Airbag deployed while 4WDing

[Marko]

I need some technical info regarding airbags on an 05 X5 3.0D.

While descending a (approx) 25 degree clay slope of about 10ft vertical, the skid plate under the transfer case hit a small rock and the passenger side airbags deployed (all except the dash). My passenger was injured and not impressed.

I had HDC on and was travelling very slowly. There is evidence of a scrape on the transfer case protection plate and cross-member but there was no impact anywhere else and certainly nothing from the side. The cost of replacing the airbags is $13k and the dealer says it's my fault. It's still under a 3 year warranty.

They have supplied me with diagnostics data showing a crash telegram was sent and triggered the bags - that much I know as I was in the car!

Does anyone know of similar incidents or better still about the dynamics of the airbags system and what it is meant to do (and not do)? I was doing far less than BMW say the car can do when advertising (videos, website pics, description of capabilities) and this just seems plain unsafe. The manual says 45 degrees and there is no mention that the airbags might trigger if you touch bottom or run over something mild.