Cold Wx ops...

[it.pilot737]

Hi, on the jeppesen intro ( ATC section pag 254) is reported the table about the correction for the app minima on cold Wx and the reported table is reffered on sea level. Jeppsen also say that in this way the values are conservative in case we should land on higher airport...

My question is....the temperature error on the altimiter is not greater at higher airport than at sea level?


Thanks

[Empty Cruise]

The density gradient (change of density with altitude) of atmospheric air is greater near sea level than at altitude. Therefore, a proportionate change to density (lower temperature) will have the greatest effect at lower altitudes.

Hope this helps

[Pub User]

QNH is the actual airfield pressure, reduced to sea level using ISA conditions, so your altimeter will indicate the correct reading when on the ground. The temperature error correction is for the increased density of the air between the airfield and your aircraft, and so is relative to your height above the airfield, whatever its elevation happens to be.