Boeing updates flight-control software -------------------------- Changes to Boeing’s 737 MAX flight-control software prevent the system from activating in case of erroneous data from angle-of-attack (AOA) sensors and give pilots complete nose-down stabilizer command --------------------------- Manoeuvring Characteristics Augmentation System (MCAS): Previous anti-stall system used data from single angle-of-attack sensor to detect if plane was climbing too steeply and risking stall Horizontal stabilizer Controls up-and-down 1pitch of nose Angle-of-attack sensor: One on each side of nose CFM Leap 1B 1 AOA sensors: Data from both left and right sensors to be compared continuously. If data vary by 5.5 degrees, software will inhibit MCAS from trimming horizontal stabilizer for remainder of flight. 10-degree variation alerts crew Yoke Stick-shaker Yoke vibrates if approaching stall AIR FLOW 2 Stabilizer control: Crew can override MCAS using trim switches on yoke. MCAS will allow only single stabiliser trim for each new AOA data trigger – previously erroneous nose-down trim could restart 5 seconds after trim switches were released 3 Runaway Stabilizer: Crew can override MCAS by activating stabiliser cut-out switches and using manual trim wheels. Upgrade stops MCAS from applying more nose-down trim than can be countered by pilot pulling back on yoke Trim wheel Trim wheel 1 2 3 ---------------------------------- Sources: Aviation Week & Space Technology, Boeing Bulletin TBC-19 © GRAPHIC NEWS