Date: 201206
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Aircraft: B757-200
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Taxi
Aircraft component: Pitot/Static Ice System
Component problem: Failed
Reporter organization: Air Carrier
Reporter function: Pilot Flying; First Officer
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Confusion; Communication Breakdown
Second reporter function: Pilot Flying; Captain
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural MEL / CDL; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Automation Aircraft Other Automation; Person Dispatch; Person Flight Crew
When detected: Taxi
Result: Flight Crew Returned To Gate; General Maintenance Action; General Flight Cancelled / Delayed
Contributing factors: Incorrect / Not Installed / Unavailable Part; Aircraft
Primary problem: Aircraft

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.


Second narrative: Right Aux Pitot EICAS after blockout.  Ran red tabs and referenced MEL.  Contacted Dispatch for time and initials and control number from Maintenance Control.  Received time and initials from Dispatch and mistakenly recorded the Dispatcher's employee number on the release as the control number from Maintenance Control.  We then received a ACARS message from Dispatch that we could not continue due to visible moisture along our route of flight.  We then taxied back to the gate and transferred to another aircraft.  The six digit employee number resembled that of a control number.  I think that if it had been identified as Company Employee number XXXXXX instead of XXXYYY that it would have eliminated the confusion.


Synopsis: 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.