TRACON controller providing OJT elected to partially take over the position to demonstrate a seldom ...

Narrative:

Training session on final; I was the trainer. There was a full down wind; when aircraft X came on frequency. The aircraft X asked for runway xx; which meant I had to take him over the top of runway yyl and runway yyr finals. This is a common practices. The trainee was unsure so I told him I would do it and he could watch. There were two aircraft on final at 080 on a visual approach. I turned aircraft X base over top at 090. Prior to that the developmental cleared aircraft Y for a visual approach to runway yyl off the downwind. The aircraft Y started base and descended out of 090. Aircraft Y turned a short base and started to cut off the aircraft X. I don't know if separation was lost. But as aircraft Y turned toward aircraft X; he was able to get visual separation. It was close to 3 miles. There was divergence and visual separation but at what point I am unsure. Both aircraft continued to the airport without further incident. My recommendation is during training; if I am going to take over; I should take everything over. I was still letting the developmental work other aircraft. This caused me to lose track the aircraft he had cleared. If I was working everything this would have never been an issue.

Original NASA ASRS Text

Title: TRACON Controller providing OJT elected to partially take over the position to demonstrate a seldom used technique; ultimately resulting in a near loss of separation event.

Narrative: Training session on Final; I was the trainer. There was a full down wind; when Aircraft X came on frequency. The Aircraft X asked for Runway XX; which meant I had to take him over the top of Runway YYL and Runway YYR finals. This is a common practices. The trainee was unsure so I told him I would do it and he could watch. There were two aircraft on final at 080 on a Visual Approach. I turned Aircraft X base over top at 090. Prior to that the developmental cleared Aircraft Y for a Visual Approach to Runway YYL off the downwind. The Aircraft Y started base and descended out of 090. Aircraft Y turned a short base and started to cut off the Aircraft X. I don't know if separation was lost. But as Aircraft Y turned toward Aircraft X; he was able to get visual separation. It was close to 3 miles. There was divergence and visual separation but at what point I am unsure. Both aircraft continued to the airport without further incident. My recommendation is during training; if I am going to take over; I should take everything over. I was still letting the developmental work other aircraft. This caused me to lose track the aircraft he had cleared. If I was working everything this would have never been an issue.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Attributes
ACN	970562
Time
Date	201109
Local Time Of Day	0001-0600
Place
Locale Reference	ZZZ.TRACON
State Reference	US
Aircraft 1
Make Model Name	Citation II S2/Bravo (C550)
Flight Phase	Descent
Route In Use	Vectors
Flight Plan	IFR
Person 1
Function	Departure Approach
Qualification	Air Traffic Control Fully Certified
Events
Anomaly	ATC Issue All Types Deviation - Procedural Published Material / Policy

TRACON controller providing OJT elected to partially take over the position to demonstrate a seldom used technique; ultimately resulting in a near loss of separation event.