Is "T/C OAT" the actual temperature at cruise altitude or is it the deviation from standard temperature at cruise altitude? I checked the FMC manual, but this is not addressed.Thanks,Stacey

Is "T/C OAT" the actual temperature at cruise altitude or is it the deviation from standard temperature at cruise altitude? I checked the FMC manual, but this is not addressed.Thanks,Stacey

If I remember correctly, OAT is the indicated air temp corrected for compression and heating caused by friction. I believe it's also known as true air temp. If you are looking for further information, do a forum search. This has been discussed extensively on several occasions.Also: http://forums1.avsim.net/index.php?showtopic=245586

If I remember correctly, OAT is the indicated air temp corrected for compression and heating caused by friction. I believe it's also known as true air temp. If you are looking for further information, do a forum search. This has been discussed extensively on several occasions.Also: http://forums1.avsim.net/index.php?showtopic=245586

I searched the forum before posting (SOP). The only thread with "OAT" or "air temp" is this one now. Before my post, there were none. Suggestions for keywords maybe?Thanks,Stacey Weaver

Is "T/C OAT" the actual temperature at cruise altitude or is it the deviation from standard temperature at cruise altitude? I checked the FMC manual, but this is not addressed.

You can do either ISA deviation or OAT. Fill on one of the four boxes, and the others will be populated correctly. Just depends on how the data is given to you. This is just the air temp from the winds aloft. Nothing to do with SAT RAT TAT, etc.

My understanding from real world manuals that I have is that you hould input the true OAT found in your cruise FL. This can easily be achieved by taking a look at the winds aloft charts. NOAA

My understanding from real world manuals that I have is that you hould input the true OAT found in your cruise FL. This can easily be achieved by taking a look at the winds aloft charts. NOAA

Thank you for posting this information.  It has ended my state of confusion!

 

Another way to calculate the temperature at altitude (instead of looking at winds aloft) is to times the altitude by 2 and minus 15 which gives you a negative number in degrees Celsius.

 

For example:  27,000 feet cruise altitude.  27 x 2 - 15 = -39  (note that the final value is always a negative).  It gets colder as you ascend...

 

WilloW

For those looking for US wind/temp data, it can be found here:

http://aviationweather.gov/products/nws/winds/

 

The format is:

WWSS[±TT] - where W is wind direction, D is speed, and T is temp.  Split every two numbers and add a zero to the wind direction.

 

Example:

2657-25 becomes 26 57 -25.  Add zero to the wind and you get 260 at 57, temp -25.  Temps are assumed negative over FL240, so if you see 268250 at FL340, it's 260 at 82, temp -50.

 

Extra info:

-No temp data means that the altitude is close enough to the surface that surface values are used.

-9900 mean calm wind or light and variable.

-Wind "directions" of 51-86 means wind speeds are greater than 100 knots.  7319 means wind is 230 at 119 (subtract 50 from the direction).  Something like 7799 means "I hope you're going east," because that's 270 degrees at 199 knots or greater.

 

 

 

(note that the final value is always a negative)

 

Not necessarily true.  While yes, you're nearly guaranteed a negative number by the time you're going to get to the cruise levels of a 737, you'll note that on the wind charts they only start assuming it's a negative number above FL240.

 

SWA has a flight from BWI-ORF that regularly has a + OAT/ to be entered.

 

Definitely a handy formula for figuring out freezing levels though, absent the wind/temp data.

@@scandinavian13 - Thanks for posting and setting out the deciphering of the wind aloft metars.  I didn't know of the winds aloft website - handy information.    Cheers,   WilloW

 

 

Thanks for posting and setting out the deciphering of the wind aloft

 

Welcome!

Keep in mind that OAT, TAT and SAT are three different figures. Each would be different if placed on the same aircraft.

 

 

Keep in mind that OAT, TAT and SAT are three different figures.

 

Two different figures...

OAT = SAT

 

Common mistake.

Two different figures...

OAT = SAT

 

Common mistake.

Correct.

 

SAT - Static Ambient Temperature

TAT - Total Ambient Temperature

OAT - Outside Air Temperature

 

SAT and OAT are exactly the same. 

 

TAT is similar, however, takes into account the heat increase caused by the adiabatic increase in temperature as air is brought to a stop inside a probe called the rosemount probe (gauge).  As the air flows through the probe and comes to a stop, kinetic energy (from air movement) is converted to internal energy (air at rest).  The resultant temperature increase is usually a little higher than SAT or OAT.   Simply put, air increases in temperature as its compressed and funneled into the probe before coming to standstill and measured.

 

Cheers,    WilloW.