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Wednesday, April 23, 2014

Something Rare at MMS Aviation: A Training Aid

MMS Aviation trains using an apprenticeship approach. Apprentice mechanics work 40-hours a week on missionary/ministry airplanes and study textbooks to learn theory outside the normal work week. If there is difficulty understanding a maintenance concept, MMS Staff mechanics gladly spend time one-on-one explaining the subject matter.

Training aids have not been a normal part of learning because the planes we restore, modify and overhaul provide needed experience. That is, except in turbo-prop engine maintenance experience. MMS does maintain a Beechcraft King Air 200 that has two Pratt & Whitney Canada PT6A turboprop engines. This is extremely valuable because our mechanics see the engines in a normal environment during the airplanes phase inspections each year. However, this doesn't provide the ability for each mechanic to operate the engines and perform maintenance checks (and we're OK with that).

So, early last year MMS leadership decided to raise the money to purchase a runnable PT6A at the going retail price. AVOTEK, a company in Virginia, manufactures state of the art aviation training technology. We checked the price so we'd know how much money to raise. Before fund-raising began a company that operates a lot of these Pratt & Whitney engines heard about our plan and donated an engine for the test/run-up stand AVOTEK would build for us. This brought the price within available cash on hand.

Yesterday an Old Dominion truck (Old Dominion - Virginia - get it?) pulled up at the MMS hangar complex with our new training aid and were we ever excited!

Dave is our capable lift truck driver.
It might as well been wrapped in Christmas paper.
MMS Director of Training Bob Schwartz (left) will take the lead in developing our PT6A training program. Aircraft maintenance Supervisor Mike Dunkley has a lot of experience maintaining this type of engine and teaching others about it. Mike will work closely with Bob. Other experienced MMS staff will have input as well.
A turbo-prop engine is a gas turbine engine whose rotating core is geared down to turn a propeller. It burns jet fuel which is far more available around the world than aviation gasoline is. That's why missionary aviation organizations are operating more turbo-prop engine powered aircraft.

Wednesday, April 16, 2014

Engine Overhaul Tools

Aircraft engine crankcases must be separated to allow removal of the crankshaft, camshaft and other internal engine parts. Many Lycoming engines require special tools to push the crankcase halves apart. Until very recently MMS used a quickly improvised set of tools to do this. The old tools protected the engine parts from damage and undue stress, but were inefficient and had become quite worn. New factory-made tools for this operation are very expensive; however, the engine overhaul manual has pictures of the tools and a clear description of how they are used.

Several years ago money to purchase a milling machine was donated and MMS Director of Maintenance Tim Obarow is a skilled machinist. An adequate amount of heavy steel plate and some other material were purchased and Tim went to work. Using that milling machine and a lathe, Tim fabricated the various parts of the new tooling for the engine shop.

After all the parts were made, MMS aircraft maintenance Supervisor Dale Coates ordered a sturdy case to house the new engine tooling along with copies of instructions for its use. All this cost about $3,200 less than the same commercially available tooling.

After all external parts are removed from the crankcase, the plates are installed on both sides. Here Joel puts the plate on the right side of the engine.

The plates push on the long bolts that pass through the crankcase to separate the crankcase halves. As Joel and Dale begin, the case halves are still held together by dowels that align them (as indicated by the arrow in this picture).

As large nuts on the outside of the plates are tightened the crankcase halves separate until the dowels are disengaged after about 3/8" of movement. The plates are removed and the case halves are easily lifted away from the crankshaft that is bolted to the engine stand.

So, how did the new tooling work? To quote Dale, "Great!"