reply to post by getreadyalready
I vaguely remember some story about the transponder codes, but I don't remember the details. Pilots are taught to change the transponder codes
for a number of reasons like radio outtage or hijacking.
Yes, there are three specific codes that refer to what you described. 7500 is the "hijack" squawk (it is NOT necessary to use that code in all cases,
though. Before 9/11, there was a "common strategy" that included using the xponder code 7500 as a covert
method to inform ATC....only
IF you could not "speak in the clear". That is, if the hijacker had gained access, and was listening to your radio transmissions. It was also a part
of the "common strategy" that any hijacker would be AFRAID of dying, and therefore would not harm the pilots. Now, that is no longer assumed to be
In the very unlikely event of total (most cases all three
VHF communications radios) failing, and IF the transponder still works, then
code 7600 is appropriate. But, when you are "NORDO" (no radio) on an IFR flight plan, the procedures are well outlined as to what to do, and ATC
knows what to expect, and will anticipate.
The code 7700 is for ALL emergencies....but again, really, is a bit obsolete nowadays. In fact, it changes the data block display on the ATC radar
screens, and the controllers would have you change it away form the "emergency" code, anyway, so they won't be distracted by it.
When and to what did the transponder code change? Or provide a link...
9/11 timeline, from "HistoryCommons" (link below):
Seconds later, Flight 11 also enters the area Bottiglia is monitoring and its target appears on his radar screen. The controller sitting next to
Bottiglia gets up and points to the radar blip. He says: “You see this target here? This is American 11. Boston Center thinks it’s a hijack.”
Bottiglia will later recall that his initial thought about Flight 11, based on this information, is that the hijackers “were probably going to
Cuba.” As its transponder has been turned off (see (Between 8:13 a.m. and 8:21 a.m.) September 11, 2001), he has no altitude information for
Flight 11, but can tell from the radar scope that it appears to be descending. According to author Lynn Spencer: “Even without a transponder,
controller radars calculate ground speed for all radar targets, and when a plane is descending, the ground speed decreases. The flight had been
‘grounding’ 600 knots, and now it has decreased to 320.” Bottiglia follows Flight 11’s target on his radar screen until it disappears over New
York City. Because he is focused on Flight 11, Bottiglia will not notice when Flight 175’s transponder code changes at 8:47 (see 8:46
a.m.- 8:47 a.m.)
Further down the page:
The first “operational evidence” that something is wrong is at 8:47, when Flight 175’s transponder code changes twice within a minute (see
8:46 a.m.-8:47 a.m. September 11, 2001).
Flight 175 stops transmitting its transponder signal. It is currently flying near the New Jersey-Pennsylvania border. [Guardian, 10/17/2001;
Newsday, 9/10/2002; 9/11 Commission, 6/17/2004] However, the transponder is turned off for only about 30 seconds, and then comes back on as a
signal that is not designated for any plane on this day. Then, within the space of a minute, it is changed to another new code. But New York
Center air traffic computers do not correlate either of these new transponder codes with Flight 175. Consequently, according to an early FAA report,
“the secondary radar return (transponder) indicating aircraft speed, altitude, and flight information began to coast and was no longer associated
with the primary radar return.”
8:47 At almost the same time American 11 crashed into the North Tower, United 175's transponder code changed several times. The changes
were not noticed for several minutes as the controller tried to locate American 11.
At 08:47, the plane's transponder signal changed once, and a second time within a minute, and the aircraft began deviating from its assigned
course. But, the air traffic controller in charge of the flight did not notice until minutes later at 08:51. Unlike Flight 11, which had turned its
transponder off, Flight 175's flight data could still be properly monitored. Also, at 08:51, Flight 175 changed altitude.
You should also devote the time to watching the Google video I posted, with actual ATC personnel recounting their experiences. It is less than one
hour long, as it was originally aired in a one-hour time slot, with commercials.
You will find a great deal of factual information, once stepping away from the "9/11 conspiracy" sites, which are devoid of any facts whatsoever, in
majority of cases.
edit on 25 October 2010 by weedwhacker because: BBcode