Flight Warning Systems — Page 434, Lesson 538

I want to walk you through the Flight Warning Systems chapter now. This is the part of your instrumentation syllabus where we look at how the aircraft tells you something is wrong — and more importantly, how it tells you what is wrong, in a way you can act on instantly. Let's start with the three basic ways a warning can reach you: aural, caution, and sensory. Aural warnings. An audible warning is mandatory if the pilot is required to assume control. That's a hard rule — if the situation demands you take over, the aircraft must make a sound you cannot miss. The form varies by aircraft type. It can be sounds, or synthetic voice messages, or a combination of both. And here's the critical part: when multiple alerts happen at once, they are prioritized. The priority order is: Stall, then Windshear, then GPWS, then ACAS. Stall is the most urgent, because losing control is the most immediate threat. Windshear next, then Ground Proximity Warning System, then Airborne Collision Avoidance System. Now, different manufacturers use different sounds, and you need to recognize them. On Boeing aircraft: - A bell accompanies fire messages. - A siren accompanies warnings on cabin altitude, configuration, and overspeed. - A wailer accompanies autopilot disconnect. - Synthetic voice messages are used for ground proximity, windshear, and airborne collision avoidance. On Airbus aircraft: - Continuous repetitive chimes indicate red warnings. - A cavalry charge — that distinctive rising sound — indicates autopilot disconnect. - A cricket sound is the stall warning. - Synthetic voice is used for GPWS and TCAS warnings. Cautions. These are a step below warnings. Beepers with various tones, or chimes, or musical chords are used to caution the crew to potential threats to safety. So a caution is a heads-up — something that could become a threat, not an immediate one. Sensory warnings. This is the third channel. A vibratory mode on the controls is used to indicate stall approach, and it demands immediate action to avert loss of control. In some aircraft, a stick-pusher provides guidance to prevent a further deterioration of the situation that demanded the vibratory warning. So the stick actually pushes forward to help you recover. Now, to rationalize all these warning systems, a Master Warning Indicator light is often provided near the centre of scan — that's the area right in front of you where your eyes naturally rest. In older systems, the crew member would then refer to a Master Centralized Warnings Panel, or CWP, where warnings were assembled in a rational order and annotated. In the modern Electronic Flight Instrumentation Systems, or EFIS, most of the alerts and warnings appear on the appropriate electronic screens, together with associated aural messages and master warning lights. That figure shows the cockpit displays and warnings of an Airbus A320 — you can see how the warnings are integrated into the electronic displays. Now let's get into the heart of the chapter — the Flight Warning System, or FWS. This is the system that generates alerts and warnings for three specific situations: 1. Engine and airframe systems malfunctions. 2. Aerodynamic limits exceeded. 3. Presence of external hazards. Let me take each one. Engine and airframe systems malfunctions — these are dealt with in detail in the Engines and Systems sections of your course, so we won't go deep here. Just know the FWS is responsible for alerting you to them. Aerodynamic limits exceeded — when you exceed these limits, the FWS provides three specific alerts to the crew: Altitude Alerting, Overspeed Warning, and Stall Warning. These are dealt with in the next chapter, so we'll cover them in detail there. External hazard warning — the external hazards that constitute a threat to aircraft safety are proximity to terrain and proximity to other aircraft. These hazards can be avoided by the use of two systems: the Ground Proximity Warning System and the Airborne Collision Avoidance System. These are dealt with in Chapters 34 and 35. So the structure of what's coming is clear: the FWS is the umbrella system, and it feeds into the specific warning systems you'll study next — the aerodynamic limit warnings, and the terrain and traffic avoidance systems. That's the foundation of the Flight Warning System. The key takeaways to hold onto: the priority order of aural warnings — Stall, Windshear, GPWS, ACAS — and the distinction between warnings, cautions, and sensory alerts. Those will carry you through the rest of this section.