Emergency Doors...What you may not have known.

 When I worked on slides and Emergency doors, I followed the maintenance manual religiosly, having a slide deploy is not a thing that I want to happen.  Also something else that most don't know is that the standard to empty an airplane of all passengers and crew, and get everyone out is 45 seconds.  The standard was set because of an accident on a "Boeing 737" that during a takeoff, one of the engines decided to "FOD itself" and punctured fuel tanks and the resulting fumes, not the fire killed almost half of the passengers.  The resulting investigation made huge changes in safety and training and the making of material inside of the aircraft to minimize fumes.  A little over 20 years later, another B737 had another engine fire and "Everyone escaped with 4 people having minor injuries."  No I am not disparaging the B737, she is a damm good plane.  Both instances were not the planes fault, but the engines.

I saw this article and I thought it was worth "clipping"

Latecoere has aimed to simplify door opening and positioning to speed up evacuation times.

Credit: Latecoere

In the rare event of an emergency cabin evacuation, successful egress depends on how well the exit doors and their built-in escape slides and actuators perform.

A quick emergency exit from an aircraft depends on two categories of doors, explains Thierry Eftymiades, senior vice president for engineering at Toulouse-based Latecoere, a manufacturer of cabin doors for commercial airliners and business jets. The first category consists of passenger-entry and service doors, which are opened and closed during regular aircraft cycles. The second category applies only to emergency-use doors, including cockpit escape and overwing emergency-exit doors (OWEED).

Eftymiades says Latecoere uses “functional and customer analyses” to define and specify in detail customer expectations for each door.

“These analyses help to optimize the design and manufacturing technologies as well as the development process to reduce recurring and nonrecurring costs,” he explains. “Design trends are focused on composites, specifically thermoset and thermoplastics from our composite development center.”

Major inspections of escape slides are performed every 3-5 years. Credit: AJW Technique

Another Latecoere design trend involves the “kinematics” on new types of mechanisms, Eftymiades says. “That has been driven by the regulations, which continue to evolve, while taking into consideration the events faced in real-life emergency landing conditions,” he notes. “In that regard, we have been granted specific patents to simplify the mechanisms’ actuation.”

Eftymiades cites, for example, simplified door opening and positioning that clears the way for outboarding passengers within an evacuation target of less than 90 sec. “The common objective is to make the opening as obvious and easy to use as possible,” he says.

Ease of activation is particularly important under adverse conditions that can make opening doors more challenging, Eftymiades stresses. Those conditions include high winds, fuselage icing and an awkward position of the aircraft due to collapsed landing gear or a side crash.

“[The] current development and innovation focus is on increasing robustness and decreasing costs through specific simple but high-efficiency design items taking into consideration these kinds of adverse conditions,” he says. “These design items can be selected as building blocks while defining the door baseline architecture.”

Escape slides must be inflated to carry out leak and pressure tests on the tubes. Credit: AJW Technique

Despite evolving requirements and greater system complexity, aircraft doors are becoming lighter, Eftymiades points out.

“Doors are complex systems with multiple and contradictory requirements,” he says. “They need to stay closed in flight but opened safely under all conditions, leading to optimized choices to be made. Door weight optimization can be provided for at all project stages, from concept to detail design generation.”

Eftymiades adds that during an emergency cabin evacuation, three subsystems come into play: the door, an ejector that assists emergency opening by pushing the door open and the slide. He emphasizes that during the design phase, discussions take place with the slide supplier to decide on the quality of the interfaces among the subsystems; Latecoere does not manufacture slides.

“Generally, for a passenger door, there are four types of interfaces with the slide,” he says. “They are the structural attachment of the panel holding the slide to the bottom of the door; the panel between the slide and the door lining; the laces between the slide and the bar holding the slide with the door open; and the controlled door ejection speed component, allowing the slide to be deployed safely, especially under adverse conditions.”

OWEEDs are smaller than passenger entry and service doors and do not contain the slide, which is often located at a distant nonpressurized part of the fuselage, Eftymiades explains. “This requires defining the triggering subsystem—electrical or mechanical—-that will inflate the slide on the wing,” he says.

Fuselage-installed slides deploy on pilot command, saving the cabin crew the task of arming and disarming them. In contrast, cabin-door-mounted slides automatically deploy when the door is opened if they are not disarmed.

“Usually for overwing exits, the slide pack is located at the corner between the wing leading edge and the fuselage,” Eftymiades says. “During an emergency opening, the passenger has to walk on the wing to reach the slide location to evacuate.”

It generally takes 4-5 years and as many as 20-100 engineers, depending on the scope of the project, to bring a new door and escape system on stream, taking into account design, simulation and prototype tests, according to Eftymiades. The process also involves hundreds of stress analysis reports as well as test plans and reports, especially given the number of parts.

