3 ms·
Well, the roller-coster maneuver assumes you are high enough up that you can trade off some of your height for correcting the trim. Here is a link to the descri
by _ph_ 7y ago
Well, the roller-coster maneuver assumes you are high enough up that you can trade off some of your height for correcting the trim. Here is a link to the description: http://www.b737.org.uk/runawaystab.htm#rc http://www.b737.org.uk/runawaystab.htm#rc
This obviously wouldn't work in cases like the Ethiopian, where the plane had very little height over ground due to the high mountains around the airport.
Edit: the point isn't that the maneuver had prevented the accident, but that its existance in the flight manuals shows that it was known that the trim forces could be higher than what the pilots could apply to the trim wheels.
- lmilcin 7y agoI'm not a pilot but I do sail some and the same manouver is used. You know, sails also generate huge forces which might not be possible to physically counter. What you do is, if you want to trim and are courteous to your crew, you point your yacht upwind for a moment to let them trim and then get back on your course.
- _ph_ 7y agoI also did a bit of sailing and remember it was also standard to steer a bit more upwind if the boat is listing too much. That is, if there isn't anything in the way, if you steer more upwind :p
- lmilcin 7y agoThis will actually depend on your course with regards to wind. There will be a course that will generate maximum heeling moment.
- odonnellryan 7y agoGenerally you'll heel over the closer you are into wind while your sails aren't luffing. Taking off the wind will make the boat heel less.
- cjbprime 7y agoYeah, and I think MCAS ended up fully deflecting the stabilizer on Ethiopian. Even with a somewhat more reasonable altitude, I wonder how long it takes to physically manually retrim from one end of the jackscrew to level flight. I think even the electric motor takes at least six seconds to do that.
- _ph_ 7y agoFrom what I read the situation was made worse by the fact that they where flying a bit on the fast side even when they were not going down yet, increasing the load on the stabilizer.
- secabeen 7y agoA bit of the fast side is an understatement. They were at full takeoff power the entire time they were fighting the trim. They never reduced engine power, which would have reduced the forces on the stabilizer. An easy thing to miss certainly, and it was one of many factors that contributed to the crash: https://nymag.com/intelligencer/2019/04/what-passengers-experienced-on-the-ethiopian-airlines-flight.html https://nymag.com/intelligencer/2019/04/what-passengers-expe...
- cjbprime 7y agoA possible ameliorating factor: they had an IAS Disagree warning (unreliable airspeed) since takeoff, and it may be policy to keep airspeed up in that case -- not knowing your airspeed means that reducing it may cause a stall. (Still, they could have asked ATC for an speed reading or used other measurements to convince themselves that it was safe to slow down.)