OPERATIONS
Correct Escape Slides Maintenance for Successful Slides Deployment
It is of the outmost importance to make sure that escape slides’ maintenance is properly done so that they can deploy correctly when they are the most needed.
This article recalls the importance of reporting scheduled and unscheduled slide deployment results to Airbus. It highlights the most common causes of unsuccessful slide deployments and provide recommendations to prevent them.
In the early nineties, an A300-600 aircraft overran the runway threshold and came to rest leaning to its left side. This meant that evacuation from the right hand side of the aircraft was impossible. The cabin crew also observed fire on the aft fuselage of the aircraft and decided to evacuate the passengers using only one escape slide from the forward left side door. The escape slide deployed correctly to allow all 160 passengers and crew to escape the wreckage and move to a safe distance away from the aircraft before it burst into flames.
This event highlights the importance of reliable escape slide deployment and how following correct maintenance procedures, and reporting slide deployment test results to Airbus, is essential for ensuring that escape slides will properly deploy when they are most needed.
REPORTING SLIDE DEPLOYMENTS TO AIRBUS
Reporting all slide deployments enables continuous improvement of slide reliability
Operators have to perform a certain number of slide deployment tests on a regular basis. Comprehensively reporting any slide deployment gives an overview of the slide’s reliability, and this can help to identify areas of improvement. The AMM/MP provides the slide deployment report form template (fig.1). The operator should use this form to describe the result of each slide deployment and then send it to Airbus. This form is for reporting both successful and unsuccessful slide deployments for analysis.
A detailed report facilitates failure identification
The AMM/MP procedure for operational check of slide deployment also requests the operator to record the test with video cameras from different angles. Should the deployment be unsuccessful, this video recording enables detailed analysis of the deployment sequence and providing the videos and any photos to Airbus, in addition to the deployment report, will assist in the investigation to find the root cause of the failed deployment.
(fig.1) Escape slide deployment report template in the AMM/MP
Safety precautions in the case of an unsuccessful deployment during a test
If the slide does not deploy during a test, the deployment area must remain clear of any personnel as there is the risk that the slide can suddenly inflate until the slide is correctly secured. Sudden slide raft inflation may cause injuries or damage to equipment.
It is recommended to carefully take photos from the inside and from the outside of the aircraft in addition to recording details of the position of the slide during a failed test. When it is confirmed that the slide is not obstructed by the door frame or its compartment the operator can then pull the manual inflation handle. This will ensure that the slide inflation gas cylinder is empty and that the slide is in a safe condition to handle.
COMMON CAUSES OF INCORRECT SLIDE DEPLOYMENTS
Reported slide deployments enabled Airbus to identify several common causes of unsuccessful deployments. A majority of these can be avoided by following these recommendations.
Checking for correct electrical harness routing during door slide installation
The slide’s electrical harness routing is different depending if it is installed on the left or right side of the aircraft.. Several reported cases showed that the slide harness routing was not correct for the side where the side was installed. A door slide with an incorrect routing of the electrical harness can impede the evacuation of the passengers (fig.2), or block door opening sequence and prevent the slide deployment.
(fig.2) Example of a deployed slide with an electrical harness incorrectly routed. In this case, the harness could impede the evacuation
Operators must carefully follow AMM instructions for slide installation and ensure that the electrical harness routing is correct for the position of the slide installed on the left, or on the right of the aircraft.
TIP : As a general rule, the electrical harness route should exit the slide assembly on the forward side of the door.
Incorrect packing during slide overhaul
Many incorrect slide deployments are due to incorrect packing of the slide during shop maintenance.
Slide overhaul should only be performed by certified maintenance organizations. The maintenance organizations in charge of the slide overhaul must refer to latest revision of the Component Maintenance Manual (CMM) or the folding procedure for packing slides.
System improvement: the A320 slide wrapper
A modification of the A320 slides called the “Slide Wrapper” provides more reliable deployment. The modification is a device that is installed to hold both the inflatable part of the slide and its reservoir together, which prevents early activation of the reservoir when a slide has not cleared the door (fig.3).
This modification is known as the slide wrapper and it is installed via the following Service Bulletins (SB): SB A320-25-1B81, SB A320-25-1B82, SB A320-25-1B83, or SB A320-25-1B84. Embodiment of this modification is mandated by the EASA AD 16-0043 (March 2019 compliance).
