Flying & Light Frost

[alex90]

I went for a night flight last night to keep myself current and polish my night landings. It was a beautiful clear night, good visibility but only 3 degrees on the ground when I took off and only about 1 degree when I landed.

When I got out of the plane, I noticed a very very thin layer of frost on most but not all of the fuselage of the C172 I was flying. I did check the strut and under-wing in flight but did not notice anything.

I didn't notice any adverse control effects, nor did I notice any decline in performance (in fact quite the opposite - most likely due to the cold air) I had a great climb rate and really good cruise.

So my question is: would this accumulation of very light frost be of any consequence? We're not talking about heavy ice forming, just very very thin, light frost. (perhaps even lighter than what can be seen on your car in the morning after a frosty night)

Thank you for comments!
Alex90

[Pace]

Alex

Any coating of frost will degrade the performance of the wing to a certain degree so its a no no to depart with frost on the wing.
Always remove it especially on the leading edges and tail.

Pace

[Shaggy Sheep Driver]

I was de-frosting out Yak one morning (by moving it into sunlight!) when I witnessed a C172 take off, stagger for a few seconds in ground effect, then crash back down again on the runway. Frost on the wings.

[alex90]

Thanks for your responses!

It is one thing departing with ice on the wing, and quite another to get a slight accumulation of light frost during flight (and to some degree - not much you can do should about it when already airborne).

The argument to stay on the ground if icing could happen is a valid one, but what if it wasn't forecast, and you're arriving a little later than expected from a far away destination?

By very very light - I mean less than 0.5mm, patchy frost by the way, only visible upon very close inspection, not a wing covered in 1+cm of frost / ice!

Thanks for your responses!
Alex

[Pace]

Alex

Carry a can of car windscreen deicer even for a little its not good practice to attempt a takeoff and at what point does a little become a little too much ?

Some wings are critical to any pollution or icing. The Challenger 604 crash out of Birmingham was caused by a pilot deciding that there was just a frost on the wing.

So for the price of a tin of deice spray any icing on the wing is a no go

Pace

[dash6]

Sounds like hoar frost forming on a cold soaked airframe.Might well have formed after landing.How long was the flight?

[piperboy84]

I didn't realize that frost can form in the wings in flight

[9 lives]

I didn't realize that frost can form in the wings in flight

Neither did I.

It is true that departing with frost accumulated on the wings is prohibited. Interseting that departing with the paint in appallingly poor condition is not!

[alex90]

Sounds like hoar frost forming on a cold soaked airframe.Might well have formed after landing.How long was the flight?
The flight was 1 hour, did a few circuits. It may well have formed after landing - that is quite a possibility and also why I didn't notice any whilst frequently checking the wings and struts during flight. (Also would explain the lack of degrading performance which would be expected if ice was on the wing)

Carry a can of car windscreen deicer even for a little its not good practice to attempt a takeoff and at what point does a little become a little too much ?
Should there have been any frost on the wing prior to departure, I would either have deiced, or cancelled the flight without question. I was under the impression that takeoff with ANY ice on the wing was prohibited. Very good point about the little and the too much though!

Step Turn & Piperboy84 - neither did I - that is why I was so surprised!! But Dash6 makes a good point, perhaps there was a little more moisture when I landed and it just created a thin layer of frost after landing. The surface was clean and dry on takeoff (if a little cold to the touch!)

[the_flying_cop]

excuse the potentially ignorant question, but isn't car deicer corrosive? is it ok to use on wings?

[Martin_123]

I mainly fly out of a grass field that sometimes can be muddy even if the surface seem hard and aircraft doesn't sink in. From time to time (rarely but does happen) I would arrive back to field only to find my leading edges of wings and controls covered in chunks of already dried up dirt (indicating that dirt got on the wings during take off).

