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Flying & Light Frost

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Flying & Light Frost

Old 24th Feb 2016, 09:35
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Flying & Light Frost

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
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Old 24th Feb 2016, 09:59
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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.

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Old 24th Feb 2016, 10:05
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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.
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Old 24th Feb 2016, 10:22
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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
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Old 24th Feb 2016, 10:29
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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

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Old 24th Feb 2016, 10:57
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Sounds like hoar frost forming on a cold soaked airframe.Might well have formed after landing.How long was the flight?
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Old 24th Feb 2016, 11:08
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I didn't realize that frost can form in the wings in flight
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Old 24th Feb 2016, 11:17
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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!
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Old 24th Feb 2016, 11:32
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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!)
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Old 24th Feb 2016, 11:35
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excuse the potentially ignorant question, but isn't car deicer corrosive? is it ok to use on wings?
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Old 24th Feb 2016, 11:36
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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
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Old 24th Feb 2016, 12:03
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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.
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Old 24th Feb 2016, 12:10
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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.
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Old 24th Feb 2016, 12:15
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Originally Posted by piperboy84 View Post
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.
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Old 24th Feb 2016, 13:00
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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
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Old 24th Feb 2016, 23:29
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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.
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Old 25th Feb 2016, 09:00
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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?
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Old 25th Feb 2016, 11:13
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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.
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Old 25th Feb 2016, 11:42
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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

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Old 25th Feb 2016, 14:09
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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.
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