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Analysis-Debate over pulling fuses widens regulatory cracks on 737 MAX

Boeing's 737 MAX is set to return to the skies in Canada with a local twist in the cockpit, after Ottawa became the last major Western regulator to lift a 20-month safety ban. Small print in Thursday's Transport Canada announcement sheds light on a regulatory split over the use of a less common tactic to overcome cockpit distractions, deepening international disunity over the lessons from two fatal crashes. Transport Canada joined the U.S. Federal Aviation Administration and other… ( More...

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I must be missing something. The go-to move when the MCAS starts "oscillating" the stabilizer is to cut-out the electric trim. This creates the new problem of trying to trim the aircraft by hand. So why is the stick-shaker becoming a problem since it should only be activated for a fairly short time?
Greg S 1
The stab cutout only stops MCAS from moving the stabilizer. The system will still think the aircraft is in a stall or near-stall situation because of the faulty AoA sensor, so the stick shaker will still erroneously activate. On the flight immediately preceding the Lion Air accident flight, the flight crew eventually performed the stab cutout to regain control but the stick shaker was continuously active for the entire flight. Then those moronic shitweasels simply handed an utterly broken plane back in without saying a word and went home. Unbelievable.
So in the "fixed" version this still can happen? Weren't they obliged to implement redundancy on these sensors? How do other plane types behave to a discrepancy between AoAs?
Highflyer1950 2
Don’t quote me on this, but I believe both AOA’s must agree before MCAS operates and the disagreement light is now standard as is the flight display indication.
Greg S 1
Well, the sensor logic in the new version is supposedly much more robust though I don't remember exactly what it is. I think the stick shaker circuit breaker guidance may have been inspired by the MCAS difficulties but stands on its own merits as a good idea no matter what the cause of a false stick shaker activation.
Highflyer1950 0
Actually it’s a widely used practice to disable a malfunctioning system? If years ago, the military Lear 35 driver had pulled the right engine fuel pump circuit breaker he could have landed safely instead of killing everyone on board? If memory serves, when he emptied the fuselage tank the left wing became heavy, so he opened the x-flow and tried to push from left wing tip tank to right but it didn’t work, so he jettisoned the fuel from both tip tanks. That balanced the fuel until the left wing became heavy again leading to an fuel imbalance. Leaving the xflow valve open and turning on the left engine pump was inadequate since the stuck on right fuel pump was stronger than the left and continued to make the left wing heavy. Instead of using a much higher app & landing speed the pic allowed the aircraft to get too slow and it rolled upside down into the ground on final.
belzybob 1
It used to be a common practice, but some airlines prohibit crews from doing it. Note the quote: ""Normally, pulling circuit breakers is considered an outdated practice and should only be done when directed by a checklist and not as a method of troubleshooting," said Tim Perry, president of Air Line Pilots Association (ALPA) Canada."
djames225 2
You forgot part of the dialogue "Perry said he backs Canada's procedure: "Upon thorough evaluation, we deemed it safe.""
If popping a breaker removes a false distraction quickly, perhaps the old should become part of the new.
Greg S 0
Exactly, see my comment above. It's not just a momentary distraction, the stick shaker may be erroneously active for the entire flight.


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