combustible contaminants, which may result in a fire. In addition, a request for a review of the installation instructions of the heater ribbon tape and the configuration of the related electrical circuit, including the circuit breaker, will be made.
TC contacted other foreign civil aviation authorities in January 2003 and requested their support in assessing the potential failure for similar heater ribbon installations on type certified aircraft for which they are the responsible design authority. TC will share this information with the TSB once it is available.
Long Term Risk Action
TC is awaiting a detailed report from TSB to better understand the cause of this heater ribbon’s failure so that appropriate long-term actions can be identified. In the meantime, TC is working closely with the FAA to determine corrective actions required to address this problem. Bombardier has been requested to provide TC with information regarding the type of heater tapes installed on aircraft for which they are the type certificate holder. TC is awaiting Bombardier’s response.
TC will evaluate all pending responses in determination of a future course of action in conjunction with the Risk Management Process highlighted in the general response above.
Potential for Contaminated Thermal Acoustic
Insulation Blankets and Debris to Propagate a Fire
During inspection of the occurrence aircraft and other 767 aircraft, TSB found contaminated insulation blankets and debris in all cargo compartments with open floors. Also, a considerable amount of blanket contamination in the form of dust, dirt, and lint was found under and behind panels in areas that are not readily accessible without the removal of panels. Subsequent to the occurrence, Air Canada examined the open forward and aft cargo areas of its 767 aircraft. A general clean-up of debris found in these areas was carried out. This action however did not address the contaminated blankets.
Contaminated thermal acoustic insulation blankets, as well as debris, in the vicinity of heater ribbon, provided fuel for the fire. For this occurrence, debris consisted of paper, candy wrappers, Styrofoam packing peanuts, small polyethylene beads, and rubber powder from a power drive unit. Samples of the burnt PET covered insulation blankets were analysed for the presence of fire accelerants. An isoparaffin solvent was detected which bore a resemblance to a product with the brand name ISOPAR L.
Debris and burned insulation blanket
A somewhat similar product is marketed under the brand name SOLTROL. These products are used for parts cleaning and degreasing applications, as well as for solvents in inks, paints, and agrochemical formulations, such as pesticides. ISOPAR L is a clear, colourless, combustible liquid. The liquid readily forms a flammable mixture with a flash point of 66 C (150 F). This product may have originated from sources such as aircraft cargo, luggage, recent repair/maintenance activities, or from pesticide products (the occurrence aircraft had operated in South America and may have been exposed to pesticides in association with operations in a tropical environment). The presence of the ISOPAR L contaminant would create a significant heat release once ignited. The relatively high temperature, localized fire damage observed on the floor beam web of the occurrence aircraft is consistent with a post-fire effect from the ISOPAR L alone, and/or in combination with combustible debris. It is plausible that liquid(s) might have migrated into the fibreglass batting of the thermal acoustical insulation blankets through an opening, or tear in the outer cover, or might have wetted surfaces between the airframe and the exterior of the insulation blankets. An electrical heater ribbon arcing event is considered to be a potential ignition source for any of the combustible liquid(s) in question.
Contaminated thermal acoustic insulation blankets have fuelled aircraft fires on other occasions. A Lan Chile Airlines aircraft (Miami, Florida; B767-375ER; 28 January 2002) had a fire in the forward (lower) cargo compartment which was fuelled by contaminated insulation blankets. These insulation blankets showed significant signs of contamination and wear. A Delta Airlines aircraft (Goose Bay, Labrador; Lockheed L1011; 17 March 1991) had a fire under the cabin floor area on the aft left side of the aircraft. A factor contributing to the severity of the fire was the large accumulation of dust and lint on aircraft components including insulation blankets in the area. As evidenced by Swissair 111, a self-propagating fire on board a transport category aircraft can have catastrophic results.
It is likely that many large transport aircraft contain sufficient amounts of contaminated thermal acoustic insulation blankets, dust, lint, and debris to sustain a fire.
