FCeng84
I was warned about this characteristic during my conversion line-flying. Having been 'cleared' on the line, I did on one occasion deploy the speedbrakes with some haste, and the aircraft pitched down quite rapidly. The speed was on the barber's pole in a very short time, and I had to disconnect the A/P and gently pitch up to contain the speed.
Some months later (this was in 1999), I was in the right-hand-seat training an SFO on his command course. We were heading for the Gulf, but had (most unusually) been routed over Iran. We were kept up high, late. I had warned the other guy about this characteristic, but when finally cleared to descend we were very high, and he deployed the speedbrake very rapidly. He had to subsequently disconnect the A/P to avoid busting the 'pole'. QED.
I'm sorry to say that he went to the same destination, some days later, and experienced the same set of circumstances, but this time with a manager, and on his final command check. He had to disconnect the A/P and recover. This time, however, a cabin-crew member was injured in the recovery, and the proverbial hit the fan.
Surely, every 777 pilot knows about this characteristic? It was not a problem at all if the brakes were deployed with finess. But the 777 A/P is the only one I've known to be so incredibly slow to react to such a speed increase.