As far as I know, all the tubing used to manufacture bicycles is aircraft quality. Specifically it starts as stock tubing normally used for hydraulic lines internally in aircraft wings. There are some parts and areas on aircraft that are easy to access and that get regular maintenaince - this isn't one of them. So if anyone is having fatigue issues with their titanium bikes - its a manufacturing issue - either a welding quality issue or a product design issue. The material is sound.

Kona dabbled in titanium bikes for a short period of time. They didn't drop titanium because of fatigue issues - THEY were dropped by their tubing supplier because the orders were to small to be worth dealing with relative to their regular aerospace customers.