Flying from KLAX to KSFO all goes smoothly until beginning the descent. However from then on the speed and altitude begin to vary from the required figures on the LEGS page with both being in excess of what they should be.

 

On extending the Speed Brake I received a cautionary message from the FMC and in consequence retracted it.

 

To land as planned I controlled the speed and altitude myself.

 

Was that the correct thing to do or should I have let the Autpilot do it’s job without interference?

Hi,

 

The first thing to do is to understand what is going on during the descent:

 

_ What modes is the AP engaged in?

_ What are the speed and altitude restrictions on the descent path (not talking about FMC computations but STAR/approach restrictions)

_ Weather conditions and especially the wind (is it different from the wind forecasted and entered in the CDU)?

_ What are the engine parameters? Flight idle, approach idle due to anti-ice on? (Check carefully that the thrust is idle and not higher in HLD mode due to hardware device not at zero).

 

So the goal is to understand why you are going higher and faster than the computed vertical path.

If you get a warning when you extend the speed brakes, it means that the thrust is not idle. So you need to check why it is not idle it may be because it is commanded otherwise (AP in SPD) or commanded to a higher thrust by your hardware device (AP in HLD mode but throttle not at zero).
Do you get a "drag required" message on the CDU?

 

When you say according to the required figures in the FMC, do you mean computed figures or hard restrictions?

And are faster than the magenta speed target on the PFD and higher than the vertical path displayed on the ND?

 

Last but not the least, have flown the tutorials to get yourself familiar with the aircraft?

 Also keep in mind that you can adjust those speeds in the legs page, just do it early so that the aircraft has time to achieve those speeds and make the descent rates possible. Big pet peeve I see the aircraft want to do in it's own programming and also in the vast majority of tutorial videos etc is to slow down far too early. 150-170kts on the base or 15 miles final and ATC would normally be pretty upset.

Was that the correct thing to do or should I have let the Autpilot do it’s job without interference?

The 777 will not manage the whole deceleration automatically so it is necessary to take over speed control manually. Rather than fiddling around with speed constraints in the LEGS page just select speed intervention and control speed target directly from the MCP.

My thanks to you all!

 

Much to try and much to think about.

 

Cliff

 

 

Much to try and much to think about.

 

Look at FCTM Ch 5 where there is a wealth of information from Boeing on how to operate the B777 during approaches, landing and missed approaches.

 

 

Was that the correct thing to do or should I have let the Autpilot do it’s job without interference?

 

The AP is there to assist - not to do your job.

 

I recommend flying the tutorial flight, as it explains very clearly what you should, and shouldn't do. One of those things is that you need to control the speed, and interact with the altitude limiter.