Thursday, March 22, 2012

2012 Annual Inspection (iv)

When I spoke with Mike the IA this morning about progress on N631S's annual, he pointed out that both magnetos were due for their 500 hour inspections. This did not require a difficult decision...the work needs to be done. He'll be taking both mags apart, inspecting their innards, and replacing any worn parts.

The Slick magnetos that generate spark for the airplane's ignition system are very simple devices, but subject to wear and tear. Failing to maintain them properly can ruin one's day. This point is made well in this post from the blog of the late and sorely missed Neptunus Lex.

And, by the way, Lex links to a delightful site that explains the design and operation of magnetos in an innovative way. Most highly recommended!

As I was leaving the hangar, Mike was about to start inspecting the seats and seat rails in compliance with an applicable Airworthiness Directive (AD 2011-10-09). This AD is a recent revision to one of long standing that required inspection of the seat rails for wear (Cessna seats having exhibited an unpleasant tendency to come adrift at awkward times in cases of excessive wear). The 2011 version added new guidance covering wear of the roller assemblies that ride on the rails as the seat is adjusted.

A couple of hours later I got an e-mail telling me that there was good news and bad news. The good news was that the rails are fine – within the wear limits specified by the AD. The bad news is that one of the roller assembly housings (see photo) is worn out of limits and will have to be replaced.

The full width of the housing is 0.900" and the maximum gap permitted between the tangs, as annotated on the picture, is 0.440". This one is worn to a gap of about 0.465". It has to go. And Cessna is, it seems, very proud of their parts. A new roller assembly, P/N 1714000-33, will be setting me back $426.66. Fortunately, it's a simple bolt-on installation so there won't be much additional cost for labor. And I can count myself as fortunate that only one roller assembly needs to be replaced. This time.

The only other bit of significant news is that a new muffler (discussed previously) has been ordered and is expected to arrive Tuesday next. That keeps everything on schedule.


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