This wasn't a 'deep stall' which is more normally associated with turbulent air from the stalled wing impinging on the tailplane and reducing its ability to control the aircraft in pitch so that the angle of attack can't be reduced to exit the stall. In this particular circumstance the pitch moment of underslung engines at full power had a similar effect, but that was recoverable, a deep stall isn't always. Was in not the Caravelle that first brought the problem of a deep stall to light?