How does weather affect take off performance?

[Espada III]

Lets assume some fixed points of reference: -

Airbus A320 with 90% passenger loading and an equivalent luggage load.
Flight from say Manchester to Malaga
The temperature in Manchester is 20C.

What difference is there in take-off performance and/or procedure for: -


Dry day
Humid day
Raining relatively heavily


Thanks

[ARNSpoty]

if the atmospheric pressure and temperature remain the same, where there is an increase in humidity, one needs a longer takeoff distance; the air is less dense.
Temperature wise to sum up, the cooler it is, the less the engines have to preform. So cool temperatures better than hot.
And the heavy rain you could refer to the previous humidity explanation.

E

[wiggy]

if the atmospheric pressure and temperature remain the same, where there is an increase in humidity, one needs a longer takeoff distance;

Whilst we await the Performance experts to chip in my twopence would be:

Having never knowing entered humidity (either as a Dew Point or a percentage) into a pre-flight takeoff performance calculation I'm guessing the increase in takeoff distance, if any, is pretty small..........


As for heavy rain; again AFAIK, you're far more interested in the rain's effect on braking action and your ability to stop in a hurry rather than the rain's effect on engine performance.

What difference is there in take-off performance and/or procedure for
1. Dry day
2. Humid day
3. Raining relatively heavily:

In (very, very) simple terms if you decide the runway is wet then we use the calculated "wet" V1 speed ( "decision speed") for the day, which will be lower than the dry runway value. By doing this you are forced into making any stop/go decision earlier in the take off roll than in the dry runway case, which reduces the changes of a having to attempt a high speed stop on a possibly wet slippery runway. There is however a trade off - on a wet day if things go wrong (engine failure) at just above V1 you won't be as high above obstacles at the runway end as you would be on a dry day - you need to be aware you're swaping one area of risk against another.