In 1991, following an occurrence involving a fire in a Lockheed L1011 (TSB report A91A0053 refers), TSB issued a Safety Advisory (A910106) concerning the fire hazard associated with lint accumulation. The advisory suggested that TC notify maintenance inspectors and operators of transport category aircraft of the fire hazard and require that maintenance procedures be amended as required to ensure inspection and cleaning of areas where lint and debris can accumulate. In response, TC issued Service Difficulty Advisory AV-92-04 on 10 April 1992, which, in part, recommended that whenever planned inspections allow, an inspection be carried out for accumulation of lint, dust and cabin debris, and that visible accumulations be cleaned out to remove the fire hazards presented by them. In the United States, the National Transportation Safety Board (NTSB) issued recommendations A-91-71 and A-91-72 to address the safety deficiencies identified in the TSB occurrence investigation. NTSB recommended that the FAA notify principal maintenance inspectors and operators of transport category aircraft of the fire hazard posed by accumulations of lint and other debris on wire bundles. They also recommended that FAA require that transport category aircraft manufacturers and airlines amend maintenance manuals as necessary to ensure thorough inspection and cleaning of areas where lint and other debris may accumulate and pose a potential fire hazard. In response to the recommendations, FAA issued an airworthiness inspector's handbook bulletin, entitled "Origin and Propagation of Inaccessible Aircraft Fire Under Inflight Airflow Conditions". The bulletin provides information on the potential safety hazard applicable to all transport category aircraft from the accumulation of lint and other debris on wire bundles. It also requests that principal maintenance inspectors disseminate this information to all operators of transport category aircraft and review their operators' maintenance programs to ensure that they include inspection of aircraft wiring and removal of contaminants, especially in accessible areas.
In March 1998, as a result of a fire in a cargo compartment of a 747-200 freighter, Boeing issued service letters for all its aircraft models (Multi-Model Service-Related Problem 25-0103). An investigation by Boeing revealed that the presence of corrosion inhibiting compounds may have contributed to the fire, and could have been the reason the fire was not self-extinguishing. The investigation also looked at the accumulation of dust, lint, and other debris on insulation blankets in the outboard sections of the passenger/cargo compartment, and concluded that it was conceivable that a large buildup of contaminants on these blankets could ignite as a result of a high temperature source. The service letter informed operators that applicable Boeing manuals would be revised to address the effects of corrosion-inhibiting compound and other materials on the flammability of aircraft insulation blankets. It also informed operators that Boeing would provide presentations on this subject at future airline conferences to increase airline awareness. Operators were advised to increase attention to periodic inspections and cleaning of aircraft during maintenance to avoid insulation blanket contamination, and to remove foreign materials.
The issue of flammability of non-contaminated insulation blanket material is also of significant concern. The TSB issued safety recommendations concerning flammability test criteria (A99-07 and A99-08), and material flammability standards (A01-02 to A01-04) in association with the Swissair 111 accident investigation (A98H0003). The recommendations, however, did not specifically address the fire hazards associated with contaminated insulation materials, dust, lint or debris.
On 28 September 2000, FAA issued Flight Standards Information Bulletin for Airworthiness (FSAW) 00-09, entitled Special Emphasis Inspection on Contamination of Thermal/Acoustic Insulation. As well, on 08 November 2001, TC published Maintenance Staff Instruction (MSI) #42, Procedures for the Inspection of Thermal/Acoustic Insulation During Heavy Maintenance Checks for Contamination, which reflected the FAA requirements of FSAW 00-09. Recognizing that the flammability of most materials can change if the materials are contaminated, and that contamination may be in the form of lint, dust, grease, etc., which can increase the material's susceptibility to ignition and flame propagation, the FSAW and MSI require specific action on the part of Principal Maintenance Inspectors (PMIs) with responsibility for 14 CFR parts 121 and 125 operators. PMIs should ensure that the operator has established procedures in their approved maintenance program for the inspection of contamination on thermal/acoustic insulation during heavy maintenance checks. If the operator discovers contamination of the insulation, the operator should take corrective action, i.e., cleaning or replacement of the insulation as appropriate. As evidenced by the recent Air Canada and Lan Chile 767 cargo area fires, blanket contamination has persisted.
TC raised the issue of contamination at the International Aircraft Materials Fire Test Working Group. A Task Group has been formed to address this issue.
Air Canada's campaign to clean up debris will reduce the risk of readily available fuel. However; it will not reduce the risk of contaminated insulation blankets fuelling fires. The risk will not be reduced in those areas of Air Canada's 767s that were not inspected or in other aircraft types in Air Canada's fleet. Also, the risk will not be reduced in the long term.
