When 'hiring' an aircraft for training or private hire the engine cannot have completed more than 120% of TBO.
So, with a TBO of 2000 hours, the aircraft can be 'hired out' whilst on extension up to 2400 hours. Beyond this it can continue in use ('on condition') but for private use only.
CAA CAP747 Generic Requirement No 24:
http://www.caa.co.uk/docs/33/CAP%207...203%202014.pdf
Para 3.1.2:
3.1.2 Engines that have complied with paragraphs 3.1 and 3.1.1, and have completed 120% of the recommended operating time or calendar time, whichever occurs first, may
continue in service indefinitely, subject to compliance with a), b), c) and d).
a) The engine being installed in an aircraft which is not used for the purposes of Public Transport or Aerial Work (with the exception of aircraft utilised for the purposes of towing gliders/sailplanes which are owned, or operated under arrangements entered into, by a club affiliated to the British Gliding Association).
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