por930

5.5 Degree ILS Glide Slope

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One of my favorite airports is EGLC with a 5.5 degree approach. When using the GTN 750, it seems to have a mandated 3 degree operation, making the approaches with the GTN 750 unworkable. Is there a way of changing the Glide Slope degrees on the GTN 750? 

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I just tried that Lctr ILS DME 9 approach with the latest Garmin GTN 750/G600 trainer... it worked fine for me. The glideslope is the glideslope. The 750 can't change the glideslope signal any more than it can change a VOR or LOC signal.

I wonder if its the scenery/navdata you are using?

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7 hours ago, por930 said:

One of my favorite airports is EGLC with a 5.5 degree approach. When using the GTN 750, it seems to have a mandated 3 degree operation, making the approaches with the GTN 750 unworkable. Is there a way of changing the Glide Slope degrees on the GTN 750? 

What type of approach were you trying - the ILS? If you were, the GTN is only the radio receiver for the ILS - it has nothing to do with the glide slope other than that.

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This is a good question David.

I was wondering when this question would come up in fact, as we've been working on the upcoming update and I've ask myself if this would indeed be supported.

Have you tried the same approach with the trainer standalone?

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Hi guys, thanks for the replies.

This is my first flight with the GTN 750 and using light metal like the Carenado P3Dv4 PC12. My usual choice for the last several years has been the PMDG 737/777, or FSL A320 with the lightest being the Majestic Q400. With the FMC style aircraft, you insert the flight plan, the STAR, and set up the approach runway and ILS frequencies. Approach the glideslope from underneath. Intercept the LOC, when locked, you approach the ILS glideslope, noticing the glideslope active, when captured, upon which the aircraft travels down the glide slope to the threshold if you left it. The aircraft is sort of 'captured' in the glide slope unless you disconnect the autopilot.

I notice with the GTN 750, once you have set up the flight plan/SID, and upon takeoff, ensure the altitude target is set, fire up the Autopilot, select nav, making sure the GTN indicates GPS, and the GTN750  follows the flight plan very well. During the flight I insert the Arrival and approach, making sure the arrival ILS runway is set. When finished with the GPS route, and close to the FAF, I change frequency to the ILS, select approach on the PC12. I notice the GTN automatically changes from GPS to VLOCK. The a/c steadily lines up with the LOC, and approaches the glide slope. I see the glide slope become active. With a 3 degree slope, I see the a/c travel through the glide slope centre marker, then recover it ( is there a capture moment??) and we slide down the slope as what you would expect. The 5.5 EGLC slope gets busted very quickly and the aircraft simply descends very much higher than the glide slope of course.

Now, as I said, this is my first approach ever with the GTN 750, so I simply need to get used to it and its methods. (AND maybe my technique is wrong??) I have the GTN750 installed in my yet to be flown Phenom 300, and also the yet to be flown FSW Falcon 50. The FSW Learjet 35A and the 441 conquest have also been fitted with the GTN750, and also need a few flights...So, I have quite a learning curve for these a/c sorted as well as their interaction with the GTN. 

"Have you tried the same approach with the trainer standalone"? ummm, I do not understand this statement I have seen that little triangle on the screen bring up the 'trainer', though, have no idea what it is for!

I was using the ILS approach...I think I was. Could some one provide a concise ILS approach with the GTN 750 for me...eg, step 1,2,3 etc any airport will do and I will use this method to see what I am/was doing different. Jean-Luc, The insertion of the GTN flight plan is sooooo easy as well as the arrival and approach. I still need to work out how to get the direct to working...first things first..  

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As far as I know, the GTN is out of the picture as soon as you switch to VLOC mode.

The NAV radios are steering the autopilot at this point, and if the autopilot cannot keep you on the ILS glideslope, you may have to rethink your approach speed..

There is nothing in the GTN that controls the autopilot at this moment..

LPV approaches are different.. here the GTN (in GPS mode) steers the autopilot.

Edited by Bert Pieke
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42 minutes ago, por930 said:

The 5.5 EGLC slope gets busted very quickly and the aircraft simply descends very much higher than the glide slope of course. 

A 5.5 deg G/S is pretty steep. I doubt an "average" autopilot could manage that. I've never encountered such an ILS in real life, and I don't know what (if any) mods are done to real aircraft to be able to handle these ILS's. Maybe it's just too steep for the autopilot and it needs to be flown by hand.

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Bert is right. The only way you can change the glide slope angle is to open the AFCAD and change it there. Most are set at 3 - 3.5 deg. by default.

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On the ILS approach charts for EGLC, there is a comment at the top of the approach diagram that says:

"ONLY FOR ACFT CERTIFIED TO CARRY OUT APPROACHES AT 5.5 DEG."

I suspect not many, and possibly NO aircraft with a GTN would be certified to fly a 5.5 deg. GS. Probably has something to do with both aircraft performance, and navigation equipment capability.

Kind Regards,

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@Bert Pieke Hi, Agree, I need to use the GTN750 on different approaches and learn its various ways. It was unfair of me expecting it to take on EGLC, especially with my limited GTN750 knowledge, coupled with its undoubted abilities.

@DavidP Correct, While some aircraft do have the mods for steep approaches( eg A318 for BA KJFK-EGLC) the actual approach and ILS at EGLC is initially autopilot, but soon taken over by the captain in the corporate world. The CS100, E170, E190 along with some DH4 seem the main users.

@Scorp no thoughts at all about modifying the GTN performance for one or two airports.

@somiller Other than the corporates, a fair percentage of users are the biz jets guys, I guess with the appropriate, "ONLY FOR ACFT CERTIFIED TO CARRY OUT APPROACHES AT 5.5 DEG." Maybe most if not all Biz Jets use "better" avionics than the GTN750??. 

Edited by RXP
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@por930 Hi, you might want to also use the '@' prefix on the forum so that member names gets cross-referenced and the ones subscribing gets notifications as well (very handy)!

PS: I've edited your message accordingly.

Edited by RXP

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13 minutes ago, RXP said:

@por930 Hi, you might want to also use the '@' prefix on the forum so that member names gets cross-referenced and the ones subscribing gets notifications as well (very handy)!

PS: I've edited your message accordingly.

Thanks Jean-luc...I wondered how to let the guys know without creating a reply each. I will know in the future.😊 

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