Text in force at 27-51: from 27-16, effective 1 Dec 1978.
[(a)] The methods of fabrication used must produce consistently sound structures. If a fabrication process (such as gluing, spot welding, or heat-treating) requires close control to reach this objective, the process must be performed according to an approved process specification.
[(b) Each new aircraft fabrication method must be substantiated by a test program.]
43 FR 50599 · Source