PixelFlight wrote:Trin wrote:I do agree that the AOA sensor issue is starting to look more like something downstream of the actual vane itself. Which would also explain why Lion Air was repeatedly unable to rectify the issue despite replacing it in between flights.
Yes. Nobody have yet come up with a plausible technical scenario that fully fit the JT10 official public data (disagree before and after AOA replacement). Many here have searched, and the possibility that the problem was in the ADIRU or FCC was raised since months, but lack of public information about it makes hard to refine this scenario. The best description I have found yet of the FCC internals is still this one:
https://www.satcom.guru/2018/11/737-fcc ... mmand.html
If someone have spot something better, please post it.
Thanks for posting that. The problems with ADIRU documented on Wikipedia, IIRC, included gyro issues.
FAA Airworthiness directive 2000-07-27
On May 3, 2000, the FAA issued airworthiness directive 2000-07-27, addressing dual critical failures during flight, attributed to power supply issues affecting early Honeywell HG2030 and HG2050 ADIRU ring laser gyros used on several Boeing 737, 757, Airbus A319, A320, A321, A330, and A340 models.
This explains why the SMYD system diagram on Peter's website shows the ADIRU producing roll rate, roll angle, lateral acceleration. The ADIRU must have a gyro internal or data received from an external gyro. I guess I'll find out how a Yaw Damper system (aka SMYD) affects pitch (lateral axis) after reading Peter's description.
So, assuming the ADIRU contains a gyro for pitch, a gyro for roll, and a gyro for yaw, does this support a root ADIRU issue affecting roll out and takeoff?
Finally, one has to wonder what the outcome would be in all this had (assuming it's ADIRU/power issue) the ADIRU/AOA/airspeed data never failed. Would anyone ever know about MCAS? Would it be touted as this wonderful new system that makes flying the 737 easier (compared to the NG)? Obviously things fail eventually, but it isn't inconceivable to see a situation where an AOA/airspeed/ADIRU failure doesn't happen until 5+ years into a new plane's lifetime.
But let's just state right now, since we're in the middle of an impending software patch from Boeing, the only way the Max gets up into the sky again is:
(1) Either the MCAS is updated to look at 2 or more redundant AOA/airspeed sensors, or a redundancy is inserted in a system feeding the MCAS
(2) The sensing system itself, whether the AOA sensors themselves, or the ADIRUs, or the power bus supporting the ADIRUs, has to be addressed
(3) The current AD for disabling the MCAS in the case of a cyclic runaway trim, remains (for the remote case of now two sensors going bad simultaneously)
(4) The above I would expect to take 6 months to a year, on what is there currently to work with (shorter if it's a software thing, longer if it included wiring sensors and fixing a power issue)