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 (See Reference 5 and my comments below)? 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. See Reference 9.
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”
The Angle of Attack (Image courtesy of Reference 1)
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
Reference 6 has a really nice article about AOA calibration using Kalman filters. In this case, calibration requires having 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)
Definition of Flow Angles (Image courtesy of Reference 6)
Please share your comments and expertise with our audience on this subject.
1 Angle of Attack Sensor using Ball Mouse Encoder Wheel, Sumantra Bhattacharya, Akshay Mule, Subhasis Bhaumik, 2016 International Conference on Intelligent Control Power and Instrumentation (ICICPI), IEEE
2 Boeing AOA discussion
3 Satcom Guru
4 Not just the 737: Angle of Attack Sensors have had problems
5 Development of Alpha Sensor for Unmanned Aerial Systems Mi-Hyun Park, Sung-Su Kim, Chang-Kyung Ryoo, Keeyoung Choi, and Choonbae Park Department of Aerospace Engineering, Inha University, Incheon, Korea, SICE Annual Conference 2008 August 20-22, 2008, The University Electro-Communications, Japan
6 Wind identification via Kalman filter for Aircraft Flow Angles Calibration, F. Schettini, G. Di Rito, E. Denti and R. Galatolo, 2017 IEEE
7 Method of Estimating Angle-of-Attack and Sideslip Angle Based on Data Fusion, Hao Long, Shujie Song, 2009 Second International Conference on Intelligent Computation Technology and Automation, IEEE
8 Attitude Determination Using a MEMS-Based Flight Information Measurement Unit, Der-Ming Ma, Jaw-Kuen Shiau , I.-Chiang Wang and Yu-Heng Lin, Department of Aerospace Engineering, Tamkang University, Tamsui, New Taipei City 25137, Taiwan, Sensors 2012
9 Doomed Boeing Jets Lacked 2 Safety Features That Company Sold Only as Extras, NY Times, March 21, 2019