A320 w/ IAE flaps icing buffeting

[safelife]

Looking forward to this one,
as I know some of you folks with have an answer.

Flew A319/320/321 with cfm engines for years, and have never come across this one.
Had to go flaps 2 early in the approach as ATC demanded a lowish speed, then went thru clouds with quite a bit of ice.
Eventually on the ILS, flaps from 3 to full, slowing to Vapp we encountered a quite pronounced airframe buffeting, and a perceived loss in stability in roll.
After landing asked the FO to retract flaps only till 2, went outside and saw a bit of ice on the leading edge of the flaps.
Had another go a few days later, again with flaps 2 thru the ice, same result.

I'm aware the IAE bus extends flaps till 40° whereas the cfm version does only 35. And heard before that flaps 40 can induce turbulence at the stab.
But this came a little unexpected, never heard of this effect before. Anyone can enlighten me please?

[Fursty Ferret]

I've also noticed this on the IAE engined aircraft. Only happened once, can't remember if 319 or 320.

It was a particularly pronounced buffet though only became apparent at Vapp.

We added 5 knots and accelerated out of it.

[CaptainMongo]

We have a caution and a warning regarding ice buildup (IAE Engines) . I haven't seen ice buildup on the heated surfaces, but have felt it on the unheated surfaces. My technique is if I see ice buildup on the ice probe (which of course is unheated) I assume some ice has built up elsewhere on the aircraft. (Could be a wrong assumption, but it works in my mind...)

If ice accumulates on heated surfaces, either the capacity of the anti-ice system has been exceeded or there is a possible anti-ice system fault. Minimum speeds should be:
• Clean configuration: VLS + 15 knots
• CONF 1, 2, 3, or Full: VLS + 10 knots


If ice buildup is suspected on unheated surfaces and landing with flaps Full, approach speed must not be lower than 5 knots above VLS as displayed on the PFD. Multiply the landing distance by 1.1.

If ice buildup is suspected on unheated surfaces and landing with flaps 3 or less, approach speed must not be lower than 10 knots above VLS as displayed on the PFD. Multiply the landing distance by 1.15.

[safelife]

Thanks!
Well, neither the stab nor the leading edge of the flaps are heated, so ice with always form there when in icing conditions.
I've never noticed this effect on the cfm bus, but here it's a bit startling. Had my WTF 😳 moment that night. Also it feels like the aircraft wants to roll left and right, like almost all roll stability is suddenly gone.
Flying 5 kts faster didn't get us out of it, didn't try higher as a slippery runway was so be expected.

[Sidestick_n_Rudder]

I have experienced this as well, as a newly type-rated FO on the bus, in what amounted to severe icing on final. We rolled left and right all the time up to the point that it was uncomfortable.

My CA was unimpressed and kept telling me to "stop stirring the stick", or words to that effect. Couple of hours later we were conducting the same approach in the same conditions with the CA being PF and the thing repeated.

I was looking for any info on this in Airbus publications, but haven't found anything...

[safelife]

Yes, there seems to be no comment from Airbus about this effect.
Some mitigation strategies would be handy. VLS+10 didn't suffice for me. Maybe landing flaps 3 would help, but the book calls for an even greater speed increment then.
And landing flaps 3 plus higher speeds is not the ideal configuration on a winterly runway.

[FlightDetent]

Much interesting.

with good will and intent to help the on-going forensics, however:In flight, hot air from the pneumatic system heats the three outboard slats (3-4-5) of each wing. Also the W-AI shutsdown once on ground. (I noted you specifically said LE of the slats.)

[Check Airman]

Observed the same thing on approach in icing one morning. All was well until flaps full, and we noticed significant buffeting. Adding 5kts to Vapp made it a lot better. After the flight, we noticed a VERY thin layer of frost on the LE of the THS.

Oddly enough, only seems to happen on the 320, not the 319 or 321. All IAE engines.