A-68-003
NTSB Safety Recommendation — Aviation
Recommendation text
IT IS RECOMMENDED THAT THE FOLLOWING PROPOSALS BE CONSIDERED: 1. THAT THE AIRWORTHINESS DIRECTIVE ADEPTED ON FEBRUARY 14, 1968, BE MODIFIED TO (A) REQUIRE THE USE OF A MAGNIFYING GLASS IN THE EXAMINATION OF THE BEARING BOSS RADIUS AND (B) REQUIRE A FILLET RADIUS AT THE BEARING BOSS OF 0.040 INCH AS SPECIFIED BY THE BRANTLY DRAWING RATHER THAN THE 0.020 INCH RADIUS SPECIFIED IN AD 65-28-1. THE GLASS USED IN THE INSPECTION SHOULD HAVE A MAGNIFYING POWER OF ABOUT 10 DIAMETERS DUE TO THE SMALL SIZE OF THE PITS FOUND IN THE BLADES FROM N2287U. 2. THAT CONSIDERATION BE GIVEN TO THE POSSIBILITY OF MODIFYING THE BLADE DESIGN TO PROVIDE FOR PRESSURIZED LUBRICATION AND CADMIUM PLATING OF THE OUTER SURFACE OF THE THRUST BEARING. FREQUENT PRESSURIZED GREASE PURGING OF THE ROTOR HUB SHAFT CAVITY AND THE THRUST BEARINGS WOULD REMOVE TRAPPED AIR AND MOISTUREAND REDUCE THE DANGER OF CORROSION. CADMIUM PLATING THE SURFACE OF THE THRUST BEARING THAT IS IN CONTACT WITH THE ALUMINUM SPAR WOULD REDUCE THE DANGER OF GALVANIC CORROSION IF MOISTURE DOES GET INTO THE ASSEMBLY.
In plain language (FlightFinder summary)
The FAA is urged to update airworthiness rules requiring inspectors to use a ten-power magnifying glass and to ensure bearing bosses have a larger radius than previously mandated. Additionally, the agency should evaluate changing blade designs to include pressurized lubrication and protective plating on thrust bearings. These measures aim to eliminate trapped moisture and prevent corrosion that could compromise aircraft safety.
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 | MKC68A0050 |
| Addressees | FAA |
External links
NTSB safety recommendations are advisory; addressees are not legally required to adopt them. Source: NTSB CAROL (public domain).