On 31 May 2013, upon reaching Endhover Airport a Boeing 737-800 was redar vectored to runway 21 for a landing using the instrument landing system (ILS). During the approach, clouds obstructed the view of the ruway in IMS. Within 2 km distance from the runway, a false glide slope' was captured, followed by a pitch-up upset. The incident revealed a characteristic of the ILS that had previously been unknown. The DSB launched an investigation into the Eindhoven incident and after concluding that the event was inconsistent with the existing theories of ILS operations, it launched an investigation into ILS.