A sikorsky S76 suffers a broken main rotor hub causing vibration.

Attributes
ACN	536946
Time
Date	200202
Day	Fri
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : zzz.airport
State Reference	CA
Altitude	msl bound lower : 500 msl bound upper : 4500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zhu.artcc
Operator	general aviation : corporate
Make Model Name	S-76/S-76 Mark II
Operating Under FAR Part	Part 91
Flight Phase	cruise : level
Flight Plan	None
Person 1
Affiliation	company : corporate
Function	flight crew : captain oversight : pic
Qualification	pilot : multi engine pilot : instrument pilot : commercial pilot : cfi pilot : atp
Experience	flight time last 90 days : 150 flight time total : 14000 flight time type : 4000
ASRS Report	536946
Person 2
Affiliation	company : corporate
Function	flight crew : first officer
Events
Anomaly	aircraft equipment problem : critical non adherence other other anomaly other
Independent Detector	other flight crewa
Resolutory Action	flight crew : landed in emergency condition
Consequence	other
Supplementary
Problem Areas	Company Aircraft
Primary Problem	Aircraft

Narrative:

Ears that hold main rotor damper to the main rotor hub broke allowing damper to rotate 180 degrees and strike the main rotor blade. The aircraft gave a moderate shudder and began a moderate 1 to 1 vibration with vertical and lateral components. My copilot and I discussed the possible sits, there were several structures in site but none were known to be suitable for our size of aircraft or known to be clear. We were 8 mins from our intermediate stop which we knew was suitable and clear. We reduced speed slightly and began a descent. The vibration decreased slightly so I decided to descend to 500 ft where we would be close to the surface for ditching if things got worse. I decided to continue to the known structure for a precautionary landing. We landed without incident. Callback conversation with reporter revealed the following information: there was an alert bulletin from the manufacturer for an inspection of the hub. However this aircraft had not been done yet. The hub rotated on its 1 remaining fitting doing damage to the trailing edge of 1 rotor.

Original NASA ASRS Text

Title: A SIKORSKY S76 SUFFERS A BROKEN MAIN ROTOR HUB CAUSING VIBRATION.

Narrative: EARS THAT HOLD MAIN ROTOR DAMPER TO THE MAIN ROTOR HUB BROKE ALLOWING DAMPER TO ROTATE 180 DEGS AND STRIKE THE MAIN ROTOR BLADE. THE ACFT GAVE A MODERATE SHUDDER AND BEGAN A MODERATE 1 TO 1 VIBRATION WITH VERT AND LATERAL COMPONENTS. MY COPLT AND I DISCUSSED THE POSSIBLE SITS, THERE WERE SEVERAL STRUCTURES IN SITE BUT NONE WERE KNOWN TO BE SUITABLE FOR OUR SIZE OF ACFT OR KNOWN TO BE CLR. WE WERE 8 MINS FROM OUR INTERMEDIATE STOP WHICH WE KNEW WAS SUITABLE AND CLR. WE REDUCED SPD SLIGHTLY AND BEGAN A DSCNT. THE VIBRATION DECREASED SLIGHTLY SO I DECIDED TO DSND TO 500 FT WHERE WE WOULD BE CLOSE TO THE SURFACE FOR DITCHING IF THINGS GOT WORSE. I DECIDED TO CONTINUE TO THE KNOWN STRUCTURE FOR A PRECAUTIONARY LNDG. WE LANDED WITHOUT INCIDENT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THERE WAS AN ALERT BULLETIN FROM THE MANUFACTURER FOR AN INSPECTION OF THE HUB. HOWEVER THIS ACFT HAD NOT BEEN DONE YET. THE HUB ROTATED ON ITS 1 REMAINING FITTING DOING DAMAGE TO THE TRAILING EDGE OF 1 ROTOR.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.