Assume ATC issues a clearance or instruction such as: "N123 turn right heading two two zero, vectors for the visual approach to runway 4, descend and maintain eight thousand" and the pilot responds: "Roger out of twelve for seven, right to two twenty, 123."
If ATC does not correct the pilot's incorrect altitude read-back and an incident occurs (e.g.,loss of separation, airspace violation, etc.) does ATC bear some/all responsibility for the error or does the pilot bear some/all responsibility for the error?
The focus of my question is whether or not there can be some shared responsibility for the ultimate error. For example, if the pilot uses non-standard phraseology in the readback such as (pilot's response to the example instruction above) - "out of twelve for seven, right to two twenty, 123." Instead of "N123 roger, right turn heading two two zero, descend and maintain seven thousand."
The ability of the controller to correctly interpret an incorrect pilot read back is reduced when the pilot uses non-standard phraseology. The cognitive "pattern-matching" verbiage helping a busy controller interpret an incorrect read-back is negatively affected when the pilot's verbiage is missing contextual clues such as reading back the instructions in the same sequence (heading first then altitude) as given by ATC and saying "seven" instead of "seven thousand."
This is one reason (in my opinion) that the Aeronautical Information Manual-AIM describes proper phraseology for ATC-Pilot communication. The pilot's response to the instructions from ATC in the example above conflicts with the AIM's guidance on the use of proper phraseology.
The use of proper, well researched communication procedures is critical in ensuring that misunderstandings are minimized.
Perhaps there may be other factors that may lead to "shared" responsibility. Anyway, I am interested in the feedback from the ASE community. There is no question that mis-heard or misinterpreted ATC-Pilot communication has resulted in serious incidents in the past.