The New York Times article Boeing Believed a 737 Max Warning Light Was Standard. It Wasn’t. includes the following:

When Boeing began delivering its 737 Max to customers in 2017, the company believed that a key cockpit warning light was a standard feature in all of the new jets.

But months after the planes were flying, company engineers realized that the warning light worked only on planes whose customers had bought a different, optional indicator.


The warning light notifies pilots of a disagreement in the sensors that measure which direction the plane is pointed, a potential sign of a malfunction. This light could have provided critical information to the pilots on two flights that crashed shortly after takeoff in recent months.

and later:

Because only 20 percent of customers had purchased the optional indicator, the warning light was not working on most of Boeing’s new jets. Neither Lion Air nor Ethiopian had the indicator.

note: All instances of boldface have been added for emphasis.

My question is asked to clarify the nature and appearance of the warning light itself.

Is this a physical light bulb-based indicator on a physical panel, or is it graphically implemented within a flat panel display screen? In either case, if the option described above was not purchased, is the (now non-functional) warning light still present and visible?

In that case, is there any secondary visual indication that would allow one to know that it's not working?

  • 2
    $\begingroup$ It is an ECAM message, but I can't find an image for you right now to post it as an answer. It is not a "bulb light". $\endgroup$
    – Ron Beyer
    May 6, 2019 at 1:13
  • 1
    $\begingroup$ @RonBeyer ECAM (Electronic Centralized Aircraft Monitor) is a term exclusively used by Airbus. The equivalent Boeing term is EICAS (Engine Indication and Crew Alert System). $\endgroup$
    – Bianfable
    May 6, 2019 at 8:02

1 Answer 1


In the B737MAX, being a full glass cockpit, the light 'AOA Disagree' is indicated by an alert on the PFD (rather than a physical bulb). This is why Boeing was selling it as an option: it is just a software change to show or hide 'AOA Disagree'.

B737 MAX AOA Disagree Altert

Image taken from B737 MAX FCOM 10.10.33

  • $\begingroup$ Thanks for the clear and concise answer. To complete the answer; when there is no disagreement, I assume that there is no "AOA AGREE" indicator. One wouldn't be able to tell the difference between agreement and absence of the optional feature, correct? $\endgroup$
    – uhoh
    May 6, 2019 at 10:10
  • 3
    $\begingroup$ That's correct. Further insight (anyone correct me if wrong): in the B737NG the light is not an option so pilots expected the light to be present in the B737MAX, too. Management who chooses aircraft may have thought to save money on this "option" (just one line of code for Boeing...) or Boeing wasn't clear. Result is aircraft with missing alerts. $\endgroup$
    – Afe
    May 6, 2019 at 10:21
  • 2
    $\begingroup$ Unfortunately, this repeats a misconception spread by mass media. The AOA Disagree indicator is not an optional feature. The issue was that there was a bug where the AOA Disagree indicator doesn't work unless the optional AOA gauge was selected. The bug was scheduled to be fixed in the next release. See this Boeing statement for an accurate description of the situation. $\endgroup$
    – user71659
    May 6, 2019 at 21:44
  • $\begingroup$ @Afe can you look into this, and then update (by reposting) your comment? I don't have any personal expertise here and it's hard for me to understand the nuances here. Thanks! $\endgroup$
    – uhoh
    May 6, 2019 at 22:25
  • 1
    $\begingroup$ @Afe The AOA indicator is a gauge on the PFD that indicates the readout relative to the stall limit. $\endgroup$
    – user71659
    May 6, 2019 at 23:52

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.