Analysis provided by Robert Nicholson Sept. 2011

ASSUMPTIONS: 
1.  The placard descended essentially straight down with respect to the local air mass.  Its lateral movement was caused only by the wind.

2.  As found, the door placard probably did not measure more than 6 inches by 6 inches, 0.25 square feet area, and probably did not weigh 
more than one ounce.  A picture of this placard can be seen on page 2 of "Photo Evidence" on Sluggo's web page.

3.  The location of the found coordinates is about 5 nautical miles south-southeast of Toutle and indicate that the placard was found at about 
1500 feet above sea level.

4.  The airliner is assumed to be flying at 10,000 feet ASL and the result is a free-fall of 8500 feet for the placard.

5.  It is assumed that the winds aloft are all from the southwest (225 degrees true, or with respect to the grid lines).

6.  To vastly simplify the computations, it is assumed that the winds at 6000 feet ASL can be used to represent the conditions for the entire 
free-fall and that value is 18 knots from the southwest.

7.  It is also assumed that the air density at 6000 feet ASL can be used for the entire free-fall.  Both this assumption and the one above with 
respect to the average winds are reasonable.  About two years ago, I did calculate the atmospheric conditions at Portland for the time of the 
hijacking and found the air density to be about two percent greater than the density for the US Standard Atmosphere which is used here.

8.  The drag coefficient for the placard was estimated to be 1.0 based on information in Sandia Laboratories Report SC-RR-68-132, August 
1968, title: Free-Fall Rotation and Aerodynamic Motion of Rectangular Plates.  This report can be downloaded free online at 
http://dodreports.com/pdf/ada395124.pdf .  The major points in the report are that all of their rectangular plates, which were made of wood, 
started to rotate about one or more axes after falling a relative short distance and that the drag coefficient was always in the vicinity 
of 1.0 regardless of how the plates tumbled.

9.  When the placard separated from the airliner, it would be greatly affected initially by the downwash from the airliner but would soon settle 
down and start a free-fall based only on its own aerodynamics.

RESULTS:
The information based on the above assumptions  was used in standard formulas and techniques.  They indicate that the placard's free-fall 
took 8.93 minutes and that it travelled a distance of 2.68 nautical miles in that time.  The distance travelled would be all downwind on a 
heading of 045 degree true, or with respect to the grid lines.