Many thanks to all!
To save anybody else looking it up, the NTSB document says:
"Aircraft accident means an occurrence associated with the operation
of an aircraft which takes place between the time any person boards the
aircraft with the intention of flight and all such persons have
disembarked, and in which any person suffers death or serious injury, or
in which the aircraft receives substantial damage."
"Incident means an occurrence other than an accident, associated with
the operation of an aircraft, which affects or could affect the safety
of operations."
(The document then defines fatal and serious injury, and substantial damage, in more detail.)
Those definitions also fit in far better with common usage than my too restrictive definiton.
So the first event quoted in the thread start qualifies as an accident (substantial damage), the second one does not, even if it definitely qualifies as an incident (loss on power on both engines....).