The 9/11 Time Discrepancy Oddity: Distress Signals Indicated Planes Crashed Minutes BEFORE Flights 11 and 175 Hit the WTC
Radio transmitters that are carried aboard aircraft and that are supposed to activate only in the event of the aircraft crashing went off in the New York area several minutes before the two planes hit the World Trade Center on September 11, 2001. In events that, according to the official account of 9/11, should have been impossible, emergency locator transmitters (ELTs), which are intended to help locate crashed aircraft by broadcasting a distinctive signal, were activated over two minutes before American Airlines Flight 11 hit the north WTC tower and over four minutes before United Airlines Flight 175 hit the South Tower. And yet no ELTs went off at the times these planes hit the towers, when we might have expected them to have been activated.
EMERGENCY TRANSMITTER WENT OFF OVER TWO MINUTES BEFORE FLIGHT 11 CRASHED
American Airlines Flight 11 hit the North Tower of the World Trade Center at 8:46 a.m. and 40 seconds.  But two and a half minutes earlier, David Bottiglia, an air traffic controller at the FAA's New York Center, had received an important message from one of the planes in the airspace he was monitoring. At 8:44 a.m., the pilot of U.S. Airways Flight 583 told Bottiglia: "I just picked up an ELT on 121.5. It was brief, but it went off." (121.5 megahertz is an emergency frequency that ELTs are designed to transmit their distress signals on.) A minute later--about 90 second before Flight 11 hit the WTC--another plane in the New York Center's airspace reported the same thing. The pilot of Delta Airlines Flight 2433 told Bottiglia: "We picked up that ELT, too. But it's very faint."  According to author Lynn Spencer, "several" facilities picked up the ELT signal around this time. 
Peter McCloskey, a traffic management coordinator at the New York Center, later recalled that the ELT had gone off "in the vicinity of Lower Manhattan."  And, around the time Flight 11 hit the WTC, a participant in an FAA teleconference stated, "We got a report of an ELT in the area that [the radar track for Flight 11] was in." (Before it disappeared from radar screens, the track for Flight 11 had indicated the plane was about 20 miles from New York's JFK International Airport.) 
However, while an ELT went off minutes before Flight 11 hit the WTC, it appears that no ELT went off at the time of the crash itself.
EMERGENCY TRANSMITTER WENT OFF OVER FOUR MINUTES BEFORE FLIGHT 175 CRASHED
United Airlines Flight 175 hit the South Tower of the World Trade Center at 9:03 a.m. and 11 seconds.  But, as with the first crash, an ELT was activated in the New York area several minutes before this plane hit the tower.
At just before 8:59 a.m., over four minutes before the Flight 175 crash, the pilot of Flight 583, who had reported the ELT signal before the North Tower was struck, told David Bottiglia at the New York Center that he had noticed another ELT going off. The pilot said, "I hate to keep burdening you with this stuff, but now we're picking up another ELT on 21.5." 
As with the previous crash, although an ELT went off minutes before Flight 175 hit the South Tower, it seems that no ELT went off at the time of the crash itself.
ELT SHOULD ONLY GO OFF IN EVENT OF A CRASH
An emergency locator transmitter is a battery-operated radio transmitter carried by aircraft, which can emit a distinctive signal on the emergency frequencies of 121.5 and 243.0 megahertz. When "armed," an ELT is designed to automatically activate in the event of a crash and then continually emit the emergency signal, thereby helping rescuers to locate the crashed aircraft.  ELTs are required to be installed in almost all U.S.-registered civil aircraft. 
Paul Thumser, an operations supervisor at the FAA's New York Center on 9/11, has over 20 years' experience as an air traffic controller and is also an experienced airline pilot. He provided the 9/11 Commission with detailed information about ELTs. Thumser said the ELT in a Boeing 767--the type of plane that hit both of the WTC towers--cannot be activated by a pilot. Therefore, with a 767, "impact would be the only way to trigger one." Furthermore, the sensitivity setting of the ELT in a 767 "is not low," and so it should be impossible for one to be set off by the plane making a hard turn or a hard landing. Thumser therefore judged that "it would have to be a serious impact to set the ELT off."  Terry Biggio, the operations manager at the FAA's Boston Center, similarly told the 9/11 Commission: "An ELT is not a signal sent by pilot operators. It is clearly indicative of a crash." 
This means that an ELT should not have been activated over two minutes before Flight 11 hit the North Tower, nor should one have been activated over four minutes before Flight 175 hit the South Tower. If such transmitters on Flights 11 and 175 had been set off, this should have happened when these planes struck the WTC, and yet that did not happen. It was perhaps for this reason that Mike McCormick, the air traffic control manager at the FAA's New York Center, told the 9/11 Commission that his "best hypothesis" was that the ELT signal transmitted "moments before the impact of AA 11" was "unrelated to the event" of the crash. 
McCormick also told the 9/11 Commission that ELT signals sometimes "happened accidentally," and that "the vast majority are false alarms."  However, this could not have been the case with the signals before the WTC crashes. None of the air traffic controllers who were involved with monitoring Flights 11 and 175 have reported any planes' ELTs going off by accident around that time. And for one plane in the New York area to have its ELT set off accidentally just before Flight 11 hit the WTC, and then the ELT on another plane in that area going off accidentally just before Flight 175 hit the WTC, would have been too big a coincidence to be plausible.
