I do not know about liability regarding helicopter lease but if hired\leased equipment IS insured, the cost is high, on small plant a lot of hirers don't, and try and recover from hirer.
We hire a large amount electronic equipment, there is a clause in our hire agreement that "The hirer is responsible for loss or damage other than through normal use" This is allways pointed out at time of hire, & on delivery\ collection.
So either the cost is built in as self insurance or via an insurance Co.(Very Costly) or the hirer bears the cost, it has to be one or the other ??.