Cargojet 727 Overrun at CYQM
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It flew out a few days ago, on the night of the 27th, I believe. Someone on Avcanada mentioned that it was ferried back to Cargojet's main base at Hamilton with gear down.
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Here is the link for the Benefit-cost analysis of procedures for accounting for runway friction... Great Document!
http://www.tc.gc.ca/innovation/tdc/p...000/14082e.pdf
http://www.tc.gc.ca/innovation/tdc/p...000/14082e.pdf
The report at (#23) only deals with friction aspects on runways contaminated with snow and ice and specifically excludes wet runways in the definition of ‘slippery’.
The document which the FSF refers too (#7) is TP14842E “Risk and Benefit-Cost Analyses of Procedures for Accounting for Wet Runway on Landing” dated July 2008. This is not yet available on line.
This document focuses on wet runways and the importance of runway grooving. Most of the significant points are identified in the FSF article.
Although CRFI is not measured on wet / flooded runways, the background principles in ( AC 164 and AIM AIR Para 1.6 and table 1-4) provide excellent guidance for the performance degradation on wet runways, but even this requires judgement in considering additional factors such as non grooved runway, tyre condition.
An advantage of CRFI is that it attempts to provide a similar safety margin to that required for dry operations, i.e. attempts to accommodate the variability in everyday operations.
Some of the landing distances required for low friction operations shown in the CRFI tables approximate to safety factors of 2.0 to 2.4 which are well in excess of the wet 1.92.
Unfortunately, all of the above suffer the weakness of the crew not knowing what the actual condition of the runway surface is, either through difficulties of measurement, communications, and interpretation; and even with good data, it has to be applied sensibly.
The above does little to progress an understanding of the Moncton event. However, from CRFI principles / tables, assuming that the runway was ‘very wet’, the landing distance (with reverse) on this 6000ft runway would equate to an ‘AFM’ unfactored dry landing distance of 2800-3200ft. Could any 727 pilots comment on the practicality or likelihood of this data applying to this situation.
The document which the FSF refers too (#7) is TP14842E “Risk and Benefit-Cost Analyses of Procedures for Accounting for Wet Runway on Landing” dated July 2008. This is not yet available on line.
This document focuses on wet runways and the importance of runway grooving. Most of the significant points are identified in the FSF article.
Although CRFI is not measured on wet / flooded runways, the background principles in ( AC 164 and AIM AIR Para 1.6 and table 1-4) provide excellent guidance for the performance degradation on wet runways, but even this requires judgement in considering additional factors such as non grooved runway, tyre condition.
An advantage of CRFI is that it attempts to provide a similar safety margin to that required for dry operations, i.e. attempts to accommodate the variability in everyday operations.
Some of the landing distances required for low friction operations shown in the CRFI tables approximate to safety factors of 2.0 to 2.4 which are well in excess of the wet 1.92.
Unfortunately, all of the above suffer the weakness of the crew not knowing what the actual condition of the runway surface is, either through difficulties of measurement, communications, and interpretation; and even with good data, it has to be applied sensibly.
The above does little to progress an understanding of the Moncton event. However, from CRFI principles / tables, assuming that the runway was ‘very wet’, the landing distance (with reverse) on this 6000ft runway would equate to an ‘AFM’ unfactored dry landing distance of 2800-3200ft. Could any 727 pilots comment on the practicality or likelihood of this data applying to this situation.
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Airplanes with tail mounted engines have an interesting characteristic. Just when you are having fun keeping the nose straight in a crosswind on a slippery runway, going into reverse can blank out the rudder. Slow down or go off the side? The MD-80 is particularly cute in this regard.
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However, from CRFI principles / tables, assuming that the runway was ‘very wet’, the landing distance (with reverse) on this 6000ft runway would equate to an ‘AFM’ unfactored dry landing distance of 2800-3200ft. Could any 727 pilots comment on the practicality or likelihood of this data applying to this situation.
Maurice, I think that you have missed the point which I was making with the help of the CRFI tables, and of trying to establish a rough order of landing weight which could provide a safe landing in the reported conditions.
We don’t know exactly what the runway conditions were in this event, and it is possible that the crew did not know either.
The 6000ft runway is not grooved, and on the day it was wet, very wet, and possibly ‘flooded’ with a layer of surface water.
In very wet conditions, the maximum landing weight with similar safety margins as on a dry runway would probably be equivalent to that required to stop on a 3000ft dry runway (based on CRFI interpolation – AC 164, and speculative application to a very wet runway)
If all safety margins were discarded, then assuming a 1000ft air distance (threshold to touchdown), then the landing weight could be increased to that which would stop the aircraft in approximately 2500ft ground roll; a weight which is unlikely to be available directly from aircraft data.
