AN MD81 CREW WERE ADVISED AFTER TKOF THEY WERE TO FLY RWY HDG FOR VECTORS. THE CREW DID NOT RECALL RECEIVING THAT CLRNC AND FLEW THE SID AS PUBLISHED FOR NOISE ABATEMENT.

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AFTER A RWY SWITCH DUE TO WINDS; OUR FLT WAS CLRED BY PHX TWR TO TAKE OFF RWY 26. AS FILED; WE FLEW THE ST JOHN 3 DEP EXACTLY. WE HAVE RECEIVED CONSIDERABLE ATTN BY OUR COMPANY AND VIA FAA PAMPHLETS TO FLY THE DEP EXACTLY AS TO AVOID SETTING OFF NOISE ABATEMENT SENSORS. IF YOU FLY RWY HDG OFF RWY 26; YOU WILL SET OFF THE NOISE ABATEMENT SENSORS. AFTER BEING TOLD 1 HR LATER BY ZAB TO CALL PHX DEP WHEN WE LAND; WE WERE TOLD THAT WE WERE GIVEN 'FLY RWY HDG.' NEITHER I; NOR THE CAPT; RECALLED THIS INSTRUCTION. WE EITHER DIDN'T HEAR THE INSTRUCTION OR IT WAS BLOCKED. IF I HAD HEARD IT I WOULD HAVE QUESTIONED IT BECAUSE IT WOULD CONCERN ME THAT WE WOULD SET OFF THE NOISE ABATEMENT SENSORS AND BE FINED AND OR PUNISHED. CONTRIBUTING FACTORS MAY HAVE BEEN OTHER ACFT ON THE FREQ; WORKLOAD; CONCERN WITH NOISE ABATEMENT PROCS; AND THIS INSTRUCTION IS OUT OF THE NORM FOR PHX. IN MY 6 YRS FLYING INTO PHX WITH THE ACR; I DO NOT RECALL EVER GETTING 'FLY RWY HDG' AS DUE TO THE GREAT ATTN TO AVOID A NOISE COMPLAINT.