Narrative:

We were cleared for position and hold on runway 17 at phl. While in position, a takeoff clearance was issued to another of our company aircraft on runway 27L. This airplane had several of the same digits as our flight number. The first officer on my aircraft acknowledged the takeoff clearance with our flight number and commenced the takeoff roll. As we were lifting off, I observed an aircraft crossing our departure path in the process of landing on runway 27R. I also observed an aircraft departing runway 27L which turned out to be our company aircraft with the similar call sign who had actually been cleared for takeoff. I contacted tower and informed him we were airborne. Apparently, the first officer had acknowledged the takeoff clearance simultaneously with the other company aircraft. His transmission blocked ours. Several factors to be considered: 4 digit flight numbers are a constant source of confusion. Occasionally you will find 2 different carriers on frequency with the same call sign. At the hub airports ATC sometimes is handling multitudes of same company flts, sometimes with several identical digits. ATC and pilots need to be reminded to be more vigilant. Situation occurred at night, last leg of a long day. Company downsizing, first officer pre-occupied with impending furlough. As PNF, I was supposedly working radios. When takeoff clearance was given, I hesitated in the acknowledgement because it didn't sound right. The first officer, because we were in a known dead spot for communication on airport, assumed I had missed the clearance, and responded to it. Because there was no response from tower I assumed I had heard it wrong. Supplemental information from acn 279271: we sat on the runway for approximately 2 mins, when I heard tower say our company name, our 4 digit flight number, and 'cleared for takeoff.' it was my leg, and it's company policy for the PNF to work the radio once we are on the runway. However the captain failed to answer the call. Thinking that he may not have been on both communications and missed the call, I read back the clearance, then looked to the captain who nodded, as I advanced the power levers. After we cleaned up the airplane, we contacted the tower who told us that we had only been cleared for position and hold. He confirmed the takeoff clearance was for another company aircraft, on runway 27L. The first and last digits of the other aircraft's call sign were the same as our own. Reaching cruise I asked the captain if he was on both communication radios, and if he also understood the clearance to be for us. He told me that he was on both radios, but had serious doubts that the clearance was ours! He withheld comment however, when tower did not challenge my readback. An added factor was over the duration of the 2-DAY trip, the captain missed a few calls. I suspected that this was the case again. The most grievous error was the captain's failure to stop the takeoff from happening if he had any misgivings, let alone a 'serious doubt' about the validity of our takeoff clearance. I was 100 percent sure in my mind, that the takeoff clearance issued was for us. However, if the captain had said even, 'I'm not so sure...' I would have locked up the brakes.

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Original NASA ASRS Text

Title: REPLY TO WRONG CALL SIGN SPONSORS AN UNAUTH TKOF.

