A bell 407 with two reports of a vertical vibration in cruise was inspected a second time and found ...

Attributes
ACN	570760
Time
Date	200301
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	agl single value : 3000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	common carrier : charter
Make Model Name	Bell 47
Operating Under FAR Part	Part 135
Flight Phase	cruise : level
Flight Plan	VFR
Person 1
Affiliation	company : charter
Function	flight crew : single pilot
Qualification	pilot : commercial pilot : instrument
Experience	flight time last 90 days : 91 flight time total : 5000 flight time type : 2540
ASRS Report	570760
Person 2
Affiliation	other
Function	maintenance : technician
Events
Anomaly	aircraft equipment problem : critical other anomaly other
Independent Detector	other flight crewa
Resolutory Action	none taken : detected after the fact
Consequence	other other
Supplementary
Problem Areas	Environmental Factor Aircraft Chart Or Publication
Primary Problem	Aircraft

Narrative:

While conducting the 21ST flight of the day part 135 operation to an offshore location solo, with no cargo in a bell 407 to pick up personnel, a slight vertical vibration was noted in cruise flight. The vibration was not severe, however since it had not been noticed previously the determination was to make a precautionary landing (19 miles south, 174 degree of ZZZ to inspect the aircraft. During the landing phase, below translational lift the vibration was not noted. After shutdown a thorough inspection of the aircraft was made. The inspection included the control tubes, transmission mounts, landing gear, rotor blades and the possibility of a bird strike. No damage or discrepancies were noted. The aircraft was run-up and hovered with no vibration and the determination that the aircraft was airworthy was made. The aircraft was flown back to ZZZ. During the return flight the vibration was noted again in cruise flight. The aircraft was landed and the vibration was recorded as a discrepancy in the aircraft logbook. During maintenance inspection a crack was found on the mast of the aircraft. Callback conversation with reporter revealed the following information: the reporter stated the aircraft was a bell 407 and was built in 1996 and is operated and maintained in a part 135 operation. The reporter said a slight vertical vibration was noted in cruise and a precautionary landing was made. The aircraft was inspected, run up and test hovered with no vibration. The reporter stated the helicopter was flown to the base and the vibration was again noted and written up in the log. The reporter said an inspection was made and the rotor mast was found at first to be cracked 120 degrees but the crack continued under the paint to a total of 60 degrees around the mast circumference. The reporter stated this was the first incident of a cracked rotor mast known to our maintenance organization.

Original NASA ASRS Text

Title: A BELL 407 WITH TWO RPTS OF A VERTICAL VIBRATION IN CRUISE WAS INSPECTED A SECOND TIME AND FOUND THE ROTOR MAST CRACKED 60% AROUND THE CIRCUMFERENCE.

Narrative: WHILE CONDUCTING THE 21ST FLT OF THE DAY PART 135 OPERATION TO AN OFFSHORE LOCATION SOLO, WITH NO CARGO IN A BELL 407 TO PICK UP PERSONNEL, A SLIGHT VERTICAL VIBRATION WAS NOTED IN CRUISE FLT. THE VIBRATION WAS NOT SEVERE, HOWEVER SINCE IT HAD NOT BEEN NOTICED PREVIOUSLY THE DETERMINATION WAS TO MAKE A PRECAUTIONARY LNDG (19 MILES S, 174 DEG OF ZZZ TO INSPECT THE ACFT. DURING THE LNDG PHASE, BELOW TRANSLATIONAL LIFT THE VIBRATION WAS NOT NOTED. AFTER SHUTDOWN A THOROUGH INSPECTION OF THE ACFT WAS MADE. THE INSPECTION INCLUDED THE CTL TUBES, XMISSION MOUNTS, LNDG GEAR, ROTOR BLADES AND THE POSSIBILITY OF A BIRD STRIKE. NO DAMAGE OR DISCREPANCIES WERE NOTED. THE ACFT WAS RUN-UP AND HOVERED WITH NO VIBRATION AND THE DETERMINATION THAT THE ACFT WAS AIRWORTHY WAS MADE. THE ACFT WAS FLOWN BACK TO ZZZ. DURING THE RETURN FLT THE VIBRATION WAS NOTED AGAIN IN CRUISE FLT. THE ACFT WAS LANDED AND THE VIBRATION WAS RECORDED AS A DISCREPANCY IN THE ACFT LOGBOOK. DURING MAINT INSPECTION A CRACK WAS FOUND ON THE MAST OF THE ACFT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE ACFT WAS A BELL 407 AND WAS BUILT IN 1996 AND IS OPERATED AND MAINTAINED IN A PART 135 OP. THE RPTR SAID A SLIGHT VERTICAL VIBRATION WAS NOTED IN CRUISE AND A PRECAUTIONARY LNDG WAS MADE. THE ACFT WAS INSPECTED, RUN UP AND TEST HOVERED WITH NO VIBRATION. THE RPTR STATED THE HELICOPTER WAS FLOWN TO THE BASE AND THE VIBRATION WAS AGAIN NOTED AND WRITTEN UP IN THE LOG. THE RPTR SAID AN INSPECTION WAS MADE AND THE ROTOR MAST WAS FOUND AT FIRST TO BE CRACKED 120 DEGS BUT THE CRACK CONTINUED UNDER THE PAINT TO A TOTAL OF 60 DEGS AROUND THE MAST CIRCUMFERENCE. THE RPTR STATED THIS WAS THE FIRST INCIDENT OF A CRACKED ROTOR MAST KNOWN TO OUR MAINT ORGANIZATION.

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.

A bell 407 with two reports of a vertical vibration in cruise was inspected a second time and found the rotor mast cracked 60% around the circumference.