A320 QNH-Bleeds Correction
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A320 QNH-Bleeds Correction
Hi fellow pilots,
I have a question regarding the use of the QNH/Bleeds Correction chart. I'm trying to calculate the MTOW and speeds using the Quick Reference Tables. Step 1 says I should take the Pressure Altitude to correct the QNH, i.e. say QNH is 989 and chart says I need to add 700ft to airport elevation 276ft (which I now get 976ft) in which I would use the Conf 1+F Pressure Altitude = 1000 ft chart. That part I get.
Now, when does one use the QNH/Bleeds Correction chart (Effect of QNH & Bleeds up to 9200 ft)?? Would that be during the MTOW calculation process?? Example, chart says if QNH is below 1013 hPa, I need to subtract 140 kg/hPa.
Rwy length = 3000(m)
OAT 20C
Looking at the QRT where above the values intersect, I get the following: 80,200 kgs
Then below I make the corrections:
A/C on = -2,200 kgs
QNH/Bleed correction = (1013-989)*140 = -3,360 kgs
Total = 80,200 - 2,200 - 3,360 = 74,640 kgs
Then I look on chart in the 3000(m) column to find 74,640 kgs (in this case I round up to 75,000) and see the speeds as 142/149/150 or look across in the Temperature column to read what the flex temp is (in this case 48). Is what I did in the above calculation process the correct way to take into account the QNH/Bleeds Correction rule??
I have a question regarding the use of the QNH/Bleeds Correction chart. I'm trying to calculate the MTOW and speeds using the Quick Reference Tables. Step 1 says I should take the Pressure Altitude to correct the QNH, i.e. say QNH is 989 and chart says I need to add 700ft to airport elevation 276ft (which I now get 976ft) in which I would use the Conf 1+F Pressure Altitude = 1000 ft chart. That part I get.
Now, when does one use the QNH/Bleeds Correction chart (Effect of QNH & Bleeds up to 9200 ft)?? Would that be during the MTOW calculation process?? Example, chart says if QNH is below 1013 hPa, I need to subtract 140 kg/hPa.
Rwy length = 3000(m)
OAT 20C
Looking at the QRT where above the values intersect, I get the following: 80,200 kgs
Then below I make the corrections:
A/C on = -2,200 kgs
QNH/Bleed correction = (1013-989)*140 = -3,360 kgs
Total = 80,200 - 2,200 - 3,360 = 74,640 kgs
Then I look on chart in the 3000(m) column to find 74,640 kgs (in this case I round up to 75,000) and see the speeds as 142/149/150 or look across in the Temperature column to read what the flex temp is (in this case 48). Is what I did in the above calculation process the correct way to take into account the QNH/Bleeds Correction rule??
