Below Freezing Temperatures at Low Level
 

Hi,

First time having to consider flying in below freezing temps. Just wanted to ask you what needs to be taken into account when flying in such conditions? Obviously, plenty of carb. heat... But what happens when you fly a C152/172 in below 0 temps.? Do the wings and tail ice up and how do you deal with such a situation when descending is not an option, say -2celcius at 1000ft?

Any advice would be greatly appreciated!

NO - carb heat is nothing to do with low outside temp. Carb heat is what you use to safeguard against (or melt) the ice in the carb venturi which is caused by the temperature drop in the venturi, and in the right conditions (humid, not too cold, not too hot) this can otherwise cause an ice buildup. Loads of stuff online e.g. this.

Low outside temps are a hazard for structural (airframe) icing. This is not an issue if you stick to clear VMC, but for flight in IMC you have a problem in that any ice you pick up [cue the usual dire warnings about icing and death] you will be landing with, and if you picked up a lot, then your landing speed has to be so much higher to maintain control... basically if the 0C level is below the MSA then you have cut off the obvious escape route from structural icing; not a good idea.

The other issue is ground icing (frost) which does need to be cleaned off pretty well before flight.

If it helps, I flew a PA28 today in the only clear slot (Benson vis was <400M in FZFG until 1300...) and the temperature was never above minus 4 in the air. No problem at all. Mind you, we do keep it in a heated hangar which avoids the frost problem... :}

Basically as stated, watch out for frost and ice on the airframe before you start (MUST be COMPLETELY clear before flight) and visible moisture (IMC) during flight; otherwise you will be fine.

And watch out for low sun in hazy conditions - all I did was (small RAF style) circuits yet I almost lost sight of the runway several times.

Tim

My top tips:

Clear ALL ice off the aircraft before flight. In standard GA aircraft (152/172 etc) there is no such thing as an acceptable layer of frost.
Don't go into cloud (there are some exceptions but that is like trying to figure which one of 30 snakes doesn't bite)
Don't fly into precipitation - if you do, turn around and get out quickly.
Carb heat - as you should normally be doing it. Note the biggest threat is actually at slightly warmer temps

http://www.microlighters.co.za/downl...le.php?id=9178

When you land, plan on having minimal/no braking. I was flying this afternoon and an apparently damp runway turned out to be rather interesting!

Enjoy!!

Watch out for the effects of extreme cold on flying controls. :eek:
In my case very stiff ailerons, due contraction of the control cables inside wooden wings. Having taken off in gin clear conditions at -1 temp and climbed to 12,000 ft for a superb view over the Preseli hills.

The most vital thing to realise is that water can exist in the liquid droplet state below 0 degrees C, down to about minus 10. This is because water droplets need a nucleus / suitable surface to freeze onto.

If you fly in temperatures below zero, your aircraft will become cold soaked but you are generally safe in clear air, as IO540 said, due to the lack of liquid water (although it is possible for hoar frost to form by deposition).

However, if you then fly your cold airframe through some of this "supercooled" water (i.e. mist, fog, cloud), it provides a nucleus for freezing for any water droplets that come into contact with it.

Airframe icing can form very rapidly, destroying lift, cloaking radio and navaid aerials, coating the windscreen with an opaque layer you can't see through, perhaps also getting into vulnerable flying control mechanisms, possibly preventing flaps (or one flap) from being lowered, for example, in severe cases.

Stay well out of icing conditions; some days it's not just safe to fly a light aircraft (or helicopter) at all. However, generally speaking, provided you comply with the ANO PPL weather limits for VFR (moisture is what reduces the vis, in most cases), you should stay safe. However, it's always a good idea to check the icing level via the Met Office F214 before planning your flight, (or not!).

Note that the metman's definitions of icing (light, medium, moderate, severe) refer to icing accretion (build up) RATES, not total icing. If you fly for long enough in light icing, it can be just as bad as that from a short time in severe icing.

Don't forget the airfield
 

Don't forget the airfield conditions either.

A long time ago at EGPE just as I went to shout 'Clear prop!' someone skied past the nose!

With ice on the taxiway and runway, braking had to be non-existant or extremely gentle. On landing there was more than sufficient runway for my C-150 to come to a halt without braking, using flaps40 to slow down. (There wasn't a breath of wind.

Boy, was it worth it! Not a cloud in the sky and the north of Scotland completely white.

