Communiqués

TSB # A 14/98

(For release 26 October 1998)

(Hull, Quebec) - As a result of its on-going investigations into a fatal accident last June at Mirabel International Airport involving a Fairchild/Swearingen Metroliner II, operated by Propair Inc., the Transportation Safety Board of Canada (TSB) has identified several safety deficiencies and has issued five interim aviation safety recommendations.

Examination of the wreckage revealed extensive pre-crash fire damage to the Propair plane's left wheel well. Specifically, the examination found overheated left brake assemblies, burned tires, melted aluminum hydraulic and fuel lines and fittings, and a fire-damaged rubber fuel crossover line. Overheated left brake assemblies could have provided an ignition source for a wheel well fire.

There have been numerous service difficulty reports of overheated brakes on Metroliners equipped with the same brake assemblies as those on the Propair plane. Seven reports made specific reference to fires or the burning of tires or aircraft components and systems. In addition, there have been two occurrences where overheated brakes on Metroliners have caused major airborne fires. In these two accidents, the aircrews were not aware that their aircraft had overheated brakes and raised the landing gear with the overheated brakes into the wheel wells after takeoff, creating the potential for an onboard fire. Furthermore, flight crews have demonstrated some confusion with respect to the detection systems provided for wheel well and wing overheat conditions.

Fairchild/Swearingen SA226/SA227 Metroliners do not have a brake temperature monitoring or overheat detection system and under current regulations these systems are not required for certification.

The TSB's examination of the accident aircraft wreckage shows that flammable fluids flowing from melted or damaged aluminum hydraulic or fuel lines or from the rubber fuel crossover line may have added to the intensity of the fire.

In addition, the TSB's analysis of fluid from the Propair aircraft's main and brake hydraulic systems revealed a mixture of hydraulic fluids of two different types. These hydraulic fluids are almost identical in colour and consistency. However, when mixed, their flash point is significantly below the rated flash point of the newly required fluid. Since there are no warnings to maintenance personnel on the consequences of using a mixture of the two fluids, the TSB believes that hydraulic fluid of the wrong specifications is being mistakenly used as an alternate hydraulic fluid to the one specified, creating an increased risk of fire.

The TSB is continuing its investigation into the accident and the National Transportation Safety Board (NTSB) of the United States, as the accredited representative of the state of the aircraft manufacturer, is assisting with the investigation under the provisions of Annex 13 to the Convention on International Civil Aviation. Based upon the investigation's preliminary findings, both Safety Boards believe there are several safety issues that need to be addressed at this time.

Transport Canada has already issued an advisory to alert Canadian flight crews and operators of Canadian Metroliners to the hazards associated with the overheating of brakes on Fairchild/Swearingen SA226 and SA227 Metroliners aircraft. Nevertheless, the TSB believes that further safety action is urgently required and has made recommendations to the Department of Transport to address safety deficiencies in the following areas:

The need for a timely amendment to the Aircraft Flight Manual for the Fairchild/Swearingen SA 226 and SA227 Metroliner aircraft with respect to the risk of wheel well fires caused by overheated brakes.

The adequacy of protection against fires in wheel wells in terms of overheat detection systems and/or making hydraulic and fuel lines passing through wheel wells more resistant to damage from bursting tires or wheel well fires.

Inadequate understanding by operators of these types of aircraft of the risks of using other than the specified type of hydraulic fluid.

The TSB and NTSB have liaised closely in developing independent, yet mutually supportive, recommendations that include actions which could be quickly implemented to reduce the risks to the safety of persons operating and flying in Fairchild/Swearingen SA226 and SA227 Metroliners.

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.

-(30)-

---

INTERIM AIR SAFETY RECOMMENDATIONS

DATE ISSUED: 21 October 1998
FORWARDED TO:

The Honourable David Michael Collenette, P.C., M.P.
Minister of Transport

SUBJECT: Overheating of Brakes/Wheel Well Fires

Background

On 18 June 1998, a Fairchild/Swearingen SA226-TC Metroliner II aeroplane,⁽¹⁾ C-GQAL, operated by Propair, Inc., crashed after the left wing failed during an emergency landing at Mirabel Airport near Montreal, Quebec (TSB occurrence A98Q0087 refers). Earlier, after departing from Montreal's Dorval Airport at 0701 eastern daylight time (EDT) and climbing through 12 500 feet above sea level (ASL), the flight crew had reported a loss of hydraulic pressure and, subsequently, a fire on the left side of the aircraft. The pilot had shut down the left engine and declared an emergency. As a result of the accident, the aircraft was destroyed and the two crew members and nine passengers sustained fatal injuries. The flight was operating as a charter from Montreal to Peterborough, Ontario.

The Transportation Safety Board (TSB) of Canada is conducting an investigation into this occurrence. The National Transportation Safety Board (NTSB) of the United States, as the accredited representative of the state of the aircraft manufacturer, is participating under the provisions of Annex 13 to the Convention on International Civil Aviation.

