AIM Text
- Temperature has an effect on the accuracy of barometric altimeters, indicated altitude, and true altitude. The standard temperature at sea level is 15 degrees Celsius (59 degrees Fahrenheit). The temperature gradient from sea level is minus 2 degrees Celsius (3.6 degrees Fahrenheit) per 1,000 feet. For example, at 5000 feet above sea level, the ambient temperature on a standard day would be 5 degrees Celsius. When the ambient (at altitude) temperature is colder than standard, the aircraft's true altitude is lower than the indicated barometric altitude. When the ambient temperature is warmer than the standard day, the aircraft's true altitude is higher than the indicated barometric altitude.
- TBL 7-3-1 indicates how much error may exist when operating in non-standard cold temperatures. To use the table, find the reported temperature in the left column, and read across the top row to locate the height above the airport (subtract the airport elevation from the flight altitude). Find the intersection of the temperature row and height above airport column. This number represents how far the aircraft may be below the indicated altitude due to possible cold temperature induced error.
TBL 7-3-1
ICAO Cold Temperature Error Table
Source: FAA Aeronautical Information Manual · current edition · paragraph 7-3-1.
Research Notes
AIM 7-3-1 introduces Wake Turbulence — the air disturbance created by lift-generating aircraft, particularly large/heavy aircraft.
Wake vortex physics: Wing-tip vortices are continuously generated by ANY aircraft producing lift. The vortex strength is proportional to aircraft weight and inversely proportional to airspeed and wingspan. Heavy slow aircraft (e.g., a B-757 on approach at minimum speed) generate the most severe wake.
Vortex behavior:
- Vortices sink at 400-500 fpm below the generating aircraft
- Vortices drift with the wind
- Vortices persist for 2-3 minutes in calm air; longer in stable conditions
- Vortices on the runway diverge laterally as they age
Wake turbulence consequences for small aircraft: Encountering a wake vortex can cause: sudden roll (up to control-limit), uncommanded yaw, structural overload, loss of control. Multiple fatal accidents are attributable to wake encounters.
Avoidance strategies:
- Stay above the flight path of preceding aircraft
- Touch down beyond the preceding aircraft's touchdown point
- Stay upwind of crossing aircraft
- Allow at least 2 minutes after a heavy departure before taking off behind it
- Decline reduced spacing behind a heavy if conditions are unfavorable
Reference: AC 90-23G (Aircraft Wake Turbulence); AIM 7-3; FAA-H-8083-25 Chapter 11.