Technically the correct answer is yes - it will have an effect. In reality, as you already noted - you will not feel it.. As long as you don't fly close to stall speeds it should be fine. The thing about GA spam cans is none of their wings are really factory spec - all of them have some sort of bends, rivets etc that make them already imperfect, I think it's very unlikely for a thin layer of ice make things any more difficult to you. I have yet to find two C150's that stall the same way or at the same speed

but the emphasis here is, as already mentioned - when does it become too much? Although thin layer it self will not cause problems, that thin layer may have a tendency to start growing rapidly if the humidity is there to support it

[alex90]

excuse the potentially ignorant question, but isn't car deicer corrosive? is it ok to use on wings?

I have no idea - I have aeroplane deicing fluid in the back of the plane - although I have never used it as normally if it is icy, or forecast to be icy, I just don't even consider taking off.

[eckhard]

I went for a night flight last night to keep myself current and polish my night landings. It was a beautiful clear night, good visibility but only 3 degrees on the ground when I took off and only about 1 degree when I landed.


As it was a beautiful clear night, it's highly unlikely that the frost formed in flight. For ice to form on the leading edges in flight, there has to be a concentration of super-cooled water droplets (like in a cloud) that the aircraft impacts as it flies through them.

Another way that ice can form in flight is when a super-cooled airframe flies through rain or drizzle.

As neither of these conditions pertained on the night in question, I would suggest that the frost formed after landing, while you were taxying in what was probably a high-humidity environment. The airframe was cooled during its recent flight and the water vapour in the air sublimated directly to ice.

There are two scenarios to consider:

1. Pre-flight.
As others have mentioned, taking off with any ice on the wings or tail is a mug's game. Thin frost may be acceptable on the fuselage, provided that any aerials, intakes, vents or probes (and the areas ahead of them) are clear. Heavy frost or ridges formed by previously-melted ice are unacceptable. If in doubt, the best way is a perfectly clean airframe.

2. In flight.
Dealing with ice accumulation in flight depends on the certification and equipment fitted to the aircraft. In a C.172, no ice accumulation is certified, therefore avoidance is the only sensible policy. If an inadvertent encounter with ice is experienced, the following may be a sensible course of action:

Full Carb Heat (Adjust Mixture as required)
Pitot heat ON
Windshield heat ON
Try to exit the icing (180* turn, climb, descent)
Be aware of MSA
Cross-check instruments
Use Alternate Static Source if required

If landing with residual ice, conduct a low-speed handling check at a safe altitude before making the approach. Be very careful when lowering flaps and be prepared to retract them if handling is degraded. Consider making a flapless landing.

[TURIN]

I didn't realize that frost can form in the wings in flight

That is quite a scary statement.
Remember, if it's only just above freezing on the ground it will be below zero at altitude. An hours flying in sub zero temp will cold soak the structure and pick up any moisture as frost.

It doesn't need to be metal either. Years ago I flew a hang glider on a cold New Years day. After a short 30 min flight I landed and noticed frost on the Mylar leading edge.

[Pace]

Turin

Not always true especially in high pressure and clear skies you can find that the air above the ground increases in temperature
I have had -2 on the ground and plus 8 at 8000 feet
In flight ice will normally slowly vaporise off over time depending on how much you accumulate!
Even with an ice capable aircraft and boots! Blowing it off the leading edges doesn't take it off the airframe
I had one occasion after leaving a front I asked for a temporary descent out of airways to loose the airframe ice as I had a long way to go and substantially reduced airspeed!
After it melted off I climbed back into the airway and carried on )

Pace

[thing]

Depending on how cold and long you were up for the fuel in the tanks can act as a cold soak. When you descend/land the higher humidity causes frost to appear on the airframe next to the tanks, in fact you can quite nicely see the outline of the tanks sometimes which shows you where they are and how big they are if you didn't know!

I agree with Martin to an extent, most club hacks have that many dents and bumps in the leading edges that you're probably simulating icing every time you take off in them.

[piperboy84]

I guess I've been labouring under the false belief that the only way you can pick up icing while in the air that will inhibit the safe operation of an aircraft was when you have the combination of temps being near or below freezing AND flying in visible moisture.

As far as on the ground any frost that has accumulated on a parked aircraft must be removed prior to flight ( I believe there was a C210 silver eagle turbine that crashed because it took of with a coating of frost recently) but I was unaware that once the frost has been removed it can re-accumulate while in flight without being in visible moisture.

can someone clarify for me?

