Hi all
I am getting different answers to a couple of the questions in excersises 1.4 & 1.5.
In Question 2, Ex. 1.4 the elevation is given as 1800 ft so I have worked out ISA as 2 x 1.8 giving me an answer of 11.4, that give me a deviation of +14.6 leading to pressure hight deviation if 1752 (120 x 14.6). When all is worked out the Density Hight comes to 3132. When checking my answer I have discovered the the ISA Deviation has been calculated at 15 - 2 x 1-5 (1500 ft) leading to a totally different answer to the question. Confused???? Is there a rule of thumb for round up or down?
In Question 1, Ex. 1.5 The ISA calculation is given in the answer as 16 deg (2 x .5 = 16) Aerodrome Elevation 270 ft. I am confused because in Question 5 of Ex 1.4 the Aerodrome Elevation is 430 ft and ISA Temp remains at 15 deg with no calculation for ISA Deviation. Is there something I have missed as to whether a calculation for ISA Deviation is to be applied?
After calculating your pressure height, round to the nearest 500' for the purposes of calculating your ISA deviation. Once you know the ISA deviation, multiply that figure by 120' and then add or subtract that as required to your pressure height (the exact pressure height, not the rounded off one). This will give you the correct density altitude.
Thank You.. Now I know what is going on..
