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Questions and Answers – Acrylic Windshield Repairs, a Leaky Compass

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February 2012

 Q: Hi Steve,

I haven’t been flying my Piper Pacer very much lately. Money is tight, and Avgas is expensive right now. I do tie my Pacer down outside.

I was out there with my broom brushing the snow off of the wings, tail and fuselage when I accidently whacked the windshield with the broom handle. I hit it right next to the snap vent. (The snap vent is in a two-inch hole in the lower left corner of the window. —Ed.)

Now I have a big crack radiating out from that hole. It’s about four inches long.

I called one of the local A&Ps for some advice. I flip-flop between this guy (who is competent at inspecting the must-do items, and does a good job of assessing the general health of the airplane) and getting aircraft repairs and advice from a more established and better equipped shop located 50 miles away.

Anyway, my tailgate guy—I’ll call him Larry—told me that it’s okay to sew up the crack with safety wire. Is he kidding? I’ll replace the acrylic windshield eventually, but right now, sewing it up would be much more affordable. Can I legally sew it up?

—Cracked

 

A: Dear Cracked,

Larry is correct. In Section 4, “Windshields, Enclosures and Windows” of Advisory Circular (AC) 43.13-1B, repairs are described. This AC says that when acrylic windshields or side windows are damaged, they are usually replaced “unless the damage is minor and a repair would not be in the field of vision.”

Under “Minor repairs” it says that if safety is not impaired, the crack may be repaired by drilling a hole at the end of the crack with a 1/8 inch (or #30) drill. Next, drill a series of holes with a #40 drill. The recommendation for these holes is that they be spaced ½ inch from the edges of the crack, and also spaced ½ inch apart for the length of the crack. Then a length of brass safety wire is threaded through the holes to “sew” the crack together. Cover the repair with clear silicone sealant.

AC 43.13-1B, which is titled “Aircraft Inspection Repair and Alterations; Acceptable methods, techniques and practices,” not only outlines the safety wiring sewing minor repair (which is very noticeable and may cause nervous passengers to express concern about the airworthiness of your Pacer), it also outlines a simple permanent repair.

The simple permanent repair goes like this: Stop drill the end of the crack with the 1/8 inch or #30 drill. Then use a hypodermic syringe and needle to fill the crack with a polymerizable two-part cement such as PS-30 or Weld-On 40. (Weld-On 3 is one-part cement, will also work fine for this repair, and is considerably less expensive than the two-part cements.) The hole is plugged by soaking the end of a 1/8-inch acrylic rod in the cement and then inserting it into the hole. Let the repair dry for about 30 minutes and then trim off the end of the rod.

After the repair is dry, the clarity can be restored by polishing. The polishing process consists of sanding the surface with finer and finer grits of sandpaper. Start with 320 or 400 grit sandpaper wrapped around a rubber or felt pad. Use light pressure and circular motions.

Rinse the sandpaper often in a bucket that contains fresh water and a mild liquid soap as a lubricant. Flush the newly sanded acrylic with running water, then move to 500 grit paper and repeat. Keep moving to higher grit paper until all the sanding and repair marks have been removed. Finish using fine rubbing compound and a circular motion.

Even for those of you who don’t have a window crack to fix, your aircraft might be ready for some TLC, too. There are also a number of kits that supply all the materials needed to polish out scratches and restore clarity to acrylic windows and windshields. A few names include Micromesh, Micro-Surface, Scratch Off, and Polysand. These are available at most aircraft supply houses.

Happy flying.

 

 

Q: Dear Steve,

My compass is leaking. I can smell it, and can see the fluid level halfway down the window. Is this easy to fix, or do I need to bite the bullet and buy a new fancy compass? I really like the looks of the SIRS compasses but wonder whether buying a new compass is money well spent since I always fly with both a panel mount and handheld GPS navigators.

—Catching a Buzz

 

A: Dear Buzz,

Your primary compass is probably an Airpath, which has been the standard in almost all production airplanes for decades. Variations in the fluid level due to changes in air temperature and atmospheric pressure are accommodated by a flexible diaphragm. Leaks are almost always caused by deterioration of the diaphragm or the front face glass gasket.

Repair kits, which include a new diaphragm, a new face glass gasket and a half-pint of compass fluid are very reasonably priced (less than $20) and readily available from almost all aviation supply houses.

Unfortunately, the only approved repair scheme requires that the compass be sent to an approved repair station, or back to Airpath Instrument Co. The Airpath repair manual is quite specific about the procedure. I checked the prices at Century Instruments in Wichita and they want $110 plus parts to overhaul and certify a customer’s Airpath compass; $178 outright and $155 exchange.

Since the price for a SIRS Navigator NV2-2400 compass is approximately $255 plus $30 to $40 for the mounting bracket, your decision will boil down to overhauling your Airpath, or upgrading to the SIRS.

I have a SIRS in my Comanche and I really like it. It’s got big numbers, the numbers are a highly visible day-glo green, and I believe it’s a little higher tech than the Airpath. Since you are well equipped with the navigation equipment you said you carry on every flight, it boils down to where you want to spend your money.

Happy flying.

 

Steve Ells has been an A&P/IA for 38 years and is a commercial pilot with Instrument and Multi-Engine ratings. Ells also loves utility and bush-style airplanes and operations. He’s a former tech rep and editor for Cessna Pilots Association and served as Associate Editor for AOPA Pilot until 2008. Ells is the owner of Ells Aviation (www.EllsAviation.com) and the proud owner of a 1960 Piper Comanche. He lives in Paso Robles, Calif. with his wife Audrey. Send questions and comments to .

 

 

Resources

 

Advisory Circular 43.13-1B

www.faa.gov, then type “AC 43.13-1B” in the Search window

Airpath Instrument Co.

www.airpathcompass.com

 

Century Instrument Co.

www.centuryinst.com

 

 

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