Passenger windows in aircraft are amazing piece of science ..... yet, they are rarely the topic of 'plane talk' ......... not any more!!
The passenger window serves two main purposes – from a passenger's perspective, it is there for them to see the beautiful world underneath and makes the cabin less claustrophobic. From regulatory view point, the windows are a safety requirement on all aircraft carrying passengers - typically, the windows are the first port of call for the Flight Attendants and the 'First Responders' in case of an accident ...... Considering a post accident situation, the Flight Attendants / passengers can look out through these windows to assess the situation outside in case of a fire, water landing etc and decide on the appropriate Exits Doors that can be opened for evacuation (reminds us of the Hudson river landing of US Airways flight 1549 by Capt Sullenberger) ...... on the other hand, in case of smoke or fire inside the cabin, the 'First Responders' can see in through these windows to assess the state of passengers and decide on speedy evacuation.
Aircraft windows came to limelight after the recent air incident of Southwest flight 1380 this month wherein a passenger window got damaged and got dislodged by shrapnel and the passenger sitting next to it was injured, apparently sucked out partially and died later. The exact sequence of events will not be clear until the investigation by NTSB of United States, but, the incident has brought to fore the concerns about vulnerability of the passenger windows.
However, this particular article is triggered by the recent incident on board a domestic flight of Air India ( AI 462 operated with Boeing 787) on 19 Apr 18 when a window panel got dislodged during a flight and fell off inside the aeroplane as it went through severe turbulence.
The two incidents stated above are the two extreme ends of the spectrum of concern - yet, from passenger perspective, both of the incidents are testimonials of failed window panes and the fears of safety thereof. It is sheer coincidence that both the planes were from Boeing.
Is the aircraft window really a matter of concern? Is there a requirement to review the already stringent specifications for passenger windows? The answer is a YES and a NO.
Typically, Boeing airplane windows are triple layered with an additional layer. Let's call them -
(a) Outer layer (the one that we see while looking at the plane from outside)
(b) Middle layer (a blended layer which can be seen only from inside the plane)
(c) Inner layer (or the dust cover - the one which we can touch while seated inside an airplane)
(d) Additional layer (the window shutter in older planes or the photochromatic plate in modern planes)
The layers of windows are usually made of plexi glass or some fiber material. Whatever be the material, it would have the following common properties -
(a) Light in weight.
(b) Strong - good mechanical strength.
(c) Optical visibility
We know that the aircraft is pressurised from inside to make out air travel possible (you may cross refer the previous blog article for a clearer understanding). The aeroplane structure and the skin takes on the pressure exerted by the air inside the cabin. ..... in that context, the window pane acts as the skin for that area, leaving the window as the possible weak point in a pressurised aeroplane. To address this apprehension, the windows of commercial airliner are designed to be strong, self locking and tamper proof.
The outer layer (that we see from outside) is bonded to the aircraft structure from inside and takes the pressurisation load. The window size is kept small so that its strength is sufficient to hold against pressurisation. Additionally, the corners are rounded to distribute the load equally. In the newer aeroplanes like Boeing 787, the windows are comparatively larger - thanks to emerging technology in material sciences. Whatever be the size, the outer layer can take the usual brunt of rain, hail etc that the aeroplane goes through occasionally. However, it doesn't appear to guarantee damage from projectiles comprising foreign objects / debris of engine etc hitting it at right angles from outside.
So, the designers installed a middle layer, (as viewed from inside the aeroplane) as backup.The middle layer is made of equally strong material which is fitted just before the outer layer. Passengers can rarely make out the difference between the outer and middle layer as they are placed close to each other.
The inner layer (which fell off in the incident Air India flight) is essentially a protective cover over the middle layer and is part of the aesthetic panel to beautify the inside of the plane These aesthetic panels actually cover the aircraft parts underneath (including the outer window layer) which can otherwise look ugly to passengers. This layer of window is fixed to the aesthetic panel using plastic locks as in the case of our mobile back covers !! It is also kept scratch proof for obvious reasons. The inner layer is made shatter proof to avoid injury inside cabin. This layer of window pane has no role in the safety aspect of the plane.
Conventional planes have an additional layer over the inner protective layer in form of a shutter to keep sunlight away. However, in modern aeroplanes like the Boeing 787, the shutters are replaced with another layer coated with photo sensitive material and works as an electric curtain to simulate various light conditions outside . As in the conventional planes, this layer also doesn't have any role in the structural strength of the aeroplane.
The incident on board SW 1380 and the AI 462 has for the time being increased the anxiety levels of passengers. Falling panels (albeit due to turbulence) is indicative of poor maintenance or aging panels of their planes. Falling panel is embarrassing for the airline but definitely not a safety concern. On the other hand, the Southwest flight incident has demonstrated the vulnerability of the windows to the flying debris (usually from an uncontained damage to engine) that can come towards them and cause harm.
Passengers expect to see aeroplane windows made of impregnable material .....something like the bullet proof glass. They expect all the concerned industries to work togther and come up with solutions for known issues from shrapnel hitting and damaging window panes. Given the technological advancements in material sciences, this seems possible.
In conclusion, we can say that incidents like that on SW 1380 and AI 462 trigger avoidable anxiety. The designers and airlines need to work harder to make sure that these incidents are matters of past. Until the dust settles, more and more passengers are likely to take the isle seat in preference to the window seat.
A global mantra in the aviation safety - Always keep your seat belt on when seated in an aeroplane.
About the Author
Wing Commander K Dinesh is a former Indian Air Force officer and the founder of Cockpit Vista, an innovative Aircraft Simulator based set up in Mumbai (India). He is an Aviation Safety Consultant with emphasis on Flight Anxiety Removal amongst air travelers using a full size Aircraft Simulator. The Simulator is also utilised by pilots and corporates.
For details / booking please visit www.cockptvista.com or call +91 9833892747 (India)
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