We need to look very carefully at what Subpart Q is and what it apparently sets out to achieve.
It opens with a section titled "FLIGHT AND DUTY TIME LIMITATIONS AND REST REQUIREMENTS" and requires an operator to establish a flight and duty time limitations and rest scheme. Compare that to the title of the UK CAA CAP371.Titled "The avoidance of fatigue in Aircrews".
Throughout its "objectives and scope" subpart Q does not identify that the avoidance of fatigue is its purpose, and the employer or operator is not required to produce a roster that takes account of fatigue. The only person or persons who are responsible for fatigue in the whole of Subpart Q are identified in paragraph 4 headed "Crew Member’s responsibilities".
"4.1 A crew member shall not operate an aeroplane if he/she knows that he/she is suffering from or is likely to suffer from fatigue or feels unwell, to the extent that the flight might be endangered"
It follows therefore that Subpart Q has not been published to minimise fatigue, but is simply a common maximum limit for duty and flight times within Europe. This is reinforced by Article 8a paragraph 1 "Within a period of three years following the entry into force of the present Regulation, the European Aviation Safety Agency will proceed to a scientific and medical evaluation of the provisions of Annex III, Subpart Q" The clear inference of this paragraph is that Subpart Q is not the same as, or could replace CAP371, but it might be some time in the future.
This leaves aircrew with a problem. They are required by "Q" not to fly while fatigued, but given no scientific or medical guidance on which to base their judgement. Surely the answer is for ECA to provide guidance. I would suggest that as it is impossible for crews not rostered to CAP371 to adopt its guidelines on fatigue unless the companies agree to roster to 371 limits. The alternative is for the ECA to use the medical and scientific evidence that they already possess to produce a software programme that enables pilots not covered by "avoidance of fatigue" rules to enter their rostered and actual duties and provide guidance as to whether the rostered duty is liable to cause fatigue. If it was found to be so the obligation of "Q" is clear. The aircrew is legally obliged by Subpart Q not do the duty. More importantly, complying with "Q" will not absolve the crew from flying while fatigued because it clearly isn't designed to do so.