As a member of the electronics design community, I am angry and disappointed with the recent deaths of 346 people due to the Boeing MAX 8 design. I always say, “Follow the money” and you will likely find the cause of most problems. Whether it is a rush to get a product to market before your competitors, or an effort to make more money on product options, the result is often not going to be good.

Regarding technology, why is it that we have developed reliable cell phones that can sense movement, compass direction, and much more? Why is it that we have developed an amazing MEMS technology that is rugged as well as improving so many innovative electronic systems? Can’t we do something to make an Angle of Attack sensor, which relies on micro-electro-mechanical movement, more rugged? It seems like the present designs have such a relatively high failure rate.

Of course, having two AOA’s, one on each side of the aircraft for redundancy and comparison, is a good solution. However, the second AOA was deemed an option by Boeing. That has changed since the accidents.

CNN has found that Boeing relied on single sensor for 737 Max that had been flagged 216 times to FAA

What is the Angle of Attack?

The definition of Angle of Attack in an aircraft is the angle between the aircraft wing chord line and the incoming air passing by the aircraft in flight.

Why is the AOA important?

An aircraft will stall, regardless of speed, if it exceeds a high AOA known as the “critical angle of attack”

Figure 1 The Angle of Attack
(Source: IEEE)

Safe Flight Instrument Corp. has a number of AOA solutions---see them here.

MEMS AOA sensors

It seems that MEMS5 devices in an AOA design have only been used in Wind Tunnels and on Unmanned Aerial Systems (UAS) to date. I can’t find one that is in production.

Calibration of the AOA6

In the case of calibrating AOA using Kalman filters, it requires reference data to compare with actual output measurements of the sensor to be calibrated.

Determining flow angles (See Figure 2) requires high-accuracy reference measurements of AOA using measurements coming from an inertial navigation system and an air data sensor, and analytically reconstructing them using calibrated airspeed measurements and inertial data and the use of a Kalman Filter that was implemented in MATLAB/Simulink (Check out the Design of a high angle of attack pitch mode control in MATLAB Simulink)

Figure 2 Definition of Flow Angles
(Source: IEEE)

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