4 ms·
> Pitch changes with increasing angle of attack, however, are quite another thing. An airplane approaching an aerodynamic stall cannot, under any circumstances,
by lamontcg 5y ago
> Pitch changes with increasing angle of attack, however, are quite another thing. An airplane approaching an aerodynamic stall cannot, under any circumstances, have a tendency to go further into the stall. This is called “dynamic instability," and the only airplanes that exhibit that characteristic—fighter jets—are also fitted with ejection seats.
I still don't get how this design was ever allowed to happen or continue to happen. Passenger jetliners shouldn't be dynamically unstable.
- adgjlsfhk1 5y agoAll planes are only stable within certain flight parameters. The problem wasn't that the plane was unstable, it was that the stability region was different than that of previous 737s. If the plane had been given a different name and required simulator training, none of this mess would have ever happened. (Or if they'd just correctly classified MCAS as a safety critical feature and made it have redundant inputs).
- tiahura 5y agoOr if they’d just done a sanity check on the AOA data.
- WalterBright 5y agoYou're right, but that's a different issue from requiring the airplane to be dynamically stable in all its flight modes.
- WalterBright 5y ago> Passenger jetliners shouldn't be dynamically unstable. Well, they are. The active yaw damper is required by the FAA. https://en.wikipedia.org/wiki/Yaw_damper https://en.wikipedia.org/wiki/Yaw_damper
- mulmen 5y agoWhere does that wiki say that the FAA requires the active yaw damper?
- WalterBright 5y ago"several airliners were deemed to be unsafe to fly without an active yaw damper."
- mulmen 5y agoThe string "FAA" does not appear in that wiki nor the cited article. The cited article just says that descent to FL260 is required in one model of 727 if one of the yaw dampers fails. The cited article doesn't even seem to support the line in the wiki. I don't see the word "unsafe" anywhere in the cited source and the only "requirement" is the descent to FL260 in case of a failure.
- WalterBright 5y agoAnything deemed unsafe has the FAA involved in it. You might also be interested in fatal crashes resulting from yaw damper failures: https://en.wikipedia.org/wiki/Dutch_roll#Accidents https://en.wikipedia.org/wiki/Dutch_roll#Accidents
- deleted 5y ago[deleted]
- VBprogrammer 5y agoAmusingly enough, the 737 is one of those few airframes which are dynamically stable in yaw. The yaw damper is not on the required equipment list. Others like the 757, the failure of one of the two fitted yaw dampers is enough to prevent dispatch.
- mulmen 5y agoThe 737 Max is not aerodynamically unstable to the point of causing these crashes. Any airplane can stall in any attitude or at any airspeed. The Max is not inherently unstable or aerodynamically unsuitable for flight. The Max could fly without MCAS just fine, but pilots would have to be re-trained. Airlines didn't want to foot the bill for such an expense so Boeing applied the Maneuvering Characteristics Augmentation System (MCAS) to literally augment the maneuvering characteristics of the Max to match the 737-NG, which pilots are already familiar with. Bugs in the system then led to runaway trim which caused a stall and crashes.
- WalterBright 5y agoThe runaway trim was driving the nose down into a dive, not up into a stall.
- sofixa 5y ago> Bugs in the system And most of all, and the truly inexcusable part, zero redundancy.
- lamontcg 5y agoThen the correct and simple solution is to rip out the MCAS and re-train all the pilots.
- VBprogrammer 5y ago