I'm in a similar boat, in that I'm looking to purchase a simple SEP, PA28, 172 or similar and I am just starting to gather costs to calculate costs per hour. So far I have the following in my spreadsheet...
Purchase Price: doesn't really matter as it holds it's value pretty well and as phiggsbroadband has said, it can be ignored.
Running Costs:
Yearly Costs
Parking: from £1,500 per year - tarmac
Service: Annual: £4,000 approx
Insurance: £3,000 per year approx
Hourly Costs
Service: 50 hr = £ 200
Service: 150 hr = £ 500
Fuel: Estimated 40 litres per hour: £79.20
Engine: 2000 hrs = £16,000
Therefore prices can be calculated as follows:
Hourly: £90.80
Monthly Costs: £708.33
The difficult calculation is guessing how many hours per year the aircraft will be flown. Therefore to fly it at 1 hour per month will cost the owner £799.13 per hour. Or fly 100 hours per month will cost just £97.88 per hour.
Am I even close? Have I missed anything?
