Flight 77's speed on impact - Greater than 600mph?

[Ezlivin]

It was previously given that the cruising speed of a 757 is approx. 600 mph. According to the FAA report, AA77 was last reported doing 458 kts, which is 527 mph at 8:56 am. Just prior to the strike, the jet passed over the White House then completed a hair-pin 270 degree turn before slamming into the Pentagon. This hair-pin turn would have bled-off a lot of air-speed; however the dive into the Pentagon with engines at full thrust might have brought the final approach speed back up to around 600 mph/521kts. So let's take that as a worse-case scenario. (The plane's air-speed was most likely slower than 521 kts. due to the hair-pin turn it just completed.)

Assumed AA77 Inbound Velocity: 600 miles/hour = 10 miles/minute = 1 mile or 5280 feet every 6 seconds = 880 feet/sec.

Most North American A/V equipment operates at a rate of 30 interlaced frames per second (NTSA). That is one complete frame every 30th of a second and one partial or interlaced field scan every 60th of a second, which is essentially slaved to the AC line frequency of 60hz.

So if you take the plane's velocity of 880 feet/sec. and divide that by the full frame rate of 1/30th of a second, the camera will capture a complete image of the plane every 29.3 feet, given a constant speed of 600 mph. Or if your video equipment can freeze-frame on individual interlace fields it will capture a partial scan (every other scan line) of the plane's travel in 14.6 foot intervals, given a constant rate of speed of 600 mph.

According to the surveillance video the plane crossed the camera's field of view on an inbound trajectory of approximately 35 - 45 degrees, so the apparent velocity of the plane across the camera's field of view will be approximately 1/3 less than that actually travelled by the plane along its inbound trajectory.


Blue Dot: Camera Position
Red Line: Centerline of Field of View
Yellow Lines: Approx. Field of View Borders
Green Line: Approx. Path of AA77
Red Dot: Tail Position in Photograph
Pink Line: Angle from Camera to Point of Impact

Using the sky view and the surveillance camera views above we determine the approximate angles involved to assist us with determining how far the plane travelled in a single frame or 1/30th of a second. Now assuming the photo was not doctored and assuming this is AA77 (not a small commuter jet) partially hidden behind the traffic post, we will use the length of the 757-300 as our base measurement: 155 feet. It can been seen in the video frame that there are approximately 2 plane lengths (310 feet) remaining between the nose and the building face and 3 plane lengths (465 feet) between the tail and the building face.

In the following frame 1/30th of a second later, the tail of the plane has completely disappeared into the building and resulting explosion, so obviously the tail of the plane had to have travelled a minimum of 465 feet in 1/30th of a second. And keep in mind we are not factoring in the extra distance resulting from the tangent the flight path is on perpendicular to the camera angle or the deceleration that would suddenly occur as the plane struck the building. These figures are very conservative.

Now let's work backwards to see what the minimum approach velocity of AA77 would have to be in order for these two "undoctored", "back-to-back" video frames to be captured exactly as we have been told they were by government officials.

465 feet traveled in 1/30th of a second = 13950 feet/second = 2.64 miles/second = 158.5 miles per minute = 9511.36 mph = 8263.5 kts. = Mach 12.48

According to "official Pentagon sources" the released surveillance camera frames cover 4/100s of a second. They do not specify if that is 4/100s of a second per frame (25 frames/sec) or 4/100s of a second for all four frames (100 frames/sec). Let's re-examine the visual data we have to determine what the velocity of AA77 would be under these two additional "officially stated" scenarios.

Pentagon's claim assuming video ran at 25 frames/second: 465 feet traveled in 1/25th of a second = 11625 feet/sec. = 2.20 miles/sec. = 132.1 miles/min. = 7926.14 mph = 6886.30 kts. = Mach 10.43

Pentagon's claim assuming video ran at 100 frames/second: 465 feet traveled in 1/100th of a second = 46500 feet/sec. = 8.8 miles/sec. = 528.4 miles/min. = 31704.54 mph = 27545.21 kts. = Mach 41.7

Now if we assume the plane was not travelling in excess of Mach 1, (761.6 mph) but at its rated speed of approximately 600 mph and the camera was operating at the standard 30 frames/sec. this would result in an image of the plane being captured every 29.3 feet travelled. It becomes undeniably apparent that a minimum of 16 frames (1/2 of a second) of the video have been cut or edited from between the point the plane is last seen behind the traffic post and the next frame where the impact in complete and the explosion is already well under way.

