Deductions & credits

I'm not sure there are two different questions, but there may be two different deductions involved.

The argument for full expensing and depreciation of vehicles does have its place.  When I ran a Part 135 air taxi operation out of Detroit, we used leased airplanes and paid air crew a salary based on a per mile rate.  The customers paid for freight or passage based on a distance in miles, the specific airplane used and any ground/layover time the airplane spent waiting beyond a reasonable amount.  For those operations it simply makes sense to garner as large a deduction as is permitted by law.  This would not be the GSA rate!

As far as the listed property argument, so are automobiles.  The key factor is: are they used more than 50% in the business.

On the other hand, taking a reasonable deduction which can be back calculated if need be to show it is, if anything in the government's favor, for a personally owned and operated airplane (Part 91, pleasure and business), seems very reasonable to me and I think if push came to shove, would certainly meet the reasonableness test the Tax Courts have consistently upheld. Flight and nav logs provide the necessary documentation and the logbook is an adequate contemporaneous record of the trip.  If the business purpose of the trip is also noted, it may be a complete record, but I keep other expense reports, just in case.

Consider GSA schedules further:  The GSA publishes a lodging and meals per diem schedule, which the IRS uses to calculate reasonableness of lodging and meal allowances.  In Chicago, this is $229/day lodging, Meals and incidentals $76 per day.  If I stay at the Ritz-Carleton I lose a a few bucks a day, the Drake, I'm ahead.   I suspect this rate will suffer greatly due to current events in the next iteration.   IRS Pub 463 discusses exactly this:  For travel expense away from home, for meals you can use, the actual expense, or a Standard Rate to determine the 50% deduction.  If you use actual expense, you must keep records (meaning receipts, I think).  Under the Standard meal/lodging allowance, you must keep records of the business purpose of the trip, location and dates.  Namely, an expense report.  You can deduct more, and likely would if you actually added the expenses and tips, or accept the federal per diem rate and call it a day, provided you actually write a contemporaneous expense report for each trip.  I keep my hotel receipts, but use the per diem as it simplifies my record keeping. 

The IRS specifically references GSA per diem rates in Pub 463 as acceptable for standard rate reimbursement.  I think that the IRS does not write a specific pub for occasional personal use of aircraft is the vast majority of air travelers use the airlines, not the family Cessna.  For those few that do, it is not worth their effort as nearly all NBAA (turbine/turboprop powered) aircraft will use the full tax code to maximize their rather significant deductible costs, while we have very limited costs.  

I think there is ample precedent throughout the IRS publications to make an solid argument, if called upon to do so, that the GSA is eminently qualified to determine a reasonable per mile cost, that cost is provable and does understate the overall operating and ownership costs, and therefore it is acceptable for a less than 50% business use, and certainly for a less than 10% business use.  It is reasonable to use that cost as the cost of my time for the 21+ hours of annual record keeping far outweighs any additional tax savings I might otherwise be entitled to.  Now, if I buy an MU-2, I might have a different approach.