Final answer:
The pressure altitude of airport 'A' is 200 feet. The standard temperature for airport 'A' at 4000 feet elevation is 7°C, and using this standard temperature, the density altitude would remain at 200 feet. If the ambient temperature were 35°C, the density altitude would be 3,560 feet.
Step-by-step explanation:
To determine the pressure altitude of airport 'A' with an elevation of 4000 feet MSL (Mean Sea Level) and an altimeter setting of 30.30 inches of mercury (Hg), we must first understand that pressure altitude is the elevation above the standard datum plane (29.92 Hg at sea level under standard conditions) when the altimeter is set to 29.92 Hg. Since the altimeter setting is higher than the standard, we subtract 1,000 feet for every 0.10 inch above 29.92 Hg. In this case, the altimeter is 0.38 inch above the standard, or 3.8 increments of 0.10 inch. This equates to a decrease in assumed elevation of 3,800 feet (1,000 feet x 3.8). Therefore, the pressure altitude is 4000 feet - 3800 feet = 200 feet.
The standard temperature at sea level is 15°C. However, we need to correct this for the airport's elevation, with a standard lapse rate of -2°C per 1,000 feet. Thus, the standard temperature for airport 'A' at 4000 feet would be 15°C - (2°C/1000ft x 4000ft) = 15°C - 8°C = 7°C.
Now, let's look at the density altitude. It is the pressure altitude corrected for non-standard temperature, found by increasing pressure altitude by 120 feet for each 1°C above standard temperature. Since the ambient air temperature is 35°C, this is 35°C - 7°C = 28°C above standard temperature. Therefore, the additional density altitude is 28°C x 120ft/°C = 3,360 feet. The total density altitude is the pressure altitude plus this value: 200 feet + 3,360 feet = 3,560 feet.
To calculate the density altitude using the standard temperature of 7°C, we find that since the temperature is standard, there is no correction necessary, and therefore the density altitude is equal to the pressure altitude, which is 200 feet.
Leveraging the information in Figure A4 and the standard conditions, the pressure required to yield a density of 0.64 kg/m³, given that the temperature and number of molecules constant is half the standard pressure because density is directly proportional to pressure at constant temperature. Therefore, at half the density (from 1.28 kg/m³ to 0.64 kg/m³), the pressure would be 0.5 atm.