This is some of the content from the Sikorsky Safety Advisory (SSA) that came out for operators. I don't think it takes too much reading between the lines to see that there is no need for an AD! Good job by the crew
1. Introduction
An S-92 helicopter operator reported loss of tail rotor control in flight following replacement of the Tail Rotor Pitch Change Shaft. Inspection revealed that the pitch change shaft nut and washer were missing after the flight.
WARNING
When performing maintenance manual SA S92A-AMM-000 Task 64-22-01-900-002, Installation of Tail Rotor Pitch Beam Assembly, make certain that the procedure is performed in its entirety. Failure to follow all steps may lead to loss of the pitch change shaft nut and washer and may lead to loss of tail rotor control.
2. Corrective Action
To preclude loss of tail rotor control after maintenance of the Tail Rotor Pitch Change Shaft or Tail Rotor Pitch Beam Assembly, adhere to procedures in maintenance manual SA S92A-AMM-000 Task 64-22-01-900-002, Installation of Tail Rotor Pitch Beam Assembly.
It's a pity there is such secrecy by the operator though. Hopefully in due course some of the circumstances surrounding the error will be made public and can be incorporated into Engineering Human Factors courses etc. Similar examples would be the Bond AS332 high speed shaft misassembly (leading to overspeed and shutdown while doing a topping check with the other engine in idle!) a few years ago, and the BMI A320 mag plugs with missing oil seals (leading to total oil loss on both engines.) Both of these incidents feature heavily in human factors courses, and have lead to changes in practices that are designed to prevent re-occurrence.