Narrative:

The outside air temperature at the destination was 33 degrees C below zero (negative 33 degrees C). As a crew; we discussed the ramifications that this lower than standard temperature would have on our indicated altitudes at cache intersection on the ILS and our decision altitude that evening flying the ILS 1L approach to fai. Given the temperature at the airport (negative 33 degrees C) we would expect to cross cache (5 DME off the 1L ILS at pafa) on the GS at an indicated altitude of 2374 ft MSL; not the charted value of 2047 ft MSL. The nonstandard; and much colder temperature; at the airport would cause the altimeter to read some 327 ft higher when we were on the GS at cache intersection than it would read if the temperature was international standard atmosphere (isa) at the airport. Conversely; if we flew to an indicated altitude of 2047 ft; we would be actually the same 327 ft but lower and closer to the ground than we would be if the temperature was international standard atmosphere at the airport. As we were being vectored; the approach controller assigned us a final altitude to intercept the localizer of 2200 ft MSL. It was clear to me that should we descend to 2200 ft MSL we would not intercept the GS until we were inside cache intersection (5 DME) which serves as the FAF for the purpose of verifying our GS crossing altitude check. I complied with the clearance descending to 2200 ft MSL; and we did intercept the GS inside of cache intersection. We were in and out of IMC and I had the terrain in the vicinity of the airport in sight. Later on the same night we flew into fai a second time and I asked to intercept the GS at 2500 ft MSL; not the 2200 ft MSL we had been issued earlier. The later and second approach worked out much better. I believe in canada vectoring altitudes are compensated for nonstandard temperature. And I also believe that vectoring altitudes are compensated for nonstandard temperature by united states military controllers. Regardless; ATC vectoring altitudes should be modified for nonstandard temperatures in the united states. Most of the time it isn't a major issue; however; when the temperature is colder than 30 degrees below zero it takes on greater importance. When it is much colder than standard temperatures; flying the same published altitudes or assigned altitudes will result in the aircraft being closer to the ground.

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Original NASA ASRS Text

Title: ACR PLT DESCRIBED VERY LOW TEMP OPS AT FAI AND THE ALT ADJUSTMENTS NECESSARY; SUGGESTING FAA ADOPT PROCS TO ADJUST ALTS.

Narrative: THE OUTSIDE AIR TEMP AT THE DEST WAS 33 DEGS C BELOW ZERO (NEGATIVE 33 DEGS C). AS A CREW; WE DISCUSSED THE RAMIFICATIONS THAT THIS LOWER THAN STANDARD TEMP WOULD HAVE ON OUR INDICATED ALTS AT CACHE INTXN ON THE ILS AND OUR DECISION ALT THAT EVENING FLYING THE ILS 1L APCH TO FAI. GIVEN THE TEMP AT THE ARPT (NEGATIVE 33 DEGS C) WE WOULD EXPECT TO CROSS CACHE (5 DME OFF THE 1L ILS AT PAFA) ON THE GS AT AN INDICATED ALT OF 2374 FT MSL; NOT THE CHARTED VALUE OF 2047 FT MSL. THE NONSTANDARD; AND MUCH COLDER TEMP; AT THE ARPT WOULD CAUSE THE ALTIMETER TO READ SOME 327 FT HIGHER WHEN WE WERE ON THE GS AT CACHE INTXN THAN IT WOULD READ IF THE TEMP WAS INTL STANDARD ATMOSPHERE (ISA) AT THE ARPT. CONVERSELY; IF WE FLEW TO AN INDICATED ALT OF 2047 FT; WE WOULD BE ACTUALLY THE SAME 327 FT BUT LOWER AND CLOSER TO THE GND THAN WE WOULD BE IF THE TEMP WAS INTL STANDARD ATMOSPHERE AT THE ARPT. AS WE WERE BEING VECTORED; THE APCH CTLR ASSIGNED US A FINAL ALT TO INTERCEPT THE LOC OF 2200 FT MSL. IT WAS CLR TO ME THAT SHOULD WE DSND TO 2200 FT MSL WE WOULD NOT INTERCEPT THE GS UNTIL WE WERE INSIDE CACHE INTXN (5 DME) WHICH SERVES AS THE FAF FOR THE PURPOSE OF VERIFYING OUR GS XING ALT CHK. I COMPLIED WITH THE CLRNC DSNDING TO 2200 FT MSL; AND WE DID INTERCEPT THE GS INSIDE OF CACHE INTXN. WE WERE IN AND OUT OF IMC AND I HAD THE TERRAIN IN THE VICINITY OF THE ARPT IN SIGHT. LATER ON THE SAME NIGHT WE FLEW INTO FAI A SECOND TIME AND I ASKED TO INTERCEPT THE GS AT 2500 FT MSL; NOT THE 2200 FT MSL WE HAD BEEN ISSUED EARLIER. THE LATER AND SECOND APCH WORKED OUT MUCH BETTER. I BELIEVE IN CANADA VECTORING ALTS ARE COMPENSATED FOR NONSTANDARD TEMP. AND I ALSO BELIEVE THAT VECTORING ALTS ARE COMPENSATED FOR NONSTANDARD TEMP BY UNITED STATES MIL CTLRS. REGARDLESS; ATC VECTORING ALTS SHOULD BE MODIFIED FOR NONSTANDARD TEMPS IN THE UNITED STATES. MOST OF THE TIME IT ISN'T A MAJOR ISSUE; HOWEVER; WHEN THE TEMP IS COLDER THAN 30 DEGS BELOW ZERO IT TAKES ON GREATER IMPORTANCE. WHEN IT IS MUCH COLDER THAN STANDARD TEMPS; FLYING THE SAME PUBLISHED ALTS OR ASSIGNED ALTS WILL RESULT IN THE ACFT BEING CLOSER TO THE GND.

Data retrieved from NASA's ASRS site as of May 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.