Crosswind reduction for contaminated runway?
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Crosswind reduction for contaminated runway?
We're considering reducing the max allowable crosswind component for our DC-9 fleet based on runway contamination. Right now, we use the manufacture's 31 kts or 38 kts, (depending on the series)and don't make any consideration for contamination. Does anyone else take a reduction for runways that are wet? Braking action less than good? etc? If so, how much? 
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There's an excellent schematic put out by SAS who've used the '9'for years.As the coificient(forgive the spelling)of friction decreases so should the Crosswind component.The original info for this was put out years ago by who-Douglas of course.there's an Ideal paper on this factor put out on the DC10(about83,I think)still available from MDC.Same info applies to the '9',includes good stuff like cancelling reverse if she don't go straight.re-aligning her and reversing again.Surprised you don't have this generic info.. 
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Another consideration relates to the usual practice of reducing V1 for contaminated or wet runways.
If the V1 is reduced down towards min V1, then consider that Vmcg is determined for nil wind (FARs) or 7 kt crosswind (BCARs) and I presume that the JARs are somewhat similar.
The "real" Vmcg increases around half the crosswind, other things being equal.
This results in a sensible need for an airline's operational crosswind limits to take into account how close to the certification Vmcg the takeoff is planned to be - or for the V1 reduction to be limited to provide some sort of equivalent margin. I suspect that most, however, don't give it a thought....
[ 05 September 2001: Message edited by: john_tullamarine ]
If the V1 is reduced down towards min V1, then consider that Vmcg is determined for nil wind (FARs) or 7 kt crosswind (BCARs) and I presume that the JARs are somewhat similar.
The "real" Vmcg increases around half the crosswind, other things being equal.
This results in a sensible need for an airline's operational crosswind limits to take into account how close to the certification Vmcg the takeoff is planned to be - or for the V1 reduction to be limited to provide some sort of equivalent margin. I suspect that most, however, don't give it a thought....
[ 05 September 2001: Message edited by: john_tullamarine ]
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Thanks for the info, folks! I wasn't able to find anything from Douglas (MacBoeing), but I did find the chart you referred to in the SAS DC-9 AFM. It's exactly what I was looking for. Good point on the Vmcg, allowances need to be made.
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In Canada, airports report the CRFI (Canadian Runway Friction Index). You look up the number at the bottow of the crosswind chart (the one with the lines for different angles and arcs for different wind strengths) and it shows you the maximum acceptable crosswind for the conditions.
It doesn't apply to rain, though, just to ice and snow.
It doesn't apply to rain, though, just to ice and snow.
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Please define contaminated runway as applicable to your type of aircraft.
My last company used 10 kts x wind with a half inch of contamination on the runway, this for the L1011 and the 767.
If the huge reduction in tow was acceptable there was also a long list of must be servicable equipment also.
My last company used 10 kts x wind with a half inch of contamination on the runway, this for the L1011 and the 767.
If the huge reduction in tow was acceptable there was also a long list of must be servicable equipment also.
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Mutt,at one time the CAA used to increase the VMCG by 7knots for a crosswind additive,but with time(and poss JAA involvement have dropped this reference).
There are quite a few variations of the SAS chart,AIP Canada etc(althought the danger of the AIP is that it shows the max'crosswind component at 45knt on a 'dry' runway) the SAS chart depicts a more realistic 35knt(certification/demonstrated)..Contact a SAS airline/pilot for the chart.
There are quite a few variations of the SAS chart,AIP Canada etc(althought the danger of the AIP is that it shows the max'crosswind component at 45knt on a 'dry' runway) the SAS chart depicts a more realistic 35knt(certification/demonstrated)..Contact a SAS airline/pilot for the chart.
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Mutt,
Short answer no. Like most certification performance data, I view Vmcg as a reference or information limit in that, if the real world boundary conditions are much the same as the certification assumptions, then the numbers will more or less line up - real world with the book. This is not to suggest that one may ignore the application of the basic certification rules. Rather, one has a responsibility to consider whether the use of additional fat (margins of safety, fudge factors - whatever sort of term you fancy) may be appropriate when the real world varies from the contrived certification boundary conditions.
