I really don't care enough to put that much effort into this. You do realize, however, that air pressure changes in both directions, right? If what you're saying it true, I'm shocked he even had to open it inflight–I would've expected the case's rapid decompression to take care of that, unless you want me to believe this company has designed a camera case with a latch that can support my entire body weight. If that's true, color me impressed.

Now this is getting interesting :)

Turns out I opened my other watertight box while in the air too, but I'm probably just going to wait that one out instead of breaking. Also stuck, so it's definitely the pressure.

You only need to create a tiny gap between the o-ring and the case for a fraction of a second to equalize the pressure because the volume of air inside the case is so small. With no knowledge of the particular case it's hard to say how to accomplish that. But whatever works, and hammer it is. :)

When you take it up in the plane the pressure difference causes air inside to leak out. If the o-ring is very tight and sticky, it would take a fraction of a psi to pop it open. It would not be violent. The latch doesn't actually do much: it holds the case together only tight enough to get it safely into the water and then the water pressure forces the halves together against the o-ring.

I don't think it's reasonable to assume that the average person understands the effects of pressure changes while flying. I think it's a fair point.

That explains it. I originally tried nailing into the case to create a hole and normalize pressure, but the polycarbonate was too hard, and bent but would not break. I guess the force of the hammer bent the seal, normalizing pressure, and popping the seal open.

Late to the party but most of these cases do not seal plastic to plastic so you can insert a flat head screw driver and turn it. It will mar the case a bit but that will break the seal. Conversely if you have wide stiff piece of metal like a pry bar you can put that in between and pry it open which will distribute the force and less chance of the case being marred.

This case sandwiches a piece of plastic between two other pieces, which creates a pretty solid seal.

I had an Olympus semi weathertight (not underwater like some of them, but snow and rain proof) point and shoot film camera that had a clamshell case with full Oring. I changed the film at altitude in the plane. Later I had a HECK of a time opening it at sea level, just like the OP. I finally figured out the pressure was keeping it shut and managed to twist the case enough to warp open the Oring seal and let in air.

Long ago on a solo cross country I took a Cessna 150 up to about 8 or 9K for the heck of it. Took a LOOONG time, as the rate of climb gets real slow over 5K. Also takes a long time to get down. ATC won't let you get over the airport and put it in a spin and come straight down fast.

Wine bottles have no pressure or vacuum in them. Champaign bottles have about 5 ATM or 80 PSI PRESSURE inside pushing the cork out, hence the wire safety cage to hold the cork. Vacuum would suck the cork IN.

I amuse myself and fellow pax by keeping a pint disposable water bottle at my seat. I carry an empty one through TSA and fill it airside or in the plane to have my own supply esp. on long transocean flights.

The Fasten Seatbelt and Turn Of Electronics warnings are at 10K feet. Since the cabin is at about 8K pressure altitude, I finish the water and tightly cap the bottle and place it in my lap or on the tray table. Sure enough right about 8K feet the bottle starts imploding and by about 1K feet is really smashed. Nonscientific seatmates watch the slow motion crush and have to ask “Why is that bottle doing that?” I tell them the bottle is my Poor Man’s Passenger Altitude Indicator. :D

Try any high end restaurant. Most of them now have chamber vacuum sealers for Sous Vide cooking

That's awesome. Doing that on my next flight. Here's the question. Crush and seal a water bottle on the ground. Does it expand at cruising altitude back to normal shape?

But if you put it inside a vacuum chamber, how will you then open the case once its under vacuum?

Just a rubber band to pull it open?

Take some bubble wrap on a flight. I'm sure it won't explode because they use it for shipping stuff all the time. But you should feel a few more pounds of pressure when you test it by squeezing.

The case wouldn't happen to be one of these inexpensive Case Logic boxes from Walmart, would it?
http://www.walmart.com/ip/Case-Logic.../21671991?_mm=

I've got one of those, and I can see where it might be difficult to pop the seal if the interior got depressurized. The bottom plastic half has aan edge which presses into the soft rubber gasket in the top half, but the top half has a lip which overlaps the gasket so you can't stick anything in between the halves to break the seal. And because of the lip, the two halves wouldn't slide sideways, even if you pop the hinges and latches off.

A nice problem, as they say. If my camera got stuck in that box, I'd probably take a drill to it rather than a hammer; with a drill and a small bit, I could control direction, but hammering on the outside risks translating the impact to the camera inside. At least, if the box in question actually IS one like mine, because mine is only padded on one side, not the other, so impacts translate to the camera quite readily.

Simple - when you put it in there, unlatch it. When the chamber depressurizes until it's a few PSI lower than the interior of the case - and it won't take much - then the interior pressure of the case will pop it open like a champagne bottle. Dink... voila!

Given the rampant paranoia on planes these days, anything which has the potential to make a POP POP POP sound poses a grave danger - to you. Scare the pax, wind up in Gitmo. Personally, I wouldn't take that risk.