Attitude when occupying height: scaffolder ready to go off at any moment (11)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

[AIR (=attitude, aura) + HT (=height)] + RIGGER (=scaffolder); according to Chambers , when used adjectivally, hair-trigger means “responding to the slightest stimulus”, hence “ready to go off at any moment”