ABSTRACT
One morning in October 1996, a TWR-controller at Schiphol Airport (Amsterdam, The Netherlands) observed that an inbound aircraft was deviating from the ILS localiser. This observation was done on an electronic Traffic Situation Display, for at the time the cloud base was around 200 feet AGL while the height of the tower is 300 feet - in other words, the tower was in IMC (Instrument Meteorological Conditions). The visibility (Runway Visual Range) was approximately 500 meters.
