Robert Nicholson is a retired Aeronautical Engineer and also a retired general aviation power and sailplane pilot with 750+ hours of powered aircraft time and 1000+ hours of sailplane time (in exactly 1000 sailplane flights). Upon retiring, he held an FAA Commercial Pilot Certificate with private privileges for airplanes and commercial privileges for sailplanes. He also held an FAA Ground Instructor Certificate with Advanced and Instrument Ratings. In the classical tradition, he started learning to fly at the age of 15, soloed a Piper Cub at the age of 16, and received his Private Certificate for powered aircraft at the age of 17. One of the three Piper Cubs he trained in is now suspended over the right wing of the Boeing 707 prototype (the "dash 80") at the National Air and Space Museum Annex on the east side of Dulles International Airport near Washington, DC. That specific Piper Cub is also the only powered aircraft in which he ever experienced a total engine failure. Fortunately, he was still pre-solo with an instructor on board and the instructor made a perfect dead-stick landing into a farm field.
He made a limited number of parachute jumps in the 1963-1964
period using surplus military parachutes with the 5T-U modification. On his 9th jump, he had a big-time
inversion which destroyed the main canopy but the reserve did its job. He then borrowed a rig and made a 10th
jump but decided after that to sit things out until he could get one of the new
parachute rigs that were just being introduced. But before that happened, he spent most
of one year working on an aircraft test program at a famous location in the
Basically, he considers himself to be a “nitty-gritty, number-crunching nerd”.
The Piper J-3C-65 Cub hanging in the National Air and
ANALYSIS of NWA 305 FLIGHT TRACK
This post is the first of several posts in which I propose to discuss the information that is available for determining the actual flight track of the hijacked airliner. My intent is to dissect the available communication logs and other records and, hopefully, refine the original proposed flight track and jump zone area. I am not interested in third-hand accounts of various alleged actions, do not believe in fairy tales, and have a very low tolerance for nonsense (to use a politically correct word). I agree with Sluggo that the "myths" surrounding this hijacking are obstructing the solution of the problem, which at this point is to determine where D. B. Cooper returned to earth.
In this first part, I want to discuss the 1970s era sectional maps that are on Sluggo's web page and that depict the track of the airliner from about 7:54 PM PST to about 8:18 PM PST. Unless otherwise stated, all times used in these posts will be PM PST on November 24, 1971.
The plots on these maps consist of a total of 9 red points and 15 blue
points that are connected by a line to represent the supposed flight path of
the aircraft as it flew from
The "plot" mentioned above is presumably a radar plot
and the radar location is apparently in the
In the early 1970s, the radar systems used in aviation had rotating antennas that operated at about six revolutions per minute (or about once every 10 seconds). Each time the beam transmitted from the radar antenna hit the aircraft's transponder antenna, the transponder would transmit a reply that appeared as a light point on the radar scope. Consequently, during each sixty second period of time, if the antenna was rotating at 6 RPM, six different light points would appear on the radar scope. Individually, these light points would indicate the location of the aircraft at that instant and, collectively, the six light points would indicate the track of the aircraft. Therefore, a clock showing a given minute on its face could have six different aircraft locations related to it.
As can be seen by looking at the 20:05 to 20:11 red dots, these dots indicate segments of various lengths and cannot be exactly one minute intervals since the airliner was flying at essentially a constant speed. The famous missing 20:04 dot, whether red or blue, apparently did not show up on anyone's radar plot or in their estimate of position. In my opinion, the blue dots should be used with the greatest caution or not at all. However, they will be discussed more in later posts.
In summary, the red dots may accurately document the position of the aircraft at some point in time but the times associated with the red dots are not reliable. But again, there is a possibility that the red dot associated with the 7:54 time is reasonably accurate. This will also be discussed further in later posts.
Comments are welcome and if you have any, please reply online so that everyone can see them. I'm sure that there any number of people who can contribute constructively to resolving the Cooper hijacking. And, in my personal opinion, we need to get out of our "compartments" and start working together.
All of the information for the following discussion is obtained from various documents on Sluggo's web page.
While on the ground in
The flight crew discussed only the V23 route south. Neither V23 East, V23 West, or any other airway was discussed. In addition, there is no documented reference to any changes in the V23 route to Red Bluff or to any flight clearance changes.
The following times and locations are given in various documents and all locations refer to those plotted on the L1 and L2 IFR Low Altitude Airways charts that were effective on the date of the hijacking and which can be view on Sluggo's web page. However, it should be noted that the flight crew probably used the Jeppeson version of these charts rather than the government version.
