Prevailing Cultural / Organizational Factors

For critical holes produced with multiple processes (drilling, boring and honing) it was generally accepted, based on metallurgical data, that any material flaws introduced by the drilling process would be removed by the subsequent boring and honing processes. This practice proved flawed for the production of the Pensacola JT8D-219 hub when material anomalies introduced by drilling extended much deeper into the hole sidewall than previously anticipated by Pratt & Whitney and were not completely removed by the boring and honing processes.

The fan hub is a "safe life" or "life-limited" part and was certified by the FAA, based on Pratt & Whitney engineering data, to operate safely for its total design life of 20,000 cycles. The hub does not require inspection unless it is removed from the engine. FPI and visual inspections were conducted on fan hubs at the Delta overhaul facility only if they were removed during engine overhaul or disassembly. Delta stated that with a "safe life" part, it is assumed that the part is defect-free on delivery and inspection techniques are selected to find normal wear and tear and abuse not pre-existing damage. Delta also stated if they were required to assume pre-existing damage was present then an alternate inspection technique such as eddy current or ultrasonic would have been employed. Safe life assumes the part will operate safely throughout its design life even without an inspection. The FAA fundamentally ascribed to this position at the time of the accident. However, the FAA has changed its assumption that Life Limited Parts (LLP's) are delivered defect free, and as such, now mandates repetitive inspection (Enhanced Engine Inspection Initiative) of all LLP's at all levels of exposure.

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