My heater is a Kelly Aerospace Factory Rebuilt unit that was installed in the aircraft in November 2009. Currently it has 274hrs on the heater hobbs. From it's external appearance it looks "like new" to me.
Due to my landing gear refub project we removed the heater from the nose. This is required to get the nose gear out since the RH NLG trunnion bolt cannot be removed with the heater in place. While I was at it I had the metal straps that hold the heater to the airframe cad plated with other parts of the gear... but I digress...
The other day I took the heater home to weld a nut / fitting that had come loose (one of four that hold the heater to the air control box) which we did (my brother has a nice shop with welding equipment and did this for me). Anyway in the process I noticed the heat shield / shroud around the heater exhaust pipe was loose. To resecure it properly I loosened the band clamp and removed the shroud. What I discovered to my dismay was that there were cracks in the exhaust pipe itself!
Here is a picture of the heater with the shroud in place around the heater exhaust pipe..
As you can see here, once the shroud is removed the exhaust pipe itself is visible...
Here is a close up of the cracks in the exhaust pipe...
The cracks are at the radius bend of the exhaust pipe which make sense - as the heat is pushed out the exhaust the exhaust is forced to turn as it goes through the radius bend. As a result the pipe area on the outside of that radius turn will take a greater portion of the exhaust heat than will other parts of the exhaust pipe.
Here for reference is Figure 19 from the IPC. The exhaust pipe is #5 on the diagram which depending on your model of PA-30/39 will be one of three possible part numbers depending on your aircraft serial number. In my case it's P/N 30670-02. This part is held on by a simple clamp which is #3 in the diagram.
I've ordered a new exhaust pipe P/N 30670-02 from Phillip at Webco and it's on it's way. Phillip told me that what I've found is "common". This surprised me since the heater does not hit it's first AD for internal inspection until 500hrs. During a number of pre and post flight inspections I have often looked up in the heater exhaust tube with a flashlight and small mirror. I've never seen or detected any cracks. In retrospect I wonder if I might have if I had been using something like a Dental Pick to "feel" for cracks or weak metal. Otherwise I don't know how I would have easily found this without taking the heater out and removing the shroud.
My heater is a B2500 with the "B" core. The January 2014 issue of Twin & Turbine Magazine had a good article by Dale Smith on these heaters. They interviewed Harold Haskins (owner of Harold Haskins, Inc.) for the article. The article of course stressed the importance of inspections and maintenance. The Article quoted an anonymous source and said; "Cabin heaters are like toilets. You only think of them when they don't work". Harold Haskins said; "Pilots don't give a flip about the heater until they need it and nothing happens." In my case the heater worked fine I just had NO idea the exhaust pipe was cracked and really didn't expect that at this age / condition.
The Twin & Turbine article also went on to say that owners of B series heaters can replace the core with a new I-Series Core to get rid of the repetitive AD- 2004-21-05 inspection that starts after 500hrs heater time. I called Haskins and this upgrade costs a bit over $1K. My plan is to do that upgrade once I hit, or get close to, the the magic 500hr point. However that upgrade has nothing to do with the exhaust pipe.
It makes sense that the exhaust pipe would wear faster than the rest of the heater I suppose but I would have thought the core would be subject to the same heat and the first AD inspection of that is 500hrs. Given the radius bend in the exhaust and the added heat on the metal in that turn I am going to start inspecting more frequently and more carefully. Hopefully I'll be good for a while with a new exhaust in place. By the way that exhaust pipe was $145 plus shipping from Webco. They do not carry the clamp - that has to come from elsewhere.
- Charles
