THIS accident occurred shortly before a Sikorsky S‐16N helicopter was due to depart Sumbrugh on its first flight of the day. The crew of 2 and 16 passengers were embarked. Normal pre‐engine start checks were carried out and after receiving start clearance from ATC, both engines were successively started. The crew encountered no abnormailities during pre‐rotor engagement checks and approximately 1 minutes after starting engines, the rotors were engaged and brought up to 100% rotor speed (Nr) in the usual way. All indications remained normal until an estimated 3–4 minutes later, the crew members became aware of an abnormal whining noise. At the time they were carrying out a standard automatic flight control system check, scheduled prior to the first flight of the day.
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