Take care to prevent accidental APU fire extinguisher discharge

Effectivity: Learjet 60 aircraft equipped with APU  

ATA: ​26 - Fire Protection​ 

By: Chris Hyde – Customer Services Engineering 

Extra care should be taken when operating the auxiliary power unit (APU) on the Learjet 60 aircraft to avoid accidental discharge of the fire extinguisher. Inadvertent discharges are the leading cause for unscheduled removals.   

The Learjet 60 APU cockpit control panel contains a guarded switch which delivers fire detection notification and fire extinguisher discharge. The switch illuminates when an APU fire is detected. The guard must be raised and the switch depressed to discharge the fire extinguisher.   

The APU fire detect/extinguisher discharge switch is active any time that the main aircraft batteries are selected on. Raising the guard and depressing the switch will discharge the fire extinguisher, regardless of APU master switch position.  

Other aircraft platforms may not be configured this way and may have a guarded APU start switch. Learjet is currently evaluating switch identification or marking methods that could help prevent accidental discharges.  

For additional information or questions, please contact your regional Field Service Representative.