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Understanding the Successful Evacuation from an A340
by the Aircraft Certification Branch of Transport Canada, Civil Aviation

On August 2, 2005, an Airbus A340, with 309 passengers and crew aboard, overran Runway 24L at Pearson International Airport, in Toronto, Ont., and came to a stop approximately 200 m beyond the end of the runway in the Etobicoke Creek ravine. All passengers and crewmembers evacuated successfully before the post-crash fire consumed the airplane. The accident scene was shown live on television and widely reported in the media.

Many of the media commentators described the outcome as miraculous
Many of the media commentators described the outcome as miraculous

While the Transportation Safety Board of Canada (TSB) is investigating, this type of accident scenario is considered in detail by Transport Canada and other regulatory authorities in developing the regulations applicable to the design of transport category airplanes, such as the Airbus A340. The primary objectives of these regulations are to prevent accidents and, when they do occur, to minimize injuries and fatalities. The latter involves providing a survivable environment for occupants during a crash landing, and the means to rapidly evacuate the airplane as soon as it has stopped, considering the possibility of fire. Some of the design-related regulations intended to improve survivability in a post-crash fire scenario are discussed below, and some advice is given on how we, as users of the system, can contribute to safety.

Impact sequence

For the accident to be survivable, the fuselage structure must remain substantially intact and provide a liveable volume for the occupants throughout the impact sequence. The cabin interior furnishings must not break loose and injure occupants or hinder rapid evacuation, and each occupant must be safely restrained until the airplane comes to a complete stop. Structural and crashworthiness requirements ensure these objectives are achieved in what the regulations describe as “a minor crash landing.”

Consider an example such as the certification of seats. The seat and occupant restraint system must be designed to provide the same level of impact injury protection and structural performance as that provided by the airplane structure itself. Crashworthy seat design involves two major considerations. First, under high forward crash loads, the seat must not break loose from the floor, and the occupant must not suffer serious head injury when striking adjacent furnishings. Second, under high descent crash loads, the seat design must minimize the likelihood of serious spinal injury. The seat structural and occupant injury protection performance is verified during the certification process by dynamic tests of the seat assembly and occupants, who are represented by anthropomorphic test dummies with the physical characteristics of the average male (50th percentile). In the forward load test, the seat is brought to a stop from approximately 48 km/h in less than ¼ of one second. Parameters are measured throughout the deceleration pulse and must not exceed specific limits to prevent serious injury. High-speed cameras are needed to capture the action, millisecond by millisecond, to analyze the results.

External fuel-fed fire protection

Once the airplane has come to a stop, the next challenge is to safely and rapidly evacuate the airplane. Speed of evacuation is critical in the event of a water landing or where fire is a factor.

Survivability in post crash fire scenarios is related to how rapidly an external fuel-fed fire penetrates into and spreads within the airplane interior. Extensive research and testing has been conducted on ways to increase the useful evacuation time by delaying the spread of fire within the airplane. In 1978, the U.S. Federal Aviation Administration (FAA) established the Special Aviation Fire and Explosion Reduction (SAFER) Advisory Committee to examine the factors affecting the ability of the aircraft cabin occupant to survive in the post-crash environment, and the range of solutions available. The Committee was composed of fire safety experts from the National Aeronautics and Space Administration (NASA), the aerospace industry, and the general public.

Early efforts focussed on improving the flammability of cabin interior materials so as to delay the spread of interior fire and, in turn, delay a phenomenon known as “flashover.” (Flashover is a condition in which certain gases and other products emitted during the combustion process and trapped in the upper portions of the cabin reach their auto-ignition temperature and are ignited spontaneously.) Due to the almost total involvement of the cabin atmosphere, survival after flashover is virtually impossible. As a consequence of the Committee recommendations and research, conducted primarily at the FAA Technical Center in Atlantic City, two very significant regulations were adopted. The first regulation upgraded the material flammability standards for airplane seat cushions, as full-scale fire testing found these items to be the dominant factor in the spread of cabin fire. Research data indicated that an additional 40 seconds of useful evacuation time could be achieved from this change. While this may not seem substantial in absolute terms, it can be very significant in a time-critical evacuation. In the regulatory benefit analysis conducted at the time the regulation was adopted, a range of benefits was calculated, including a lifesaving potential of 14 lives per year. The second regulation also substantially upgraded the flammability standards for other cabin interior materials, such as sidewalls, overhead stowage bins, ceilings and partitions. Material meeting these standards further delays flashover.

