Final answer:
True altitude is the actual height above mean sea level and is calculated by correcting indicated altitude for non-standard temperature and pressure. In this case, the air temperature is colder than standard atmosphere conditions, suggesting a true altitude that is lower than the indicated altitude. An exact figure cannot be given without correction tables or altimeter settings.
Step-by-step explanation:
The student is asking about the calculation of true altitude when given the indicated altitude, pressure altitude, and outside air temperature. Calculating true altitude involves correcting indicated altitude for non-standard temperature and pressure conditions. The standard atmospheric model assumes a temperature of 15°C at sea level with a decrease of 2°C per 1,000 feet of altitude. Since the air temperature given at 8,500 feet is -20°C, which is much colder than the standard temperature expected at this altitude (which would be about 1°C), the actual air density is higher, meaning the aircraft is flying lower than the indicated altitude suggests. However, without the necessary correction tables or the altimeter setting, which would be required for an accurate calculation, we cannot provide a definitive answer to the true altitude.