… if the cockpit designers of our two main competitors or their avionics suppliers conducted an in-depth testing of their respective man-machine-interface?
Yes, there were extensive human factors based evaluation programmes in order to meet the requirements of CS 25.1302 and AMC 25.1302.
The main regulation states:-
(d) To the extent practicable, installed equipment must enable the flight crew to manage errors resulting from the kinds of flight crew interactions with the equipment that can be reasonably expected in service, assuming the flight crew is acting in good faith. This sub-paragraph (d) does not apply to skill-related errors associated with manual control of the aeroplane.”
Note the last sentence.
For info, the background information in the AMC states:-
“Flight crews make a positive contribution to the safety of the air transportation system because of their ability to assess continuously changing conditions and situations, analyse potential actions, and make reasoned decisions. However, even well trained, qualified, healthy, alert flight-crew members make errors. Some of these errors may be influenced by the design of the systems and their flight crew interfaces, even with those that are carefully designed. Most of these errors have no significant safety effects, or are detected and/or mitigated in the normal course of events. Still, accident analyses have identified flight crew performance and error as significant factors in a majority of accidents involving transport category aeroplanes.
Accidents most often result from a sequence or combination of errors and safety related events (e.g., equipment failure and weather conditions).”
And the AMC allows the designer to assume that the crew is qualified and trained in the use of the installed equipment.