How do I use VNAV in the FlyByWire A32NX?

The FlyByWire A32NX has no Boeing-style VNAV button. In Microsoft Flight Simulator, programme a valid MCDU flight plan and performance data, make sure NAV is active, set the cleared altitude on the FCU, then push the altitude knob for managed CLB or DES. Confirm every change on the PFD Flight Mode Annunciator (FMA).

What must I enter in the MCDU before VNAV works?

Enter a continuous route, cruise level, weights, fuel and performance data, then verify every altitude and speed constraint in the active flight plan.

These instructions apply to the custom FlyByWire A32NX and its MCDU and FCU systems, not the default A320neo's vertical guidance.

• F-PLN: Select the departure, arrival and approach, then remove unwanted discontinuities and duplicate waypoints. Keep an operationally intentional discontinuity until you know how it will be cleared.
• INIT: Enter the cost index and cruise level, plus zero-fuel weight, centre of gravity and block fuel. Missing data makes descent and fuel predictions unreliable.
• PERF: Complete the take-off page, including V-speeds and flap setting. Before descent, complete the applicable arrival and approach data.
• Constraints: Step through the F-PLN page and check that SID, STAR and approach altitude restrictions are present and plausible.

A dispatch route saves time, but it still needs checking. Our instructions for importing a SimBrief plan into the A32NX cover the connection and import process; after importing, inspect the active route and constraints rather than assuming every entry is correct.

The FCU altitude remains the clearance limit. Managed guidance will follow FMS constraints, but it will not climb or descend through the altitude selected on the FCU.

How do I use VNAV for a managed climb?

For a normal managed climb, keep NAV active, select the cleared altitude above the aircraft and use the altitude knob's push action.

1. Set the first cleared altitude. Do not select the cruise level unless ATC has cleared you that high.
2. Fly the take-off modes. Follow SRS and NAV, then move the thrust levers into the CL detent when the aircraft prompts for climb thrust.
3. Engage managed climb. At the appropriate point after departure, push the altitude selector if CLB has not already armed or engaged automatically from the take-off mode sequence.
4. Read the FMA. Look for CLB, not OP CLB. The autopilot will fly the command when engaged; with the autopilot off, the flight directors provide the guidance.
5. Monitor restrictions. The aircraft may capture ALT CST at a climb constraint, then resume CLB after passing it if the FCU altitude remains higher.

Moving the thrust levers beyond or below CL after take-off can interfere with autothrust and speed control. If the virtual levers will not remain in the correct detent, calibrate the A32NX throttle detents before diagnosing VNAV.

How do I start managed descent at the TOD?

Managed descent begins only after you select a lower FCU altitude and command DES; reaching the calculated top of descent does not make the A32NX descend by itself.

1. Prepare before TOD. Check the STAR, approach, altitude restrictions and PERF pages. Resolve any unwanted flight-plan discontinuity before it breaks the vertical profile.
2. Select the cleared altitude. Dial the altitude issued by ATC, or the next permitted altitude when flying without online ATC.
3. Push the altitude knob. At or near the TOD marker, use the push action and confirm DES on the FMA. An early command may produce a shallow descent while the aircraft intercepts its calculated profile.
4. Watch the energy state. Monitor managed speed and the vertical-deviation indication. If the aircraft is high and displays MORE DRAG, use the speed brake as required and retract it once the profile is recovered.
5. Continue after level-offs. A required constraint may produce ALT CST. If the aircraft reaches the FCU-selected altitude, obtain or choose the next clearance, select it and command managed descent again.

Do not chase a fixed vertical speed during DES. The commanded rate changes with speed restrictions, winds, path geometry and idle-thrust capability.

Managed and selected vertical modes

The push or pull action determines whether the FMS profile or a pilot-selected vertical mode controls the aircraft.

Use managed CLB or DES for the normal published profile. Choose OP DES when ATC requires an immediate descent, or when recovering from being high, only if no intervening restriction must be honoured. Use V/S for an assigned rate or a short, closely monitored correction.

Why is A32NX VNAV not following altitude constraints?

Most constraint failures come from the wrong active mode, an incomplete flight plan or an FCU altitude that prevents the commanded climb or descent.

• The FMA shows OP CLB, OP DES or V/S: A selected mode is active, so the FMS constraints are not controlling the vertical path. Push the altitude knob and verify CLB or DES.
• The aircraft remains level at TOD: Select a lower cleared altitude and command DES. The TOD symbol is advisory, not an automatic descent trigger.
• There is no sensible TOD: Check the cruise level, destination, arrival, weights, fuel and route continuity. Insert any pending temporary flight-plan revision after verifying it.
• A restriction is missing: Inspect the active F-PLN entry. A constraint absent from the active route cannot be followed, even if it appeared in a planning document.
• The aircraft is high on profile: Late descent clearance, excessive speed or a tailwind can leave insufficient distance. Use drag, selected speed or OP DES as appropriate, while respecting every clearance and restriction.
• The aircraft stops at an unexpected altitude: Compare the FMA with the FCU setting. ALT normally means the selected altitude has been captured; ALT CST indicates a flight-plan constraint.

Approach vertical guidance is separate

Managed DES takes the A32NX towards the approach, but it is not a generic glidepath mode to the runway. An ILS uses glideslope guidance, while an RNAV approach may use a different supported final-approach mode depending on the procedure and aircraft implementation.

Arm the appropriate approach mode and verify its status on the FMA rather than assuming DES will continue to touchdown. Our explanation of RNAV lateral and vertical guidance in Microsoft Flight Simulator covers the procedure-specific part.