Unless you are flying a Part 103 gyroplane, in which case there are no altitude limitations. The only operational limitations for Part 103 Ultralights are:
Sec. 103.9 Hazardous operations.
(a) No person may operate any ultralight vehicle in a manner that creates
a hazard to other persons or property.
(b) No person may allow an object to be dropped from an ultralight
vehicle if such action creates a hazard to other persons or property.
Sec. 103.11 Daylight operations.
(a) No person may operate an ultralight vehicle except between the hours
of sunrise and sunset.
(b) Notwithstanding paragraph (a) of this section, ultralight vehicles
may be operated during the twilight periods 30 minutes before official
sunrise and 30 minutes after official sunset or, in Alaska, during the
period of civil twilight as defined in the Air Almanac, if:
(1) The vehicle is equipped with an operating anticollision light visible
for at least 3 statute miles; and
(2) All operations are conducted in uncontrolled airspace.
Sec. 103.13 Operation near aircraft; right-of-way rules.
(a) Each person operating an ultralight vehicle shall maintain vigilance
so as to see and avoid aircraft and shall yield the right-of-way to all
aircraft.
(b) No person may operate an ultralight vehicle in a manner that creates
a collision hazard with respect to any aircraft.
(c) Powered ultralights shall yield the right-of-way to unpowered
ultralights.
Sec. 103.15 Operations over congested areas.
No person may operate an ultralight vehicle over any congested area of a
city, town, or settlement, or over any open air assembly of persons.
Sec. 103.17 Operations in certain airspace.
No person may operate an ultralight vehicle within Class A, Class B,
Class C, or Class D airspace or within the lateral boundaries of the surface area
of Class E airspace designated for an airport unless that person has prior
authorization from the ATC facility having jurisdiction over that airspace.
EFFECTIVE DATE NOTE: Amdt. 103-4, 56 FR 65662, Dec. 17, 1991, revised
Sec. 103.17 effective September 16, 1993. The text of Sec. 130.17 in effect
until September 16, 1993 reads as follows:
Sec. 103.17 Operations in certain airspace.
No person may operate an ultralight vehicle within an airport traffic
area, control zone, airport radar service area, terminal control area, or
positive control area unless that person has prior authorization from the air
traffic control facility having jurisdiction over that airspace.
[Doc. No. 23708, 50 FR 9259, Mar. 6, 1985]