First officer of a B737 responded to another aircraft clearance and climbed from cruise altitude.

Attributes
ACN	465223
Time
Date	200003
Day	Sun
Local Time Of Day	1801 To 2400
Place
State Reference	AL
Altitude	msl bound lower : 28000 msl bound upper : 28500
Environment
Flight Conditions	VMC
Light	Dusk
Aircraft 1
Controlling Facilities	artcc : ztl.artcc
Operator	common carrier : air carrier
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : multi engine pilot : instrument pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 60 flight time total : 11000 flight time type : 9000
ASRS Report	465223
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : multi engine pilot : commercial
Experience	flight time last 90 days : 200 flight time total : 4600 flight time type : 600
ASRS Report	465720
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	other controllera
Resolutory Action	flight crew : returned to assigned altitude other
Supplementary
Problem Areas	Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

First officer answered a climb from FL280 to FL310 for another aircraft with similar call sign. She asked twice and received the same response. I (the captain) was talking on the PA when I noticed the climb. Since I was not expecting or wanting to climb higher, I slowed the rate of climb to see if we absolutely had to because of traffic. ATC responded that it was intended for another aircraft. Climb was stopped at FL285 and then descended back to FL280 promptly. Our flight number was air carrier X from newark to new orleans.

Original NASA ASRS Text

Title: FO OF A B737 RESPONDED TO ANOTHER ACFT CLRNC AND CLBED FROM CRUISE ALT.

Narrative: FO ANSWERED A CLB FROM FL280 TO FL310 FOR ANOTHER ACFT WITH SIMILAR CALL SIGN. SHE ASKED TWICE AND RECEIVED THE SAME RESPONSE. I (THE CAPT) WAS TALKING ON THE PA WHEN I NOTICED THE CLB. SINCE I WAS NOT EXPECTING OR WANTING TO CLB HIGHER, I SLOWED THE RATE OF CLB TO SEE IF WE ABSOLUTELY HAD TO BECAUSE OF TFC. ATC RESPONDED THAT IT WAS INTENDED FOR ANOTHER ACFT. CLB WAS STOPPED AT FL285 AND THEN DSNDED BACK TO FL280 PROMPTLY. OUR FLT NUMBER WAS ACR X FROM NEWARK TO NEW ORLEANS.

Data retrieved from NASA's ASRS site as of July 2007 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.