This approximate distance is based on the performance analysis in the TP14842E report which states that the stopping distance on a [very] wet un-grooved runway is twice that of a dry runway. Thus for the 6000ft runway, minus 1000ft air distance, the available stopping distance is equivalent to half of the remaining 5000ft.
Will a 727 stop in this (2500ft) ground distance?
Alternatively what is the max landing weight for a 3500ft dry runway, i.e. landing on a very wet 6000ft runway with no safety margin?
Perhaps some other significant findings published in report TP14842E are:-
“It would be operationally difficult to issue accurate reports of the runway being flooded during short-term transient rainstorms”.
“During the summer months the runways are reported as “bare and dry”, damp or “bare and wet”, and rarely reported as flooded unless there is pooling of water in depressions”.
And based on interviews with airfield operations managers at two major Canadian airports: -
“… airport operators do not currently make a determination of whether water on the runway is greater than 3 mm in depth during heavy rainfall, and they do not report that the runway is flooded, rather than wet, when the depth is greater than 3 mm.”
We don’t know exactly what the runway conditions were in this event, and it is possible that the crew did not know either.
The 6000ft runway is not grooved, and on the day it was wet, very wet, and possibly ‘flooded’ with a layer of surface water.
In very wet conditions, the maximum landing weight with similar safety margins as on a dry runway would probably be equivalent to that required to stop on a 3000ft dry runway (based on CRFI interpolation – AC 164, and speculative application to a very wet runway)
If all safety margins were discarded, then assuming a 1000ft air distance (threshold to touchdown), then the landing weight could be increased to that which would stop the aircraft in approximately 2500ft ground roll; a weight which is unlikely to be available directly from aircraft data.
This approximate distance is based on the performance analysis in the TP14842E report which states that the stopping distance on a [very] wet un-grooved runway is twice that of a dry runway. Thus for the 6000ft runway, minus 1000ft air distance, the available stopping distance is equivalent to half of the remaining 5000ft.
Will a 727 stop in this (2500ft) ground distance?
Alternatively what is the max landing weight for a 3500ft dry runway, i.e. landing on a very wet 6000ft runway with no safety margin?
Perhaps some other significant findings published in report TP14842E are:-
“It would be operationally difficult to issue accurate reports of the runway being flooded during short-term transient rainstorms”.
“During the summer months the runways are reported as “bare and dry”, damp or “bare and wet”, and rarely reported as flooded unless there is pooling of water in depressions”.
And based on interviews with airfield operations managers at two major Canadian airports: -
“… airport operators do not currently make a determination of whether water on the runway is greater than 3 mm in depth during heavy rainfall, and they do not report that the runway is flooded, rather than wet, when the depth is greater than 3 mm.”
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I'm enjoying the discussion; almost something for Tech Log.
The mainstream of discussion is going down the path of considering performance on a very wet or flooded runway, and the side issue of grooving, which is the most logical path for the discussion to take with the information available so far.
At the same time, let's keep minimal texture and shallow surface water in the back of our minds as a possibility until we know the macrotexture and microtexture of the runway.
Most runways have reasonable macrotexture and microtexture and performance calculations assume those conditions being present. But it is possible to have a runway where the macrotexture or microtexture have been effectively destroyed by rubber build-up or by inappropriate maintenance or rehabilitation (trust me – I've seen this with my own eyes twice this year
). Under those circumstances, even a small amount of surface water can significantly affect the braking performance, and we can experience the braking problems that are normally associated with very wet or flooded conditions. One of safetypee's earlier quotes touches on this: not provide an adequate safety margin for landings on wet runways, particularly those with low texture or rubber contamination.
Because 9 times out of 10, overruns in the wet are associated with lots of rain and with poor macrotexture or lack of grooving, I've been guilty of sloppily thinking in the past that overruns always go with these conditions. Clearly I am a dynamic/viscous hydroplaning or aquaplaning sort of person – i.e. occurring when an aircraft lands fast enough on a wet runway.
I was therefore surprised recently looking at an overrun accident which occurred in only light rain. It wasn't until I measured the minimal macrotexture and virtually nil microtexture of the runway that I remembered reverted rubber skidding - akin to viscous skidding in that it occurs with a thin film of water and a smooth runway surface.
