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Old 14th Nov 2018, 17:22
  #1203 (permalink)  
hans brinker
 
Join Date: Nov 2010
Location: Atlanta
Age: 52
Posts: 17
Originally Posted by KenV View Post
This has been a basic design philosophy at both Boeing and Douglas since forever. And because that is the way it is designed, it is tested to ensure it behaves as designed and is part of the type certification. Indeed, when Boeing provides the flight training, that training includes flying the aircraft (in the sim) with a hardover trim condition. No it's not easy and may require both pilots. But yes it is very much possible.

Remember the 737 flight control system was designed in the 60s and is fully mechanical. The 737 has a measure of SCAS (Stabililty Control Augmentation System) with STS and MCAS, but those systems act entirely thru the mechanical flight control system (more specifically, the trim portion of the mechanical flight control system). Further, the exact action (though not the reason why) of these systems is easily discernible by looking at the trim wheel, the action is over ridden/cancelled with the push of the trim switch on either pilot's yoke, can be cut out completely with a cutout switch, and if all else fails, can be overpowered by applying high stick forces. The Boeing and Douglas design philosophy is to always give the pilots the ultimate say and the ability to overpower whatever an electronic system wants to do. Indeed that is why these systems only operate through the trim system, because the base flight control system can overpower trim. Yes, this means that unlike many Airbus aircraft, the pilots of Boeing/Douglas aircraft can do stupid things and endanger the aircraft. It's not like the A320 where if you have the wrong flight control mode selected the pilots cannot simply overpower the system by pushing on the stick and/or the throttle to over ride envelope protection, and must instead deselect the current mode and select another. I'm not saying or even suggesting one design approach is "better" or "safer" than the other, I'm saying the approaches are fundamentally and significantly different.
Not the only one saying this already, but I think you are wrong on how easy it would be to overpower the stabilizer. There is a thread about a Ryanair 737 losing control in the Go Around in Eindhoven a few years ago, I think they managed to get to 42 degrees ANU at a speed of 80 KIAS while pushing all the way forward, before they started trimming AND and were able to regain control (I think since added to the checklist is something about using trim in unusual attitudes). Also the 737 in Rostov-on-Don was likely trimmed full AND and the pilots were unable to pull out at 300+ KIAS, so very different sides of the envelope, but similar problem.
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