B737NG Quick Turnaround Limit Weight
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B737NG Quick Turnaround Limit Weight
Hi!
In the Performance Dispatch section of the FCOM1, there is a Quick Turnaround Limit Weight table related to the brake cooling. In regards to this and also the Recommended Brake Cooling Schedule I have the following questions:
1. Can anyone tell me what configuration the Quick Turnaround Weight Limit is based on (Autobrake setting/Reverse thrust/Flaps)?
2. Does brake cooling times for the 737NG in general require the parking brake to be released if a specific cooling time is stated (i.e. the
Event Adjusted Brake Energy exceeds 16 million of foot pounds)?
I have of course tried to find the information in the manuals, even the AFM but without any luck.
Looking for a firm answer, preferably with a reference to something published by Boeing and not just "I think it is...."
Many thanks!
/L
In the Performance Dispatch section of the FCOM1, there is a Quick Turnaround Limit Weight table related to the brake cooling. In regards to this and also the Recommended Brake Cooling Schedule I have the following questions:
1. Can anyone tell me what configuration the Quick Turnaround Weight Limit is based on (Autobrake setting/Reverse thrust/Flaps)?
2. Does brake cooling times for the 737NG in general require the parking brake to be released if a specific cooling time is stated (i.e. the
Event Adjusted Brake Energy exceeds 16 million of foot pounds)?
I have of course tried to find the information in the manuals, even the AFM but without any luck.
Looking for a firm answer, preferably with a reference to something published by Boeing and not just "I think it is...."
Many thanks!
/L
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Some companys' manuals present quick turnaround limit weights for both flap 30 and 40. Those who operate from high altitude and high temperature airports, a flaps 40 landing may not be an option because of the approach climb limit weight.
Generally, approach climb performance is not a factor at low elevation airports. If the operator ala FR is looking for a quick turn time of 25 minutes then flaps 40 may be the only option, unless the crew wants to fly with the gear extended after takeoff for a period of time.
Get your hands on your company's actual Planning and Performance Manual (P&P). The P&P contains data for both flaps 30 and 40 quick turn limit weights, while the FCOM PI/PD sections contain excerpts from the actual P&P. You will see that a flaps 30 landing will result in a lower quick turn limit weight due to the higher break energy limit required to stop the aircraft.
Generally, approach climb performance is not a factor at low elevation airports. If the operator ala FR is looking for a quick turn time of 25 minutes then flaps 40 may be the only option, unless the crew wants to fly with the gear extended after takeoff for a period of time.
Get your hands on your company's actual Planning and Performance Manual (P&P). The P&P contains data for both flaps 30 and 40 quick turn limit weights, while the FCOM PI/PD sections contain excerpts from the actual P&P. You will see that a flaps 30 landing will result in a lower quick turn limit weight due to the higher break energy limit required to stop the aircraft.
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MQTW is based on either flap 30 or 40, both tables exist.
However, be careful and look into your AFM (should be on the aircraft), as the MQTW requires 67 minutes of cooling time for the 737-800 for instance. Most operators do not have such turn around times, thus the MQTW is slightly arbitrary.
Regarding cooling, yes the brakes need to be released to allow airflow around the stators and so on, this is the medium after all which absorbs the heat from the brake assembly.
See this presentation for a Boeing FLOE explaining the works! You could be surprised...
However, be careful and look into your AFM (should be on the aircraft), as the MQTW requires 67 minutes of cooling time for the 737-800 for instance. Most operators do not have such turn around times, thus the MQTW is slightly arbitrary.
Regarding cooling, yes the brakes need to be released to allow airflow around the stators and so on, this is the medium after all which absorbs the heat from the brake assembly.
See this presentation for a Boeing FLOE explaining the works! You could be surprised...
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Skyjob; many thanks for that link. I am searching for some answers to the whole brake cooling calculation and this article does not give the answers. Perhaps you, or others, can help. The TQTGW is calculated assuming brakes ON at Vref, max braking and no Rev.
So, the table QRH PI) titled Recommended Brake Cooling Schedule requires you to enter with Brakes On speed v G.Wt. This table does not mention RTO or Landing. From this tabel you find a Ref Brake Energy (per brake). Over the page and there are tables to enter with this number. What confuses me is this then compared to a degree of autobrake to find an Event Adjusted Brake Energy, and from this you find a Brake Cooling Scedule.
Back to the first step. If this is a Landing calclation, and normal 2nd detent Rev is used till 60kts, what is the Brakes On Speed to enter the table? Some people use Vref and then find they need 10mins ground cooling at a weight that is 20.000kgs less than MQTGW. This to me seems a wrong assumption. I've been trying to find what a Quick Turnround is in Time, but the whole thing seems to be based on fuse plugs blowing and not based on an RTPO after so many minutes.
What confuses me is that the Brake Energy Table does not declare the amount of braking applied, and then the following tables tell you to enter with an autobrake setting.
What I'm seeking is a 100% guaranteed authorative answer. I have enough opinions at work to sink an aircraft carrier. I'm chasing Boeing, but no replies yet.
HELP?
So, the table QRH PI) titled Recommended Brake Cooling Schedule requires you to enter with Brakes On speed v G.Wt. This table does not mention RTO or Landing. From this tabel you find a Ref Brake Energy (per brake). Over the page and there are tables to enter with this number. What confuses me is this then compared to a degree of autobrake to find an Event Adjusted Brake Energy, and from this you find a Brake Cooling Scedule.
