1. Selected Airfield: Kaneohe Bay Marine Corps Air Station
2. ICAO identifier (the ICAO identifier is the 4-letter airport code, starting with a ‘K’ for the continental US): PHNG
3. Field elevation [ft MSL] (field elevation can be found in the location information section at skyvector.com or the overview section at AOPA’s flight planning tool): 23ft
4. Current weather report at the time of work on this assignment:
a) Date and time: 08JUN2018 522PM EDT
b) Current altimeter setting [in Hg]: 30.10″ Hg
c) Current temperature [°F or °C, but stay consistent]: 27.8 C / 82.0 F
I need to answer this question below:
A. Using your researched data, find the Pressure Altitude of your airfield [ft]. Use the found altimeter setting and the rule of thumb lapse rate of 1 in Hg = 1000 ft, i.e. 00.01 in Hg = 10 ft change from the field elevation, with standard atmospheric altimeter setting being 29.92 in Hg (see also tutorial and example problems). Keep in mind that an increase in altimeter setting above standard will lead to a positive shift of Indicated Altitude above Pressure Altitude (or in other words, a lower pressure altitude than what is indicated) and vice versa.
Note: In some cases (low field elevation, coupled with high altimeter setting) it may lead to negative pressure altitudes, which is completely correct. However, to allow further work in the atmospheric table excerpt in your textbook (Table 2.1, which does not include the negative values), you may change your altimeter setting in 4.b) to a lower value (please include a note) for all further work or select a different airfield (preferably above 1000′ MSL).