What happened
On 18 July 2012, a Jetstream 4100, registration G-MAJA, was operating a scheduled passenger flight from Southampton to Aberdeen. While cruising at 22,000 feet approximately 80 nautical miles north of Newcastle, the aircraft entered an area of airframe icing and light turbulence. During this period, the Electronic Flight Instrument System (EFIS) screens began to blank, and the autopilot disconnected.
The crew attempted to rectify the issue by following the Quick Reference Handbook (QRH) checklist, which involved switching between symbol generators. However, these actions failed to restore the displays. Shortly after, all three remaining EFIS screens went blank. The commander took manual control of the aircraft, relying on the standby instruments and the main altimeter located on the left side of the panel.
Due to the unsuitability of the weather ahead, the crew declared a PAN to Air Traffic Control and elected to divert to Newcastle International Airport. During the descent, the crew noted that the standby compass appeared stuck. After resetting the avionic master switches, the EFIS screens partially recovered, displaying the compass rose and speed tape. The aircraft subsequently completed a visual approach and landed safely at Newcastle.
The investigation
The AAIB examined the aircraft at Newcastle, finding no evidence of a lightning strike. Technical analysis focused on the windscreen heating circuit. The aircraft was equipped with 'transzorbs'—electrostatic transient absorbers designed to prevent EFSD blanking by absorbing static charge accumulation on the windscreens.
Laboratory testing revealed that the left inboard windscreen anti-ice transzorbs had failed but maintained residual resistance. This specific failure mode meant the windscreen anti-ice controller could not detect the malfunction, leaving the avionics vulnerable to electrostatic discharge.