I've re-written my post to remove unnecessary details. You may skip post #1 and go directly below to post #6.
Sorry for the inconvenience
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Hello. My question is about A310 Flex power takeoff on wet runways.
Either I am making some mistake in my calculations or if I am calculating correctly then it appears that at lower takeoff weights there is no Flex power takeoff when runway is wet as compared to heavy weights.
Following is an example to explain my querry (sorry its a bit too elaborated)
A/C Data:
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A310 GE Engines:
MTOW Limit (Brake Release) = 157,000
Max Landing wt limit = 124,000
Max ZFW wt limit = 114,000
For a Slats 15 / Flaps 15 Takeoff
From Dubai Rwy 12L
Taxi Fuel = 300
Trip Fuel = 13,000
Block Fuel = 23,700
ZFW = 113,000
Takeoff Data:
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Please refer to these charts: (sorry for the poor quality)
Runway Analysis Chart
http://64.176.58.144/runwaychart.jpg
Takeoff Regulatory Chart
http://64.176.58.144/takeoffcorrection.jpg
OAT = 25
QNH = 1005
Wind = 0
Grad 1 = 0
Grad 2 = 400
T Ref = 34
Anti-Ice = OFF
Packs = ON
Upper Box Temp = 49
Upper Box Weight = 157100
MTOW Capability = 161740
Structure Ltd MTOW = 157000
Landing Ltd MTOW = 137000
ZFW Ltd MTOW = 137400
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Thus MTOW Limit = 137000
Actual TOW = 136400
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For TOW of 136.4
V1 = 154 (from dry runway analysis chart)
VR = 163
V2 = 166
Flex = 64
Now the Runway becomes Wet!
Please refer to the Wet Runway Chart
http://64.176.58.144/wetcorrection.jpg
After applying corrections according to A310 Wet Runway Operations.
MTOW Capability = 161740-2500 = 159240
V1 = 154-10 = 144
VR = 163-2 = 161
V2 = 166-2 = 164
Flex = 64-2 = 62
Min V1 = 124 (mentioned in the foot notes of A310 Wet Runway Operations)
Corrected V1 is above min V1
No Issues So Far
Now due to some reason a large amount of payload has to be off-loaded.
ZFW now becomes 96,600
Rest of the data remains unchanged.
Actual TOW now becomes 120,000
For TOW of 120.0
V1 = 131 (from dry runway analysis chart)
VR = 138
V2 = 142
Flex = 65
After applying corrections according to A310 Wet Runway Operations.
MTOW Capability = 161740-2500 = 159240
V1 = 131-10 = 121
VR = 138-2 = 136
V2 = 142-2 = 140
Min V1 = 124 (mentioned in the foot notes of A310 Wet Runway Operations)
Corrected V1 (121) is below min V1 (124)
Thus Note #2 Applies:
If V1 corresponding to actual takeoff weight is lower than min V1 (which is the case):
We will keep Min V1 as our V1 for takeoff.
Thus V1 = 124
Regarding Flex Temperature, Note #2 says:
"If Max TOW has a V1 equal to or above Min V1 decrease Flex Temp by 3 deg C per knot difference between both values"
If I understand correctly, Max TOW is the MTOW Capability (calculated earlier on) which is 159,240
According to the note, we have to check its V1.
The maximum weight given on the airport analysis chart is 157100 (which is the a/c limit)
So if I am not wrong we will check its V1, which comes out to be 159
According to the Note #2:
V1 of 159 is above min V1 of 124
So 159 - 124 = 35
Decreasing Flex Temp by 3 deg per knot difference between these values means:
35 x 3 = 105
Flex at TOW of 120.0 was 65
So 65 - 105 Means No Flex
Either I am making some mistake in my calculations or if I am calculating correctly then whats the reason that at lower takeoff weights there is no Flex takeoff when runway is wet as compared to heavy weights?
Thankyou for your patience and time.