Learn why PMDG 777 VNAV information disappears from the FMC and restore it by checking the route, PERF INIT, discontinuities and AIRAC data.
PMDG 777 VNAV information usually disappears because the FMC has changed flight phase, the active route is incomplete or sitting in an unexecuted modification, or PERF INIT data is missing. Confirm the active route, repair its LEGS sequence, execute pending changes, restore performance entries and verify that the navigation database matches the flight plan.
Is disappearing VNAV information always a fault?
No. PMDG 777 versions in Microsoft Flight Simulator, Prepar3D and FSX broadly follow the same Boeing flight-phase logic, although individual page labels can vary. The FMC removes passed constraints and changes between climb, cruise and descent pages as the flight progresses.
| What the FMC shows | Likely meaning | Required action |
|---|---|---|
| Passed waypoints or constraints disappear | Normal route sequencing | None, provided the next waypoint is correct |
| VNAV CLB changes to CRZ or DES | Normal flight-phase change | Review the page for the active phase |
MOD RTE appears or the EXEC light is illuminated | A route modification has not been accepted | Execute the intended change or erase it |
| Speeds, altitudes, predictions and top of descent all vanish | Incomplete route or performance data | Check RTE, LEGS and PERF INIT |
| The FMC shows a valid path but the aircraft ignores it | Mode-control or guidance problem | Check the MCP and flight-mode annunciations |
How do you restore missing PMDG 777 VNAV data?
Restore the active lateral route first, then supply the performance information from which the FMC calculates its vertical profile.
- Stabilise the aircraft if airborne. Use an appropriate selected lateral and vertical mode before working through CDU pages. Do not attempt hurried route surgery while the aircraft is following an uncertain path.
- Check the route title. Open RTE or LEGS and confirm that you are viewing the active route rather than an inactive second route. During initial programming, activate and execute the route; after an edit, either execute the displayed modification or erase it.
- Read the scratchpad message before clearing it. A rejected waypoint, invalid entry or database message identifies where the calculation broke down. If a waypoint is rejected, follow our checks for diagnosing a NOT IN DATABASE route entry rather than repeatedly trying to execute the same leg.
- Inspect the LEGS page from start to finish. Look for a route discontinuity, duplicate waypoint, reversal or missing connection after a departure, arrival or approach change. Close a discontinuity only when you know which waypoint should follow; vector and manual legs can be intentional.
- Complete PERF INIT. Confirm the cruise altitude, cost index, reserves and aircraft weight entries. Depending on the PMDG generation and loading method, some weights may populate automatically, but every boxed required field must be resolved with a valid value.
- Review the terminal procedures. If the problem began after changing the runway, SID, STAR or approach, reselect the correct procedure and inspect every resulting leg and altitude constraint before pressing EXEC. A mistake we see often is deleting constraints along with a discontinuity, leaving the FMC without a useful descent profile.
- Check the navigation-data cycle. Compare the FMC IDENT page with the data used to create the flight plan. An imported route built from another AIRAC cycle may contain renamed or missing fixes. MSFS users can use our procedure for refreshing the PMDG navigation database; FSX and Prepar3D users should use the supported data installer for their PMDG version.
- Let the FMC recalculate. Return to the active VNAV and LEGS pages after executing the corrected route. Predictions should repopulate once the FMC has a continuous route, valid performance data and a usable destination profile.
Why is the VNAV path visible but the 777 will not follow it?
Visible FMC predictions mean the vertical path exists; failure to follow it is usually an MCP or flight-guidance problem rather than disappearing data. Check the flight-mode annunciations on the primary flight display, not just the illuminated VNAV button.
Before descent, the MCP altitude must be set below the aircraft when clearance permits. Leaving it at cruise altitude can prevent automatic descent at top of descent, but it does not normally erase FMC predictions. Flight directors, the active lateral route and the relevant VNAV mode must also be available; MSFS users can work through our focused PMDG VNAV engagement and FMA checks.
Can an IRS problem remove VNAV information?
An unaligned or incorrectly initialised IRS can prevent dependable navigation guidance, but it does not normally delete stored PERF INIT values by itself. If the navigation display has no valid position, initialise the FMC position and complete IRS alignment before troubleshooting VNAV further. Do not reset the IRS casually once airborne.
When should you reset or reinstall the PMDG 777?
Only consider repair after a clean test route also loses its VNAV data. Load a standard panel state, manually enter a short continuous route, complete PERF INIT and avoid importing a saved flight plan. Load any panel state before programming the FMC, because loading one afterwards can restore older route and performance data.
If the manual route works, the original import, procedure selection or saved state caused the problem. If every route fails, update or repair the aircraft using our PMDG Operations Center update procedure and repeat the clean test before attempting a full reinstall.