Emergency Escape Slides:
The invisible Lifesavers
Scheduled maintenance program maximises reliability
Many safety features incorporated in large modern civil airplanes are never put to the final test of a life-threatening situation. Generally, these features remain concealed from passenger view. If a real emergency should occur, it is even more important that all safety equipment performs 100 per cent and exactly as required. A good example are the emergency escape slides which enable passengers to make a safe and rapid exit from an airplane under the most difficult circumstances. This requirement is at the core of a dedicated and extensive maintenance program, designed by Lufthansa Technik to ensure maximum safety and reliability of emergency escape slides.
Under current regulations each emergency escape slide must be removed from the aircraft every three years and checked in the workshop. The slide is tested by "flat firing" the slide on the floor; the test confirms that the slide inflates properly within two to ten seconds, depending upon the aircraft and type of slide.
The inflated slide is also checked in the workshop at over-pressure to test that seams retain their integrity under extreme loads. The slide is also tested for its ability to remain properly inflated for several hours. If the slide sags, it may be damaged in some way or have a puncture. Provided that any holes are less than a given maximum size, a repair according to a certified process is possible.
Emergency escape slides are inflated by gas bottles, which are also thoroughly checked. Gas is stored in the bottles at pressures of about 200 bar. The gas is a fire-retardant mixture of nitrogen and carbon dioxide discharged from the bottle through a constant-pressure valve. At the regular inspections the valve is normally completely overhauled and time-limited components such as seals are replaced. The valve and all relevant parameters are then tested. The gas bottle is checked for strength in a carefully regulated hydrostatic test. If there is any doubt at all, the bottle is scrapped. In addition to inflating the escape slide, the gas bottle also drives an aspirator (a type of injection pump). The aspirator draws in ambient air to mix in a ratio of about two-thirds air to one-third gas from the bottle. This reduces the size of the gas bottle required to achieve full slide inflation.
At regular intervals, emergency escape slides are tested for correct operation on an aircraft. At given intervals, technicians check-"fire" a sample escape slide, one slide for each door position in the respective fleet of aircraft. Lufthansa Technik engineers carefully analyse the test with a video camera. Any problems are corrected in the onset with long-term corrective action.
The emergency slide release system is usually linked to the door opening/shutting mechanism. When the "in-flight" mode is selected for the aircraft door, if the door is opened the emergency slide is then automatically deployed. Should the slide not deploy when the door is open, the cabin crew can still activate the slide manually.