Update

I've completed a more accurate and detailed analysis of the photographs. My initial estimate was that the tail of the plane was 465' from the impact point. Upon further examination it appears it could have been closer to 450' from the impact point, based on the following photo analysis.



The Pentagon measures 921.6 feet along each external face, half of this distance, marked on the diagram between the central corridor and the upper-left corner of the Pentagon (cyan) is 460.8' Take this base measurement as a scale and measure the distance from the rear of the plane in the photo (red dot), along the approximate path of the jet (dark-green line) to the impact point. The distance the tail travelled between frames (heavy red line) is approx. 450', which is just short of the originally estimated 465' or 3 lengths of a 757, which is 155'.

So, 450 feet traveled in 1/30th of a second = 13500 feet/sec. = 2.55 miles/sec. = 153.4 miles/min. = 9204.54 mph = 7997 kts. = Mach 12.11
Even if you alter the path of the jet to a direct (90 degree) impact trajectory you still end up with a final velocity exceeding Mach 6.

I had hoped that someone had undertaken a basic trigonometric analysis of the Pentagon video footage and uncovered the information printed above.

Any contributions to this?

[DrDebug]

1. Let's assume that the camera makes one capture per second

Because then the math will be more or less correct and 1 fps is quite common for CCTVs and often those cameras can go up to higher rate if required, so the 25fps could be max speed of the camera. There are lots of security cameras which have a normal recording speed of 1fps and can speed up to 25fps.
1/25 = 10.41 Mach
1 sec = 10.41 / 25 * 761.6 = 317 mph

Even though that's a lot slower it is still within the ranges mentioned for the airplane and ~300 mph is extremely fast as well.

[Ezlivin]

4. We have a disparity in frame rates, then

According to "official Pentagon sources" the released surveillance camera frames cover 4/100s of a second.

[Tin Man]

5. link?

[DrDebug]

6. 25 fps doesn't make sense because of the speed

1 fps (~300mph) is possible and 2 fps (~600mph) are possible according to your own calculation and most gate cameras are on "slow" mode, so 25fps, 30fps or even 100fps (which are high quality cameras) doesn't seem plausible.

[Pacifist Patriot]

2. Wow!

I didn't understand a bit of that. I remain in awe of people who have an aptitude for math. Sadly, I have to sit back and wait for the conclusions to be translated into the vernacular.

[Marie26]

3. But wasn't the security camera here slower?

In another thread, someone said it only took one frame every half second. If that's true, would it have been able to capture the plane as it flew by? Great analysis, thanks!

[Zynx]

7. Um, the cameras are recording at 1 FPS.

http://www.youtube.com/watch?v=TAaP4Z3zls8

Note that the image moves only once every second. These are not normal video cameras, they are the cheap things used to just catch faces and license plate for still analysis, if that later proves necessary.

[Duer 157099]

8. Shutter speed -- isn't that what we're talking about here?

There's no way the shutter speed is 1fps, or else you would see just one long blur as the plane passed by (not sure how CCTV cameras work, if they have shutter speeds or the equivalent)

I'm guessing that 1/30 would be a good ballpark estimate, so the exposure lasts 1/30th of a second. Assuming 800 feet per sec, and assuming the distance from the wall to the right side of the frame is about 400 feet, the object would move about 27 feet on a frame capture.

The main point is that there's no way the object could be captured more than once on this camera.

The frame rate of the camera was I believe 1 fps -- so, only 1 frame per second was recorded, but it was recorded for only 1/30th of a second (or whatever the shutter speed equivalent was)

[Duer 157099]

9. I think your 450' estimate is off

I used the side of the pentagon wall (922 feet) to calibrate the red line to 155 feet (length of a 757), so it looks like the total distance from the pentagon wall to the road is at most 400 feet -- and I don't think the far right edge of the video shows the road

[FogerRox]

10. I went here to DL the video

http://www.defenselink.mil/pubs/foi/index.html

scroll down to the flt 77 video number 2

The video is 3 minutes, 22 seconds long. @ 24 seconds
I see the "object".



@23 seconds................... @ 24 seconds................. annotated

This video seems to be playing at 1 fps.