HS 125 Series
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 70; Flight Crew Total 9000; Flight Crew Type 725
Situational Awareness
Aircraft Equipment Problem Critical; Deviation - Altitude Excursion From Assigned Altitude; Inflight Event / Encounter Other / Unknown
Flight Crew Overcame Equipment Problem
Aircraft
We had a sudden instrument malfunction which caused the Autopilot to dive; then climb abruptly to FL350 before we could recover and return the aircraft to FL340. Center understood and confirmed it was not a problem. They asked us if we would be able to maintain FL340 of which we replied yes; and we had no further problem or deviation. Our EFIS displays rolled down; then up; then started to spin with no direction or orientation. We used basic gauges to take control of aircraft until the EFIS System reset and [were] reliable. There were no further problems. I reported this to the Avionics Shop.
Pilot reports a sudden EFIS System instrument malfunction in a Hawker-Siddeley HS-125 aircraft; caused the autopilot to dive then climb abruptly to FL350 from FL340 before crew could recover. EFIS displays rolled down; then up; then started to spin with no direction or orientation. Crew used basic gauges to take control until EFIS System reset.