Narrative:

We were involved in a suspected hijacking event. The suspicion arose due to our inadvertently squawking 7500. Compounding the situation was an ACARS message I sent to dispatch in which I included the humorous postscript: 'ps. It's dark and we're scared.' unbeknownst to us, the cryptic message, combined with the squawk we were unaware of, prompted operations control to believe we were being hijacked and could not communicate freely. Thus began a full scale 'red alert' on 2 continents preparing for a hijacked international flight. Flight dispatch felt that communicating with us directly would put us at increased risk and so did not send us an ACARS message inquiring as to our status. Gander center says they requested confirmation of our squawk but both of us have no recollection of such a request. The first officer and I have no explanation of how 7500 got into the transponder. When we cleared the coast by 30 mins the first officer put XXXX in the transponder as prescribed. He jotted down the previous squawk without being conscious of the numbers. When we were in ACARS range of ireland we got a message to contact dispatch on phone patch HF. We also got several ACARS messages using the word 'trip.' I had a discussion with the director of flight operations and assured him we were safe and secure. He asked me if we had squawked 7500 and I told him 'absolutely not.' he told me gander had reported the squawk. At this time the first officer looked at the note he had jotted down and realized with distress that we had, in fact, been squawking 7500 somewhere over gander. We realized this after having terminated the phone patch and assuring the control office that everything was fine. The remainder of the flight was uneventful except that we were met, boarded and questioned by the dutch airport and security departments, the united states fbi, state department and FAA security officials. I cannot explain how the squawk of 7500 got into the transponder. The first officer and I have run through every possible scenario and all of them fail at some point. We are awaiting the ATC tapes from gander center to see if it can clear up some discrepancies or suggest a plausible scenario. I have learned not to broadcast humorous messages on the ACARS, to pay more attention to the innocuous transponder and to listen more carefully to changes of squawk when I am the PF. I think it would be helpful for each company to devise a coded message to ask if the flight is being hijacked and the pilot's ability to communicate is being compromised. This code would appear even to an educated hijacker as a normal operational request. Supplemental information from acn 442772: on departure from dtw, the initial squawk transponder code was XXXX. Upon reaching gander airspace as the ATC controller gave us a squawk transponder change, the flight attendant came in with food trays. One of the food trays was put in the pedestal instrument panel close to the transponder box. After I reached to change the transponder code, the captain removed the tray and moved it to the jump seat. 30 mins after entering nat track airspace I changed the transponder code to XXXX as per procedures. I wrote down on a piece of paper the previous code which had been set in the transponder box, the code had been 7500. At that point I did not recognize the importance and the meaning of these numbers even though I had been taught that the code represented a hijack situation. At 30W on nat track victor and flying at 36000 ft with operations normal, dispatch had been trying to contact us. We understood the company wanted our airspeed, altitude and destination ETA. At 15W we received an ACARS message from company on whether we were a trip and squawking 7500. The company director of operations was on the line and he specifically asked us whether we were secure and whether we had been squawking 7500. The captain responded in the negative on the squawk of 7500 and that we were a secure and normal flight. After his conversation was over and phone patch terminated, I recovered the note in which I had written down the previous transponder code prior to being established on nat track victor. In any case, at 15W the company was advised through our captain thateverything was normal and the aircraft was secured.

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Original NASA ASRS Text

Title: ACR CREW XMITS INAPPROPRIATE XPONDER CODE CAUSING ACTIVATION OF HIJACKING PROCS BY GND AUTHS. ERROR DISCOVERED BEFORE ARR.

