Date: 201512
Local time of day: 1801-2400
Location: ASE.TRACON, CO
Light: Night
Aircraft: SR22
Operating under: Part 91
Flight plan: IFR
Flight phase: Descent
Airspace: Class E ASE
ATC / advisory: TRACON ASE
Second aircraft: Cessna Citation Sovereign (C680)
Reporter organization: Government
Reporter function: Approach; Instructor
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Time Pressure; Training / Qualification; Situational Awareness; Communication Breakdown; Distraction
Second reporter function: Approach; Trainee
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Air Traffic Control
When detected: In-flight
Contributing factors: Human Factors; Procedure
Primary problem: Procedure

Narrative: I was acting as On the Job Training Instructor (OJTI) for a developmental controller on the terminal control position. Another controller was acting as our handoff. Denver Center requested Aircraft X to enter our airspace at FL170 and outside of the arrival gate. Handoff approved this request from ZDV. I did not hear the request and handoff did not ask me or the developmental if we would approve it. Aircraft X checked on and was kept at FL170 and given a heading of 110 to be sequenced. On heading 110; Aircraft X must be kept at or above FL170 because the heading took him directly over our SID which takes departures to FL160. The developmental keyed up to descend Aircraft X to FL160 and during the transmission I raised my voice at the developmental to keep the aircraft at FL170. The trainee corrected his instruction to FL170 in the same transmission and Aircraft X did not hear it. Aircraft X responded before the developmental had said FL170 and therefore they were talking at the same time. Aircraft X was heard on the tapes saying '...six-thousand...' Aircraft X went on to make a suggestion that I proceed straight-in VFR to the airport and was told to continue heading 110 but was again told to descend to FL160 by the trainee. I corrected him again; the developmental corrected himself but Aircraft X was already descending from the first time he was told FL160. I stepped in; issued a traffic alert to Aircraft X and instructed him to climb immediately. Aircraft X lost lateral and vertical separation with a departure Aircraft Y. I reviewed the tapes with the ATM [Air Traffic Manager] and saw on the replay that they came within 1.48 miles and 600 feet of each other. Better communication on the part of handoff controller. Better control of the situation by me; the OJTI. Better listening on my part and developmental's part to ensure correct read back of instructions.


Second narrative: Aircraft Y was on a missed approach due to weather climbing to 160 when Aircraft X was crossing over the departure corridor at 170. I accidentally descended Aircraft X to 160 and my trainer told me to fix it. I tried but was unable to reach him and Aircraft X was observed descending. My trainer then took over and issued a safety alert and climbed Aircraft X back up to 170.I made a mistake in training and my trainer took over when he should have. I don't recommend any changes.


Synopsis: ASE TRACON Instructor and Developmental reported of a loss of separation due to a read back error. Developmental descended an aircraft incorrectly; Instructor caught it and told Developmental to fix it. While transmitting the pilot transmitted also responding to descent given in error. Separation was lost between arrival an missed approach aircraft.