Text in force at CS23-6: from CS23-5, effective 15 Aug 2017.
(a) Aeroplanes not certified for aerobatics must:
(1) have static longitudinal, lateral, and directional stability in normal operations;
(2) have dynamic short period and Dutch roll stability in normal operations; and
(3) provide stable control feedback throughout the operating envelope.
(b) No aeroplane may exhibit any divergent longitudinal stability characteristic so unstable as to increase the pilot’s workload or otherwise endanger the aeroplane and its occupants.
ED Decision 2017/013/R · Source