Autopilot — Page 377, Lesson 461

I want to walk you through the autopilot limitations and operational restrictions now. This is where we move from what the autopilot does to the rules and warnings that govern its use — the stuff you'll actually see in the cockpit. Let's start with the disengage warnings. When an autopilot disengages, the "A/P" light flashes red and a tone sounds. That's your immediate cue that something has changed. You can reset that warning by pressing either disengage light or either A/P disengage switch — so there are redundant ways to silence it. Now, the A/P warning light stays at a steady red under four specific conditions. I want you to hold onto these because they're distinct failure or configuration states. First: the stabilizer is out of trim below 800 feet RA on a dual channel approach. Second: Altitude Acquire mode is inhibited during an A/P go-around — and note the parenthetical, the stabilizer is not trimmed for single A/P operation, so see the A/P go-around notes. Third: the disengage light test switch is held in position 2, which is the red filament test. Fourth: an automatic ground system test fail. Then there's the amber side. The light illuminates a steady amber when the disengage light test switch is held in position 1 — that's the amber filament test. And the light flashes amber if the A/P automatically reverts to CWS pitch or roll while in CMD. That's a big one — CWS is control wheel steering, and if the autopilot drops out of command mode back into CWS, you get the flashing amber. The light resets when either light is pressed or another mode is engaged. Now let's talk about the maximum pitch and bank angles. During normal autopilot operation, the maximum pitch is ±10 degrees and the maximum roll is ±30 degrees. But here's the critical caveat: these limits are not stipulated legally, and they will vary from aircraft to aircraft. So don't memorize these as universal law — they're typical values, but each aircraft type sets its own. Next, gain adaptation. This is a concept you need to understand properly. Variations in flight parameters — altitude, speed, aircraft load, configuration, and rate of manoeuvre — all affect the handling characteristics of an aircraft. So flight control systems incorporate what are called 'gearing' elements. These adapt the parameters to the aircraft so their effect on handling characteristics is reduced. In automatic systems, the response is altered by changing the 'gain' of the system to a given level of input signal. Think of it like changing gear ratios in a mechanical system — that's the analogy the text gives you. Gain adaptation is particularly important for maintaining handling characteristics with changes in IAS — indicated airspeed — during the different phases of flight. And it's similar to the gain scheduling in the flight director system. Finally, the approach/land mode. During an autoland sequence, the autopilot has to execute many important manoeuvres. Those are described in the Autoland notes — so that's where we'll pick up the detailed sequence when we get there. Let me make sure you've got the key distinctions straight. Red flashing means disengagement. Steady red means one of those four specific conditions. Steady amber is the filament test at position 1. Flashing amber is the CWS reversion while in CMD. And the pitch and bank limits — ±10 and ±30 — are typical, not legal, and vary by aircraft. That's the core of this section.