When a disgruntled JetBlue flight attendant made a dramatic exit from his job via the aircraft’s escape slide in August 2010, it momentarily focused the public’s attention on this invisible but vital life-saving component.

A slide’s deployment looks simple, but the evacuation system is extremely complex. “They are prone to activation problems and have generated a considerable amount of service bulletins and airworthiness directive (AD) activity,” says Jeff Runciman, general manager of Canadian Aero Accessories in Calgary. “Over the past four years, we have seen some nine service bulletins generated by the OEMs of the slides used on the Boeing 737-700. So, airlines that do the work inhouse need to establish a unit within their own shops, using trained mechanics who focus specifically on evacuation slides.”

Along this line, based on discussions with representatives of major MROs, the evacuation systems can be an issue—both during maintenance and while in service.

“We see a lot of damage to evacuation systems caused by people who don’t always know or follow the correct procedures after an inadvertent or scheduled deployment,” says Macel Peray, an emergency equipment servicing technician with SR Technics in Zurich. “Damage also happens when people, such as the catering staff and others who service the aircraft, accidentally deploy the slide. We have seen slides come in with tears, punctures and even tire marks from having been run over by forklifts.”

Problems with evacuation systems center on the integrity of the slide surface material, according to Philippe Delisle, executive VP of component services for Sabena Technics. “As soon as the slide lane is exposed to high humidity and different temperatures, we encounter problems with the porosity of the slide surface, which requires replacement.”

Pedro Rosa, an evacuation systems engineer in the components maintenance engineering and quality department at TAP Maintenance and Engineering in Lisbon, points out that most of the problems his organization detects relate to contamination of exposed parts due to the operation of the airplane and damage, mainly to the pack board surface and slide attachment system.

“With the attachment system, most of the problems detected are corrosion and fractures, with the last ones occurring mostly on the Airbus A320 slides,” he explains. “After disassembly, typical problems that we find are lighting system faults, leakage and aging-related degradation on the inflatable component’s fabric; as well as pack board damage. At the same time, we find life-limited parts requiring replacement.”

Udo Janssen, Lufthansa Technik’s director of wheels and brakes services, emergency equipment and cabin electronics, reports that the most common repair and maintenance problems his company sees with evacuation systems, following removal from the airplane, are holes in the slide fabric. Others, he says, are lamp harnesses with burnt bulbs and broken cables; delamination in the slide pack board; and cracks, holes or corrosion of attaching parts.

“At approximately 15 years of age, the first signs of aging appear with the materials—porosity of the fabric, seam peal, or pack board delamination,” explains Janssen. “That is the reason why, after 15 years, the OEMs change the inspection schedules from three-year intervals to yearly cycles.”

What They Endure

Janssen adds that while heat and humidity lead to increasing aging of the material bonding, the fact is that the slide endures the most stress during the packing process. “A good technique and less usage of force in the repacking will help to increase the service life of a slide,” he says.

Weight-savings concerns complicate the packing of the slide, says Canadian Aero Accessories’ Runciman. “The slides today are made out of sealed dacron, which is lighter and more prone to wear. One reason for that is that they are being packed very tightly into the bustle [the container attached to the aircraft door], or fuselage-mounted container, which tend to be smaller to save weight. But the aircraft are larger, so the slides must be bigger to evacuate more people within the allowable time.”

Lufthansa Technik’s Janssen explains that while new materials are being designed to decrease slide system weight and volume, there has been no increase in durability. “The Airbus A380 slides are the first ones with a service life limit of 15 years. However, on the Boeing 747-400, we are maintaining slides that are 23 years [old]—and older,” he notes. “On that aircraft, they are using materials of the 1980s, because state-of-the-art materials are only used for newly designed evacuation systems.”

Laura Neel, marketing communications specialist for Goodrich Interiors, which along with the Zodiac Group’s Air Cruisers is one of the world’s two major suppliers of commercial aircraft evacuation systems, points out that removal for service should happen at three-year intervals, and that typically, the service life of an evacuation slide system is 12-18 years. Air Cruisers made no one available for comment, despite repeated requests.

