Reference Temperature

[Another St Ivian]

Hello all,
I was looking through the Aerodrome AIP's the other morning and came across a section on the front page of each airfields entry in the AIP called the Reference Temperature. The entry was along the lines of;

Elevation/Reference Temperature 150ft/20 C

Could anyone say for sure what exactly the Reference Temperature means? Many ideas were put forward but no one had a definitive answer.

Thanks,
A.S.I.

[Zeke]

Going out on a limb I would say its the mean maximum temperature of the hottest month. Dont know what the statistical basis or how it is calculated.

It would mainly be used for performance calculations to "adjust" to the runway length for density altitude.

Takeoff

Altitude Correction
(7% per 1,000' above sea level)

E = Elevation
L = Takeoff length @ sea level
L1 = Length corrected for altitude
L1 = (.07 * E / 1000) * L + L

Temperature Correction
(0.5% per degree above stnd temp in hottest month)
(Stnd Temp adjusted to Sea Level)

T1 = Adjusted Stnd Temp
T = Mean Max High Temperature
L2 = Length corrected for altitude & temperature
T1 = 59 - (3.566 * E / 1000)
L2 = ( .005*( T - T1)) * L1 + L1

Effective Gradient Correction (takeoff only)
(10' for each 1' difference between Hi / Lo Pt)

G = Difference between Hi / Lo point in feet
L3 = RW length corrected for alititude, temperature & gradient
L3 = G * 10 + L2

Landing

Altitude Correction
(7% per 1,000' above sea level)

E = Elevation
L = Landing length @ sea level
L1 = Length corrected for altitude
L1 = (.07 * E / 1000) * L + L

Temperature Correction
(0.5% per degree above stnd temp in hottest month)
(Stnd Temp adjusted to Sea Level)

T1 = Adjusted Stnd Temp
T = Mean Max High Temperature
L2 = Length corrected for altitude & temperature
T1 = 59 - (3.566 * E / 1000)
L2 = ( .005*( T - T1)) * L1 + L1

Wet Pavement Correction (landing length only)
(15% increase in length based on dry conditions)

L3 = Landing RW length corrected for altitude, temperature & wet cond.
L3 = 1.15 * L2

[OverRun]

From ICAO "The aerodrome reference temperature should be the monthly mean of the daily maximum temperatures for the hottest month of the year (the hottest month being that which has the highest monthly mean temperature). The temperature should be averaged over a period of years."

Since this can be quite performance limiting in hot countries, some operational planning might take a look at temperatures throughout the year to establish the 85% percentile annual temperature (good for tourist resorts where most of the traffic is during the cooler seasons), and more commonly might look at the evening temperatures with operations scheduled for 9pm onwards.