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Feb. 19, 2016 // Cold Temps Can’t Keep You Down

Voluntary reporting from the field recently led to yet another safety enhancement in the National Airspace System (NAS) – this time for cold-weather operations during what has been a snowy winter across much of the United States.

Altimeters, which translate air pressure into altitude, may tell pilots they are flying higher than they actually are in sub-freezing temperatures. The colder it is, the higher the deviation. This is especially dangerous on approaches with high terrain or other obstacles present.

Cold temperature altimeter errors have always been present. Prior to 1992, the Aeronautical Information Manual recommended pilots correct for cold temperature, but did not provide a where, when, and how to correct. In 1992 the FAA was asked to provide a procedure and indicate in the Instrument Approach Procedures where this procedure should be accomplished.

Finding a solution to the request was a difficult task for the FAA. In 2010, new technologies allowed the FAA to determine that cold temperature altimeter errors were a risk, at not only a specific airport, but on a specific segment of the approach. With this knowledge and the full backing of the FAA’s Air Traffic Safety Action Program, a solution was created. Through the ATO’s voluntary safety-reporting program for air traffic operations, and in collaboration with Flight Standards, the FAA published new guidance for controllers and pilots in 2014 to help bring closure to this hazard.

“Perseverance finally paid off,” said Mike Blake, ATSAP representative for the NATCA National Safety Committee. “We filed a Corrective Action Request in 2010 on the issue and have been working hard to get procedures established.”

The published procedure will help controllers and pilots do their jobs safely. The procedure tells pilots when, where and how to correct for cold temperature altimeter errors. It also dictates what information the pilots must give controllers, so controllers can provide safe separation from other aircraft and a clearance for the approach. The interaction and cooperation between pilots and controllers is an integral part in making this a successful operation within the NAS.

Altitude adjustment tables that provide an altitude correction based on the reporting station’s altitude and reported temperature are also new to publications. The table serves as a quick reference for operators to compensate for altimeter errors and remain at a safe altitude on the approach. In addition, aeronautical charts denote airports where altitude correction is required due to cold temperatures.

“There are snowflakes charted to let the pilot know there is a correction factor that needs to take place,” said Mike Vermuth, Safety and Technical Training representative for the ATSAP Analysis Team, ATSAP-X, and representative for Federal Contract Control Towers.

The initial ATSAP report that helped spur action on the issue came from Vermont’s Burlington Tower in 2010. Not only do pilots and controllers experience altimeter errors every winter during cold temperatures, one of the airport’s instrument approaches crosses Vermont’s third-highest mountain, Camel’s Hump, which stands at 4,088 feet. In one instance, a pilot reported to controllers that it appeared to him that he was flying at the same height as the mountain summit when flying at the published altitude on the approach.

The ATSAP program office has received 15 reports on the issue — from towers in New Mexico, Alaska, Utah, and Washington State, in addition to those from Burlington.

“What ATSAP does is it gets eyeballs on issues, and that focus doesn’t move,” said Micah Maziar, NATCA’s subject matter expert on the Safety Risk Management panel, who ensured that the new procedures don’t introduce new risks.

“With ATSAP, there’s a clear way of tracking the issues,” he said. “And anytime we can increase the bar for safety is a success.”

ATSAP is a voluntary, non-punitive safety reporting program that encourages controllers to identify and report all events that may or did lead to a breakdown in safety or increase risk to air traffic operations.

This article has been published in a joint effort by NATCA and the FAA.