Turning off the transponders. How easy? How hard?

[QuettaKid]

Getting some comflicting answers on this question. All 4 planes had their transponders turned off. Is this simply a matter of flicking a switch somwhere in the cockpit? Or is it more complicated than that? Anyone know?

[DoYouEverWonder]

1. You would think something like that

would be hardwired in? Or at least a little more difficult to mess with?

[screembloodymurder]

2. If it wasn't classified information before 911,

it is now. IMHO no commercial pilot should have access to the transponder. In fact, every plane should have a receiver that allows a separate transponder to be turned on from the ground. That said, I'd like to know the answer to your post. How easy was it?

[KJF]

3. The 9/11 CR says:

"Minutes later, United 175 turned southwest without clearance from air traf-
fic control. At 8:47, seconds after the impact of American 11, United 175's
transponder code changed, and then changed again." (p. 21)

So three of them were turned off (and United 93's back on again), whereas the other was changed twice.

[QuettaKid]

4. "less than obvious"

From the WaPo.

""Aviation sources said the plane was flown with extraordinary skill, making it highly likely that a trained pilot was at the helm, possibly one of the hijackers. Someone even knew how to turn off the transponder, a move that is considerably less than obvious.""

http://www.washingtonpost.com/ac2/wp-dyn?pagename=article&node=&contentId=A14365-2001Sep11¬Found=true

[KJF]

5. Hani had 21 hours on 737 simulators

The other pilots also had about 20 hours on Boeing simulators between them. I guess some/all was with an instructuor and they could have asked about switching transponders off. However, some people at the flight schools have been interviewed and I don't recall them saying anything about this.

[MercutioATC]

10. Turning the transponder on would have been part of the preflight checklist

They didn't have to ask, it would have been part of their training.

[KJF]

11. Is it the same on all Boeings?

737s, 727s, 757s and 767s?

So the guys on United 175 probably couldn't remember how to do it, and changed the frequency twice instead of switching it off.

And on United 93, the hijackers maybe just turned it back on inadvertently - is that the most likely explanation?

[MercutioATC]

12. It's the same on all airplanes, Boeing or otherwise.

I won't speculate on the reasons they were or weren't turned off, I'm just providing technical info.

[KJF]

13. Thanks anyway (n/t)

[Jeroen]

6. On the ground, transponders are off to prevent clutter on ground radar

Pilots turn the transponder ON just before take-off.
So yes, you can turn the transponder off easily.
You can also change the transponder code (squawk)

[MercutioATC]

7. Correct. It's as easy as turning a radio on or off.

(or changing the station)

[KJF]

8. So why would they fail to do it twice on United 175?

And why would it come back on on United 93?

Just curious.

[MercutioATC]

9. I don't know. It's a simple process, though.

...flip a switch...

[DoYouEverWonder]

14. Considering what happened on 9-11

have the airlines considered installing some kind of beacon that is automatic and that you can't override?

[Artdyst]

15. No, because that would be bad for business. Better to just allow NSC

to monitor communications worldwide, pay close attention whenever signals point to "a ratcheting up of chatter on the chatterbox" and hire a professional to write a more effective script for the PDB the next time the "chatter" suggests an upcoming event like 9/11. It's unlkely there will be another such event anytime soon. Once the novelty wears off enthusiasm wanes, and the brilliant brains behind such "spectaculers" cook up something new and more awfully awesome. Osama bin Laden knows all about how that works. He's smart and he learns from his mistakes.