Air Testing
If you're a junior pilot, you may find yourself doing quite a bit of this, anything from just engine running to full C of A air tests, although many engineers are cleared for engine runs. The reason why junior pilots tend do them is because they're boring and regarded as a waste of time by anyone except engineers. Nevertheless, Air Testing demands your full concentration and everyone due to fly in the aircraft later deserves it as well. One point to bear in mind is that the aircraft is only technically serviceable for the air test—if in doubt, insist that an engineer goes with you; if he won't fly, then don't you bother either.
The least taxing are straight engine runs. When a sliver of metal is detected in oil, there can follow an engine run for anything up to two hours or so (I have known one for five) to see if it happens again. Then there are compass swings where you place the aircraft on a series of headings on an isolated spot well away from large hangars and other machines, while someone with a landing compass stands outside in the cold and rain taking readings. Comparison of your readings with his, adjusted with certain formulae, give the corrections (fixed Wing ATPL holders in UK can do compass swings).
The shorter air tests tend to concern themselves with the proper rigging of flying controls. The longer ones creep into the full-blown C of A air tests which are Extremely Official and done under strict procedures. For these, you must be on the Maintenance Contractor's approved list of test pilots , which means having some experience on type and flying accurately.
The basic idea is to perform a series of prescribed manoeuvres (timed climbs, for instance) while an engineer takes notes of temperatures and pressures, etc. The results are plotted on performance graphs (by you) so they can be compared against the standard figures in the Flight Manual, which is where you see how accurate your flying really is, when the plotted points end up all over the place instead of being in a straight line. Before you start, though, be sure that the rotors are as clean as you can get them, because their state will make a surprising difference on the climb figures.