Narrative: WE WERE INVOLVED IN A SUSPECTED HIJACKING EVENT. THE SUSPICION AROSE DUE TO OUR INADVERTENTLY SQUAWKING 7500. COMPOUNDING THE SIT WAS AN ACARS MESSAGE I SENT TO DISPATCH IN WHICH I INCLUDED THE HUMOROUS POSTSCRIPT: 'PS. IT'S DARK AND WE'RE SCARED.' UNBEKNOWNST TO US, THE CRYPTIC MESSAGE, COMBINED WITH THE SQUAWK WE WERE UNAWARE OF, PROMPTED OPS CTL TO BELIEVE WE WERE BEING HIJACKED AND COULD NOT COMMUNICATE FREELY. THUS BEGAN A FULL SCALE 'RED ALERT' ON 2 CONTINENTS PREPARING FOR A HIJACKED INTL FLT. FLT DISPATCH FELT THAT COMMUNICATING WITH US DIRECTLY WOULD PUT US AT INCREASED RISK AND SO DID NOT SEND US AN ACARS MESSAGE INQUIRING AS TO OUR STATUS. GANDER CTR SAYS THEY REQUESTED CONFIRMATION OF OUR SQUAWK BUT BOTH OF US HAVE NO RECOLLECTION OF SUCH A REQUEST. THE FO AND I HAVE NO EXPLANATION OF HOW 7500 GOT INTO THE XPONDER. WHEN WE CLRED THE COAST BY 30 MINS THE FO PUT XXXX IN THE XPONDER AS PRESCRIBED. HE JOTTED DOWN THE PREVIOUS SQUAWK WITHOUT BEING CONSCIOUS OF THE NUMBERS. WHEN WE WERE IN ACARS RANGE OF IRELAND WE GOT A MESSAGE TO CONTACT DISPATCH ON PHONE PATCH HF. WE ALSO GOT SEVERAL ACARS MESSAGES USING THE WORD 'TRIP.' I HAD A DISCUSSION WITH THE DIRECTOR OF FLT OPS AND ASSURED HIM WE WERE SAFE AND SECURE. HE ASKED ME IF WE HAD SQUAWKED 7500 AND I TOLD HIM 'ABSOLUTELY NOT.' HE TOLD ME GANDER HAD RPTED THE SQUAWK. AT THIS TIME THE FO LOOKED AT THE NOTE HE HAD JOTTED DOWN AND REALIZED WITH DISTRESS THAT WE HAD, IN FACT, BEEN SQUAWKING 7500 SOMEWHERE OVER GANDER. WE REALIZED THIS AFTER HAVING TERMINATED THE PHONE PATCH AND ASSURING THE CTL OFFICE THAT EVERYTHING WAS FINE. THE REMAINDER OF THE FLT WAS UNEVENTFUL EXCEPT THAT WE WERE MET, BOARDED AND QUESTIONED BY THE DUTCH ARPT AND SECURITY DEPTS, THE UNITED STATES FBI, STATE DEPT AND FAA SECURITY OFFICIALS. I CANNOT EXPLAIN HOW THE SQUAWK OF 7500 GOT INTO THE XPONDER. THE FO AND I HAVE RUN THROUGH EVERY POSSIBLE SCENARIO AND ALL OF THEM FAIL AT SOME POINT. WE ARE AWAITING THE ATC TAPES FROM GANDER CTR TO SEE IF IT CAN CLR UP SOME DISCREPANCIES OR SUGGEST A PLAUSIBLE SCENARIO. I HAVE LEARNED NOT TO BROADCAST HUMOROUS MESSAGES ON THE ACARS, TO PAY MORE ATTN TO THE INNOCUOUS XPONDER AND TO LISTEN MORE CAREFULLY TO CHANGES OF SQUAWK WHEN I AM THE PF. I THINK IT WOULD BE HELPFUL FOR EACH COMPANY TO DEVISE A CODED MESSAGE TO ASK IF THE FLT IS BEING HIJACKED AND THE PLT'S ABILITY TO COMMUNICATE IS BEING COMPROMISED. THIS CODE WOULD APPEAR EVEN TO AN EDUCATED HIJACKER AS A NORMAL OPERATIONAL REQUEST. SUPPLEMENTAL INFO FROM ACN 442772: ON DEP FROM DTW, THE INITIAL SQUAWK XPONDER CODE WAS XXXX. UPON REACHING GANDER AIRSPACE AS THE ATC CTLR GAVE US A SQUAWK XPONDER CHANGE, THE FLT ATTENDANT CAME IN WITH FOOD TRAYS. ONE OF THE FOOD TRAYS WAS PUT IN THE PEDESTAL INST PANEL CLOSE TO THE XPONDER BOX. AFTER I REACHED TO CHANGE THE XPONDER CODE, THE CAPT REMOVED THE TRAY AND MOVED IT TO THE JUMP SEAT. 30 MINS AFTER ENTERING NAT TRACK AIRSPACE I CHANGED THE XPONDER CODE TO XXXX AS PER PROCS. I WROTE DOWN ON A PIECE OF PAPER THE PREVIOUS CODE WHICH HAD BEEN SET IN THE XPONDER BOX, THE CODE HAD BEEN 7500. AT THAT POINT I DID NOT RECOGNIZE THE IMPORTANCE AND THE MEANING OF THESE NUMBERS EVEN THOUGH I HAD BEEN TAUGHT THAT THE CODE REPRESENTED A HIJACK SIT. AT 30W ON NAT TRACK VICTOR AND FLYING AT 36000 FT WITH OPS NORMAL, DISPATCH HAD BEEN TRYING TO CONTACT US. WE UNDERSTOOD THE COMPANY WANTED OUR AIRSPD, ALT AND DEST ETA. AT 15W WE RECEIVED AN ACARS MESSAGE FROM COMPANY ON WHETHER WE WERE A TRIP AND SQUAWKING 7500. THE COMPANY DIRECTOR OF OPS WAS ON THE LINE AND HE SPECIFICALLY ASKED US WHETHER WE WERE SECURE AND WHETHER WE HAD BEEN SQUAWKING 7500. THE CAPT RESPONDED IN THE NEGATIVE ON THE SQUAWK OF 7500 AND THAT WE WERE A SECURE AND NORMAL FLT. AFTER HIS CONVERSATION WAS OVER AND PHONE PATCH TERMINATED, I RECOVERED THE NOTE IN WHICH I HAD WRITTEN DOWN THE PREVIOUS XPONDER CODE PRIOR TO BEING ESTABLISHED ON NAT TRACK VICTOR. IN ANY CASE, AT 15W THE COMPANY WAS ADVISED THROUGH OUR CAPT THATEVERYTHING WAS NORMAL AND THE ACFT WAS SECURED.

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.