Failure of Correct an Erroneous Readback ( hearback errors )
Most pilots perceive the absence of an acknowledgement or correction following a clearance readback as an implicit confirmation of the readback.
The lack of acknowledgement by the controller usually is the result of frequency congestion, requiring the controller to issue clearances and instructions to several aircraft.
Uncorrected erroneous readback (known as hearback errors) may cause deviations from the assigned altitude or noncompliance with altitude restrictions or with radar vectors.
A deviation from a clearance or instruction may not be detected until the controller observes the deviation on his/her radar display.
Less-than-required vertical or horizontal separations (and near midair collisions) or runway incursions usually are the result of hearback errors.
Perceiving What Was Expected or Wanted (not what was actually said)
The bias of expectation can affect the correct understanding of communications by pilots and controllers.
This involves perceiving what was expected or wanted and not what was actually said.
Effective Pilot / Controller Communications
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The bias of expectation can lead to:
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Transposing the numbers contained in a clearance (e.g., an altitude or FL) to what was expected, based on experience or routine;

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Shifting a clearance or instruction from one parameter to another (e.g., perceiving a clearance to maintain a 280-degree heading as a clearance to climb / descend and maintain FL 280).

Failure to Seek Confirmation (when a message is not understood)
Misunderstandings may include half-heard words or guessed-at numbers.
The potential for misunderstanding numbers increases when a given ATC clearance contains more than two instructions.
Failure to Request Clarification (when in doubt)
Reluctance to seek confirmation or clarification may cause pilots to either:
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Accept an inadequate instruction (over-reliance on ATC); or,

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Define by themselves the most probable interpretation.

Failing to request clarification may cause flight crew to believe erroneously that they have received an expected clearance (e.g., clearance to cross an active runway).
Failure to Question an Incorrect or Inadequate ATC Instruction
Failing to question an incorrect or inadequate instruction may cause a crew to accept an altitude clearance below the sector MSA or a heading that places the aircraft near obstructions.
                                                                                       Getting to Grips with                                            Approach-and-Landing Accidents Reduction

Taking a Clearance or Instruction Issued to Another Aircraft
This usually occurs when two aircraft with similar-sounding call signs are on the same frequency and are likely to receive similar instructions or if the call sign is blocked by another transmission.
When pilots of different aircraft with similar-sounding call signs omit the call sign on readback, or when simultaneous readback are made by both pilots, the error may go unnoticed by the pilots and the controller.
　
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