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paulyg123

Flight Director Help

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I searched the forum and can't seem to get this right.

By looking at my question, you'll see I lack the skills needed here, so I need a simple answer please.

 

When hand flying an ILS approach, (there are two queues I can go by.)

1. In approach mode (the round knob next to VOR L) - I  look at the glide slope indicator and the HSI indicators and keeping those ticks centered and I guess keeping the magenta HSI lined up.  That's all I need to land the plane in the fog

2.  Using the flight director and keeping the square dot centered.  That also works for me when I can it to actually work correctly.

 

So assume I am 7 miles out (ILS is tunes and active) and my glide slope and HSI are both centered - I am configured for landing.  All is good.

I hit the APP button on the Autopilot (but still flying manually - I am trying to get the flight director to now guide me.  I indeed get the  magenta heading line to swing around and line up with the runway heading

 

A.  True or false?  APP must be selected to have FD guide me.

So how do I know I can rely on the flight director?  what is displayed to give me a clue I am good?.

Look at the photo, the FD disagrees with the glideslope.  FD wants me to go higher - even though G/S is saying lower.   this is my problem

It seems like I need to turn on the auto pilot for a split second to get Autoland 3 showing up to then get the FD to work.  Then I can de-select the auto pilot and my flight director will then work.  Is this the correct method?

 

B. how far from runway can I rely on Flight Director to be able to follow it for  landing? - remember - entire flight is without autopilot

One point here is that I did 1000's of ILS appraoches on the PMDG 777 and I guess I just learned when to dismiss the FD.

sfo%20approach_1.jpg

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A.  True or false?  APP must be selected to have FD guide me.
So how do I know I can rely on the flight director?  what is displayed to give me a clue I am good?.

 

True - for an ILS approach.

As always, the most important cue is the flight mode annunciator at the top of the PFD.

 

 

 


B. how far from runway can I rely on Flight Director to be able to follow it for  landing? - remember - entire flight is without autopilot

 

Far enough out that you approach it from below. Additionally, while it's not directly related here, you should get in the habit of setting the speed cue to where it should be...especially with the A/T armed like that.

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So why the discrepancy between FD and ILS cues? 

The FD is commanding pitch up because of your excessive speed. 200 KIAS on a glideslope is very very much too fast.. slow her down mate.

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The FD is commanding pitch up because of your excessive speed. 200 KIAS on a glideslope is very very much too fast.. slow her down mate.

 

Think I need  glasses  since  his  speeds looks like  around  the  163  on the speed  tape  although he  has  200  selected  on the mcp  

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You're right, Peter, I didn't look close enough; however, the problem remains excessive speed with Vr at 140 Vapproach should be 145 in most cases.  Pitch plus power equals performance... old adage from a great author of pilot handbooks.

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Yes speed is 164, A/T is off here - so 200 is meaningless.  I'll use AT at 145 and see if this makes a difference.

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SOLVED!

 

OK thanks. - you guys nailed it.

 

 The excessive speed the reason D was not lining up with the glideslope cues.  I was off.

I set AT to 145 kts and FD tracked perfectly.

Before I was manually controlling the speed - I never never FD took into account speed in APP mode and speed would over-ride my position on the glideslope..

 

Thanks

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The FD is commanding pitch up because of your excessive speed. 200 KIAS on a glideslope is very very much too fast.. slow her down mate.

This isn't right. After G/S capture the FD commands a path to follow the glideslope. Speed control is only by thrust. If you are fast the FD should still command the G/S path, it won't command pitch up to slow you down.

 

This doesn't explain the OP's problem or how he managed to solve it, but the cause can't be to do with not having the speed at Vref.

 

Edit:

 

I can reproduce this if I takeoff without engaging A/T or AP and never select any mode on the MCP except APP. This way the FD remains in TOGA mode until ILS capture. The LOC and G/S capture OK according to the FMA but the FD continues to command a pitch up, as if it's still in TOGA. Possibly a bug?

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Agree except... pitch mode is glideslope. I've never seen it command pitch up when in GS pitch mode... we're not even sure if OP had GS indicated on FMA. However, there is overspeed protection and I'm not sure how that is applied when pitch mode is glideslope. Good question.

