FAA Safety Team Maintenance Safety Tip-1404

Substituting a recommended compound with a non-recommended compound can have unintentional consequences. An example of this is when an operator substituted a lubricant with a non-lubricant during an installation of a threaded rod end. The procedures only called for grease on the threaded rod end. The operator’s intent was to enhance corrosion protection but instead he unknowingly affected the preload on the threaded connection by using the torque value for threads with lubricant. This led to premature thread wear (see image below). Unfortunately the damage remained undetected until the threads eventually failed in flight causing loss of control and resulting in a fatal aircraft accident.  

See the linked photo. https://www.faasafety.gov/files/notices/2014/Jun/Worn_Threads.pdf

Are you following the manufacturer’s procedure for the use of a particular compound on the threads of a threaded connection? Are you absolutely sure? Beware that substituting a lubricant with a non-lubricant can affect the preload on the threads and can result in premature thread wear and ultimately thread failure. Furthermore, substituting a non-lubricant with a lubricant can lead to excessive loading on the threads and can also result in thread failure. Either of these may affect the required torque on the threaded connection.
 
The sinister thing is that failures may be latent and might be catastrophic. Review the procedures for the equipment you work on or have worked on. Advise your fellow mechanics and the operator about using the correct compounds that are called for by the manufacturer’s recommended procedures. Add the torque procedures or highlight them on work instructions, checklists or work cards. Finally, if a compound is to be substituted, be sure you know how it will affect the torque value. The best practice is to (first) verify with the manufacturer that it is a suitable substitute. If there is any doubt, check it out!

The National FAA Safety Team values your input. We would appreciate your input using the websites below.
http://www.faa.gov/about/office_org/headquarters_offices/avs/stakeholder_feedback/afs/field/sf_faasteam/


 

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