B737-400
Situational Awareness
ATC Issue All Types; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Wake Vortex Encounter
Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Environment - Non Weather Related; Human Factors
Upon descent into LAX on the SADDE 6 arrival we were assigned speed 250 KTS over SYMON. Shortly after SYMON; we were given the speed 220 KTS. We then began to get light to moderate wake turbulence due to the aircraft ahead of us showing less than 5 miles separation on our TCAS. The Captain began slowing to give us more separation from our traffic. Shortly before SMO VOR we were queried on our speed. We were at 200 KTS and stated so. The Controller told us to speed up to 220 KTS to which we promptly did. The flight continued the arrival and approach with no further incident. The Captain spoke with the supervisor at SoCal Approach over the phone and explained his intentions. The primary cause of this event was our airplane entering an area of wake turbulence from the aircraft ahead of us. Based on our TCAS; it appeared we were less than 5 miles from them. The Captain began to slow in order to give space and lessen the turbulence. Our failure was to inform ATC of our speed reduction.
B737-400 First Officer reported deviating from ATC assigned speed when they encountered wake turbulence from preceding aircraft on arrival to LAX.