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Rime or frost covered runway Airbus TO perf

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Rime or frost covered runway Airbus TO perf

Old 6th Feb 2019, 09:17
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Rime or frost covered runway Airbus TO perf

Say you have the following runway state report: R10/390041=

So the runway is covered in rime or frost, 51-100-%, <1mm.

How would one go about calculating take off performance for the Airbus, since no such runway state is discussed in the perf manual?

Does your airline offer any guidance outside the FCOM?
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Old 6th Feb 2019, 11:16
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Our guidance does not mention frost in the Take Off matrix, but it does have wet and dry snow, slush, water (all under 3mm) and says to use wet figures. In the landing grid, frost is mentioned and is given an equivalence of Wet. I therefore use Wet figures for takeoff on a ‘frosty’ runway.
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Old 7th Feb 2019, 08:07
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I don’t fly Airbus, but frost and rime are very different from wet.
On the 737 we use dry ice.
If you use wet on a limited, frost covered runway, you can get a nasty surprise if you abort near V1.
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Old 7th Feb 2019, 10:06
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Airbus publication “Getting to Grips With Cold Weather” Dec 15 version.

p64.

“Frost is equivalent to wet”.
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Old 7th Feb 2019, 11:38
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If they say so, but one of them is liquid and one is frozen. Guess which one?
Clearly a difference in opinion between Airbus and Boeing. I know which one I’m more comfortable with.
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Old 7th Feb 2019, 12:12
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They, the reporters, are usually covering thei asses.

use full power and full length.

eventually, if you operate here long enough, you'll realise that 'wet and flex' works ok.

but if in doubt.....
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Old 7th Feb 2019, 12:41
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You can operate with WET your entire lifetime without any issues. Unless you abort at high speed.
Correct me if I’m wrong, but Airbus only use assume temp derate? So, WET allows you to derate.
Boeing can only use fixed derate on contaminated runways so you normally have a lot of margins when you have RIME or FROST on the runway.
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Old 7th Feb 2019, 22:07
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No temp FLEX on contaminated runways for AB.

But Airbus do not determine that Frost is a contaminant.

If the layer of contaminant on the runway is thin enough, the runway is not considered contaminated, but only wet.
FLEX takeoff is not allowed from a contaminated runway.
As far as performance determination is concerned, the following guidelines should be considered, as mentioned in the FCOM:

In terms of performance a fluid contamination is equivalent to wet, up to and including a maximum depth of 3 mm (1/8") of:
  •  dry snow
  •  wet snow
  •  standing water slush.

    "Frost" is equivalent to wet.
Same reference (note that the Getting to Grips with Cold Weather easily available online is the older version which does not have these references).

Out of genuine interest, do you have a Boeing reference for frost? Performance on contaminated runways is a hot topic in some parts of the world and the subject of much recent study.
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Old 8th Feb 2019, 11:37
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Runway reports are determined and reported by ATC; it is assumed that this based on the TALPA matrix.
Frost is considered wet, but rime is not stated; this problem involves judgement of the difference between frost and rime; how ATC assess and report rime.
Many situations in aviation consider rime to be associated with ice. Technically rime should not be reported, if it is then question ATC; beware of other pilots interpretation.

Thus, if frost use wet performance, but there is some uncertainty reduce the reported condition by one category and check the safety margin, and a further reduction if the OAT is +/- 3C.
If rime = ice, then no go.
If still not clear then Air Safety Report to operator, regulator, and manufacturer.
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Old 9th Feb 2019, 12:46
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Originally Posted by safetypee View Post
Runway reports are determined and reported by ATC; it is assumed that this based on the TALPA matrix.
Frost is considered wet, but rime is not stated; this problem involves judgement of the difference between frost and rime; how ATC assess and report rime.
Many situations in aviation consider rime to be associated with ice. Technically rime should not be reported, if it is then question ATC; beware of other pilots interpretation.

Thus, if frost use wet performance, but there is some uncertainty reduce the reported condition by one category and check the safety margin, and a further reduction if the OAT is +/- 3C.
If rime = ice, then no go.
If still not clear then Air Safety Report to operator, regulator, and manufacturer.
Maybe I should be careful to say Boeing as we use a third party performance tool.
Contamination can be of two types: The one that creates resistance: Snow, wet snow, dry snow, standing water, slush. No resistance, Dry ice, wet ice, rime, frost, wet.

If any type of ice is a no go for you, then I understand why rime and frost would be classified as wet.
We can take off on dry ice and use the required performance calculations for this. Rime and frost (reported by ATC) is classified as dry ice.
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