14 CFR § 91.309

No person may operate a civil aircraft towing a glider or unpowered ultralight vehicle unless—

The pilot in command of the towing aircraft is qualified under § 61.69 of this chapter;

The towing aircraft has:

A standard airworthiness certificate and is equipped with a tow-hitch of a kind, and installed in a manner, that is approved by the Administrator;

A special airworthiness certificate for which a type certificate has been issued, and is equipped with a tow-hitch of a kind, and installed in a manner, that is approved or otherwise authorized by the Administrator; or

A special airworthiness certificate, for which the aircraft has not been previously issued a type certificate, and is equipped with a tow-hitch of a kind that is approved or otherwise acceptable to, and is installed in a manner acceptable to, the Administrator;

The towline used has breaking strength not less than 80 percent of the maximum certificated operating weight of the glider or unpowered ultralight vehicle and not more than twice this operating weight. However, the towline used may have a breaking strength more than twice the maximum certificated operating weight of the glider or unpowered ultralight vehicle if—

A safety link is installed at the point of attachment of the towline to the glider or unpowered ultralight vehicle with a breaking strength not less than 80 percent of the maximum certificated operating weight of the glider or unpowered ultralight vehicle and not greater than twice this operating weight;

A safety link is installed at the point of attachment of the towline to the towing aircraft with a breaking strength greater, but not more than 25 percent greater, than that of the safety link at the towed glider or unpowered ultralight vehicle end of the towline and not greater than twice the maximum certificated operating weight of the glider or unpowered ultralight vehicle;

Before conducting any towing operation within the lateral boundaries of the surface areas of Class B, Class C, Class D, or Class E airspace designated for an airport, or before making each towing flight within such controlled airspace if required by ATC, the pilot in command notifies the control tower. If a control tower does not exist or is not in operation, the pilot in command must notify the FAA flight service station serving that controlled airspace before conducting any towing operations in that airspace; and

The pilots of the towing aircraft and the glider or unpowered ultralight vehicle have agreed upon a general course of action, including takeoff and release signals, airspeeds, and emergency procedures for each pilot.

No pilot of a civil aircraft may intentionally release a towline, after release of a glider or unpowered ultralight vehicle, in a manner that endangers the life or property of another.