Hot brakes can occur for a number of reasons. The most obvious reason is due to heavy braking on landing. A large jet aircraft landing on a short, contaminated runway is a likely candidate for hot brakes. On large jet transport aircraft, hot brakes are indicated by a cockpit warning. On the Airbus 320, for example, a brake temperature greater than 300 degrees Celsius will trigger a hot brake ECAM (Electronic Centralized Aircraft Monitor) warning. Hot brakes can also occur when the brakes are applied while taxiing, whether intentionally or due to antiskid or brake failure.
Whatever the reason for the hot brake condition, the procedure is to allow the brakes to cool before taxiing or taking off. The most important thing is to not set the brakes when the aircraft is parked. Have the wheels chocked and leave the parking brake off. A visual inspection by the crew and/or maintenance is also recommended. If the brakes are extremely hot, it's a good idea to have a fire extinguisher nearby.
If you landed with hot brakes, they may not have had time to cool sufficiently on a quick turnaround. Large jet aircraft have certain temperature limits that prohibit you from taking off when the brake temperature exceeds a certain value. In that case, you have no choice but to wait until the temperature decreases below the threshold. Aircraft that do not have this limitation can achieve some additional cooling by leaving the gear down a few extra seconds prior to gear retraction.
