Find why the FlightFactor A350 stays high on RNAV approaches in X-Plane 12, with checks for descent mode, constraints, approach setup and navdata.
The FlightFactor A350 usually stays high on an RNAV approach because managed descent was never authorised, the selected altitude blocks further descent, or the aircraft has no usable vertical path for that procedure. Late approach activation, a shortened route, incorrect constraints, stale navdata and intercepting the final path from above produce the same symptom.
What causes the A350 to fly above the RNAV path?
In X-Plane 12, a high FlightFactor A350 is usually experiencing a mode or flight-plan problem rather than an autopilot failure. Check these causes first:
- The FCU altitude is still too high. The selected altitude is a hard limit during descent. Dialling a lower cleared altitude does not itself start descent; managed DES or another suitable vertical mode must also be selected.
- Descent started after the calculated top of descent. The top-of-descent marker is advisory. The A350 will remain level until the pilot authorises descent, leaving it with too much height and energy to lose near the approach.
- A direct-to shortened the route. Removing several miles can put the recalculated descent point behind the aircraft. Late vectors to final have the same effect.
- The approach is not active or correctly sequenced. A discontinuity, manual leg, wrong transition or inactive final leg can prevent the FMS from constructing usable vertical guidance.
- The procedure contains no supported vertical path. RNAV does not automatically mean there is a glidepath. The selected procedure, navdata coding and FlightFactor systems implementation must all support the required guidance.
- An altitude constraint is wrong. A manually entered constraint, or one taken from a different procedure revision, can force an unnecessary level-off or create an impossible descent angle.
Our guide to RNAV vertical guidance and database mismatches in X-Plane 12 explains why the displayed profile can disagree with an expected charted descent.
Does every RNAV approach provide vertical guidance?
No. The minima and equipment required by the procedure determine whether the A350 should calculate or capture a vertical path.
| Procedure or minima | Expected behaviour |
|---|---|
| LNAV | Lateral guidance only. Fly published step-down altitudes using an appropriate selected vertical mode. |
| LNAV/VNAV | Barometric vertical guidance may be available when the procedure is coded correctly and the add-on supports it. |
| LPV | Requires modelled SBAS approach capability. Do not assume an LPV glidepath is supported merely because the procedure appears in the FMS. |
| RNP AR | May require capabilities or procedure logic not fully represented by every aircraft build. |
If the FMS shows lateral legs but no descent angle, vertical deviation or final vertical mode, treat the approach as lacking automatic vertical guidance. Use the published step-down constraints rather than trying to make the autopilot capture a path that does not exist.
How should I set up the RNAV descent?
A correctly prepared route, authorised descent and on-path interception give the FlightFactor A350 the best chance of following the profile.
- Verify the exact approach and transition. Confirm the runway, approach identifier and transition in the FMS. Make sure the reference procedure and aircraft navdata describe the same revision.
- Inspect every remaining leg. Remove only discontinuities that are genuinely meant to be connected. Check waypoint order, altitude constraints and whether each restriction is hard, at-or-above or at-or-below.
- Complete the approach performance data. Enter the correct QNH, temperature, wind and minima where the aircraft requests them. Change from standard pressure to local QNH at the appropriate point and check that hPa and inHg have not been confused.
- Authorise descent before the profile runs away. Set the next ATC-cleared altitude and engage managed DES near top of descent. Do not dial below a clearance simply to recover the computed path.
- Control the aircraft's energy. Observe speed restrictions and reduce excess speed early. A fast aircraft with a tailwind may need earlier deceleration or speedbrake within the aircraft's operating limits.
- Activate and arm the approach correctly. Approach-phase activation controls approach speeds; it is not the same action as arming final approach guidance. Ensure the correct final leg is active, establish lateral navigation and use the approach control only when the selected procedure supports it.
- Confirm the mode annunciations. Watch the flight mode annunciator rather than assuming the autopilot is following the magenta profile.
What should the flight mode annunciator show?
The flight mode annunciator is the authoritative indication of what the autopilot is actually doing.
- ALT means the aircraft is holding altitude. If the RNAV path is descending beneath it, check the FCU altitude and initiate descent.
- DES indicates managed descent along the FMS profile, subject to constraints and the selected altitude.
- OP DES commands a descent towards the selected altitude but does not mean the aircraft is following the calculated RNAV profile.
- APP NAV with FINAL APP, or the equivalent modes modelled by that aircraft build, indicates lateral and vertical final-approach guidance.
Seeing an approach drawn on the navigation display is not proof that vertical guidance is armed. Likewise, activating the approach phase without seeing a final vertical mode will not make the aircraft descend along the final path.
Why will FINAL APP not capture from above?
RNAV vertical guidance should normally be intercepted from on or below the path; it is not designed to command a steep dive from above. A late direct-to, close vector, prolonged level-off or missed top of descent can leave the aircraft outside a sensible capture envelope.
If the vertical-deviation indication is already well below the aircraft, descend using an appropriate selected mode while respecting every cleared and published altitude. Re-arm final guidance only after returning to a credible intercept position. Our detailed RNP path-capture and altitude-constraint checks cover level-offs, unsupported glidepaths and capture from above.
Do not use the PAPI alone to diagnose the FMS. The visual glidepath, threshold crossing point and coded RNAV path can differ slightly. A large or increasing vertical deviation, however, indicates a genuine profile problem.
How do I recover when the A350 is already too high?
Recover early with a controlled descent, or go around if a stabilised approach is no longer achievable.
- Confirm the selected altitude, active leg, next constraint and vertical mode.
- If cleared, use managed descent, open descent or a suitable selected flight-path angle to regain the profile without violating restrictions.
- Reduce speed and use speedbrake where permitted if excess energy is preventing recovery.
- Level at any mandatory constraint rather than chasing the path through it.
- If the aircraft remains high, fast or incorrectly configured near final, discontinue the approach and try again with an earlier descent.
Could this be a FlightFactor A350 bug?
It may be an add-on limitation or fault when the FMS has a valid path, the aircraft approaches it from below, the correct modes are armed and the autopilot still refuses to capture. First repeat the test using an X-Plane 12-compatible aircraft build, the same documented approach and a clean flight without unrelated control or autopilot plug-ins.
If the failure is repeatable, record the runway and approach, navdata cycle, selected transition, active leg, altitude constraint, FCU altitude and flight mode annunciations. Also inspect X-Plane's Log.txt for aircraft-plugin errors. Those details distinguish a reproducible FlightFactor systems problem from an unsupported procedure, bad route sequencing or a simple descent-mode error.