B737-700
Flight Crew Last 90 Days 174
Deviation - Speed All Types; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Wake Vortex Encounter; Inflight Event / Encounter Weather / Turbulence
Flight Crew Took Evasive Action
Environment - Non Weather Related; Procedure
On transition to the ILS 24R after the SEAVU Arrival; we were cleared for the ILS approach and asked to maintain 180 KTS to JETSA. We had already received moderate turbulence from a preceding heavy 757 going to the south complex. We were asked to maintain visual separation from that aircraft and then were given additional traffic turning onto the ILS 24R in front of us; a 747 jumbo and were told by ATC 'Caution; Wake turbulence' (All this with low visibility requiring ILS approaches.) Additionally; we had a slight quartering headwind than generated just enough crosswind to put the wake turbulence in our path. As the pilot flying I perceived on the TCAS we were gaining didn't have enough separation to prevent another wake turbulence event. Thus; I slowed 20 KTS and began flying one dot high on the ILS glideslope. Cockpit workload was high and the radios were busy and the Captain was unable to advise ATC; who then asked what our speed was and complained that he had to slow following aircraft. Perhaps we could have cut in on the radio and advised ATC of the decision to slow for safer separation. I believe that in this case ATC at LAX paid lip service rather than actual respect of the seriousness of the wake turbulence threat. My perception is that they are far more concerned with running a standard spacing than providing safe separation from wake turbulence. I'm not sure what 'caution wake turbulence' even means if they don't want pilots doing anything about wake turbulence. It also seems inappropriate to ask pilots to maintain visual separation from aircraft on the ILS with two miles of visibility while at the same time issuing cautions for wake turbulence from multiple preceding aircraft with speed assignments that generate closure. Thankfully; we were able to avoid wake turbulence from the 747 that would have been worse than what we had just experienced from the 757 only seconds before. Safe separation behind 747s; not a compact final; should be everyone's objective.
[Narrative 2 contained no additional information.]
B737-700 flight crew; after encountering wake from preceding B757; deviated from assigned speed on arrival to LAX to avoid further wake turbulence.