posted on Dec, 6 2017 @ 11:42 AM
It's a required piece of data for ATC to give landing aircraft.
Let's say the field elevation for a runway is 256' above sea level. If the atmospheric pressure is low that day, your altimeter could tell you that
you're at 340', when you are actually on the ground at 256'. Prior to taking off, the field gives you the pressure altitude and may say 28.94. You
dial that up into your altimeter and should get right around 256'. Now, let's say you go flying out and about for 2 hours, you return to the same
airfield but a high pressure system has moved in. ATC tells you that the pressure altitude is now 30.12. You dial that in and begin to use that
gauge as your main input for altitude. After you land, you park at the gate and your altimeter should read 256'. If you had not changed your
pressure altitude setting, you would NOT read 256'
The video was awesome. I love how saying the M word gets you whatever the heck you want. The pilot declared Mayday and the controller responded
with, You can land on any runway you want. The controller does a great job and coordinated with another airport (typically in front of the Mayday
aircraft) got them clearance to land and passed the info to the aircraft in distress. At that point, the controller would be telling every other
aircraft in the sky to get the heck out of the way until this is sorted out. It's literally the only time you can do whatever you want in aviation.