Aircraft acquisition price is the visible 60-70% of the five-year cost picture. The hidden 30-40% — engine reserves, avionics compliance, scheduled inspections, hangar, insurance, fuel exposure, and crewed operations — is where buyers who anchored on asking-price get hurt.
Engine reserves
Hourly engine reserves on PT6s, FJ44s, PW535s, and HTF7000s run $200-$1,200/hr depending on hot-section status, cycle history, and program coverage. A pro-rated program turns reserves from a balance-sheet liability into an operating cost, and re-aligns resale.
Avionics compliance
2020 ADS-B Out is now table stakes; 2026 brings tighter scrutiny on FANS 1/A and CPDLC for international ops. A nominally cheap airframe that needs $400-$800k of avionics modernisation is not actually cheap.
Scheduled inspections
2C, 3C, and gear overhaul cycles are predictable. Build them into the five-year model up front. A jet bought one cycle ahead of a 3C can carry $300-$600k of deferred inspection on the books.
Hangar and insurance
Hangar is regional and lumpy. Insurance is named-pilot and rated against type. Both compound on resale — an airframe insurance underwriters dislike is harder to sell.
Fuel exposure
Jet-A at $5.50 vs $7.50/gal moves a 350-hour annual fleet by $80-$140k. Hedge if you can; budget for the upper end if you cannot.
Crewed operations
Owner-flown vs crewed: 2 type-rated pilots, training, recurrent, simulator slots, plus a chief pilot or operations director above 350-400 hours/year. The crew layer is real and material.
Bottom line: if your TCO model only has acquisition, fuel, and "maintenance," it is missing 25-40% of the picture. The CompAeros TCO model breaks all seven layers out separately.