The sticky slide, Air India evacuation

Emergency evacuation by deploying and using the escape slide is the most expeditious means of leaving the aircraft. Certification standards require a demonstration of passenger evacuation in 90 seconds using half the available exits.

The key word here is ‘half’. The regulators assume that there would be damage to the slides or conditions outside that prevents the usage of a door on the affected side.

Synopsis

On 09.06.2017, Air India A320 aircraft was operating a scheduled flight
AI821 from Delhi to Jammu. The aircraft overran the runway 36 after landing at Jammu Airport. The cabin crew in-charge informed the PIC that there is some smoke in the rear cabin. An emergency evacuation of the passengers was carried out using escape slides.

Escape slide status

Emergency evacuation using escape chutes were carried out. The doors 1R, 2L and 2R were used on the A320. The 1L door couldn’t be opened and no evacuation was carried out from over wing windows. There was no injury to any person during evacuation. However, after the evacuation, the escape slides R1 and L2 collapsed. The member of the committee visited the Jammu Airport door L1 was opened in armed condition. However, the escape slide of L1 also collapsed after 3 minutes of deployment.

Finding

The escape chutes were examined at the shop and it was found that all escape chutes were more than 15 years and crossed manufacture recommended life. The age of escape chutes were 16, 17 & two with 18 years.

Collapsed slide
Collapsed slide

Read the final investigation report.

Background of the 15 year life

On September 16, 2013, while taxiing at McCarran International Airport, Las Vegas, Nevada, a Boeing MD-80 series aircraft encountered smoke in the aircraft cabin. An emergency evacuation of the aircraft was subsequently ordered, and the evacuation slides were deployed. Upon activation of the evacuation slides, the Left Hand Forward (L-1) slide deployed but did not remain inflated. No injuries resulted from the failure of the slide due to the actions of a flight attendant preventing passengers from evacuating the aircraft through the L-1 exit. 

After an investigation into the failed slide, Air Cruisers, the evacuation slide manufacturer, concluded that the slide failed due to a seam separating. The slide’s seam peel strength test results indicated that the seams of the inflatable no longer had sufficient adhesive strength to ensure the integrity of the inflatable. Additionally, the deterioration of the adhesive strength was most likely a result of age or age related effects. 

OEM and FAA issued a notification which emphasizes the importance of the inspection and testing protocols at recommended intervals. Specifically for ageing evacuation systems 15 years and older.

Other failures

Incidence of slide problem
Incidence of slide problem

Based on a review of UK data on 268 maintenance/test slide deployment from 1980-1994 the study summarised the following slide problems:

  • Incorrect assembly of slides 29.1%
  • Girt bar mechanism failure 14.9%
  • Misrigging 11.2%
  • Inflation device malfunction 7.8%
  • Failure to deploy with no obvious cause 6%
  • Other unknown slide problems 31%

Asiana Flight 214 accident at San Fransisco

According to the National Transportation Safety Board, only two of the Asiana Boeing 777’s eight emergency slides properly deployed outside the plane after the crash. Two slides inflated inside the cabin, pinning flight attendants and forcing other crew members to deflate them with an axe. That malfunction delayed passenger evacuations. Two of the 307 passengers died in the crash.

NTSB final investigation report

Emirates Flight 521 evacuation at Dubai

The winds reported at the time of the evacuation was 15 kts. A number of slides could not be used since they could not touch the ground. As per design and certification, they must be capable of being deployed into 25­knot winds from any direction.

EK521 prelimenary report

mindFly analysis

Emergency evacuation is the most critical eventuality/procedure due to imminent danger t lives on board the aircraft. The safety equipment associated with such a critical procedure must also be the best since lives are dependent on its successful operation.

As with any other equipment, there is a technical, environment and a human factor aspect. Surprisingly, the maintenance schedule of this critical equipment and the life of the slide is not an area which is a matter of concern for the regulators or the OEM.

Considering the high failures of deployment due malfunction or wind speed, there is a need to review the design and testing of the equipment.

Human failures can be due to shock, startle or distracted attention.

Mindfulness in door operation

Research

Researchers at the Transport Safety Board of Canada in 2013 re-examined accidents involving commercial passenger transport aeroplanes in 1978–1992 and others from 1993 and 1994 (see References below). Their report described several recurrent functional issues — calling them “slide failures” — and stated: “Slides were deployed in 15 of the 21 evacuations examined. In seven of the evacuations where slides were used, there were problems related to their deployment or to their angle of inclination. The study report also contained the following event descriptions:

  • “Wind had an adverse effect on the use of escape slides. In two evacuations where slides were used, the wind blew them up against the sides of the aircraft, thereby preventing their use until someone was able to exit the aircraft via another exit, reposition the affected slide, and hold it in place. Other exits were unusable for the entire evacuation. Wind velocity was recorded as southeast 17 kt gusting to 22 kt in one of these occurrences and at approximately 18 kt gusting to 28 kt in the second.
  • “There were two occurrences where the slides did not deploy automatically. In both occurrences, they were deployed manually. However, on deployment, one slide went straight down into the ground and had to be repositioned from the outside before the exit was useable.
  • “At Wabush, neither of the rear slides deployed properly. The slides were twisted, tangled, and curled back, almost under the aircraft, and they were only partially inflated. Both exits were temporarily blocked while fire fighters repositioned the slides. … Finally, there was one occurrence where the R4 slide would not deploy either automatically or manually. …
  • “There does not appear to be a simple explanation why some slides did not deploy automatically or properly. In one instance, the problem was traced to excessive clearance between the bar on the door and the aft latch on the floor, which allowed the bar to pull free. … The Board recommends that: The Department of Transport, in concert with industry, re-evaluate the performance of escape slides on all large passenger-carrying aircraft registered in Canada, to confirm that they can be functionally deployed in accordance with the criteria of the Airworthiness Standard.”

Researchers at the National Aerospace Laboratory (NLR)–Netherlands, in a study based on accident/incident data and data from other sources, in the early 2000s, found that the most significant slide problem was failure to inflate. Examination of NLR’s study sample of 150 survivable aircraft accidents in which slide were used during 1970-2003 showed that in 81 of those accidents one or more slides did not function properly. The most significant slide problems involved inflation, aircraft attitude, wind, fire, incorrect rigging, and rips.

 

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