EMB ERJ 170/175 ER/LR
Situational Awareness
ATC Issue All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Other / Unknown
General None Reported / Taken
Airport; Procedure
We were [waiting to takeoff] Runway 28C at ORD. After being cleared to Line Up and Wait; Tower crossed a B-747 at either Tango or Foxtrot and cleared him to the Cargo Ramp. After the aircraft crossed the runway; he stopped and requested confirmation he was cleared into the ramp. Tower confirmed this for him and then cleared us for takeoff. As we rolled down the runway; the other aircraft must have just started to throttle up as he was still just across the hold short line and was emitting a lot of jet blast as we passed behind him at around 120 KIAS and got a yawing action off of it as it hit our tail and a slight; momentary; wing dip from it as well. I kept the aircraft under control and we were still stable for the takeoff so we continued the takeoff since we were over 80 KIAS. We rotated maybe 1;000 feet beyond the jet blast and had no further complications. We let Tower know that we got his jet blast and received only a roger in reply. This could have easily been prevented if ATC had waited a little longer to allow the heavy to adequately clear the runway before he gave us a takeoff clearance. There are wake turbulence time limits between takeoffs and landings; but the Controller didn't seem to allow the proper space for the 747 to clear the runway to insure we wouldn't hit his jet blast. After that aircraft stopped; it required extra power to start moving again and we were probably right behind him whenever he resumed his taxi. If we were a smaller aircraft or were in our rotation when we hit his jet blast; we probably would have had a much harder time keeping the aircraft under control. We could also have requested a little longer hold in position to allow the aircraft to start his movement again; but seeing as it was night; we thought he had cleared the runway a little further than he had.
During his takeoff roll an ERJ-175 First Officer had to cope with jet blast from a B747 which had crossed the runway and stopped prior to spooling up to continue taxi after clarifying their taxi clearance.