Fairly close Laikim Liklik Susu, it was a training flight, initiated by the perpetrator inadvertantly applying the "deliberate entry" procedure I described, by sharply applying full BACK elevator as the stall warning sounded, taking the AoA beyond the stall. I'm not so sure that they went supersonic, but the said perpetrator's hair (and beard) turned white shortly thereafter. A severe roll and dive ensued.
The DC9 did obligingly drop a wing to the vertical in the fully developed stall (usually the right) providing a good lateral airflow to the tail assembly enabling recovery, and it was from just that that the 'last ditch' recovery was developed for other T-tail aircraft. Not all manufacturers may recommend it.
Not funny for the poor guy, but the compresser stalls on one such occasion were so loud that an engineer riding in the cabin thought that the main spar had "gone".
Regards,
Old Smokey