Mike Rellihan has called our attention to a serious issue he has come across during his work on numerous member aircraft. The issue deals with corrosion caused by old CEET ducting. We feel this is an issue all BAC members should be aware of. BAC will make more information available as it is developed. Mike’s message follows:
(There is now a thread regarding this in the Discussion Forums.)
Subject: C23-C24 Duct Corrosion
A great deal of information has been posted on the BAC website (www.beechaeroclub.org), concerning replacement of the original CEET heat and ventilation ducts (with the far better SCEET ducting from Custom Ducts). Of special concern are the underfloor ducts found in the 1966 and later planes. The 1975 and 1976 4-seat models (C23 and B24R) are at extreme risk; they actually have TWO pairs of underfloor ducts. One pair rises just aft of the cabin door jamb, into the overhead, feeding the rear seat overhead Wemac vents. The pre-1970 Supers that have the aft child’s seat also have sidewall ducts, though they run up aft of the second window.
Most owners have purchased these planes while the planes still contained the original ducts. Pre-buy inspections typically have not included removal of the interior window trim and side panels, for corrosion and duct inspection. Subsequent Annual Inspections also typically do not include this level of disassembly (except Initial Inspections performed at 34A).
The corrosion goes undetected until interior refurbishment, window replacement, or duct replacement brings it to light. By then the required repairs can be very time-consuming and expensive.
We are advising our fellow members to take one or more of the following actions as soon as possible, to preserve your safety, minimize the scope of repair costs, and to protect your investment. The worst time to find this corrosion will be after a piece of structure fails. The second-worst will be during a pre-buy, underway by a prospective customer some day.
1. Immediately determine the status of your ductwork. 100% original?
Partially replaced? Fully replaced?
2. If still all original, IMMEDIATELY soak all of the ducts, for their entire lengths, with Corrosion X or ACF 50. Typical commercial applications are inadequate for this purpose. Some interior trim removal is required, and can be an owner-performed activity. Get help from a fellow member if you are not familiar with trim removal and reinstallation.
3. If you go through the trim removal process, get some personal training in corrosion detection, and carefully check all the areas occupied by the ducts. You must check brake and gear hydraulic lines for pitting and pin-holing, in addition to structure and skin panel corrosion.
4. It would probably be least expensive to continue with duct replacement while the trim is off. But if you must re-install the trim over old ducts, make certain that they have been well treated with the anti-corrosion spray. The most highly recommended replacement ducting is the high-quality
(lined) SCEET from Custom Ducts, having molded cuffs on each end. This is the all-silicone and stainless-steel red-orange duct. Unlike the black CEET duct with the piano wire, the SCEET will not hold moisture regardless of age. There are FAQs on BAC that can help you determine the needed duct pieces.
Even if you install the SCEET as recommended, be sure to lightly spray the duct routing areas with anti-corrosion spray. This will guard against any fretting corrosion should any SS wire become exposed. This is not nearly the risk that is posed by rusting piano wire, which often triggers galvanic corrosion leading to exfoliation corrosion, in adjacent aluminum structure.
5. Virtually all of the planes with original ducting will have some degree of corrosion in spots. These will have to be corrected and treated (corrosion removal, etching primer). Count your blessings (and bless your
hangar) if you get off this light.
6. If serious corrosion is discovered, you can contact fellow member Chad Moser for parts fabrication and repair assistance, if needed. Most related parts will be extremely hard to locate in the Beech parts system, will be very costly due to the rarity, and/or will have very long lead times.
Beech Aero Club
P.O. Box 899
Georgetown KY 40324
https://www.beechaeroclub.org/