The great thing about helicopters is you can fart and nobody can hear it so most of the time you can get away with it....problem is with only 2 in the helicopter...well if it wasn't me it must have been him..!!!
The only thing you can do is ensure that the airconditioning system (a.k.a Doors Off) is working.
Other options: don't fly so high, no eggs before departure!
On the other hand, the kudos with getting the free ride in the heli, far outweighs any 'fart' that I know, so maybe let him trump away, and take some smelling salts in your top pocket!
Good post Ninginoo
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