The strange evidence of emergency locator transmitter signals being broadcast in the New York area before the World Trade Center towers were hit raises serious questions about the official account of the 9/11 attacks. According to that account, if ELTs had been activated, this should have been at the times the planes hit the towers, not several minutes beforehand.  The evidence appears inexplicable, and so proper investigation is imperative to make sense of it. But while a number of air traffic controllers mentioned the ELT signals in their interviews with the 9/11 Commission, the 9/11 Commission Report offered no explanation for this anomalous evidence.
Many questions remain unanswered. For example, were the sources of the ELT signals ever determined? If so, did the signals indeed come from the planes that hit the WTC, or were they from somewhere else? And were the transmitters themselves ever found? After all, according to the FAA, "In most installations the [ELT] is attached to the aircraft structure as far aft as practicable in the fuselage; or in the tail surface, in such a manner that damage to the beacon will be minimized in the event of a crash impact."  So the transmitters should have survived the crashes, if they were in the planes that hit the Twin Towers. If the ELTs were found, then, were they indeed in the rubble of the World Trade Center? Or were they somewhere else?
Paul Thumser told the 9/11 Commission that "credible" ELT signals (i.e. those not determined to be false alarms) had to be reported to the Air Force Rescue Coordination Center (AFRCC), which, at the time of the 9/11 attacks, was located at Langley Air Force Base in Virginia.  So did the AFRCC locate the sources of the ELT signals or determine anything else about them? The only relevant information provided by the 9/11 Commission appears in one of its memorandums, which stated, "We visited the RCC and they receive all ELTs; so many, in fact, that they are a nuisance, and they have special procedures and software to manage that." 
We clearly need to know a lot more, since a proper investigation of these emergency signals could help determine what exactly happened on September 11, and point investigators toward those really responsible for perpetrating the terrorist attacks.
 9/11 Commission, The 9/11 Commission Report: Final Report of the National Commission on Terrorist Attacks Upon the United States. New York: W. W. Norton & Company, 2004, p. 7.
 "Transcript of United Airlines Flight 175." New York Times, October 16, 2001; "Memorandum for the Record: Federal Aviation Administration (FAA) New York Air Route Center Interview With David Bottiglia." 9/11 Commission, October 1, 2003; "Sensitive Security Information: Chronology of September 11, 2001." Federal Aviation Administration, n.d.
 Lynn Spencer, Touching History: The Untold Story of the Drama That Unfolded in the Skies Over America on 9/11. New York: Free Press, 2008, p. 50.
 "Memorandum for the Record: Federal Aviation Administration (FAA) New York Air Route Center Interview With Peter McCloskey." 9/11 Commission, October 1, 2003.
 FAA Audio File, Herndon Command Center, Position 14. Federal Aviation Administration, September 11, 2001.
 9/11 Commission, The 9/11 Commission Report, p. 8.
 FAA Audio File, New York Center, Position R42, 8:51 a.m.-9:10 a.m. Federal Aviation Administration, September 11, 2001; "Memorandum for the Record: Federal Aviation Administration (FAA) New York Air Route Center Interview With David Bottiglia"; "The Hunt for American Air Eleven After WTC 1 is Hit." 9/11 Commission, n.d.
 Christopher G. Morris (Editor), Academic Press Dictionary of Science and Technology. San Diego, CA: Academic Press, 1992, p. 739; U.S. Army Field Manual FM 3-04.300: Airfield and Flight Operations Procedures. Washington, DC: Headquarters, Department of the Army, 2008, p. E-6.
 "Regulatory Brief: Emergency Locator Transmitters (ELTs)." Aircraft Owners and Pilots Association, January 22, 2009.
 "Memorandum for the Record: Federal Aviation Administration (FAA) New York Air Route Center Interview With Paul Thumser." 9/11 Commission, October 1, 2003.
 "Memorandum for the Record: Federal Aviation Administration (FAA) Interview With Terry Biggio, Facility Deputy Manager, Boston Center." 9/11 Commission, September 22, 2003.
 "Memorandum for the Record: Federal Aviation Administration (FAA) New York Air Route Center (ZNY) Follow-up Interview With Mike McCormick." 9/11 Commission, December 15, 2003.
 "Memorandum for the Record: Federal Aviation Administration (FAA) New York Air Route Center Interview With Mike McCormick, Air Traffic Manager." 9/11 Commission, October 1, 2003.
 Note that while ELTs are activated in a majority of aircraft crashes, they are not perfect, and have sometimes failed to go off when planes have crashed. See "Regulatory Brief: Emergency Locator Transmitters (ELTs)."
 "Emergency Locator Transmitters." Federal Aviation Administration, April 2, 1990.
 "Memorandum for the Record: Federal Aviation Administration (FAA) New York Air Route Center Interview With Paul Thumser"; "Air Force Rescue Coordination Center." U.S. Air Force, November 12, 2008.
 "Memorandum for the Record: Federal Aviation Administration (FAA) New York Air Route Center Interview With Paul Thumser."