I'm reading manuals for the 777 and when I finished with Autopilot section from SmartCockpit I realized that I haven't seen an indication that would show wich autopilot is the master (737 has a green MA light above left or right F/D, depending on which side is the master). Looking at the AFDS schematics made me realize that the 777 has three independent autopilots, all simultaniously activated by EITHER A/P button. Nice feature, all 3 active all the time but that made me thinking. If there is no indication which side is master, then how does the aircraft know which VOR to follow? If I decided that I wanted to fly a certain radial, how do I do that? 737 is simple, just hit VOR/LOC but 777 manuals only mention localizer and the only button there is on MCP is the LOC, without VOR. I then googled it and found on pprune that 747 is not capable of tracking VOR radials, only localizer. Is my assumption right that this thing is the same with 777?

There are a couple ways to fly radial, 1 is using raw data and trk mode on the heading selector secondly you can use place/bearing in the fmc to construct the radial or you can select direct to the vor in the fmc and use the intercept course as the radial

Yeah. NG has VOR option, 777 has TRK option, otherwise it's the same thing (FMS). Makes kinda sense that it's the way the've made it.

If I remember correctly, in the PSS T7 a VOR radial could be tracked by setting the frequency and heading in the CDU radio page in NAV 1 and then using the localizer button.  Don't know if this is RW or not.

 

Mike

The 777 FM does not follow follow the radio signal from the VOR station if in LNAV mode, unless you use Track/HDG to track the radial using raw data. Like most of the modern FM, it draws a radial based on a FM position of the particular VOR you tuned ( which is already in its database ), and the position accuracy is monitored using GPS signal. Therefore theoretically it can track the to a VOR station or do VOR approach without the VOR station actually working as long as the navigation accuracy is high enough.

 

AP wise if I remember correctly, the AP decides which one to use is the master without letting the crews know. And you will get an EICAS message if any one of them inoperative. Just like the IRS on the 777 ( which only has one button as well ).

 

Hopem it helps.