Aircraft Maximum Outside Air Temperature Limit

[Pilot12345]

Im sure there is an easy answer for my question but it's just not clicking with me......Ok if your aircraft has a Maximum Outside Air Temperature Limit of "ISA + 37 C", then you can operate your aircraft up to a Maximum OAT of 52 C, if it's a "Standard Day", right?
Standard Day meaning:
ISA International Standard Atmosphere in which:
1) the air is a dry, perfect gas;
2)the temperature at sea level is 15 Celsius;
3)the pressure at sea level is 29.92 inches of mercury;
etc. etc.

So my question is, let's say im going to operate an aircraft at a Sea Level airport but the temperature is 50 Celsius and the pressure is 29.70, how would I adjust the ISA to add to 37 C since it would be something other than 15 C since it's a non standard day?

Thanks for your help!

 

[MauleSkinner]

Im sure there is an easy answer for my question but it's just not clicking with me......Ok if your aircraft has a Maximum Outside Air Temperature Limit of "ISA + 37 C", then you can operate your aircraft up to a Maximum OAT of 52 C, if it's a "Standard Day", right?
Standard Day meaning:
ISA International Standard Atmosphere in which:
1) the air is a dry, perfect gas;
2)the temperature at sea level is 15 Celsius;
3)the pressure at sea level is 29.92 inches of mercury;
etc. etc.

So my question is, let's say im going to operate an aircraft at a Sea Level airport but the temperature is 50 Celsius and the pressure is 29.70, how would I adjust the ISA to add to 37 C since it would be something other than 15 C since it's a non standard day?

Thanks for your help!

I've always used pressure altitude...in your example, pressure altitude would be 220 feet, so the limit would be about 51.75 degrees on your little analog tempreature gage

Fly safe!

David

 

[SPilot]

PA=(Pisa-Pactual)*1000+Field Elevation
DA=PA+120*(Tactual-Tisa at pressure altitude)

 

[Mickey]

If you were at sea level PA your temp limit would be 52 degrees. If you were out in Colorado and had a PA of 6000 ft. your limit would be 40 degrees. You have to adjust the ISA for the altitude that you are at and then add your 37C to find the limit.

Take care.

 

[SPilot]

If you were at sea level PA your temp limit would be 52 degrees. If you were out in Colorado and had a PA of 6000 ft. your limit would be 40 degrees. You have to adjust the ISA for the altitude that you are at and then add your 37C to find the limit.

Take care.

Now thats confusing. Because if his altimeter is 29.70, his actual pressure altitude for performance purposes is 220 feet above the field elevation. So wouldnt you say he need to adjust the ISA for the altitude his airplane is feeling? (Pressure altitude, not field elevation).

 

[Pilot12345]

Now im really confused.........

 

[SPilot]

Sorry.

 

[charter dog]

Set the altimeter to 29.92 " hg and read the indicated altitude as pressure altitude. If your altimeter read SL (0') when set to the local station pressure setting of 29.70, It should now read 220'.

Determine the standard temperature for this pressure altitude by subtracting the standard atmospheric temperature lapse rate of 2 degrees C for each 1,000' PA above SL, or fraction thereof. ( .2 per hundred, .02 per ten, etc..)

OR 15 - (PA X 2/1000)

Standard temperature for 220' PA = 15 - (220 x 2/1000) = 14.56 C

14.56 + 37 = 51.56 C. That's the maximum temperature allowed under the stated limitation.

I've never run up against our ISA + 35 limit, but have come pretty close in PHX. I understand it does happen occasionally.

MMTO (Toluca, Mx elev. 8,400') is forecast to reach 38 C tomorrow. We would have to wait for it to cool down to 33 C to meet our ISA + 35 limitation.

15 - (8,400 X 2/1000) = - 1.8 C. -1.8 + 35 = 33.2 C (35.2 C for your plane)

So you can see that while it is not that common in North America, the ISA + limitation can occasionally become a factor in a few areas. I've not done much flying in the tropical latitudes and I'm not regretful!

Best,

 

[MauleSkinner]

I've never run up against our ISA + 35 limit, but have come pretty close in PHX. I understand it does happen occasionally.
...
So you can see that while it is not that common in North America, the ISA + limitation can occasionally become a factor in a few areas. I've not done much flying in the tropical latitudes and I'm not regretful!

Best,

I've run into it in LAS...the ISA+35 limit becomes a problem LONG after the "you know, it's just too darn hot to do much of anything" limit

Fly safe!

David

 

[charter dog]

I've run into it in LAS...the ISA+35 limit becomes a problem LONG after the "you know, it's just too darn hot to do much of anything" limit

David:

When I said I have never run up against the ISA +35 limit, I just KNEW I'd regret it! Left Vegas today at an advertised temp of 44 C, just a degree or two short. The temp on the ramp felt even worse. Even when I went back there after 10:00 PM, it was still 38 C. Just too friggin hot! I still havn't cooled down.

Best,