Inform an aircraft maintaining “VFR-on-top” when a report indicates the pilot is not complying with 14 CFR Section 91.159(a).
As required by 14 CFR Section 91.159(a), the appropriate VFR altitudes for aircraft (not in a holding pattern of 2 minutes or less, or turning) operating more than 3,000 feet above the surface to and including 18,000 feet MSL:
Magnetic courses 0-179- odd cardinal altitudes plus 500 feet; e.g., 3,500, 5,500.
Magnetic courses 180-359- even cardinal altitudes plus 500 feet; e.g., 4,500, 8,500.
VFR-ON-TOP CRUISING LEVELS FOR YOUR DIRECTION OF FLIGHT ARE:
more than 3,000 feet above the surface to FL 180:
ODD/EVEN ALTITUDES/FLIGHT LEVELS PLUS FIVE HUNDRED FEET.