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mutt
13th Jun 2006, 06:23
Having a discussion regarding the use of the aspirated TAT guage as a means of obtaining OAT on the ground.

Considering the heat generated off the gound, sitting in direct sunlight or even the exhaust heat from ground power trucks/air conditioning trucks.

At what point would you consider the TAT to be accurate?

Rgds.

Mutt

BOAC
13th Jun 2006, 07:30
The 'true' BA 737-400s had this and it was pretty reliable. If you are dubious at all I would say that certainly once you got moving off stand it was as good as a met observation.

Frank Poncherello
13th Jun 2006, 09:03
On the 'bus, I wouldnt trust the TAT gauge on the ground. I think an approximation for OAT can be made by looking at the SAT and taking 2 deg of the indication.

FP

777AV8R
13th Jun 2006, 15:18
Having a discussion regarding the use of the aspirated TAT guage as a means of obtaining OAT on the ground.
Considering the heat generated off the gound, sitting in direct sunlight or even the exhaust heat from ground power trucks/air conditioning trucks.
At what point would you consider the TAT to be accurate?
Rgds.
Mutt
If you're referring to the TAT on the 777, Mutt..having flown this airplane for over 8 yrs now, its amazingly accurate while sitting on the ground, however; nothing beats 'the real thing' from ATIS/MET.

78deg
26th Jun 2006, 20:37
B767 and 757

TAT measured by probe that is continualy deice by bleed air, on the ground this is unreliable as no or lack of airflow. This is why eng anti ice temp requirements are based on OAT on the ground(ATIS) and TAT/SAT in flight EICAS/CDU

rhovsquared
26th Jun 2006, 21:13
Mutt, the Triple Seven sounds truly amazing :ok:

doesn't reflection of heat off of a hot ramp cause some deviation? i.e TAT = SAT
How exactly are OAT temperature measurements taken... is this standardized?

mutt
27th Jun 2006, 05:16
Not really talking about the 777... more interested in the antique B747 :)

rhovsquared
Thats the problem, with summer temperatures getting close to 50°C and where temperatures can rise 10° in 1 hour, the use of the old ATIS isnt reliable. As the aircraft has an aspirated TAT system, it needs airflow. Question is, how reliable is it without that airflow.

Met measurements should be taken by the aerodrome met office in a standardized way.

Mutt

rhovsquared
27th Jun 2006, 20:28
Mutt, I should read more carefully :O ... that is a quite quandry, maybe a cross check during taxi where may TAT aproximates SAT approximates OAT, but then the TO data is already set and decided, I suppose :\

Thank God I have no such choice, ATIS it is, but then again I don't have the lives of 421 pax and a multimillion dollar machine, that can cause billions in damage, to worry about

Ah, the -747- is and alway will be the Queen of the Skies, what a Lady

rhovsquared :)

Edited: to say the Phrase "should be taken ... standardized way" the should scares me, but alway very conservative ...
John Tullamarine, I heard you loud and clear, especially with General Aviation props... you won't see me at night, in the winter, flying IFR or VFR in the Rockies :\

even better the thermometer attached to the wooden post .along with the windsock but I love it.