Old 2nd Jan 2019, 21:38
  #71 (permalink)  
Join Date: Jul 2013
Location: Everett, WA
Age: 64
Posts: 2,263
Originally Posted by DaveReidUK View Post
If only Boeing had thought to Murphy-proof the AoA sensor, say by incorporating a locating pin that ensured it could only be fitted in one orientation ...
What makes you so sure they didn't? Murphy can be extraordinarily creative. In the early days of the PW4000, it used a motor driven actuator for the high pressure fuel shutoff in the fuel control - and for some reason it wasn't the same as the one they used on the JT9D - basically RUN and CUTOFF were reversed. To prevent use of the JT9D actuator, they changed the locating pin location. Turned out that due to the vibration environment on the PW4000, the actuators failed quickly and often (quickly replaced by a solenoid setup that they should have used in the first place).
We got more than one JT9D motor actuator back - with complaints that it didn't work on the PW4000 - with the locating pins neatly machined off so it would fit.
We saw similar issues with throttle resolvers - the locating mechanism to prevent left/right swap being neatly machined off. I think it was Wernher von Braun who said 'It's really hard to make something idiot proof, because the idiots are so creative.'

I can't help but wonder if for some reason they changed the AOA sensor for the MAX (with appropriate Murphy Proofing). When the Lion Air mechanics determined that the NG sensor wouldn't fit the MAX, they "made it fit".
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