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C-130H2.5 FD109 Floating command bar Altitude hold issue


Steven
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Currently having an issue on a 92 model 2.5 that I haven’t been able to crack. When engaging altitude hold on either side, the horizontal command bars float around 5 degrees up.  No LRU swap/r2 has fixed the issue and after shooting wires between ADC’s, flight computers, mode selectors, mode couplers, and yaw damper everything checks as advertised. Also have tried SCNS relays. It does it in all flight director modes.  If anyone has come across this problem I would love some help. The issue has been on and off for the last 5 months. 
 

thanks everyone 

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Let me get this right, so I might be of help. The command bars on the ADI start floating around only if the A/P Alt Hold is engaged? Otherwise, they work as they should?

Can I get the tail number?

Tiny

Edited by tinyclark
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Hi there,

Yes, the command bars start floating when Altitude hold is engaged. It happens on both sides (#1 and #2). I wouldn’t consider it an A/P issue, as it happens when FD109 Altitude hold is engaged, whether coupled to A/P or not. I should also mention there is a flashing computer flag when it occurs as well. 
 

Considering it happens on both sides when the systems are separated 1 and 2 it has me to believe it is a power issue somehow, it also does it in AC and DC. We checked all LRU’s that feed both sides of flight director and they all operate as advertised.

tail: 92-3024

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I am going to ask some stupid questions because I only worked E's, 74 H's, early gunships and MC-130E's. 

Does the altitide signal for the ALT Hold come from a Air Data Computer? Are there two? I reallyneed to know where the ALT info comes form going to the Flight Director.

The info in the GS-34 is marginal, and I couldn't find anything in the old H-2-13. All of my material is at least 22 years old as well.

After looking for info, I remembered how lousy the books really were.

What base are you at with this Herk?

Tiny

 

Edited by tinyclark
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  • 2 weeks later...

I am still looking at the books. Can't see power causing this since everything works unless the ALT Hold is set to ON.

 

A few more questions...

When this started 4-5 months ago, was any peculiar work done on the aircraft right before it started happening?

Were all boxes swapped between two aircraft or from supply?

Was the Acceleration sensor changed out? Doesn't that feed both systems? 

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  • 2 weeks later...

Hi sir, I am sorry I haven’t responded due to not knowing you responded. I have a happy conclusion to our issue.
 

The problem ended up being multiple LRUs failing at the same time. This is why no box swap or mock up change out helped us narrow it down.

We found that we had a bad Acceleration sensor, mode coupler, and mode selector. The acceleration sensor was causing the rising command bars AND a computer flag only on the pilots ADI (odd).  The #1 mode selector was also causing a intermittent computer flag. On top of all of that, the pilots mode selector Altitude hold would disengage intermittently causing vertical monitor signal errors. 
 

The herk is at Youngstown Air Reserve station. To answer your other questions because you took the time out of your day to write me, our swaps were including supply parts, aircraft parts, parts from other aircraft, and back shop mock ups. This particular plane has had FD109 demons for roughly 20 years (usually involving the #1 side of the system. The altitude hold information does come from the Air Data Controllers, and there is one for each side of flight director.  This issue started while I was with the plane in a deployed location early this year after the plane had AC bus issues. The 34GS is basically worthless. I used the WDs (formally known as the 13s) to finally figure this one out. It was especially difficult due to how many parts of flight director receive or input the vertical monitor, and vertical fail signals.

I appreciate you looking into TOs, and using all the right verbiage obviously showing you know your stuff. We were on the same track the whole time.

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Really glad you solved this one. I found out the aircraft was at Youngstown from my buddy, Joel. I think he may be your SCNS rep.

I really do wish I had more experience on the newer birds. I retired in 2011 before the J models arrived at Moody. 

Keep up the good work. I miss sinking my teeth into a good problem now and then.

Tiny

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