Flying on VATSIM lst night, the controller did not clear me for a decent before reaching TOD. Just after passsing TOD, I noticed the FMC controlled airspeed dropping. I let it drop to about 250 and then went FLCH to keep the speed up.My question is what was happening? Why was the FMC reducing speed after passing TOD?

Flying on VATSIM lst night, the controller did not clear me for a decent before reaching TOD. Just after passsing TOD, I noticed the FMC controlled airspeed dropping. I let it drop to about 250 and then went FLCH to keep the speed up.My question is what was happening? Why was the FMC reducing speed after passing TOD?

Energy compensation. The FMC is getting rid of kinetic energy since it can't get rid of potential. It helps you regain the VNAV path.

Flying on VATSIM lst night, the controller did not clear me for a decent before reaching TOD. Just after passsing TOD, I noticed the FMC controlled airspeed dropping. I let it drop to about 250 and then went FLCH to keep the speed up.My question is what was happening? Why was the FMC reducing speed after passing TOD?

Had you set a higher altitude in the MCP than your next waypoint altitude ?Maybe what Matt said.See page 880 Fcom Vol 2.Fred.

I let it drop to about 250 and then went FLCH to keep the speed up.

If you were still at your cleared altitude and wanted to stay at your cruise speed, just use the SPD INT. Don't use LVL CHG for that.

Energy compensation mode - the idea is that once you do get cleared down you'll speed back up and descend at a quicker rate to regain the VNAV path.