Narrative:

ZZZ is on a north operation; runway xxl and xxr; simultaneous visuals and runways more than 4300 ft apart. Training in progress. My trainee turned aircraft X onto the final for xxr from the southwest at 3000 ft descending to 2600 ft. Soon after he then turned aircraft Y from the opposite downwind to base turn descending to 3000 ft from 4000 ft. I asked my trainee if he thought he would have 5 miles behind the heavy and he thought that because the aircraft were going to different runways that 5 miles was not necessary because aircraft Y would not be operating behind the heavy. I replied well yes it will be; momentarily; while he is the base turn; he will fly through the heavy's wake. I said continue working and we will talk about it later. I thought he would have his 5 miles and continued to let the trainee work. I should have stepped in and given aircraft Y a slight turn to the southwest to build in more space. Because aircraft X was going to the right runway and flying from the southwest and aircraft Y was doing exactly opposite of that aircraft Y didn't end up hitting the wake until right before joining the final for runway xxl while they were both the same altitude.while my trainee and I discussed whether wake turbulence was a factor; this took our attention away from the scope for a short time. I knew that I was in the right matter and should have turned aircraft Y away from the wake instead of watching it and thinking the separation will be there. I will not be hesitant to do so in the future.

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Original NASA ASRS Text

Title: Approach Controller reported his trainee failed to follow established procedures and as a result a B717 encountered wake turbulence from an MD11 on approach.

Narrative: ZZZ is on a north operation; runway XXL and XXR; simultaneous visuals and runways more than 4300 ft apart. Training in progress. My trainee turned Aircraft X onto the final for XXR from the southwest at 3000 ft descending to 2600 ft. Soon after he then turned Aircraft Y from the opposite downwind to base turn descending to 3000 ft from 4000 ft. I asked my trainee if he thought he would have 5 miles behind the heavy and he thought that because the aircraft were going to different runways that 5 miles was not necessary because Aircraft Y would not be operating behind the heavy. I replied well yes it will be; momentarily; while he is the base turn; he will fly through the heavy's wake. I said continue working and we will talk about it later. I thought he would have his 5 miles and continued to let the trainee work. I should have stepped in and given Aircraft Y a slight turn to the southwest to build in more space. Because Aircraft X was going to the right runway and flying from the southwest and Aircraft Y was doing exactly opposite of that Aircraft Y didn't end up hitting the wake until right before joining the final for runway XXL while they were both the same altitude.While my trainee and I discussed whether wake turbulence was a factor; this took our attention away from the scope for a short time. I knew that I was in the right matter and should have turned Aircraft Y away from the wake instead of watching it and thinking the separation will be there. I will not be hesitant to do so in the future.

Data retrieved from NASA's ASRS site 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.