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Lycoming engines in certain specific airframe types have been approved by the CAA for the use of unleaded Mogas, using the process described in CAP747, See Section 2, Part 4, General Concession 5. This involves purchasing an STC (Supplemental Type Certificate) from either the EAA or Petersen Aviation in the USA and carrying out the actions called for by the STC.  The procedures stated in CAP747 may be followed for LAA aircraft but only for aircraft with the exact same engine/airframe combinations quoted on in CAP747..

An LAA inspector must check that the aircraft operator has obtained a copy of CAP747, Section 2, Part 4, GC5 and of the appropriate STC and complied with the actions called for therein, and signed off a suitable logbook entry accordingly before the aircraft may be flown with unleaded Mogas.

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