The investigation is ongoing; however, based upon the preliminary findings of the investigation, the Safety Boards of both Canada and the United States believe that there are several safety issues that need to be addressed at this time. In this regard, the TSB and NTSB have liaised closely in developing independent, yet mutually supportive recommendations that include actions which could be quickly implemented to reduce the risks to the safety of persons operating and flying in Fairchild/Swearingen SA226 and SA227 Metroliners.

The investigation has indicated that during the takeoff roll, the crew apparently had to deal with an aircraft veer towards the left side of the runway. Then, approximately 12 minutes later, the crew advised the air traffic controller that the aircraft had a hydraulic problem, and requested a return to the Dorval airport. A warning light for a left wing bleed-air overheat condition subsequently came on and, at 0719, as the aircraft was descending through 8 600 feet, the crew reported to air traffic control that the left engine of the aircraft had been shut down and there was a fire in the left engine. The flight was then cleared to the Mirabel Airport. At 0723, as the aircraft descended through 3 500 feet, the crew advised that there was no more fire. However, while executing the vectored approach to runway 24 at Mirabel, the pilot reported that the fire had resumed. The landing gear was extended after the aircraft descended through 1 000 feet; shortly thereafter, the left wing failed.

Examination of the wreckage revealed extensive pre-crash fire damage to the left main landing gear (MLG) wheel well. The left wheel well contained, among other components, the hydraulic power pack, main landing gear (MLG) assembly, aluminum fuel and hydraulic lines and fittings, an overheat sensor, and a rubber fuel crossover line. The overheat sensor illuminates either the left or right wheel well and wing overheat (L or R WING OVHT) annunciator light on the pilot's instrument panel when temperatures in the corresponding wheel well reach 350 Fahrenheit (F) (177 Celsius (C)).

The examination of the left wheel well showed overheated MLG brake assemblies, burned tires, melted aluminum hydraulic and fuel lines and fittings, and the fire-damaged rubber fuel crossover line. The majority of the brake pads were worn unevenly (out-of-flat), exposing the base metal. The thermal insulators were out-of-flat. Both brake disks were worn unevenly, but the wear was well within the thickness requirements specified in the airplane's maintenance manual. The accident aircraft was equipped with B. F. Goodrich part number (P/N) 2-1203 wheel brake assemblies.

Wheel Well and Wing Overheat

The investigation to date indicates that the crew applied right rudder and/or brake during the takeoff roll, possibly to compensate for a dragging left wheel brake and, when airborne, raised the landing gear, with an overheated brake, into the wheel well. The investigation has determined that both left brake assemblies were significantly overheated; this "hot brake" condition would have provided an ignition source for a wheel well fire.

When comparing the service difficulty history of the B.F. Goodrich 2-1203 series brake assemblies installed on Fairchild-Swearingen SA226 and SA227 Metroliners to the brake systems on similar aircraft, such as the Beechcraft King Air, the number of reports of overheated brakes on Metroliners is disproportionately higher. Moreover, seven of the Metroliner service difficulty reports make specific reference to fires or the "burning" of tires or aircraft components and systems. In addition, two occurrence investigation reports document that overheated brakes on the SA226s and SA227s have caused major airborne fires.⁽²⁾

In both occurrences, the investigating agency (NTSB and TSB, respectively) determined that the aircrews were not aware that their aircraft had overheated brakes, and that the crews had unknowingly created the potential for an onboard fire by raising landing gear with overheated brakes into the wheel wells after take-off.

Fairchild/Swearingen SA226 and SA227 Metroliners do not have an aircraft system that specifically warns aircrew of an overheated brake condition. However, these aircraft have a wheel well and wing overheat annunciator light that provides, when "on steady," a warning of a "wheel well or air conditioning duct overheat," or when "flashing," an indication of a "wing leading edge bleed air line failure or an overheated generator wire." The Wheel Well and Wing Overheat Warning Light ON check in the Aircraft Flight Manual (AFM) outlines actions that deal solely with the overheat situations arising from an air conditioning duct or bleed air failure. Investigations into previous incidents and accidents involving overheated brakes in the SA226 and SA227 Metroliners have determined that the wheel well and wing overheat detection system has been activated when there were wheel well fires. Yet, the AFM makes no reference to the possibility that other heat sources, such as a fire in the wheel well, can be detected by the overheat sensor and cause the annunciator panel warning light to illuminate. By using the existing AFM procedures, aircrews have their thinking and actions directed toward handling a possible failure in the bleed air system when, in reality, the illumination of the L or R WING OVHT light may be indicating a fire in the wheel well. This extremely critical situation requires more-immediate attention, and different action, than a bleed air problem. In the occurrence at Mirabel, the investigation has determined that, at approximately 13 minutes after take-off, the crew was responding to a "steady" illumination of the L WING OVHT indicator light, and was referring to the corresponding AFM emergency procedure.

