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Old 18th Nov 2018, 08:03
  #1375 (permalink)  
Lifer01
 
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Originally Posted by Hi_Tech
There has to be more protection in the system design for this not to happen. (Single source failure)
In the B777 which I am familiar with, each of the two ADIRUs (Air Data Inertial reference unit) receive both AOA inputs (There are two AOA sensors on most aircraft, same config on B737 also). This is compared with 'Calculated AOA' and a mid value is used. This is the redundancy built in the system on B777. Also each of the AOA sensor has two outputs, feed into two different computational channels. See the redundancy. There are actually 4 signals from two AOA sensors. Also there are two computed AoA values. So in total 6 signals.
I don't have access to the MAX AMM, but on the NG, there are two AOA sensors - each with two resolvers. The left AOA signals go to the left ADIRU and the SMYD 1 (Stall Management Yaw Damper) box and the right AOA sensor signals go to the right ADIRU and SMYD 2. The two ADIRUs and the two SMYDs cross check.

The resolvers are all analogue outputs.

I can only presume that the MAX and NG have very similar ADIRU and SMYD set-ups - with the MAX having additional MCAS software/logic in the SMYD stall warning functions.
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