I don't know why they didn't cross check sensors. Maybe the changes were perceived as too invasive and someone made the conscious decision that the risk of screwing that up was greater than the potential gain.
The reasoning behind not doing sensor validation was all to do with crew training. The interview with Rick Ludtke
Former Boeing Engineers Say Relentless Cost-Cutting Sacrificed Safety (Bloomberg) documents this.
In a nutshell, the logic was this:
- Invalid sensor = Mandatory warning to crew
- Mandatory crew warning = mandatory Simulator (Level D) training
- Mandatory Simulator Training = unacceptable to the MAX business model (Some Airlines building in penalties from mandatory Simulator training of $1 million per aircraft)
therefore...- No dual channel validity checking
A quote from the interview
Managers didn’t merely insist to employees that no designs should lead to Level D training. They also made their desires known to the FAA team in charge of 737 training requirements, which was led by Stacey Klein, who’d previously been a pilot at now-defunct Skyway Airlines for six years. “She had no engineering background, her airplane experience was very limited,” Ludtke says. “It was just an impossible scenario.” FAA spokesman Greg Martin says the position Klein occupies, “while substantial,” is primarily that of “an organizer, facilitator, and executor of the FAA policy and guidelines,” and that in her role she calls on experts from multiple organizations.
Another from
Forbes
Rick Ludtke, a former Boeing engineer who worked on 737 MAX cockpit features but not the MCAS system, told the Journal that midlevel managers told their staff members that Boeing had committed to paying Southwest Airlines -- which has ordered 280 MAX aircraft -- $1 million per plane if the 737 MAX ended up requiring pilots to spend more time training on simulators.
It really was that simple. This whole crisis was to increase profit by $1 million per airframe in reduced training costs, for some large operators.