John Lear just set the record straight in regards to the Pentagon. Take your time and enjoy.
Originally posted by johnlear
Originally posted by ThreadTrekker
John,
Very interesting post... but I was wondering if you could put some of this in layman's terms. What is the normal purpose of setting field barometric
pressure. And what does FL180 mean?
Thanks for the post ThreadTrekker. FL180 means Flight Level 18,000 feet.
Above 18,000 feet altitudes are called Flight Levels and all airplanes operating at or above 18,000 feet manually set their altimeters to Standard
Pressure which is arbitrarily 29.92 or 29.92 inches of mercury.
Below 18,000 eet all airplane altimeters are set to Field Barometric or however many inches of mercury at the particular field, in the case of the
Pentagon (Reagan International) 30.24 inches of mercury.
The altimeter pressures are set so that each airlane is flying with an altitude reference that all the other airplanes around him are flying. This is
to maintain 1000 foot separation in case you are passing over or under somebody else. Above 18,000 they set a common standard which is 29.92 because
it would be unnecessary to have everybody changing their altimeters to field barometric because at that altitude and speed they would be changing the
altimeter every 5 minutes.
So in a descent at FL180 (18,000) altimeters are reset to local field barometric. When you are cleared below FL180 ATC will say something like
'United 456 descend and maintain one zero thousand feet Chicago altimeter 30.15."
If somebody has been flying for a long time setting your altimeter passing through FL180 is second nature. But for somebody who has just hijacked an
airliner its unheard of for the simple reason that the hijacker is not in contact with anybody so how did he get the altimeter setting?
But not only was the altimeter of Flight #77 reset it was reset to 30.24 which was local barometric pressure at Reagan. The reason this is significant
is if somebody wanted to argue that the hijacker tuned in an automatic weather station he would have gotten the past hours altimeter for that area
which was 30.22 not the current Reagan International setting which was 30.24. So my question is where did he get it?
It is highly unlikely that a hijacker would know all this. He is sitting in the seat trying to figure out where in the heck the Pentagon is, not in
the frame of mind to be attending to the minutiae of a current altimeter setting to keep him separted from other aircraft at specific altitudes. He is
not even talking to ATC, so he has not been assigned an altitude, so he doesn't have to worry about separation.
So what this means is that whoever was flying the airplane and whoever was the co-pilot had hundreds if not thousands of hours in the Boeing 757. The
professional use of the autopilot including the use of the scratch pad is not consistent with pilots who have just hijacked a Boeing 757 30 minutes
prior. The reseting of the altimeters at exactly FL180 and to Reagan International current field barometric is consistent with pilots who were
professionals. The use of the autopilot including scratch pad and its disconnect at 7000 feet is consistent with professional use of the
autopilot.
The steep stable bank and accurate descent rate for the last turn into the Pentagon and level off at 20 feet is consistent with a pilot who had many
thousands of hours, and probably had fighter jet training. This profile is not consistent with a hijacker whose total time in the Boeing 757 is about
an hour.
John Lear More
[edit on 17-3-2007 by Realtruth]
[edit on 17-3-2007 by Realtruth]
[edit on 17-3-2007 by Realtruth]