Question for the performance guru's
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Join Date: Feb 2002
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Question for the performance guru's
Hello all,
Flew over Bucharest today (LROP) and was listening to the ATIS. The runway state was reported as '51-100% covered in frozen ruts with a depth of 2mm. braking action medium to good.' For the landing, not a problem...
Now, if I were to take off from this runway, how would you make the calculation?! Airbus does not publish equivalent water depths for 'frozen ruts'. Is takeoff allowed?! Do you regard the runway as 'wet', because the contamination is less than 3 mm? But what if the depth was > 3mm?
P.S. This runway state was also mentioned in the METAR that was pulled earlier, using the (relatively new) RODEX decode.
Flew over Bucharest today (LROP) and was listening to the ATIS. The runway state was reported as '51-100% covered in frozen ruts with a depth of 2mm. braking action medium to good.' For the landing, not a problem...
Now, if I were to take off from this runway, how would you make the calculation?! Airbus does not publish equivalent water depths for 'frozen ruts'. Is takeoff allowed?! Do you regard the runway as 'wet', because the contamination is less than 3 mm? But what if the depth was > 3mm?
P.S. This runway state was also mentioned in the METAR that was pulled earlier, using the (relatively new) RODEX decode.
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Use the more limiting of ice and reported braking action.
"Frozen" IMHO implies ice, so wet would not be appropriate and might result in an over-optimistic calculation.
"Frozen" IMHO implies ice, so wet would not be appropriate and might result in an over-optimistic calculation.
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Well, there is some guidance in FCOM PER/TOF/CTA/Takeoff Performance/Takeoff from a runway with BA less than good/How to proceed.
But at least in the iPad take off performance module there is no direct option to select braking action, just contamination. That might be configured by the airline though, i don't know.
But at least in the iPad take off performance module there is no direct option to select braking action, just contamination. That might be configured by the airline though, i don't know.
Ask your Company. Our Company deems that frozen ruts and ridges do not directly affect take off and landing performance calculations. However the reduced, reported braking action would be taken into account. Pretending that it is icy, whilst honourable in intention, might mean needlessly leaving half of your passengers behind in the terminal.
Only half a speed-brake
While the response provided by Anvaldra explains the logic behind ignoring ruts and ridges, the key factor is still the coverage.
R&R are normally found at THR and by runway exit turnoffs due to snow being compacted by whell loads, thawing and re-freezing. This is when otherwise there is no contaminant - evaporated. Given the physical location it can be agreed that effects on ASDA are negligible.
Quite unlike the original question with coverage above 50% up to 100%. In this particular case, upon visually seeing what it is like, decision to assume contaminated might be prudent, probably selecting COMPACTED SNOW in the TKOF PERF tool.
R&R are normally found at THR and by runway exit turnoffs due to snow being compacted by whell loads, thawing and re-freezing. This is when otherwise there is no contaminant - evaporated. Given the physical location it can be agreed that effects on ASDA are negligible.
Quite unlike the original question with coverage above 50% up to 100%. In this particular case, upon visually seeing what it is like, decision to assume contaminated might be prudent, probably selecting COMPACTED SNOW in the TKOF PERF tool.
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That's interesting. Braking action medium to good, but the powers that be deem frozen rutts of no impact to takeoff performamce.
If it has no impact we should be using dry figures for takeoff, but MG for landing? Does it mean we can take off with 38 knots of crosswind, but only land with 29? (A320 RCAM) How about a "specially prepared winter runway" (Norway) that is covered with ice, but chemically treated, with a reported BA of good. What to do then? Land but not take off?
This stuff has been clear as mud for years. Why we can't just simplify things and use BA/Mu for both TO and landing performance I do not understand.
If it has no impact we should be using dry figures for takeoff, but MG for landing? Does it mean we can take off with 38 knots of crosswind, but only land with 29? (A320 RCAM) How about a "specially prepared winter runway" (Norway) that is covered with ice, but chemically treated, with a reported BA of good. What to do then? Land but not take off?
This stuff has been clear as mud for years. Why we can't just simplify things and use BA/Mu for both TO and landing performance I do not understand.
