A-90-008
NTSB Safety Recommendation — Aviation
Recommendation text
THE NTSB RECOMMENDS THAT THE FEDERAL AVIATION ADMINISTRATION: DETERMINE THE MINIMUM SIZE OF PATCH REPAIR PROCESSING CRACKS THAT COULD INITIATE FATIGUE CRACKS IN PRATT & WHITNEY JT9D MODEL ENGINE FAN BLADES AND DETERMINE THE LIMITS OF THE EDDY CURRENT INSPECTION OR OTHER INSPECTION TECHNIQUES TO DETECT SUCH CRACKS. IF THE MINIMUM SIZE OF THE PATCH REPAIR PROCESSING CRACKS IS SMALLER THAN THE DETECTABILITY LIMIT OF THE INSPECTION, ISSUE AN AIRWORTHINESS DIRECTIVE TO REQUIRE ON ALL BLADES THAT HAVE BEEN PATCH REPAIRED, RECURRING INSPECTIONS CAPABLE OF DETECTING A PROPAGATING FATIGUE CRACK BEFORE IT REACHES A CRITICAL LENGTH.
In plain language (FlightFinder summary)
The NTSB asks the FAA to determine the smallest patch repair processing cracks that could initiate fatigue cracks in Pratt & Whitney JT9D model engine fan blades, and to find the detection limits of eddy current or other inspection techniques for such cracks. If the minimum crack size is smaller than what inspections can detect, the FAA must issue an airworthiness directive requiring recurring inspections on all patch-repaired blades, capable of catching a propagating fatigue crack before it reaches a critical length.
This plain-language summary is written by FlightFinder to explain the recommendation above. It is not the official wording — the verbatim NTSB text is quoted above.
Details
| Status | Closed - Reconsidered |
|---|---|
| Mode | Aviation |
| Closed | Aug 2, 1990 |
| NTSB number | DCA89IA066 |
| Addressees | FAA |
External links
NTSB safety recommendations are advisory; addressees are not legally required to adopt them. Source: NTSB CAROL (public domain).