Pro Line 21 + Gps Appch Question

[Big Picture]

I am relatively new to Pro Line 21 and thought maybe one of you guru's could help me out.

The situation is this: We're on vectors for the approach and ATC clears us for the GPS XX. We have been in HDG and VALT prior to the clearance. When we are cleared for the approach, we select MAP altitude in the altitude preselect and press APPR. This arms APPCH FMS1 and GP (Both white).

The problem is that APPCH FMS1 has a line through it, indicating there's a problem. It will not capture the inbound course unless I hit NAV, let it activate and then reselect APPR. When I reselect APPR, it arms APPCH FMS1 and GP as before. When it gets to the glidepath VGP activates and flies the approach as it should. During the approach FMS1 and VGP are active and APPCH FMS1 is armed with a yellow line through it.

Any thoughts as to what we're doing wrong? I should also note that all other type of approaches using VNAV guidance seem to be working properly.

Thanks.

 

[HMR]

Are you talking about arming "APPR" on the autopilot? APPR should only be used on an ILS.

For GPS approaches you stay in NAV mode all the way to touchdown.

PS- I'm also new to the PL21 and asked the same question while attending school at the Collins factory. If you get a chance, read the PL21 supplement in your AFM. It's a good Reader's Digest version of what all the buttons do.

 

[Big Picture]

Yes, sorry, I am talking about the FGP modes.

In the supplement under "Principles of VNAV", it says to arm APPR during a GPS approach. The advantage of pressing APPR is that it activates VGP mode. This allows you to dial in your missed approach altitude once it captures the glidepath. The system no longer respects the preselect altitude once it is in VGP mode.

Pressing NAV, as you know, arms VPATH mode and you have to keep the preselect altitude at MDA until the missed.

 

[fu69atacafyeah]

Are you talking about arming "APPR" on the autopilot? APPR should only be used on an ILS.

For GPS approaches you stay in NAV mode all the way to touchdown.

The Proline 21 manual says you can use either, "APPR mode" OR "NAV mode" for GPS approaches. With that it also tells you the difference between, VNAV and VGP.

 

[HMR]

The Proline 21 manual says you can use either, "APPR mode" OR "NAV mode" for GPS approaches. With that it also tells you the difference between, VNAV and VGP.

Can you give me a page # where it says to use either APPR or NAV for GPS approaches? I've been through Collins school and read the manual cover to cover several times in the past few months since we installed the PL21. I can't think of a benefit to arming APPR instead of NAV for a GPS approach (again, I'm new so I could be missing something).

Big Picture- I think your problem stems from hitting APPR on the FGP. VGP should only show up when the approach is armed in the FMS, no? (pg.15-5 in the FMS-6100 Pilot's Guide). Once the approach is selected in the FMS and the aircraft is within 2nm of the FAF, the FMS will automatically transition into APPR mode. When the "Principles of VNAV" section says "VNAV arms for VGP when approach mode is armed" (also on pg.15-5), I believe they're referencing the FMS approach mode- not the FGP "APPR" mode. In your scenario, I think going straight from HDG to NAV will solve the problem.

Hopefully, some PL21 experts will chime in.

 

[Big Picture]

HMR,

We may be working out of different manuals. I don't have anything on 15-5 but at the top of 17-35, it reads:

"To enable the VGP mode, the pilot must select APPR on the FCP. VGP mode allows the preselector to be set at the missed approach altitude and continue descent to the runway."

I do see what you're referencing regarding 2nm from the FAF, but I read that as an advisory that it is going to approach sensitivity and is monitoring RAIM.

I'm going to try to call Collins today and see what they say.

Thanks for you input.

 

[HMR]

"To enable the VGP mode, the pilot must select APPR on the FCP. VGP mode allows the preselector to be set at the missed approach altitude and continue descent to the runway."

It doesn't get much clearer than that!

I don't have a 17-5 nor can I find a reference to using APPR on the FCP for GPS approaches in any of my manuals. I wonder if it's aircraft specific? What are you flying and what FMS are you using? We have a DA50 with FMS-6100's.

 

[jagmagic]

If you are going to do a normal GPS app it should be done in nav mode. If you are going to do the GPS Vnav app then you need to hit App mode and then Vnav it will bring you to 50 feet above the runway. If you are in app mode it is not going to level you off at the MDA it is going to bring you all the way down with VNAV selected. Hope this helps

Nav + Vnav level at MDA
App + Vnav 50 feet above ( can only do if company has it in Ops specs)

 

[Big Picture]

HMR,

We have the same setup as you do. FA50 with PL21 conversion.

I spoke with Collins today and we may have an issue with our particular aircraft. I think we are pressing the right buttons but for some reason, it's not arming properly.

I'd be curious to hear how yours works in the same scenario. Do you get any flags on a GPS appch?

Thanks.

 

[HMR]

Big Picture- We took the plane up empty today and shot a few practice approaches. NAV + VNAV is the correct selection for a GPS approach. As soon as you're cleared for the approach, set your BARO MIN to the correct altitude and let the FMS and AP do the rest. If the approach ends with a "RWY", Vpath will sequence to VGP automatically. No flags or funny indications either.

I still stand by my claim that "APPR" should only be selected for ILS approaches.

 

[Big Picture]

HMR,

Thanks for the follow-up. I arrived at the same conclusion after trying another practice approach this weekend.

I checked with Collins and apparently there is an error in our manual (see quote above). Apparently in a FA50 retrofit, there is no such thing as APPCH FMS mode. In other airplanes there is. So for our airplanes, NAV works for everything but a BC and an ILS.

Thanks again.

 

[stuckinGFK]

Big Picture- We took the plane up empty today and shot a few practice approaches. NAV + VNAV is the correct selection for a GPS approach. As soon as you're cleared for the approach, set your BARO MIN to the correct altitude and let the FMS and AP do the rest. If the approach ends with a "RWY", Vpath will sequence to VGP automatically. No flags or funny indications either.

I still stand by my claim that "APPR" should only be selected for ILS approaches.

In the CJ3 we use APPR for GPS approaches that have LPV minimums. If it has an MDA, we use NAV along with VNAV.