What action should you take if you experience brake failure on a bus?

When experiencing brake failure on a bus, the most appropriate action to take is to find a safe way to slow down using engine compression. This method involves downshifting to a lower gear, which can utilize the engine's resistance to slow the vehicle. This technique is effective as it helps to reduce speed without relying solely on the hydraulic brakes, which are not functioning properly.

In addition to engine compression, it is also crucial to remain calm and assess the situation to ensure the safety of passengers and other road users. This may involve maneuvering the vehicle to avoid hazards or obstacles while also considering the environment around the bus.

Using the parking brake in isolation, as suggested by another option, is not advisable because it can cause the rear wheels to lock up, potentially leading to a loss of control. While signaling your intention to stop and checking mirrors may be important actions in general driving situations, they do not address the immediate need to safely reduce speed when brakes have failed. Thus, employing engine compression is the most effective and safe response in this scenario.