B737-700 flight crew reported a track deviation occurred on departure from MDW as a result of a wake turbulence encounter from the preceding aircraft.

Reporter 1

Cleared for takeoff from Runway 4R. Tower cleared previous aircraft to take off approximately one minute prior to clearing us to take off. Shortly after takeoff, we experienced some wake turbulence from the aircraft in front of us. I elected to keep the wings level and delayed our turn until the wake turbulence dissipated. Initially, I started the turn using a bank angle of about 15 to 20 degrees in the event we encountered any additional wake turbulence. Departure asked us to tighten up the turn to heading of 230 degree. Departure cleared us to 4,000 ft. and asked up to expedite the climb. Departure then called out traffic, which I visually acquired off my left (about my 9 o'clock position). We received a TA (no RA) Alert while in the turn to a heading of 240 degrees. I had the traffic in sight and saw that the traffic was not a factor due to us climbing and increasing separation laterally. After switching frequency, we were told to call Chicago Approach when on the ground. After landing, I called Chicago Approach and they stated that we did not complete our turn within the required four miles. I explained our situation to Chicago Approach and why we had delayed our turn. Perhaps ATC could provide a little more spacing/timing between takeoffs. I should have mentioned why our turn was delayed to Chicago Approach prior to switching to the next frequency.

Reporter 2

We were cleared for takeoff on Runway 4R in MDW in between an aircraft that had departed less than a minute prior and another aircraft on final approach. Spacing was sufficient to be legal, but the timing was tight, as is so often the case in MDW. Our clearance was left turn 250, maintain 3,000 ft. Shortly after rotating, probably 400 ft. or 500 ft. AGL, we experienced a "bump" and the tell-tale "wing-dip" of wake turbulence from the aircraft ahead of us. The Captain, who was Pilot Flying (PF), opted to stay wings level for a moment to stabilize the aircraft, then gently rolled into a slightly shallower than normal turn to our cleared heading to prevent an undesired aircraft state, should the wake turbulence worsen. During this time, Tower handed us off to Departure and I checked in with our altitude and heading clearances. Once it smoothed out and we had reasonable assurance it was safe to do so, the Captain began to tighten the turn from about 20 degrees to the standard 30. As he was doing that, ATC asked us to verify that we were on a 250 heading. I replied that we were still in the turn to 250, which we were. He asked us to tighten up the turn and continue it to 230 because we were getting close to "O'Hare's stuff". I replied with the new heading, saying we'd tighten it up, which had already done. Somewhere around then, we leveled at 3,000 ft., and ATC gave us a climb to 4,000 ft. As we were dialing that in, he called back and mentioned traffic to our left and asked us to expedite our climb and assigned us 13,000 ft. We did so, and did not receive an RA from the other aircraft. As we were climbing, he turned us slightly back to the right, heading 240, then eventually on course. No further mention of the event was made by that Controller and he handed us off to Center. Several minutes after checking in with the next Controller, he informed us of a possible Pilot Deviation and gave us a phone number. The rest of the flight proceeded uneventfully. This one's difficult, because closely spaced operations are common here, and I, myself, have departed MDW multiple times with no issues. ATC has no way of knowing what the weight/flap settings are of any aircraft that's taking off ahead of any other, and of course, we as Pilots have no way of knowing that either. I would suggest increasing space between aircraft, but I know that would have significant consequences in surface congestion, which may lead to unforeseen safety issues too. For myself, I will figure out some way to increase my awareness of where the 4 NM limit is from MDW. This too is tricky, because we had the 3.8 NM ring for the engine- out procedure depicted on the Navigational Display (ND), and as we were busy cleaning up the aircraft, climbing, responding to wake turbulence, turning, switching frequencies, communicating, leveling off, and looking for traffic, I honestly couldn't say that I ever even noticed that green ring on the ND moving past us. I think probably the most important thing that I should have done better, and will in the future, is to say something promptly to ATC, when we experience wake, especially when it affects our compliance with their clearance. Maybe if I had said something right away, they could have coordinated to allow us into ORD's airspace for a moment, and this whole thing would not have been an issue at all.