Simulated Instrument Flight is subject to Rule 23
Simulated instrument flight
23 (1) An aircraft shall not be flown in simulated instrument flight conditions unless the
conditions in paragraph (2) are met.
(2) The conditions referred to in paragraph (1) are as follows:
(a) the aircraft is fitted with dual controls which are functioning properly;
(b) an additional pilot (in this rule called a 'safety pilot') is carried in a second control
seat of the aircraft for the purpose of providing assistance to the pilot flying the
aircraft; and
(c) if the safety pilot's field of vision is not adequate, both forwards and to each side
of the aircraft, a third person, who is a competent observer, occupies a position
in the aircraft from which his field of vision makes good the deficiencies in that
of the safety pilot, and from which he can readily communicate with the safety
pilot.
Instrument approaches are covered by Rule 24
Practice instrument approaches
24 (1) An aircraft shall not carry out an instrument approach practice within the United
Kingdom if it is flying in Visual Meteorological Conditions unless the conditions in
paragraph (2) are met.
(2) The conditions referred to in paragraph (1) are as follows:
(a) the appropriate air traffic control unit has previously been informed that the flight
is to be made for the purpose of instrument approach practice; and
(b) if the flight is not being carried out in simulated instrument flight conditions, a
competent observer is carried in such a position in the aircraft that he has an
adequate field of vision and can readily communicate with the pilot flying the
aircraft.