When a helicopter is on fire it is really hard to extinguish it. First you have to land in time on a helipad. This can be done. But after that you have to get a wrench out of the helicopter. Walk to the front select extinguish and wait about 20 sec until the fire extinguish bar is full. Usually that is when it explodes. That al is a bit fiddly.
Why not put the fire extinguishing on every repair position. and stop the damage the helicopter is taking while extinguishing. Otherwise it is really hard to do. And also make it able to do it if you do not have a wrench because its like an emergency.