'Burp' your suit
What ever dry suit you eventually use, please remember to expel as much air as possible from it before entering the aircraft. Any air in the suit will trap you in a submerged aircraft just as efficiently as an inflated lifejacket. You can do this by squatting down and squeezing in with your arms while holding the neck seal open. It doesn’t get all the air out, but it helps.
I’ve seen a couple of ‘entertaining’ incidents when using immersion suits as cheap diving dry suits. The first involved someone diving headfirst in to a swimming pool and subsequently floating head-down with two air filled sausage legs. The other was finding the meaning of the term suit squeeze at twenty foot down while using an ex mil. helicopter crew suit as a cheap dry suit. Thankfully the booties were thin enough to be able to fin back to the surface, because the rest of my body was locked rigid!
Safe Flying,
Richard W.