Narrative: WE WERE CLRED FOR POS AND HOLD ON RWY 17 AT PHL. WHILE IN POS, A TKOF CLRNC WAS ISSUED TO ANOTHER OF OUR COMPANY ACFT ON RWY 27L. THIS AIRPLANE HAD SEVERAL OF THE SAME DIGITS AS OUR FLT NUMBER. THE FO ON MY ACFT ACKNOWLEDGED THE TKOF CLRNC WITH OUR FLT NUMBER AND COMMENCED THE TKOF ROLL. AS WE WERE LIFTING OFF, I OBSERVED AN ACFT XING OUR DEP PATH IN THE PROCESS OF LNDG ON RWY 27R. I ALSO OBSERVED AN ACFT DEPARTING RWY 27L WHICH TURNED OUT TO BE OUR COMPANY ACFT WITH THE SIMILAR CALL SIGN WHO HAD ACTUALLY BEEN CLRED FOR TKOF. I CONTACTED TWR AND INFORMED HIM WE WERE AIRBORNE. APPARENTLY, THE FO HAD ACKNOWLEDGED THE TKOF CLRNC SIMULTANEOUSLY WITH THE OTHER COMPANY ACFT. HIS XMISSION BLOCKED OURS. SEVERAL FACTORS TO BE CONSIDERED: 4 DIGIT FLT NUMBERS ARE A CONSTANT SOURCE OF CONFUSION. OCCASIONALLY YOU WILL FIND 2 DIFFERENT CARRIERS ON FREQ WITH THE SAME CALL SIGN. AT THE HUB ARPTS ATC SOMETIMES IS HANDLING MULTITUDES OF SAME COMPANY FLTS, SOMETIMES WITH SEVERAL IDENTICAL DIGITS. ATC AND PLTS NEED TO BE REMINDED TO BE MORE VIGILANT. SIT OCCURRED AT NIGHT, LAST LEG OF A LONG DAY. COMPANY DOWNSIZING, FO PRE-OCCUPIED WITH IMPENDING FURLOUGH. AS PNF, I WAS SUPPOSEDLY WORKING RADIOS. WHEN TKOF CLRNC WAS GIVEN, I HESITATED IN THE ACKNOWLEDGEMENT BECAUSE IT DIDN'T SOUND RIGHT. THE FO, BECAUSE WE WERE IN A KNOWN DEAD SPOT FOR COM ON ARPT, ASSUMED I HAD MISSED THE CLRNC, AND RESPONDED TO IT. BECAUSE THERE WAS NO RESPONSE FROM TWR I ASSUMED I HAD HEARD IT WRONG. SUPPLEMENTAL INFO FROM ACN 279271: WE SAT ON THE RWY FOR APPROX 2 MINS, WHEN I HEARD TWR SAY OUR COMPANY NAME, OUR 4 DIGIT FLT NUMBER, AND 'CLRED FOR TKOF.' IT WAS MY LEG, AND IT'S COMPANY POLICY FOR THE PNF TO WORK THE RADIO ONCE WE ARE ON THE RWY. HOWEVER THE CAPT FAILED TO ANSWER THE CALL. THINKING THAT HE MAY NOT HAVE BEEN ON BOTH COMS AND MISSED THE CALL, I READ BACK THE CLRNC, THEN LOOKED TO THE CAPT WHO NODDED, AS I ADVANCED THE PWR LEVERS. AFTER WE CLEANED UP THE AIRPLANE, WE CONTACTED THE TWR WHO TOLD US THAT WE HAD ONLY BEEN CLRED FOR POS AND HOLD. HE CONFIRMED THE TKOF CLRNC WAS FOR ANOTHER COMPANY ACFT, ON RWY 27L. THE FIRST AND LAST DIGITS OF THE OTHER ACFT'S CALL SIGN WERE THE SAME AS OUR OWN. REACHING CRUISE I ASKED THE CAPT IF HE WAS ON BOTH COM RADIOS, AND IF HE ALSO UNDERSTOOD THE CLRNC TO BE FOR US. HE TOLD ME THAT HE WAS ON BOTH RADIOS, BUT HAD SERIOUS DOUBTS THAT THE CLRNC WAS OURS! HE WITHHELD COMMENT HOWEVER, WHEN TWR DID NOT CHALLENGE MY READBACK. AN ADDED FACTOR WAS OVER THE DURATION OF THE 2-DAY TRIP, THE CAPT MISSED A FEW CALLS. I SUSPECTED THAT THIS WAS THE CASE AGAIN. THE MOST GRIEVOUS ERROR WAS THE CAPT'S FAILURE TO STOP THE TKOF FROM HAPPENING IF HE HAD ANY MISGIVINGS, LET ALONE A 'SERIOUS DOUBT' ABOUT THE VALIDITY OF OUR TKOF CLRNC. I WAS 100 PERCENT SURE IN MY MIND, THAT THE TKOF CLRNC ISSUED WAS FOR US. HOWEVER, IF THE CAPT HAD SAID EVEN, 'I'M NOT SO SURE...' I WOULD HAVE LOCKED UP THE BRAKES.

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.