GFC500 ILS help wanted

[Greg Ellis]

00658IL31.PDF
 

For any of you experienced GFC 500 pilots.  Let’s say I am flying the ILS to Mineral Wells (KMWL).  I am going to fly the procedure turn.  According to the chart, I maintain 3000 until inbound from the procedure turn then I can descend to 2500.  I have activated the approach prior to reaching the Millsap VOR and turning outbound.  What do I do to tell the GFC to descend to 2500 once turning inbound?  My altitude hold is set at 3000 because that is what I am flying out bound at.  I have the GFC500 working with a GNS 530W.  Thanks.

[LANCECASPER]

36 minutes ago, Greg Ellis said:

00658IL31.PDF 193.32 kB · 2 downloads
 

For any of you experienced GFC 500 pilots.  Let’s say I am flying the ILS to Mineral Wells (KMWL).  I am going to fly the procedure turn.  According to the chart, I maintain 3000 until inbound from the procedure turn then I can descend to 2500.  I have activated the approach prior to reaching the Millsap VOR and turning outbound.  What do I do to tell the GFC to descend to 2500 once turning inbound?  My altitude hold is set at 3000 because that is what I am flying out bound at.  I have the GFC500 working with a GNS 530W.  Thanks.

I'll let GFC500 pilots chime in on the buttonology, but only if there was a NOTAM or a RAIM message or a GPS outage would I fly the ILS 31.

But if not, I would definitely fly the RNAV (GPS) 31. I find the WAAS approaches that have vertical guidance to be much smoother than the ILS, laterally and vertically.

[201Steve]

I believe you have to set your bug to 2500 and descend via ias or vs mode. Only until you’ve reached the FAF will it capture GS. If I’m following correctly. 

[Greg Ellis]

19 minutes ago, LANCECASPER said:

I'll let GFC500 pilots chime in on the buttonology, but only if there was a NOTAM or a RAIM message or a GPS outage would I fly the ILS 31.

But if not, I would definitely fly the RNAV (GPS) 31. I find the WAAS approaches that have vertical guidance to be much smoother than the ILS, laterally and vertically.

I agree with you.  But I chose this just as an example.  It could apply to any ILS where you are told to maintain an altitude by approach that is higher than the ILS intercept etc…. I just picked this one because it is close to me and easy to practice.

[Greg Ellis]

1 minute ago, 201Steve said:

I believe you have to set your bug to 2500 and descend via ias or vs mode. Only until you’ve reached the FAF will it capture GS. If I’m following correctly. 

Thank you.  I think that is what I am looking for.  I appreciate the response.

[201Steve]

I don’t have a ton of experience with it yet so, there may be further explanation to be had. 

[201Mooniac]

For a 500 ft decent like that I will typically just maintain 3000 until I intercept the glideslope outside the FAF and then verify the crossing altitude when crossing the FAF inbound rather than add another configuration change.

[Mooney Dog]

24 minutes ago, Greg Ellis said:

I agree with you.  But I chose this just as an example.  It could apply to any ILS where you are told to maintain an altitude by approach that is higher than the ILS intercept etc…. I just picked this one because it is close to me and easy to practice.

ATC will clear you for whatever the point your going to normally is vs their MVA for that area. They will say "maintain X till established" which in short means until you're using whatever nav aid for the approach you're on, keep that altitude 

 

In your case, (direct MQP, maintain 3000, cleared for the ils), you would fly direct to the VOR at 3000. You would remain within 10NM of the VOR as you do the procedure turn. Once inbound you're able to descend to 2500 where you would capture the GS and follow it in. 

 

Using a AP i would have it in nav and alt mode as you go to the vor. As you turn outbound for the turn start to bug up 2500, and either turn the AP into heading mode and manually adjust the turns, or disconnect the AP and fly the turn. As you turn inbound and have the LOC captured descend down to 2500, at which point arm the approach for the AP. There should be no problem from that point for the AP to follow the LOC and GS down to the minimums. You should not arm the approach until you are inbound to the FAF. 

 

or as Mooniac says just stay at 3 and follow the GS from there, just verify you're at 2500 at CUTIS to ensure you're on the proper GS. v

[PT20J]

I believe @201Steve is correct. However, as a practical matter, I would just exit the procedure turn at 3000' in ALT with APR armed and capture the GS at 3000' since the 2500' is a minimum altitude. Less fumbling around. 

If you happen to have a GTN Xi, you could bug 2500' on your way to Millsap and put the GFC 500 in VNAV and let it do the driving.

Skip

Edit: I see some of you type faster than me and already suggested maintaining 3000 until intercept 

[rbp]

a few people said that you can descend once you're inbound

a strong crosswind can blow you off course in the procedure turn sufficiently so that by the time you're turned in bound the CDI is pegged

the nit-picker in me says: you have to be ESTABLISHED inbound, which means the needle is on the correct course and the CDI is off the peg

 

[PT20J]

22 minutes ago, rbp said:

a few people said that you can descend once you're inbound

a strong crosswind can blow you off course in the procedure turn sufficiently so that by the time you're turned in bound the CDI is pegged

the nit-picker in me says: you have to be ESTABLISHED inbound, which means the needle is on the correct course and the CDI is off the peg

 

Agree. I you are not established, and you descend, you will bust your checkride! Of course, people debate the meaning of the term "established" endlessly. But I think we know what it means: You know where you are and you are navigating to where you want to go. Needle centered: certainly. Needle pegged, certainly not. Needle somewhere in between: probably, if you are intercepting and the needle is converging; probably not if it is behaving like a windshield wiper.

