C152 - you may find this (Doc 7030 extract) of use regarding an emergency descent from a random track. (My bold and see reference to 'organised tracks' eg Nat Tracks). It would be foolish to merely offset 15nm from the
random track and then steam blissfully across
all the others
9.1.1.1.2 An aircraft compelled to make a descent through MNPS airspace, whether continuing to destination or turning back, should,
if its descent will conflict with an organized track:
a) plan to descend to a level below FL 280;
b) prior to passing FL 410, proceed to a point midway between a convenient pair of organized tracks prior to entering that track system from above;
c) while descending between FL 410 and FL 280,
maintain a track that is midway between and parallel with the organized tracks; and
d) contact ATC as soon as practicable and request a revised ATC clearance.
As we say, it depends on knowing where you are and they are
I think you will find Mutt's ref should read 13.3.1 in 007