Just noticed the last image shows the left transponder. Trust me  it was the same for the right.....

ATC transponder unit with self test lights not working when button pushed.
  
     
  
I suspected a air/ground sensing issue which seems to be the norm for numerous systems on the aircraft (boxes that shouldn't be tested while in the air).

On the 767 (at least this -300 aircraft) two air/ground relays provide the control panel and transponder an electrical ground signal when the aircraft is in a "weight on wheels"  (on terra firma) condition.

Relay "K143" for the left system. "K200" for the right. My problem was right, but the print below shows the left.
  
     
  
Bad relay "K200" which kept the right panel/transponder in the air mode.
  
     
  
After replacing relay.....
  
     
 

767-200 with 80A engines.

"Bleed Off" light on during flight. Bleed air test box  showed "Fan Air Valve Temp Sensor" fault.

Compared left and right engines.....
  
     
  
Sensor located behind "D" panel in pylon, just below PRSOV.
  
     
     
  
Removed.....
  
     
  
Replacement with resistance measurement.
  
     
     
  
What seems to be missing on removed unit?
  
     
  
The whole temp probe is gone. Sheared right off at the base. Where did it end up?

We looked down with a borescope. It wasn't laying on heat exchanger. It must of been blown up and down-stream..... possibly setting on primary heat exchanger in left pack bay????

Well.....

Here's the compass card from an aircraft coming into our fleet.
  
     
  
A tad out of date???

I haven't had a moment to look at my company's GMM to see if there are specific requirements for standby compass indicators.

As far as the newer liquid crystal compass (incorporated with standby attitude/air data), it receives initial heading from the IRS's. It will only use its own internal circuitry if IRS info is lost.

Wet compass's (to me) should be verified once a year, because they are stand alone mechanical units.

Every once in a while..... thay do leak. What is the liquid???? Varsol.

Why do wet compass need calibration annually?

My best guess is that these come as a pre-built assembly and they should not have individual parts replaced on the line.

The IPC only shows one installed, so we're not talking two units that must be matched by part number.

Without verification..... I believe the old style "Wet Compass" needs calibration once a year. This is not to say it must come off the aircraft and go to shop, but rather taking the aircraft out to a compass rose (which hardly any airports have any more) and checking the compass on 30 degree radials.

With a digital standby compass, I would say spinning the aircraft is not needed.

It really is a joke though..... if you're down to just the standby compass for navigation, your problems are much larger than just what heading you're on.

Each airline should state requirements needed in their GMM or General Maintenance Manual.

Should air carriers conduct compass swing at regular intervals?

No answer yet, but here's your images.....