A/P Approach mode

[flyboy0681]

Very interesting explanation. Who would think that if you were doing everything so right, that you could get it so wrong? You are approaching the FAF, nicely intercepting the GS, you have everything setup so nicely when suddenly - you blew it.

It appears that what others have said here apparently is true, look to push the APR button at least 30 seconds out, if not more.

All this begs the question. Say you flew through the FAF, is there a way to salvage things so that the GS would engage, and if so, what are the tolerances?

[moosebreath]

Well, this is just my take ... but I have never had any luck messing with the AP inside the FAF.  It is time for the big red button and hand flying the approach or a miss and try again.

[moosebreath]

The manual does state that the altitude hold mode is automatically disengaged when the glideslope is captured in approach mode.  This is indeed how my KFC 150 acts.

It is a simple enough thing to test in a given airplane.  

[carusoam]

It seems that the simple computer doesn't technically know where the FAF is...

Approach mode seems to be only an adjustment to the tightness of the algorithm that is controlling the plane. Tight, quick, noticeable, control inputs.

It seems that glide slope intercept occurs on an exact line.

It also seems that the exact line is hard to see on any analog instrument in our cockpits.

the thickness of the line is often used in reference to attitude control inputs.

 

What would be an adequate indication that you have crossed (given the AP opportunity to intercept) the glide slope?

Measured in 1/2 dots and full dots,  a half dot low should be a reliable indication that the intercept isn't happening?

How well does your plane do during an ordinary intercept does it oscillate more than a dot?  (Speed and weather dependent, I'm sure).

PP thoughts only, nothing else...

Best regards,

-a-

Edited February 19, 2017 by carusoam

[flyboy0681]

As an epilogue to this, it turned out that when my A&P re-installed the head unit, he didn't connect the static line. The only way we found this out was during our biannual altitude reporting inspection last week. The inspector noticed the line was not connected and took care of it for us. Yesterday I took her up and the glideslope worked like a charm.

Question: When the static line was disconnected, the KAP 150 still held perfect altitude. What input does it use for that? I would have thought the static line would have played a role in that function as well.

[carusoam]

Expect if the static line is not connected.  The static pressure the KAP gets in the cabin is slightly lower than what is in the static line...

When using the KAP to hold altitude. Push the button and it holds altitude based on the pressure being read in the cockpit, as it would using the alt-static system.

The important thing to know... on a usual flight, the change from using static to using alt-static will make a difference.

The static and alt-static will work pretty well. But the alt static system isn't calibrated for airspeed and altitude precision.

See where I'm going?

PP thoughts only, not a CFI...

Best regards,

-a-

[Piloto]

On ‎2‎/‎16‎/‎2017 at 8:16 PM, flyboy0681 said:

Looking at the manual, it appears that it only captures the GS from above or below, but not at - which is where I was both times today.

Now for a stupid question: why? Why won't it capture it if I'm right on the glideslope when arming it?

 

 

By having a deviation offset it assures that a GS signal is received. When there is no GS signal the deviation voltage is zero. So zero deviation could mean centered on the GS or no GS signal. With no GS deviation the A/P assumes you are flying a LOC only approach with no GS.

José

Edited March 14, 2017 by Piloto

[jaylw314]

If the KAP 150 is like the KFC 150, there is an air pressure transducer in the autopilot computer.  IIRC, it is NOT attached to the static system, it is simply open to the cabin air pressure.  You can test this by opening and closing the alternate static source--this should not affect altitude hold mode at all.

On the other hand, if you have the altitude preselector unit, that part IS attached the static system, so selecting alternate static while in climb or descent mode will lead to a VERY exciting ride.  Ask me how I know... 

[flyboy0681]

10 hours ago, jaylw314 said:

If the KAP 150 is like the KFC 150, there is an air pressure transducer in the autopilot computer.  IIRC, it is NOT attached to the static system, it is simply open to the cabin air pressure.  You can test this by opening and closing the alternate static source--this should not affect altitude hold mode at all.

On the other hand, if you have the altitude preselector unit, that part IS attached the static system, so selecting alternate static while in climb or descent mode will lead to a VERY exciting ride.  Ask me how I know... 

You hit the nail on the head. While flying somewhere last year I was bored to death and decided to pull the alternate source while the A/P was engaged just to see what would happen. The "bump" that resulted scared the daylights out of my wife, not to mention myself. 

Some things you only need to learn once.

[carusoam]

That's a good reminder on why to drain the static system...

Best regards,

-a-

[peevee]

54 minutes ago, flyboy0681 said:

You hit the nail on the head. While flying somewhere last year I was bored to death and decided to pull the alternate source while the A/P was engaged just to see what would happen. The "bump" that resulted scared the daylights out of my wife, not to mention myself. 

Some things you only need to learn once.

I also have done that.

[Jerry 5TJ]

 

On 2/16/2017 at 11:20 PM, thinwing said:

This sounds like a config prob between the gtn 750 and kap150.Both kap 150 and 225 have no way to tell if Rnav Lpv appr is ..... 

It is the 140 and 225 which exhibit the NAV versus APR issue you described.  

The 150 and 200 are older units They don't need the message flag from GPS navigator saying "Enable AP Outputs" like the 140 and 225 must use.    

Garmin 750 manual:

 

 

 

Edited March 15, 2017 by Jerry 5TJ