During the investigation of a recent serious incident, the Dutch Safety Board (DSB) found a “factor of interest” — an uncommanded climb and subsequent activation of the aircraft’s stick-shaker (stall-warning) system during an autopilot-coupled approach.
This finding prompted a follow-up investigation that revealed previously unknown and potentially dangerous idiosyncrasies of instrument landing system (ILS) signals.
The aircraft, a Boeing 737-800, was inbound from Palma de Mallorca, Spain, to Eindhoven, Netherlands, with 124 passengers and seven crewmembers the morning of May 31, 2013.
The flight crew was receiving radar vectors for the ILS approach to Runway 21 at Air Base Eindhoven, a joint-use facility operated by the Royal Netherlands Air Force. Instrument meteorological conditions prevailed, and the crew had the autothrottle and the autopilot engaged with the approach mode armed, according to the DSB report.
A key element in the incident was that the aircraft remained …
