![Engine overhauls can take weeks or even months to complete, and all of that is time out of your calendar that you can’t fly. [Credit: Shutterstock]](https://www.flyingmag.com/wp-content/uploads/2024/10/shutterstock_10140554921-e17134561022881.jpg)
Every hour aloft, your engine is building toward an invoice you haven’t paid yet. Fuel, insurance, and hangar rent show up predictably on a calendar.
The overhaul bill doesn’t show up until the day a mechanic pulls a cylinder, finds metal in the filter, or simply tells you the clock has run out. By then it’s not a line item. It can be a $30,000 to $65,000 surprise with your airplane grounded until you write the check.
With a reserve, funded hour by hour, you can mitigate the bulk of overhaul expenses. The owners who don’t get surprised are the ones treating the overhaul like a loan they’re paying down in advance.
Math Is Usually Simple
The Aircraft Owners and Pilots Association’s guidance on estimating direct operating costs boils the whole exercise down to one formula—overhaul cost divided by the engine’s time between overhauls (TBO) equals your per-hour reserve rate.
AOPA’s worked example is a Cessna 172 facing a $17,000 overhaul over a 2,000-hour TBO, and it pencils out to $8.50 an hour. Swap in a factory remanufactured engine at $27,000 with 900 hours left on the clock, and that jumps to $30 an hour.
Same airplane, wildly different reserve, depending entirely on what’s bolted to the firewall and how much life is left in it.
Run the same formula across the fleet and the spread gets wider.
Jake Naviation’s 2025 overhaul cost guide puts a Lycoming O-360 overhaul at $25,000 to $35,000, a Continental IO-520 at $38,000 to $55,000, and a turbocharged Lycoming TIO-540 as high as $65,000. Those figures translate to reserve rates of roughly $15 to $18 an hour for a 172, $20 to $30 for a Cirrus SR22, and $22 to $32 for a Bonanza. At 75 hours a year, that’s the difference between setting aside roughly $1,125 and $2,400 annually.
AOPA’s guidance adds 25 cents an hour for a fixed-pitch prop and $1 an hour for constant-speed. Items like that are small compared to the more major overhauls, but they can still be a headache if you’re not prepared.
Lycoming extended TBO to 2,600 hours this year across seven popular engine families—O-320, IO-320, O-360, IO-360, IO-390, O-540, and IO-540. The change added 400 hours before the overhaul clock runs out on fixed-wing applications. More hours between five-figure bills lowers the effective annual cost of ownership.
What it doesn’t do is erase the calendar.
Lenders and appraisers still apply a roughly 12-year limit regardless of hours flown, because metal fatigue and corrosion don’t care how many hours are on the tach. An owner who flies 50 hours a year is getting 2,600 hours of runway or 12 years, whichever comes first. The extended TBO helps active flyers more than it helps hangar queens, and in either case, it’s not a substitute for a funded reserve.
Budgeting and Financing an Overhaul
Engine condition doesn’t only determine what you’ll owe a shop someday. It determines what a bank will lend you today.
Appraisers price remaining engine time directly into the aircraft’s value, and lenders advance loan amounts against that appraised value, meaning a run-out engine shrinks your borrowing power even if the airframe and avionics are pristine. Most lenders also expect a minimum 15 percent down payment on post-1960 singles, with the understanding that many owners will refinance once the engine is overhauled and the aircraft’s value resets upward. An underfunded reserve means less leverage to finance the shortfall.
Turbine owners face a version of the same pressure, just formalized.
AOPA’s finance desk notes that lenders frequently require enrollment in an hourly-cost engine program as a condition of the loan itself, specifically because an unmaintained engine on a repossessed jet is a liability the bank doesn’t want. Programs like JSSI’s hourly cost maintenance plans work exactly like the reserve math above, just outsourced. Owners pay a fixed rate per flight hour into what JSSI describes as a “piggy bank” that covers scheduled overhauls, hot-section inspections, and even unscheduled failures.
New aircraft typically get full coverage from hour one with no upfront cost. Aircraft already in service either pay a lump-sum buy-in for immediate full coverage or enter a pro-rata structure where coverage builds gradually.
Either way, lenders like seeing a reserve in place.
Fund Like You Mean It
The owners in the best position are calculating the per-hour number for their specific engine and TBO, moving that amount into a dedicated account every time they fly, and revisiting the figure whenever TBO guidance changes or the engine crosses into higher-wear territory.
Piston owners without the scale to justify a formal program can replicate the discipline with a simple separate savings account. Turbine owners should treat program enrollment as part of the financing conversation, not an afterthought after closing.
Either way, the reserve is a loan payment you’re making to your own future self. Skip it, and the bank or the mechanic collects the difference later, with interest.
Talk to our team of experts at FLYING Finance today for any financing questions or concerns.
