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Contents

Illustrated technical information covering Vol 2 Over 800 multi-choice systems questions Close up photos of internal and external components Illustrated history and description of all variants of 737 Databases and reports of all the major 737 accidents & incidents History and Development of the Boeing 737 - MAX General flightdeck views of each generation of 737's Technical presentations of 737 systems by Chris Brady Detailed tech specs of every series of 737 A collection of my favourite photographs that I have taken of or from the 737 Press reports of orders and deliveries Details about 737 production methods A compilation of links to other sites with useful 737 content Study notes and technical information A compilation of links to major 737 news stories with a downloadable archive A quick concise overview of the pages on this site

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EASA and Transport Canada requested “design enhancements” to the MAX beyond the fixing of MCAS. The requested changes and Boeings responses are:

A Third AoA Source

Although the revised MCAS now has split vane monitor and Mid Value Select (MVS) input from the AoA probes, there are still only two probes on the aircraft so the FCCs do not know which one to trust in the event that one misbehaves. It is probably significant that this concern is raised by EASA and the Airbus has three AoA probes. EASA is not insisting upon a third probe but instead agreed to a synthetic sensor which computes AoA data from a variety of other existing sources on the aircraft. Boeing already uses synthetic airspeed on the 787 so this is achievable, albeit expensive and time-consuming.

Mike Fleming, senior vice president of the 737 MAX return to service, Commercial Customer Support and Commercial Derivative Programs said in November 2021 that "The enhanced system will monitor five different parameters, that will help us determine whether we have an erroneous signal or not. And then if we determine that we have an erroneous signal, then we'll suppress that and you won't get the issue.”

Boeing has agreed to introduce synthetic AoA with the MAX-10 and then retrofit it to the rest of the MAX fleet. Boeing completed the synthetic AoA critical design review in October 2021 and will flight test it in 2022. When certified, it will then be retrofitted to the rest of the MAX fleet.

Silencing the Stick Shaker

In both MAX accidents the stick shaker was erroneously active throughout the entire flight from takeoff to impact. The fix to MCAS does not address the issue that a single erroneous AoA sensor can cause continuous activation of the stick shaker. This was deemed unacceptable by EASA and Transport Canada who requested a way for crew to silence these warnings, either by pulling circuit breakers or an inhibitor, if the crew consider them to be erroneous. This would reduce noise and stress levels in the flightdeck thereby making the situation easier to handle.

This issue was addressed by the FAA and EASA in their "ungrounding" ADs which are described here. A significance difference of opinion still exists between the regulators.

Boeing also announced in 2021 that they were adding a stall warning inhibitor switch.

Confusing Multiple Warnings

In both MAX accidents multiple warnings were generated as a result of a single AoA fault. EASA believe that this is unsatisfactory. It is possible that EASA are again comparing the non-EICAS 737 with the A320 and its ECAM system which tries to prioritise multiple failures to assist the crew. How this can be achieved with a master caution system is hard to know.

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*** Updated 14 Nov 2021 ***

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For a full description of MCAS see this video presentation:

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