Narrative:

After blockout on 'south' taxiway the right auxiliary pitot light came on. Coordinated with the dispatcher to get time/init/control number. We were blocking exiting traffic attempting to taxi so the ramp controller asked us to taxi abeam gate X. As we arrived abeam gate X we received an ACARS message from dispatch. The message stated: 'mx says MEL 30-31-02-01 and that says no visible moisture....358XXX/pc/XA18Z.' we concurred the MEL was correct and assumed the dispatcher had just sent us the time/init we had been waiting for. I thought the (358XXX) was the necessary control number we had requested. I told the captain we had the necessary information; printed the ACARS message and annotated the release. We taxied towards the runway. As we taxied; I realized we had received the dispatchers east number and not the necessary control number needed for a legal departure. I sent another message to the dispatcher inquiring on the missing control number. He sent us 2 additional messages; 1- 'I did not because I knew you had to come back.' 358XXX/pc/XA30Z 2- 'the MEL was never official...I gave you the MEL as a reference to inform you we could not go due to visible moisture.' 358XXX/pc/XA36Z. We coordinated with ground and taxied back to the gate. The cargo was transferred and we took off in a different airplane. We landed 2 plus hours late. Uneventful flight. A clear standardized ACARS message has to be created to avoid confusion when crews are trying to coordinate for time/init/control numbers.

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Original NASA ASRS Text

Title: B757-200 flight crew reports a R AUX PITOT light after pushback and contacts Dispatch for an MEL. A failure to communicate ensues when the Dispatcher assumes that the crew is aware that the flight cannot be dispatched with this failure. Eventually the crew comprehends and returns to the gate for an aircraft swap.

Narrative: After blockout on 'S' taxiway the R AUX PITOT light came on. Coordinated with the Dispatcher to get Time/INIT/Control Number. We were blocking exiting traffic attempting to taxi so the Ramp Controller asked us to taxi abeam Gate X. As we arrived abeam Gate X we received an ACARS message from Dispatch. The message stated: 'MX SAYS MEL 30-31-02-01 AND THAT SAYS NO VISIBLE MOISTURE....358XXX/PC/XA18Z.' We concurred the MEL was correct and assumed the Dispatcher had just sent us the Time/INIT we had been waiting for. I thought the (358XXX) was the necessary control number we had requested. I told the Captain we had the necessary information; printed the ACARS message and annotated the release. We taxied towards the runway. As we taxied; I realized we had received the Dispatchers E number and not the necessary control number needed for a legal departure. I sent another message to the Dispatcher inquiring on the missing control number. He sent us 2 additional messages; 1- 'I DID NOT BECAUSE I KNEW YOU HAD TO COME BACK.' 358XXX/PC/XA30Z 2- 'THE MEL WAS NEVER OFFICIAL...I GAVE YOU THE MEL AS A REFERENCE TO INFORM YOU WE COULD NOT GO DUE TO VISIBLE MOISTURE.' 358XXX/PC/XA36Z. We coordinated with ground and taxied back to the gate. The cargo was transferred and we took off in a different airplane. We landed 2 plus hours late. Uneventful flight. A clear standardized ACARS message has to be created to avoid confusion when crews are trying to coordinate for Time/INIT/Control Numbers.

Data retrieved from NASA's ASRS site as of July 2013 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.