EASA AIRCREW
MED.B.001 Limitations to medical certificates

(d) Operational limitation codes

(1) Operational multi-pilot limitation (OML – class 1 only)

(i) When the holder of a CPL, ATPL or MPL does not fully meet the requirements for a class 1 medical certificate and has been referred to a medical assessor of the licensing authority, that medical assessor shall assess whether the medical certificate may be issued with an OML ‘valid only as or with qualified co-pilot’.
(ii) The holder of a medical certificate with an OML shall only operate an aircraft in multi-pilot operations when the other pilot is fully qualified on the relevant class and type of aircraft, is not subject to an OML and has not attained the age of 60 years.
(iii) The OML for class 1 medical certificates shall be initially imposed and only removed by the medical assessor of the licensing authority.