269. Wherever in this Order there is provision for the issue or grant of a certificate, authorisation, approval or permission by the CAA, unless otherwise provided, such a certificate, authorisation, approval or permission—
(a)must be in writing;
(b)may be issued or granted subject to such conditions as the CAA thinks fit; and
(c)may be issued or granted, subject to article 253, for such periods as the CAA thinks fit.