No vehicle shall be permitted in or upon an operational area unless it is in sound mechanical order, with adequate lights, horn and brakes and clear vision from the driver's seat. Trailers and semi-trailers shall not be permitted unless they are equipped with reflector buttons and proper brakes or are adequately secured so that neither aircraft propeller blast nor wind will cause them to become free rolling when disengaged from a towing vehicle. Positive locking couplings shall be required for all towed equipment. (Res. No. 149 75-76 (part))