[Ragsf15e]

I’ll chime in here, but this is from a gfc700 and g1000 (both cirrus and Piper).  Usually Garmin has them work the same as gfc500 but not always…

If you select APR on the autopilot prior to the iaf as you said, you’ll check the white standby autopilot mode for GS in the vertical guidance and LOC in lateral.  The green active guidance will remain ALT (3000’) and GPS.  The autopilot will fly the procedure turn and then exit the hold inbound still in the same modes.  It will switch to LOC before the faf but after it passes a bunch of internal validity testing (maybe @PT20J can expound on the switch to LOC?).  It will switch to GS at the glideslope intercept at 3000’.  Since it never descended to the FAF altitude, this will be before the faf.  It will not switch to GS mode and descend if it’s not already tracking the inbound course (ie if you’re not established).

Many people will select APR on the autopilot prior to the iaf and let all this magic happen.  That’s good in 99% of cases, but just be aware that there are a few approaches in busy airspace that have mandatory altitudes or maximum altitudes between the iaf and the faf.  Since the autopilot is in Altitude hold until GS intercept, it will still be at the iaf altitude and may be too high. These approaches are relatively rare and most of the intermediate fixes are at/above, so holding the iaf altitude to gs intercept typically is fine.

If you want more control over the approach, use a descent mode after exiting the hold to get down to the faf altitude, then double check the white GS is still in standby for your vertical mode.  It will engage at the GS intercept point which is usually right at the FAF.

[Ragsf15e]

22 hours ago, PT20J said:

Agree. I you are not established, and you descend, you will bust your checkride! Of course, people debate the meaning of the term "established" endlessly. But I think we know what it means: You know where you are and you are navigating to where you want to go. Needle centered: certainly. Needle pegged, certainly not. Needle somewhere in between: probably, if you are intercepting and the needle is converging; probably not if it is behaving like a windshield wiper.

The FAA left that pretty grey for us, but your definition seems reasonable.  The USAF defined it a little more thoroughly for us… on a LOC or TERM (gps) CDI, “off the wall and intercepting” (so just inside full deflection) counted as established.  On a VOR or Tacan, the CDI had to be half deflection or less.  I don’t advocate for these, but I guess it’s something to use as a guide.

[PT20J]

1 hour ago, Ragsf15e said:

I’ll chime in here, but this is from a gfc700 and g1000 (both cirrus and Piper).  Usually Garmin has them work the same as gfc500 but not always…

If you activate the approach prior to the iaf as you said, you’ll check the white standby autopilot mode for GS in the vertical guidance and LOC in lateral.  The green activate guidance will remain ALT (3000’) and GPS.  The autopilot will fly the procedure turn and then exit the hold inbound still in the same modes.  It will switch to LOC before the faf but after it passes a bunch of internal validity testing (maybe @PT20J can expound on the switch to LOC?).  It will switch to GS at the glideslope intercept at 3000’.  Since it never descended to the FAF altitude, this will be before the faf.  It will not switch to GS mode and descend if it’s not already tracking the inbound course (ie if you’re not established).

Many people will activate the approach prior to the iaf and let all this magic happen.  That’s good in 99% of cases, but just be aware that there are a few approaches in busy airspace that have mandatory altitudes or maximum altitudes between the iaf and the faf.  Since the autopilot is in Altitude hold until GS intercept, it will still be at the iaf altitude and may be too high. These approaches are relatively rare and most of the intermediate fixes are at/above, so holding the iaf altitude to gs intercept typically is fine.

If you want more control over the approach, use a descent mode after exiting the hold to get down to the faf altitude, then double check the white GS is still in standby for your vertical mode.  It will engage at the GS intercept point which is usually right at the FAF.

The Garmin documentation is a bit vague on the switching to localizer other than to say that the localizer signal has to be valid, the GPS position has to be valid and the CDI deflection a half scale or less.

[Ragsf15e]

One clarification from what I posted above.  It’s pretty easy to get confused between “Activating the Approach” on the gps and “Selecting approach mode” on the autopilot.  They are two different things.  Both need done at some point.  Mostly.  If you steer direct to the IAF, the gps will activate the approach for you.  If you’re steering to a different point and are cleared to the IAF, you can activate the approach on the gps and it will select the iaf you entered with the approach.  In either case, you still need to select approach mode on the AP to see GS and LOC.  or GP on an LPV approach.

If you load vectors to final, you will need to activate the approach (gps) and select the APR mode (AP).

As a technique for vectors to final, when you contact approach control, you’re typically steering to a gps point.  They will generally give you a vector at some point.  When they do, that’s when you activate the approach on the GPS.  It will sequence to the Iaf or faf and give you some awareness about your position.  You will not activate approach mode on the AP until dogleg to final when they say cleared for the approach.  That’s your cue to hit APR button on the GPS.

If they instead say “maintain xxx’, track the localizer inbound”, do not hit APR as this will select GS and Loc which allows the AP to descend at the glide slope.  Instead hit NAV which will select Loc in lateral guidance since you already activated the approach on the gps and have a loc freq and green cdi.  It will leave the vertical selection in Alt hold.  When the eventually clear you for the approach, hit APR on the GPS and see GS pop up in the vertical guidance.

[Greg Ellis]

1 hour ago, Ragsf15e said:

If you want more control over the approach, use a descent mode after exiting the hold to get down to the faf altitude, then double check the white GS is still in standby for your vertical mode.  It will engage at the GS intercept point which is usually right at the FAF.

Thank you for your response.  This is what I was looking for.