Date: 201511
Local time of day: 1201-1800
Location: EWR.Airport, NJ
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: Medium Transport; Low Wing; 2 Turboprop Eng
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Takeoff / Launch
Airspace: Class B EWR
ATC / advisory: Tower EWR
Second aircraft: Commercial Fixed Wing
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; First Officer
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Flight Instructor; Flight Crew Air Transport Pilot (ATP)
Human factors: Communication Breakdown; Confusion
Anomaly: ATC Issue All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Procedure; Company Policy
Primary problem: Company Policy

Narrative: Leaving the ramp we were told by Newark Ground to follow our company aircraft (flight YYYY) to runway 22R at Whiskey for an intersection departure.  Our flight number (XXXX) was similar to our company's callsign; so I made a mental note of that since we would be directly behind them. We were never told by ATC to use caution for similar sounding callsign.  Once arriving at the takeoff intersection; flight YYYY was given a takeoff clearance and we were instructed to line up and wait runway 22R intersection Whiskey.  I read that clearance back and we held in position on the runway.  About 30 seconds later we were given a takeoff clearance and I read that back; and because of the similar callsign situation I read it back slowly and annunciated the flight number clearly to be sure it was for us.  After I read the clearance back there was no reply from tower so I assumed we were correct and it was us who were cleared for takeoff.  As we accelerated down the runway passing 100 knots I hear tower say 'flight XXXX runway 22R whiskey line up and wait'.  I did not respond as we were in the middle of a takeoff roll.  As we lift off tower says 'XXXX cleared for takeoff 22R at whiskey'.  Since we are now airborne we quickly tell tower we are airborne and he might have flight numbers confused.  Tower just responded with 'roger contact departure'. Looking back; because of the confusion and similar sounding callsigns; I am not 100 percent sure that when we were cleared for takeoff that Newark tower used our actual callsign; but might have used our company's who lifted off before us and was already airborne. There was never any loss of separation that we are aware of and am pretty sure that we were actually cleared for takeoff. However; my take away from this is a reinforcement of what we are all already aware of: when you have similar sounding callsigns; USE EXTREME CAUTION.  And this can come on both ends; pilots and ATC.  Pilots need to listen with extreme caution and ATC needs to listen to read backs carefully with similar callsigns.




Synopsis: Two company aircraft with similar call signs were taxiing out and departing at the same time. As one aircraft was lifting off it was cleared for takeoff by the Tower Controller.