@bobmor. Have you tried starting the 777-200 Cleared for takeoff (KSEA) flight? See if that works.

Another thing. Sometimes the gear lever is UP instead of DOWN (like it should be), so it could be that once you gain enough speed, the 777 gets light on the gear and they start to retract. You should be getting a horn warning if the gear lever is up. Took me a while to figure out what it was the first time I heard it though. :-[