About one month ago I was received some violation for over speed when flying with A330-300. Problem was that in cruise flight on AP with speed 5kts close to max speed I have in one second about 10-15kts over speed. I try to slow down but was very slow reaction. But how it is possible? I was not sure, I spend some time on low grade than return to Grade 5.
Today I was made another flight with A330-300, I need to fast move this aircraft for about 1h flight so used low FL260 and fast speed to reach destination ASAP. And what happened? In cruise flight stabilized flight about 30 minutes from TO I heard alarm for over speed. My reaction was fast and I find the bug. Maximum airspeed was not stable in stable condition. So this is bug and must be repaired otherwise everybody can receive lots of violation.
What I find? After TO and climb to FL260 you can see max speed limit around 344kts. But randomly this maximum drops to about 339kts so if you select 340kts as your cruise speed you will receive lots of violation on long haul flights.
Because nobody understand this problem so one more time: This time was difference only 5kts, in my previous experience was 25-30kts change. Please understand that problem is not AP and/or winds, problem is that maximum speed limit changed for 30-60 seconds than moved back. All in stable cruise flight, no climb no descend. No altitude change. I am sorry I have no pictures from 25-30kts change because I was so shocked by this bug.