Fire crews were called around noon on Saturday to reports of the fallen banner, which became entangled with power lines in the area of Brannan and Fifth streets, according to a fire captain.
No injuries were reported, but the incident caused a power outage for 2,000 PG&E customers in the area, according to utility spokesman J.D. Guidi.
Some 125 customers remained without power and crews remained on the scene repairing the downed power line spans as of 3:15 p.m.
Power is expected to be fully restored by 5:30 p.m., Guidi said.
Information about the aircraft carrying the fallen banner was not immediately available.