Seagull From United States of America, joined Jun 2001, 340 posts, RR: 1 Reply 1, posted (12 years 4 months 1 day 5 hours ago) and read 2045 times:
The time varies. First experimental test pilots from the manufacturer run the aircraft through systems tests, then ground tests, then a series of several thousand flight tests, with FAA participating. It is a long and detailed and very rigid process. Once that's done and the aircraft goes into producting, then production test pilots check the aircraft out before delivery, then the airline's flight test pilots check them out again before they fly the line.