FAA notification on fasteners
FAA notification on fasteners
2
berkshire (Aeronautics)
(OP)
This one just came over my desk today, it is extremely broad reaching. An SAIB HQ 14 16 on fastener quality.
B.E.
B.E.
You are judged not by what you know, but by what you can do.





RE: FAA notification on fasteners
Mike Halloran
Pembroke Pines, FL, USA
RE: FAA notification on fasteners
Yeah, nothing could ever go wrong with taking a "trust a vendor to do it right" approach.
RE: FAA notification on fasteners
Must be a bunch of kids running the FAA!
RE: FAA notification on fasteners
Quando Omni Flunkus Moritati
RE: FAA notification on fasteners
It was something that Eng tips did when the link was posted.
The original SAIB was HQ 14-16 and was applicable as follows
HQ-14-16 - Small Airplane/ All/ All Models
HQ-14-16 - Large Airplane/ All/ All Models
HQ-14-16 - Engine/ All/ All Models
HQ-14-16 - Rotorcraft/ All/ All Models
HQ-14-16 - Small/Large Airplane/ All/ All Models
It was because of the broad coverage of this Special Airworthiness Information Bulletin that I posted it up here, I know that not all of you are privy to the FAA airworthiness reports, and airworthiness directives.
B.E.
You are judged not by what you know, but by what you can do.
RE: FAA notification on fasteners
The SAIB describes the problem as being fracture failures in the locknuts due in part to hydrogen embrittlement. The NASM21042 spec requires hydrogen embrittlement relief after plating, so this should only be a problem with locknuts that were not processed correctly. However, the SAIB also recommends checking the prevailing torque of new locknuts at installation to verify there is not excessive interference in the deformed threads of the locking feature that would cause fracture failure in the locknut body. I have personally seen the condition numerous times where the prevailing torque of a few parts in a lot of brand-new conforming MS21043 locknuts was way above the range prescribed in the procurement spec. The problem is worse with smaller thread sizes from 1/4-28 to 6-32. Everywhere I have worked as a design engineer, it is established practice to verify the prevailing torque of deformed thread locknuts (like MS21042) is within spec at each installation. In my own experience, it is common to discard around 5% of brand-new 1/4-28 or 10-32 MS21043 locknuts for excessive prevailing torque, and with brand-new 6-32 MS21043 locknuts the discard rate for excessive running torque is often 25% or more.
Due to the way large batches of deformed thread locknuts are acceptance tested, and the difficulty in controlling the prevailing torque with small thread diameters, there will always be a certain percentage of these new locknuts that have excessive running torque. The best way for the FAA to deal with this issue would be to make sure that all guidelines for design, manufacturing and maintenance require the prevailing torque range of all self-locking threaded fasteners to be published and measured at each installation.
Interesting topic.
RE: FAA notification on fasteners
RE: FAA notification on fasteners
B.E.
You are judged not by what you know, but by what you can do.
RE: FAA notification on fasteners
RE: FAA notification on fasteners
http://www.everyspec.com/MIL-SPECS/MIL-SPECS-MIL-D...
http://www.everyspec.com/MIL-SPECS/MIL-SPECS-MIL-D...
I've also attached a table listing the sample sizes for acceptance of large batches of metal locknuts. For example, a batch of up to 10,000 locknuts would only require a sample size of 5 pieces for acceptance.