Flight Warning Systems — Page 434, Lesson 540

Let me walk you through the Flight Warning System — the FWS. This is the aircraft's central nervous system for telling the crew something is wrong. I want you to think of it in three clear parts: inputs, a processing unit, and outputs. First, the inputs. The FWS gathers information from a huge number of sources. We're talking hundreds of engine and airframe sensors — that's everything from temperature probes on the engines to pressure switches in the hydraulic systems. On top of those, it takes in air data sensors, which measure things like airspeed and altitude. And it also receives inputs from two very important safety systems: GPWS and ACAS. GPWS is the Ground Proximity Warning System — it warns you if the aircraft is getting too close to terrain. ACAS is the Airborne Collision Avoidance System — it detects other aircraft and helps prevent mid-air collisions. So the FWS is pulling data from all of these at once. Second, the processing unit. This is the brain. It's made up of one or two flight warning computers. Notice that "one or two" — on many aircraft there's redundancy, a second computer, so that if one fails, the other keeps the warnings coming. These computers take all those inputs, decide what's a problem, and generate the appropriate output. Third, the outputs. And here's where the classification matters. The outputs are classified either as alerts or as warnings, and which one you get depends on the nature of the malfunction or the threat to safety. Let me make that distinction very clear, because it's a professional standard. An alert is a lower-level notification. Alerts can be visual — that's amber lights, or amber text on VDUs. VDU stands for Visual Display Unit — the electronic screens in the cockpit. Or alerts can be aural — chimes or tones. So if something is developing but not immediately dangerous, you get an amber alert. A warning is the serious one. Warnings are given in the form of red lights, or red text on electronic screens — and that red text can be steady or flashing. Plus, warnings come with aural signals — a siren, a bell, or a hooter. So the red means danger, and the sound grabs your attention even if you're not looking at the panel. And there's one more layer. Additionally, there are red and amber lights on the glare shield in front of the pilots. The glare shield is that panel at the top of the instrument panel, right in the pilots' forward field of view. These lights act as attention getters — they make sure the crew looks up and sees what's happening, even if their eyes were down on the instruments. So the whole picture: hundreds of sensors feed the flight warning computers, and those computers decide — is this an alert, amber, or a warning, red? And they present it visually and aurally, with the glare shield lights as the final attention-getter. There's a block diagram of a Boeing 767 warning and alert system that shows exactly how all these pieces connect. Let me show you. That's the FWS architecture in a nutshell — inputs, processing, and classified outputs.