B757 Undifferentiated or Other Model
Air Traffic Control Fully Certified
Situational Awareness
ATC Issue All Types; Deviation / Discrepancy - Procedural Published Material / Policy
General None Reported / Taken
Procedure
A B757 was on a right downwind for ILS 10L at 4;000. He was turned in to follow another aircraft; join the LOC and cleared. An A321 was on a right downwind following the B757 but for the ILS Runway 10R. The B757's descent performance from where he was cleared from 4;000 to 3;000 was at least lackluster. The A321 was turned base behind the B757 for [Runway] 10R; however; apparently there was a 'wake remnant' from the B757 for [Runway] 10L that according to TARP was at 3.9 miles.  The lackluster descent by the B757 along with the descent clearance of the A321 led to a 'wake remnant' situation. One change in the procedure at PDX is that usually aircraft are told to expect runway assignments that are closer to their gate. This is to help expedite arrivals to their gate and to assist the Tower in preventing problematic taxi situations. Since the runways are almost the same length; it might be best to put aircraft on a north downwind to the north runway and the south downwind to the south runway. This would help avoid runway crossover situations such at the event above. In addition; in STARS; there is no tool/ software application to measure 'wake remnant' of any aircraft. It seems there should be a tool for controllers to be able to judge where the remnant is such as a 'bread crumb' trail with an altitude associated with the last 'crumb' so that controllers can avoid this situation. Wake turbulence can be a serious issue and if it is necessary to measure performance via programs such as TARP; it would seem that prevention of the potential safety issue should be addressed and prioritized to provide controllers with capable tools to measure this.
P80 Controller voiced concern regarding the 'Wake Remnant' issue and the fact that controllers are expected to provide separation when no tool is avaiable to detect same.