Conspiracy or Incompetence? The 9/11 USAF Stand Down

"The US military has spent billions of dollars developing stealth aircraft which are invisible to radar so they can mount surprise attacks on adversaries, but it seems they should have saved their money and bought a fleet of airliners because they appear to be far more effective.
On 9/11 the world's only military superpower was apparently oblivious to the location of rogue airliners in it's airspace for more than an hour, and military commanders were left totally perplexed on how to deal with the situation of hijackers using these planes as flying bombs. This confusion resulted in fighter jets staying on the ground whilst the hierarchy fully assessed what was going on, and this total lack of cohesion ultimately led to the loss of nearly 3000 lives.
All that was required to overcome America's military might on 9/11 were 19 hijackers on 4 airliners.
Does this sound plausible to you?
It's what you're expected to believe.
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NORAD was unusually prepared on 9/11, because it was conducting a week-long semiannual exercise called Vigilant Guardian.
On 9/11, North American Aerospace Defense Command's (Norad) Northeast Air Defense Sector (NEADS) was fully staffed, its key officers and enlisted supervisors already manning the operations center "battle cab." [Aviation Week]
COLONEL ROBERT MARR, US AIR FORCE: We had the fighters with a little more gas on board. A few more weapons on board. [...] We had 14 aircraft on alert, seven sites, two aircraft at each site. [ABC News]
That's a ratio of 3.5 'hot' fighter jets per hijacked airliner.
In the map shown below MediaLab has merged a map of the 9/11 planes' flightpaths with a map of military bases in those areas. The flights went through some of the most heavily militarized parts of the country.
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The USAF response against Flight 11

None
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The USAF response against Flight 175

By the time the F-15s were airborne, United 175 was nine minutes away from plowing into the south tower of the World Trade Center, and the fighter planes were more than 100 miles away.
''We had a nine-minute window, and we had in excess of 100 miles to intercept 175,'' [Maj. Gen. Paul Weaver] said. ''There was just literally no way.''
The pilots flew ''like a scalded ape,'' topping 500 mph but were unable to catch up to the airliner, Weaver said. [St. Augustine Record]
The maximum speed of an F-15 is 1,665 mph (2.5 Mach).
NORAD's response times notes the F-15 interception flown against Flight 175 was "calculated at 9 miles per minute or .9 Mach". 9 miles per minute = 540 mph. This is not .9 Mach, it is .7 Mach (flying at sea level). To put this speed into perspective, the scrambled fighters were travelling just 3 mph faster than Flight 175's WTC impact velocity. The cruise speed of an F-15 is 570 mph, so is flying one of these fighters at less than its cruise speed defined as flying ''like a scalded ape''?
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The USAF response against Flight 93

None?
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The USAF response against Flight 77

The US military knew Flight 77 had been hijacked at approximately 08:50:
During the hour or so that American Airlines Flight 77 was under the control of hijackers, up to the moment it struck the west side of the Pentagon, military officials in a command center on the east side of the building were urgently talking to law enforcement and air traffic control officials about what to do. [New York Times]
Its approach into Washington was tracked on radar:
Eight minutes before the crash, at 9:30 a.m. EDT, radar tracked the plane as it closed to within 30 miles of Washington. [CBS News]
The plane's descent over Washington was tracked on radar:
Radar shows Flight 77 did a downward spiral, turning almost a complete circle and dropping the last 7,000 feet in two-and-a-half minutes. [CBS News].
At 09:38 the plane hit the Pentagon:
"We heard what sounded like a missile, then we heard a loud boom," said Tom Seibert, 33, a network engineer at the Pentagon. "We were sitting there and watching this thing from New York, and I said, you know, the next best target would be us. And five minutes later, boom." [Guardian]
This page from the Andrews AFB web site (removed 9/12) shows the base had F-16 fighter jets which could have intercepted Flight 77.
Instead, two F-16s were scrambled from Langley AFB which is 120 miles south of the Pentagon.
If the NORAD departure time of 09:30 is correct then the two F-16s would have had to travel at slightly over 700 mph to reach Washington before Flight 77 - this should have been no problem as the maximum speed of these fighter jets is
1,350 mph (915 mph at sea level). The fighters didn't reach Washington, in fact, NORAD states they were 105 miles from the aircraft impact location at 09:38.
If NORAD's times and distances are correct then the two F16s either took a wrong turn or they travelled toward Washington at roughly 120 mph.
Question: How was a plane which was known to be hostile able to have an unimpeded 48 minute joyride around US airspace before slamming into the heart of the US military?
Answer: Stand down.
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November 11, 2003: Plane flies into restricted White House airspace

The incident began around 11 a.m. when the airplane crossed into the Air Defense Identification Zone, a 23-mile area encompassing the Washington area's three major airports. NORAD scrambled two F-16 fighter jets from Andrews Air Force Base in suburban Maryland when the plane neared a restricted 17.25-mile flight zone around the Washington Monument.
How times change...
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FAA Manager Mangled, Cut, Destroyed 9/11 Tapes

Each of at least six air traffic controllers and some ten other employees who were on the job at the New York Air Route Traffic Control Center (ARTCC) in Ronkonkoma, N.Y., during the World Trade Center attacks gathered several hours after to recall their version of events. But that tape, which could have helped determine how the agency responded to clues that four planes had been hijacked, was destroyed before it was ever heard.
In fact, officials at the ARTCC were never even told of the tape's existence. According to the report given to the 9/11 Commission by Department of Transportation Inspector General Kenneth Mead, the audiotape was crushed in the hand of the unnamed FAA employee, then cut into small pieces and tossed into different trash cans around the ARTCC building.
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Like his father, Bush tries to keep a daily diary of his thoughts and observations. That night, he dictated: "The Pearl Harbor of the 21st century took place today." [Washington Post] Pearl Harbor wasn't a surprise. In 2000 PNAC called for a New Pearl Harbor. On 9/11 they got it."