As mentioned above, one of the key factors in determining useful evacuation time, and therefore survivability, is how quickly the external fire penetrates the fuselage. Recently adopted regulations will require that thermal/acoustic insulation installed in the lower half of the fuselage of new airplane designs have a minimum of five minutes of fuselage burn-through protection. Longer-term research is underway with the objective of eliminating cabin interior material combustion products as a cause of death in airplane accidents.

Evacuation

There are many design regulations whose cumulative objective is to ensure that safe, orderly, and rapid evacuation is feasible. These include specifying the type and number of emergency exits that are required, the maximum distance between the exits, their distribution in the passenger cabin, the design of the means to open the exits under normal and emergency conditions, the markings and placards that inform passengers of the location and operation of the exits, emergency lighting and marking systems to ensure visibility under night conditions, and the provision of means (e.g. slides) to allow the passengers and crewmembers to descend safely to the ground from the passenger cabin exits. The ability to move from your seat to the exits is addressed by requiring minimum widths for longitudinal aisles and access paths from the aisles to the exits. Flight attendant stations must be provided in locations that ensure that cabins can be managed effectively under normal and emergency conditions and also be in close proximity to exits. These stations must protect the flight attendants during the impact sequence to ensure their availability to manage the subsequent evacuation.

The escape slides provided to safely reach the ground are worthy of some discussion. They are typically inflatable devices stowed on the door itself. As the door is opened in an emergency, the slide is pulled from its stowed position. As the slide drops, the inflation cycle begins and the slide erects very quickly. If automatic inflation does not occur, there is a means to manually activate the inflation system. On an Airbus A340, the passenger emergency exits are approximately 5 m above the ground with the landing gear extended normally. These distances may increase or decrease for landing gear failure conditions, and the escape slides must still be useable. They must be capable of deploying in windy conditions, up to 25 kt, and resist radiant heat from a fuel-fed fire. Typical wide-body airplane exits must be capable of being ready to allow evacuation to commence within 16 seconds from the beginning of the exit-opening sequence. On airplanes involved in extended over-water operations, slides are often designed to function as life rafts in the event of a water landing.

In addition to the regulations that specify the above features, there is also a requirement for manufacturers of airplanes with more than 44 passenger seats to show that all occupants can be evacuated from the airplane to the ground under simulated emergency conditions within 90 seconds. Compliance is typically shown by a full-scale demonstration using a representative passenger complement and a trained crew, and using half of the available emergency exits. This standard is intended to demonstrate emergency evacuation capability under a consistent set of prescribed conditions, but is not intended to demonstrate that all passengers can be evacuated under all conceivable emergency conditions.

Overview

Each accident is unique, and usually the result of a multitude of factors. However, the design regulations are updated continuously to address specific accident scenarios based on in-service experience. The above provided an overview of some of the post-crash fire design related regulations that airplane manufacturers must address in order for aviation regulatory authorities to issue a type certificate for a new airplane design. These are part of the overall system that regulates the design, manufacture and operation of aeronautical products. Of course, the users of this transportation system also have an important role to play in achieving the required level of safety, and this will now be discussed in the conclusion of this article.

Airplane design and the role of the passenger

Should you have the misfortune of being involved in a time-critical evacuation, you can, by establishing a simple pre-flight routine and following the crewmembers’ instructions, maximize the possibility of a successful evacuation, similar to this event.

