I'm certainly not arguing that point. I'm asking because I want to know.
91.7(a) says it's a big no-no to fly when the plane is not airworthy, in addition of course to such a thing being incredibly stupid. But that's immediately followed by 91.7(b), which says that as PIC it's my call whether the airplane is airworthy or not.
What 91.7(b) really says is that you are responsible to recognize an unairworthy condition and stop the flight if one develops. It does not repeat
not allow you to set your own standards for airworthiness that are lower than the FAA's. There are cases on file in which someone with appropriate qualification (e.g., an A&P mechanic) told the pilot the aircraft wasn't airworthy for some specific reason, and the pilot then flew it anyway saying s/he didn't agree with the mechanic's opinion. Those cases ended badly for the pilot, and if the NTSB web site wasn't still down, I'd provide examples.
While an FAA Ops Inspector usually isn't a mechanic, s/he is generally presumed to know whether something is airworthy or not when that something is clearly visible, such as in this case where the condition of the tire is easily discerned. The FAA still requires the Ops Inspector to coordinate with an Airworthiness Inspector before hanging an ACN on a plane, but that doesn't stop the Ops Inspector from telling the pilot, "I think this is unairworthy," and then initiating an enforcement action for a deliberate violation of 91.7 if the pilot then chooses to fly the plane "as is."
The reason I wonder is this... Engine manufacturers also specify TBO, both in operating hours and years regardless of tach time. But for Part 91 operations, you're free to ignore that and overhaul when you feel it's needed.
That's correct. TBO's are only recommendations in this case.
I just wonder if tires are the same.
Depends on what we're talking about. If it's a
recommendation to replace the tire ever X number of flight hours or Y number of landings or the like, yes, you're free to ignore it. However, if it's written in the manufacturer's "instructions for continued airworthiness" (or ICAW's) that a crack of a certain depth, or wear of the tread beyond a certain point renders the tire unairworthy, then you do not have the freedom to continue to fly that tire no matter what you think or believe about the situation. In the absence of ICAW's for that tire, I suspect there are standards in AC 43-13.1B or some other FAA publication which address tire wear, too, and if those say the tire is unairworthy, you have a difficult burden to prove that your less-strict assessment is valid.
So assume that the tire does show very slight weather cracking, but in my opinion it's not critical enough to need immediate replacement. My call, or not my call?
Depends what's in the ICAW's or relevant FAA publication, but if push comes to legal shove, the presumption will be that the Ops Inspector's assessment of unairworthiness was valid unless you can prove otherwise. That would mean either showing the tire really did meet the ICAW's or other established standard of airworthiness (i.e., the tire wasn't as worn as the Inspector thought) or that your own lower standards were still safe. I suppose the first could be proven by physical evidence if you're really sure the tire was OK by the established standards, but the latter is a very tough sell.
