Flight Director Commands In B777 (And In 737Ngx)

[richjb2 195]

I have noticed that the flight director commands are lag behind those required when hand flying the aircraft.   I have noticed this both in the 777 and 737NGX.

 

For example, when in turn towards a selected heading, the flight director command bars do not command wings level until the aircraft's heading has passed beyond the heading bug.  Even then, the command to wings level appears to follow the manual reduction of bank (roll out) rather than commanding a roll-out.  A similar characteristic can be noticed in pitch where the command bar does not command a level off until past the selected (bugged) altitude, in either climb or descent.  I also noticed that localizer deviations occur without roll command to correct. 

 

Many times, it almost appears that the flight director command bars are waiting for a pitch or roll attitude change to occur before they indicated some type of command to return to the tracked value (e.g. altitude hold, heading bug, localizer, glideslope, etc.).

 

Anyone else experiencing this tendency with the flight director.  I find it occurring both in the dual cue and single cue options.

 

Thanks!

 

Rich Boll

Wichita KS

[tcas_climb 45]

I have noticed it myself.

[jetsflier 87]

I have noticed that the flight director commands are lag behind those required when hand flying the aircraft.   I have noticed this both in the 777 and 737NGX.

 

For example, when in turn towards a selected heading, the flight director command bars do not command wings level until the aircraft's heading has passed beyond the heading bug.  Even then, the command to wings level appears to follow the manual reduction of bank (roll out) rather than commanding a roll-out.  A similar characteristic can be noticed in pitch where the command bar does not command a level off until past the selected (bugged) altitude, in either climb or descent.  I also noticed that localizer deviations occur without roll command to correct. 

 

Many times, it almost appears that the flight director command bars are waiting for a pitch or roll attitude change to occur before they indicated some type of command to return to the tracked value (e.g. altitude hold, heading bug, localizer, glideslope, etc.).

 

Anyone else experiencing this tendency with the flight director.  I find it occurring both in the dual cue and single cue options.

 

Thanks!

 

Rich Boll

Wichita KS

 

I have that observation as well, but, is this correct behavior in the actual aircraft or not?

[777simmer 117]

Noticed it as well but like the challange.

Before SP1 it was the same.

 

It is not like that in the real thing, no.

 

Strange thing is the AP works beautifully.....so it is not like it is impossible to programm the FD in the same way I would think.

[richjb2 195]

With 6000+ hours flying the Collins ProLine4/ProLine 21 along with the Honeywell PRIMUS 1000, I can say that the flight director behavior that I described is not correct.  The command bars should move independently and command the necessary pitch and roll changes to satisfy the selected flight guidance modes, and do so ahead of the actual aircraft attitude.  In other words, not wait until the desired attitude has been exceeded.  It appears almost as if there is a latency in the system whereby the flight director reacts only after a deviation is sensed. 

 

I have noticed a common error with many flight simulators that the flight director command bars appear to at first follow the aircraft's attitude change (i.e. move with the airplane wing or delta symbol) and then provide a correction once the airplane deviates from the commanded value.  The actual performance of the flight director command bars is to present a computed roll and pitch attitude that will maintain the commanded flight guidance target.  The commanded roll & pitch attitude does change with an aircraft pitch and/or roll change.  Following a roll or pitch change, the command bars provide the necessary attitude correction to return the aircraft to prescribed values.

 

I have no experience with the Boeing products.  However, with the ProLine and Honeywell systems that I do fly, I know that the flight director actually computes the required roll and pitch attitude necessary to satisfy the flight guidance commanded modes (e.g. ALT HOLD, HDG, LNAV, APP, etc.).  The autopilot then commands pitch and roll attitude changes, through the servos, to follow the flight director's commands.  In the PMDG simulation, it appears that the reaction is exactly the opposite.  The autopilot is making pitch and roll changes to match the flight guidance modes and with the flight director command bars following up to match the autopilot change.  Like I said, I have no experience in the Boeing aircraft, but that doesn't appear to be correct given modern flight guidance design logic.  Perhaps someone with greater knowledge of the system will chime in?

 

Still love flying the PMDG aircraft.  They are the best simulations available!

 

Thanks!

 

Rich Boll

Wichita, KS

[CaptWilliam 0]

I noticed the "lack of anticipation of the F/D" as I call it too.

But then again, I only have experience on the B737-300/400.

 

Willem

[zmak 331]

I wish I was confident enough to bring this up when it felt wrong ages ago but hesitated just because the answer may have been buried somewhere  ITFM

[scandinavian13 5,192]

support.precisionmanuals.com - submit tickets.  It could help the team track it down.

[richjb2 195]

Thanks Kyle,

 

I will submit a ticket and perhaps make a video or two to demonstrate the issue.

 

I will submit the ticket today or tomorrow, but I will be unable to follow up with the video until next week.  I am leaving on a four day trip this afternoon.  Will not have time today.

 

Thanks again for your help!

 

Rich Boll

[scandinavian13 5,192]

 

 

Thanks again for your help!

 

Welcome - thanks for helping the community out with the feedback.

[richjb2 195]

Hi Kyle,

 

I submitted a support ticket yesterday.  I also made a video of what was describing.  I am not very good with video editing.  It was 81MB, so it wouldn't upload.  I did share with them a Dropbox link that contains the video.  Hopefully, support can download it from there.

 

Thanks for your help!

 

Rich Boll