In United States aviation, VFR-on-top is defined as air traffic control authorization for an aircraft operating under instrument flight rules (IFR) to do so in visual meteorological conditions (VMC) at any appropriate visual flight rules (VFR) altitude.
[1] VFR-on-top permits pilot operation above, below, between cloud layers, or in areas where visual meteorological conditions can be met.
[2][3] Pilots must request air traffic controllers (ATC) to obtain the VFR-on-top clearance.
ATC authorization will include a cloud top report and a request to report upon reaching the top; it may also include a clearance limit, routing, and an alternative clearance if VFR-on-top is not reached by a specified altitude.
Pilots operating on a VFR-on-top clearance must advise ATC before any altitude change.