Page 21 - Dec 2022

that temp sensor. We ohm’d it out and it checked perfectly, but when we applied heat, the CD circuit was out of whack. What were the chances of two bad temp sensors? That wasn’t what we hoped for.
This little sensor lists around $6,100 (that’s correct – six-thou- sand, one hundred dollars for a ther- mostat). He ordered it and got it the next day. We put the thermostat through its paces and it passed all tests with flying colors. Even when heat was applied, it met all the pre- scribed parameters. We installed it along with new heat ducts and a new tail deice line. To date, the new ducts and deice line appear to be holding up. He uses his borescope to check periodically. The jury is still out, though. He needs to fly more and keep monitoring it.
The big question is: What happens when the CD circuit goes high on resistance after 300°F is applied? The Maintenance Manual does not elaborate.
Tail Deice
My overriding concern is the deice line going to the tail. The only way to verify if the tail boots are working is to test them during a ground run and have someone stand outside to watch them inflate. If air is not getting to the tail boots, the gauge for deice boot pressure will still be reading the proper pressure. The pressure gauge cannot differentiate if the line going to the tail boots is blocked.
As we go forward, my client is monitoring his situation and if he finds anything I will let everyone know. Further, I would love to hear if anyone out there has seen melted heat ducts below the floorboards on any model of King Air. Please forward any and all details to me by phone or email. I’m very keen to know if this “mystery melt” is something we all should be digging into or if it’s an oddball occurrence. KA
After the repair was completed: The ducting (right) is wrapped with insula- tion and the new deice line (left) is a different color but has the same “deice” tags – one above the rib and one below it.
Dean Benedict is a certified A&P, AI with
over 45 years of maintaining King Airs. He’s the founder and former owner of Honest Air Inc., a maintenance shop that specialized
in Beech aircraft with an emphasis on King Airs. Currently, with BeechMedic LLC, Dean consults with King Air owners, operators and maintenance shops on all things pertaining
to King Air maintenance. This includes troubleshooting, pre-buys and maintenance management. He can be reached at dr.dean@ beechmedic.com or (702) 524-4378.
DECEMBER 2022
KING AIR MAGAZINE • 19