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MY STEC 55X Bats .500 On Glideslope Intercept


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57 minutes ago, TGreen said:

My Stec 55x reliably intercepts the localizer but, about half the time, fails to couple with the glideslope, leaving me to manage descent with VS. Anyone else have this issue?

I had an STEC 55X on a Piper Malibu and and STEC 550 on a Piper Meridian and experienced the same if I came in above the glideslope.

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Ditto.  Had an STec 55X on a Cirrus and it had the same behavior - it would only intercept if I was below the glideslope and it descended into the zone.  Typically, if coming in above the glideslope, I’d have to go down manually to intercept and then it would engage.

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The System 55x will not dive to intercept GS on its own. If you are above the GS push the ALT button to manually engage the GS. Be very careful this will make the airplane dive to the GS intercept.

There are other specific signal requirements needed to engage the autopilot on an approach, if any are missing the unit will not control the path on its own. 

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1 hour ago, Cruiser said:

The System 55x will not dive to intercept GS on its own. If you are above the GS push the ALT button to manually engage the GS. Be very careful this will make the airplane dive to the GS intercept.

There are other specific signal requirements needed to engage the autopilot on an approach, if any are missing the unit will not control the path on its own. 

Works like the 60-2 but I never had too much problem as long as not ridiculously above glide slope. Not as good on approaches overall as kfc 150. I have heard that the 55X is problematic in other areas too, such as porpoising in cruise, etc.

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Descending to catch a glide slope has some inherent danger associated with it...

So APs have their limitations...

The user manual will have a paragraph on what to expect regarding intercept angles and rates for both lateral and vertical intercepts...

Each AP is going to be different even from within the same manufacturer of several devices...

The FAA even plans for pilots to intercept the GS from under it, by flying into it while level... mostly...

PP thoughts only, not a CFI...

Best regards,

-a-

 

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When are you pressing the NAV/APR button before GS intercept?

To capture the GS requires the following:

#1 to be in ALT mode

#2 to have the precision approach flag from the NAV/COM/GPS

#3 that the GS not be flagged

#4 That you have pressed a NAV/APR button after #2 is available. 

the S55 will then indicate APR ALT GS... and as soon as the GS crosses center the ALT will go off. 

We had a discussion about this about a year and a half ago.  (G1000 & S55X)  especially after the WAAS upgrade and LPV GP tracking. 

https://mooneyspace.com/topic/24552-stec-55x-ils-capture/page/2/

the 55X will capture from above use ALT at less than 10% above, but be ready for it to dive hard for the GS.  

I suspect that you are not talking about capture from above.. but the issues we discuss in that other thread. 

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9 minutes ago, PaulM said:

I suspect that you are not talking about capture from above.. but the issues we discuss in that other thread. 

Thanks. Yeah, not talking about capture from above.

My AP often fails to capture the GS when intercepting from below. The manual says (essentially) that the aircraft needs to be below the GS and tracking the localizer for 10 seconds before GS intercept in order for automatic GS capture to occur. That's a long time.  At KSNA, I am vectored onto the localizer below but (I think)  too close to GS intercept for automatic GS capture to occur. Never tried to manually arm the GS when that happens. Instead, I have either disengaged the AP or managed descent with VS.

Will check out the earlier thread.

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Ok, with vectors you will be going from HDG to NAV/APR.. so the button is pushed.  I'm never vectored that close.   With a standard pre-FAF segment I have never had a problem with it coupling as long as the display says APR ALT GS.    All of the issues we documented were transitioning from GPSS to LOC/ LPV which I have been doing more of. 

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For programmer/computers with mod code AC/AC or higher, automatic GS arming will occur
after the following conditions have existed for 1 second:
APR Mode Engaged
ALT Mode Engaged
Navigation Flag Out of View
Glideslope Flag Out of View
Localizer Frequency Channeled
Aircraft within 50% of Localizer Centerline
Aircraft more than 10% Below Glideslope Centerline

It has always been a challenge to satisfy the needs of an autopilot during the approach phase when you are rushed.

I was commissioned to do a recertification flight in Mananas, VA. years ago. It was in a Lear 60, I had to  stand between the pilots to verify accuracy after a service bulletin. The approach had what seamed to be a 30° turn to the right pretty close to the airport, the pilots got a kick out my reaction to that last turn that close to the water.

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