Correct. And you could pay for the MCAS to use both sensors which all US airlines did.
Edit: I was misremembering. Both sensors were enabled on all planes and MCAS only used one at a time on all planes.
What was disabled, unless paid for, was software which displayed to the pilots that the 2 sensors were disagreeing, which would immediately have alerted them to what may have been wrong.
> According to Bjorn Fehrm, Aeronautical and Economic Analyst at Leeham News and Analysis, "A major contributor to the ultimate loss of JT610 is the missing AoA DISAGREE display on the pilots' displays."[109]
> The software depended on the presence of the visual indicator software, a paid option that was not selected by most airlines.[110] For example, Air Canada, American Airlines and Westjet had purchased the disagree alert, while Air Canada and American Airlines also purchased, in addition, the AoA value indicator, and Lion Air had neither.[111][112] Boeing had determined that the defect was not critical to aircraft safety or operation, and an internal safety review board (SRB) corroborated Boeing's prior assessment and its initial plan to update the aircraft in 2020. Boeing did not disclose the defect to the FAA until November 2018, in the wake of the Lion Air crash.[113][114][115][116] Consequently, Southwest had informed pilots that its entire fleet of MAX 8 aircraft will receive the optional upgrades.[117][118] In March 2019, after the second accident of Ethiopian Airlines Flight 302, a Boeing representative told Inc. magazine, "Customers have been informed that AoA Disagree alert will become a standard feature on the 737 MAX. It can be retrofitted on previously delivered airplanes."[119]
Boeing: Do you want a two line code which triggers a potentially life-saving warning when your flying sausage with wings has an important sensor malfunction?
Customer: Of course!
Boeing: That'll be $25K, thanks.
Also, no-smoking light toggle labeled Off - Auto - On is being relabeled and rewired to On - On - On is hilarious.
Airlines don't negotiate prices based on the exact options selected, they select a list of options and then negotiate on price from there. This particular option does not appear to have a price associated with it, it just increases the cost of training and documentation for pilots and some airlines would opt out of using it.
People talking about MCAS seem to simultaneously pound the line that everything on the aircraft the pilots encounter should be trained for and forget that adding new stuff to the flight displays will incur additional training that an airline may not want to deal with.
Such a terrible business decision considering the crashes and their impact on Boeing's reputation. If you think a feature will keep the product from catastrophic failure, it should be standard on every unit you sell.
This kind of thing is not new. In 1998 I worked for a large corporation (I think they were an F100 at the time) that built machines with a feature that could only be enabled if the customer paid an extra fee and had a field technician come out to "install" it.
Unknown to the customer was that all machines were identical. The technician's "installation procedure" was to enter the Service Mode password, select the feature enable option, and exit Service Mode then run a test to make sure it worked.
This is pretty common in commercial/industrial manufacturing. The exception cost to omit certain hardware subsystems when building a product is often higher than the cost of the hardware itself, so it makes more sense to build everything identically and enable/disable features in software.
There was no redundancy AOA sensor option for MCAS.
All the planes were built with two AOA sensors, with the original MCAS implementation only using data from 1 sensor.