AWB 29-1 Issue 1, Hydraulic Filter Assembly Indicator Buttons
Hydraulic Filter Assembly Indicator Buttons
AWB 29-1 Issue 1, 10 October 2003
Bell 206 Jet Ranger helicopters that have hydraulic filter assemblies with pressure differential indicator buttons.
To alert maintainers and operators to the possibility that the hydraulic filter blockage indicator buttons may not be capable of functioning in accordance with the filter design.
Defect reports received by CASA show that these indicator buttons may become stuck in the "OK" or flush position. The filter may then become blocked without an associated warning. That is, the indicator button may not pop up to show that the pressure differential has increased to an unacceptable level. If the filter becomes fully blocked, loss of hydraulic pressure to the flight controls would result.
The pressure differential indicator buttons have become stuck or seized due to grit, dirt and corrosion between the button and the housing in which it moves.
If the hydraulic system is serviced in accordance with the manufacturer's instructions, and no blockages occur, it is possible that inoperative indicator buttons would not be discovered.
Since the Bell maintenance program does not currently contain a requirement to functionally check the operation of the hydraulic filter indicator button, it is recommended that operators incorporate a periodic functional check / inspection in the maintenance program in order to ensure that the indicator button pops up at the specified pressure differential.
Operators may send the housing back to the filter manufacturer for testing, or alternatively, develop an approved method of functionally testing the indicator.
Enquiries with regard to the content of Airworthiness Bulletins should be made via the direct link e-mail address included on the Airworthiness Bulletin web site, AirworthinessBulletin@casa.gov.au or in writing to Airworthiness Standards Branch, GPO Box 2005, Canberra, ACT, 2601