just want to know why when I programmed a route from ottawa to toronto direct with no waypoints etc when i reached my crz altitude of 18000 all of a sudden i got an altitude sound and the plane started to descend? is this because it did not have any waypoints programmed in between so theFMC did not know when to begin its descent and got confused?

Generally,The FMC does not get confused - people programming it do.Need some more information. Was your autopilot engaged? Were you in VNAV?Were you in LNAV?Was your preflight of the FMC complete?Did you use V/S to climb?Was it a full moon?Did you use FLCH to climb?Was the A/T engaged?What was your MCP altitude set at?Ian Elchitz CYWG

gooper,I don't know why you saw what you did but here is some "operational" information to help you on your next YYZ-YOW flight.Typical routing is YOW J546 YSO SIMCO# FMS arrival.On departure you may be given DIRECT the CELAR intersection but more usually (off RWY 25)a vector of 290 deg (after 3000ft noise abatement) to intercept the on-course or 280 to 300 deg to intercept the on-course west of the YOW VOR with a RWY 07 departure.Typical altitude for a 762/3 on this segment would be FL280 or more usually, FL310, never at FL180.Try that routing and see if you get the same "error".Cheers,Kevin in CYOW

Gooper,Kevin is correct.. Try his suggestion. FL180 is too low for this leg. The lowest I've seen is FL240 on CYYZ-CYUL route.Best,Haroon