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Wing Contamination - Frost

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Wing Contamination - Frost

Old 31st Jan 2009, 08:13
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Wing Contamination - Frost

A friend of mine was travelling from YYC to the UK a couple of months ago on a 767.

When I saw him again he had a question with regards frost on wings. He said that during pushback he noticed some frost on the upper surface of the wing which he brought to the attention of the CC. He was relieved to see that this was brought to the attention of the flight crew, as the FO came down to look at the wings. After a few minutes the CC member came to inform him that it was only frost, and that they could depart (which of course was uneventful).

This got me wondering, and next time I went to work I dug out my supplementary procedures for the 757. This is what it says.....

Surfaces ............................................................ ..............................Check
Takeoff with light coatings of frost, up to 1/8 inch (3mm) in
thickness on lower wing surfaces due to cold fuel is permissible;
however, all leading edge devices, all control surfaces, and upper
wing surfaces must be free of snow or ice.
Thin hoarfrost is acceptable on the upper surface of the fuselage
provided all vents and ports are clear. Thin hoarfrost is a uniform
white deposit of fine crystalline texture, which usually occurs on
exposed surfaces on a cold and cloudless night, and which is thin
enough to distinguish surface features underneath, such as paint
lines, markings or lettering.
There is one line in this statement that suggests all leading edge devices, all control surfaces, and upper wing surfaces must be free of snow or ice, with no mention of frost, but the bit before it suggests; takeoff with light coatings of frost, up to 1/8 inch (3mm) in thickness on lower wing surfaces due to cold fuel is permissible. From this statement alone I would infer that de-icing was required.

I personally believe in the clean wing concept and would de-ice every time.

Would anyone else have departed without de-icing?

Last edited by gatbusdriver; 31st Jan 2009 at 08:54.
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Old 31st Jan 2009, 08:48
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Join Date: Nov 2008
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Frost IS ice

Frost IS ice and therefore should be removed before flight (737's do have slight differences, as in acceptable 'areas', maybe the 767 does too!)
The upper surface of a wing is the most critical and must be clean, the underside may have up to 3mm, often caused by cold soaking at altitude followed by re-fuelling.

If there is any doubt then de-ice (even at the expense of a slight delay)

Rgds

CL747
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Old 31st Jan 2009, 08:57
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I totally agree CL.

I was just wondering how a crew could interpret it differently.
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Old 31st Jan 2009, 09:04
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I can't comment on their 'opinion' but there is some interesting information regarding de-icing, especially in Canada in the Rumours section, Cabin crew on trial..... thread.

Rgds

CL747

(Sorry! Just noted your profile - hope you didn't think I was teaching you to suck eggs

Last edited by Centreline747; 31st Jan 2009 at 09:27.
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Old 31st Jan 2009, 09:38
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I would di-ice with any frost present or likely between stand and getting airborne, making sure the holdover time was enough for the conditions, but I fly a TP and maybe the 767 / 757 has a system to warm the area of near the cells??
If the book says it is ok - it is ok....ours does not.

With high lift slats / LE flaps the boundary layer is extremely energized and separation leading to wing stall is unlikely on that aircraft, with frost on the cells anyway. Other aircraft, however, are not so fortunate and with rear mounted engines and a T tail - a definite no-no.
The fuel is heated from access heat from a heat exchanger from either excess bleed air or from the engine oil. This thaws any ice crystals that would clog the filters, bringing the fuel to approx room temp, which may be enough to thaw the hoar frost on the cells on the 767 / 757.

Last edited by PAPI-74; 31st Jan 2009 at 12:44.
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Old 26th Aug 2019, 01:34
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Originally Posted by PAPI-74 View Post
With high lift slats / LE flaps the boundary layer is extremely energized and separation leading to wing stall is unlikely on that aircraft, with frost on the cells anyway. Other aircraft, however, are not so fortunate and with rear mounted engines and a T tail - a definite no-no.
The fuel is heated from access heat from a heat exchanger from either excess bleed air or from the engine oil. This thaws any ice crystals that would clog the filters, bringing the fuel to approx room temp, which may be enough to thaw the hoar frost on the cells on the 767 / 757.

This was ground icing on top of the wing. In flight icing is typically more on the leading edge, so it is different. But here is an interesting statement about the 767 with regards to in flight icing to show its capability.....

"According to the manufacturer, the aircraft was designed so that flight in icing conditions should not affect its control, trim, or handling. The horizontal tail, with no de-icing capability, was designed to minimize its susceptibility to the accumulation of ice. The size of the horizontal tail was designed to allow it to operate at tail lift levels at or below the levels where leading edge ice would affect the tail's ability to generate the required lift.

The CAI Boeing 767 Operations Procedure, which discusses the effect of wing ice contamination, indicates that lift decreases and drag increases at high angles of attack. The manufacturer indicates that there is no lift loss attributable to ice contamination until the wing angle of attack increases above 15."

Aviation Investigation Report A96A0035 - Transportation Safety Board of Canada

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Old 26th Aug 2019, 12:58
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I'm not aware that there is any latitude in dispatching an aircraft with visible ice on the upper surface of the aircraft, even with mach 1 eyeball inspection.
It's not a good idea to permit subjective judgements by the pilots in regard to dispatch in this case. On the ground examination outside the aircraft would be better.
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Old 26th Aug 2019, 13:57
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5 times, completely caked in ice, everyone else getting de-iced. But not the flight I am sitting on!!!! Russian national carrier. Complaint letter sent. No reply. It's only time separating this airline from a winter death toll! (actually another winter death toll) So so so glad to be away from these suicide merchants!
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