Utility of non-deiced aircraft during fall and winter

Hello!

There has been a long thread (or even two or three) going about this in the past. It is probably worth searching for it, there have been some good suggestions.

So basically I'm asking: how you decide go/no-go?

Experience, common sense and respecting rules. I fly non deiced singles and light twins as an IFR instructor. Not flying whenever there are icing conditions somewhere along the route of the intended flight would mean not to fly at all from September to April on nine days out of ten. When the freezing level is above the minimum safe enroute altitude (as would be the case in your 6 deg .C example over most non-mountainous areas) you can always descend into positive temperatures. When there are layered clouds, you can always (almost always) climb or descend to a cloud free space between the layers.

But when the temperature on the ground is at or near freezing level in cloudy conditions (with clouds prevailing in the altitudes/levels we can reach with our non-turbo non-oxygen training aicraft), I refuse to fly non-deiced aircraft. Verboten. Very simple.

And - most importantly - how does European ATC cooperate with pilots in a non-FIKI aircraft flying around in subzero temperatures?

They are as helpful as they can (at least in southwestern Germany and regarding training flights, I don't have any other recent experience) but they can not do miracles. They can't let you descend below MRVA unless you cancel IFR and they can't let you change levels when there is a lot of traffic everywhere. Unless you declare an emergency, which some of my instructor colleagues had to do in the past due to rapid ice buildup.

Experience of winter IMC in a normally aspirated piston twin over nearly ten years suggests that the boots were used in moderate conditions around 3-5% of the time. They were reasonably effective to get you out of an icing layer, although given typical airways flight levels any icing encountered, say, above FL120 (usually associated with convective or orographic lift), made it clear that de-icing in a piston is only modestly effective.

IMC over Europe's various mountain ranges makes you a believer in turbine equipment.

If you are talking plain SEP aircraft, the most important factor in the decision process is the "profile" of the clouds. Cruising in IMC is basically a no-go in late fall, winter and spring, so that rules out frontal activity weather. Climbing through or descending through a layer is usually no big problem. Therefore, the most important WX planning instrument becomes the satellite image, in order to estimate cloud thickess. You'll soon find that in winter, there are many many very "benign" high pressure days that look grey from the ground, but are actually wonderful for IFR in SEP aircraft.

As outlined above, one has to choose the conditions one flies in, carefully.

Obviously remove ice from flight-critical surfaces before departing (which can be a huge hassle, and you don't really want to be scraping it off windows because it will damage them).

Most IFR flight is done at high altitude, due to the Eurocontrol route system, and the objective (if not deiced) is to climb above any cloud.

But even a deiced plane will ice up too much eventually if you sit in the stuff for hours.

One has to make a judgement on the thinkness of any layer in the departure and arrival areas. If the 0C level is below the MSA that is a big problem because any ice you pick up you will have to land with (unless you are certain for a nice enroute section in sunshine which can remove it by sublimation) but that's the price you pay for flying a non-deiced plane

ATC are no problem. As always, you must keep decisionmaking in the cockpit. Usually, if just above a cloud layer, at say FL180, and your ceiling is FL200, and they ask you to descend due to traffic, you say "unable due to icing conditions below" which they can't argue with - especially as the "traffic" is prob99 an Airbus/737 which is not performance limited... I had that recently over Switzerland; they told me I had jet traffic behind me and they took a little while to absorb the "situation"... The problem can be in some countries where they can't speak enough English to know words like "icing" (Spain is a popular one) and they can get very upset but you just ignore them and look after yourself.

I am OK to depart if the 0C level is high enough and the departure cloud layer is a few k feet thick, or less. I estimate that visually (look for blue holes especially). The cloud top forecasts are nowhere near good enough for this purpose. In any case, the return option is available.

If the 0C level is too low then I won't depart into IMC unless the layer is scattered and thin.

OTOH if the surface temp is say -5C and the cloudbase is 5000ft, the cloud will be -15C or colder which is again OK (for stratus) - for a departure.

The effect on despatch rate of likely icing conditions is less than the effect of frontal weather, fog, etc, anytime of the year. I get maybe 75% despatch rate (TB20). Some detailed trip writeups here.

But then to be fair I fly much fewer long trips in the winter because the places one can reach (in S. Europe) are not going to be nice to hang out in anyway

There is no one answer, but I take a cautious approach in the winter. My PA28 doesn't have the performance to quickly try and out climb a potentially thick layer of negative temperature cloud. But if there was as you say it was +6 on the ground, and cloud was at 3000 ft, then I'd be planning a route that allowed me to stay in VMC (so it wouldn't be a IFR flight in controlled airspace) if I was unable to break through the cloud in something like 2 or 3 minutes, which at say 700ft/min would mean I want to be in sunshine by 5000ft. If not, down I come.

There are other factors you can try and take in - the Ogimet site, satellite images, other pilot reports, visibly trying to anticipate the thickness but the amount of sunlight coming through (very unscientific I know, but sometimes you can sense it's a thin layer), don't do it if there is frontal weather.

For me, I begrudgingly have to accept my aircraft is just not FIKI and I don't have the money to buy such a machine, so I have to make compromises and accept the limitations, and that may well mean my IMC flying in colder months is extremely limited. You have to stay safe, and be comfortable.

What met people traditionally call medium level cloud tends to be 5000-20000ft or so, so I would check that. High level cloud is cirrus, or CBs (say FL300).

The GRAMET cloud tops can be out by several thousand feet, in my experience, so while useful one needs to treat that forecast with some caution.

The temperature of the plane will track the temperature of the ambient air (plus a little bit of aerodynamic heating - maybe 1C at 150kt) virtually instantly (in seconds). There is no inertia - except a little bit with fuel tanks if the fuel goes right up to the leading edge. But you aren't going to get significant ice via that mechanism.

In stratus cloud, ice starts to collect at -1C, is worst around -5C, and tends to stop around -15C.

If you have cloud 3000-7000ft and the 0C level at 5000ft, and the MSA is say 1000ft then I would go. The problem is that 4000ft of cloud one can't see through (no holes) and the 7000ft could be 10000ft. My worst ever ice collection cases were in smooth stratus... But the fact that you can descend into warm air and melt the stuff off before having to land means you have an escape route so this is not actually dangerous so long as you take action early.

According to the GRAMET I would have spent at least one hour at -2C.

The GRAMET is nowhere near good enough for data like that. The -2C could be -5C, etc... You need to work with bigger margins.

What are you flying? Some planes can carry more ice than others.

The one thing that is easy to forget is that the aircraft surface warms very quickly as it has a lot of airflow. So if you are 0 to plus temps, you really don't pick up ice (other than in my case a bit of frost over fuel tanks due to cold fuel).