The cargo area fire detection and suppression system did prove effective in this occurrence. The primary function of the system is to protect against the spread of fires outside the cargo compartment by suppressing the fire and keeping it in the cargo compartment. It is designed to do this until the aircraft can be landed. The cargo liner provides the last line of defence. When the cargo area fire suppression system on the 767 is armed, electrical power is cut to the galleys and some systems in the cargo area, but not the heater ribbons. Failure of a heater ribbon could thus continue to provide a source of ignition.
Although ASB 767-30A0037 and associated AD 2002-11-11 reduce the risk that a heater ribbon fire will propagate, they are not comprehensive defences for a number of reasons:
- They provide for a one time inspection only. Unsafe conditions that occur in the future could go undetected.
- Action is not required for areas that contain heater ribbons that are not visually accessible. The TSB investigation of this occurrence indicates that areas that are not visually accessible often contain a considerable amount of dust, dirt, and lint.
- Consequently, risks associated with heater ribbon fire will still exist for these areas.
- The required action is only applicable to 767-200, 300 and 300F aircraft. Because the unsafe condition exists on other types of aircraft, the risk of fuelling heater ribbon fires on these other types remains.
The wide spread existence of contaminated thermal acoustic insulation materials and debris on transport category aircraft exposes the travelling public to the risk of a self propagating fire. Recent actions taken to reduce these risks are not comprehensive and do not adequately address risk in the long term. Consequently, there remains inadequate defences against contaminated insulation materials and debris propagating a fire, therefore the Board recommends that:
The Department of Transport take action to reduce the short term risk and eliminate the long term risk, of contaminated insulation materials and debris propagating fires, and coordinate and encourage a similar response from other appropriate regulatory authorities. (A02-05)
Transport Canada's Response to A02-05
Short Term Risk Action
The current regulations require that, with respect to thermal/acoustic insulation, an applicant need only demonstrate compliance to Airworthiness Manual (AWM) 525.853(a). This requirement, Appendix F Part 1 (a)(1)(ii) provides the test method details and acceptance criteria. The samples used in the test are new material. There is no requirement to test the samples in any kind of aged or contaminated state.
TC recognized the potential for contamination to negatively affect the flame propagation characteristics of thermal/acoustic insulation materials; accordingly, on November 8, 2001, TC published Maintenance Staff Instruction (MSI) #42, ‘Procedures for the Inspection of Thermal/Acoustic Insulation During Heavy Maintenance Checks for Contamination’. The MSI requires that Primary Maintenance Inspectors ensure that operators of large transport category airplanes have established procedures in their approved Maintenance Schedule for the inspection of thermal/acoustical insulation during heavy maintenance checks.
In addition, TC has raised the issue at the International Aircraft Materials Fire Test Working Group. A Task Group (TG) has been formed and work has already been initiated to review the subject and develop potential means for mitigation. As a first step, the TG is focusing on identifying ‘controllable’ contaminants (i.e. those that are ‘normally’ used) in three main areas: design/construction, maintenance, and service. The purpose is to ascertain their potential effect on flame propagation, with the goal of establishing criteria which would cater for such effects at the outset, i.e. at the certification stage. It is clear that this approach, which will require extensive testing, will not be able to address ‘uncontrolled’ substances/unknown spills (nor all possible ‘controllable’ substances), and that, given the wide range of materials and possible contaminants (both ‘controllable’ and ‘uncontrollable’), maintenance and operational actions to reduce/correct the incidence of detrimental contamination, will need to be taken.
In the short term, the actions taken as a result of the MSI may lead to Canadian operators discovering contamination of the insulation, and taking follow-up corrective action, i.e. cleaning or replacement of the insulation, as appropriate.
Long Term Risk Action
TC has recognized the requirement to identify/develop “Harmonized International Standards” applicable to materials and material flammability that will address the aspects associated with material composition and the effects of contamination that will minimize the potential risks.
TC is working with the Aging Transport Rule Making Body on the Equalized Zonal Maintenance Program (EZAP) to implement an inspection program in wiring areas to remove debris.
The Risk Management Process described in the general response above will identify and quantify specific risk issues. This process will then lead to action plans and completion targets to be developed and implemented to reduce or mitigate these risks.
Should you require further information, please contact Aviation Safety Analysis at asi-rsa@tc.gc.ca