History of the Flight
On 7 August 2008, a Raytheon 390 Premier I, registration G-FRYL, departed Copenhagen for Farnborough on a non-revenue commercial air transport flight with two crew and no passengers. Approximately 20 minutes after takeoff, while cruising at FL400 with an outside air temperature of -62°C, the aircraft encountered significant turbulence for about 10 minutes. The commander reduced thrust to decelerate, but noted an unexpectedly rapid decrease in indicated airspeed from 220 to 180 knots on his Primary Flight Display (PFD1). The aircraft climbed to FL410, where conditions were smooth.
During the cruise, an amber IAS comparator message appeared on both PFDs, indicating a disagreement greater than 10 knots between left and right air data systems. The commander interpreted this as an Air Data Computer failure and selected the ADC reversion switch to position 2, aligning both PFDs to ADC2. Before descent, the crew noticed that PFD1, PFD2, and the standby airspeed indicator all indicated the same airspeed.
As descent commenced, all three indicators showed decreasing airspeed, with the rate of decrease varying with descent rate, suggesting a blocked pitot source. The crew declared an emergency and advised ATC of airspeed difficulties. The commander disarmed the stick pusher. At approximately 60 knots IAS, a click was heard, and most PFD information disappeared, replaced by red fail messages. The standby airspeed indicator read zero, but other standby instruments functioned. The Multifunction Display went blank. Below FL150, a combined PFD/MFD presentation appeared on the MFD. The crew cancelled the mayday and flew visually to Farnborough, where the remainder of the flight was uneventful.
Meteorological Information
A complex low-pressure system was present along the route. The flight was mostly in a warm sector, later encountering a cold front near the Kent coast. The coldest temperature encountered was about -61°C at 38,000 ft. AMDAR reports indicated moderate to severe turbulence in the area, possibly transported from thunderstorms over northeast France and the Netherlands. Icing conditions were possible in cirrus containing cumulonimbus anvils.
System Description
The aircraft was equipped with a Rockwell Collins Proline 21 integrated avionics system, including an Integrated Avionics Processor System (IAPS) that manages sub-systems such as the Electronic Flight Instrument System (EFIS), Air Data System, and others. The EFIS consisted of two Primary Flight Displays and one Multifunction Display.
Investigation
The AAIB investigated the incident. The loss of air data information was attributed to a blockage in the right pitot system caused by moisture ingress that subsequently froze. Despite exhaustive testing, the cause of the loss of all three EFIS displays could not be determined. One Safety Recommendation was made.