My understanding is that what you describe can happen when the aneroid capsule looses its elasticity and thus distorts ununiformly (I guess unevenly would have been a better word!), a phenomenon that I believe is called "hysteresis" (sp?). I guess, above a certain altitude the problem may become evident as the capsule expands, below a certain altitude the problem may be masked; pure conjecture on my part.
If the propblem was upstream in the static system then I would have thought, certainly for the type schematics I have seen, that the other static instruments, incl the ASI, would play up too.
Last edited by High Wing Drifter; 2nd March 2006 at 14:28.