Take off from
V23 14 DME from SEA VORTAC. This and the following time will be discussed at length in a later part.
V23 19 DME from SEA VORTAC. This and the above time will be discussed at length in a later part since both cannot be correct.
23 DME south of PDX VORTAC. Presumably on V23.
Over EUG VORTAC. This is probably not the time of "station passage".
Over MFR VORTAC. This is probably not the time of "station passage".
One DME mile south of FJS VORTAC. Confirmed by two controllers so it should be an excellent fix.
On V23 50 DME northwest of RBL VORTAC.
On V23 10 DME ("exact") northwest of RBL VORTAC.
Over RBL VORTAC and turning toward
The above times and positions will be used in later parts. It should also be noted that even at the relatively low weight that the aircraft was at when passing the Red Bluff area, the crew requested descents of only 300 to 500 feet per minute and less than standard rate turns (that is, less than two minute turns or three degrees per second) since they could not maintain speed in standard rate turns.
There is a highly significant difference between the radio logs
The next part will go into the flight dynamics and navigational aspects of the flight.
If you have any comments, please post them online so everyone can see them.
The key to finding D. B. Cooper is determining the flight track,
and the appropriate times along that track, between
At the take-off from
At 8:10 and at 9:28 in the FBI notes, enough information is given to calculate the true airspeed. At each of these times the indicated airspeed was 170 KIAS and the true airspeed was calculated to be 195 KTAS. The flight crew had been informed that 170 KIAS was the speed for best range in their particular configuration and they seem to have stayed within about 5 knots of that speed most of the time. It should be noted that the aircraft was probably not more than about 25 knots above stall speed at any time and, therefore, was operating on the "backside of the power curve" for the entire flight. That is one of the factors that contributed to the aircraft being so difficult to control during the flight.
In the following remarks, it is assumed that the aircraft was on
the centerline of V23 all the way from
SEA to PDX (now BTG) - 105 NM
PDX to EUG - 101 NM
EUG to MFR - 99 NM
MFR to FJS - 62 NM
FJS to RBL - 85 NM
The distance from RBL to the
TIME: (7:36 to 10:08) - 2:32 Hours
GROUND SPEED: 179 Knots average
The average ground speed should be reasonably accurate since it minimizes the error in the times. Using the previously calculated 195 KTAS as an average, the average headwind component is 195 - 179 = 16 Knots. There is nothing remarkable about this headwind magnitude.
Several segments of the above track will be individually considered where times are available:
1. SEA to 23 DME south of PDX - 128 NM. Time (7:36 to 8:22) - 0:46 Hours. Ground Speed - 167 Knots. Headwind component - 28 Knots.
2. 23 DME south of PDX to EUG - 78 NM. Time (8:22 to 8:52) - 0:30 Hours. Ground Speed - 156 Knots. Headwind component - 39 Knots.
3. EUG to MFR - 99 NM. Time (8:52 to 9:28) - 0:36 Hours. Ground Speed - 165 Knots. Headwind component - 30 Knots.
4. MFR to 1 DME south of FJS - 63 NM. Time (9:28 to 9:45) - 0:17 Hours. Ground Speed - 222 Knots. Tailwind component - 27 Knots.
5. 1 DME south of FJS to RBL - 84 NM. Time (9:45 to 10:08) - 0:23 Hours. Ground Speed 218 Knots. Tailwind component 23 Knots.
All of the above information for the segments should be used with caution. But if these numbers are correct, the strongest head winds would be about 50 to 75 NM south of the PDX VORTAC. And from about MFR on south the aircraft would have a tailwind.
Nevertheless, some conclusions can be drawn from the above:
1. There is no evidence the aircraft passed east of the PDX (now BTG) VORTAC.
Even if, as Captain Bohan reportedly claimed,
the winds at 14,000 feet were 80 knots from 160 degrees in the
The individual who prepare the original jump zone estimate stated that he had used data from the aircraft flight recorder. If so, and if this data exists today, it would probably be in the form of computer print outs in someone's file cabinet. And it would most likely be printed on the old style green and white lined IBM paper that was about 12 to 14 inches wide. Needless to say, this information would be extremely important in resolving this matter.
Comments are welcome, and if you have any, please post them online.
Welcome to Hammer and Tong Engineering 101. This continues the number crunching from Part 3. The calculations below are made using different assumptions.
