5 ms·
this may be a naive question but with all of the advanced technology on these planes, why isn't there a check for altitude before any automated command runs whi
by holler 8y ago
this may be a naive question but with all of the advanced technology on these planes, why isn't there a check for altitude before any automated command runs which says "hey we just took off, are 400ft above ground, MCAS is saying nose down, we will crash if that command runs, CANCEL"
- cjbprime 8y agoYou'll 100% for sure crash if you stall at 400ft above ground. MCAS is designed to prevent stalls.
- deleted 8y ago[deleted]
- Rooster61 8y agoNot at take-off. See above comment about flaps.
- javagram 8y agoMCAS system is supposed to stop the plane from stalling. The faulty AoA sensor is causing the plane to think it’s about to stall and therefore MCAS works as designed to prevent the pilot from putting the plane into a stall. Of course the design is wrong because the plane is actually pointing toward the ground and MCAS thinks it’s pointing to the sky...
- robryan 8y agoWhat about a single button to turn MCAS off and return to trim to a neutral position? Or a setting where the pilot is telling the system to ignore the sensor input. Maybe a bit like a self driving car planes will eventually have a system where they can use visual markers as a check on what sensors are reporting.
- weaksauce 8y agoThat may be where they will go with this but it may require a new certification and training.
- javagram 8y agoIndeed there are many ways to design this better. The 737 max was designed to not be any different to fly than previous 737s, so adding a button to disable this system was not allowed as I understand it. As these two tragic accidents have made clear that specification was pretty wrongheaded...
- fgonzag 8y agoSeriously, a MCAS indicator light (if MCAS is actively issuing commands), a big red button below it called "Disable MCAS" , and a MCAS disabled light (so pilots actually remember when it is disabled) should be more than enough to prevent this. Besides adding the AoA disagree light AND having MCAS use a triple AoA sensor vote to determine the AoA angle.
- sidlls 8y agoIt's not that simple. If the AoA is too high that can cause a stall and crash, too.
- Rooster61 8y agoI just took a look at the take-off procedure in the checklist, and it lists that one should extend flaps before and during take-off/ascent. The checklist says that one should start retracting the flaps at 1000'AGL, the altitude where they seem to have started having problems. MCAS is disabled while flaps are extended. It would have activated the second they retracted the flaps.
- paulmd 8y agoBecause right after takeoff is the single most common point at which you might stall the aircraft. What's more, at that point it is likely to be a power-on stall, which is the specific situation that MCAS is intended to fix (because the 737 MAX has a tendency to pitch upwards in power-on scenarios). Really there should just have been a separate cutout for MCAS itself, but that would have triggered retraining requirements, so Boeing wanted to avoid that. But very simply, there should just be an 'off' switch to disable this system if it starts to run away, distinct from the whole runaway trim procedure. (as well as 2-of-3 redundancy on the sensors, the lack of redundancy is seriously exacerbating the rate of incorrect MCAS system activations)
- cjbprime 8y ago> is the specific situation that MCAS is intended to fix Well, not quite: if they wanted it to protect against stalls at very low altitude, it would be operational with flaps extended.
- kalleboo 8y agoAnd the AoA disagree needs to be actually used and not just an "option feature pilot warning". AoA disagree on ground = plane doesn't take off. In flight = MCAS cuts out.
- cjbprime 8y agoYou can't have an AoA disagreement when stationary on the ground. It is a wind vane.
- djmips 8y agoYou don't know that. If it's malfunctioning it could be in the electronics and nothing to do with how it operates.
- cjbprime 8y agoAnd if it's reporting a difference, it could just be because there's no airflow and the vanes aren't at identical positions. You can't rely on the difference meaning anything.