Improvement of a High-Level Sensor

Effectivity: Challenger 300 and Challenger 350 

ATA code: 28-41 

By:  Jean Felix D’Souza Department- Aircraft Systems, Technical Services, Global / Challenger Series 

Bombardier would like to inform operators of an improved High-Level Sensor (HLS) part number 722707-1-0 that is gradually making its way into the fleet.  

Following an increased number of failures in operation, the Advisory Committee launched an investigation. The failed sensor would cause a steady "ON" HLS light on the Refuel/Defuel panel, regardless of the quantity of fuel present in the tank.  

A campaign was launched in April 2017 to encourage operators and maintenance personnel to return – instead of discard – units that failed the HLS investigation. Thanks to this campaign, an analysis of the returned units was completed, which revealed some defects inside the sensors. A closer internal examination of the sensor revealed solder failures of various electrical components on the electrical board. The likely cause was attributed to thermal expansion of the compound used internally to seal the unit.  

As described in AW 300-28-0269 Rev 02, a new compound was required to seal the unit. This new compound has a better environmental effect, better dielectric strength and a lower thermal expansion coefficient. Consequently, the compound lowers the stress on the sensor’s internal components.  

The new compound was introduced on HLS with serial number 2400 and up. The first aircraft with the improved sensor was delivered at the end of August 2020. Operators in service who order a new HLS from Bombardier will receive the improved sensor.