MD-11
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 65; Flight Crew Total 12000; Flight Crew Type 3000
Aircraft Equipment Problem Less Severe; Deviation - Speed All Types
Aircraft
On the arrival today we had an anomaly that I have never seen before on the MD-11. We were in the descent with the speed brakes deployed and we were about 10 knots under the max foot and stable. Suddenly the yellow foot shot down 20-30 knots followed by the red foot. An overspeed warning alert sounded with a high speed protection annunciation. No weather; turbulence or pitch changes occurred to cause this. Within a few seconds the foot returned to normal about 10 knots above our descent speed and all was well. A few seconds later the yellow and red foot repeated the sudden downward movement and we received the same warnings again. A few seconds later the feet returned to normal and we resumed our descent.At this point we were trying to diagnose the issues and figure out what was wrong and without knowledge to us the aircraft was no longer in prof and went to level change and we descended past our clearance limit of 11;000 to 10;600 before we reversed our descent to a climb back to 11;000. [ATC didn't say] anything and we remained at 11;000 feet until ZZZZZ and continued our clearance to 10;000 after we passed ZZZZZ. I'm not sure what caused the speed/foot/overspeed anomalies. I wrote it up in the logbook and briefed maintenance as a theoretical overspeed from the warnings; but I don't actually believe we had an overspeed; but I can't be sure with the quick changes that appeared and disappeared.
[Report narrative contained no additional information.]
MD-11 crew reported an anomaly with the overspeed warning alert twice during descent which also caused the profile decent system to miss a level off.