F/D disappearing on final

[kevinh 409]

Which AP is selected will also affect which side is master. If AP A becomes master for some reason then the Capt FD becomes master too. If only AP B is engaged the F/O FD will definitely be master and should stay that way.

[threexgreen 3,139]

Thanks I will try that. But it seems a bit odd to me that the F/O's F/D disappeares on approach just because the other one is master or because AP A is engaged. Can't believe this is the case in reality.

[downscc 1,327]

You are right, it shouldn't happen and I've use the right PFD 2D popup for approaches before when flying the left seat (to prevent a CTD in P3D by using the left PFD popup), I've never seen the FD bars disappear.

[Angelo Cosma 61]

You are right, it shouldn't happen and I've use the right PFD 2D popup for approaches before when flying the left seat (to prevent a CTD in P3D by using the left PFD popup), I've never seen the FD bars disappear.

 

Ive never heard of this happening, I use the Left PFD all the time. This causes CTDs??

[downscc 1,327]

Different subject, it's a problem that only appears after hours and only to a few.  Most the time I don't use a PFD popup in the NGX because I've gotten used to and favor the HUD.

[threexgreen 3,139]

Doesn't cause CTDs, all fine. Like I said, first the vertical part disappears and as soon as the glideslope is captured the horizontal one leaves me as well.

[rsvit 16]

Thanks I will try that. But it seems a bit odd to me that the F/O's F/D disappeares on approach just because the other one is master or because AP A is engaged. Can't believe this is the case in reality.

Both master F/D and autopilot must be choosen for PF's side. Because when you select autopilot it sets the FD on a corresponding side as a master. So if flying as FO - you use FD B and AP B.

Two FCCs are calculating flight path differently using their own sensors and flight computers, thus their data might mismatch sometimes. And you don't want captain and FO FDs to show different things, so master-slave logic is used, where slave just "copies" the master FD guidance. However, on approach, probably due to safety reasons, slave FD requires its own nav radio to be set for ILS frequency, otherwise it will not show GS. That is because on automatic approach both FDs become masters and the GS data is compared between them and only if tolerances on and between both the FDs are met, autoland would be available.

[threexgreen 3,139]

So I'll have to select AP B, F/D B and set the nav radio 'B' to the ILS frequency?

[rsvit 16]

That's correct.

[ALF1 15]

Both master F/D and autopilot must be choosen for PF's side. Because when you select autopilot it sets the FD on a corresponding side as a master. So if flying as FO - you use FD B and AP B.

Two FCCs are calculating flight path differently using their own sensors and flight computers, thus their data might mismatch sometimes. And you don't want captain and FO FDs to show different things, so master-slave logic is used, where slave just "copies" the master FD guidance. However, on approach, probably due to safety reasons, slave FD requires its own nav radio to be set for ILS frequency, otherwise it will not show GS. That is because on automatic approach both FDs become masters and the GS data is compared between them and only if tolerances on and between both the FDs are met, autoland would be available.

 

SPOT ON!!! GREAT THREAD!!

 

I want to thank both the OP and Rostyslav for enriching my knowledge today. I had never flown an ILS from the F/O side. With only the NAV1 frequency tuned into the ILS, VORLOC and GS arm in the FMA's, because the airplane is still flying other roll and pitch modes. Notice however that during this time the VORLOC and GS triangles in the PFD are not shown in the F/O side PFD.

 

As soon as CMD A goes into approach mode however, the FD and FMA's in the F/O side disappear. Now tune the ILS frequency in NAV2 radio, everything back to normal. Except that now channel B is providing FD clues for the F/O side.

 

Learn something every day.

 

 

EDIT: I want to ADD to this post instead of correcting what might be a wrong last sentence. This for knowledge base reasons. It appears I am still a bit confused and would like further enrichment. So now that we have the ILS freq. tuned in NAV2 radio, is the FD on the F/O side now receiving clues from channel B ? or from the MASTER channel ?

Then, what happens during DUAL CHANNEL AUTOLAND with both CMD A and CMD B engaged ? is each one independent and the aircraft flying from which FCC ?

[KevinMM 22]

BOTH Nav radios need to be tuned to ILS. Also once the approach becomes active, turn on the other AP. (If you do it too soon it will just swap over.)

[downscc 1,327]

 

 

BOTH Nav radios need to be tuned to ILS

 

Not true, you can tune one to ILS and other to a VOR/DME for example, which is actually how some published approaches work.  Without both set to ILS you don't have autoland but you will still have an ILS approach.

[ALF1 15]

You guys are not answering my question. Please see my not being clear on the FCC providing clues for the FD when both nav radios are tuned in to ILS. I THINK that the master provides clues unless both masters are active with both A and B systems engaged but I am not sure.

[Jet Tech 31]

Alberto,

 

F/D modes are controlled directly from the respective FCC under certain
conditions. This independent F/D operation occurs when neither A/P is engaged
in CMD, both F/D switches are ON and one of the following mode conditions
exists:
• APP mode engaged with LOC and G/S captured
• GA mode engaged and below 400 feet RA
• TO mode engaged and below 400 feet RA.

[ALF1 15]

Ahhhh!!, Thanks so much Paul. And or else it is the master or engaged command system A or B which becomes automatically the master that provides the clues correct ?

 

One last question: Back from old school the flight Director the brains and the autopilot the muscle, but in small piston we never did dual channel autolands. What happens exactly when dual channel autoland engages at 1500 RA I believe and both masters, which FCC flies the airplane ?