Engine TBO: what it means and whether you can exceed it

What time between overhaul means for piston engines, calendar limits, and when private owners may fly beyond it.

The short answer

TBO is the manufacturer’s recommended number of hours, and often years, between engine overhauls. Many light piston engines have a TBO around 1,800 to 2,000 hours or 12 years. For privately operated aircraft under Part ML, the maintenance programme may allow going beyond it on condition, with extra checks.

Hours and calendar

Engines age even when they do not fly. Corrosion inside a rarely used engine can be worse than wear in one flown every week. That is why a calendar limit exists alongside the hour limit.

Flying beyond TBO

Where permitted, owners typically add regular compression tests, oil analysis, borescope inspections and filter checks. The decision must be written into the maintenance programme and agreed with whoever reviews it. Commercial operations generally cannot do this.

Planning for it

An overhaul costs a significant share of a light aircraft’s value. Setting aside an engine reserve every flying hour means the bill does not come as a shock.