Back to the first step. If this is a Landing calclation, and normal 2nd detent Rev is used till 60kts, what is the Brakes On Speed to enter the table? Some people use Vref and then find they need 10mins ground cooling at a weight that is 20.000kgs less than MQTGW. This to me seems a wrong assumption. I've been trying to find what a Quick Turnround is in Time, but the whole thing seems to be based on fuse plugs blowing and not based on an RTPO after so many minutes.
What confuses me is that the Brake Energy Table does not declare the amount of braking applied, and then the following tables tell you to enter with an autobrake setting.
What I'm seeking is a 100% guaranteed authorative answer. I have enough opinions at work to sink an aircraft carrier. I'm chasing Boeing, but no replies yet.
HELP?
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An authorotive answer I cannot give you, but an educated one, yes:
- The first table in the PI is an energy reference chart; in other words, this is a table representing the energy the aircraft contains just prior to touching down (you could read kinetic energy); Vfly on top, Weight on left, the corrections for pressure altitude and temperature, plus some footnotes to correct for wind (1/2 HWC and 1+1/2 TWC) when planning in-flight or without a known groundspeed; if the actual Vtouchdown is known, use this speed and enter at 15 degrees (ISA) and Sea Level (0' Pressure Altitude)
- The second set of tables is a correction to this energy amount, to allow for the cummulatative friction during landing (ground friction, aerodynamic drag, slip ratio, etc), the selected auto brakes during landing and the reversers used. This corrected energy is that amount which is absorbed by the brakes during landing.
- The corrected energy is the amount that needs dissipating in some way or another, prior to departure, to allow for a safe aircraft starting the takeoff roll, in case of a high energy reject.
The entire calcualtion is very much so based on assumptions, such as the fact that brakes heat and cool evenly, which in reality cannot be the case.
The MQTW tables are there to enable the maximum possible weight to land with prior to reaching the Caution Area using the FCOM descibed landing technique. These weights are limitations be observed and the cooling time varies slightly by type variant, but for -800 is 67 minutes.
The Advisory data allows for different landing techniques (autobrake, reversers, less weights, ...) and less cooling time to achieve a safe departure sooner. In most airline operations you will never fly near the MQTW thus not usually need the full cooling time.
In an RTO, you enter the first table (kinetic energy) at sealevel with TOW and achieved speed during RTO. No corrections are made for reversers, autobrake, etc as it will go into full RTO braking (uncontrolled, maximum pressure available). Thus the uncorrected energy levels are identical to the corrected levels which then need refering to when cooling afterwards.
Looking at the tables you will see that the Reversers account for a lot of stopping capability and indeed are very capable of stopping the aircraft in good time with little use of any autobrake when required, thus low corrected values afterwards.
Remember that the lower autobrakes is selected, the lower the rate of deceleration, thus the longer it takes to stop from Vref, thus the longer the brakes are applied (be it less hard), thsu the longer time brakes are heated up. A downside to lower autobrake settings, but taken into accoutn in the tables.
Also remember that to release the brakes on stand improves the airflow around the brake stack, which is required to cool them down. No airflow, no or little cooling possibility!
More later, if required....
- The first table in the PI is an energy reference chart; in other words, this is a table representing the energy the aircraft contains just prior to touching down (you could read kinetic energy); Vfly on top, Weight on left, the corrections for pressure altitude and temperature, plus some footnotes to correct for wind (1/2 HWC and 1+1/2 TWC) when planning in-flight or without a known groundspeed; if the actual Vtouchdown is known, use this speed and enter at 15 degrees (ISA) and Sea Level (0' Pressure Altitude)
- The second set of tables is a correction to this energy amount, to allow for the cummulatative friction during landing (ground friction, aerodynamic drag, slip ratio, etc), the selected auto brakes during landing and the reversers used. This corrected energy is that amount which is absorbed by the brakes during landing.
- The corrected energy is the amount that needs dissipating in some way or another, prior to departure, to allow for a safe aircraft starting the takeoff roll, in case of a high energy reject.
The entire calcualtion is very much so based on assumptions, such as the fact that brakes heat and cool evenly, which in reality cannot be the case.
The MQTW tables are there to enable the maximum possible weight to land with prior to reaching the Caution Area using the FCOM descibed landing technique. These weights are limitations be observed and the cooling time varies slightly by type variant, but for -800 is 67 minutes.
The Advisory data allows for different landing techniques (autobrake, reversers, less weights, ...) and less cooling time to achieve a safe departure sooner. In most airline operations you will never fly near the MQTW thus not usually need the full cooling time.
In an RTO, you enter the first table (kinetic energy) at sealevel with TOW and achieved speed during RTO. No corrections are made for reversers, autobrake, etc as it will go into full RTO braking (uncontrolled, maximum pressure available). Thus the uncorrected energy levels are identical to the corrected levels which then need refering to when cooling afterwards.
Looking at the tables you will see that the Reversers account for a lot of stopping capability and indeed are very capable of stopping the aircraft in good time with little use of any autobrake when required, thus low corrected values afterwards.
Remember that the lower autobrakes is selected, the lower the rate of deceleration, thus the longer it takes to stop from Vref, thus the longer the brakes are applied (be it less hard), thsu the longer time brakes are heated up. A downside to lower autobrake settings, but taken into accoutn in the tables.
Also remember that to release the brakes on stand improves the airflow around the brake stack, which is required to cool them down. No airflow, no or little cooling possibility!
More later, if required....
