Commercial Fixed Wing
Flight Crew Air Transport Pilot (ATP)
Communication Breakdown; Confusion
ATC Issue All Types
General Police / Security Involved
Airspace Structure; Human Factors
We entered French airspace in the REIMS sector at FL320. All communications appeared to be normal. At approximately XA20Z we were cleared direct to RLP. At approximately XA30Z we transitioned into the France sector and once again the communications seemed normal with one exception. Air Carrier Y Flight ADC was about 6 or 7 minutes in front of us at this time and on our route of flight. There seemed to be some confusion on the part of the Controller as well as the verbalization between our Flight ABC and Air Carrier Y's call signs (Controller was difficult to understand). We listened very closely and read back clearances to verify. We were assigned a heading and even became pro-active at one point asking the Controller 'do you want us to continue on this heading or proceed direct to VESAN?' We also thought there was some confusion when we were assigned the next frequency only to be sent back to the previous one were the Controller seemed unsure why. It was South of VESAN at approximately XA45Z we were intercepted by a Fighter Jet. We asked ATC if they were aware of this and their short reply was in affirmative. We established communication with the interceptor and verified our identity and the frequency we were on with France control. Once this was confirmed the Fighter Jet broke off the intercept. I'm not sure how or why it got to this point; as we were always in communication with French ATC on an active frequency. Albeit a lower set volume; we were also monitoring 121.5. Other than what I'd describe as a mild confusion between flights ABC and ADC; I'd have to say everything appeared normal.
The flight was Air Carrier X ABC ZZZZ to Washington Dulles. A few facts are in order first in order to unravel the mystery. We were on the same frequency with another Air Carrier X Flight ADC and were just 6 minutes in trail and were constantly on the same frequency. We were in constant contact with Air Traffic Control and switching frequencies as normal. We were given a few directs and the last direct before the incident was direct VESAN. We were then given a clearance to fly present heading which we complied with and a few minutes later asked if they still wanted us on that heading. The Controller then said to again proceed direct VESAN. I believe a few minutes later we were asked if we were proceeding direct VESAN and we acknowledged that we were. Sometime later we received a TCAS caution alert. The contact appeared on the screen at our 2 O-Clock position at 26;100 climbing rapidly toward our 6 and the Captain and I both commented on the climb rate and I even said only a fighter can climb that fast. The contact then ended up in our 6 O-Clock position and disappeared off of TCAS at 31;000. I chocked it up to a ghost TCAS and pressed on with normal duties. All the time we were talking to Air traffic Control. I then noticed the fighter at our 9 O-Clock position and called it out to the Captain. I then immediately notified the Controller that we were just intercepted by a military fighter. The Controller simply said something to the effect of 'Roger.' I then switched radios to Comm 2 and called the fighter on Guard. I said 'this is Air Carrier X Flight ABC tail number NXXXXX and we are talking to Control on Frequency XXX.' I do not remember the frequency and actually read the previous first; but the Captain pointed to the current frequency which I then correctly stated to the fighter. He acknowledged and said nothing further that I could tell. We were given no directions from ATC and just continued on our route of flight. The fighter stayed with us for 5 minutes longer then broke left and departed. I believe there could and I say could have been some confusion due to similar call signs but we were never aware of either one of us (ADC or ABC) answering the wrong call. I did start to answer once; but the Captain stopped me and said it was for ADC. We did have one questionable frequency change and was told to return to the previous frequency. I even said something to the effect 'haven't we been around this mountain before' jokingly. But; we were never told that we had answered.
Similar call signs and a language barrier between ATC and the flight crew of two aircraft resulted in a military interception of the reporters' flight.  The propriety of the flight was established with the intercept pilot and the flight was completed uneventfully.