TBO is the manufacturer's recommended operating time between engine or component overhauls — typically 1,800–2,200 hours for piston training engines. Overhauls are a school's largest single maintenance cost, so forecasting TBO across the fleet is central to budgeting and fleet planning.
Time Between Overhaul (TBO) is the manufacturer's recommended maximum operating time between complete overhauls of an engine, propeller or component — typically 1,800–2,200 hours (often paired with a 12-year calendar limit) for the piston engines that power training fleets. At overhaul, the unit is disassembled, inspected, restored to defined tolerances and re-certified.
Whether TBO is binding depends on the operational context: for many private and light-training operations it is a recommendation that can be exceeded 'on condition' with appropriate monitoring, while commercial frameworks and specific national rules often make it a hard limit. Either way, TBO drives the largest single line in a training fleet's maintenance economics — a piston overhaul runs €25,000–45,000+ per engine.
Why it matters for flight schools
TBO forecasting is fleet-level financial planning disguised as maintenance data. Three trainers converging on overhaul in the same season is a six-figure cash event plus weeks of lost capacity — visible years in advance to anyone tracking hours against limits, and a crisis to anyone who isn't. Per-hour engine reserves only work if the hours are captured accurately, which is exactly the Hobbs/tach discipline many schools lack.
How FlightLogger handles it
FL Maintenance projects every engine and propeller against its TBO from live utilization data — so overhauls appear on next year's budget and downtime plan, not this month's emergency list.
Frequently asked questions
Can a training aircraft engine legally run past TBO?
In many non-commercial and light-training contexts, yes — 'on condition' operation with oil analysis, compression checks and trend monitoring is common and legal. Commercial operations and some national regimes treat TBO as mandatory. Insurance and school policy often decide in practice.
How should a school budget for overhauls?
Set an hourly engine reserve — overhaul cost divided by expected TBO hours — per aircraft, and track accrual against actual hours flown. Fleet-level TBO forecasting then shows when the reserves will be called on.