Not saying for a moment that this happened here at Moncton – we simply haven't got the data to judge yet. But while I'm enjoying the discussions here about water great than 3mm and the rest of it, I'll still keep in mind the danger represented by light rain and smooth surface.
The mainstream of discussion is going down the path of considering performance on a very wet or flooded runway, and the side issue of grooving, which is the most logical path for the discussion to take with the information available so far.
At the same time, let's keep minimal texture and shallow surface water in the back of our minds as a possibility until we know the macrotexture and microtexture of the runway.
Most runways have reasonable macrotexture and microtexture and performance calculations assume those conditions being present. But it is possible to have a runway where the macrotexture or microtexture have been effectively destroyed by rubber build-up or by inappropriate maintenance or rehabilitation (trust me – I've seen this with my own eyes twice this year
). Under those circumstances, even a small amount of surface water can significantly affect the braking performance, and we can experience the braking problems that are normally associated with very wet or flooded conditions. One of safetypee's earlier quotes touches on this: not provide an adequate safety margin for landings on wet runways, particularly those with low texture or rubber contamination.Because 9 times out of 10, overruns in the wet are associated with lots of rain and with poor macrotexture or lack of grooving, I've been guilty of sloppily thinking in the past that overruns always go with these conditions. Clearly I am a dynamic/viscous hydroplaning or aquaplaning sort of person – i.e. occurring when an aircraft lands fast enough on a wet runway.
I was therefore surprised recently looking at an overrun accident which occurred in only light rain. It wasn't until I measured the minimal macrotexture and virtually nil microtexture of the runway that I remembered reverted rubber skidding - akin to viscous skidding in that it occurs with a thin film of water and a smooth runway surface.
Not saying for a moment that this happened here at Moncton – we simply haven't got the data to judge yet. But while I'm enjoying the discussions here about water great than 3mm and the rest of it, I'll still keep in mind the danger represented by light rain and smooth surface.
‘how wet is a wet runway?’
OverRun, I agree with your points about runway texture. The discussion re 3 mm water depth related to the TC report and common operational definitions; it was not intended to limit the discussion to this area.
A good research reference on the problem areas is Wet Runways, but note that the information on antiskid systems and friction measurement devices have probably been overtaken by more recent information.
The operational problem might be seen as ‘how wet is a wet runway?’
In this domain, wet relates primarily to the water depth, but significantly includes runway texture, and tyre characteristics (fig 1 in the ref), noting that water depth need not necessarily be very great if either the texture and/or tyre characteristics are poor. It’s surprising how quickly we forget critical items, e.g. an 80% worn tyre is virtually ineffective in wet conditons – poor retardation and directional capability, yet in this commercially sensitive era we might allow tyre wear to the limit value.
Landing performance is published for wet conditions, but usually this is based on factored dry distances and crosschecked with computed / assumed friction levels with some measured distances.
ICAO ‘Good’ on a wet runway may be equivalent to 0.4 mu and above. The conditions are illustrated thus:- Aircraft can expect to land comfortably within the scheduled ‘wet’ distance, without undue directional control problems, but this definition might now only apply to a well drained runway with average texture.
With increasing water depth / decreasing runway texture and poor tyre characteristics, the braking friction reduces and the estimated braking characteristics can range Medium to Poor. ATM should report this estimate which is often based on their view of the runway’s ‘wet’ condition, i.e. how wet is wet – how deep is the water in relationship to the texture.
However, ATM have little knowledge of the runway texture (except when NOTAM as slippery when wet) and no knowledge of the aircraft’s tyres, thus estimates of braking action can be very poor.
Braking action PIREPS are often quoted by ATM, but due to human limitations in assessment, particularly when thrust reverse and autobrake are used, these reports can result in highly misleading information as well as a source of peer pressure.
Thus, the pilot has the burden of the assessment and landing decision, but often lacking adequate information – how much water, what’s the runway texture, and what’s the condition of the tyres (should know, but who remembers).
The majority of current operations are on good runways (grooving/texture, drainage), which reduces opportunity to experience lower than expected friction (also a problem of reverse/autobrake use); this, and the reliance on thrust reverse, can lead to complacency when assessing the conditions for landing.
Factored landing distances provide a distance margin for maintaining a safe operation against the operational variability in normal operation (speed, height, position, brakes). The additional distance does not specifically consider variability in runway condition (although some reports suggest otherwise), and thus wet factors do not necessarily provide the same degree of safety as a dry runway.
As a wet runway becomes more wet (poor runway texture and tyres) the safety margin can vanish – greater reliance on reverse or the potential for an accident. In these latter conditions, pilots are expected to change their operation – reduce the variability of normal operations – use max braking, land on-speed, correct position, etc, but even with all of these, the unknowns in the runway condition may exceed all of the distance safety margin.
