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When he got his King Air to my shop, I duplicated the discrepancy on the ground run.
First, I calibrated the temp system and it was fine. Next I ohmed-out the temp stick and sure enough, it was open. When I checked the data plate, I happened to check both sides and found they both had the same ohm reading. Rarely do both engines have the same class temp stick, but it gave me the unique opportunity to illustrate the problem to the pilot. I put the bad temp stick on the other engine and the problem went to that side. Then I reinstalled the good stick where it was originally. We ordered a new one for the problem side, and everything was fine once the new temp stick was installed.
Typically, swapping temp sticks from side to side is a bad idea because the temp sticks do not match from engine to engine. Swapping temp sticks can really make a mess of things. I once unraveled an engine temp problem complicated by earlier troubleshooting where they swapped the temp sticks. This created problems with both engines.
I tested both sticks with an ohm meter. One was good and the other was bad (open). The class on the good stick married up with the left engine data plate so that’s where we put it. The class on the bad stick was not the correct class for the right engine! That told me they had engine temp problems even before the stick went bad on the right side. The wrong stick throws off the engine temp reading. When the correct class temp stick was installed on the right side, all their engine temp problems finally went away.
On the ground versus in the air
Remember the King Air 200 with two bad sticks? Years later, I found another trim stick squawk on that very same King Air, which I discovered completely by chance. They had a problem with the cabin door. It had developed a leak that wasn’t resolving and was bothersome to the passengers. When a short trip cropped
DECEMBER 2024
Here’s a look at the other end of the temp stick, where it’s wired into the T5 harness. The way a PT6 sits on a King Air, this T5 harness is forward of the ambient air inlet and the temp stick extends aft to the engine inlet.
up, I went along to troubleshoot the door in the air. I figured out the door seal problem right away, but I was surprised to see the left engine was running hotter than it should. I’d been maintaining this King Air for over 12 years – I knew it inside and out – and I had never seen this in any ground running.
I asked the pilot about it. He didn’t seem too concerned. He chalked it up to age and time past overhaul. By this time, both engines had been on the M.O.R.E. program for several thousand hours. In spite of the pilot’s blasé attitude, I couldn’t let it go.
To complicate things, this pilot was not into trend monitoring, so there was no history of engine parameters to look at. I asked him to perform a number of tests during his next few flights and report back to me. Although he didn’t really do what I asked, I managed to eke enough information out of him to indicate we might be looking at another temp stick problem – but this time it was one that didn’t show up on ground running.
The next time that aircraft was in my hangar, I did an ice test on the L/H temp stick to fool it into thinking it was at altitude. The stick opened right up! So, I checked the data plate, ordered the corresponding class of temp stick, installed it on the left engine and suddenly the L/H engine temp was back in line.
It’s something for your technician to think about when everything points to a bad temp stick but the ohm meter doesn’t agree. Rub an ice cube along the stick for a bit and see what happens.
Moral of the story
If an engine is running hot, why split the engine and jump into hot section sticker shock if it’s just a faulty temp stick? And the other moral of this story? Trend monitoring, trend monitoring, trend monitoring. Make that your new mantra. If you are regularly recording your engine parameters and the only change is a spike in temperature, chances are a new temp stick is all you need.
As always, fly safely. KA
Dean Benedict is a certified A&P, AI with 50 years of experience in King Air maintenance. He was an inaugural inductee to the King Air Hall of Fame. He owned and ran Honest Air Inc., a Beechcraft maintenance boutique with a strong following of King Airs, for 15 years. Currently, with BeechMedic LLC, Dean and his wife, Lisa, consult with owners, pilots and mechanics on King Air maintenance issues, troubleshooting and pre-buys. Dean performs expert witness work on request. He can be reached at 702-524-4378 or via email at dr.dean@beechmedic.com.
KING AIR MAGAZINE • 23