767 FMC question
 

The 737 NG FMC has the ability to change the descent speed (via the VNAV descent page) after the descent has been initiated. Is this true for the 767? I was told it wasn't and the only way around was to use speed intervention but I argued against this.

I fly the 757 which obviously isn't a 767 but basically the same.

It works just like the 737 you mention really - just overwrite the ECON or whatever speed is in there by default with what you want to do on the DESCENT page...for example, as some of our less fuel conscious pilots like to do, M0.82/330!

I fly the 767 (both Pegasus + non pegasus FMC) and can confirm what mbcxharm says. .

You simply re enter the desired descent speed in the descent page, execute and voila!

Right, that's what i thought but this guy wouldn't have it. He said the 767 FMC doesn't have the ability to change the descent profile after the descent phase has been initiated. I thought that's rubbish... what's the use of the FMC in that case! If the 73 can do it they all can do it.

Rather than use the speedbrake to regain the descent profile it was standard practise on the 757,767 and 777 to add five knots to the FMC descent speed and execute. If still too high try another five knots. Worked like a dream

Wouldnt increasing the speed in the FMC to a higher decsent speed, just make you even higher on the profile? Or am I being thick?

The faster airspeed means more drag, the more drag means you can lower the nose more and increase the descent speed without exceeding the airspeed you (or the FMC) selected. It's kinda like using airspeed as a speedbrake. My understanding is that drag is a square to airspeed and descent rate/lift are a more direct relationship, so drag wins.

Just my guess.

The Boeing FMCs allow you to change the descent speed and they will calculate the new profile for you, whereas the Airbus will not allow a change to the descent speed once the descent is initiated, except by going to Selected Speed, and no new profile will be generated. Rather a pain!

Datboy
Maybe your guy meant you couldn't change the cost index after the descent has been initiated, which will also affect descent speed.