Some people probably think that this subject is a pet bee in the bonnet thing with me. However, the facts remain
(a) that a Vmcg departure is very speed sensitive (I wasn't convinced of this until I became involved in a series of flight tests revolving around this matter many years ago).
(b) crosswind adds a not insignificant stabilising/destabilising yawing moment into the cauldron depending on the side of the engine rundown.
(c) simulators may not model the test point with a high degree of fidelity - certainly that has been my experience within a range of sims with which I have worked in training.
(d) many line pilots will, without any additional thought, reduce V1 into the Vmcg regime when, perhaps, there are more appropriate options.
It is up to the operator or pilot, circumstances permitting, to consider adjusting the min V1 on the day to address such real world considerations.
m&v,
The UK CAA required Vmcg to be reduced to the 7kt crosswind case. The has seen the rather silly situation where performance numbers differ for the nominally same aircraft depending on whether the certification basis is US or UK.
The only documented Vmcg variation I have seen having some authority behind it is for the DC9, where Douglas provided some test data indicating, for the particular model with which we were concerned at the time, that the Vmcg increase was around half the crosswind. I suspect that the figure will be applicable with some generality. Certainly, one sees it bandied about from time to time.
[ 08 September 2001: Message edited by: john_tullamarine ]
Short answer no. Like most certification performance data, I view Vmcg as a reference or information limit in that, if the real world boundary conditions are much the same as the certification assumptions, then the numbers will more or less line up - real world with the book. This is not to suggest that one may ignore the application of the basic certification rules. Rather, one has a responsibility to consider whether the use of additional fat (margins of safety, fudge factors - whatever sort of term you fancy) may be appropriate when the real world varies from the contrived certification boundary conditions.
Some people probably think that this subject is a pet bee in the bonnet thing with me. However, the facts remain
(a) that a Vmcg departure is very speed sensitive (I wasn't convinced of this until I became involved in a series of flight tests revolving around this matter many years ago).
(b) crosswind adds a not insignificant stabilising/destabilising yawing moment into the cauldron depending on the side of the engine rundown.
(c) simulators may not model the test point with a high degree of fidelity - certainly that has been my experience within a range of sims with which I have worked in training.
(d) many line pilots will, without any additional thought, reduce V1 into the Vmcg regime when, perhaps, there are more appropriate options.
It is up to the operator or pilot, circumstances permitting, to consider adjusting the min V1 on the day to address such real world considerations.
m&v,
The UK CAA required Vmcg to be reduced to the 7kt crosswind case. The has seen the rather silly situation where performance numbers differ for the nominally same aircraft depending on whether the certification basis is US or UK.
The only documented Vmcg variation I have seen having some authority behind it is for the DC9, where Douglas provided some test data indicating, for the particular model with which we were concerned at the time, that the Vmcg increase was around half the crosswind. I suspect that the figure will be applicable with some generality. Certainly, one sees it bandied about from time to time.
[ 08 September 2001: Message edited by: john_tullamarine ]
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I fly Fokker 50 for SAS, and we always consider reduced braking action when determining our crosswind limits:
Max crosswind component on slippery runways is: Friction coefficient -10.
Eg: FC .32 = max crosswind component is 22KTS, both for takeoff and landing.
In addition, max X-wind component on wet runways (no FC reported) is 25 KTS (Dry runways 33 KTS.)
I believe the same, or quite similar, restrictions apply for all SAS aircraft.
Max crosswind component on slippery runways is: Friction coefficient -10.
Eg: FC .32 = max crosswind component is 22KTS, both for takeoff and landing.
In addition, max X-wind component on wet runways (no FC reported) is 25 KTS (Dry runways 33 KTS.)
I believe the same, or quite similar, restrictions apply for all SAS aircraft.
