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I have experienced this a few times in the last couple of months. When the ATC assigns me a squawk code and I enter it in the transponder, a few minutes later when I try to reconfirm the squawk code, they give me a new code. I know that they can see me on the radar anyway, just may not identify me positively. I noticed this more on an inbound flight to a towered airport.

This happened yesterday too. I was assigned to squawk 6451. I replied to confirm it and entered it in the transponder. While holding short for takeoff, when I asked the controller to reconfirm the code, he said that it is 6455.

What is the controller's responsibility if they confirm an incorrect read back? Since this happened to me several times, I am concerned if such incident can impact safety, traffic advisories or aircraft separation?

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    $\begingroup$ Didn't your instructor teach you to write down your clearances? $\endgroup$ – rbp Jul 26 '15 at 4:52
  • $\begingroup$ Terrible handwriting + writing while flying = questionable results for squawk codes :-D sometimes I have to write without looking. On the ground everything is fine, but this has also happened on the ground and I wrote the wrong code down clearly, then read it back and was not corrected! $\endgroup$ – Pugz Jul 26 '15 at 13:18
  • $\begingroup$ If you can't even bother to write 4 digits, you'll never be able to get an instrument rating. What would you do with this? “Cessna 12345 cleared to Nashville as filed, fly runway heading, climb and maintain three thousand, expect seven thousand one zero minutes after departure, departure frequency one two four point six five, squawk two seven one three.” $\endgroup$ – rbp Jul 26 '15 at 21:40
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    $\begingroup$ @rbp I agree and know I need to work on it :-) like I said on the ground is fine for me, it's while flying that gets me... Either way, my question was about the controller's responsibility to ensure correct read back if I clearly repeat it back wrong $\endgroup$ – Pugz Jul 26 '15 at 23:15
  • $\begingroup$ I think the question is misplaced. The responsibility of the controller is clearly stated in the AIM. You are the PIC, however. If you're asking who is responsible you shouldn't be flying a plane unless you're just doing research or asking the question for some other reason. $\endgroup$ – user6035379 Oct 22 '16 at 8:57
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Yes a controller absolutely must listen to read-backs and ensure they are correct. This is commonly referred to as hear-backs.

Consider the following excerpt from ICAO Annex 11, Air Traffic Services (emphasis mine):

3.7.3 Read-back of clearances and safety-related information

3.7.3.1 The flight crew shall read back to the air traffic controller safety-related parts of ATC clearances and instructions which are transmitted by voice. The following items shall always be read back:

a) ATC route clearances;

b) clearances and instructions to enter, land on, take off from, hold short of, cross and backtrack on any runway; and

c) runway-in-use, altimeter settings, SSR codes, level instructions, heading and speed instructions and, whether issued by the controller or contained in ATIS broadcasts, transition levels.

3.7.3.1.1 Other clearances or instructions, including conditional clearances, shall be read back or acknowledged in a manner to clearly indicate that they have been understood and will be complied with.

3.7.3.1.2 The controller shall listen to the read-back to ascertain that the clearance or instruction has been correctly acknowledged by the flight crew and shall take immediate action to correct any discrepancies revealed by the read-back.

If, after a read-back by a flight crew, the controller neither acknowledges nor corrects the read-back, most flight crews will percieve this as an implicit confirmation of the read-back. This makes hear-back errors very dangerous, and is the reason why the pilot-controller communication loop has, not two, but three steps, the third step being the hearback:

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While your example of an incorrect transponder code is rather trivial, incorrect read-backs can be extremely dangerous. For instance, they could result in a level bust, mid-air collision or runway incursion.

Therefore, performing appropriate hear-backs is an essential part of ATC training, and is taught to ATC trainees from day one. The importance of active listening is demonstrated in a simulator environment, where simulator pilots will occasionally - either intentionally or by mistake - make incorrect readbacks, the result of which will be a dangerous situation, if not corrected promptly.


Further reading:

Pilot-Controller Communications

Read-back or Hear-back

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A controller, should be on the lookout for all incorrect readbacks. But controllers are human, and can easily miss them, or say things in correctly. Incorrect squawk codes are often more of an annoyance versus an actual separation issue. It'd become an issue if they didn't take action when it was noticed that there was an incorrect code airborne, and let you truck on your way and not perform appropriate handoffs or inform others of any issues with your flightplan/target.

Most of the time, an incorrect beacon code will be flashing on the scope, if it's not assigned to someone else, and the controller will look through their list to find the correct code. If you tag up under someone else's code, then it becomes more of an issue, as they have to realize it's incorrect, suspend the datablock, and flightplan(or most likely drop it out of the system and reenter it) (flightplan issue is often delegated to others in the operation), and hunt for your correct code.

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