Boeing’s optional safety features, in part, could have helped the pilots detect any erroneous readings. One of the optional upgrades, the angle of attack indicator, displays the readings of the two [angle of attack] sensors. The other, called a disagree light, is activated if those sensors are at odds with one another.
Boeing declined to disclose the full menu of safety features it offers as options on the 737 Max, or how much they cost.
When it was rolled out, MCAS took readings from only one sensor on any given flight, leaving the system vulnerable to a single point of failure. One theory in the Lion Air crash is that MCAS was receiving faulty data from one of the sensors, prompting an unrecoverable nose dive.
As I noted in a previous posting, the Pilatus PC-12, a much cheaper and simpler airplane (1 engine and 9 passenger seats), doesn’t do any nose-down pushing unless two separate angle-of-attack sensors, and their respective computers, agree. Boeing’s ideas of
- a system that works silently (so pilots don’t realize it is operating)
- a system that works if just one sensor suggests a high angle of attack
- a system that has the authority to drive the airplane into a full nose-down trim situation
- a Band-Aid on the above in the form of a “disagree” warning light
are all terrible ones, as far as I can tell, and unconventional within the industry.
Does that mean we need much more stringent oversight by regulators? (as noted in this other previous posting, the “regulators” in the case of the above system were mostly Boeing employees) Maybe.
The prices of these optional items that would have made Boeing’s unsafe design a little less unsafe were too shocking for Boeing to admit or the NY Times to publish. But reasonably high-quality systems for homebuilt 2-seat and 4-seat airplanes are less than $2,000, including both the sensor and indicator. Examples:
- Garmin, probably as good as anything in the airliner world (and also supposedly available for small certified planes)
- A $389 LIFT system
- AOA Sport, Angle of Attack Instrument
- iFlyAOA (can be added to small certified airplanes as well)
- LevilBOM (my favorite! can be mounted under the wing of a certified airplane; gets its power from the moving air)
So it is tough to know whether regulation should have been relaxed so that Boeing’s costs of putting reasonably modern avionics into the airplane were reduced or toughened so that the crazy bad ideas were squashed. (Or, as my previous posting suggests, shifted so that an independent private engineering service would do the steps that Boeing’s employees were doing while nominally wearing FAA hats.)