Robinson R44 – Engine Mount Bolt Head Sheered Off

Submitted by: AK

This was on an R44 Raven II. During pre-flight/Daily/DI I found a washer on the fairing/deck below the engine when looking through the aircraft's left cowling (where you check the oil). When I looked for the source of the washer I discovered one of the cadmium plated screws that hold the block for the engine mount had sheared at the head and was being held on only by the lockwire.

Additional Photos

Maintenance Notes

Outcome: Grounded

Replacement screws were obtained and put in. It is believed (still waiting for a response from Robinson) that this issue was from a phenomenon called 'hydrogen embrittlement' which can happen to any metal where hydrogen is introduced during the manufacturing process. It happens at a higher rate in cadmium plated metals.

These notes reflect reported observations at the time of submission and are provided for educational purposes only. They are not a determination of airworthiness and do not constitute maintenance or regulatory advice.

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