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A/C off the runway in CPH

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A/C off the runway in CPH

Old 29th Dec 2005, 21:19
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A/C off the runway in CPH

Heard there was an a/c off the runway in CPH tonight (29/12) in poor vis and heavy drifting snow. Lots of cancelled flights and unreliable braking action on r/w.

Is this correct?
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Old 29th Dec 2005, 21:46
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The Snowtam indicates less then perfect conditions......


SWEK0166 EKCH 12292152
(SNOWTAM 0166
A) EKCH
B) 12291939
C) 04L
F) 975/975/975
G) 6/6/6
H) 28-9/25-9/30-9 SFH
N) 975
B) 12292148
C) 04R
F) 975/975/975
G) 5/5/5
H) 25-9/26-9/22-9 SFH
N) 975
B) 12291902
C) 12
F) 975/975/975
G) 8/8/8
H) 24-9/23-9/25-9 SFH
N) 975
R) 975
T) ALL RWYS COVERED 100 PERCENT.
ALL TWYS AND APRON B/A POOR.
CHEMICALS HAS BEEN SPREAD OUT.
SNOW AND ICE ON SHOULDERS RWY 04L, 04R AND 12.

Frozen ruts or ridges, ice and wet snow on all the runways is not good. The fact that they put "unreliable" behind all the frition numbers says a lot too........
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Old 29th Dec 2005, 23:59
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The fact that they put "unreliable" behind all the frition numbers says a lot too........
In the UK, that's ALL that we're legally able to say, now. We mustn't even quote the numbers at all. This is partly because there is still no International agreement on
a) what all the different readings mean that different machines come up with on the same surface, or even the different readings you get on the same surface with the SAME machine on consecutive runs
b) the lack of correlation between a friction reading taken at 40MPH using a machine you can lift with one hand and the braking action of an a/c doing 100kt+ and massing 50tonnes or more.

This lack of progress has been going on for years and the UK CAA have finally said 'OK. you lot, until it's sorted out, no promulgation of friction readings to ATC or pilots'.

We're working for this winter on a 'back to black' principle and won't re-open following closure for snow removal until we're 'WET, WET' WET' or better.

It probably makes the publishing of a SNOWTAM irrelevant.

Cheers,
The Odd One
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Old 30th Dec 2005, 00:54
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This sounds to me like a bunch of idiot bureaucrats ( ICAO , CAA , you pick the agency ..) who , for lack of coming to an agreement , are putting the travelling public , and flight crews at risk.
Where are the journalists ?
What are the conflicting opinions ?
Get off your asses and come to a decision.
How simple is it to come up with a worldwide standard for runway braking coefficient ?
.... an easy to understand system and not the BS snowtam report or runway braking reports that we recieve now.
This I believe is a crack in the system that could result in a disaster.
What a load of bollocks.
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Old 30th Dec 2005, 05:10
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Angel

Funny how those who actually have to deal with these conditions regularly have a more pragmatic approach.
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Old 30th Dec 2005, 07:21
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b) the lack of correlation between a friction reading taken at 40MPH using a machine you can lift with one hand and the braking action of an a/c doing 100kt+ and massing 50tonnes or more.
I find that odd, back in the late 60's or early 70's (can't remember exactly) I did a long series of trials @ Waddington & Scampton doing just that with all RAF aircraft. The aircraft ran through a 2000ft long test section on the runway, full braking used on a dry runway we would then flood the runway & repeat. I wasn't involved with the analasys work so I don't know what the outcome was
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Old 30th Dec 2005, 09:19
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Anyone know which runway the aircraft was off last night? We were waiting in the queue last night and aircraft were being offered a departure runway of 12 with the surface wind 130@22 or departure on 22R with the wind 250@06. With all the blowing snow around our stand the wind looked a lot more like 130@22 than it diid 250@06. A number of voices on the radio commented on how different the two winds were at the same airport.
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Old 30th Dec 2005, 12:16
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Well, there are some nations which have to take winter condition reporting serious.

