Jeppesen charts and below ISA temperatures

[320DRIVER]

Do standard (non-customised) Jeppesen approach plates cater for low temperatures (below ISA)? I.e. do you have a lower limit temperature until when they can be used in order to assure terrain clearance as per PAN-OPS or does the pilot ALWAYS have to correct the charted altitudes when temperature is below ISA?

Thanks for any info.

[GlueBall]

At "Transition Level" and before any approach to anywhere, the Altimeter is set to the local area altimeter setting, QNH, which keeps you covered, altitude wise.

[NextLeftAndCallGround]

I don't know about Jepps but ICAO PANS-OPS describes how IAPs are designed (using ISA conditions) and has tables for the corrections to be applied by the pilot when the temperatures are low.

I have heard that some States - where it is routinely cold - apply the corrections before publishing the IAP but I don't know whether it's true.

[quid]

Be careful, glueball. That's not correct. See the same thread on Tech Log.

[Chimbu chuckles]

Glueball and others.

ISA Devn is NOT acounted for on ANY approach plates ANYWHERE.

In some places it IS accounted for by ATC when issueing cruise levels below transition I believe.

Barometric Altimeters are calibrated to ISA. ISA minus causes them to OVERREAD, the amount is related to how far above the datum you are flying and how cold it is.

The temperature of the air in which you are flying is irrelevant.

The temperature of the air at the datum(airfield) is all that matters.

I use the following formula as a rule of thumb, although have yet to use it in anger,

+ or - 4'/deg of ISA Devn x (height above datum/1000)

It gives answers within a few feet of every temperature correction table I've seen.

example OAT - 5(ISA-20) at MSL airfield. MSA 9000'

+4x20(x 9)= +720'

Thus your altimeter will be OVERreading by 720'. If you level off at 9000'(MSA) you will have only 280' clearance above the highest obstacle withing the splay.

An ILS to a minima of 400' will yeild the following.

+4x20(x.4)=+32'

Not as likely to kill you as the MSA/LSA example but to be absolutely legal you should add the, in this case 32', to the DA.

Hope this helps.

Chuck.

[fms146]

Chimbu chuckles...Excellent post and spot on..my company has a table in the opps manual for quick reference...

[GlueBall]

Thanks for info. One never stops learning something new. Been into and out of ANC a few times in very cold winter weather, but never made any Temp corrections to QNH. Does ATC include QNH corrections when Temp goes out of ISA Barometric Altimeter envelope? I don't recall the temperature during my last approach into ANC, but the Radar Altitude and Barometric and Electric Altimeter altitudes all jived. <img src="confused.gif" border="0">