Date: 201501
Local time of day: 1801-2400
Location: U90.TRACON, AZ
Light: Night
Aircraft: Fighter
Operator: Military
Operating under: Part 91
Flight plan: IFR
Mission: Tactical
Flight phase: Climb
Airspace: Class E U90
ATC / advisory: TRACON U90
Second aircraft: Medium Large Transport
Reporter organization: Government
Reporter function: Instructor; Approach
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Situational Awareness; Confusion; Communication Breakdown; Training / Qualification
Second reporter function: Trainee; Approach
Anomaly: Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Air Traffic Control Separated Traffic
Contributing factors: Procedure; Human Factors
Primary problem: Human Factors

Narrative: Training in progress; we were working departure; west radar and satellite combined; moderate VFR conditions. Aircraft X eastbound restricted to 10;000 feet with Aircraft Y also eastbound climbing above Aircraft X. The trainee restricted Aircraft X at 10;000 feet; at some point the pilot asked for a block altitude 9000 feet block 10;000 feet; the trainee responded 'I have your request'; it was never approved. The trainee started to fall behind; there was a lot of frequency congestion on multiple frequencies. The amount of traffic and frequency congestion was beyond the trainee's capability so I took the frequencies. Aircraft X was blocked on the frequency at least once but I knew he was restricted below Aircraft Y and I had higher priority transmissions. I heard the controller-in-charge (CIC) ask what Aircraft X was doing; I saw him at 103 and immediately descended him back to 10;000 feet; I gave him the brasher warning. The Pilot stated that I didn't answer him so he decided to climb (paraphrasing). I never saw a loss of separation; the closest altitudes were 10;700 feet and 11;700 feet.Although this was not a result of a phraseology error; I did review 'On request' phraseology with the trainee. I don't believe the pilot was confused about the altitude restriction. The pilot did not receive a reply from ATC due to frequency congestion and decided to climb. Even if I would have taken control of the position and frequencies sooner; it would not have prevented this situation because I had other higher priorities. I would recommend monthly or quarterly meetings with the squadrons; an exchange of knowledge; rules and restrictions from both sides (pilots and controllers; not office staff or management) would be beneficial.


Second narrative: The two aircraft involved in the incident were Aircraft X and Aircraft Y which departed Tucson Int'l. Both aircraft departed simultaneously off their respective airports simultaneously which are separated by only 4.1 miles. Both aircraft are filed to go out the same exit fix 'MESCA'; but Aircraft X has an assigned altitude of 13;000 feet prior to getting shipped to center; and Aircraft Y has an assigned altitude of 17;000 feet; but is expected to get direct El Paso however that would require Aircraft Y going over the top of Aircraft X once separation is established. I noticed the aircraft were climbing at similar rates so Aircraft X was capped at 9;000 feet and Aircraft Y continued to climb. When Aircraft Y reached 10;000 MSL I would put him over the top of Aircraft Y and give him direct El Paso. I tried calling traffic for Aircraft Y on two occasions; but he could not get the aircraft in site. Also going on in the airspace was a guard recovery of multiple aircraft checking in with requests on different frequencies that I was monitoring. There were also different departures checking in at the same time. The frequencies were getting congested as people started stepping on each other. I am only [time removed] training hours into this position and I was starting to get a little overwhelmed. I then noticed that Aircraft Y had left 11;000 feet so I went back and assigned Aircraft X 10;000 feet which was read back correctly by the pilot. At that point Aircraft X requested a block altitude of 11;000 feet to 13;000 feet. My response was 'Aircraft X; I have your request'. I went back and talked to other aircraft. A moment later my trainer took over the frequency and told Aircraft X he can not climb on his own and warned of a possible pilot deviation. I looked at the data blocks and Aircraft X had climbed through 10;000 feet and was indicating 10;400 feet while Aircraft Y was still going over the top indicating 11;300 feet. My trainer took over the frequency to catch me up a little bit; and also to warn Aircraft X of a possible pilot deviation; and advise he call the radar facility. I was unsure if there was an actual loss of separation. The Falcon replay looked to show 1;000 feet at all times; but I was told that the there was a loss of separation. The final was 800 feet and 3.84 miles. I feel this was a pilot deviation as Aircraft X was assigned and read back 10;000 feet; a safe altitude that met all upcoming Minimum Vectoring Altitude (MVA); but he decided to climb on his own.As a trainee I learned a lot from this incident especially after a debrief with my trainer; and more discussion with a FLM as I discussed what were some different techniques to act sooner; and get better control of the frequency. The plan I had did ensure separation; but there were different techniques to not even make this a factor had I acted on the conflict sooner. I know there are techniques to such as expediting climbs if able; or stopping one of the aircraft sooner. I am new to radar and am learning a lot; but this was an unfortunate event that I was able to learn a lot from.My original plan to separate the aircraft could have worked; but as a result of this deviation I learned ways to better control the frequency and resolve conflicts closer to the airport as opposed to further out when aircraft are at higher speeds.


Synopsis: U90 Approach Controller describes a confusing reply from his trainee to a pilot. Pilot requested a block altitude; Controller answered 'On request.' Pilot later climbs on his own and separation was lost.