We:

1. Allways report the numbers, and what they are measured with (SFH, SKH etc)
2. It's regulated in the norwegian BSL (equal to your CNO I think) on what, and on how much contamination the different friction devices can be used on. (Don't have the table at hand, but as an example, I think it's prohibited to use the GRT or TAP on wet snow.)
3. It's regulated in what increments each type of contamination is measured, the increment for dry snow is 8mm, slush 3mm etc)

On all the 'proper' airfields we use the SFH or SKH, and if the measurement is fresh, and not 4 hours old, condtions are monstly better then measured in pretty much all conditions. I belive that all incidents with runway excursions due to slippery surfaces in Norway the last 10 years have been due to

1. Late reporting, last snowtam not reflecting the actual condtions. (The watch commander of the field maint. unit not doing his job)
2. Airline SOP not up to scratch, crew landing/departing in conditions well outside aircraft capabilities.
3. Aircrew unfamiliar with operating on contamination, this is allso VERY true when it comes to TWYs and aprons.
(The concept of not trying to make a 90 degree runway exit at the same speed as in the summer etc......)
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Old 30th Dec 2005, 13:15
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Thumbs up

M609 ( and all other diligent ATCOs )

Days / weeks spent operating multiple sectors around Europe in winter are a nightmare without your accurate reports.

Thank you
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Old 30th Dec 2005, 18:56
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I can find nothing about this on any of the Danish radio or news papers' websites.
Even the mother-in-law hasn't called to ask if I was at work so it can't be true! She knows everthing.
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Old 1st Jan 2006, 20:46
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Re: A/C off the runway in CPH

Originally Posted by green granite
I find that odd, back in the late 60's or early 70's (can't remember exactly) I did a long series of trials @ Waddington & Scampton doing just that with all RAF aircraft. The aircraft ran through a 2000ft long test section on the runway, full braking used on a dry runway we would then flood the runway & repeat. I wasn't involved with the analasys work so I don't know what the outcome was
Green granite - Did you take part in some of these tests?

Early UK Research

ICAO Study Group on Snow, Slush, Ice and water on Aerodromes.
Memorandum No. 16
10 November 1970
Attachment B, Presented at Langley in November 1968 and published in the NASA report SP-5073.

Correlation between Runway Coefficient of Friction Values Produced by Different Types of Instruments and the Prediction of Aircraft Stopping Distances.

1. Introduction

The 5th Air Navigation Conference recommendation 5/32 states inter alia that ICAO invite interested States to co-operate in the further development of practical methods, suitable for international standardization, for calibrating coefficient of friction measurement devices and wet coefficient of friction of runway surfaces. In the UK research has been going on for a number of years to determine the possibility of predicting aircraft stopping distances using vehicular device and also to investigate the correlation between various devices. As the most hazardous conditions for a landing aircraft would occur when there was sufficient water or slush to cause aquaplaning or with surface ice, it was decided at the outset that a particular effort should be made to authenticate the prediction method in these situations. As trials with full scale aircraft under these extreme conditions with three different types of aircraft and three ground vehicles using different principles for measuring friction.

2. Trials between a Swift Aircraft and Road Research Laboratory Trailer

The first set of trials was conducted with a Swift fighter aircraft weighing approximately 18,000 lb and the Road Research Laboratory light friction trailer. The aircraft was instrumented to measure drag and vertical load as well as velocity from which the friction speed relationship curves were obtained at up to 140 knots for a number of runway surfaces, These curves were compared with those from the Road Research trailer at speeds up to 161 kph (100 mph= on the same surfaces. It was hoped that the ratio of friction coefficients at the same speeds might be a constant or at least that the change with speed might follow the same pattern from one type of surface to another. However, neither of these hopes was realised and it was concluded that there was no correlation between the actual friction values produced by an aircraft and the Road Research Laboratory Trailer.

3. Trials between a Hunter Aircraft and Heavy Load Friction Vehicle

The next series of trials in this study occurred some years later when the opportunity arose to compare the performance of a Hunter aircraft weighing about 17,000 lb and a Heavy Load Friction Vehicle which was fitted with a Hunter wheel, brake, tyre and braking system. The same tyre pressures, wheel loads, wetness conditions and surfaces were used. It was thought that under such closely comparable test conditions there should not only be correlation, but the actual figures themselves should be the same. This was however not the case and it led to the inevitable conclusion that correlation between friction values of aircraft and ground vehicles was most unlikely.

