Jump to content
Aero Precision provides OEM part support for military aircraft operators across more than 20 aircraft

APN-59 Radar Problem


prior22usaf
 Share

Recommended Posts

I have some suggestion, but you\'ll still have to duplicate it on the ground to fix it.

One of the things you need to ascertain is if the antenna quits turning, or if it is just the display not moving. If the antenna is turning, the sweep trace will flash brighter when the heading marker switch hits. They can chech that while they are flying.

If the antenna is rotating, then they need to check it on the Nav and pilot displays, in REL and STAB modes.

Are you at the \'Rock?

I\'ll send you something that may help if it is an indication problem. I\'ll also send some other diagrams I have done up for the system to aid in other problems.

Link to comment
Share on other sites

Had on incident where the nose radome had a delamination (soft spot).

In flight, the aerodynamic force would push the soft spot in, and the radar antenna feedhorn would rub on it, but only when the tilt, pitch, and roll were at the right angles to cause the antenna to scan that specific spot.

This would not show up on the ground.

Link to comment
Share on other sites

Thanks guys for the responses. I actually just made up a questionnaire to give to the Nav so we can get some more insight on when the problem happens, whether or not the heading flash still occurs to see if the antenna itself is actually not rotating and what position the bearing switch is in(Stab or Relative). Our crews usually don’t fly with the Pilot Radar scope in (they fly with the SKE scope installed), but we are trying to get them to fly with it installed to help us troubleshoot.

Any further ideas of what to try or what to look for would be greatly appreciated. Thanks-Dennis

Link to comment
Share on other sites

  • 3 weeks later...

Oh if it were that easy TOPS. The heading reference comes from the compass and goes thru the ECA, antenna J-Box, antenna, RADAR J-box, Control panel for the Nav\'s, power supply, then the scope. Any one of the X,Y or Z wires opening alond the way will cause the sweep to freeze. [img size=1383]http://herkybirds.com/images/fbfiles/images/radar_hdg_reference_loop.JPG

Link to comment
Share on other sites

EClark wrote:

Tiny you are a very smart man what is your afsc I was a afsc 43151f

Not that smart, just been doing it for 34 years. I was a 32871 when I got out. That was Airborne Navigation System Repairman. I don\'t know what that AFSC is now. I\'ve been a civilian for many years. I have my info in my profile.

APN59 was MY bench at my first base. They usually chained a big guy to that mock-up so moving the antenna and R/T was no problem.

Link to comment
Share on other sites

\"What Has been done Already:

The antenna, ECA, Gyro, Control box, Synchronizer, and the scope has been changed as well as the N-1 compass slaving control and amplifier. Wiring has been checked with a multimeter and it has checked good.\"

As stated if the Pilots scope works the nav power supply is bad its the only non-common component [img size=1024]http://herkybirds.com/images/fbfiles/images/Copy_of_radar_hdg_reference_loop.jpg

Only other question is can you see returns (variations in the trace) in the frozen trace or just a bright HDG MRK flash each revolution?

Link to comment
Share on other sites

We still have yet to be able to duplicate the problem on the ground. Heck, the problem doesn\'t even occur every flight. It has now flown 4 times in a row with no problems..... I wish I could give you a vivid picture of what is happening, getting a good debrief from the flight crew isn\'t exactly the easiest thing in the world to do. We have started handing the NAV a detailed questionare to describe the problem with troubleshooting procedures. I\'ll keep you posted if I learn more from them....

Link to comment
Share on other sites

Sorry natops, but it has to be a wiring problem on the Nav display side. I\'m sure they swapped the power supply, they just didn\'t say. You are correct that it is the only non-common component, but for the most part, if an APN59 component is bad, it stays bad 100% of the time. Pretty much over the years, I\'ve found that bad wire connections are responsible for a very large majority of intermittent problems like this.

In the diagram, you\'ve highlighted only one synchro input. We don\'t know if the pilot\'s works in STAB or REL, or at all. They can\'t seem to get the aircrew to help, and we can\'t here at Moody either. Hell, it\'s a miracle if they do a requested in-flight op check the first or second flight.

The only thing I can suggest is taking apart all the connectors where the wires run. Only problem with that is that you are screwing around with wires that were soldered 40 some odd years ago, and the possibility of breaking more is great.

Seeing the returns will tell you the antenna is rotating as well. But, the HDG MKR flash is controlled by a microswitch on a huge cam. If it flashes, the antenna has to be rotating.

Link to comment
Share on other sites

  • 1 month later...

It appears the problem may be fixed. The guys at the Rock found a loose ground lug coming off of Pin A on the small plug on the N-1 compass ME-1 amp. Without the ground, the 26 VAC that comes from the ECA (shown in the side left of the previous diagram) that feeds pin B of that same connector on the ME-1 amp, won\'t supply voltage across the synchro to send a compass signal to the RADAR. Hoo-rah to thorough technicians.

Link to comment
Share on other sites

  • 1 year later...
  • 11 years later...

I well remember my days up in the nose wheel well of C-130s on the frozen, wind blown flight line at Elmendorf replacing APN-59 RTs and antennae alone, freezing to death and breaking my back without any help. That system was at least half our workload there which included ALL avionics systems, as we were severely undermanned and expected to fix it ALL right after we transitioned from AAC to MAC. As they told me right after I got there from Moody AFB in December 1979, “You’re no longer a comm/nav troop. You’re an avionics troop”.

  • Thanks 1
Link to comment
Share on other sites

  • 1 month later...
On 6/21/2021 at 2:10 AM, Bigfoot said:

I well remember my days up in the nose wheel well of C-130s on the frozen, wind blown flight line at Elmendorf replacing APN-59 RTs and antennae alone, freezing to death and breaking my back without any help. That system was at least half our workload there which included ALL avionics systems, as we were severely undermanned and expected to fix it ALL right after we transitioned from AAC to MAC. As they told me right after I got there from Moody AFB in December 1979, “You’re no longer a comm/nav troop. You’re an avionics troop”.

Been there, done that way too many times. 

 

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...