When should hydraulic or air brakes not be fanned?

Fanning, which refers to lightly applying the brakes repeatedly to control speed and prevent overheating, is particularly problematic on slippery pavement. When brakes are fanned under these conditions, it can lead to a loss of traction because the vehicle may begin to skid if the tires lose grip on the icy or wet surface. This can be dangerous, as it reduces the driver's ability to maintain control of the vehicle. Therefore, avoiding the fanning of brakes on slippery pavement is crucial for safety and effective vehicle operation.

In contrast, the other options do not present the same level of risk for such brake usage. For instance, using brakes on dry pavement can be done more safely without the risk of sliding, and while hot weather or long downhill grades may present challenges, they do not possess the same inherent risk associated with slippery conditions. Thus, the focus on slippery pavement emphasizes the need for careful braking techniques in adverse driving conditions.