Air carrier B737-800 Captain reported encountering wake turbulence just before landing in ATL in trail of a B757 that resulted in airspeed and sink rate deviations.
Synopsis
Air carrier B737-800 Captain reported encountering wake turbulence just before landing in ATL in trail of a B757 that resulted in airspeed and sink rate deviations.
Narrative
Landing Runway 8L in ATL; 10 mile final. Reported proceeding 757 in sight and cleared to visual approach. When cleared visual approach; we were 4 miles behind the 757 according to TCAS. Previous Controller had assigned 210 kts; but when we were cleared visual approach; no airspeed was assigned by the new Controller.As we intercepted final; TCAS indicated that our range to the B757 had begun to decrease. Not wanting to get into wake turbulence; we began slowing to stabilize the distance. We slowed to 180 kts. About a minute later; Atlanta Approach queried us on our speed and admonished us that we needed to maintain our airspeed until directed; and then issued us a speed of 180 kts until the final approach fix; which we complied with.By the time we configured at the final approach fix; our distance to the 757 was just under 3 miles. Winds were reported as 090/8G14. Approach was normal until approximately 300 [ft.] when we encountered a sudden increased airspeed (15 kts) and then a sudden sink rate; which caused a 'SINK RATE; SINK RATE' caution. Immediate action was taken to correct both the airspeed deviation and the sink rate. Landing was normal.We debriefed this event. Both pilots agreed our understanding was that when cleared visual approach; unless specifically given an airspeed to follow; we were cleared to maneuver the aircraft at our discretion. No airspeed restriction was given to us and our speed reduction was in response to the aircraft preceding us. Even with just under three-mile spacing; we encountered wake turbulence that resulted in a speed excursion and a sink rate caution. Approach Control needs to issue speed restrictions on a visual approach if they are required. We also need to ensure proper separation from heavy aircraft. The 757 was not using a heavy callsign; however; we still encountered wake turbulence.
Second reporter narrative
On vector to join localizer to Runway 8L in ATL at assigned speed of 210 [kts]; we reported preceding 757 traffic in sight and were cleared the visual approach with no airspeed assigned. I mentioned to the Captain that 757's have the most extreme wake turbulence. He suggested I slow; which I did; to 190 [kts] as we were approximately four miles behind the 757. Atlanta Approach called to assign 180 [kts] until the final approach fix and asked if we had already slowed. We told them we had. They responded not to slow until told to do so and not to do it again; but no harm this time. When we slowed from 180 [kts] to landing speed at the final approach fix; we had closed to approximately three miles from the 757. Wind reported with landing clearance had an unplanned gust (090/8G14). On short final; I noticed airspeed rapidly increasing to plus 15 kts and pulled thrust back. As I added thrust to capture landing airspeed; we got the automated sink rate caution. I adjusted aim point slightly; to account for the sink rate since thrust was already coming back in. Crossing the runway threshold; airspeed was stable within 10 kts of target and sink rate was commensurate with a normal approach. Landing was normal.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.