Throughout the Mirabel investigation, the TSB has been providing Transport Canada (TC), through its Minister's observer, any factual information that could be used to prevent similar occurrences or otherwise improve aviation safety. The information relayed to date has dealt mainly with the potential for overheated brakes in Fairchild/Swearingen SA226 and SA227 Metroliner aircraft to cause fires and/or explosion in the wheel wells. As a result of this information, TC has issued Commercial and Business Aviation Advisory Circular (CBAAC) No. 0146, dated 1998.09.16, to alert Canadian flight crew and operators of these aircraft to the hazard associated with the overheating of the brakes. CBAAC No. 0146 outlines the warning 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 both the susceptibility of the Metroliner brakes to overheating and the conditions for suspecting potential brake overheating. Although the CBAAC also states that TC has communicated a recommendation to the aircraft manufacturer, in fact, the communication was with the FAA regarding amendments to the AFM and checklists.

The Board commends the timeliness of TC's action and believes that, in the short term, CBAAC No. 0146 will improve the awareness within the Canadian SA226 and SA227 Metroliner community of the potential hazard caused by overheated brakes on these aircraft.

However, the Board believes that to help ensure that there will not be a continued risk to the safety of the crew and passengers on Fairchild/Swearingen SA226 and SA227 Metroliners, the definitive operating manual, the AFM for these aircraft, must be amended and that both ab-initio and recurrent aircrew training 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, inter alia:

• the susceptibility of the brakes on Metroliners to overheating, the precautions to deal with or prevent brake overheating, the symptoms of potential problematic brakes, and the fact that overheated brakes can cause wheel well fires;
• that a L or R WING OVHT warning light may be indicative of a wheel well fire and that there are other key symptoms associated with the L or R WING OVHT light which are indicative of an onboard fire; and
• 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 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, and the NTSB is making recommendations to the FAA in this regard. TC has communicated with the FAA concerning amendments to the AFM and checklists. Therefore, the Board recommends, 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 and, under current regulations, these systems are not required for certification. Such systems, especially in an aircraft with wheel brakes that are susceptible to overheating, would allow aircrew to monitor the temperature status of the wheel brakes and take appropriate precautions to prevent an overheat condition or to preclude the inadvertent raising, into the wheel well, of MLG with overheated brakes.

Also, as indicated previously, post-occurrence examination of the aircraft involved in the Mirabel accident determined that there had been a pre-crash fire in the left MLG wheel well as evidenced 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, may have also resulted from bursting tires, since the wheels on the MLG of Fairchild/Swearingen SA226 model aircraft do not incorporate fuse plugs (which melt when hot, giving a controlled release of excessive tire pressure built up from the heat).⁽³⁾ 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.

The measures outlined in CBAAC No. 0146, and associated with the above recommendation, are focused 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 recommends 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

A98-03Transport 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 flash point of approximately 237F (114C).

The SA226 and SA227 specification originally called for MIL-H-5606, with a rated flash-point of 82C, to be used in both the aircraft's main and brake hydraulic systems. However, following two Swearingen SA226-TC Metroliner II cockpit fire accidents in which the MIL-H-5606 hydraulic fluid was involved,⁽⁴⁾ the FAA in the United States issued Airworthiness Directive (AD) 83-19-02 applicable to certain Swearingen SA226 series 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 rated flash point of 205C, 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 both the main and brake hydraulic systems of the aircraft; however, there is no reference to indicate either 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 flash point than the 205C of 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 AMEs as an alternate hydraulic fluid in systems requiring MIL-H-83282.⁽⁵⁾ 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 recommends 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

As the investigation proceeds, should the Board identify additional safety deficiencies in need of urgent attention, it will not hesitate to make further aviation safety recommendations.

Original signed by the Chairman

Benoît Bouchard
Chairman

On behalf of the Board

1. Fairchild/Swearingen SA226 and SA227 Metroliners are used widely in Canada and throughout the world in commuter and courier operations. There are 70 Metroliners registered in Canada and a total of approximately 350 worldwide.
2. On 27 July 1988, a Fairchild SA227-AC Metroliner III experienced a loss of hydraulic pressure, wheel well and wing overheat indications, exploded tires and substantial fire damage in the left wheel well. An emergency landing was performed successfully at Anchorage, Alaska. Additionally, on 10 February 1990, a Swearingen SA226-TC, Metroliner II experienced a loss of hydraulic pressure, wheel well and wing overheat indications, exploded tires, and substantial fire damage to the left wheel well. The left engine was shut down and an emergency landing carried out at Winnipeg, Manitoba.
3. The wheels on some models of the heavier Fairchild/Swearingen SA227s incorporate fuse plugs.
4. On 15 October 1982, a Swearingen SA226-TC Metroliner II caught fire at Palm Springs, California, when an electrical arc from a cockpit panel light rheostat ignited wires contaminated with hydraulic fluid. And, on 27 August 1983, a Swearingen SA226-TC Metroliner II had a similar fire underneath the instrument panel at Hot Springs, Arkansas, when an electrical arc also ignited wires contaminated with hydraulic fluid.
5. The TSB has determined that at least one other Canadian operator of Swearingen SA226s had a mixture of MIL-H-83282 and MIL-H-5606 in the hydraulic systems of an aircraft.

-(30)-