[foxmoth]

Just to add, if you see frost building up on the wings during flight i would add a bit to my approach speed, on most aircraft i would look at adding 5kts, though if i had proper icing, say having descended through cloud I might add a bit more, also with something with a more critical wing I might add a bit more, maybe worth doing a low speed handling check at height as well.

[Pace]

I would concur with Foxmoth but add that if you are carrying ice on landing as well as adding speed keep the turns shallow

The problem with taking off with Ice is that you are at a relatively slow speed on rotation.
The challenger 604 which crashed at Birmingham dropped a wing and crashed into the runway! Ok a wing which is critical to any contamination ice or otherwise and a much bigger faster aircraft, but the warnings are there

Pace

[The Flying Pram]

I witnessed a C172 take off, stagger for a few seconds in ground effect, then crash back down again on the runway. Frost on the wings.Several years ago I was asked to help the AAIB dismantle and recover the wreckage of a flexwing microlight. The wing had been left rigged in an open sided barn the previous night during winter, and was observed to have a thin coating of frost the next morning. It got off the ground O.K. but wouldn't climb. Faced with a hedge at the end of the field, the pilot put it back down on the strip but lost control and overturned whilst trying to stop. Unfortunately, the passenger died, and the pilot was seriously injured.

[BillieBob]

Some misunderstanding/confusion here between frost and ice. Frost is formed when air is cooled below its dewpoint and that dewpoint is below 0°C. If conditions are right, a cold-soaked airframe (well below 0°C) descending into a relatively warmer/moister environment will cool the air in contact with it, perhaps sufficiently to form a layer of frost - the presence of supercooled water droplets/visible moisture is not required. The effect is more common in aircraft descending rapidly from high altitude (e.g. military/commercial jets) but is not unknown in light aircraft.

[eckhard]

Yes, frost and ice (when discussing flight) are two different things, even if they both comprise frozen water.

Pre-flight:
Frost may form on any exposed surface if the conditions are right. Think of it as 'frozen dew'.
Ice may also form if conditions are right, e.g. freezing fog with a light breeze. The windward edges of the airframe can build up rime ice due to the super-cooled water drops being blown onto the impinging surface. I have even experienced rime ice on my motorbike's mirrors and my gloves while riding in such conditions.

Both frost and ice (and snow) must be removed before flight (Exceptionally, a few allowable areas may have light frost remaining, as described in #13).

In-flight:
Frost may form on super-cooled surfaces if a flight in sub-zero temperatures is followed by flight through humid air as described by BillieBob. Normally, the actual airframe warms up quite quickly but the fuel will stay at a sub-zero temperature for quite a while and the skin in contact with the fuel may get some frost, normally on the underside of the wing, unless the tanks are really full. I have not seen frost developing on any other part of the airframe, e.g. on the fuselage as described by the OP.
Ice can form in many ways; the most common being rime ice. As previously described, super-cooled water droplets impact the leading edges and a small proportion freezes immediately with the remainder flowing back a distance until it too freezes. The proportion that freezes instantly is greater, the colder the water droplet. This implies that temperatures just below freezing can result in more 'flow-back' before total freezing occurs, which is bad news as the area covered will be greater. Nevertheless, the formation of rime ice tends to restrict itself to 'leading edges' only.

As frost will (generally) only form in the vicinity of the fuel tanks, there is not much that can be done to remove it until after landing. If you are concerned about a build-up of frost (and you can see it), then consider a handling check and an increased approach speed, as described in previous posts.
Ice however is much more serious and therefore should be avoided or removed, if you have the equipment fitted to do so.

Post-flight:
Frost may form anew in the same way as it did pre-flight, i.e. as 'frozen dew' on a cold surface. This is what I believe happened to the OP as he taxied in.
The pre-existing frost in the vicinity of the fuel tanks may persist and even grow, depending on the air temperature and humidity. It may require removal prior to further flight
New Ice could form if you were taxying in freezing fog, but then the preceding landing would have been quite 'interesting' as well!