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I kind of thought speed was my issue, but since I am at Vref +5 the FD behaves perfectly.  Now the last 2 replies lead me to believe this was just luck.  Ok now keep it simple, you say "not sure if I had Glide Slope indicated on FMA"  - what is FMA? glide slope is tuned and active - see photo on initial post.  (3 white / 1 red, 1 tick low on the glide slope - I am a bit high - YET FD says raise nose -why???

 

Now Kevin mentions a key point.  If autopilot and AT is never selected (which is the case as I am manually flying from KOAK to KSFO, the FD has a hard time picking up the GS,  I noticed if I set up APP for autoland and activate the AP, then the FD is right on.  If I deactivate AP, then I am still good with the FD as far as matching up with my GS cues.

 

So someone do a quick flight manually (no autopilot or AT) and see if the FD mimics the GS, only hit the APP button on final approach  (with AP off) to get the FD working and see what happens.

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Agree except... pitch mode is glideslope. I've never seen it command pitch up when in GS pitch mode... we're not even sure if OP had GS indicated on FMA. However, there is overspeed protection and I'm not sure how that is applied when pitch mode is glideslope. Good question.

The OP's screenshot shows the FMA with LOC and G/S green so he definitely did have GS capture. I got exactly the same thing if I didn't do anything which engages A/T.

 

GS commands a path so it isn't a pitch for speed mode. Any overspeed protection would be via the FBW system, not the FD.

 

Of course, if you takeoff using TOGA to set thrust as per normal procedure then this can never happen. The A/T would be engaged during takeoff and the FD will behave itself.

So someone do a quick flight manually (no autopilot or AT) and see if the FD mimics the GS, only hit the APP button on final approach (with AP off) to get the FD working and see what happens.

I've already done that. What you should do is try a flight using TOGA thrust for take off but flying manually. Then see if the FD guides you in pitch correctly on the ILS.

 

It's all very well flying completely manually but the 777 is not meant to be flown in the way you seem to have done. Normal procedure is to use TOGA to set thrust for takeoff. If you had done this the FD would have worked properly in APP mode as the A/T would have been engaged on takeoff, even if you had disconnected it afterwards. Another MCP mode which engages A/T speed mode automatically is ALT HOLD.

 

Also, if you plan to use the FD for guidance you are supposed to set the MCP for the FD to follow. You left SPD and ALT as initialised on power up. Otherwise switch the FDs off as the FD bars are not showing you valid information. Note, the MCP controls both the AP and FD.

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what is FMA?

 

FMA is the Flight Mode Annunciator: the text that appears above the artificial horizon on your PFD. There are three columns: the first indicates the autothrottle mode, the middle column the roll mode and the rightmost column the pitch mode. Assuming the 777 is the same as the B747 in this regard, white text indicates an "armed" mode (i.e. it's waiting in the background for the appropriate conditions to be met for engagement) and green text indicates an "active" mode (i.e. the AFDS is actively guiding the aircraft in this mode). So in your case, the first column is BLANK (the A/T is off). The middle column shows LOC in green, indicating that the roll commands generated by the FD are guiding you along the localiser. The right column shows GS in green, indicating that the FD should command pitch to follow the path of the glideslope.

 

The FMA is the final authority as to what the aeroplane is trying to do (what "mode" it is in) -- whatever buttons you press on the MCP or otherwise, it's only relevant if the correct mode is subsequently annunciated and active on the FMA. So, for example, if you press the APP button on the MCP, you might see SPD | HDG SEL | ALT in green with | LOC | GS in white below. This would indicate that the AFDS is maintaining the selected heading and altitude, but when the conditions for localiser and glideslope capture are met (generally, needle deflection within a certain tolerance), LOC and GS will take over. Of course, if you never meet the conditions for LOC and/or GS capture (for example, you're flying away from the localiser), those modes will never engage (hence why when people post questions like "I pressed APP but the aeroplane didn't land", my first question is "what did the FMA say?").

 

The thing to remember about the AFDS is that the Flight Director is the "brain" -- the autopilot is just the "muscle" -- all the autopilot does is follow the Flight Director commands to keep the bars centred.

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