FSX Delta 777x airspeed indicator stuck around 300 knots and showing overspeed

Airspeed “stuck” ~300kts + constant overspeed: a few things to check

That behavior usually isn’t the airplane “capping” your speed so much as FSX/the gauge thinking you’re hitting a limit (often due to an indicated vs true airspeed mix-up, wrong pitot/static behavior, or a corrupted aircraft/gauge install after a reinstall).

Here’s how I’d work through it, step by step.

1) Confirm what speed you’re actually looking at (IAS vs TAS)
At FL370 you’ll often see something like ~280–310 KIAS while KTAS is much higher (your “485” number sounds like TAS/GS territory, not IAS). Many 777 panels show IAS in the tape and TAS/GS as small readouts.

1. On the PFD, make sure the tape is showing IAS (that’s normal to be ~300-ish up high).
2. Check if there’s a separate TAS/GS readout anywhere on the display (often small text).
3. If you have a headwind/tailwind, compare with groundspeed too (GS can easily be far from IAS).

If what you’re calling “485kn” was actually your GS/TAS, then the “300” you’re seeing now may be completely normal IAS at FL370.

2) Verify you’re not actually overspeeding the indicated limit (VMO/MMO)
In jets, overspeed is usually tied to IAS at lower altitudes and Mach at higher altitudes. If the panel’s barber pole / overspeed cue is wrong (or stuck), it’ll scream overspeed early.

1. During climb, note the Mach number when it starts calling overspeed.
2. See if the overspeed indication changes with altitude (it should transition as Mach becomes limiting).

If it’s showing overspeed at, say, 0.70–0.75M with clean config up high, that’s suspicious and points to a gauge/aircraft data issue.

3) Check for pitot/static icing or failures
Even if the needle “moves,” pitot/static issues can make the airspeed unreliable and can trip overspeed logic in some add-on gauges.

1. Make sure pitot heat is ON.
2. In FSX realism/failures settings, make sure you don’t have random failures turned on (or any current pitot/static failures active).
3. Try a fair-weather theme test flight (no clouds/icing) and see if it still happens.

4) Confirm you didn’t load the flight with a weird saved state
FSX saved flights can carry over odd electrical/avionics states and sometimes break add-on logic.

1. Load the default trike at Friday Harbor first.
2. Then switch to the 777x from the Aircraft menu.
3. Test again.

5) Re-check the 777x install (gauges/air file/config)
Since this started right after a reinstall, I’d keep “corrupt/mismatched files” on the table.

1. If the add-on has multiple variants/models, test another livery/variant.
2. If only this one “Delta 777x” does it, that points to that specific aircraft.cfg/air file/gauge set.
3. If you have any tweaks backed up (old aircraft.cfg/aircraft airfile), temporarily revert to stock as installed and test.

A couple quick questions so I can narrow it down

1. Which “777x” add-on is this exactly (developer/name as it appears in the FSX aircraft list)?
2. When you say “485kn at FL370,” was that IAS, TAS, or GS (and where were you reading it on the panel)?
3. Are you seeing an overspeed clacker/visual cue at ~300 KIAS up at cruise, or is it happening lower in the climb too?
4. Any weather/icing, and is pitot heat definitely on?

Answer those and I’ll tell you which of the above is most likely (and what to change first).