S291 Momentary Timed Switch

 Effectivity: Global 7500 and Global 8000 aircraft     

 ATA: 33 

 By: David Gosselin - Technologist Specialist, Engineering   

The Momentary Timed Switch (P/N: G03300110-103) is installed at 13 locations throughout the Global 7500 aircraft and combines three key functions: door position monitoring, service light control and an automatic timer feature. 

One of its most critical applications is the Refuel/Defuel Service Door Switch (S291), where it also provides the door-status and power logic required by the refueling system. When the switch becomes intermittent at this location, refueling operations can be disrupted, resulting in significant operational impact and increased aircraft downtime. If the Refuel/Defuel Service Door Switch (S291) fails, refueling from the External Refuel/Defuel Panel (RDP) becomes unavailable, and the AUTO function of the Virtual Refuel/Defuel Panel (VRP) cannot be used when centre-tank refueling is required. However, refueling of the wing and aft tanks remains possible. For the alternate refueling procedure, please refer to RIL GX-0823 available on the CIC Portal. 

The investigation identified manufacturing-related factors consistent with the intermittent failures reported in service, including design vulnerabilities that increased the switch's sensitivity to mechanical stresses and intermittent electrical contacts. To improve product quality and reliability, the supplier implemented corrective actions to enhance the robustness of the switch design, reducing its susceptibility to mechanical stress and minimizing the risk of intermittent contact failures. 

The improvements produced Momentary Timed Switch (P/N: G03300110-103 S/N: 6393883 & up) implemented in production on aircraft 70232 and up following the stock purge date of January 2025. 

In parallel, Bombardier released IS700-33-7002 – Refuel/Defuel Service Door Switch (S291) Disconnect Addition on the CIC Portal. This modification simplifies replacement of the S291 switch in service by improving accessibility, thereby reducing maintenance time and aircraft downtime. 

Bombardier will continue to monitor field experience and work closely with operators to support product reliability and customer satisfaction.