Aircraft Brakes — Page 141, Lesson 192

We've just covered the brake system's hydraulics and the anti-skid side. Now I want to walk you through the temperature monitoring side of it — the Brake Temperature Indicators. On the larger aircraft types — the B747, B777, A340, A380 and so on — the brakes get hot enough that the crew needs to know exactly what's happening thermally. So these types may be fitted with Brake Temperature Indicators. The key word there is "may" — it's not on every aircraft, but on the big ones it's standard. Here's how it's built. Sensors are arranged to sample the temperature of the brakes of each individual wheel. So every wheel has its own sensor, giving you per-wheel data, not just a single average for the whole gear. Now, how does the crew see this? An indicator can be used to display the temperature of each pair of wheels, as selected on the system control panel. So you don't see all wheels at once — you select a pair on the control panel, and the indicator shows you that pair's temperatures. The system is constantly monitoring. If the temperature of any brake assembly rises above a predetermined level, then a "HIGH TEMP" indicator light illuminates. That's your first warning — something is getting hot. Once that light is on, switch selection on the control panel now enables the operator to locate the wheel brake or brakes which are triggering the alarm. So the HIGH TEMP light tells you something's hot, and the panel selection lets you pinpoint exactly which wheel or wheels are causing it. Now here's the escalation. Should any brake temperature go above that level at which the High Temp warning light illuminates — so even hotter than the HIGH TEMP threshold — then a brake "OVERHEAT" caption will come on. That's a more serious condition. And this last event — the OVERHEAT — is duplicated on the Central Warning System. So the overheat condition isn't just on the brake panel; it's also flagged centrally where the crew is sure to see it. Figure 6.8 illustrates a Brake Temperature Warning Panel — that's the panel showing you the HIGH TEMP and OVERHEAT indications. So to tie it together: per-wheel sensors, pair selection on the control panel, a HIGH TEMP light as the first warning, then an OVERHEAT caption if it goes beyond that, and the overheat is also sent to the Central Warning System. That's the full temperature monitoring chain on the big aircraft.