B737 Undifferentiated or Other Model
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 2
Distraction
ATC Issue All Types; Conflict Airborne Conflict; Deviation - Speed All Types; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Separated Traffic
Procedure; Human Factors
Aircraft X was vectored onto a 10 mile ILS Runway 6. 6 nm in trail Aircraft Y was vectored onto a 11 mile ILS Runway 6. Both aircraft were in a constant high speed descent from initial contact so no speeds were issued because it would have been impossible to slow and still make the approach altitude. Aircraft Y was approximately 6 miles behind Aircraft X when turned onto final. I knew of the speed difference; at the time Aircraft X was indicating about 170 on a 5 mile final. Aircraft Y was indicating about 270 turning onto the 11 mile final. I had two IFR popups that had to be issued around the same time. I issued one and then took a coordination call from ZBW about a conflict they were pointing out between two aircraft they had just handed me off at 070; both just on the border of my airspace. I observed the continued speed overtake just before I took the call but thought that Aircraft Y would be slowing anyway and that I would have time to take the call; then go back and adjust speed if necessary. After hanging up I observed Aircraft Y on a 5 nm final indicating 260KT with Aircraft X about 4 nm ahead indicating 140KT. I issued reduce speed to 170KT to Aircraft Y; to which I received the reply; 'we are slowing' leading me to believe they were already trying to slow down but not very successfully due to the rate of descent. At 3.3 nm separation I cancelled Aircraft Y approach clearance and climbed and turned him to the North. Separation decreased to 2.83 nm and 900ft prior to divergence. In this situation I trusted that Aircraft Y would be slower than they actually were due to the proximity to the airport but the high speed descent prevented that from happening. Due to volume and complexity I elected to turn them on final 6 nm behind Aircraft X rather than go through and turn right back because I didn't have time to explain and issue that; and thought that the distance would be adequate with a normal approach speed. A lack of airspace contributed to the high speed descent. I was unable to turn Aircraft Y to the right to make a longer final due to airspace; unable to turn left prior to that because of crossing traffic and I was worried about going through the final due to parachute jumping 5 SE of the final approach course on Aircraft Y's current heading. The design of the airspace and routes in this area is inherently flawed. Both Aircraft X and Aircraft Y were taken off a descend via clearance due to crossing traffic just ahead handed off from ZBW as well; I had to call them to request the heading prior to handoff. On this arrival routing conflicts are built in because of crossing traffic right at the sector boundary. Until ZBW puts the aircraft in handoff status we are not aware of the potential conflicts; requiring almost no preplanning time and immediate call for alternative action upon seeing the handoff flash. Further complicating the situation is the MHT arrivals are on a VNAV descent where the conflict point is not always known and vertical separation cannot be ensured. I recommend changing the arrival STAR by pushing it north by 5nm to deconflict this area. On Runway 6 there is little to no opportunity to sequence aircraft because of the airspace limitations; crossing traffic and parachute activity. Speed control is highly ineffective because of the high speed descent profile and short distance to the final approach course from initial contact.
A90 TRACON Controller reported of a loss of separation of final due to speed control. Controller observed aircraft on final and slowed the following aircraft. Following aircraft did not slow as fast as the controller anticipated. Controller attempted to save the operation by removing the following aircraft off of final; but did so too late.