MD-88
Flight Crew Flight Engineer; Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 250; Flight Crew Total 15000; Flight Crew Type 2500
Deviation - Speed All Types; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Wake Vortex Encounter
Flight Crew Regained Aircraft Control
Procedure; Environment - Non Weather Related
The ATL weather was reporting a ceiling of 300 FT overcast and 1/2 mile of visibility in fog. Due to the low ceiling and visibility we planned on a CAT 2 ILS with an automatic landing. Upon arrival into ATL we were vectored behind a B757 and told to slow to 180 KTS; on the TCAS we appeared to be about 4 NM behind them. As we were turning to intercept the ILS to Runway 27L the aircraft rolled into a 40 degree banked turn to the right and the autopilot disconnected. Corrective flight control inputs were applied to roll wings level and the aircraft rolled past level to 30 degrees to the left. ATC must have sensed that we were too close they then instructed us to slow to 170 KTS to the DEPOT. As we began our descent on the glide slope near SEJAY the aircraft again rolled 30 degrees to the right and the autopilot disconnected again. The aircraft was recovered and the automation restored. At this point the aircraft was approximately 2 NM prior to DEPOT and we assumed that the ATC speed correction to 170 would provide us with adequate separation. We appeared to be closing in on the B757 so I rolled the speed back 10-15 KTS in an attempt to get the 5 NM of separation. The radios were so busy that we did not have a chance to inform the Controller of our speed reduction. I wanted to prevent another wake turbulence encounter this time we would be in the clouds and closer to the ground. Approaching the DEPOT ATC queried us as to our speed and the First Officer responded that we had slowed down due to wake turbulence. The Controller responded; 'I told you to maintain 170 KTS to DEPOT! THERE IS NO WAKE TURBULENCE!' At this point we were over the DEPOT and I instructed the First Officer to contact the Tower. I realize that our slowing might have impacted the spacing making his job more difficult; however I think it was more important and safer to slow down to avoid another potential upset in IMC. Our flight continued to landing with no further upsets and landed uneventfully.
MD-88 Captain reported wake vortex encounter inbound to ATL that resulted in enough roll to cause the autopilot to disconnect. When he slowed to increase spacing he was chastised by ATC.