Falls das hier mal für irgendwen irgendwann wichtig wird, in einem anderen Forum kam der Hinweis auf eine EASA Definition für primary flight controls, zu finden in der EASA CS 23.673 (European Aviation Safety Agency - Certification Specifications for Normal, Utility, Aerobatic, and Commuter Category Aeroplanes, CS-23).

https://www.easa.europa.eu/certification-specifications/cs-23-normal-utility-aerobatic-and-commuter-aeroplanes

Dort steht:

CS 23.673 Primary flight controls: (a) Primary flight controls are those used by the pilot for the immediate control of pitch, roll and yaw.

Aus den Part FCL hier noch mal die 2016er Regelungen,

E-IR:

AMC2 FCL.825(h) En route instrument rating (EIR)
TRAINING AIRCRAFT
The aeroplane used for the instrument flight time under instruction provided outside an
ATO by an IRI(A) or FI(A) should be:
(a) fitted with primary flight controls that are instantly accessible by both the student and
the instructor (for example dual flight controls or a centre control stick). Swing-over flight
controls should not be used; and
(b) suitably equipped to simulate instrument meteorological conditions (IMC) and for the
instrument flight training required.

IR / CB-IR:

AMC4 to Appendix 6 Modular training courses for the IR
SECTION Aa IR(A) – COMPETENCY-BASED MODULAR FLYING TRAINING COURSE
FLYING TRAINING
(a) The instrument flight instruction outside an ATO provided by an IRI(A) or an FI(A) holding the
privilege to provide training for the IR in accordance with Appendix 6 Section Aa (6)(a)(i)(A) may
consist of instrument flight time under instruction or instrument ground time or a combination
thereof.
TRAINING AIRCRAFT
(b) The aeroplane used for the instrument flight training provided outside an ATO by an IRI(A) or
FI(A) should be:
(1) fitted with primary flight controls that are instantly accessible by both the student and the
instructor (for example dual flight controls or a centre control stick). Swing-over flight controls
should not be used; and
(2) suitably equipped to simulate instrument meteorological conditions (IMC) and for the
instrument flight training required.
(c) The FSTD used for the instrument flight instruction provided outside an ATO by an IRI(A) or FI(A) should
be suitably equipped to simulate instrument meteorological conditions (IMC) and for the instrument flight
training required