Originally Posted by
megan
Well, some one better tell the FAA
FAR 43, Appendix A, (c), (20) states "Replacing or cleaning spark plugs and setting of spark plug gap clearance" as part of preventative maintenance. The famed Len Morgan of Braniff, besides his aviation publishing business, ran a side line in cleaning and gapping his airlines plugs back in the day.
My bad. Someone with more knowledge on maintenance that I do told me on the Radials P&W one rotate the plugs and check gaps indeed on the periodic maintenance.