On this morning’s flight from GVA to LHR we picked up quite a bit of ice. As 
I was sat right next to the wing I could see it build up rather quickly. Didn’t get off the wing until well after Paris – here are the remnants at cruise…
It also built up on the vortex generators on the engine.
This does not seem to be any significant amount of ice to me. I would say tiny bit of ice in this case…
Does airliners put their de-ice or anti-ice while on cruise say at Mach 0.8?
Though I do not speak as a jet pilot, that is not a worrisome amount of ice. Yes, the airliner’s wings and other frontal areas are deiced with engine bleed air. Once through the freezing level, and climbing, any moisture in the air is well below freezing, and will not accumulate on the airframe. Deicing at high altitudes and speeds is likely not necessary. Small amounts of ice, such as that pictured will disappear by sublimation over time.
That said, that amount of ice accumulating on a small plane should cause worry, and pilot action. This is mostly because it is much less certain that the airframe can deice itself, or that it is possible to climb out of the ice. Any accumulation of ice on a non deiced GA plane would cause me to prioritize getting away form the icing conditions. I’ve had four occasions of flying and descending not entirely in control of an aircraft due to airframe ice, and it scares the dickens out of me! Airframes will carry some ice, but a low experience pilot has no idea how much, and the flying qualities will steadily decline as ice accumulates, to the point where controlled flight is no longer possible. It’s really hard to anticipate than point, so avoid entirely!
That looks like very dense and sticky ice.
On most jets: Anti ice system works automatically in flight using ice detectors (probes that swing and change frequency when icing occurs). On the ground engine anti ice needs to be switched on manually. Wing anti ice is only used in flight. Icing condition = -10C and visible moisture. On Boeings the tail does not have anti icing, supposedly the aerodynamics keep it clear of ice, but there is a small landing climb limit weight performance effect. Ibra wrote:
Ibra04-Mar-19 14:01 03Automatically yes if icing conditions are present. Very very rare for the WAI and EAI to be on during cruise, but it happens.Does airliners put their de-ice or anti-ice while on cruise say at Mach 0.8?
Snoopy wrote:
Very very rare for the WAI and EAI to be on during cruise, but it happens.
With aerodynamic heating of 20°C or so, OAT would have to be less than -20°C for icing to happen and it would indeed be very unusual at those temperatures.
Snoopy wrote:
Automatically yes if icing conditions are present
Does that relate to outside weather only?
Or it does account for aircraft cruising speed or its ability to accelerate to high speed numbers?
At Mach 0.99 you should not collect that much ice due to kinetic heating and the absence of a boundary-layer but I guess that starts to get true from Mach 0.7
A TAS of 350kt produces aerodynamic heating of 15C which is roughly* the temperature band over which supercooled water can exist. So once this speed is reached, you won’t likely get any airframe ice.
At piston GA speeds this temp rise is 1-2C only so not useful.
I too am surprised to see that icing on the wing, but what do I know about big jets 
* I have a photo of light rime collected at -19C; posted it here previously.
I wasn’t worried about the amount of ice, just surprised by the rate of accumulation and the fact it remained on the wing for 45mins. It had me wondering what would happen in case of prolonged icing and was thinking maybe they forgot to turn on the de icing if that is something that happens in a big jet.
In the case of this airbus they switched wing anti ice on and then probably off again once in cruise and some ice stuck…
Ibra wrote:
Does that relate to outside weather only?
To outside temperature, yes.
Found this on google for boeing:
