It was rough weather and i was flying to go a rescue mission. i was using alt hold and cruise hold. then the heli flipped upside down and plummeted into the ocean. idk if thats a bug or the weather or something i did.

So what can happen is if you fly on cruise control at 150kph or above that the may stabilizer overreact, especially in bad weather. Might have been that. Its something thats sadly not really worth fixing since the computer systems are kind of a mess due to many iterations. I am working on a far better twin rotor air rescue craft, but I also hit a snag with the flight control system I was making for it

That makes sense becuse i was going like 175kph thanks. one more thing how do i lose altitude. if i lower throttle it does nothing and i lower the altitude hold the thing just falls out of the sky thanks.

So the altitude hold kinda is similar to cruise control in its limitations, so to change altitude try only making small steps of maybe 20-30m at a time. Although if I have time this is an issue I *might* be able to fix quickly.
All in all many of the flight systems on this were prototypes for me, so there is a lot of redundancy and weirdness in the systems thats hard to get rid of.