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They had to install MCAS because the plane was unstable in high AoA mode, i.e. during takeoff. And it was unstable because larger CFM engines could not fit und
by mcsoft 7y ago
They had to install MCAS because the plane was unstable in high AoA mode, i.e. during takeoff.
And it was unstable because larger CFM engines could not fit under the wing anymore so they had to put it further forward and a bit up. This increased the pitch up moment when a full power is applied.
Also, can't really see how the height of the fuselage above the ground affects fuel efficiency.
- hotsauceror 7y ago"Also, can't really see how the height of the fuselage above the ground affects fuel efficiency." It doesn't. They wanted to use a larger, more fuel-efficient engine but the 737's ground clearance couldn't accomodate it. So they moved the engine forward.
- cesarb 7y ago> They had to install MCAS because the plane was unstable in high AoA mode, i.e. during takeoff. Forgive me if I'm missing something, but isn't MCAS disabled while the flaps are extended, which is the case during takeoff and landing?
- ummonk 7y agoYup. The real danger was during climb I believe. And it wasn’t unstable, just had a backwards feel at high angle of attacks which could lead to pilots inadvertently stalling it.
- mcsoft 7y agoYou are right though pilots prefer to retract flaps soon after liftoff since extended flaps mean more drag and less efficiency. And the danger comes from the low altitude thus no margin for error. In the doomed ET302 flight they retracted flaps 62 seconds after liftoff at only about 1200ft above the ground. MCAS kicked in 5 seconds later. Had autopilot been engaged it'd also had saved them from MCAS trim down commands.