i was in the speed descent. and i couldn't reach the next alt restriction in that mode! how can i change to path descent in the FMC? thanks!

Your problem, as is very much too common with this sim, is your idle power. If you have the Engine Anti-Ice on at 16,000' your idle N1 should be about 34%. That is why you are above the VNAV PATH. Because you are above the path, the FMC has changed to VNAV SPEED.Try to get your idle speed on the N1 down. Maybe try some different settings for your throttles. This is a common problem, but I don't know the solution.

Edited January 29, 201214 yr by Spin737

thanks i will take a try. but i still have a question: where is the PTH prompt in the DES page?

I believe if you were on path, you could switch back to PATH, but because you are above the path, the FMC has changed automatically to VNAV SPEED. I sometimes get my software versions confused, so I could be mistaken. :)The root of your problem is that you have too much thrust, though.

ok i see what the problem is thanks

Edited January 29, 201214 yr by sunxuyang

i knew what i did i was asked by ATC to leve off at 26600, so when i reach 26600, the FMC starts the energy compensation program------it slows the speed down to 210 while keeping the MCP alt . After i was cleared to continue to descend, the FMC used VNAV SPD to speed up back to the ECON speed, then that explains why it was in SPD mode( i didn't turn on the Anti-ice this time, and the idle N1 level is 38.6% ) . but what puzzled me was why it didn't change itself back to PTH!So my question is If i am in the SPD mode, HOW CAN I CHANGE TO PTH?

Edited January 29, 201214 yr by sunxuyang

So my question is If i am in the SPD mode, HOW CAN I CHANGE TO PTH?

I believe that if VNAV SPD is entered automatcially because you are above path, then the only way is to get back on path, then it will automatically re-enter VNAV PATH.If you are in VNAV PATH and use SPD INT to enter VNAV SPD, then you can cancel VNAV SPD by exiting SPD INT.So, if you get into VNAV SPD becase you were high, you much get back to the path and then it will automatically revert to PATH. If you entered SPD manually, then you can exit manually.