Owners, operators and maintainers of Bell 206/206L/407 helicopters
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The purpose of this Civil Aviation Safety Alert is to alert operators of:
- the vulnerability of the main transmission freewheel lubrication system to contamination
- to emphasize how critical it is to ensure a conforming filter is installed
- to follow the manufacturer's recommended procedures for aircraft storage and reactivation
There have been two accidents involving model 206 helicopters where a malfunction of the main transmission freewheel system led to a failure of the main rotor mast. In both occurrences, the failure occurred after landing and led to separation of the main rotor blades, rotor hub and a portion of the mast from the helicopter.
The investigations of these two accidents revealed that contamination of the freewheel lubrication system was the root cause. In one case, the contaminant was a piece of sealant that had probably been introduced during maintenance of the system. In the other case, the contaminants were corrosion products generated within the transmission oil system.
Bell Helicopter Textron Canada (BHTC) has released Alert Service Bulletins (ASB) for each affected helicopter model. The ASBs provide instructions to:
- Inspect the filter and restrictors in the freewheel lubrication system of all helicopters to confirm they are free of contaminants. If contaminants are found, the ASBs provide instructions to determine if critical components have been adversely affected by loss of lubrication.
- Install a filter in the freewheel lubrication system if that filter was not installed during production or retrofitted by incorporation of a technical bulletin. This filter protects the downstream components from contamination.
- Inspect the filter and restrictors in the freewheel lubrication system to confirm they are free of contaminants any time an opening occurs to the freewheel oil supply system between the restrictors and the filter. Opening is defined in the ASBs as any time there is a detachment of any fitting, hose or component of the freewheel oil supply system upstream of the restrictor where contamination could enter the oil supply.
Transport Canada has issued Airworthiness Directive CF-2016-13 to mandate compliance with the BHTC ASBs. This will substantially reduce the risk of a recurrence of an accident caused by loss of lubrication to the freewheel assembly. However there continues to be a risk associated with improper preservation and reactivation. Corrosion products generated from within the transmission lubrication system because of improper preservation may accumulate at the filter, block lubrication flow and lead to failure of the freewheel system.
In 2005, Bell issued Information Letter 206L-05-78 to inform operators of the 206L series helicopter that in some filter units 50-075-1, the screen portion of the filter was not manufactured with the correct number of holes. Testing has confirmed this condition is not detrimental to the normal operation of the transmission and freewheel oil system. However, BHTC recommended that filter units with an incorrect hole pattern be identified and replaced. A non-conforming filter would be more vulnerable to clogging and in the event of storage-related contamination could increase the risk of loss of lubrication.
It is recommended that operators of the affected helicopters:
- Follow the procedures for preservation and reactivation contained in Chapter 10 of the Bell Standard Practices Manual
- Document completion of these actions in helicopter maintenance records
- Perform the inspection specified in Part I of the following Bell ASBs when reactivating a helicopter from storage if there is any doubt whether proper preservation procedures were followed:
- Models 206A/206B: ASB 206-14-132
- Models 206L/206L-1, 206L-3 and 206L-4: ASB 206L-14-174
- Model 407: ASB 407-14-106
- Review BHTC Information Letter 206L-05-78, determine if it is applicable to their helicopter and, if applicable, perform the actions specified in the Information Letter to identify and replace filters with an incorrect hole pattern. Completion of these actions should be documented in the helicopter maintenance records.
For more information concerning this issue, contact a Transport Canada Centre; or contact Ross McGowan, Continuing Airworthiness in Ottawa, by telephone at 1-888-663-3639, by fax at 613-996-9178 or by e-mail at CAWWEBFeedback@tc.gc.ca.
ORIGINAL SIGNED BY
THE TRANSPORT CANADA CIVIL AVIATION SAFETY ALERT (CASA) IS USED TO CONVEY IMPORTANT SAFETY INFORMATION AND CONTAINS RECOMMENDED ACTION ITEMS. THE CASA STRIVES TO ASSIST THE AVIATION INDUSTRY'S EFFORTS TO PROVIDE A SERVICE WITH THE HIGHEST POSSIBLE DEGREE OF SAFETY. THE INFORMATION CONTAINED HEREIN IS OFTEN CRITICAL AND MUST BE CONVEYED TO THE APPROPRIATE OFFICE IN A TIMELY MANNER. THE CASA MAY BE CHANGED OR AMENDED SHOULD NEW INFORMATION BECOME AVAILABLE.
Importance of proper storage practices
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