4. Trials between the Ministry of Technology Runway Friction Meter and a Convair 990 and F4 Aircraft

At the invitation of the NASA, the UK Ministry of technology conducted a joint Friction Correlation Programme at Wallops Station, Virginia, during 1968. Nasa had used a Convair 990 and F4 aircraft to determine the speed friction relationship of nine runway surfaces with widely differing friction coefficients. The programme was to compare these aircraft values with those from the Heavy Load Friction Vehicle, Road Research Trailer and a newly developed runway friction meter called the Mu-Meter. Once again the friction values did not correlate with the aircraft nor in fact with each other.
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Old 1st Jan 2006, 20:51
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Re: A/C off the runway in CPH

Oh Joy - so all the data used to determine whether it's safe to land is cr*p then?
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Old 1st Jan 2006, 21:36
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Thumbs down

Yes - but remember, they have been so for several years! That means that we have safely operated with these figures for decades - but suddenly, we cannot have them any more - so finally, the lawyers have managed to get around to airport ops as well...

Now, that leaves us as pilots in a tight spot. If the runway is contaminated, but no B/A of F/C figures are forthcoming - I cannot legally land the aircraft. Ergo - if snow or other contaminant is forecast @ a UK airport, I should therefore treat that airport as below planning minima, and carry fuel to the farthest of 2 destination alternates. So if all the UK is affected by e.g. snow - I'm better off filing SVG or BGO as alternate - since they will give me the info I legally need to land the aircraft!

This is utter BALOX (yep, I miss CPH!) to me - and believe me, the Norwegians, Swedes, Finns & Danes have a lot of experience keeping their airports operating, even in snowy conditions. And somehow, despite risking similar lawsuits as UK airports, they manage to know when to give the figures (i.e. the airport carries the can) and when to report them unreliable (i.e. the PIC carries the can).

Honestly - if you cannot give us the info we need - why bother? Perhaps the airlines should start filing compensation lawsuits when unnecessary diversions occur due to this practise. If an SFH comes up with unambigous figures - yet they are still reported by ATC as "unreliable" - my feeling is that the airline stands a good chance of winning such a lawsuit. Perhaps FlyingLawyer has an answer for this one?

Best regards fm
Empty
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Old 1st Jan 2006, 22:11
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Re: A/C off the runway in CPH

Originally Posted by Wing Commander Fowler
Oh Joy - so all the data used to determine whether it's safe to land is cr*p then?
Green granite, Wing Commander Fowler and others

The rest of the (1970) document reads:

5. Other Prediction Methods

As a result of the failure to correlate with the system described above, two other methods were investigated. It had been suggested that the ratio of the wet to dry stopping distance of a locked wheel vehicle and of an aircraft might be the same on the same surface when the former was using plain tyres. As the Mu-Meter was a trailer it could not measure its stopping distances, but it was possible to obtain a relationship curve between the value it read on a number of surfaces at 64 k.p.h. (40 m.p.h.) and the calculated stopping distance from 113 k.p.h. (70 m.p.h.) as defined by its speed friction curve. The wet over dry ratio was then only a matter of reading off the appropriate values from the curve.

Results from Wallops Station on the Convair 990 and F4 indicated this method had considerable promise and in fact a 1:1 relationship between Mu-Meter and aircraft was achieved on a number of the surfaces so it was decided to continue this verification by further trials in the United Kingdom with a Hunter and Beverly aircraft. It soon became apparent however that these two aircraft gave different values for the wet to dry stopping distance ratio on the same surface, in fact it varied from 1 to 1.7 and therefore a system using wet to dry ratios for the prediction of stopping distance could be in error by as much as 70%, and as this was considered unacceptable the method was discarded.

Having discarded the wet to dry ratio method it was decided to determine the aircraft stopping distances on a number of surfaces with as wide a friction range as possible and to plot these against the values given by the Mu-Meter at 64k.p.h (40 m.p.h.) obtained as close to the time of the aircraft friction run as possible. In fact a technique was developed ehere the friction meter made a run immediately before and after the aircraft and the value used was a mean of the two. This method was successful and can produce individual curves for each aircraft provided sufficient points are obtained. The possibility of predicting aquaplaning for individual aircraft types and undercarriage configurations is under investigation. By making use of snow and ice covered runways it was possible to determine the Hunter correlation curve down to very low values under natural conditions. (attached figure).

