Tis the Season
- Ryan Retelle
Tis the season for aircrews to make a seasonal adjustment to their operational mindset. This change is forced by the onset of frigid air masses pushing named winter storms across the continent. As aircrews are reminded to pack their heavy coat, gloves, and hat for comfort, they are also reminded to review the altimetry errors induced by cold temperatures.
Cold temperatures have always affected barometric altimeters, but many times the techniques to compensate for the error are not commonly practiced. How many times have you briefed an approach into a cold-soaked airport and not asked your flying partner for the cold temperature error correction? It is an easy mistake to make. Some aircraft automation allows for deviations from ISA to be entered into the FMS, showing the correction figure. Those aircraft not equipped with this feature must rely on the traditional method of tabulated data and mental math.
This correction figure should be added to the barometric referenced segments of the instrument approach and maneuvers in the terminal environment. Remember that this error becomes greater the colder the static air temperature is from ISA and/or the higher the aircraft is above the reporting station. Large deviations can occur in maneuvers such as intermediate step-downs, circle to land, holds, and missed approach altitudes if not adjusted properly.
During the enroute phase while the workload is low, take the time to review the ICAO Cold Temperature Correction Table for the proper correction figure(s). This chart is found in the FAA’s Aeronautical Information Manual (AIM), section 7-2-3 or Transport Canada’s AIM section 9-17-1. You should either have a hard copy laminated or save the table on an iPad for quick reference in the flightdeck.
How do you coordinate the adjustments you’re making with ATC? Announce it to them: “Boston Center, Hawker57 is unable holding at 4,000 feet due to cold temp errors, requesting minimum 5,000 feet.” Human psychology will show that you’ll probably hear other aircraft on frequency soon making the same request after you. The aircraft’s terrain warning system (EGPWS) and being in VMC conditions (eyeballs outside) are the only safety nets that a crew has to catch the deviation. Don’t assume that ATC adjusts for this error either, because their computer systems are not programed to do so. The adjustment must be a proactive step by the aircrew.
For more information on Cold Weather Operations or to meet your IS-BAO training requirement for Surface Contamination see Advanced Aircrew Academy’s Winter Operations online training module.