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Friday, July 25, 2014

There is an angel among us

Here at MMS we have the great privilege of maintaining airplanes from all over the world. One of these airplanes that we are currently maintaining is an Angel aircraft. This particular airplane was designed by a missionary for missionary use. It can seat between 6-8 people. It utilizes Lycoming IO540 engines that push from behind the wing. This basically means the engines look like they are on there backwards with the props on the back rather than facing to the front. By doing this it allows for easy cargo loading in the front of the wings. These are very unique airplanes and there are only five of them in the world. The one that we have in our hangar has a serial number of #002. To learn more about these unique aircraft you can go to their website at Here at MMS we have been given the task of  preparing the airplane for export to Bolivia. Some of the tasks that we are performing are: The overhauling of both engines, the over- hauling of both propellers, the annual inspection, servicing of the struts, the fixing of some fuel seepage, and other various maintenance items as needed.

This particular airplane has been donated to. South America Mission. You can learn more about South America Mission by going to their website at . Currently we have helped serve 106 missions organizations around the world with their needs. God has brought many talented individuals to serve here at MMS. Each individual brings a unique gifting and set of talents that balances the work that we do here. Part of our mission is to prepare people and we do this through a 30 month apprenticeship where they will get the necessary hands on training to qualify them for their airframe and power plant certificate, working on real air planes in a real shop. These apprentices then will move on to serve with one of the 165 Christian mission flight organizations around the world. Here is a look into part of the many projects for the Angel aircraft.

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!"

Monday, March 24, 2014

Horizontal Stabilizer Talk

It is said that necessity is the mother of invention. The truth of that saying is seen in the modifications MMS Aviation mechanics make to airplanes used in missionary service. In fact, the Federal Aviation Administration provides a way changes can be made to production aircraft that are approved by the FAA and issued a Supplemental Type Certificate. As in any acronym-ridden system, we simply refer to this approval as an STC.

One STC we have installed several times was developed by a company in Alaska to improve the durability of the horizontal stabilizer on Cessna 206 and 207 airplanes. The stabilizer skins are removed, new skins are installed in a slightly different configuration, and the leading edge skin is held on with screws instead of rivets. This is valuable because, when a plane is operated on unpaved airstrips, stones kicked up by the wheels and propeller blast can beat up the horizontal stabilizer leading edge quite badly.

Phil works on leading edge attachment. The yellow frame in the picture is a fixture to keep the stabilizer straight while giving good access to it for repair.
After the original aluminum sheet skins are removed the horizontal stabilizer structure is cleaned, inspected, and repaired as necessary. Additional pieces are added to hold the "plate nuts" for the leading edge screws. The leading edge material is thicker than the original and is more resistant to damage.

Josh, a LeTourneau University student on spring break, drives rivets while Phil (standing) bucks the rivets. This swells the aluminum rivet to hold the layers of sheet metal together. 
Skins aft of the leading edge skin are riveted in place as they don't need changed as often as the leading edge. With this STC installed, a damaged stabilizer leading edge can be changed with a screwdriver instead of drills, a rivet gun, and bucking bars. Considerable time is saved as well.

Bob bucks a rivet while Phil drives it with the rivet gun. The more skins in place reduces easy access for the bucking bar (a piece of smooth steel). Added concentration is often required to achieve desired results.
Riveting 101: The repeated hammering of the rivet gun on the rivet head (outside the structure) against the bucking bar (inside) swells the rivet and holds the pieces together. The FAA publishes standards the driven rivet must meet.

An FAA Advisory Circular gives guidance.

Friday, February 21, 2014

What Happened Next

After the cylinders of the Lycoming engine for a ministry in Alaska (previous post) were ready, the engine's crankcase with its internal parts was assembled.  Cylinder assemblies were installed and the nuts that hold them were torqued.

Joel (left) and Dale torque thru-bolts that hold cylinders five and six.
Cylinder number three goes into place.
Cylinder valve trains were put in place as well as the accessory gears and accessory housing on the back of the engine.

Joel "safeties" oil passage plugs on the accessory section with lock wire.
Engine assembly is nearly complete as Dale does a final visual inspection of a fuel injector line.
Dale explains fuel injector line inspection criteria to Joel.
The engine test cell is being prepared with the engine mount and instrumentation appropriate for this engine's operational test.  When the test runs are done the maintenance record (read paperwork) will be completed.  It will then be crated for shipping and the engine will be on its way.

Friday, February 7, 2014

Sizing-up Progress in the Engine Shop

The engine shop at MMS Aviation has been a busy place lately.  Dale is supervising the assembly and test of a Lycoming engine for a ministry in Alaska.  Today cylinders and pistons were measured to assure proper clearance between them. 

Tim gave a mini refresher course about how to set up and use the cylinder bore gauge.  Dale, right, observes.

Dale measures each cylinder, checking dimensions in several places of the cylinder bore.

Joel records the dimensions on the engine build-up sheet as Dale gives him the gauge's reading.

Thursday, December 19, 2013

Refurbish or Restore

The dictionary says refurbish means to repair and make improvements, or to brighten or freshen up.  Restore is to return (something) to an earlier or original condition by repairing it, cleaning it, etc.  At MMS Aviation we do a lot of heavy-duty maintenance on airplanes so I wanted to know which word best described our work.  My conclusion is that both terms pretty well captures what goes on at MMS, but rather than just writing about it, here are a few pictures to illustrate it.

Work began in the upper forward cabin of this Cessna U206F.  Chuck cleans the wing support structure so it can be properly inspected.  Disassembly was accomplished by removing rivets that held the various pieces together. 
Airworthy parts were cleaned and painted before reassembly.  Parts that were damaged were replaced with new parts.

Work progressed from the upper forward cabin to the tail cone.

When the tail cone repair was complete the fuselage was rotated onto its left side to work on the belly and landing gear support structure.  The last two skins to be replaced have been removed.

Chuck and Jake use floor support structure to check rivet hole patterns because sometimes there are more holes in the old skin than need to be in the new one.  New aluminum sheet is below the original skin that is the pattern for the new skin.

The airplane being refurbished/restored was used most recently in Indonesia and may have been in Africa before that.  It will next be used in Suriname and based in a costal city so corrosion prevention is a priority.
This plane is a 1976 model and it's important to remember that it has been well maintained and safely operated by missionary aviators for nearly 37 years.  With the work MMS Aviation mechanics are doing, who knows, we may see it serve another 37 years in missionary aviation.