Shear Rate
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Shear Rate
Does Anybody know how to judge the shear rate value in the Lido OFP? What are the values depicted to express light, med, and severe Turb?
Thanks
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Hi mcgiever
It's not an exact science unfortunately. I've been in the silky smooth core of a 150kt jet stream, and also been bumped around the edges of much smaller ones.
From our Lido explanation:
"Shear rate.
Vertical windshear value in metres per second per thousand feet at the current position. The SR value is determined by quantifying the difference in wind speed and direction for the wind 2,000 feet above and 2,000 feet below the planned altitude at the current position using the ??? Airlines vertical windshear algorithm.
NOTE:
SHR is to be used as an indicator of the potential for Clear Air Turbulence (CAT) only. The higher the SR value the greater the difference in wind speed and direction between the two altitudes. No studies have been carried out to validate the relationship between SR values and the probability and severity of CAT. This information is to be used as guidance only and must be correlated with other available information such as SIGMETS and SIG WX Charts."
It's not an exact science unfortunately. I've been in the silky smooth core of a 150kt jet stream, and also been bumped around the edges of much smaller ones.
From our Lido explanation:
"Shear rate.
Vertical windshear value in metres per second per thousand feet at the current position. The SR value is determined by quantifying the difference in wind speed and direction for the wind 2,000 feet above and 2,000 feet below the planned altitude at the current position using the ??? Airlines vertical windshear algorithm.
NOTE:
SHR is to be used as an indicator of the potential for Clear Air Turbulence (CAT) only. The higher the SR value the greater the difference in wind speed and direction between the two altitudes. No studies have been carried out to validate the relationship between SR values and the probability and severity of CAT. This information is to be used as guidance only and must be correlated with other available information such as SIGMETS and SIG WX Charts."
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LIDO uses the "singapore model" to calculate this value. The model mathematically quantifies both the velocity and direction differences between two altitudes. Generally 2000 feet above and below the planned altitude are used. The value presented is a value in knots/1000 ft.
The challenge is that this is an instantaneous value at a specific waypoint and is only an indicator of the potential for CAT.
No studies have been done to correlate the value and CAT.
There is also no ability to relate the shear value and the level of potential turbulence i.e. a value of 3 is not moderate or 5 severe, there is NO established relationship.
I have flown using these values for years and seen values of 5 or 6 and been smooth and had 0 and been in moderate turbulence.
The expectation is that you look at this value and then couple it with SIG WX charts and PIREPS to formulate the best decision.
Also be aware that there are several SIG WX models that produce the SIG charts and different models produce quite different predictions.
The challenge is that this is an instantaneous value at a specific waypoint and is only an indicator of the potential for CAT.
No studies have been done to correlate the value and CAT.
There is also no ability to relate the shear value and the level of potential turbulence i.e. a value of 3 is not moderate or 5 severe, there is NO established relationship.
I have flown using these values for years and seen values of 5 or 6 and been smooth and had 0 and been in moderate turbulence.
The expectation is that you look at this value and then couple it with SIG WX charts and PIREPS to formulate the best decision.
Also be aware that there are several SIG WX models that produce the SIG charts and different models produce quite different predictions.
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never used lido before . what do they mean by +1 FL abv do they mean 1000 ft above or they take into consideration RVSM and the next available FL is 2000 ft in the same route ?
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Hi guys,
Definition of VWS:-
"Vertical wind shear in knots per 1000ft at the respective waypoint and is calculated using the forecast wind 1000ft above and below the waypoint.
Moderate CAT may be encountered if the value exceeds 6, especially when accompanied by a horizontal wind shear greater than 18 knots per 150 NM and / or a temperature gradient greater than 5°C"
From my limited experierence, the VWS act as a guide should you need to do a CRZ climb or descent in the region. Basically, it tells you about the Wind characteristics above and below your PLANNED CRZ LEVEL. You might encounter aome turbulence if you are climbing or descent in an area with VWS greater than 6.
To forecast if there's any turb, I will first look at the significant charts, look out for any CAT area and significant cloud prediction along my flight plan.
Next, I will look into the LIDO CFP for any significant OAT changes and ISA changes at the SAME LEVEL. This will show if we are flying through different airmass and it will increase the probability of encountering any CAT.
LIkewise, if we are flying through an area with significant cloud activities, we can be certain that it an area of unstable air conditions which equate to possible turbulent conditions.
Any comments?
Cheers,
lion-g
Definition of VWS:-
"Vertical wind shear in knots per 1000ft at the respective waypoint and is calculated using the forecast wind 1000ft above and below the waypoint.
Moderate CAT may be encountered if the value exceeds 6, especially when accompanied by a horizontal wind shear greater than 18 knots per 150 NM and / or a temperature gradient greater than 5°C"
From my limited experierence, the VWS act as a guide should you need to do a CRZ climb or descent in the region. Basically, it tells you about the Wind characteristics above and below your PLANNED CRZ LEVEL. You might encounter aome turbulence if you are climbing or descent in an area with VWS greater than 6.
To forecast if there's any turb, I will first look at the significant charts, look out for any CAT area and significant cloud prediction along my flight plan.
Next, I will look into the LIDO CFP for any significant OAT changes and ISA changes at the SAME LEVEL. This will show if we are flying through different airmass and it will increase the probability of encountering any CAT.
LIkewise, if we are flying through an area with significant cloud activities, we can be certain that it an area of unstable air conditions which equate to possible turbulent conditions.
Any comments?
Cheers,
lion-g
Last edited by lion-g; 21st May 2011 at 06:25.
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Citation 2 +1 FL in LIDO means that the system recalculates the entire flight plan on the same lateral route using one "usable" FL above or below and provides the time and burn difference.
One usable FL means that LIDO looks at each flight segment from waypoint to waypoint and adds/subtracts the correct FL based on the airspace rules for that particular area i.e. RVSM or non-RVSM, FL in feet or meters or the combination of both.
One usable FL means that LIDO looks at each flight segment from waypoint to waypoint and adds/subtracts the correct FL based on the airspace rules for that particular area i.e. RVSM or non-RVSM, FL in feet or meters or the combination of both.
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Bottom line - shear rate is not a measure of turbulence. On LIDO, it's recently gone from a scale of 0-5 to 0-10. It is suggested that upwards of 4, there may be a risk of significant turbulence, and I would brief the cabin crew accordingly. It's better that they are warned about potential turbulence before the flight, even if it comes to nothing. That's the non-technical users' guide .... which shouldn't be in this forum, of course 
