I’ve noticed a behaviour with the Fokker 100 during the final approach that I’m not sure is intended or possibly a bug.

When established on the ILS, I regularly find that once I extend the flaps to 25, and especially 42, they seem to generate a huge amount of drag. When reducing speed from around 180/170 knots down to the approach speed, e.g. 132 knots, the autothrust seems unable to keep up with the deceleration.

As a result, the aircraft repeatedly gets into the red/low-speed range. If I leave ATS engaged, it then seems to apply almost TOGA thrust to recover the speed, which results in the aircraft accelerating back up to around 160–170 knots.

At this point I’ve started taking over manually because otherwise the speed oscillations become quite excessive during the final approach.

Is this behaviour intentional and representative of the real Fokker 100, or could there be an issue with the flight model/autothrust logic?

I’d be interested to hear if anyone else has experienced the same thing or if there is a specific technique/procedure I might be missing.

Thanks!