Emergency safety equipment onboard aircraft only has to work in emergencies, thankfully rare in commercial aviation. But when necessary, equipment must perform perfectly to save hundreds of lives. Regulators and OEMs thus subject emergency gear to some of the most stringent tests in aviation and prescribe inspections to ensure performance in a crunch.
United Technologies Aerospace Systems (UTAS) manufactures evacuation slides to get passengers out of aircraft quickly and safely after a crash or fire, and life rafts for water incidents.
The general manager for evacuation, lighting and propulsion systems, Jim Erickson, says both slides and rafts are subject to rigorous tests, specified by the FAA but conducted by UTAS. “We put them in wind and dark night, and in rain and sea trials. Then we run people through,” he says. “They must stand up as robust structures to handle the personnel load. The slides must get to the ground and not be blown around in the wind. They must function for rapid egress.”
Tests that combine a number of difficult environmental conditions are toughest, especially those that involve strong winds. These are done to ensure slides are not blown across one another and deploy correctly to the ground in a limited time. Real emergencies on tarmacs, runways or taxiways are quite likely to involve strong winds.
New evaluations are necessary because UTAS continues to look for better inflatable materials, fabrics and composites to save weight and space while preserving safety functions. The company works with OEMs to pack inflatables densely and reduce volume.
Seat cushions are not, strictly speaking, emergency equipment. But they must function satisfactorily in any emergency, from a laptop battery fire to a very hard landing or even a crash with high G-forces and possibly a fuel fire.
Supracor is now introducing Stimulite cushion material that it says is superior to traditional foam in a number of ways. Vice President Susan Wilson explains that Stimulite had to pass both dynamic and flammability tests.
Trials by Fire
Govmark is one of the major U.S. companies that conducts fire and flammability tests on materials used in aircraft interiors, especially passenger cabins. Aircraft components must undergo rigorous fire and flammability testing, according to Mike Magee, an FAA-designated engineering representative. “From the passenger cabin to the cargo area, all materials must be tested,” he notes.
Tests for components include but are not limited to smoke density, Ohio State University (OSU) heat release, vertical flammability, oil burns for cargo liners and seat cushions, insulation flame propagation and insulation burn-through.
Smoke density, OSU heat release and vertical flammability are the most common tests for cabin interiors. Smoke density measures the opacity of smoke from a burning specimen in a sealed chamber to ensure passengers can still see through it. OSU heat release measures the heat emitted by an ignited specimen.
The vertical-flammability test measures flame propagation in the form of char length as well as after-flame time and burning drip. The oil-burn test throws a 1,900F flame 4 in. away from a seat cushion. It aims to ensure a fire in one seat will not spread or burn through to the interior foam.
Magee says FAA and European Aviation Safety Agency standards have only slight differences: for example, in the allowable duration of an igniting flame or its distance from the tested specimen. OEMs have their own requirements, and Airbus’s are a bit more stringent than Boeing’s, Magee notes. Every Govmark burner is calibrated daily to ensure it yields the right temperature within a very small tolerance, for example plus or minus 50F within the 1,900F for the oil-burn test.
Specimens customarily are tested in triplicate. Govmark puts submitted specimens in a room with controlled temperature and humidity for a specified period, such as 24-48 hr. It then attempts to test promptly, usually over 2-3 days. The company can turn around a specimen received on a Monday by Friday. Magee says it may take an OEM much longer to properly configure its specimens for testing.
OEMs that do their homework before testing usually pass. Those that just wing it usually fail. Tests can cost from less than $100 to more than $1,000 apiece, perhaps $10,000 for a full suite.
For two decades, STG has been making Saf-Tglo photo-luminescent emergency floor-path lighting and Saf-Tsign emergency signage. Sean O’Kell, director of innovation, says certification of a product often can be accomplished by showing regulators it is sufficiently similar to a previously approved item. But in the early days of a product’s life or for novel designs, effectiveness must be demonstrated by proving photo-luminescence works as well as powered lights in a “naive evacuation.”
In 2005, STG joined the FAA at an Arizona aircraft graveyard to demonstrate new Saf-Tglo lighting in a parked Boeing 767. The 767 was chosen because it has the worst designs for exits and lighting levels. STG staff let their photo-luminescent system charge within cabin lighting for 30 min., then left it in a blacked-out cabin for 12 hr. before coming back to test two emergency scenarios.
