without an MEL any snag can ground the machine.
Accepting that there are probable differences between EASA and Transport Canada, none the less, in Canada, as regulated by:
Unserviceable and Removed Equipment - Aircraft without a Minimum Equipment List
605.10 (1) Where a minimum equipment list has not been approved in respect of the operator of an aircraft, no person shall conduct a take-off in the aircraft with equipment that is not serviceable or that has been removed, where that equipment is required by
(a) the standards of airworthiness that apply to day or night VFR or IFR flight, as applicable;
(b) any equipment list published by the aircraft manufacturer respecting aircraft equipment that is required for the intended flight;
(c) an air operator certificate, a private operator certificate, a special flight operations certificate or a flight training unit operating certificate;
(d) an airworthiness directive; or
(e) these Regulations.
(2) Where a minimum equipment list has not been approved in respect of the operator of an aircraft and the aircraft has equipment, other than the equipment required by subsection (1), that is not serviceable or that has been removed, no person shall conduct a take-off in the aircraft unless
(a) where the unserviceable equipment is not removed from the aircraft, it is isolated or secured so as not to constitute a hazard to any other aircraft system or to any person on board the aircraft;
(b) the appropriate placards are installed as required by the
Aircraft Equipment and Maintenance Standards; and
(c) an entry recording the actions referred to in paragraphs (a) and (b) is made in the journey log, as applicable.
605.11 to 605.13 Reserved
The pilot has some discretion to fly with minor snags, if that pilot can demonstrate that the snag or U/S item was not required for the flight, under the prevailing conditions. So if the ashtray lid won't open, you can still fly the Citabria.
Ironically, it is the aircraft with the MEL, which is more severely bound, as
because it has the MEL, the pilot does not have the same freedom of determination any more!
I wonder how CAA is adding to safety asking for MEL's (or even the concept) for a Citabria.....