Automatic Flight Control, Flight Management and Electronic Displays
Autopilot modes
Lateral modes include heading/track, VOR/LOC, approach and LNAV; vertical modes include altitude hold, vertical speed, flight-level change (IAS/Mach), VNAV path, glide slope and take-off/go-around. Modes arm before they engage: selecting APPROACH arms LOC and GS, which engage when the beams are captured. Autoland (CAT III) requires multiple autopilots, redundancy and a fail-passive or fail-operational architecture, with automatic flare and rollout.
Autothrottle and flight director
Autothrottle modes include speed, thrust reference and hold; the flight director provides command bars for manual flying. Mode annunciations must be monitored - armed, engaged and captured are different states, and a mode that silently drops out is a classic error.
VNAV and descent planning
VNAV follows a vertical path computed from the navigation and performance databases. The 3:1 rule gives a quick cross-check: about 3 nm of descent distance per 1,000 ft, plus deceleration distance.
Displays
The PFD shows attitude, airspeed, altitude, flight director and approach information; the ND shows route, weather and traffic; EICAS/ECAM shows engine and system data. Colour conventions (red warnings, amber cautions, green normal) and reversion modes must be understood, and standby instruments checked after a display failure.
Worked example
Cruising at FL350, cleared to 5,000 ft: 30,000 ft of descent needs about 90 nm on the 3:1 rule, plus about 10 nm to decelerate, so the top of descent is roughly 100 nm before the fix.
Traps
Confusing armed with engaged modes; letting VNAV descend below a cleared altitude; forgetting that autoland needs specific ground and airborne equipment; and missing a display reversion.