Originally Posted by Chris Meutsch
I wonder if the banner detached and sent the plane into some kind of lurch forward that they couldn't correct.
Nope...just acceleration. Towing banners was my first flying job.
As pilottravis said, all speculation at this point. But if this situation is anything like ones I am familiar with, the pilot waited too long to detach the banner after starting to have a problem. Waiting too long, especially with loss of power while towing, you sacrifice maneuverability, range and most importantly, time to manage the situation.