Dreamflight767

FA50 How to do a RNAV APP?

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Hi:

I've attempted two RNAV approaches without success.  The approaches were loaded via the GTN750.  As I approached the 3% glidepath at the intercept altitudes, I armed approach on the autopilot.  But the airplane doesn't follow.  I noticed I got G/S warning flags on the ADI.

Thanks.

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Posted (edited)
3 hours ago, Dreamflight767 said:

Hi:

I've attempted two RNAV approaches without success.  The approaches were loaded via the GTN750.  As I approached the 3% glidepath at the intercept altitudes, I armed approach on the autopilot.  But the airplane doesn't follow.  I noticed I got G/S warning flags on the ADI.

Thanks.

Of course the approach must have vertical guidance, which is shown in the GTN.

Occasionally I have seen that happen if I tried to intercept the glide slope above the FAF altitude. I generally see the GTN switch modes at the FAF, assuming the altitude of the aircraft is at or slightly below the FAF altitude. I always make sure on the approach that I am at the FAF altitude when engaging APPR.

Edited by Wink207

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18 hours ago, Dreamflight767 said:

Hi:

I've attempted two RNAV approaches without success.  The approaches were loaded via the GTN750.  As I approached the 3% glidepath at the intercept altitudes, I armed approach on the autopilot.  But the airplane doesn't follow.  I noticed I got G/S warning flags on the ADI.

Thanks.

If you got a GS flag then the glideslope is not active. Make sure you first have the ability to tune to an approach frequency and get the glideslope to become active. make sure your in the VLOC mode on using the GPS unit option.

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Posted (edited)

Another recommendation, make sure the GTN is not in GPS mode.

I've done that a couple of times.

 

 

Edited by bill62

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20 hours ago, Dreamflight767 said:

Hi:

I've attempted two RNAV approaches without success.  The approaches were loaded via the GTN750.  As I approached the 3% glidepath at the intercept altitudes, I armed approach on the autopilot.  But the airplane doesn't follow.  I noticed I got G/S warning flags on the ADI.

Thanks.

What was the actual approach you were flying? Not all RNAV approaches have vertical guidance.

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4 hours ago, bpcw001 said:

What was the actual approach you were flying? Not all RNAV approaches have vertical guidance.

Tired to fly the RNAV/GPS-B at PHMK and GPS-A at Libby, MT (S59)

5 hours ago, Flysimware said:

If you got a GS flag then the glideslope is not active. Make sure you first have the ability to tune to an approach frequency and get the glideslope to become active. make sure your in the VLOC mode on using the GPS unit option.

Thanks, but on the GPS/RNAV APP. I don't believe there is a freq. to tune.  On an GPS/RNAV APP shouldn't the GPS create a GS on the ADI and the pilots/autopilot follow?

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Posted (edited)

On a RNAV approach there is no frequency to tune in. You just need to be in GPS mode, and to select, load and activate the approach in the GTN750 GPS. If the approach has vertical guidance you must intercept the glide path from below (sim requirement for capture) . If the AP APR mode is on, the glide path (GP) should capture just as the yellow glide path indicators reach the center position. At that point the AP APR light should switch from ARMed to CAPture. If after GP capture you deviate to far (GP indicators almost at the top or bottom of the scale) , the APR will switch back to ARM and you have to recapture again from below.

Al

Edited by ark

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It helps to study and understand the approach plate. GTN has them.

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The GPS approaches at S59 and PHMK have circling minimums only. There is no vertical path encoded in either procedure that would allow the use of a GP.

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Hand fly the approach if you don’t get vertical guidance,fly the step downs on the plate

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Posted (edited)
On 3/11/2019 at 5:01 PM, Dreamflight767 said:

Tired to fly the RNAV/GPS-B at PHMK and GPS-A at Libby, MT (S59)

Thanks, but on the GPS/RNAV APP. I don't believe there is a freq. to tune.  On an GPS/RNAV APP shouldn't the GPS create a GS on the ADI and the pilots/autopilot follow?

As I was suspecting, none of the GPS approaches you mentioned has vertical guidance by design. The RNAV part only gives lateral guidance.

An RNAV approach with vertical guidance requires RNAV/LNAV or RNAV/LPV designations and minima.

Compare to e. g. the RNAV approach charts for Teterboro (KTEB) which should come up with vertical guidance.

 

Edited by bpcw001

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13 hours ago, bpcw001 said:

As I was suspecting, none of the GPS approaches you mentioned has vertical guidance by design. The RNAV part only gives lateral guidance.

An RNAV approach with vertical guidance requires RNAV/LNAV or RNAV/LPV designations and minima.

Compare to e. g. the RNAV approach charts for Teterboro (KTEB) which should come up with vertical guidance.

 

Thanks.  I was reviewing the charts again and noticed neither support the vertical guidance.  My bad.

Appreciate the help! 

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