Autopilot — Page 377, Lesson 458

We're starting the "Autopilot in Operation" part of the chapter now. I want to walk you through what happens to the autopilot modes during each phase of flight, and then we'll look at a couple of special features. First, let's finish the thought about V NAV. During a V NAV path descent, V NAV stays engaged until one of four things happens: glide slope capture, another pitch mode is selected, flaps are extended beyond 15 degrees, or L NAV is disengaged without glide slope capture. So V NAV is the vertical navigation mode, and it holds until you either capture the ILS glide slope, pick a different pitch mode, put out more than 15 degrees of flap, or drop lateral navigation without capturing the glide slope. And remember, proper MCP altitude selections ensure correct altitude alerting — the Mode Control Panel altitude setting drives the altitude alert. Now, the heart of this section is the table of autopilot modes by flight phase. Let me walk you through each phase, and I'll explain the three columns: ROLL, PITCH, and AUTOTHROTTLE. At take-off, the roll mode is TOGA, the pitch mode is TOGA, and the autothrottle is in THR REF. TOGA stands for Take-Off/Go-Around, and THR REF means thrust reference — the autothrottle is holding a reference thrust setting. In climb, roll can be LNAV, HDG, or VOR — that's lateral navigation, heading select, or VOR tracking. Pitch can be FLCH SPD, VNAV, or V/S — flight level change speed, vertical navigation, or vertical speed. Autothrottle is THR REF, SPD, or MACH — thrust reference, airspeed, or Mach hold. In cruise, roll is again LNAV, HDG, or VOR. Pitch is ALT HOLD or VNAV — altitude hold or vertical navigation. Autothrottle is SPD or MACH. In descent, roll is LNAV, HDG, or VOR. Pitch is FLCH SPD, VNAV, or V/S. Autothrottle is THR REF, SPD, or MACH — same set as climb. In approach, roll is LNAV, HDG, or LOC — localizer. Pitch is ALT, G/S, or FLARE — altitude, glide slope, or flare. Autothrottle is SPD. In land, the roll mode is ROLLOUT. And in go-around, roll is TOGA, pitch is TOGA, and autothrottle is THR REF. Now let's look at the other autopilot features. First, the approach mode, APP. This allows the localizer and glide slope elements of the ILS system to be coupled to the roll and pitch channels of the autopilot. That lets the aircraft be controlled automatically down to decision height, or even to effect a fully automatic landing. So APP couples the ILS lateral and vertical guidance into the autopilot's roll and pitch channels. Second, Control Wheel Steering, or CWS. This is provided in some automatic flight control systems, like the Boeing 737-400. Its purpose is to let the pilot manoeuvre the aircraft in pitch and/or roll through the automatic control system without disconnecting the autopilot. The signals for the autopilot are produced by transducers in the control column. So when you press a CWS engage switch, it engages the autopilot pitch and roll axes in CWS mode, and displays CWS P and CWS R on the Flight Mode Annunciators — the FMAs. CWS P for pitch, CWS R for roll. Let me show you the Mode Control Panel and the flight mode annunciations so you can see how these modes are selected and displayed. So to tie it together: the autopilot has distinct roll, pitch, and autothrottle modes for each phase, from TOGA at take-off through ROLLOUT at landing. And the special features — APP for ILS coupling, and CWS for manual manoeuvring through the autopilot without disconnecting — give you the flexibility to handle approach and in-flight adjustments.