Date: 201701
Local time of day: 1201-1800
Location: SCT.TRACON, CA
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: Small Aircraft; Low Wing; 2 Eng; Retractable Gear
Operator: FBO
Operating under: Part 91
Flight plan: VFR
Mission: Training
Flight phase: Descent
Airspace: Class C ONT
ATC / advisory: TRACON SCT
Second aircraft: Any Unknown or Unlisted Aircraft Manufacturer
Reporter organization: FBO
Reporter function: Instructor
Reporter qualification: Flight Crew Flight Instructor; Flight Crew Commercial; Flight Crew Instrument; Flight Crew Multiengine
Human factors: Confusion; Communication Breakdown; Distraction; Situational Awareness; Training / Qualification
Anomaly: ATC Issue All Types; Airspace Violation All Types; Conflict Airborne Conflict; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Detector: Person Flight Crew; Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew Took Evasive Action
Contributing factors: Human Factors; Procedure
Primary problem: Procedure

Narrative: I was flying long cross country to Chino via Ontario and Ramona and with touch and go landings at Ontario and Ramona. As soon as we cleared the mountains; we started our descent from 11500 feet. SoCal Approach (app) asked us what altitude we were going to descend down to. We said 4000. As Ontario Airport appeared from behind the clouds and was getting close; we started to descend to below 4000.Approach told us to fly heading 090; which we thought was going to put us to a right downwind entry for 26R. A few seconds later; app told us to fly heading 130. A few seconds later; we realized that 130 heading would take us across the departure corridor of Ontario runway 26 and we saw a jet just taking off. As soon as we saw the airplane; for safety reasons; we requested resume own navigation to avoid the traffic and we told Approach we have the airport insight. Upon approval; we turned back north away from the departure corridor to the northeast to avoid the departing traffic. That's the moment when we realized that Approach didn't know we were going to land at Ontario and that's the moment when Approach realized we were going to land at Ontario. Approach asked us what altitude we were going to descend down to. We said pattern altitude at 2000. He told us we should have informed him before descending through 4000. He told us to contact tower. We were on the right downwind at 2000. We got a possible pilot deviation warning from Ontario Tower and SOCAL Approach. We called SOCAL quality control when we landed at Ramona. SOCAL told me that we showed on the jet's TCAS. It's a case of lost separation. SOCAL was going to listen to the tape and investigate. After I got back from the flight; I talked to our chief instructor. We should have been more careful when in the unfamiliar LA area and notified the ATC for altitude changes. I should have clarified more when there's a suspected confusion. I briefed my student and we talked about the incident. We learned from the case that we need to more cautious and listen more carefully and notify ATC of the altitude change. I also talked with other instructors so we could help prevent similar situations in the future.




Synopsis: Instructor pilot reported a loss of separation due to confusion on where they wanted to land. Their aircraft came close to aircraft departing ONT. Pilot did not advise ATC prior to descending that they wanted to land at ONT.