A-68-005
NTSB Safety Recommendation — Aviation
Recommendation text
THE FOLLOWING PROPOSALS IS RECOMMENDED: 1. THAT AN IMMEDIATE INSPECTION PROGRAM FOR FATIGUE CRACKS AND EVIDENCE OF LOCALIZED FRETTING IN MCCAULEY HUBS FOR TWO AND THREE BLADE PROPELLERS BE INITIATED. THIS INSPECTION SHOULD BE ADEQUATE TO DETECT SMALL FATIGUE CRACKS IN THE ROOTS OF THE BLADE RETAINING THREADS OF BOTH TYPES OF HUBS AND AT THE LATCH PLATE SLOT AND STUD HOLES OF THE TWO BLADE HUBS. THE EXAMINATION FOR FRETTING SHOULD BE DIRECTED SPECIFICALLY TO THE INBOARD FLANKS OF THE BLADE RETAINING THREADS AND THE MATING FLANKS OF THE BLADE RETENTION NUT. 2. THAT A RADIUS REQUIREMENT BE SPECIFIED FOR THE EDGES OF THE LATCH PLATE SLOTS IN BOTH EXISTING HUBS AND THESE MANUFACTURED IN THE FUTURE. 3. THAT THE FEASIBILITY OF SHOT PEENING THE BLADE RETAINING THREADS IN EXISTING HUBS AND FORMING THESE THREADS BY ROLLING IN HUBS MANUFACTURED IN THE FUTURE BE INVESTIGATED. 4. THAT A REVIEW OF THE DESIGN OF THE HUBS BE CONDUCTED TO DETERMINE WHETHER THEIR FATIGUE STRENGTH IS ADEQUATE IN THE AREAS WHERE CRACKS HAVE ORIGINATED.
In plain language (FlightFinder summary)
The FAA is asked to launch an urgent inspection program to find small fatigue cracks and wear in specific McCauley propeller hubs, particularly around the threads that hold the blades in place. The agency should also establish design standards for smoother edges on hub slots and study whether strengthening these threads through surface treatment or new manufacturing methods would improve durability. These steps aim to verify that the current hub designs are strong enough to prevent cracks from starting in vulnerable areas.
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 - Acceptable Action |
|---|---|
| Mode | Aviation |
| Closed | Jan 1, 1975 |
| NTSB number | MKC68A0052 |
| Addressees | FAA |
External links
NTSB safety recommendations are advisory; addressees are not legally required to adopt them. Source: NTSB CAROL (public domain).