wrote in message
...

The only regulation I know about in that regard is that I have to fly at a
VFR altitude.


VFR-on-Top relieves the pilot of the requirement to maintain an altitude
assigned by ATC found in FAR 91.179(a), but it does not relieve him
of the minimum altitude requirements of FAR 91.177(a). While
operating VFR-on-Top the pilot must still maintain the minimum altitude
applicable to his assigned route. If operating on airways, that would be
the MEA or MOCA. If operating off-airways, the pilot would have to
determine the
minimum altitude that complies with FAR 91.177(a).


Sec. 91.177 Minimum altitudes for IFR operations.

(a) Operation of aircraft at minimum altitudes. Except when necessary
for takeoff or landing, no person may operate an aircraft under IFR below--

(1) The applicable minimum altitudes prescribed in Parts 95 and 97 of
this chapter; or

(2) If no applicable minimum altitude is prescribed in those parts--

(i) In the case of operations over an area designated as a mountainous
area in part 95, an altitude of 2,000 feet above the highest obstacle within
a horizontal distance of 4 nautical miles from the course to be flown; or

(ii) In any other case, an altitude of 1,000 feet above the highest
obstacle within a horizontal distance of 4 nautical miles from the course to
be flown.

However, if both a MEA and a MOCA are prescribed for a particular route or
route segment, a person may operate an aircraft below the MEA down to, but
not below, the MOCA, when within 22 nautical miles of the VOR concerned
(based on the pilot's reasonable estimate of that distance).


Sec. 91.179 IFR cruising altitude or flight level.

(a) In controlled airspace. Each person operating an aircraft under IFR
in level cruising flight in controlled airspace shall maintain the altitude
or flight level assigned that aircraft by ATC. However, if the ATC clearance
assigns "VFR conditions on-top," that person shall maintain an altitude or
flight level as prescribed by Sec. 91.159.