744 Refuses to Decend Under VNAV

[Guest piper99]

Hi Ryan,Here is what the LEG page is telling:L1: the FMC is planning to reach 3545 FT at a speed of 180 KTS.L2: you told the FMC to fly over the fix ILL7.5 at 152 KTS 2500 FT.How come then that the airplane is flying level at 3500 FT?Have a look at what the PFD is telling:The Autopilot Pitch Mode is VNAV PTH. This means the FMC is flying the VNAV calculated vertical path.The current target speed is 213 KTS as shown on the airspeed tape. The DES page also shows that on L2. However it says SEL SPD, not the usual ECON SPD. This means there is another restriction on the normal VNAV Economy Speed.What is it?Well look at the EICAS: your current flaps setting is FLAP 1. Now look at the PFD: the lowest speed for FLAP 1 is about 208 KTS.There is your speed restriction! The FMC wants to fly at 213 KTS so as to have a safety margin above the minimum FLAP1 speed.The airplane cannot descend and slow down at the same time. My guess is it is waiting for you to put more flaps so it can slow down to 152 KT and then it will descend to 2500 FT.Give it a try!Christophe.