Aircraft fabric covering: required grade and breaking strength limits
Owners of fabric-covered aircraft often need to know whether their covering is still airworthy and what grade it must be. The assistant answers from Chapter 2 of AC 43.13-1B, which sets fabric grades and breaking strength limits.
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Free account requiredAnswers are written by a language model solely from this base's documents, with numbered sources. They can be wrong and aren't legal, medical or financial advice: check the sources before any important decision.
Choosing the fabric grade
Grade A mercerized cotton airplane cloth (TSO-C15d, AMS 3806G) has a minimum new tensile strength of 80 lb per inch. It may be used on all aircraft and is required when wing loading is 9 psf or greater or the placarded never exceed speed is 160 mph or greater.
Intermediate grade (TSO-C14b, AMS 3804E), with 65 lb per inch new, is for aircraft with a wing loading under 9 psf and a Vne under 160 mph. A lighter cotton to AMS 3802 is listed for gliders with a wing loading of 8 psf or less and a placarded Vne of 135 mph.
When fabric becomes unairworthy
Fabric condition must be determined at every 100-hour and annual inspection. Fabric stays airworthy until its breaking strength falls below 70 percent of the new strength required for that aircraft.
In practice: below 46 lb per inch for aircraft under 9 psf and under 160 mph, regardless of grade; below 56 lb per inch for 9 psf and over or a Vne of 160 mph and over; below 35 lb per inch for gliders and sailplanes of 8 psf or less and 135 mph or less.
Frequently asked questions
Are punch testers FAA approved?
No. Mechanical devices that press against or pierce the fabric are not FAA approved and are used at the mechanic's discretion to form an opinion. They do not work on glass fiber fabric, which shears easily and reads very low.
How is a more accurate field test done?
Cut a 1-1/4 inch by 4 inch sample from the top exposed surface, remove all coatings and ravel the edges to 1 inch. Clamp it and load it, for example with sand in a suspended container. If still in doubt, a laboratory can test to ASTM D5035.
If I used Grade A on an aircraft needing only intermediate fabric, which limit applies?
The limit follows what the aircraft requires. The chapter's example: Grade A cotton on an airplane needing only intermediate fabric can deteriorate to 46 lb per inch before replacement.
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