1. For these
calculations, the assumptions are no wind, 195 KTAS (which also becomes the
ground speed), along V23 from VORTAC to VORTAC, and a take-off time of 7:36 in
a. SEA to PDX - 105 NM, Time - 0:32 Hours (8:08).
b. PDX to EUG - 101 NM, Time - 0:31 Hours (8:39).
c. EUG to MFR - 99 NM, Time - 0:30 Hours (9:09).
d. MFR to FJS - 62 NM, Time - 0:19 Hours (9:28).
e. FJS to RBL - 85 NM, Time - 0:26 Hours (9:54).
SEA to RBL - 452 NM, Time 2:21 Hours (9:57).
The difference between 9:57 and 9:54 is due to rounding errors.
2. For these calculations, the same assumptions as above are used except that the points are those for which times are available. The times in brackets are from sources on Sluggo's web page.
a. SEA to 23 DME south of PDX - 128 NM, Time - 0:39 Hours (8:15) [8:22].
b. 23 DME south of PDX to EUG - 78 NM, Time - 0:24 Hours (8:39) [8:52].
c. EUG to MFR - 99 NM, Time - 0:30 Hours (9:09) [9:28].
d. MFR to 1 DME south of FJS - 63 NM, Time - 0:19 Hours (9:28) [9:45].
e. 1 DME south of FJS to RBL - 84 NM, Time - 0:26 Hours (9:44) [10:08].
The problem with these times seem to be random rather than systematic. A possible explanation is that, since most of the numbers between SEA to FJS are from the FBI Notes, the time from the transmission of the information from the aircraft to the time it arrived at the location where the agent was located, differed by five or 10 minutes in some cases. The FBI Notes include mention of lost communications and other aircraft relaying messages between NWA 305 and the ARINC ground stations from which it was then phone patched to various locations. So the times in the FBI Notes must be used with caution.
Everything up to this point is subject to revision as new information is obtained.
Your comments are welcome and please post them online.
The next part will be an analysis of the original jump location estimate.
This part will discuss the document on Sluggo's web page that explains how the original jump landing positions were estimated.
The document states that the radar data came from McChord AFB, the wind information was provided by the NWA Meteorology Chief, and the human free-fall body trajectories were obtained from Boeing Aircraft and a NWA pilot who was also a parachutist. The time correlation was from the radar data and the NWA communications network tape recording. And the airplane speed and altitude from the airplane's flight recorder.
If these statements are correct, then this is probably the most accurate document available, or that can be produced, relative to the probable landing area.
In reviewing the jump location map and the supporting write-up, several problems with the points are evident. First, points W1, W2, W3, and W4 are never explained and there is no indication of what they represent. Other such problems are discussed below.
In constructing the chart, apparently a line was drawn based on the radar data and that line would include points C, S, D, A, E, and F in that order from top to bottom. Then, using a radar tolerance of plus or minus 0.5 NM, the easternmost and westernmost limits are drawn to form a corridor.
The eastern boundary of the corridor is the line with points L, T, M, N, and O. The western boundary of the corridor is the line with points G (which is not shown but is adjacent to points C and L), H, I (the top "J" should be "I"), J, and K. This corridor is one NM wide and, since there is no other information about scale available, that width is used for scaling purposes.
A time tolerance of plus or minus one minute is used. At the ground speed the aircraft was traveling, each minute represents about three NM over the ground.
In the possible jump locations on the chart, points H, S, and T should have been drawn in the same manner as points K, F, and O. Then the wind drift line should only go from point H to point P, which is not shown but is apparently coincident with point W1. This is the earliest estimate of the jump and the time is apparently 8:10.
The predicted jump location is at point A and the time is estimated to be 8:11. The wind drift for an immediate parachute opening is estimated to be the line from point A to point B. Point A is also estimated to be the ground impact point for a total free-fall to the ground and does not include any movement down track.
The latest estimate for the jump is the line connecting points K, F, and O with the drift being along the line from point O to point R.
Each of the drift lines is slight more than three NM in length and represents a jump from 10,000 feet with an immediate opening.
No information is given on the assumed parachute descent rate. However, if the parachute descends at 1000 feet per minute for 10,000 feet, 10 minutes would be required to reach sea level and indicates a wind of about 20 knots from the southwest. If the descent rate is higher, then the wind speed will be greater.
The diagram does not provide any scales or times directly and I cannot find enough well defined geographical points on the chart to transfer the diagram to another chart. However, the overall shape of the jump corridor bears at least some resemblance to the 8:09 to 8:12 interval on the sectional charts with the red and blue dots.
Further, the bottom lines on the diagram indicate that the aircraft is about two NM west of the PDX VORTAC still heading slightly west of true south. If no course changes were made, then the aircraft would pass several miles west of the PDX VORTAC.
