Date: 202008
Local time of day: 0601-1200
Location: SEA.Airport, WA
Flight conditions: VMC
Light: Daylight
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Mission: Passenger
Flight phase: Taxi
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Human factors: Situational Awareness
Anomaly: Deviation / Discrepancy - Procedural Clearance; Ground Event / Encounter Other / Unknown
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: We were at gate setting up for pushback. I had run numbers for Runways 34R and 34C. The Captain had mentioned to me about being prepared for a Runway 34R/Q departure in regards to numbers. Because of our 2 line entries for runways in the new ACARS (Aircraft Communications And Reporting System) setup I ran a second set for 34R/Q after some time had went by and I remembered. We had already put in numbers for 34R full length. Right about this time there was a 757 being pushed back just behind gate and disconnecting. Then ramp tower cleared us to pushback tail on Wiskey deep after the 757 vacates. The Captain spoke to the ramp personnel regarding the pushback. At this time the numbers for Runway 34R/Q came back and the ATIS (Automated Terminal Information Service) had changed; causing our TO (Takeoff) temp to be greater and the N1 values different from the original data. I mentioned this and not making a good prioritization prompted with the numbers. We put the new numbers in and it was busy doing this and setting flaps etc. The ground crew headset was also very poor quality with lots of background noise during part or all of the pushback and subsequent events.Somewhere in the course of the push; I took note of the 757; which I probably would have normally done much earlier; but was focused and saturated with the new numbers and setup. I noticed it didn't look like the 757 had moved; but I second guessed that maybe they had pulled forward and sort of assumed the ground crew knew what they were doing or the hazards associated. However when rounding onto Whiskey; it appeared we were very close and I was concerned about jet blast for the ramp crew; yet didn't speak up and say something. At this time the 757 powered up making a turn towards the West. The ramp crew encountered intense jet blast; such that one of the rampers on subsequent post brief told me 'That was so scary' and something like she couldn't stay in one place or stand upright. The plane buffeted a bit and I also noticed that gate and the equipment (jet bridge; etc) seemed to be getting blasted pretty good. This is also an area where passengers could be out on the ramp in the open air (next to gate and gate). At this point the ground crew told us that there had been a problem and they lost some things and a box had flew under the airplane and out behind and now there was FOD (Foreign Object Debris) and it may have hit the airplane and they would want to pull back in and do an inspection. We coordinated with ramp and ops; pulled back in; had a post briefing with various people from ramp; I performed a full walk-around inspection; maintenance came out and performed an inspection; and we subsequently prepared for gate departure.There were multiple causes and factors: Bad headset quality making communication difficult; ramp personnel pushing when the 757 had not vacated; me not prioritizing the hazards at hand and having inattention to the given clearance and what was actually being done; and me not speaking up when I saw the hazard and potential for a dangerous situation and questioned if we were actually or if the ramp crew was doing what the clearance was. I also do not know whether the 757 was single engine taxi or both; but I believe they at least had the Left engine running.Making sure the ramp personnel understands the given clearance (there might have been some confusion with that). Not neglecting to prioritize rightly and monitor clearance vs what's actually happening. Speaking up right when something doesn't look right. Also it may not be a good location to have a large jet turn with the jets facing the outside gates on the end of the Q spots there. The ground crew should also be aware; if they were not; on the danger of the jet blast and know the hazards of what they were doing if they are getting that close behind another aircraft.




Synopsis: Air carrier First Officer reported that push back crew prematurely positioned aircraft behind departing B757 and encountered jet blast.