By way of background have spent a fair amount of time in icing conditions in piston engine GA, and can recall around four or five severe icing encounters. By severe icing I would define it as the de icing boots, or TKS, were not coping with the ice formation, and I had to request a descent. Why not climb? Because the aircraft had lost around 15-20 KIAS and considering a climb might result in a stall. More on that below. One severe icing experience was in a non FIKI aircraft, I regret to say, and resulted from an unforeseen freezing rain encounter. Fortunately my SEP non FIKI SOP is that the freezing level be comfortably above MSA, so a descent resolved the issue.
The turbine class have the advantage of de-rated turboprops putting out tons of excess power and can punch through most icing layers, although freezing rain from nimbostratus, or convective SCLD ice might also overwhelm them. These are usually subject of a severe icing SIGMET. My incidents in MEP FIKI aircraft were not in severe icing SIGMET areas, and I would regard a severe icing SIGMET a no despatch condition for any piston aircraft. In effect this proves the point that light GA FIKI can only cope with light to moderate icing at best, and you should exit icing whenever you encounter it.
My point is that I worry there is an increase in risk tolerance with piston FIKI aircraft, which potentially leads to over optimism on despatch.
It would be interesting to collate what SOPs are used when considering launch into icing? eg
Relationship of temperature to MSA, and what altitude safety margin do you have between MSA and freezing level?
SIGMET tolerance
Type of weather tolerance, or conversely no go items eg convective, nimbostratus, freezing rain
Does your type publish an icing exit speed? for example on the Beechcraft Baron this is 130 KIAS
Conversely do you exit icing at the first encounter, which could even be conservatively defined as 5oC in visible moisture, or do you wait for KIAS deterioration and how much? 10 KIAS? 20 KIAS? or do you wait to see icing building on flying surfaces? windscreens?
Do you modify approach SOPs if flying with visible ice on the flying surfaces? eg Flapless approach, actually a limitation on some types
Use of fuel anti ice additives?
On icing exit speeds, critical alpha reduces dramatically with icing on the flying surfaces. For example a Beech B58 has a clean stalling speed of 84KIAS, but an icing exit speed of 130 KIAS. If a ‘normal’ critical alpha might be 15 degrees, with icing this might reduce to 5 degrees, and obviously in due course to zero!
The following article illustrates some of the issues of piston FIKI.
https://www.aviationsafetymagazine.com/features/when-flying-in-ice/
Another example is a good colleague who paid his dues flying cheques at night in Beech 18s in Texas. The colleague has basically lived in FIKI MEP for around 3 years equivalent 24/7. Not so long ago on reaching the FAF and extending flaps, in very garden variety icing conditions, the FIKI aircraft had a tail-plane stall with a pitch down of around 45 degrees at platform altitude in IMC. Exciting!
One type of MEP FIKI TKS, doesn’t take a genius to know which, is notorious for ice bridging behind the TKS screen and ahead of the ailerons – great!
Using the /100k hour statistic I estimate my IMC severe icing encounters at around 25-50 equivalent incidents, hence my strong scepticism on the true benefits of piston FIKI on despatch into hard IMC.
AFAIK no aircraft is certified to fly into known icing so I wouldn’t launch into an area where severe icing is expected.
I am a leisure pilot and can usually choose when and where I fly.
When planning.a flight in an MEP with anti-icing or de-icing I tend to think in the same terms as I would flying an SEP without any anti icing or de icing equipment.. IOW I avoid any area where icing of any sort is forecast like the plague.
I also make sure that if I am going to fly in cloud I am well above MSA. In fact my SOP is always to fly above MSA. In a twin that means planning with an engine failure in mind and that the single engine ceiling is above MSA.
As well as the 0° level and if there is any cloud at that level I would be looking at wherher or travelling towards a front particularly a warm front ir a temperture inversion.
So my prerequisite is that I can’t keep away from cloud below freezing level, I don’t go.
I don’t tend to fly at very high levels where the the temperature is too low for icing. Not in a piston engine aircraft anyway.
But of course we all know that things don’t always go as planned and you find yourself picking up un predicted ice.
In that case my SOP would be to leave it as soon as i can, whether or not I have anti or deicing equipment on board. If possible I will descend out of it ie if I can stay above MSA. But much will depend on the conditions of the day and the aircraft I am flying.
On a DA42 for instance I would start to think about engine icing if i am in cloud and the temperature falls below +5°C. That means pulling on ambient air. I would also be keeping a very close eye on the exterior for any sign of icing and at the first hint of concern I would be switching on the TKS system as it it an anti ice system and struggles to be of any use once ice has formed. From a personal viewpoint this has come about when I notice what seems to be
whitening or frosting on a spinner.
Of course with boots you have to wait for a build up of ice before you switch them on.
You then sit and hope that the boots work. So my SOP is to get out of the icing zone in the fastest way possible and the first route that pops into ones head is to descend but keeping MSA a priority as lower than that is the fastest way to meet your maker.
gallois wrote:
AFAIK no aircraft is certified to fly into known icing
The TKS-equipped TB20 is. Quote from section 2 (limitations) of the POH: “Flight into known icing conditions is approved provided that the following equipment is installed … and is serviceable.” The POH page is marked “DGAC approved.” (This is from the POH for factory-installed TKS. The POH supplement for Peter’s retrofit TKS may have a different wording.)
Not to mention transport category aircraft…
I think I wrote " no aircraft is certified to fly into severe icing" or at least that’s what I meant to write.
This includes CAT aircraft.
gallois wrote:
I think I wrote " no aircraft is certified to fly into severe icing" or at least that’s what I meant to write.
Well, yes. By definition “severe icing” is relative to the deicing capabilities of the aircraft. But what is severe icing to one aircraft may be moderate icing to another.
No both FAA and EASA and the DGAC here have published papers which say that NO AIRCRAFT is certified to fly into severe icing.
Severe icing is indicated with the severe icing symbol on met reports. Whether an aircraft has FIKI,(FAA term) through TKS, thermal wing, rubber boots or whatever, no NAA has yet certified an aircraft to fly into severe icing.
So it is not dependent on any particular anti or de icing equipment or.how good it is perceived to be.
In the eyes of certifying NAAs flying into severe icing, however well equipped is just too dangerous.
gallois wrote:
No both FAA and EASA and the DGAC here have published papers which say that NO AIRCRAFT is certified to fly into severe icing.
Please give a reference. As far as I can see, the EASA Air Ops regulation makes no reference to the absolute intensity of icing (neither for CAT nor NCO). It only refers to the intensity of icing relative to the capabilities of the aircraft.
What DGAC has said in the matter isn’t relevant — it is not within their power to regulate.
I gave the reference in a previous report which I posted in an earlier thread on icing.
I mentioned DGAC because the report was co- authored by FAA EASA and the DGAC.
It would not be in NCOs or Air Ops as it is not an operational matter but a certification matter and should really be carried in the limitations section of the AFM.
I will see if I can find it again.
But I would point out that severe icing is incredibly dangerous and I have yet to see a system that could clear it faster than it grows.
Been there once and don’t want to go there again thanks🙃
RobertL18C wrote:
On icing exit speeds, critical alpha reduces dramatically with icing on the flying surfaces. For example a Beech B58 has a clean stalling speed of 84KIAS, but an icing exit speed of 130 KIAS. If a ‘normal’ critical alpha might be 15 degrees, with icing this might reduce to 5 degrees, and obviously in due course to zero!
very interesting, thanks for sharing
there is also this article describing how cruise and stall speeds are affected by wing contamination.
@RV14 thank you for the link, great author’s name for an RV pilot, Mr Speedy :)
