Date: 201510
Local time of day: 1801-2400
Location: IAD.Airport, DC
Light: Night
Aircraft: EMB ERJ 190/195 ER/LR
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Takeoff / Launch
Airspace: Class B IAD
ATC / advisory: Tower IAD
Second aircraft: B737 Undifferentiated or Other Model
Reporter organization: Government
Reporter function: Local
Reporter qualification: Air Traffic Control Developmental
Human factors: Situational Awareness; Distraction; Time Pressure
Anomaly: ATC Issue All Types; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Separated Traffic; Flight Crew Executed Go Around / Missed Approach
Contributing factors: Human Factors; Procedure
Primary problem: Procedure

Narrative: Evening Departure Bank: Departing Runway 30 and arriving and departing Runway 01C. I was receiving OJTI on Local 2; which was responsible for Runway 01C. I cleared a Heavy Jet for takeoff and then advised Aircraft X to Line Up and Wait on Runway 01C for Wake Turbulence separation and then issued traffic of a B737 on an eight mile final. I then cleared Aircraft Y to land on Runway 01C; issued traffic of the aircraft in Line-Up and Wait on the runway; and Instructed the pilot to reduce to his final approach speed. While I was waiting to achieve the required Wake Turbulence spacing between Aircraft X and the Heavy that departed prior; I noticed the Aircraft Y was still indicating 170 knots at about 3 and a half mile Final. I then instructed Aircraft Y to make an S-Turn to the east for spacing; which the pilot complied. Then I cleared Aircraft X for Immediate takeoff. As Aircraft X was rolling and passing the 6;000 feet point on the runway; Aircraft Y was approaching the landing threshold. My monitor began prompting me to do something quickly with Aircraft Y so I began to Issue Go-Around instructions to Aircraft Y. While in the process of issuing the instructions; I noticed that Aircraft X had become airborne as Aircraft Y was about to cross the landing threshold so; in the same transmission; I said; 'Aircraft Y Go-Around for Traffic on the Runway; Disregard.' However; my monitor instructed me to re-issue the Go-Around instructions to Aircraft Y; who had already started to Go-Around. I then re-issued the Go-Around instructions and told Aircraft Y to turn left heading 340 and climb and maintain 2;000. I advised the Departure sector of the go-around and told them that I will continue his climb to 3;000 feet.I recommend that the IAD training department create simulations in the lab that covers departing and arriving the same runway. Then they can ensure that all CPC's and DEV's become thoroughly familiar with this type of operation; seeing as we do not conduct this operation very often.




Synopsis: IAD Developmental Controller reported a departure flight was held in takeoff position for wake separation; so controller delayed arrival flight with S turns. When departure was released; the separation continued to close so the Controller issued go-around only to change mind while in same transmission and advised arrival to disregard. Instructor mandated that developmental send aircraft around.