ZJX Controller described a loss of separation event at the boundary between enroute and terminal when the leading aircraft apparently slowed below assigned speeds; the reporter recommending a transition area between centers and terminals allowing for reduced separation standards.
Synopsis
ZJX Controller described a loss of separation event at the boundary between enroute and terminal when the leading aircraft apparently slowed below assigned speeds; the reporter recommending a transition area between centers and terminals allowing for reduced separation standards.
Narrative
I was training on the RADAR as a CPC-IT. I had 4 aircraft handed off to me with minimal separation and had to space them for arrival to MCO. An A321 was leading the group and was assigned 300 KTS until reaching LAMMA where they needed to slow to 250 KTS. A B737 was the next aircraft and was initially assigned 280 KTS and a 20 degree right turn for spacing. I then issued the B737 a 140 heading because the aircraft was getting too close to an adjacent sector. I then issued the B737 a clearance direct LAMMA and maintain 300 KTS once I had about 7 miles because of following traffic 7 miles behind the B737. I then handed off the A321 and transferred communication to MCO Approach (F11). At that time; the B737 had an overtake of about 20 KTS. The next few RADAR hits showed speed differences of 30; 50; and then 70 KTS creating a bad overtake situation. I think it is possible that the RADAR was not giving accurate; or up to date; ground speeds or that MCO Approach slowed the A321. MCO Approach was in communication with both aircraft at the time of incident. I believe it would be helpful to have a separation requirement of 3 miles entering the terminal environment from the enroute. In this case; the RADAR was less than 40 miles from the incident.
Second reporter narrative
I was training a controller. Rides were constant light to moderate chop and turbulence at most of the middle altitudes. The A321 came over at 240 and the B737 was descending to 340 from 400 with right at 5 miles. We descended the B737 and assigned a slower speed; but we still had to vector him twice to stay behind the A321. The crossing restriction was LAMMA at 120 and 250 KTS. The A321 was asked to keep the speed up until they needed to slow. The B737 I thought slowed down to much; because we had another aircraft behind in the sequence. The B737 was 7 behind the A321 and we increased his speed back up to the same speed as A321 and to cross the fix at 120 and 250 KTS. LAMMA is the fix on the Approach Control boundary. We switched the A321 and when the B737 was one minute from the fix he was 20 KTS faster than the A321 with 6 miles between. The next update was 30 KTS; then 40 KTS; then 70 KTS. The B737 was already below 130 and the A321 was in approach airspace descending. We then told the B737 to slow to 250 KTS and shipped them. I don't know if Approach slowed the first aircraft in the airspace. Create a 3 mile box so separation can go below 5 when needed and so you get better updates on ground speed. Change LOA to cross the fix then slow to 250 KTS so that the speed transitions in approach airspeed where they only need 3 miles.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.