QUESTION: Thanks for your great column. It is wonderful having a resource like yourself. My question is regarding an intercooled TIO-540-S1A installed in an Aerostar 601P. The right engine MAP has been rapidly increasing past the 29.5″” limit. This has happened on takeoff as well as in cruise. In each instance the power has been reduced then slowly increased and the engine then operates normally. The turbocontrollers were overhauled 200 hours ago (four years) and mouse milk has been applied to the wastegate. The MAP gauge has also been replaced. What are your thoughts as to the problem? Do these occurrences — approximately four times with MAP increasing up to 45″” — warrant a tear down and inspection? Thank you for your time and keep those columns coming.
Hot Springs, Ark.
ANSWER: This situation may require more research on your behalf or that of your maintenance facility, but I think I can at least point you in the right direction. I’m not certain I can completely answer your question because of the particular “”nature of the beast”” and the way this engine/airframe combination came together. Just to make things even more difficult, even though this engine does carry a TIO engine model prefix, it actually leaves Lycoming as a non-turbocharged engine. The turbochargers were installed by the airframe manufacturer under a Rayjay FAA STC SE6WE. I’d suggest you review the FAA Type Certificate Data Sheet A17WE for this aircraft for additional information.
Now let’s get closer to your situation and see if we can offer some advice. First of all, the TIO-540-S1A5 engine model is rated at 2,575 rpm and 29.5″” Hg MAP for all operations. These limits are not to be exceeded. If, as you say, the right engine MAP has been exceeding the 29.5″” as spelled out in the FAA TC, it almost sounds like it’s got to be a controller problem of some kind.
I do have a question that may help sort this out. You claim that the MAP has gone as high as 45″”, so my question is: were you flying sideways when this occurred? If one engine was pulling 45″” MAP and the other was at 29.5″” MAP, I can tell you the aircraft should have been flying sideways with that much difference in power. If you didn’t notice that in the rudder pedals, I suspect you weren’t drawing that much power from the right engine. To simplify this question, if you had not been looking at the MAP gauge when this situation occurred, would you have realized it was happening? If the answer is no, then I’d be looking for a gauge or indication problem. Maybe just swapping the MAP gauge lines behind the panel to see if it stays with the engine would be the easiest way to begin your troubleshooting. I know you changed the gauge, but there may not have been a problem with the gauge itself but somewhere else in the system.
If you can confirm the MAP has exceeded the 29.5″” limit, then I recommend you review and comply with the requirements set forth in Lycoming SB 369J or its latest revision.
The routine maintenance you mentioned seems appropriate and I’d suggest you continue with that.
I think these suggestions may get you off to a good start towards solving this mystery.
QUESTION: I recently read a question you responded to about an old O-320 (How do I figure what parts to use for an early O-320? Nov. 4 issue). You mentioned SSP 488. I cannot find it. I did find SSP 499, the numerical history. Was the 488 a typo?
ANSWER: Lycoming Technical Publication Supplement SSP-488 on the crankshaft would be a supplement to the Parts Catalog PC-103. The supplement is dated August 1988 so if you’ve got a Parts Catalog that you’re using before that date I can understand why you couldn’t locate it. I’m certain the staff at Lycoming would provide you one via fax if you contact them.
I’m sorry if I caused you any confusion and hope this will help in clearing up the matter.
Paul McBride, recognized worldwide as an expert on engines, retired after almost 40 years with Lycoming.