It was at standard pressure (sea level ish)? And the nitrogen's fine for coming and going to the habitat as you wish (without the bends) because the pressure's so much lower? What about the oxygen toxicity from breathing normal air? Is that also fine because of the low relative pressure of the oxygen containing gas?
The atmosphere in the habitat is specified to be 33 atmospheres, mostly helium and oxygen.
The characters need to use "talkers" because their voices would be too high pitched to be understandable otherwise.
I think the author either forgot about the talkers when the characters were in the plane, or left them out. How he describes a voice "echoing" in the 96+ percent helium of the plane does not really make sense. Also, why does the plane have enough helium and oxygen gas to pressurize up to 33 atmospheres? Helium leaks like hell, right? It lasted that long? And it can't really have switched from something else, based on how the "wacky events" are claimed to happen in the book. If the ship has an AI, it's probably just standard control loops attached to an expert system (based on Crichton's other books, is that a fair assumption?), I doubt it would detect people outside and then adapt.
Wouldn't it get crushed before it had the opportunity to be pressurized in the first place? I doubt the mission planners knew it would jump into water, but I guess it was in shallower water and then sunk/the seabed collapsed or something?
If that's the explanation, it must have been pressurized according to an algorithm the entire time, not based on the habitat. The habitat was never connected to the plane before the characters went in, they walked over in suits.
I can't really see how something like that would last that long. Current soft plastics don't, and I don't really think that's solvable with incremental improvement, but incremental improvement is what's shown in the book.
Sure, you can add antioxidants to polymers, but that competes with dyes/carbon black for UV resistance, and flame retardants, for the filler percentage. Too high a filler percentage and the mechanical properties go in the trash, you can quite commonly see this with plastic parts that attach to circuit boards, they're really brittle. With soft plastics, you usually need plasticizers too, and those leach out/degrade over time, and I have no idea how to to fix that.
I'm thinking a fluoroelastomer with antioxidant/carbon black/some flame retardant as fillers, but fluoroelastomers don't have very good mechanical properties in the first place. I think that's really pushing it.
I'll have to revisit the chapter but I believe there was a few pages about the door, and a large hiss.
I assume the spacecraft detected and matched the artificial habitats - that's what I had meant, not surface atmosphere.