Friday, July 16, 2010

No Left Turn

After more than 33 years, it is unsurprising when some parts begin to show signs of wear. N631S has proven not to be immune to this, in common with all machinery. It's a pretty typical story.

We decided to take a bit of a holiday, and so on Monday last we flew from Potomac Airfield (KVKX) to Easton/Newnam Field Airport (KESN) on the Eastern shore of Maryland. We planned to stay at an inn in St. Michaels, MD and explore the environs. It all went extremely pleasantly and on Thursday morning we flew back to KVKX. Both of the short VFR flights were pleasant and uneventful.

After landing I stopped at the fuel island and topped off the tanks. As I set the brakes prior to starting the engine I felt a "pop" under the left pedal. Odd but unidentifiable. N631S and I proceeded to turn right onto the taxiway...then right onto the grass...then right behind the T-hangar row. Then we proceeded to NOT turn left (at least not much) to align the airplane with the hangar. Diagnosis: No braking on the left wheel.

I called Phil, the mechanic that I usually turn to when troubles arise at Potomac Airfield. He was backed up with work but referred me to Dan Fragassi of Clinton Aero Maintenance at nearby Hyde Field (W32). Danny got over to VKX this morning to examine N631S and here's what he found.

The two brackets that secure the bottom of the brake master cylinder for the left wheel (Items 13 and 14 in the exploded view at left) had failed. (See dead parts, photo below.) With the master cylinder thus adrift, there was no braking action on that wheel, and hence no (tight) left turns! So I'm at least in for new brackets, list price $35.90 for both. Not so bad.
But the next question is, why did the brackets fail? They seem unlikely to cause trouble if not subjected to unusual stresses. But examination of the rest of the pedal assembly suggested the source of the problem.
Referring back to the exploded view, the pedal is item 1. It rotates on a shaft, item 10, as it actuates the brake master cylinder via a clevis. The hole in the pedal assembly (1) in which the shaft (10) rotates is badly worn (see photo at left). So, as well as the brackets I need a new pedal, list price $218.00. It's a complex part with lots of machining and welding so that isn't so bad.

Then there's the shaft (10). It's bent. So I'm going to get the shaft. Yes, I mean that in a couple of senses. You'd think the part would be a simple steel pin. Ah, not so! It is a tube, about 4.00" long and 0.180" in diameter with a hole about 0.060" down the middle. One end is upset to retain the clevis and the other end is drilled for a cotter pin. List price for the shaft (wait for it...): $260.00. Ouch!

I'm going to ask around about why the shaft needs the hole down the middle and why a 79 cent solid steel pin won't do the job. I'm sure that the engineering rationale will be fascinating!

By the way, UPS is supposed to deliver the parts tomorrow (Saturday). If they hold up their end I should be good to go for the usual Monday trip back to Connecticut. Let's hope.

UPDATE: 7-17-2010: Gary from Clinton Aero Maintenance called me at 3:30 this afternoon. The parts arrived as promised and N631S is ready to go. Have I mentioned that I love Aviation Maintenance Technicians just as much as I love Air Traffic Controllers?

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