The end of the Ag season is drawing near and most Ag operators will be storing their aircraft for three to nine months! Engine preservation becomes an important issue at this time of year and deserves our attention, especially with the expensive engines that are flying these days.
The PT6A engine comes with a manufacturer’s Maintenance Manual that has very distinct guidelines for determining if engine preservation is necessary and what procedure is called for. These guidelines are based on the time that the engine is to be inactive. I am tempted to get technical and try to tell you how to preserve the engines, but I think I would be making a more worthwhile effort by explaining why you need to preserve your engine!
The PT6A engine is known as a free turbine! That is not a statement about the price of the engine, but is a description of the relationship of the Compressor to the Power Section. Both units turn at ridiculous speeds, and require the use of very high quality and costly steel bearings. If handled improperly or left inactive for prolonged periods of time exposed to moist air, these bearings will rust. The bearings are worth protecting especially if the protection can be accomplished relatively easy and cheap. Rust can lead to failure. Failures aren’t free!
The PT6A is a very light engine made of magnesium cases. A P&WC engineer visiting our facility once expressed frustration and amazement at finding lead weights bolted to the front of an Ag aircraft. He stated, “We spend millions making these engines as light as possible, and you people are bolting lead weights to the front!” One of the problems in dealing with magnesium is that it tends to corrode when exposed to the elements, even for a short period of time. Your PT6A engine’s cases are chromated, painted and varnished to prevent this from happening, but scratches and nicks occur and varnish can flake off occasionally (especially if an engine is left inactive for months at a time in damp conditions) leaving bare magnesium to corrode.
The large engine fuel systems have a fuel control unit that is made up of aluminum housings and highly finished steel parts. The unit is a wet bodied or flooded fuel control unit. This means that the entire inside of the unit is flooded with fuel during operation. Fuel generally has some moisture in it, it may be microscopic, but at times it may be enough to puddle up. If the engine is shut down while this moisture is moving through the fuel control unit, the moisture will settle to the bottom of the unit. Steel parts and aluminum housings corrode or rust when exposed to substantial moisture over an extended time. The likelihood of this taking place increases during the winter months when Ag aircraft are least utilized.
P&WC’s warranty is probably one of the best warranties in the industry, however, they will not cover damage to an engine or its systems caused by corrosion or rust. Especially, if it could have been prevented by complying with maintenance manual instructions. It brings to mind the HAPLESS PILOT quote, “Aviation in itself is not inherently dangerous, but to an even greater degree than the sea, it is terribly unforgiving of any carelessness, incapacity or neglect”.
I want to recommend that you get Pratt & Whitney Canada’s maintenance manual infor-mation relating to your particular engine and familiarize yourself with the instructions for pre-serving your investment, and do it the right way! You will be surprised how simple it is to do once you’re set up for it. You need these engines to run a long time trouble-free to ensure your success in this high tech world you’re working in. Y’all Fly Safe, Ron Hollis