INCIDENT - HUB-BAR FAILURE

[Waddles]

Gidday All,The pilot of a 2 seat-training gyro noticed that stick shake had suddenly manifested itself in his machine. Numerous attempts were made to locate and rectify the problem to no avail. In response to advice from the manufacturer, he removed and dismantled the rotor system and buffed, then inspected the hub-bar using a magnifying glass. No obvious defects were noted. Approximately 10 hours later, the shake was such that he decided to return the rotors to the manufacturer. During the dismantling and packing process, he noticed a significant crack on one edge of the hub-bar. Closer inspection revealed that the crack extended from about ¼” inboard of a teeter block mounting bolt hole on the upper surface, through the edge of the hub-bar to approximately half the hub-bar width on the lower surface. The rotors had accumulated approximately 200 hours in service on a 2 seat training machine.Metallurgical testing of the failed hub-bar has been authorised in an attempt to determine the cause of the crack and it is unlikely that Airworthiness Alerts or Directives will be issued prior to the receipt of the test results.The rotor system was manufactured by Advanced Kinetics and spanned a 30" diameter with a 1" thick hub-bar. This particular system was the last of a series of systems using this configuration. Subsequently, all AK systems in excess of 28" diameter use 1 1/2" hub-bar material. The manufacturer has undertaken to advise the last known owners of any of the blades still known to be in service.Nonetheless, there may be some cautious pilots out there who will want to have their hub-bars crack tested for their own peace of mind. This being the case, ASRA recommends that AD 2005.01, which is published on this site under Technical Information, be consulted and a copy of this AD supplied to the testing facility at the time the job is presented. It goes without saying, that ASRA will be extremely interested in any test that detect defects.Fly Safe.Allan Wardill.

[NiqueNaque]

Alan,I"m exceptionally pleased this one was caught in time, well done to all involved. As far as I am concerned this is two lives saved from serious injury / death.It goes to show that if you listen to what your gyro is telling you, you might save your own ass. Never ignore a nuance of extra vibration, shake, minor changes of vibration, noise, feel or anything else that might come along, if it feels wrong it is, and no, that is not your intuition playing up... check it out.I"d be interested to see how the teeter block is pinned onto the hub bar in this instance - was it drilled at the diagonals, or was it set so that the drill holes were on the centre of the hub bar?John Evans had his teeter block drilled on the centre line of the hub bar so that the bolt holes were not adjacent the edges and the end result is that the extreme fibre stress is reduced, lead /