Having my air brake endorsement I'm required to know how they function, modern air brake systems wont fail in this way, as a loss of air pressure will result in the spring brake being engaged (air pressure holds the spring in the released position), considering the age of the truck it looks likely that it still uses manual slack adjusters, which if improperly adjusted would result in a brake failure when the brakes are depressed, (drivers are responsible for adjusting manual slack adjusters and all new vehicles have automatic slack adjusters by law now) even if it was a case of neglectfully failing to check and adjust the slack of the adjusters, the driver here could have pulled the parking brake to come to a screeching halt as that engages the spring brakes.