[alex90]

Thank you Eckhard for such a detailed response. Much appreciated. I think this sheds a little light on the subject!

Thank you for everyone else for commenting! Much appreciated, especially the course of action that everyone would take. Surprising how many would consider doing control checks - I remember reading about an A380 captain for Qantas doing just that after one of the engines exploded in flight.

Hope someone other than me learnt something as a result on this!

Best Wishes,
alex

[9 lives]

I do not agree that frost can form on an aircraft in flight. The many references I can find to the formation of frost refer to calm, still, or static air being necessary for formation. My experience over four decades of Canadian winter flying has never shown "frost" forming on a moving plane - only on a motionless one, in calm air.

I support this with the knowledge that to prevent formation of frost on valuable crops, helicopters are flown over low, or fans used to disturb the air. It must work, it's been done for years. I can also assert that an aircraft flown with frost in non critical areas at takeoff, will land back with that frost gone due to sublimation in flight - moving air.

I have seen frost form on the fuel tank skins of a "wet wing", but not otherwise.

[eckhard]

Thanks Step Turn,
Your observations tally with mine. I guess the frost I have seen on the fuel tanks has formed after landing and not in flight.

So, we can deduce that the frost that the OP saw on his Cessna formed during the taxi-in and not in flight.

[Pace]

Ice can distort the flow of air over the wing, diminish- ing the wing's maximum lift, reducing the angle of attack for maximum lift, adversely affecting airplane handling qualities, and significantly increasing drag. Wind tunnel and flight tests have shown that frost, snow, and ice accumulations (on the leading edge or upper surface of the wing) no thicker or rougher than
a piece of coarse sandpaper can reduce lift by 30 percent and increase drag up to 40 percent. Larger accretions can reduce lift even more and can increase drag by 80 percent or more. Even aircraft equipped for flight into icing conditions are signifi- cantly affected by ice accumulation on the unpro- tected areas. A NASA study (NASA TM83564) showed that close to 30 percent of the total drag associated with an ice encounter remained after all the protected surfaces were cleared. Nonprotected surfaces may include antennas, flap hinges, control horns, fuselage frontal area, windshield wipers, wing struts, fixed landing gear, etc.
Some unwary pilots have, unfortunately, been caught by surprise with a heavy coating of ice and no plan

So there you go Frost no thicker or coarser than a piece of course Sandpaper can reduce lift by 30% and drag by 40% so don't risk it

Full article worth reading linked below

http://flighttraining.aopa.org/pdfs/SA11_Aircraft_Icing.pdfPace

Pace

[dash6]

So,when you put"frost"in your spellchecker, it comes out "ice" ?

[Pull what]

Some poor understanding of icing, ice and frost in the some of the above posts.

Car deicier is not an approved fluid for use on an aircraft, it is also not an anti ice, nor do you know what its holdover time is. It may well get rid of the ice but you are introducing a water based fluid onto the wing and you have no idea what will happen to that fluid in sub zero temperatures apart from at some stage it will refreeze.

I do not agree that frost can form on an aircraft in flight. The many references I can find to the formation of frost refer to calm, still, or static air being necessary for formation. My experience over four decades of Canadian winter flying has never shown "frost" forming on a moving plane - only on a motionless one, in calm air. Frost can form on and around cold soaked fuel tanks underneath the wings after high altitude flight . Certainly very common on all the jet types I have flown especially after a rapid descent and it does form in the air not just magically after touchdown!

On two types I flew you had to do an overwing tactile test before flight in temps below 6 degs. Note -overwing only.

Attempting to take of with hoar frost on the wings makes you a test pilot or just an idiot-good luck.

https://assets.digital.cabinet-office.gov.uk/media/5422f61940f0b61346000619/5-2004_N90AG.pdf

So my question is: would this accumulation of very light frost be of any consequence? We're not talking about heavy ice forming, just very very thin, light frost. (perhaps even lighter than what can be seen on your car in the morning after a frosty night)One of the problems with hoar frost, not understood by many pilots, is that if the same amount of top surface frost could (and it cant) form in the cruise the aircraft may well be perfectly flyable due to the ample margin above the stall speed. However during the low speed transition from lift off to climb speed, with a much lower margin above the stall speed caused by the ice, the pilot may experience a stall and loss of control, the other danger is that the stall characteristics in such a stall may be unconventional or more marked that a normal stall.

