Press the FCU knobs on an A320-style autopilot and watch what the FMA says and what the aircraft actually does. Then work through the classic mode traps, and see how TCAS and EGPWS decide when to warn you.
The flight mode annunciator (FMA) at the top of the PFD is the only place that tells you what the autopilot and autothrust are doing right now. Pull a knob for a selected mode, push it for a managed mode, and compare the FMA with the flight path.
1: autothrust mode. 2: vertical mode. 3: lateral mode. 4: approach capability (CAT 1, CAT 3 DUAL, and so on). 5: what is engaged: AP1/AP2, the flight directors and A/THR. Green is active, blue (cyan) is armed, magenta is an armed altitude constraint, and a white box marks a mode that has just changed.
Push a knob and the FMGS manages that target: the FCU window shows dashes and a white dot. Pull it and you select the target yourself: the window shows the number. Managed vertical modes (CLB, DES) follow the flight plan constraints; the open modes (OP CLB, OP DES) go straight for the FCU altitude.
In THR CLB or THR IDLE the thrust is fixed and the elevator holds the speed (OP CLB, CLB, OP DES, DES). In SPEED the autothrust holds the speed and the elevator flies a path (V/S, ALT*, ALT). Read the first two columns together.
Each scenario stops at the moment something changes. Read the FMA, predict what the aircraft does next, then watch the next few minutes play out in the same model as above.
Read the FMA aloud. After every FCU action, and whenever a mode changes on its own, the pilot flying reads the change and the pilot monitoring checks it. Most mode surprises are caught in that one second: the aircraft is doing what the FMA says, not what you meant.
TCAS II interrogates the transponders around you and works in time, not distance: tau is the range divided by the closure rate. Move the intruder and see when it becomes a traffic advisory (TA) and then a resolution advisory (RA).
The classic GPWS modes look straight down with the radio altimeter. The enhanced system adds a terrain database and looks ahead along the flight path. Fly each profile and see which mode speaks first.
Teaching model. The autoflight logic is a simplified A320-family behaviour with illustrative performance (climb thrust, idle descent, VLS about 205 kt clean, VMO 350 kt), managed speed 250 kt below 10 000 ft and 300 kt above, and managed descent flown as an idle descent that honours constraints. TCAS thresholds are typical TCAS II version 7.1 values; GPWS envelopes are typical shapes, not certified data. None of this is FCOM or FCTM data: always follow your operator’s procedures and the aircraft documentation.