BEA nearly lost another Trident 1 in the Clacton hold in the 70s.
We all knew the droop limitations...out by 225 knots and in by 250 knots but most didn't know the Mach limit. The Clacton hold had a max speed of 210, the skipper had gone for a leak and the new boy had selected the droop out entering the hold somewhere around fl250.
The wing went supersonic locally and they descended somewhere around 5000ft before they regained control.