Establish a routine that ensures you’re knowledgeable about the airplane you are about to travel in. Make a conscious effort to understand the interior design features provided for your safety. Begin as you arrive at the airplane. Note how the entry door looks in the open position and read the instructions on how it is opened. As you enter the airplane, note the position of the opposite exit, look for the exit marking signs above the exits and the exit locator signs, typically located above the aisle in the area of the exit access paths. As you make your way to your seat, observe the cabin layout and the location of any other exits you pass, as well as the opening instructions. Once you are comfortably seated, use the opportunity to set a good example for your fellow travellers by fastening your seat belt and finding and studying the safety features card located in the seat pocket in front of you. It will reinforce the information you acquired on the way to your seat and provide additional information on the location and operation of exits behind you. Work out a plan on how you would find the nearest exits, both forward and aft of your seat, even in darkness. Be sure you know how to operate these exits unassisted. Remember that an exit should not be opened when the external conditions would make it unsafe to do so, e.g. fire, or flooding if the exit is below the waterline. Make sure you understand the floor proximity marking system provided to guide you from your seat to an exit. Look at the illustration of the brace position required in an emergency. Become familiar with the safety features card instructions on how to don oxygen equipment in the event of pressurization system failures and the location and use of survival equipment provided for a water landing.

Pay special attention to the safety briefing that will provide you with further details on the airplane features and safety equipment, as well as information on expected behaviour on issues such as when and where to stow carry-on items, what electronic devices may be used, and the prohibition of smoking.

As the take-off roll begins, make sure your seat belt is adjusted so it sits snugly over your hips; this is very important if you are to benefit fully from the injury protection intended by the seat certification process. Repeat this prior to landing. It is recommended that you keep your seat belt fastened at all times during flight in case of unexpected turbulence. Follow your routine each time you board an airplane. Remember that your airplane may be equipped with different exit types and opening methods and that different models of the same airplane types may have unique features that you need to understand.

Flight attendants are trained to react quickly and manage any emergency that may be encountered. Follow their instructions throughout the flight as the regulatory requirements they enforce are aimed at enhancing survivablility. Any questions should be raised with a flight attendant before takeoff commences.

For additional information, visit http://www.tc.gc.ca/eng/civilaviation/standards/commerce-cabinsafety-tips-menu-3344.htm.



The Importance of Following Policies and Procedures-Fact or Fiction?
by Keith Parsons, Civil Aviation Safety Inspector, Atlantic Region, Transport Canada

In a previous life, while I was employed as Quality Manager at an approved maintenance organization (AMO), I held the position of chairperson of the health and safety committee, where I had the opportunity to investigate an accident involving an aircraft maintenance engineer (AME) who was injured while servicing a nitrogen bottle.

It was a normal working day in an active hanger, where several commercial aircraft were undergoing heavy maintenance. In a neighboring hangar, a technician had just successfully completed a scheduled task of deploying the pontoons on a Bell 206. The system used for deployment utilizes a nitrogen bottle with a shear head and squib activated by a switch in the cockpit. Following the successful deployment, the technician removed the nitrogen bottle from the helicopter, replaced the shear head and transported the bottle to our hangar for servicing. The supervisor on duty, who knew the technician, elected to fill the bottle himself. He placed the empty nitrogen bottle on a mobile table and positioned the portable stand-up nitrogen cart, carrying two nitrogen bottles with a regulator and stainless steel hoses, along side. After making the necessary connections, the filling process began; however, as the pressure passed 1 500 PSI, the shear head failed or activated, and a high volume discharge occurred causing the nitrogen bottle to make a quick violent spin impacting the supervisor in the stomach and throwing him 15–20 ft. The now out-of-control bottle, attached only by the stainless steel hose, wrapped the hose around itself until it was tight against the top of the nitrogen cart. The discharge port of the shear head was now facing the floor and propelled itself upward along with the two full vertical nitrogen bottles until the discharge could no longer sustain lift, and the now three nitrogen bottles came crashing to the hangar floor. Wow-all in the matter of seconds.

That covers the who, where, when and how; now, the why. The procedure for servicing the bottle, which was available, was to secure the bottle during filling using appropriate clamps or the designed aircraft installation, but for whatever reason, this was not followed. I used this incident as part of the AMO’s delivery of initial training to highlight the importance of using the proper procedures when carrying out tasks to all the new hires.

My thoughts on this incident can be summed up in one word-lucky. We were extremely fortunate that this incident did not turn out a lot worse. Now, here comes the advice. In this aviation world, which we have elected to become part of, there are hazards and risks that exist daily, and we must remain aware, never let down our guard, be professional, and above all, be safe at all times.

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