The spring-loaded brake has been applied on a truck which has broken down with engine failure. The air supply is exhausted. What effect does this have?

You answered correctly because when a truck’s engine fails and the air supply is lost, the spring-loaded brake automatically applies to keep the vehicle stationary for safety. The handbrake valve no longer controls the brake in this state (point 1). To tow the vehicle, these spring-loaded brakes must be manually released using an emergency release device since normal air pressure to release the brakes is absent (point 2). Removing the physical springs (point 3) is not necessary and is not the standard procedure for towing. This ensures the truck remains safely stopped if air pressure is lost but can still be moved when properly released.