6. Discussion

With the advantage of hinsight it is perhaps not surprising that the friction values of aircraft and vehicular devices do not agree. An aircraft tyre operates at far higher pressures and loads than vehicles; the aircraft uses an automatic braking system which in itself has varying degrees of efficiency depending on its design and there are differences in wheel layout, but it is perhaps surprising that the values do not agree even when a vehicle and aircraft tyre wheel brake have identical physical parameters, except for suspension.

Bearing in mind there are a number of different ways in which friction can be measured e.g. slipping wheel, locked wheel, yawed wheel with different vertical loads, tyre pressures and test speeds it is again not surprising that each equipment can give different values under the same test conditions. These are then physical facts which must be accepted, the problem is what to do about it and therefore appears to be only one sensible solution, and that is that everybody should use the same equipment.

It is suggested that a runway friction meter should be portable, rugged, accurate, able to operate at low temperatures, relatively cheap and incapable of being influenced by the operator. It is also suggested that it should be capable of providing a pictorial representation of the friction along the complete length of the runway not only for reasons given in the note to paragraph 2.8.6 in part II of Annex 14, but also to increase its usefulness by showing the extent and variation in friction caused by rubber deposits, runway damage due to jet blast etc, In addition the same equipment could be used to classify runways in their friction order if necessary by an outside agency and if airfield operators have their own equipment, they could make their own periodic check.

7. Conclusions

Correlation between aircraft and vehicular friction values at the same speed is improbable and if it does occur then it is fortuitous.

It is unlikely there is any correlation between friction coefficient values produced by equipments using different and sometime the same principles.

The only way of establishing a standard system for providing information on the presence of contaminants on runway surfaces and their effect on braking action is for all airport operators to use the same design of equipment.

References:R.W. Sugg. Tests to Determine the Usefulness of Vehicular Instrumentation to Predict Aircraft Stopping Distances S and T Memo 9/64. Ministry of Technology.

Road Research Laboratory. Tests with Heavy Load Skidding Machine to Determine Braking Force Coefficients between an aircrafdt tyre and various wet surfaces. S and T memo 8/63 and 10/64. Ministry of Technology.

Last edited by tribo; 2nd Jan 2006 at 08:20.
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Old 1st Jan 2006, 22:41
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Re: A/C off the runway in CPH

Originally Posted by Empty Cruise
Ergo - if snow or other contaminant is forecast @ a UK airport, I should therefore treat that airport as below planning minima, and carry fuel to the farthest of 2 destination alternates. So if all the UK is affected by e.g. snow - I'm better off filing SVG or BGO as alternate - since they will give me the info I legally need to land the aircraft!

Best regards fm
Empty
...if I give you the runway as WET, WET, WET, then you can rest assured that the friction that we've measured at least meets that minimum standard, even though I cannot legally give you the actual data (it might well be up to a mu of .7 or so by then). Sounds like a good idea to file for an alternate with no forecast contamination. I suppose that in the departure case you can at least wait until conditions are right.

The early ICAO work has recently been comprehensively repeated using A320 and other aircraft and all the popular makes of trailer and in-vehicle friction measuring devices. Disappointingly and depressingly, there STILL ain't no correlation between braking action and friction measurement and the range of devices are STILL out of whack with each other. How can you possibly stipulate which device to adopt as a standard when they are all different from each other and NONE of them relate to any aircraft?

Cheers,
TheOddOne
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Old 2nd Jan 2006, 08:46
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Re: A/C off the runway in CPH

Tribo et al

No they pre-dated the trials that I was involed in.
I believe that the Hunter trials were done @ Cranfield where they had ponds formed on the runway using rubber strips and could flood these (they left a strip free for the nose wheel so that the pilot could steer the a/c) upto aquaplaning depth. Told that the sight of a hunter aquaplaning is very spectacular.

