Date: 201812
Local time of day: 0601-1200
Location: ZME.ARTCC, TN
Light: Dawn
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Cargo / Freight / Delivery
Flight phase: Climb; Takeoff / Launch
Airspace: Class A ZME
ATC / advisory: Center ZME
Second aircraft: B737 Undifferentiated or Other Model
Reporter organization: Government
Reporter function: Departure
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Workload; Situational Awareness
Anomaly: ATC Issue All Types; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Separated Traffic
Contributing factors: Human Factors; Manuals; Procedure; Airspace Structure; Company Policy
Primary problem: Procedure

Narrative: Aircraft X AND Aircraft Y were one of three pairs of departures coming out of the TRACON airspace where separation was not ensured by the Departure Controller and the Center Controller had to take steps to separate airplanes that should have already had separation ensured. These two aircraft were climbing out with minimum separation and an overtake developing. When I queried the back aircraft if he had been assigned an airspeed; he replied 'yes; but the last controller gave us normal speed before he shipped us.' While this technique may technically be legal and may not require coordination; it is going to create unsafe operations if left unchecked. I believe the Approach Controller just didn't want to coordinate speeds so they resumed the aircraft instead of making a phone call.The next pair were unnecessarily close on departure with an overtake in progress. I asked the pilot of the back airplane if he took off immediately behind the one I slowed him for; and the pilot responded affirmative. The procedure of aircraft on similar/identical routes departing sequentially appears to be commonplace when it doesn't have to be. There are over one hundred departures coming out in a couple hours' time. I find it hard to believe that Tower can't apply 'route splitter' techniques so that these planes don't have to be delayed in the air or require constant monitoring across three states.Another pair that came out needed intervention. Separation was 5 miles in tail with an overtake. The Approach Controller didn't switch communications with one of the aircraft in a timely manner so that aircraft leveled off at 16;000 feet. To avoid a loss; I stopped the front aircraft at 13;000 feet to let the back aircraft climb and eventually get out of the way.In all three situations; if I had done nothing; standard separation would NOT have been maintained. The TRACON/Center Letter of Agreement requires that Approach deliver 5 miles in trail standard or increasing. They are consistently putting an MD11 out behind a DC10; or the new B767 which performs better than anyone is expecting behind a 757 or heavy Airbus.Scenarios like these are becoming commonplace; and I am only submitting because telling my Supervisor and him calling Approach to tell them about these issues is not working.I suggest require route splitters on heavy volume company departure pushes unless an aircraft would be unduly delayed. Change the TRACON/Center Letter of Agreement so that speed assignments need not be verbally coordinated during the midnight shifts. Also; familiarization trips to the ARTCC for the TRACON controllers to see what their separation looks like; and what else is going on in our airspace that diverts our attention away from their lack of separation. Involve Company in the discussion and get them to not send two airplanes with the same departure/flight plan route out sequentially.




Synopsis: ZME ARTCC Controller reported the TRACON controllers were not providing sufficient in trail spacing between departures.