How to address LH-DCPC issues in Challenger 3x0
Effectivity: Challenger 300 and Challenger 350 aircraft
ATA: 24-61
By: Abderrahman Karra - Technical Services Introduction
The Direct Current Power Center (DCPC) system is a critical component of the electrical system in Bombardier Challenger 300 and Challenger 350 aircraft. It distributes and controls the DC power from various sources – such as batteries, generators and external power – to the electrical loads on the aircraft. The DCPC system consists of three units: the left DCPC (LH-DCPC), the right DCPC (RH-DCPC) and the auxiliary DCPC (AUX-DCPC), each with its own card cage and printed circuit boards (PCB).
Since 2011, several cases of electrical system misleading indications and partial or complete loss of electrical power have been reported to Bombardier. These issues were caused by contamination of the LH-DCPC card cage and PCB, which resulted in intermittent or permanent short circuits between the PCB traces. The contamination could be caused by dust, moisture or corrosion.
This type of failure has led to misleading indications which could include flickering or erroneous OFF indications of the push button annunciators (PBA) on the electrical system control panel (ECP), as well as erroneous messages on the engine indication and crew alerting system (EICAS) and the electrical synoptic page. These indications could vary depending on the severity and location of the short circuit and could occur on ground or in flight. The pictures below show some examples of these indications.
If the crew attempts to manually reset the DC source(s) (shown OFF) during these misleading indications, this can lead to the partial or complete loss of the electrical system. In specific cases where the short circuit affected the power supply to the LH-DCPC itself, this could result in a loss of essential systems and equipment, such as flight controls, navigation, communication and lighting.
To address these issues, several service bulletins (SBs) and airworthiness directives (ADs) have been issued, as well as a Time Limits/Maintenance Checks (TLMC). These documents require operators to inspect, replace or modify their LH-DCPC units.
Service Bulletins
Bombardier has issued four SBs related to the DCPC system issues:
SB 100-24-29 and SB 350-24-004 (applicable to the Challenger 300 and Challenger 350 aircraft respectively): These SBs require operators to replace their LH-DCPC units with Y08 units that have been thoroughly cleansed of any contaminants.
SB 100-24-030 and SB 350-24-005 (applicable to the Challenger 300 and Challenger 350 aircraft respectively): These SBs require operators to install a protective tape on the deeply cleaned LH-DCPC card cage to prevent further ingress of contaminants.
Airworthiness Directives
Three aviation authorities have issued ADs that mandate compliance with the SBs mentioned above:
Transport Canada (TC) AD CF-2023-35: This AD summarizes directives from previous ADs and adds the requirement to apply a protective tape on the LH-DCPC card cage as per SB 100-24-030 or SB 350-24-005. It also sets the threshold for compliance at 3,500 flight hours.
European Union Aviation Safety Agency (EASA) AD CF-2023-35: This AD is identical to Transport Canada AD CF-2023-35.
Federal Aviation Administration (FAA) AD 2023-11-01: This AD introduces SB 100-24-29, SB 350-24-004, SB 100-24-030, and SB 350-24-005 and defines the threshold for the units at 3,100 flight hours (FH). It is expected that in this situation, the units should reach 3,500 FH by Dec. 31, 2023, which aligns with the service bulletins’ requirement.
Time Limits and Maintenance Checks
TLMC 05-10-20 (Applicable to Y04, Y05, Y06 and Y07 LH-DCPCs): For DCPCs with less than 3,500 hours COMPONENT, this task must be accomplished at, or before, 3,500 hours COMPONENT or within 12 months from the date of Aug. 9, 2023, whichever comes later.
