Temp for take off

[Bluemeaway]

Ok may sound a bit stupid but here it goes..

Ambient conditions is 15mins etc

Question.

You are at the aerodrome with a AWIS/ATIS you can use that temp for take off

Now if your at an aerodrome without one of these you use the temp probe which is fitted into the aircraft yeah?....

My real question I guess is the when your sitting on a hot taxiway/runway which would cause the temp probe to over read by a few degrees

Are you compelled to use that temperature for takeoff purposes or say a temp that you read on short final (airflow over probe) without the hot runway factor.

I'm picking the first one, hoping I'm right?

Any direction towards caps or caos would be helpful.

Thanks

[The Green Goblin]

What's the most conservative? That is your answer.

Just like an airliner will use a 'flex' temperature up to 69 degrees to reduce wear etc.

Personally I'd be using the highest forecast temperature on the TAF for the day which is how I planned my payloads in the regional days. If you can go max weight at 40 degrees for the runway Id be using that for my P charts.

When I was in GA I had a booklet that I made that had all my regular airfields with P charts based on 2000 feet/40 degrees and nil wind. I had a similar system for CPL training to make planning easier and give me more time in preflight prep to worry about how I was going to fly the route, fuel etc etc.

[Cirronimbus]

The temp measured and reported by the AWIS/ATIS equipment is the 'shade' temp inside the shelter where the thermometer/temp probe is. The temp measured and reported by the probe on your aircraft is the ACTUAL temp where it is measured and will be much closer to the ACTUAL temp of the air you are taking off in.

The AWIS/ATIS temp is not measured essentially for aviation purposes but is measured that way so that it can be compared with temps measured in other places. It is a standard way of measuring temp for comparison purposes.

Better to be safe than sorry so I'd be more inclined to trust the temp measured in the air I'm using rather than something measured in the shade in a little box somewhere in a remote corner of the airfield.

CASA may have a regulation stating that you are required to use an "authorised" source but that doesn't necessarily mean their authorised source is the most accurate for YOUR purposes.

[sillograph]

Pickup the closest can of worms and inspect.

If said can of worms casts a shadow over probe eat worms and read temp.

[Mstr Caution]

If your temp probes not aspirated, it can over read the actual OAT by up to 10'c.

It's a function of how long the aircrafts been sitting in the sun or how hot the OAT is.