That income can be expensed out fairly easily in the grand scheme of things if it is just temp work, IMO.
Now if you are planning to do this a lot over a long period of time, when/if you get audited, the IRS will probably determine that you should have paid taxes and then it will be up to you, and your lawyers, to prove them wrong or reach a settlement.
BTW, you should also ask the owner how he is accounting for it. He may be trying to expense out his plane at a loss so his hobby is being paid for as a business tax deductions. If he gets nailed by the IRS, you will get pulled into an audit as well.