I'm based at a grass strip now so I guess I'm grounded for a while yet, looking at the forecast.

Couple of things to add to the previous posts.

- When you go flying bring warm clothes, gloves and sturdy boots for the pre-flight, for hauling aircraft into and out of (heated) hangars onto (icy) aprons and so forth. Change into lighter gear when the aircraft is on the apron, de-iced and ready to go.
- Aircraft windows are perspex, not the layered glass that you find in a car. It scratches far easier than car windows, so do NOT use any hard object to scrape away frost. De-ice fluid (suitable for aircraft use) is the way to go if no heated hangar is available. (Any hangar with a temperature over 0C will eventually melt the ice.)
- Aircraft performance in cold weather is generally better than in warm weather (but you knew that already, didn't you).
- Keep an eye on the OAT while climbing out. If there's an inversion the temperature a few 1000 feet up might be higher than on the ground, and that may just be the life-saver you need.
- If you do end up in visible moisture (clouds, mist) in addition to getting out ASAP, also turn on the pitot heat and windshield demister/defroster.
- Carb heat may actually have a detrimental effect on carb icing, under certain, rather unique, circumstances. If the OAT is around the -10/-15C level and there's frozen water in the atmosphere (in the form of very light snow/hail droplets), then applying carb heat might raise the temperature just enough for it to melt, and then solidify again in the carb venturi or through the evaporation of fuel. Better not use carb heat in those circumstances. (I've never experienced this myself. No doubt the experts will be able to comment on this further.)
- Don't forget a camera. The countryside is beautiful after a snow shower.

I flew to Isle Of Wight from Lydd and back the other day and it was -4°. It was a stunning flight. I first started flying in Sweden where we regularly flew in very cold weather. Never had any problems with ice.

Even though there was no moisture in sight on this flight, I did keep the pitot heat going. And I was quicker on the carb heat than I normally am, pretty much pulling it on all descents. Don't think I needed to, but it just felt like a little extra safety.

Question: is there a little temp meter that records the temps at different heights as you climb out? This could be useful as I'm normally to busy to watch a temp meter in the climb (especially on the Cessnas where its up on the corner) and that info could be useful if one should encounter ice.

And if you're flying an aircraft with spats the other consideration is snow/slush/ice build up in them that then freezes with a resulting locked wheel on landing.

7700

That is one reason why I don't fly enroute in IMC, on long high altitude flights. Structural icing is very "statistical" but in a few hours one is bound to pick up plenty of it. VMC on top + oxygen is the way to do this.

Turning with ice
 

A couple of posts have mentioned that if you should find yourself in cloud/precipitation in freezing conditions then you should get yourself out of it ASAP.

Quite correct, but remember that if you do have any structural icing at this point it will raise your stalling speed, especially in the turn. So turn gently; no steep split-arse turns.

Broomstick.

If the fuel drains don't work it's probably water in the fuel which is frozen.
DO.

Take more than enough warm clothing. If you have an "out landing" for any reason you want to survive the outside temps for as long as it takes. No point pulling off the perfect forced landing and then not living to enjoy retelling it in the pub a few times.

If the fuel drains don't work, you don't fly...

Zero defect tolerance when it comes to anything important :)

All elemtary stuff really. Go back and read the books. These questions never arise in the north eastern USA and Canada where the temps can get very low in winter.:ok:

From my experience I'd say if the weather is fine enjoy those low temps in the UK. The average spam can goes up like a pocket rocket in the cold and is off the ground with minimal ground roll.:D

Canopy misting (or icing up) and pilot's bladder filling up more quickly in the cold (don't know if that's psychosomatic or the result of having a hot drink before takeoff). Fingers freezing (particularly when doing preflight checks). Lack of room in cockpit because you're wearing more clothes.

Thanks for all the replies.

Clears things up nicely for me. I will, out of interest, keep an eye on the OAT from now on to see how the temp. changes as I go up...

After several years of frozen fingers, I invested in a set of fueller's chemical resistant gloves (about £6) - no cold fingers, no avgas smell on your hands and probably safer - I should have done it day 1!

Wilson Winter Golf gloves...
http://www.118golf.co.uk/@@content/p...love_51258.jpg

They have really grippy palms- the glove comes off before ANYTHING slips out of your hand!

As they are designed for golf, they don't restrict your fingers at all so you never need to take them off... But aside from all of that they are really, really warm!