47 CFR 95.215 - (R/C Rule 15) Do I have to limit the length of my communications?
(a) You must limit your R/C communications to the minimum practical time.
(b) The only time your R/C communications may be a continuous signal for more than 3 minutes is when operation of the device requires at least one or more changes during each minute of the communications.
(c) Your R/C station may transmit a continuous signal without modulation only if:
(1) You are using it to operate a model aircraft device; and
(2) The presence or absence of the signal operates the device.
(d) If you show that you need a continuous signal to insure the immediate safety of life of property, the FCC may make an exception to the limitations in this rule.