14 CFR §101.39

1. (a)Each person operating an unmanned free balloon shall:
   1. (1)Unless ATC requires otherwise, monitor the course of the balloon and record its position at least every two hours; and
   2. (2)Forward any balloon position reports requested by ATC.
2. (b)One hour before beginning descent, each person operating an unmanned free balloon shall forward to the nearest FAA ATC facility the following information regarding the balloon:
   1. (1)The current geographical position.
   2. (2)The altitude.
   3. (3)The forecast time of penetration of 60,000 feet standard pressure altitude (if applicable).
   4. (4)The forecast trajectory for the balance of the flight.
   5. (5)The forecast time and location of impact with the surface of the earth.
3. (c)If a balloon position report is not recorded for any two-hour period of flight, the person operating an unmanned free balloon shall immediately notify the nearest FAA ATC facility. The notice shall include the last recorded position and any revision of the forecast trajectory. The nearest FAA ATC facility shall be notified immediately when tracking of the balloon is re-established.
4. (d)Each person operating an unmanned free balloon shall notify the nearest FAA ATC facility when the operation is ended.