Comments are welcome and please post them online.
The main purpose of this short part is to see if the Point A on the original jump map is the same as the last red dot, which was assigned a time of 20:11, on the sectional chart. All of this information is from Sluggo's web page. It should be noted that Point A is specified as being for 8:11 (or 20:11) also.
On the original jump map, the distance between the flight corridor limits is 1 NM and that is the scale that is used here. Using the NW LaCenter Road Bridge across the east fork of the Lewis River as the reference point (that bridge is on the south side of LaCenter), it was determined that Point A was 3.85 NM (or 4.43 SM) from that bridge on a "radial" of 45 degrees from true (or grid) north. This information was then plotted on a TOPO seamless topographical chart which listed latitude and longitude in the WGS 84 system. The coordinates for Point A are N 45 degrees and 54.358 minutes and W 122 degrees and 36.487 minutes.
The sectional chart containing the red dots is plotted using the NAD 29 system. In that system the coordinates for the red dot labeled 20:11 are N 45 degrees 53.5 minutes and W 122 degrees and 36.5 minutes. Coordinates for these points, plus others, are listed below:
POINT A - N 45 deg, 54.358 min; W 122 deg, 36.487 min; WGS 84.
RED DOT 20:11 - N 45 deg, 53.5 min; W 122 deg, 36.5 min; NAD 29.
PDX VORTAC - N 45 deg, 44.87 min; W 122 deg, 35.49 min, WGS 84.
SEA VORTAC - N 47 deg, 26.12 min; W 122 deg, 18.58 min, WGS 84.
TENA BAR - N 45 deg, 43.048 min; W 122 deg, 45.576 min, WGS 84.
Comparing the latitude coordinates, it is seen that Point A is about 0.8 NM north of the Red Dot 20:11. The longitude lines indicates that Point A is almost directly north of the Red Dot 20:11. At the ground speed at which the airliner was flying, these points are separated by only about 20 seconds of flying time. So even without correcting to the WGS 84 system, the Red Dot 20:11 location was apparently taken from the same plot or data set as Point A. For all practical purposes, they are the same point.
At the latitude of
In addition, Point A is about 11.3 NM north of and about 9.1 NM east of Tena Bar.
The end result here is that we need to start back at
Comments are appreciated and please post them online for all to see.
What follows below is derived from the best of Hammer and Tong Engineering, creative cross-plotting of questionable data, and other advanced techniques that I came across in my days as a practicing Aeronautical Engineer. So you have been warned!
The only time data that can be reasonably accurate is that in the ATC transcripts related to NWA 305. I used the four times that also specified altitudes during the initial take-off and climb to 10,000 feet. Those times were plotted against altitude and the resulting manipulations resulted in a projected take-off time of 7:34 PM PST, as opposed to Sluggo's estimate of 7:33 and the FBI's estimate of 7:36.
In addition, the winds aloft were estimated from the chart that depicted the original guess as to Cooper's landing zone.
All of this resulted in a three segment climb to 10,000 feet with
the entire climb being flown at 160 KIAS. First, the climb from the
The end result of the above is that the climb to 7000 feet was at a rate of only about 1000 feet per minute and the climb from 7000 to 10,000 feet was at a rate of only about 500 FPM. The aircraft reported "leveling at 10,000" at about 7:53.6 PM which would be the time that it was 50.5 NM down V23. This point is about 13.5 NM north of the Malay Intersection and several NM south of the point that is labeled "1954" on the FBI charts.
The distance from the 50.5 NM point to the PDX (now BTG) VORTAC is 54.5 NM and the aircraft would arrive at PDX, assuming it stayed on the centerline of V23 for the entire distance, at 8:11.8 PM PST. If this estimate is correct, then Cooper jumped within 3 NM of the PDX VORTAC assuming a jump during the time the aircraft clock showed 8:11 and assuming the clock was correct to begin with.
The above was done on a conservative basis (i.e., tried to slow the airplane down) insofar as possible. There is no basis for assuming that the winds aloft were ever greater than about 30 knots at 10,000 feet, regardless of what Captain Bohan reported at 14,000 feet.
While I understand the claim that Cooper jumped into a rainstorm,
the weather was generally reported as good with haze and fog south of
To make a full disclosure here, I do not think the airliner
overflew the PDX VORTAC but stayed some distance west of it to avoid flying
I understand that there are some strongly held opinions contradicting the above. But your comments are welcome and I look forward to seeing them.
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This page was last revised: December 19, 2010.