In addition to the slide, the actuating system—comprised of the cylinder (gas bottle), hoses and aspirators—also falls into three-year inspection cycles. The aspirators, SR Technics’ Peray explains, are not life-limited and can be used as long as they are in good condition. The hoses are removed and tested every three years, but annually after 15 years. Disposal of the cylinder is OEM-mandated after 15 years.

TAP Maintenance and Engineer-ing’s Rosa says that throughout their service-life spans, slide systems have a number of modifications and product improvements proposed by the OEMs as service bulletins, service information letters and in some cases, compliance with airworthiness directives. The result is a system of “continuous evolution.”

In some cases, says Rosa, the problem results from a less-than-perfect design, which could generate a high number of service bulletins.

“During operation and line maintenance inspections, slides tend not to show signs of problems. Most of the issues arise at installation time on the airplane,” he notes. “For example, we have had cases of lighting system fault and installation problems due to an over-limit on packing volume—with the last case occurring mainly on the A320 slide rafts. A service bulletin was released with an improved pack board design that helps solve these volume issues.”

Customization and Spares

For airlines, a major issue with slide maintenance involves the fact that evacuation systems, in most cases, have been custom designed—not only for specific aircraft, but also by cabin door location.

“Generally, the evacuation slide systems on an airplane are unique to each exit location due to physical parameters such as fuselage contour, sill heights and proximity to the engine, wing or fairings,” explains Julie O’Donnell, a Boeing Commercial Airplanes communications representative. “Typically there’s a unique part number at each exit location. However, for multiple model variants, such as the 737-600/700/800/900, there are some cases where the system installed at a particular door is the same.”

This factor brings up procurement and training issues for the MROs, as Sabena technics’ Delisle notes. “Evacuation slides can’t be interchangeable between aircraft types. Additionally, one aircraft is [designed] to use all the slides from the same manufacturer. This means that you are not authorized to swap one of those slides with a slide from a different manufacturer.”

According to Delisle, as soon as Goodrich and Air Cruisers put a new model on the market, MROs must source new spare parts and test units. “This means that you have to train your technicians and stock new parts in order to be competitive. This is not a cheap process.”

Procuring replacement slides becomes a little more complicated when an older, out-of-production aircraft is involved. TAP’s Rosa says that this is because some of the main components are no longer stocked and need to be manufactured as required.

“If manufacturing is required, turn times and costs increase in such a way that scrapping and replacing it becomes the considered choice,” Rosa notes. “But this is a trend throughout the aircraft maintenance market, because as inventory costs increase, manufacturers seem less willing to invest in large batches of spares. For most items, second-hand stocks can minimize the problem. In fact, we go to the surplus market ourselves if the OEMs are not able to meet our needs.”

Jan Toplund, VP technical for Copenhagen-based Jet-Time, a 737-300 operator, confirms that the surplus market for slides is a viable alternative. “With the 737-300 being phased out, the surplus market is giving us some flexibility with procurement. We have some in our consignment stock now.”

However, as SR Technics’ Peray states, even with a yearly inspection schedule mandated after 15 years, some carriers choose to retain, rather than replace, their slides. “Depending upon the aircraft, the replacement cost of an inflatable slide can start at about $20,000.That’s why a lot of airlines that operate older aircraft would really prefer to keep the systems, despite increased inspections.”

Peray adds that on older aircraft slide systems, for standard smaller parts including O-rings, batteries, and mechanical components, there is an average lead time of 90 days, but up to six months for a replacement slide manufactured by special order.

Yet, Lufthansa Technik’s Janssen points out that the prices for surplus evacuation systems depend on the number of operating aircraft. “It is getting increasingly difficult to get Boeing 747-400 slides as the worldwide fleet is aging and more evacuation systems have to be scrapped.”