Read-back requirements have been introduced in the interests of flight safety. The importance of the read-back requirement is directly related to the possible seriousness of misunderstanding. Strict read-back procedures make sure that the clearance or instruction has been received and understood correctly by the correct aircraft. The flight crew shall read back to the air traffic controller safety-related parts of ATC clearances and instructions that are transmitted by voice. The Air Traffic Controller is responsible for checking the completeness and accuracy for the read back. The following items shall always be read back: a. ATC route clearances. b. Clearances and instructions to enter, land on, take off on, hold short of, cross and backtrack on any runway. c. Runway in use, altimeter settings, SSR codes, level instructions, heading and speed instructions and, whether issued by the controller or contained in ATIS broadcast, transition level. d. Other clearances, 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. An aircraft must include its call sign in the readback, and a failure to do this shall be challenged by the controller. TAXI INSTRUCTIONS When a taxi clearance contains a taxi limit beyond a runway, it shall contain a stated clearance to cross the runway, or a stated instruction to hold short, even if the runway is not in use. Communication with any aircraft using the runway for the purpose of taxiing should be transferred from the ground controller to the aerodrome controller before the aircraft enters or crosses the runway. For more complicated taxi instructions, it may be appropriate to divide the message into segments, placing the clearances and instructions in sequential order, to avoid the possibility of pilot misunderstanding.4. What item is not included in the readback requirement?