UNEXPECTED AUTOPILOT BEHAVIOUR ON ILS APPROACH

UNEXPECTED AUTOPILOT BEHAVIOUR ON ILS APPROACH

 

SAFETY ALERT
Date: November 18, 2013
UNEXPECTED AUTOPILOT BEHAVIOUR ON ILS APPROACH

Potential severe pitch-up upset when intercepting the instrument landing system (ILS) glide slope from above, which can lead to (approach to) stall conditions.
The particulars
• Different types of Instrument Landing System (ILS) glide slope systems are used worldwide. Signal characteristics in the area above the (standard) 3 degree glide slope are system dependent. 
• Similar glide slope capture logic in automatic flight control systems (autopilot) is used for the majority of aircraft types currently in service worldwide.
• While intercepting the ILS glide slope signal from above the 3 degree flight path with 
the automatic flight control system engaged, the aircraft can capture a false glide slope resulting in an unexpected rapid pitch-up command (automation surprise). 
For more details, let this Click on the file attachment.