Originally Posted by
TonyC
Soooo ...
Your policy says an ODP is stable, and your FOQA data says it requires 60-80 control inputs per minute.
Originally Posted by
TonyC
If that's stable, I can't imagine how many more control inputs are required for "un-stable."
I think a more accurate adjective is smooth. There's nothing unstable about idle descents to step-down altitudes.
You and I know that “stable” means “on vertical and horitzontal course, properly configured, flying at the correct speed and rate of descent, and the engines spooled up or down as needed.” The exact definition varies from OM to OM, but that’s the gist you’ll find in every one. Trying to draw a relationship between stability and control inputs is like comparing apples to oranges. If it takes 60-80 control inputs per minute to be stable, so be it. It takes the same diligence to stay on speed, loc and g/s when you’re flying an ILS in gusty winds, right? But if you do a good job and keep the bars crossed the whole way down, you don't call that unstable, do you? The same applies for descend-vias. Maybe not "smooth," but definitely "stable," and I'll take the latter any day.
In fact, when you’re not stable, it is likely because you have made FEWER control inputs (i.e. corrections) to prevent the flight from destabilizing, not more conrol inputs. And when you have so many parameters for being stable, such as on a descend-via with lateral, vertical and speed restrictions, you have to make far more control inputs to be sure the flight doesn’t deviate from these standards.