WORKED ALTIMETER TEMPERATURE ERROR CALCULATION: An aircraft flies at Flight Level 100 (indicated 10,000 ft on 1013.25 hPa) through an extreme cold air mass where ambient temperature is ISA - 20°C. Using the standard altimetry rule of thumb (4% error per 10°C deviation from ISA), what is the aircraft's actual True Altitude?

1. 10,800 ft
2. 10,000 ft
3. 9,200 ft
4. 8,400 ft