ATA 34: Troubleshooting EFIS CAS Alerts After a Storm

October 2011

A Duncan Aviation customer had a morning departure from Lincoln, NE, and requested their aircraft to be staged for passenger pickup. While the aircraft was in Lincoln, a driving thunderstorm had passed through the area. The flight crew arrived after the storm and began to perform their pre-flight inspection. During pre-flight an amber EFIS crew alerting system (CAS) message posted. At the same time an “ALT” (Altitude) amber box posted on PFDs (PRIMARY Flight Display) altitude tape. These messages occur when there is a difference between the Pilot/Co-Pilot barometric altitudes greater than 60 feet.

After performing the standard shutdown and reboot of the aircraft to clear the fault, the CAS message still posted. The maintenance data computer (MDC) was interrogated and Label 350 bit 20 was set (internal pitot static sensor failed). This prompted a visual inspection of the pitot static probes in addition to verifying water drain traps. The pitot static probes were in limits and no water was noted in the pitot static water drain traps.

To further investigate, a pitot static testing was performed. The system was pumped up to 250 knots at an altitude of 18,000 feet. Another visual inspection of the water traps discovered water in them. The water was drained out and the MDC was interrogated again and no labels were posted and all related CAS messages were cleared. Pitot static system was recertified. The aircraft has made numerous trips with no reoccurrences of fault.