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I have 2500hrs and have flown over 30 types of aircraft. I am also a A&P. I have never seen a POH, manufacture or FAA suggestion for wear limits of a tire. The flight school I got my pilots license (1980), would wear the tires of Cessna training aircraft bald on the outside of the tire and flip them on the rims, then run then bald on the opposite side. On airliners and transport aircraft I have seen chunks of rubber missing, cord and belts exposed, etc more so on freight than passenger aircraft. Surely there must be some standard or legal requirement.

( I have seen FAA, mfg, and other info prohibiting flight if tire pressure exceeds +-5%)

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    $\begingroup$ I would expect the tire manufacturer would provide a limit. $\endgroup$ – TomMcW Dec 27 '17 at 18:43
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Yes, there is, but it is not by regulation. It is in Advisory Circular 20-97B.

For example, section 7 would apply to most of your pictures:

(7) In-Service Inspections (Operator).

(a) Tread Damage Removal Recommendations. Tires that exhibit any of the following characteristics symptomatic of damage should be removed from service:

(1) Cracking and/or cutting in a tread groove that is undercutting material adjacent to the crack or cutting that has lifted or can be lifted.

NOTE: Do not probe cuts or embedded FOD when the tire is inflated.

(2) Undercutting in a tread rib.
(3) Transverse cracking in the tread that is visible at the surface and shows progression along an angular path down into the rubber.

(b) General Tire Removal Recommendations. Tires with any of the following conditions should be removed from service:

(1) Sidewall cuts that penetrate the outermost structural ply.
(2) Internal separations characterized by bulges or distortions in the tread casing or sidewalls.
(3) Heat or slippage evidenced by reverted or charred rubber above the wheel flange.
(4) Tires worn or flat-spotted to the outermost casing ply (bias) or outermost belt (radial).

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    $\begingroup$ Well, that is still a "should", not a "must". Even the manufacturers use "should" a lot; the hard limit is when the first ply is worn through, see page 26 of linked PDF. $\endgroup$ – Peter Kämpf Dec 28 '17 at 21:14
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    $\begingroup$ @PeterKämpf True, not saying that these are "must" items, the OP did ask if "I have never seen a POH, manufacture or FAA suggestion", FAA Aircraft Circulars are pretty much "FAA suggestions". Your linked PDF is for Goodyear tires, it is possible that some other manufacturer includes wear indicators or some other method. Also, see 7.b.4 in the answer "Tires worn or flat-spotted to the outermost casing ply..", which matches your PDF. $\endgroup$ – Ron Beyer Dec 28 '17 at 21:44
  • $\begingroup$ The Russians have simple stud holes in the tire surface. If the holes are no longer visible (because all the rubber around them has been worn off) the tires must be replaced. TomMcW is correct, in the West the tire manufacturer and the operator decide what the limits are. You will find similar documentation from Michelin and others. But yes, the question is about suggestions also. $\endgroup$ – Peter Kämpf Dec 29 '17 at 7:56

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