Another ref: Effect of pavement texture.
… a pronounced surface texture effect and a large degradation in friction coefficient as a result of the addition of a small amount of water …
A good research reference on the problem areas is Wet Runways, but note that the information on antiskid systems and friction measurement devices have probably been overtaken by more recent information.
The operational problem might be seen as ‘how wet is a wet runway?’
In this domain, wet relates primarily to the water depth, but significantly includes runway texture, and tyre characteristics (fig 1 in the ref), noting that water depth need not necessarily be very great if either the texture and/or tyre characteristics are poor. It’s surprising how quickly we forget critical items, e.g. an 80% worn tyre is virtually ineffective in wet conditons – poor retardation and directional capability, yet in this commercially sensitive era we might allow tyre wear to the limit value.
Landing performance is published for wet conditions, but usually this is based on factored dry distances and crosschecked with computed / assumed friction levels with some measured distances.
ICAO ‘Good’ on a wet runway may be equivalent to 0.4 mu and above. The conditions are illustrated thus:- Aircraft can expect to land comfortably within the scheduled ‘wet’ distance, without undue directional control problems, but this definition might now only apply to a well drained runway with average texture.
With increasing water depth / decreasing runway texture and poor tyre characteristics, the braking friction reduces and the estimated braking characteristics can range Medium to Poor. ATM should report this estimate which is often based on their view of the runway’s ‘wet’ condition, i.e. how wet is wet – how deep is the water in relationship to the texture.
However, ATM have little knowledge of the runway texture (except when NOTAM as slippery when wet) and no knowledge of the aircraft’s tyres, thus estimates of braking action can be very poor.
Braking action PIREPS are often quoted by ATM, but due to human limitations in assessment, particularly when thrust reverse and autobrake are used, these reports can result in highly misleading information as well as a source of peer pressure.
Thus, the pilot has the burden of the assessment and landing decision, but often lacking adequate information – how much water, what’s the runway texture, and what’s the condition of the tyres (should know, but who remembers).
The majority of current operations are on good runways (grooving/texture, drainage), which reduces opportunity to experience lower than expected friction (also a problem of reverse/autobrake use); this, and the reliance on thrust reverse, can lead to complacency when assessing the conditions for landing.
Factored landing distances provide a distance margin for maintaining a safe operation against the operational variability in normal operation (speed, height, position, brakes). The additional distance does not specifically consider variability in runway condition (although some reports suggest otherwise), and thus wet factors do not necessarily provide the same degree of safety as a dry runway.
As a wet runway becomes more wet (poor runway texture and tyres) the safety margin can vanish – greater reliance on reverse or the potential for an accident. In these latter conditions, pilots are expected to change their operation – reduce the variability of normal operations – use max braking, land on-speed, correct position, etc, but even with all of these, the unknowns in the runway condition may exceed all of the distance safety margin.
Another ref: Effect of pavement texture.
… a pronounced surface texture effect and a large degradation in friction coefficient as a result of the addition of a small amount of water …
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safetypee,
My apologies for the delay in answering; you've raised many valuable points and I only got to sit down today to think them through. Your point is very well made about:
I know a crew who fit exactly into the picture you've described, and who changed their complacent attitude (and their underpants) recently on a certain runway in the land of the verdant garden with low microtexture and low macrotexture.
Thanks very much for the links as well. The Horne paper on wet runways in particular yielded this particular gem of the inter-relationship between macro/micro-texture and fluid pressure alleviation which had been pretty much lost to most airport engineers and pilots with the passage of time. In the interests of safety and education, here it is:
My apologies for the delay in answering; you've raised many valuable points and I only got to sit down today to think them through. Your point is very well made about:
The majority of current operations are on good runways (grooving/texture, drainage), which reduces opportunity to experience lower than expected friction (also a problem of reverse/autobrake use); this, and the reliance on thrust reverse, can lead to complacency when assessing the conditions for landing
Thanks very much for the links as well. The Horne paper on wet runways in particular yielded this particular gem of the inter-relationship between macro/micro-texture and fluid pressure alleviation which had been pretty much lost to most airport engineers and pilots with the passage of time. In the interests of safety and education, here it is:
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Hydroplane
It seems to me that the rigid gear is the problem. I don't believe the location of the engines are the cause. The DC-9, MD 80's and 727's all have problem with wet runways. Seldom do you see a truck gear hydroplane.
