Date: 201504
Local time of day: 1801-2400
Location: NCT.TRACON, CA
Light: Night
Aircraft: Large Transport
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Climb
Airspace: Class B SFO
ATC / advisory: TRACON NCT
Second aircraft: Helicopter
Reporter organization: Government
Reporter function: Departure; Instructor
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Confusion; Distraction; Situational Awareness; Training / Qualification; Workload
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Air Traffic Control Separated Traffic
Contributing factors: Human Factors; Procedure
Primary problem: Human Factors

Narrative: While providing OJT to a student; I had to correct control instructions that the student issued which were not safe. Aircraft X and Aircraft Y were both departures off of OAK heading northwest bound climbing to 5;000 feet. The student turned Aircraft X to the North (right) putting the aircraft in a converging course with Aircraft Y. I then keyed up and issued turns back to the left to Aircraft X so as to keep the two aircraft on parallel courses until vertical separation could be established. This action taken by me returned the aircraft to parallel courses with adequate separation.   Shortly after correcting this poor decision made by the student; the student once again turned Aircraft X to the north again creating an unsafe converging situation. What will not be heard on any play back tape is my questioning of the student about what was going on. I was awestruck that the student just repeated the error I just corrected and assumed I must have missed something.   Perhaps the student had assigned an amended altitude of 4;000 feet to the Aircraft Y; perhaps the student had climbed Aircraft X above 5;000 feet. Upon realizing that I had not missed a control instruction; I concluded that both aircraft were still assigned the same altitude of 5;000 feet and that separation was in jeopardy.     I attempted to issue a climb to Aircraft X and a turn to Aircraft Y. In both cases; I had to issue the instructions numerous times as the frequency was being blocked by a VFR aircraft repeatedly calling for flight following. After some effort both aircraft acknowledged the corrective control instructions but not be separation was reduced to about 2.8 miles and 500 feet.   If a trainee issues unsafe control instructions perhaps they should be prevented from issuing any control instructions for a brief period of 1-3 minutes until the instructor and student have a few moments to discuss the decision. If a policy was in place that stated that if an instructor has to overkey a student to ensure separation the student should only monitor the frequency the student would not have had the ability to complicate the situation with additional poor decisions. I don't know if this has to be a formal policy; but I will tell students that I train that they are not to transmit after being overridden by me until I give them permission to do so. This will allow me to get regain control of the sector and not be second guessing what the student may have done.




Synopsis: NCT Controller; while instructing; observes the Developmental turn an aircraft into the flight path of another aircraft at the same altitude. The instructor fixes the problem by turning the aircraft back to previous heading. Minutes later the Developmental issues the same turn to the same aircraft. Instructor thought he might have missed an altitude climb or descent; but did not.  Due to frequency congestion the instructor could not save the loss of separation.