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I came to the realization this morning that it has been ten years to the week since we took the then Planes of Fame East A-26C (44-35721 N9425Z) to EAA Airventure. My brother and I spent a good portion of the summer of 1996 trying to get this airplane ready to fly again.

Annual Inspection

The biggest obstacle to overcome before the trip to EAA was to get through the annual inspection. The most difficult portion of that was going to be getting the engines running again. The A-26 had spent 14 months sitting idle. The only care the engines had received was the occasional prop turning to try and keep the engine seals wet and oil from pooling in the lower cylinders. It didn’t help much.

The two engines on this airplane were Pratt & Whitney R-2800-79’s Double Wasps, typical of A-26’s. Although these were Pratt & Whitney engines, they were license built by Ford, and when they were built featured water injection to boost the horsepower. This particular set was a mismatch. The right engine had just been recently rebuilt and had only a few hours of run time on it. The left engine was a much older engine. It had originally been on Bob Pond’s other Invader, but apparently when he got N9425Z with its newly rebuilt engines, he elected to put one of those on his other Invader, and put the old one from his other Invader on this one. The bottom line was that the left engine had a lot more hours on it, and leaked a lot more oil. So much oil, that the propeller was locked in place since the lower cylinders were completely full of oil.

Spark Plugs

As part of the annual inspection, we needed to remove every spark plug from both engines and clean and check them. These kind of plugs aren’t like car plugs, where you would just replace them. There’s also a lot more of them. Your car has one spark plug per engine cylinder, and the average American car has 4-6 cylinders. Airplane engines have two spark plugs per cylinder, and an R-2800 has 18 cylinders. Doing the math says that there are 36 spark plugs per engine. Each one had to be removed to be checked.

The first step in checking the plug was to clean it. We had a bead blaster in the shop to do just that. After a good five to ten minutes of bead blasting, we could then check the gap on the plug to make sure it was still good to use. Lucky for us, the gap checking went very well. Now that the plug was clean and checked, it needed to be re-inserted into the engine. This sounds easy, but these engines are round and have cylinders on the front and back. It wasn’t always easy to reach where the plugs go. It took us about a month to finish this project.

Run Up

The final step in the inspection was to run up the engines. This posed an interesting challenge. In order to start the engines, the lower cylinders need to be clear of oil. This is usually accomplished by pulling the propeller by hand several blades to move the pistons in and out of the cylinders to move the oil around. When the lower cylinders get too full of oil, they actually hydraulically lock the piston into place. The way to clear the cylinders is to remove a spark plug and let the oil drain out. The challenge to us was we needed to put the lower plugs back in and start the engine before the cylinders filled up again. We didn’t have much time to do this since the seals that normally keep oil out of the lower cylinders were so dry from lack of use, they didn’t do much sealing.

When we finally cranked the number one engine over for the first time, two things happened. The first was the engine hydraulically locked again since the lower cylinders filled up so fast with oil. The second was the starter relay locked open, which then wouldn’t allow the starter to be disengaged. This could have been very bad indeed, as the starter motor could have bent the connecting rods to the pistons causing serious damage to the engine. We had to kill the aircraft power to shut down the starter, but thankfully no damage was done. Now we were in interesting position. We needed to figure out a way to keep the engine from locking, and we needed to find a starter relay.

The solution for the hydraulic lock was pretty simple. Since each cylinder has two spark plugs, we just removed the rear spark plugs on the back of the lower cylinders. This would make them spray oil pretty badly out of the hole left by the plug, but the engine wouldn’t be locked anymore. We just needed to make sure that we didn’t have a building downwind of the engines.

The solution for the starter relay also turned out to be pretty simple. When our director of maintenance looked at the burned out relay, he said, “Would you believe I have one of these sitting on my desk?” We had the relay changed out in about fifteen minutes, and were ready to go again. This time, there was no trouble with the run up. The engines billowed smoke and oil, but they stabilized nicely and began running quite smoothly. After about five minutes or so, we shut the engines down, and replaced the spark plugs in the lower rear cylinders. With the seals inside the engine wet again, we wouldn’t have any more issues with hydraulic lock. Now it was time to try it again. For the first run, I had kneeled in the rear of the cockpit while Sean operated the engines.
Sean smiled at me and said, “Your turn.”

Here’s me after my run up. The rag in my hand was to wipe up the copius amounts of oil streaking down the engine nacelles and propeller after the first run up.