CREW OF AN ATR42 DEPARTING ORD ON RWY 22L STOPPED THEIR CLB TO AVOID A B747 XING OVERHEAD OFF RWY 14R.

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ATR42 CREW. WE TAXIED OUT TO RWY 22L AT ORD. WE WERE CLRED INTO POS AND HOLD ON RWY 22L. THERE WERE SOME CITY VEHICLES ON THE RWY LOOKING FOR SOME FOD THAT HAD BEEN RPTED. ONCE THE VEHICLES WERE CLR OF THE RWY; WE WERE CLRED FOR TKOF AND TO TURN TO A HDG OF 180 DEGS. THE DEP CLRNC WAS READ BACK. WE ACCELERATED DOWN THE RWY AND AFTER V1; VR AND RIGHT AT LIFTOFF; WE SAW A B747 OFF OUR R SIDE TAKING OFF OF RWY 14R. TWR CALLED THE TFC AT THAT TIME. WE LEVELED OFF ABOUT 100 FT AGL. THE B747 WENT OVER OUR HEAD AT ABOUT 200 FT ABOVE US. ONCE THE B747 PASSED AND WE WERE CLR; WE CONTINUED THE CLB. THE FLT CONTINUED WITH NO FURTHER PROBS AND THERE WERE NO INJURIES. IT APPEARS THE ACFT DEPARTING OFF OF RWY 14R WAS ON A DIFFERENT TWR CTL FREQ. SUPPLEMENTAL INFO FROM ACN 481586: B747 CREW. WE WERE TAKING OFF ON RWY 14R AT ORD. THE ACFT WAS HVY BUT NOT AT MAX GROSS. THE TKOF ROLL AND LIFTOFF WERE NORMAL. WE ROTATED ABEAM TERMINAL AND WERE WELL INTO THE AIR BY RWYS 14R/27L INTXN. PASSING THE INTXN; THE OTHER PNF AND I LOOKED OUT TO THE L AND SAW AN AIRBORNE ATR. HE HAD LIFTED OFF OF RWY 27L AND WAS WELL BELOW AND TO THE L OF US. THERE WERE NO CORRECTIVE ACTIONS THAT COULD HAVE BEEN TAKEN AT THE POINT THE ATR WAS SEEN. IN ANY CASE HE WAS NOT NEAR THE INTXN FOR ANY CONFLICT TO DEVELOP. WE WERE NEAR OR PAST V1 BY THE TIME THE ATR WAS PROBABLY CLRED FOR TKOF AND AS SUCH WERE COMMITTED TO FLT.