autopilot half a dot below ILS glide slope

[bpcw001 22]

Hallo,

 

I am running the Phenom 300 with Bert's GTN Mod 4.8 on FSX SP2.

 

Whenever the autopilot is supposed to follow a given vertical guidance from ILS or GPS LPV, it tracks the glide path in a way that it consistently ends up about half a dot (and sometimes even a full dot and more!) below from what is displayed by the glide slope indicator.

Aircraft is in full landing configuration at the appropriate airspeed when the glide slope is captured, weather is calm.

 

Small deviations (maybe 1/4 dot) might be acceptable and real-world like, but half a dot and more?

 

Is that a problem of the glide slope indicator not indicating correctly, or does the auto pilot just do a lousy job of tracking the glide slope? Lateral guidance is fine, although not perfect either.

 

Any ideas?

 

Thanks

Dave

 

 

 

 

[vololiberista 205]

It's more likely to be related to your rate of descent and airspeed. You should go for 180kts to capture the localiser and then slow down to 160kts with gear down and appropriate flaps as you capture the glideslope and then at 6DME slow down to your Vref+5.

[bpcw001 22]

It's more likely to be related to your rate of descent and airspeed. You should go for 180kts to capture the localiser and then slow down to 160kts with gear down and appropriate flaps as you capture the glideslope and then at 6DME slow down to your Vref+5.

Thanks for your suggestions. I did it that way and being not too slow on the ILS definitely helps. However, at some point, you need to slow down to Vref+X which inevitably throws the autopilot off slope again. Given that I'd like to habe a stable approach established around 500ft RA latest, I must resort to hand-flying quite early.

Not a problem, I like to hand-fly my approaches, but I am wondering what the real autopilot is like and which restrictions apply.

 

Dave

[vololiberista 205]

It's quite common to disconnect the AP at 500ft or below. Sometimes at 1,000ft. It depends on the weather. You certainly don't want anything but minimal control inputs when so close to the ground. By 2,000ft you should start to slow down to your Vref+5 (or more if it's windy) Once the a/c has stabilised then fly manually.

You normally would have to ask Approach if you want to do a visual approach which is different to what I've said above. In Europe the request would most likely be denied at busy airports.

You need to always be on top of your airspeed during the approach phase and never let the engines idle until you flare.

[bpcw001 22]

It's quite common to disconnect the AP at 500ft or below. Sometimes at 1,000ft. It depends on the weather. You certainly don't want anything but minimal control inputs when so close to the ground. By 2,000ft you should start to slow down to your Vref+5 (or more if it's windy) Once the a/c has stabilised then fly manually.

You normally would have to ask Approach if you want to do a visual approach which is different to what I've said above. In Europe the request would most likely be denied at busy airports.

You need to always be on top of your airspeed during the approach phase and never let the engines idle until you flare.

Thanks for your input. I have absolutely no trouble hand-flying my approaches since I fly real world aircraft (much less sophisticated piston props. Old crates without autopilot and fancy avionics). I was just wondering why the autopilot cannot do the approach better than I (which imho it should).

[jaydor 233]

When you hit the approach button, are you selecting VLOC from GPS on the GTN and also are you selecting VOR1 on the PFD:

 

 

The HSI will change from magenta to green single arrow on the PFD for VOR 1 & double Arrow for VOR 2 and magenta on the GTN.  Also have you selected the correct Baro setting?

 

A wrong Baro setting will give a false reading on the glideslope..

 

You can see on the PFD  that the LOC is alive AP still selected and GS captured.  The gear is lowering and will slow me down to around 114kts at touchdown.  Also use your spoilers before touchdown to help take the pressure off the undercarraige and help for shorter runway use.  Do not flair to high the ideal is front wheel about 1 foot higher than the main on touchdown.

 

Let us know..

[jaydor 233]

The Phenom 300 is equipped with the Garmin G1000 and Carenado have done an excellent job in it's rendition to use in FSX, etc.,  Although we have modified the navigation to use the Flight1 GTN750, thanks to Bert Pieke.

 

It is still important to use the PFD in conjunction with the GTN.  The PFD is capable of giving you so much information.  Also the bonus is, you can still use the original MFD which is still lurking underneath the GTN.  The GTN becomes the primary navigation input when installed, but the hidden MFD is still capable of giving you so much more information also.  Use the short cut keys for the pop ups.

 

 

SHIFT + 1 for the PFD

SHIFT + 2 for the GTN

SHIFT + 9 for the original MFD

 

Use the same Shift keys to hide them.  Resize them so that you can use them in flight:

 

[bpcw001 22]

Well, like I said. Your speed is about 132 IAS, so still quite high, and the gear is just about to come down at flaps 2.

Under those conditions, no problem with me either.

 

The trouble starts when you are fully configured, i. e. gear down, flaps full, speed Vref+5.

Then, in this last phase of the approach, the autopilot is getting some trouble.

 

The real-world Phenom autopilot is usable down to 200ft RA with both engines operative.

 

Anyway, thanks for all your input. I'll see in fall/winter how things are going when ILS is really needed down to minimums in low-vis conditions.

[whamil77 183]

Hallo,

 

I am running the Phenom 300 with Bert's GTN Mod 4.8 on FSX SP2.

 

Whenever the autopilot is supposed to follow a given vertical guidance from ILS or GPS LPV, it tracks the glide path in a way that it consistently ends up about half a dot (and sometimes even a full dot and more!) below from what is displayed by the glide slope indicator.

Aircraft is in full landing configuration at the appropriate airspeed when the glide slope is captured, weather is calm.

 

Small deviations (maybe 1/4 dot) might be acceptable and real-world like, but half a dot and more?

 

Is that a problem of the glide slope indicator not indicating correctly, or does the auto pilot just do a lousy job of tracking the glide slope? Lateral guidance is fine, although not perfect either.

 

Any ideas?

 

Thanks

Dave

I have noticed this with many aircraft and I wonder if it is a problem with FSX/P3D.  The RealAir Turbine Duke is the only one that I have seen fly a "bullseye" approach, so I'm guessing they did something to fix the sim problem.  Every Carenado aircraft I own falls below the glideslope on an ILS/LPV approach.  They also search, sometimes wildly, for the selected altitude at level-off after a climb.