Incident Overview
On April 5, 1998, during a scheduled flight from Lyon to Frankfurt, an Airbus A320-200 operating as a commercial airliner encountered a significant technical disturbance while in a holding pattern near Frankfurt/Main Airport. The event was classified as a serious incident with no injuries or physical damage to the aircraft.
Technical Failure and Pilot Response
Under instrument meteorological conditions characterized by heavy icing, rain, and turbulence, the speed indicators on both Primary Flight Displays (PFD) and the standby instrument failed simultaneously. This loss of data caused the automatic flight control systems, including the autopilot and auto-throttle, to disengage. The Electronic Centralized Aircraft Monitor (ECAM) displayed various warnings.
The Pilot in Command (PIC), who had been monitoring a trainee captain, immediately took manual control. He stabilized the aircraft at 10,000 feet using pitch and power references. Within seconds, 2 to 3 cm of ice accumulated on the ice indicator. The speed indications returned shortly after stabilization. As a precautionary measure, the PIC manually switched the pitot heat system from automatic to on.
Investigation Findings
The German Federal Aviation Office (BFU) investigated the incident in cooperation with the operator and maintenance providers. Flight Data Recorder (FDR) data initially showed a 14-second interruption for System 1, while the autopilot was disconnected for 59 seconds. However, analysis of the Total Air Temperature (TAT) from System 2 confirmed that the speed signal loss affected multiple systems simultaneously, supporting the pilot's account of a longer duration than recorded by the FDR.
Maintenance inspections following the event found no blockages in the pitot tubes' drainage holes. The investigation concluded that ice accumulation blocked the pressure holes in the pitot tubes, causing the failure. This issue was linked to a known design limitation regarding severe icing conditions, which had been previously reported by other operators and addressed in Service Information Letter 34-047.
Conclusions and Recommendations
The BFU determined that the root cause was a design deficiency in the pitot tubes, as no operational restrictions for heavy icing were defined for this aircraft model. Safety recommendations included modifying pitot tube specifications to allow unrestricted flight in severe rain and icing conditions and mandating special maintenance procedures when multiple redundant systems fail simultaneously.