(fig.3) Showing an incorrect slide deployment where the reservoir was activated and began to inflate the slide before the it had cleared the door . The slide wrapper modification is designed to prevent this kind of occurrence.
“Fat packing”
The outer dimensions of a packed slide can exceed the normal envelope if the slide is not packed as per the vendor’s folding instructions. This can effect the dropping kinematics of the slide and prevent the slide from being inflated automatically.
It is mandatory to carefully follow the packing process, including the oven cycle to set the material folds, to achieve the correct packing density inside the vendor defined outer dimensions envelope.
Check the external dimensions of the slide after packing using the three dimensional check tool described in the packing documentation, and by confirming the packed slide can be inserted with sufficient clearance into its cover.
Use of incorrect restraints during packing
Calibrated restraints are used to control the slide deployment sequence in various environmental conditions. They are designed to break with a pre-determined load when pulled during the slide inflation sequence. If an incorrect restraint is used, it may not release the slide during inflation and prevent the slide extending (fig.4).
To avoid this kind of event, a color code on restraints is a visual indicator of the the correct restraints load calibration and the slide folding instructions must be carefully followed.
(fig.4) Consequence of the use of an incorrect restraint during packing. The slide extension is blocked.
Inoperative door emergency actuator
The door emergency actuator provides a dynamic momentum to rapidly open the door and and enable the release of the slide from its stowage to launch its deployment sequence. In some reported cases, the emergency actuator failed to open the door and it prevented the slide from deploying correctly. The actuator did not operate because of incorrect rigging of the door actuator percussion mechanism or the actuator was deactivated for maintenance but not reactivated at the end of the procedure.
Carefully following the AMM/MP during emergency actuator maintenance will ensure that the actuator percussion mechanism is correctly rigged and that a deactivated actuator is reactivated following the maintenance task.
Foreign object ingested by the inflation aspirator
A a foreign object can either obstruct the aspirator inlet or block the flapper valve of the aspirator in the open position and cause incorrect slide deployment.
The obstruction of the inlet blocks the air intake to the aspirator, and prevents slide inflation or it may cause an incomplete slide deployment. The blockage of the flapper valve in the open position (fig.5) can cause an inflated slide to deflate.
(fig.5) Aspirator flapper valve blocked in the open position due to a foreign object ingestion
Some operational deployment tests were reported as unsuccessful due to ingestion of the fuselage protection material (fig.6). Fuselage protection must be done according to AMM/MP procedure to avoid ingestion of any protection materials into the aspirator during any operational test of a slide. Operators must not use protection materials other than those recommended by the AMM/MP.
(fig.6) Incomplete inflation due to obstructed aspirator inlet caused by non-standard fuselage protection during a slide deployment test
Non-operational conditions during an operational deployment test
During a slide deployment test, the aircraft must be in a condition that is representative of real operations. The emergency actuator must be activated so that the test is performed in real conditions.
Analysis of previous unsuccessful deployments showed that to avoid maintenance on the emergency cylinder further to a slide deployment test, some operators de-activated it before the deployment test. As explained earlier, the emergency actuator actuation is part of the slide deployment kinematics, therefore, a de-activated emergency actuator during a test may lead to an unsuccessful deployment.
To be representative of the operational conditions, a deployment test should be done with the slide decorative cover installed (fig.7).
(fig.7) Removal of the decorative cover of a slide for a depoloyment test does not provide a realistic operational configuration
Escape slides can save lives in emergency situations.
Slide overhaul should only be done by certified maintenance organizations. Particular care should be taken to pack the slide using the latest folding instructions provided in the CMM or in the folding document. AMM procedures and recommendations must be carefully followed during installation and servicing of the slides to ensure the correct deployment of the slide.
Periodical slide deployment tests should be done on aircraft in an operational configuration and with approved fuselage protection in accordance with the AMM/MP recommendations. This will mean that the test is representative of the slide deployment in operational conditions.
A thorough reporting of both unsuccessful and successful slide deployments during scheduled tests, an inadvertent deployment or in any emergency situation is essential for Airbus and its suppliers to assess slide reliability. In case of an unsuccessful slide deployment, providing videos and photos of the event in addition to a detailed report facilitates identification of root causes and enables the continuous improvement of slide deployment reliability.
CONTRIBUTORS
Sven MACHTANS
HO Cabin Safety Equipment
Design Office
Uwe EGGERLING
Senior Director of Safety
Maintenance & Engineering Customer Support
Mohammed ALAHYANE
Product Leader Emergency Equipment
Customer Support