but why not simply require Supplemental Air Devices for all over water flights and prevent folks having to solely rely upon a single breath to escape from a submerged aircraft?
A few years ago I completed an offshore course in Rotterdam NUTEC which included a HUET course, designed for oil rig workers. We were taught the use of "Shark" brand vests that had a rebreather and a vest that had a rebreather (Shark airpocket plus) with the addition of a small bottle of 02 that inflated the rebreather bladder (not enough for it to become buoyant) so it gave another +20 seconds of air.
We were unable to have a practice with any ancillary air because according to the instructor the admin and H&S paperwork makes it onerous and also due to the number of people they teach that their would likely be a medical issue sooner or later. Shark website states that "Air Pocket Plus has been designed to minimize the risk of cerebral arterial gas embolism which results from any system which introduces supplementary gas" So perhaps this is what the training organisations worried about?
Looking far forward, what is needed is a more user friendly face mask for passengers something that can be easily donned or better yet, is comfortable enough to worn for the entire flight. All of the spare air and rebreathers don't use a mask but a mouthpiece, it is quite difficult to think about not breathing through your nose, especially if suffering cold shock. A nose clip avoids involuntary water inhalation, this they are uncomfortable to wear for the entire flight and unlikely to be deployed by a novice in an emergency in my view.
Anyway, helmets should be a priority followed by spare air?
Thinking high tech, for passengers, how about a one piece sealed helmet that, on contact with water switches from environmental air to (1 minute) of bottled air housed in the helmet? Would need some new technology to create a seal at the neck or otherwise the helmet could be incorporated into the design of the immersion suit.
Although an immersion suite protects most parts of the body it offers zero protection for the airway.
Mickjoebill