5 ms·

That's not true. The EA crew DID follow the proceedure and DID uss the cutout switches. See the report: https://flightsafety.org/wp-content/uploads/2019/04/Prel

by dlgeek 7y ago

That's not true. The EA crew DID follow the proceedure and DID uss the cutout switches. See the report: https://flightsafety.org/wp-content/uploads/2019/04/Preliminary-Report-B737-800MAX-ET-AVJ.pdf https://flightsafety.org/wp-content/uploads/2019/04/Prelimin... Timeline: "At 05:40:35, the First-Officer called out “stab trim cut-out” two times. Captain agreed and FirstOfficer confirmed stab trim cut-out." Initial Findings: "The crew performed runaway stabilizer checklist and put the stab trim cutout switch to cutout position and confirmed that the manual trim operation was not working." What happened was by the time they did, they were trimmed nose down really far and it took all their effort on the controls to keep the nose up. The aerodynamic forces prevented them from being able to manually trim. They eventually turned the trim back on because they had to use the electric manual control to try to get the nose up because it was physically impossible for them to do so manually. They adjusted the trim in the ANU direction electrically, but then "an AND automatic trim command occurred and the stabilizer moved in the AND direction from 2.3 to 1.0 unit in approximately 5 seconds" which caused them to lose control completely.

WalterBright 7y ago
Read the Airworthiness Directive sent to all MAX crews after the first crash: https://theaircurrent.com/wp-content/uploads/2018/11/B737-MAX-AD-1107.pdfhttps://theaircurrent.com/wp-content/uploads/2018/11/B737-MAX-AD-1107.pdf https://theaircurrent.com/wp-content/uploads/2018/11/B737-MA... which deals specifically with that: "Initially, higher control forces may be needed to overcome any stabilizer nose down trim already applied. Electric stabilizer trim can be used to neutralize control column pitch forces before moving the STAB TRIM CUTOUT switches to CUTOUT. Manual stabilizer trim can be used before and after the STAB TRIM CUTOUT switches are moved to CUTOUT."
- jacobush 7y ago
  Funny, that reads to me “you are screwed. Manually jackscrewed”
benrjackson 7y ago
To the best of my understanding, this is an accurate summation of events. With the MAX it isn't possible to have electric trim without MCAS, so if MCAS is malfunctioning pilots have to trim manually. The problem with the EA flight is that it occurred shortly after takeoff, so they lacked altitude (unlike the LA flight). A complicating factor was that they were flying east out of Addis Ababa (i.e uphill). (from wikipedia): Two minutes into the flight, the plane's MCAS system activated, pitching the plane into a dive toward the ground. The pilots struggled to control it and managed to prevent the nose from diving further, but the plane continued to lose altitude. The MCAS then activated again, dropping the nose even further down. The pilots then flipped a pair of switches to disable the electrical trim tab system, which also disabled the MCAS software. However, in shutting off the electrical trim system, they also shut off their ability to trim the stabilizer into a neutral position with the electrical switch located on their yokes. The only other possible way to move the stabilizer would be by cranking the wheel by hand, but because the stabilizer was located opposite to the elevator, strong aerodynamic forces were pushing on it. As the pilots had inadvertently left the engines on full takeoff power, which caused the plane to accelerate at high speed, there was further pressure on the stabilizer. The pilots' attempts to manually crank the stabilizer back into position failed. Three minutes into the flight, with the aircraft continuing to lose altitude and accelerating beyond its safety limits, the captain instructed the first officer to request permission from air traffic control to return to the airport. Permission was granted, and the air traffic controllers diverted other approaching flights. Following instructions from air traffic control, they turned the aircraft to the east, and it rolled to the right. The right wing came to point down as the turn steepened. At 8:43, having struggled to keep the plane's nose from diving further by manually pulling the yoke, the captain asked the first officer to help him, and turned the electrical trim tab system back on in the hope that it would allow him to put the stabilizer back into neutral trim. However, in turning the trim system back on, he also reactivated the MCAS system, which pushed the nose further down. The captain and first officer attempted to raise the nose by manually pulling their yokes, but the aircraft continued to plunge toward the ground.[8][9]
- WalterBright 7y ago
  The electric trim column thumb switches override the MCAS. Turning the cutoff switches back on, activating the thumb switches to bring it to normal trim, then turning the cutoff switches back off would have recovered it.

by dlgeek 7y ago

WalterBright 7y ago

Read the Airworthiness Directive sent to all MAX crews after the first crash: https://theaircurrent.com/wp-content/uploads/2018/11/B737-MAX-AD-1107.pdfhttps://theaircurrent.com/wp-content/uploads/2018/11/B737-MAX-AD-1107.pdf https://theaircurrent.com/wp-content/uploads/2018/11/B737-MA... which deals specifically with that: "Initially, higher control forces may be needed to overcome any stabilizer nose down trim already applied. Electric stabilizer trim can be used to neutralize control column pitch forces before moving the STAB TRIM CUTOUT switches to CUTOUT. Manual stabilizer trim can be used before and after the STAB TRIM CUTOUT switches are moved to CUTOUT."

jacobush 7y ago
Funny, that reads to me “you are screwed. Manually jackscrewed”

benrjackson 7y ago

To the best of my understanding, this is an accurate summation of events. With the MAX it isn't possible to have electric trim without MCAS, so if MCAS is malfunctioning pilots have to trim manually. The problem with the EA flight is that it occurred shortly after takeoff, so they lacked altitude (unlike the LA flight). A complicating factor was that they were flying east out of Addis Ababa (i.e uphill). (from wikipedia): Two minutes into the flight, the plane's MCAS system activated, pitching the plane into a dive toward the ground. The pilots struggled to control it and managed to prevent the nose from diving further, but the plane continued to lose altitude. The MCAS then activated again, dropping the nose even further down. The pilots then flipped a pair of switches to disable the electrical trim tab system, which also disabled the MCAS software. However, in shutting off the electrical trim system, they also shut off their ability to trim the stabilizer into a neutral position with the electrical switch located on their yokes. The only other possible way to move the stabilizer would be by cranking the wheel by hand, but because the stabilizer was located opposite to the elevator, strong aerodynamic forces were pushing on it. As the pilots had inadvertently left the engines on full takeoff power, which caused the plane to accelerate at high speed, there was further pressure on the stabilizer. The pilots' attempts to manually crank the stabilizer back into position failed. Three minutes into the flight, with the aircraft continuing to lose altitude and accelerating beyond its safety limits, the captain instructed the first officer to request permission from air traffic control to return to the airport. Permission was granted, and the air traffic controllers diverted other approaching flights. Following instructions from air traffic control, they turned the aircraft to the east, and it rolled to the right. The right wing came to point down as the turn steepened. At 8:43, having struggled to keep the plane's nose from diving further by manually pulling the yoke, the captain asked the first officer to help him, and turned the electrical trim tab system back on in the hope that it would allow him to put the stabilizer back into neutral trim. However, in turning the trim system back on, he also reactivated the MCAS system, which pushed the nose further down. The captain and first officer attempted to raise the nose by manually pulling their yokes, but the aircraft continued to plunge toward the ground.[8][9]

WalterBright 7y ago
The electric trim column thumb switches override the MCAS. Turning the cutoff switches back on, activating the thumb switches to bring it to normal trim, then turning the cutoff switches back off would have recovered it.