This discussion began with a question about the 737-3/400. I can only speak to the 737-800, although I believe there is great similarity in the autoflight systems.
Regarding alpha floor protection, the Boeing FCOM states: “alpha floor protection automatically engages the A/T when armed.” Can’t be much plainer than that. That said, this reminds me a bit of my insurance company claiming that they will cover the damage to a rental car. Haven’t tested it yet to see what actually happens when I crash the rental car…and I have no intention of testing the alpha floor.
Minimum speed reversion appears to be a mix of pitch and power controls to return the airplane to a speed above whatever the minimum speed is. Alpha floor is not defined anywhere except in the above statement, but appears to only an A/T mode.
Regarding the split in automation, my strong opinion coming off the 767/757 and MD80 before that was autopilot off, autothrottles off. I still prefer to fly that way for all of the reasons cited above, and have often invoked Boeing’s admonition on this topic. However, in 2006 Boeing’s Captain Mike Bryan produced a presentation at their annual operators’ forum which questioned that premise. He showed quite a bit of flight test data indicating a much better and more precise speed control in gusty crosswinds, etc. with autothrottles on during manual flight.
Unfortunately, in 2008, my access to Boeing’s operator forums and associated presentations was summarily cut off (airline folded). So I don’t know what else they may have done with this issue…perhaps some of the other graybeards on this forum might. BUT…regardless of personal tastes and historical recommendations, I am now required to manually fly a CAT III approach using the HUD…with the autothrottles on through the touchdown. So it’s a little hard to support the notion that there is something inherently unsafe about splitting the automation.
Regarding the retard action in the flare, I certainly can see Wizofoz’s experience on the Greek island happening. We were drilled on the importance of manually closing the throttles during the flare…except during the aforementioned CAT III…even if they are active. The primary issue here seems to be the relationship between landing with power and tailstrikes.
Centaurus’s description of the pitch up during go-around is a bit alarming, because despite the ground school guys talking about the second TOGA push, etc., nobody ever demonstrated that in the sim. I can recall disconnecting the A/P on the MD80 during a couple of real world go-arounds because I was pretty sure the A/P had entered the low-level loop mode. This is a something to be aware of for sure.
Last edited by Mansfield; 19th Nov 2017 at 12:23.