Time between overhauls - Misplaced Pages

(Redirected from Time before overhaul) Aspect of maintenance

Time between overhauls (abbreviated as TBO or TBOH) is the manufacturer's recommended number of running hours or calendar time before an aircraft engine or other component requires overhaul.

On rotorcraft, many components have recommended or mandatory TBOs, including main rotor blades, tail rotor blades and gearboxes.

For engines, the time between overhauls is generally a function of the complexity of the engine and how it is used. Piston-based engines are much more complex than turbine-powered engines, and generally have TBOs on the order of 1,200 to 2,000 hours of running time. They tend toward the lower number if they are new designs, or include boosting options such as a turbocharger. In comparison, jet engines and turboprops have TBOs from 3,000 hours up to 16,000 hours or more.

Since overhauling requires that the engine be disassembled, parts inspected and measured, and many parts replaced, it is typically a labour-intensive and hence expensive operation. The value of a used engine decreases as hours increase since its last overhaul, so sellers of used engines (and aircraft) typically list the engine's time since major overhaul (SMOH) when advertising the engine (or the aircraft it is fitted in) for sale.

The TBO is a time "recommended" by the manufacturer, and depending upon what rules the aircraft operates under, overhauling the engine at this time is not necessarily mandatory. Depending on the country of registration, aircraft in non-commercial use overhauls may not be mandatory; overhauls at the scheduled times are nevertheless highly recommended for reliability and safety. Likewise, overhaul at the TBO does not guarantee that the engine will last that long.

References

^ Teledyne Continental Motors (17 November 1998). "Time Between Overhaul Periods" (PDF). Retrieved 3 January 2015.
^ Government of Canada; Transport Canada; Safety and Security Group, Civil Aviation (22 July 2010). "Canadian Aviation Regulations - Part VI - Standard 625 Appendix C - Out of Phase Tasks and Equipment Maintenance Requirements". www.tc.gc.ca. Retrieved 3 February 2019.{{cite web}}: CS1 maint: multiple names: authors list (link)
Continental Motors, Inc. (17 July 2013). "Service Information Letter - Time Between Overhauls Periods" (PDF). www.continentalmotors.aero. Retrieved 3 February 2019.
"The most BANG for the Bucks -Part 1: PT6A engine TBO and HSI scheduling". www.pt6nation.com. Retrieved 3 February 2019.
"CFM56-3 Time On Wing Upgrade Performing Well In Service". CFM International. Retrieved 21 March 2024.
"* SMOH (Aviation) - Definition,meaning - Online Encyclopedia". en.mimi.hu. Retrieved 3 February 2019.

External links

What Makes an Engine Airworthy? AOPA

Aircraft piston engine components, systems and terminology

Piston engines

Mechanical components	Camshaft Connecting rod Crankpin Crankshaft Cylinder Cylinder head Gudgeon pin Hydraulic tappet Main bearing Obturator ring Oil pump Piston Piston ring Poppet valve Pushrod Rocker arm Sleeve valve Tappet
Electrical components	Alternator Capacitor discharge ignition Dual ignition Electronic fuel injection Generator Ignition system Magneto Spark plug Starter
Terminology	Air-cooled Aircraft engine starting Bore Compression ratio Dead centre Engine displacement Four-stroke engine Horsepower Ignition timing Manifold pressure Mean effective pressure Naturally aspirated Monosoupape Overhead camshaft Overhead valve engine Rotary engine Shock cooling Stroke Time between overhauls Two-stroke engine Valve timing Volumetric efficiency

Propellers

Components	Propeller governor Propeller speed reduction unit Spinner
Terminology	Autofeather Blade pitch Constant-speed Contra-rotating Counter-rotating Scimitar Single-blade Variable-pitch

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