MD-83
Air Traffic Control Fully Certified
ATC Issue All Types; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance
General None Reported / Taken
Human Factors
ZZZ was in a South flow configuration. My Trainee and I were working Arrival 1 and 2 combined which turns final to Runways 17L and 17C. Runway 17R is used for departures and not normally given to aircraft unless an emergency situation exists. Aircraft were slow on final today with an indicated airspeed of 100 to 110 KTS inside the FAF. We were notified that a medical emergency from Center was inbound from the East and would be landing. The medical emergency was Air Carrier X; an MD83. When Air Carrier X appeared on the scope; we took the hand off and he checked in at 5;000 feet. At this time we had Air Carrier Y; an MD82 on final to Runway 17C level at 3;000 feet; but cleared for the visual approach. I instructed the Trainee to get Air Carrier Y down to 2;000 feet so we would be able to base Air Carrier X above and behind them at 3;000 feet for Runway 17R. Air Carrier X was direct the final approach fix for 17R (the final approach fix is approximately 5 North of the airport). I noticed Air Carrier Y was already being affected by the winds and their indicated airspeed was around 140 KTS and slowing and Air Carrier X was remaining fast at around 250 KTS. I then descended Air Carrier X to 3;000 feet. Air Carrier Y was on about an 8 mile final and I determined lateral spacing would not exist without the use of visual separation. I was able to move Air Carrier Y out further to Runway 17L to allow more room for the emergency (Air Carrier X). Air Carrier Y was reaching their final approach fix for 17L and slowing; Air Carrier X was approximately 12 flying miles from the airport still going fast; and I began issuing traffic to both aircraft. After about two traffic calls to each aircraft; I began to plan to break Air Carrier Y off their approach in order to get Air Carrier X down quicker and expedite their landing since neither aircraft would report the other in sight. Then Air Carrier X began descending on his own out of 3;000 feet. I quickly issued traffic to Air Carrier Y on the final and asked them to report traffic in sight; which they did. I instructed Air Carrier Y to maintain visual separation from Air Carrier X and that they would pass above them. Air Carrier X then called their traffic in sight; which I quickly applied visual separation and gave a visual approach clearance to Air Carrier X for Runway 17R and shipped them to Tower. Air Carrier Y was then shipped to Tower. Before visual separation was applied; Air Carrier X had descended without clearance to 2;600 feet with Air Carrier Y level at 2;000 feet. I do not know if lateral separation was ever lost. I reported the event to the Supervisor who was already behind me monitoring the situation. Management reviewed the tapes and the video recording and told me that all read backs and instructions were correct and accurate and that the pilot did in fact descend on their own. The pilot of Air Carrier X called a few minutes later and spoke with management about the incident. Air Carrier X said they descended without clearance because they were concerned that they might be above the glide slope. I wish I had a recommendation that would prevent this incident from reoccurring; but I don't. Pilots must trust us or communicate to us that they need something different that what's being given. I thought; as well as others around me; that we had expedited the arrival of the emergency the best that could be done; taking into account the surrounding traffic in the area.
TRACON Controller described a very complex parallel runway landing event involving a crossover to accommodate a medical emergency aircraft; noting after applying appropriate separation clearances one aircraft descended resulting in a conflict situation.