A310 Flex Takeoff on Wet Runway

[Haroon]

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.

[oldchina]

Haroon

"Landing Ltd MTOW = 137000
ZFW Ltd MTOW = 137400
Thus MTOW Limit = 137000"

.. doesn't make a lot of sense, and I should have resisted jumping in because I'm not an expert on A310 and I'm not going to become one.

But I do know that from a 4000m runway at 25 deg C the maximum permissible TOW is not 137t. Almost certainly 157t.

You'd better have another look at those tables.

[Haroon]

Hi Oldchina

Structure Ltd MTOW = 157000

Landing Ltd MTOW = 137000

ZFW Ltd MTOW = 137400

The Maximum TOW limit for this particular takeoff will be the lower of the above values which is 137000. That's what I meant.

In any case I think I need to cut down on this lengthy post. I think I've given some unnecessary details.

[john_tullamarine]

Landing limited RTOW is rather conventional. MLW plus planned burn to avoid getting to destination somewhat above MLW.

[Haroon]

OK guys sorry for the mess. I've rewritten my query. Hopefully its better this time.

Please refer to the following chart:

A310 Wet Runway Correction Chart http://64.176.58.144/wetcorrection.jpg

My querry is about the flex temperature correction given in Note (point no 2) at the end of this chart. The note says:

If V1 corresponding to actual takeoff weight is lower than min V1 then keep Min V1 as V1 for takeoff.

Regarding Flex Temperature, point no 2 of the note 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.

First of all which Max TOW is under discussion?

Structure limited Max TOW, which is 157000

or

Performance regulated Max TOW, which can be above or below 157000

or

Max TOW for a particular takeoff which relates to the lower of structure limited, landing limited and ZFW limited RTOW.


For an example please refer to the following runway analysis chart http://64.176.58.144/runwaychart.jpg

Lets say the TOW is 136.4t on a runway more than 3000 meters in length.

In calm wind conditions V1 will be 154

After 10 knots of reduction for wet runway it will be 144

Considering it a slats15/flaps15 takeoff, min V1 is 124

Since Corrected V1 is above min V1 there is no issue.

Now assume the TOW is 120.0t on the same runway.

In calm wind conditions V1 will be 131

After 10 knots of reduction for wet runway it will be 121

Considering slats15/flaps15 takeoff, min V1 is 124

Since the corrected V1 is now below min V1,

Our takeoff V1 will be 124 (which is min V1) but we will have to adjust the flex temperature.

Accroding to point no 2 of the note:

"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 max TOW is 157t then its V1 is 159 for calm wind condition.

Min V1 is 124

Then 159 - 124 = 35

Decreasing Flex Temp by 3 deg per knot difference between these values means:

35 x 3 = 105

Flex at TOW of 120.0t is 65

Thus 65-105 Means No Flex

So why at lower takeoff weights there is no Flex takeoff when runway is wet as compared to heavy weights?

Thankyou for your patience and time.

[latetonite]

You really expect people to read all of this?

[westinghouse]

I think your better off delaying the flight, wait till the weather improves and the runway is dry.

Happy flying.

[kwateow]

westinghouse

Sure, Dubai runway will dry up faster than we can sort this out.

A lot of you can't even agree on the definitions: TOW, MTOW, MDTOW, RTOW, Landing Limited MTOW (wtf is this one?) ....

Lucky it's not an emergency.

[OK465]

So why at lower takeoff weights there is no Flex takeoff when runway is wet as compared to heavy weights?

After a cursory look without getting bogged down in that terribly impractical chart verbiage used for guidance (I actually read it all and at 67 and retired, every minute is precious, but challenges rare) I would offer this...

In your second example where min V1 is 124 and is higher than your calculated V1 which is 121, my logical aerospace mind says that it is this 3 knot difference between 121 & 124 which necessitates a (3 x 3) = 9 degree C reduction in the flex temperature value.

I say this only because it makes sense...

In addition, I would guess your actual allowed flex values for the heavier weights are lower than the lighter weights also.

I could certainly be wrong. Communication is a fragile thing and the guidance is poorly written and formatted. Check with your tech pilots.

Actually, I just wanted to say that during the performance section of ground school in all transport category aircraft I flew, we were required to do manual (gasp) performance calculations which included determining the most restrictive of structural, runway, WAT or landing limit weight for takeoff. Maybe not done anymore?

It's interesting to read here recently some of the comments in this thread and other threads about never having been exposed to "a range of V1's" or a 'landing limit for takeoff' from posters who are 20,000 hour & 30 year vets. However, it may be just a matter of 'use it or lose it'.

(Disclaimer: I'm not a 310 guy.)

[Haroon]

Hi OK465

Thankyou for your time. Much appreciated.

my logical aerospace mind says that it is this 3 knot difference between 121 & 124 which necessitates a (3 x 3) = 9 degree C reduction in the flex temperature value.I say this only because it makes sense...

That sounds sense to me as well but what is mentioned in the note is causing confusion. It 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"

i.e. to calculate the difference, the two V1's involved are min V1 and Max Tow V1

min V1 is 124, as clearly given.

But what is the Max Tow V1? It cant be 121.

or may be "Both Values" mean min V1 and corrected V1. In this case we have to assume that the note is not properly written, as you mentioned in your post.

Anyhow thanks once gain for your input. Greatly appreciated.

[FE Hoppy]

If V1 corresponding to actual TOW is lower than minimum V1

and xyz

retain minimum V1 as V1 and decrease flexible temperature by 3°C per kt difference between both values.


Read it like this and it makes perfect sense.


The wet reduction of V1 creates a performance reduction which we can normally live with. However, if we are so light that the performance reduction puts V1 below Vmcg then I have to use an assumed weight (the weight who's v1 = vmcg) and increase the reduced thrust to the value required for this assumed weight.
Reducing the flex temp increase the thrust and I do this until the thrust is correct for my new assumed weight.

i.e. 3 kt x 3 °C in your example.

[Haroon]

Hello Hoppy.

I was waiting for you

What you've written makes perfect sense.

Thanks a lot for your time

Regards