D10 controller providing OJT experienced a loss of separation event when an aircraft accepted the wr...

Narrative:

Conducting training on the position. Developmental assigned the E145 descent to 9;000. Several scans later I observed the E145 indicating mode C of 10;900 then 10;800. I issued an immediate climb to 110 to the E145. Crossing traffic was less than 3 miles away being worked by DR3; indicated 9;900. The wrong aircraft may have accepted the descent. I am not even sure that this aircraft was descending; but I cannot be certain that I heard the read back from the correct aircraft. I am quite certain that the developmental issued the descent to the correct aircraft. I am not sure that the correct aircraft acknowledged. The wrong aircraft may have started an early descent. The two aircraft shared similar digits and I should have been more focused on the acknowledgment. It was quite slow and I let myself get distracted by the low volume and complexity.

Original NASA ASRS Text

Title: D10 Controller providing OJT experienced a loss of separation event when an aircraft accepted the wrong altitude assignment; both the instructor and student controller apparently missed the read back.

Narrative: Conducting training on the position. Developmental assigned the E145 descent to 9;000. Several scans later I observed the E145 indicating Mode C of 10;900 then 10;800. I issued an immediate climb to 110 to the E145. Crossing traffic was less than 3 miles away being worked by DR3; indicated 9;900. The wrong aircraft may have accepted the descent. I am not even sure that this aircraft was descending; but I cannot be certain that I heard the read back from the correct aircraft. I am quite certain that the Developmental issued the descent to the correct aircraft. I am not sure that the correct aircraft acknowledged. The wrong aircraft may have started an early descent. The two aircraft shared similar digits and I should have been more focused on the acknowledgment. It was quite slow and I let myself get distracted by the low volume and complexity.

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	918197
Time
Date	201011
Local Time Of Day	1801-2400
Place
Locale Reference	DFW.Airport
State Reference	TX
Aircraft 1
Make Model Name	EMB ERJ 145 ER&LR
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Flight Plan	IFR
Person 1
Function	Instructor Approach
Qualification	Air Traffic Control Fully Certified
Events
Anomaly	ATC Issue All Types Conflict Airborne Conflict Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Published Material / Policy

D10 controller providing OJT experienced a loss of separation event when an aircraft accepted the wrong altitude assignment; both the instructor and student controller apparently missed the read back.