Originally Posted by
EXDAC
No, the DC-9, MD-80, MD-90, and B-717 all have a single nut but that single nut has two threads. ( A two start thread.). Jack screws with two independent nuts are typically arranged so the backup carries no load until the primary fails. In the two thread single nut design both nut threads wear together and they wear quickly if they are not lubricated.
Gotcha - I recalled that the claim was a dual load path that turned out to be not truly dual allowing for them both to wear at the same time. It baffles me that a single nut with two starts counts as redundant. How far back does FAA blindness go?