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The speculation I've seen is around a change to the autopilot system which pilots ave been struggling with: > Following the Lion Air crash, US aviation authori
by swarnie_ 8y ago
The speculation I've seen is around a change to the autopilot system which pilots ave been struggling with:
> Following the Lion Air crash, US aviation authorities issued an emergency directive to carriers to update flight manuals with information on what to do when the aircraft’s anti-stall system is triggered by erroneous data from what’s called an “angle-of-attack” sensor. The flight system can react to that data by pointing the plane’s nose sharply downward. Boeing, meanwhile, directed airlines to a checklist in manuals for stabilizing the aircraft. Pilots said the crash and the directives that followed were the first time that they were made aware of these changes to the flight system.
- DannyBee 8y agoTraditionally the fly-by-wire systems have at least 3 AoA sensors, which each "vote" on the output value. That way, if you have one faulty sensor, it gets outvoted. The MCAS system in the new 737-MAX's only have 2 AoA sensors, which means a single faulty sensor can cause bad things to happen.
- linuxftw 8y ago> The MCAS system in the new 737-MAX's only have 2 AoA sensors That's pretty damning if true.
- DannyBee 8y agoThis is what i was told (it was something like "they have 2 flight computers, and 1 AoA sensor hooked up to each"). The reddit thread linked from elsewhere says the same thing. The preliminary report on the Lion air crash (http://knkt.dephub.go.id/knkt/ntsc_aviation/baru/pre/2018/2018%20-%20035%20-%20PK-LQP%20Preliminary%20Report.pdf http://knkt.dephub.go.id/knkt/ntsc_aviation/baru/pre/2018/20...) says they replaced and tested the AoA sensor 2 days prior. They repeatedly refer to the AoA sensor using only singular nouns everywhere. Given the report says it was giving faulty data and that was used, the only way this can occur is either: 1. Their are multiple sensors and the software is broken 2. There is a single sensor Given all other data, i'm going with #2 :) Nobody has been enterprising enough to publish the MAX8 troubleshooting/etc manuals online, if they did, you could easily verify this.
- runxel 8y agoSome acquaintance of mine told me – which I really can't believe given the seriousness of aviation security – that there is in fact just one sensor. If true than that's preposterous.
- linuxftw 8y agoEither way, this is insanity.
- kps 8y agoFrom photos, there is (at least) one on each side. https://s3media.freemalaysiatoday.com/wp-content/uploads/2018/11/boeing-737-max-bloomberg-28112018.jpg https://s3media.freemalaysiatoday.com/wp-content/uploads/201... https://static.businessinsider.com/image/5be287c7b73c2846bb419884.jpg https://static.businessinsider.com/image/5be287c7b73c2846bb4...
- DannyBee 8y agoYeah, this would line up with "1 sensor for each flight computer".
- JohnJamesRambo 8y agoI’d like to see the math on that cost savings now.
- pdonis 8y ago> Traditionally the fly-by-wire systems have at least 3 AoA sensors, which each "vote" on the output value. That way, if you have one faulty sensor, it gets outvoted. That would make sense, but unfortunately it's not the way they're actually implemented. Several incidents with Airbus aircraft were due to one AoA sensor's faulty input being allowed to trigger uncommanded pitch down events, instead of the one faulty sensor being outvoted by the other two. I agree having only two sensors is even worse.
- nas 8y agoMCAS is not a fly-by-wire system. Pages and pages of speculation by arm-chair aircraft designers going on. So depressing.
- DannyBee 8y agoI understand it's not a fly by wire system. I was comparing it to the other common use of AoA sensors. Do you have anything real to add here other than "I am Very Smart and everyone else is not"? For example, whether it is a fly by wire system or not does not change anything about what i said about the sensors.