TM 9-2320-209-10-1 d. Tractor Trucks Controls and Indicators. 1. Airbrake hand control lever. Con- 3. Fifth wheel operating handle. Is trols semitrailer airbrake system. pulled forward to unlock jaws and When lever is moved down, brakes separate semitrailer from tractor. are on. 4. Safety latch. Makes sure that there 2. Airbrake hose coupling shut-off- is a positive locking of the fifth cocks. Are turned on (up position) wheel jaws. The safety latch must to let air enter semitrailer brake be moved left or right to move system after it is hooked up and operating handle. must be turned off (position shown) before trailer is unhooked. 4-17