Readback Error on a Conditional Clearance
Bahrain Ground is issuing taxi clearances during a busy morning push. A Boeing 787 is at the holding point of Taxiway B and requests taxi to Runway 30R via Taxiway C. The controller issues: 'Bahrain Ground, Boeing 787, taxi to holding point Runway 30R via C, give way to the A320 on Taxiway B, report holding point.' The 787 crew read back: 'Taxi to holding point Runway 30R via C, report holding point.' The controller is distracted by a phone call and does not catch the omission. A few seconds later, the A320 on Taxiway B reports ready to taxi. The 787 begins to move.
1. What is the significance of the incomplete readback, and what should the controller have done?
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The readback omitted the instruction to give way to the A320 on Taxiway B. A readback is not a formality; it is the mechanism by which the controller confirms that the pilot has correctly understood the clearance. An incomplete readback must be challenged. The controller should have listened for the full readback, and on hearing the omission, should have responded: 'Boeing 787, negative, I say again, give way to the A320 on Taxiway B, report holding point.' The controller should also have avoided taking the phone call at that moment, or should have paused the clearance until able to monitor the readback. The distraction is a human factors issue - the controller's attention was divided at a critical moment. The controller should treat the readback as a required verification step, not a courtesy.
2. What action should the controller take now that the 787 has begun to move and the A320 is ready?
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The controller must act immediately to prevent a conflict. The 787 is moving and has not acknowledged the give-way instruction. The controller should transmit: 'Boeing 787, stop immediately, give way to the A320 on Taxiway B.' If the 787 is already moving into conflict, the controller should instruct the A320 to hold position and advise both crews of the situation. The controller should then re-issue the full clearance with the give-way instruction and obtain a complete readback. The controller should also record the event and consider filing a report under the safety reporting system, since the incomplete readback and the distraction are both reportable safety occurrences. The controller should not assume the 787 crew saw the A320; visual acquisition by the crew is not a substitute for a correct clearance and readback.