[9 lives]

Frost can form on and around cold soaked fuel tanks underneath the wings after high altitude flight . Certainly very common on all the jet types I have flown especially after a rapid descent and it does form in the air not just magically after touchdown!

Should we expect the formation of "frost" on a jet wing, descending from high altitude, to be representative of typical GA flight scenario? I have never flown a jet, and perhaps these conditions can exist in that environment, but I have yet to see "frost" in four decades of flying all kinds of propeller aircraft during Canadian winters.... (I sure have seen ice though :ooh:).

I agree that we should not be test pilots with varied or worse prohibited configurations of an aircraft. However, being surprised by a stall shortly after liftoff in a light GA aircraft has me thinking that the pilot was along for the ride, rather than flying the aircraft. If you unstick an aircraft, and it flies to your liking, it should fly better as you allow it to accelerate during the climb away. If, on the other hand, you get it airborne, and then slow it down and stall, you weren't doing it right! If you try to unstick it at the appropriate speed, and it resists your effort, you might consider aborting the takeoff!

[Pace]

White frost is a solid deposition of ice which forms directly from water vapour contained in air.

White frost forms when there is a relative humidity above 90% and a temperature below −8 °C (18 °F) and it grows against the wind direction, since air arriving from windward has a higher humidity than leeward air, but the wind must not be strong or it damages the delicate icy structures as they begin to form. White frost resembles a heavy coating of hoar frost with big, interlocking crystals, usually needle-shaped.

You are both right as white frost cannot form in strong wind conditions and what forms on a wing with high speed air flowing over it is more likely to be hoar frost which technically is not frost ;)

Pace

[RatherBeFlying]

Car deicier is not an approved fluid for use on an aircraft, it is also not an anti ice, nor do you know what its holdover time is. It may well get rid of the ice but you are introducing a water based fluid onto the wing and you have no idea what will happen to that fluid in sub zero temperatures apart from at some stage it will refreeze. Perfectly correct, but on a practical basis will do a proper job of dissolving the frost. Remember that after application the stuff has to evaporate, aided perhaps with the spongy side of your windshield squeegee.

Once the wing is clean and dry with no ice in nooks and crannies, who cares how it got that way.

On a nice morning after a frosty night, this approach can get you an properly clean wing, but if there's freezing precip, I'd be turning around before I got to the airport.

Mechanical scraping between the rivet lines got me an interesting low level excursion over the ravine at the end of the runway until I had another 15 kts or so. After that I took to carrying windshield washer fluid.

[Pace]

Rather Be Flying

We are not talking about deicing larger aircraft where a proper deicing rig is used with the correct fluid but cleaning a wing on a small aircraft

Its not ideal but car stuff will cleanly remove it. Its up to you to dry the clean wing off before flight

Pace

[Gertrude the Wombat]

OK folks, you're not gonna like this story ...


Once Upon A Time some decades ago:


Me (having inspected aircraft before lesson): There's some frost on the wings
Instructor: Well spotted ... now let's go flying.


So the instructor was a test pilot, not an airline wannabee hours builder, but all the same don't try this at home kids.

[9 lives]

Its not ideal but car stuff will cleanly remove it. Its up to you to dry the clean wing off before flight

Pace

I agree that "car stuff" is not ideal. It may contain methyl hydrate, which can have corrosive affects on aluminum. Drying the wing off afterward will not prevent corrosion risk if the methyl hydrate has seeped between lapped skins or into the structure. For aircraft in my care, the only liquid I would apply would be those approved for that purpose - on aircraft.

Me (having inspected aircraft before lesson): There's some frost on the wings
Instructor: Well spotted ... now let's go flying.

The regulations (Canadian, anyway) do not state that aircraft will not fly with contaminated wings, they state that a pilot is not permitted to attempt the flight. Some aspects of flying require good preplanning, frost prevention is certainly one of them.