“For a regional airliner, there are about 500 part numbers for one passenger door and usually four doors per aircraft, plus 2-4 overwing exits,” Eftymiades notes. “For large commercial aircraft, the part numbers are 800 per door, with eight doors per aircraft. For the ejector—the emergency door-opening system—that is an additional 70 part numbers.”

Two other major aircraft door OEMs, Airbus and Collins Aerospace, declined to share their insights into door and escape system developments for this article. Airbus cited the recent Alaska Airlines inflight door-plug loss as to why; Collins did not provide a specific reason.

MAINTENANCE CONCERNS

Today’s escape slides are much lighter but more complex due to incorporation of additional features, according to Andy Wheeler, divisional vice president and managing director at AEM Ametek MRO. The UK-based company has facilities at Luton, Ramsgate and Stansted in England.

Some slides have pressure indicators that connect to the cockpit, for instance, while others contain gas generators and several are fitted with pneumatic door release components, Wheeler tells Inside MRO. “The main benefits are quicker actuation, fewer accidental deployments and improved safety features,” he notes, adding that some slides also incorporate lighting systems that are now brighter, lower energy and more efficient.

Wheeler reports that advancements in materials and design have led to better deployment, improved durability and lighter weight. “For instance, the slides used to be made of neoprene and are now polyurethane,” he says. “When lighting systems were introduced, they were chemical. Now they’re LED-battery-powered. Also, on newer aircraft, the inflation cylinders are composite instead of steel, and the slide’s enclosure—the packboards—fit into the fuselage rather than the doors.”

Wheeler stresses that regular maintenance and inspection of escape slide systems are essential to identify and address potential issues before they become problematic.

“The slides have to be maintained in accordance with the OEM component maintenance manual,” he stresses. “They require inflation to carry out leak and pressure tests on the tubes. The inflation cylinder must be hydrostatically tested and the valve overhauled and flow regulation adjustments made as necessary.”

Asked about the kinds of problems those inspections often reveal, Wheeler cites damaged light systems and low-pressure gauge indications as typical as well as cracks in the packboards from mishandling.

Louis Philippe Mallette, senior vice president of operations at AJW Technique in Montreal, reports that while “the fundamental design concept” of emergency cabin evacuation systems has remained largely consistent across newer aircraft, there have been some improvements, primarily involving materials and weight reduction.

“Advancements in material technology have led to lighter systems and quicker deployment during emergencies,” he says. “This is allowing manufacturers in some cases to extend maintenance intervals to five years while still demonstrating the required reliability over that period, thereby reducing operators’ costs.”

Despite these advancements, he says, “the interface between components and the main and over-wing exits” has remained similar to traditional designs. “Typically, the evacuation slide is still located on the door, maintaining consistency across generations of aircraft.”

Mallette stresses that as long as the slides are undisturbed, the evacuation systems are traditionally very reliable and will typically stay on wing for their full scheduled overhaul life of 3-5 years. “Where we do see issues is when they are disturbed for some reason by people servicing the aircraft, which is very often the case with front door systems and may result in an unplanned deployment,” he says.

Mallette adds that door-mounted packboards and slide actuators can be vulnerable to damage during scheduled airframe inspections, especially if technicians are careless. Accidental deployment during aircraft maintenance can also occur if the system is improperly handled or installed.

“The airframers have taken steps to reduce potential damage by providing comprehensive training and documentation for technicians on proper handling and installation procedures, implementing stringent quality control measures during maintenance and ensuring release mechanisms are protected from accidental activation,” Mallette says.

Given the risks he describes, Mallette was asked if the packboards and actuation components could be trending toward fuselage installations and away from the exit doors.

“No,” he says. “The current [design] remains consistent, with the slides in the packboard mounted on the door. One notable deviation from this pattern is observed with overwing slides, where the exit doors are physically smaller and have insufficient space for a door-mounted slide. Often the slide is airframe-mounted with a separate cylinder assembly also mounted within the fuselage. But this approach is limited to overwing slides at this point and from our experience hasn’t been extended to the main door slides.”

Mallette cites two main components as the focus of an evacuation system inspection: the inflatable slide and the air system that houses the cylinder containing the compressed gas and aspirators. “During scheduled maintenance, AJW will perform an inspection and overhaul of the cylinder assembly to ensure the regulator and the reservoir are still serviceable and functional,” he says. “Part of this process involves hydrostatic testing, which is a critical process used to evaluate the integrity of pressure vessels such as cylinders, and to detect any potential leaks or structural weaknesses.”

For the slide, the inspection focuses on its general condition—in particular looking for porosity, tears and leakages—including conducting an overpressure test.

“What we tend to see on aging slides are small tears at the folds, the buildup of porosity and weakness at the seams, all of which may result in a failure to maintain the pressure over a period,” Mallette says. “Minor tears can be repaired; however, with the older slides, we need to replace the full inflatable system.”