The trials I refered to, I think, sort of came out of those early trials, Cranfield was the trials authority, the company I worked for supplied the engineering & kinetheodolite staff (me), they took about 4 months to do, mainly because of needing dry calm conditions. Maxeret serviceability was interesting as we had lots of burst tyres on the larger a/c & the brakes seize solid on a Victor @ Scampton half way down the runway (we wer'nt very popular as it shut the airfield while they jacked the aircraft up and removed the brakes so they could tow it away)
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Old 2nd Jan 2006, 08:46
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Re: A/C off the runway in CPH

Hello there.

Firstly I can guarantee you, there was no A/C off the tarmac at any point on the 29th or 30th for that matter.

Secondly, our friction tester guys have been instructed to add "unreliable" to the numbers as soon as "wet snow" is on the surface.

Odd thing was, even though the numbers at one point was 15 14 13 or something like that. The landing pilots all reported medium to good breaking action. (Of course the Finnish guys reported it to be very good :-) ) And most of the A/C's in the holdings took thoose reports over the numbers, and landed.

Is that also the procedure where you guys collect your $?
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Old 2nd Jan 2006, 09:41
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Re: A/C off the runway in CPH

Originally Posted by Wing Commander Fowler
Oh Joy - so all the data used to determine whether it's safe to land is cr*p then?
The most surprising aspect might be that so many pilots do not know this, or do not understand the risks that are currently accepted.

More recent research is here with links to the report TP 14273 Falcon 20 aircraft braking performance on wet concrete runway surfaces.
“On a smooth, wet concrete runway surface close to the minimum maintenance standard, … the current operational dispatch factor of 1.92 for turbojet aircraft landing on wet runways at destination or alternate airports would have to be increased to a value of 2.2 to 2.4 in order to achieve the same level of safety as that which is currently accepted for dry runway operations”.

I interpret the reported data as indicating that where with current calculations an aircraft should stop, using max braking, with 40% of the runway remaining. In reality on some runways, this safety the margin is significantly less. Then add to this the actual braking level used in wet conditions, the variability of runway surfaces and maintenance condition, rubber deposits, cross wind, water damming, long and/or fast landings, etc. Then we start to consider contamination … !

“For landings on wet runways, the excess distance between the landing field length, calculated using the current method, and the actual landing distance was considerably less than the excess distance on dry runways.

TheOddOne See the values of friction test measurements for wet runways in the report (table 2); note for a ‘tanker’ (a more realistic) wet runway, all values of mu are well below 0.7, then compare these with the actual, even lower values as experienced by aircraft (figures 10 & subsequent).

Short Approach? If data is “unreliable” then why broadcast it. The figures may only serve to bias the crew’s judgment.

Humans are the weakest link in winter operations, the pilots the last link. If due to lack of information or poor understanding, our judgment can be so flawed then there should only be one option in the decision making process; don’t consider landing.
We might seek to blame others or equipment for the hazards of winter operations, but do we (pilots) really consider the risks involved with landings on contaminated runways.
There are few if any hard limits, like a low vis approach ban. Perhaps the runways should be closed until cleared, or why not consider undersurface heating like sports grounds. I am sure that those operators who have suffered cost and disruption due to accidents would be prepared to pay a small premium to support these initiatives.

Also see thread Good - Fair - Poor – Nil

”Attempts to land on heavily contaminated runways involve considerable risk and should be avoided whenever possible. If the destination aerodrome is subject to such conditions, departure should be delayed until conditions improve or an alternate used.
Operations from contaminated runways, by all classes of aeroplane, should be avoided whenever possible”
(UKCAA AIC 61-99)

Flight Safety Foundation. Managing threats and errors during approach and landing.
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Old 2nd Jan 2006, 10:41
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Re: A/C off the runway in CPH

Originally Posted by alf5071h
Short Approach? If data is “unreliable” then why broadcast it. The figures may only serve to bias the crew’s judgment.
You´re exactly right. We are currently haveing the same debate.

Is there any alterrnative? Is there a friction tester that can operate reliably in wet snow?
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Old 2nd Jan 2006, 11:18
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Re: A/C off the runway in CPH

Originally Posted by Short Approach?
Is there a friction tester that can operate reliably in wet snow?


None that we have seen. If you know of a manufacturer claiming this facility, please let us know soonest!

The Odd One
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