Blindfolded test passengers had to find exits by crawling as smoke was supposed to be billowing above 4 ft. “The FAA was cruel: When passengers got close to one exit, they shouted, ‘It’s closed, find another,’” O’Kell remembers. Yet all passengers made it out.
UTAS and other repair centers maintain inflatables, traditionally on a three-year cycle. But Erickson says the industry is moving to a five-year interval for inspections and replacements when necessary.
Sometimes batteries wear out, and airlines operate in a variety of conditions from hot to cold and in humid and salty climates. Some carriers deploy inflatables for training, so the equipment needs recharging, and damaged materials may need replacement. Inflation of slides and rafts takes up space and requires safety precautions, as “we must deal with rapid inflation,” Erickson observes.
German Alvarez, chief operating officer of the Av-Inflatables repair station, says evacuation slides typically are tested every three years, but after 15 years they may be replaced or tested annually. Valves are tested, O-rings changed, lights and batteries checked, and—on older or more abused slides—holes sometimes patched. Gas cylinders on slides last only 15 years. Rafts are checked every 3-5 years, depending on the OEM and airline. Perfect equipment can pass muster in four days, but inspections and repairs usually take 7-10 days.
Av-Inflatables inspects life vests every 5-10 years, and every two years if very old. Vests are inflated, batteries and their water-activated lights checked, and any pinholes patched.
Alvarez says radio-frequency identification (RFID) is changing maintenance, especially of vests and oxygen canisters. Airlines can now send just the items due for inspection, rather than pulling whole shipsets. RFID is slowly moving into slide and raft maintenance as well.
Safetech Aviation Safety Equipment inspects and repairs most safety equipment, including fire extinguishers, oxygen systems, slides, rafts and vests. Sales and Marketing Director Michael Lott notes that inflatable inspections require ample room. His company needs 4,000 ft.2 of space to inspect 5-7 at a time.
“We repair when required, for example if a slide has been inflated or a fire extinguisher has been used,” Lott explains. Slides and rafts are inspected every 1-3 years, depending on age and OEM. Fire extinguishers usually are checked every five years and oxygen systems every 1-5 years.
Lott has not seen much change in safety equipment in two decades, except for frequency changes on locators of rafts and RFID chips on vests. FAA and U.S. Transportation Department regulations also have been pretty stable.
Alexander Hubinger, product engineer for cabin electronics and emergency equipment at Lufthansa Technik (LHT), says most evacuation slides are inspected every three years for 15 years, after which point an inspection is required annually. O-rings and batteries are his most frequent replacements.
Most rafts have the same inspection intervals as slides, but in rare cases annual checks are required. Humidity and corrosion may require certain parts to be changed. LHT’s slide and raft inspections usually take 4-5 days. State-of-the-art life vests are checked every 10 years, but some older equipment requires a 3-5-year frequency.
OEMs have escalated maintenance intervals for slides on new aircraft. Airbus A350 slides must be inspected every five years, and those on Boeing 787s every 4.5 years until yearly inspections begin at 15 years. OEMs also are seeking briefer intervals for rafts.
Like STG, LHT has been making photo-luminescent floor lighting and exit signage since the mid-1990s. Unlike for powered lights, maintenance is minimal. LHT Senior Engineer Wolfgang Sutter recommends only a visual inspection of 15-30 min. for missing parts or obvious damage every three months.
Despite all the testing and inspections, evacuation-slide deployment may go awry after the severe damage an accident inflicts on an aircraft. In the crash of Asiana Flight 214 in 2013, two slides inflated inside the Boeing 777-200ER’s cabin, pinning two flight attendants to the ground and forcing other crewmembers to deflate the slides with axes. Only two of eight slides deployed outside the airplane.
In 2000, the NTSB found that in seven of 19 evacuations, at least one slide failed to work correctly. FAA regulations say passengers and crew must be able to evacuate in 90 sec. with half of emergency exits working.
The International Air Transport Association has estimated inadvertent slide deployments cost the airline industry more than $20 million per year and can result in serious or fatal injury.