Flight Warning Systems — Page 434, Lesson 540

I want to walk you through the Flight Warning System — the FWS — which is the aircraft's central nervous system for telling the pilots something is wrong. Let's start with what it's made of, because the whole system is built from three blocks: inputs, a processing unit, and outputs. First, the inputs. The FWS gathers information from a huge range of sources — the book says hundreds of engine and airframe sensors, plus air data sensors, and the GPWS and ACAS systems. Let me unpack those acronyms. GPWS is the Ground Proximity Warning System, which warns you if the aircraft is getting dangerously close to terrain. ACAS is the Airborne Collision Avoidance System, which watches for other traffic. So the FWS is fed by the engines, the structure, the air data computers, and these two big safety systems. Second, the processing unit. This is made up of one or two flight warning computers. So you might have a single computer, or a pair of them — typically for redundancy, so if one fails the other keeps the warnings flowing. Third, the outputs. This is the key part, and I want you to hold onto the distinction the book draws: outputs are classified either as alerts or as warnings, and that classification is generated according to the nature of the malfunction or the threat to safety. So the system decides how serious the problem is and picks the appropriate level of response. Let me define those two terms precisely. An alert is the lower level. Alerts can be visual — and here the book specifies amber lights, or text on VDUs, which are the visual display units, the electronic screens — or they can be aural, meaning heard, in the form of chimes or tones. So an alert is something like a caution — amber, a chime, a tone. A warning is the higher level, the more serious threat. 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 aural signals, and the book names three: a siren, a bell, and a hooter. So the red is the universal signal for a warning, and the sound is more aggressive than a chime. And there's one more layer on top of that. Additionally, there are red and amber lights on the glare shield in front of the pilots, to act as attention getters. The glare shield is that panel at the top of the instrument panel, right in front of the pilots' eyes. So even if the pilots are looking outside, those lights pull their attention to the problem. Red for a warning, amber for an alert — same colour logic as the screens. Now, the book references a block diagram of a Boeing 767 warning and alert system, shown as Figure 32.2. That diagram lays out exactly how these inputs flow into the flight warning computers and out to the alerts and warnings. I'd point you to it on screen — it shows the whole architecture visually. So the takeaway: the FWS takes hundreds of sensor inputs, processes them in one or two flight warning computers, and then classifies the output as either an alert — amber, chimes, tones — or a warning — red, steady or flashing, with siren, bell, or hooter — and uses the glare shield lights as attention getters. That classification is the heart of it: the nature of the malfunction decides whether you get a caution or a full warning.