CAT II / OTS CAT II operations using existing CAT I Ground Based Augmentation System

Flight tests performed in an A330 simulator have shown that the existing standardized Ground Based Augmentation System (GBAS) CAT I could be suitable for CAT II operations if anomalous ionospheric errors induced during solar storms could be mitigated either operationally or technically. Tests in an Airbus A330 Level D (fully certified training simulator) flight simulator were performed by EUROCONTROL in cooperation with Technical University of Berlin, to investigate whether the worst case errors of a GBAS CAT I precision approach system (10m vertical deviation) would still be acceptable for CAT II operations. Additionally similar assessment was performed for the new approach classification termed "Other Than Standard" (OTS) CAT II which allows operation of CAT II approved aircraft down to a decision height (DH) of 100 ft on runways not meeting full Cat II requirements. OTS CAT II relaxes the approach lighting requirements which is compensated by a higher required Runway Visual Range (RVR) and higher guidance performance requirements (i.e. autoland). GBAS CAT I suitability to support OTS CAT II and CAT II operation would provide a new potential benefit for airlines that have invested in a GBAS CAT I system. Those benefits could be increased access to runways served by GBAS in low visibility conditions. It could improve as well traffic flow in low visibility operation by replacing the standard Instrument Landing System (ILS), which requires larger separation on final approach during CAT II/III operations due to technical design. The tests have shown that the existing GBAS CAT I standardized system, with a Vertical Alert Limit (VAL) of 10 m as per ICAO Annex 10, would be operationally suitable for CAT II and OTS CAT II operations. The tests demonstrated that failures up to 10m vertical deviation are operationally acceptable for CAT II operations as the landing point was always well within the landing box criteria used for the demonstration of autoland systems. Lateral deviations were easily detected but pilots expressed difficulty in detecting the vertical errors. Some but not all pilots detected errors larger than 10m (i.e. 15m). The visual cues were sufficient at the decision height (DH) to conduct the OTS CAT II operation. The perception was that due to the increased RVR required for OTS CAT II, the visual cues at DH were even better in OTS CAT II conditions than in standard CAT II conditions.