Two aircraft at the same assigned altitude experienced a loss of separation due to a system error and controller workload.
Synopsis
Two aircraft at the same assigned altitude experienced a loss of separation due to a system error and controller workload.
Narrative
Rewritten in plain English from NASA’s original all-caps telegraphic report — facts, figures, and terminology preserved.
Aircraft X, an AC50 Twin Commander, 3 miles west of the SAC VOR at 6000 feet, was on a 090 degree vector for enroute spacing to OAK. ATX Y, a PA31, was at 6000 feet 3 miles north of the SAC VOR southbound. I instructed Y to climb and maintain 7000 feet. The pilot advised that the last controller had assigned him 6000 feet.
I then instructed X to climb immediately and maintain 7000 feet. The pilot of X did not acknowledge the instruction, but I did observe the aircraft climbing out of 6000 feet. I then advised Y to maintain 6000 feet and called traffic at his '2 o'clock, 2 miles, a Twin Commander climbing out of 6000 feet.' I advised Y to maintain visual separation with the aircraft.
The problem arose when I started getting busy flowing traffic to Oakland. When SMF tower called for release of 2 aircraft for Oakland, I was already aware of 2 overflights approaching my airspace also for Oakland. Then SAC tower called for release on an aircraft also to Oakland. I also had 3 other aircraft on frequency at the time and was working the position by myself.
When SMF called again for 2 more departures to Oakland, I told them to hold for release. It was at this time I called for a coordinator. I believe that I called late for help. I was plenty busy flowing and talking to airplanes. Having to talk to SMF and SAC towers and to SUU approach control distracted me long enough to allow these 2 aircraft to lose standard separation.
Show the original NASA report (verbatim, telegraphic)
SMT X; AN AC50 TWIN COMMANDER; 3 MI W OF THE SAC VOR AT 6000 FT WAS ON A 090 DEG VECTOR FOR ENRTE SPACING TO OAK. ATX Y; A PA31; WAS AT 6000 FT 3 MI N OF THE SAC VOR SBOUND. I INSTRUCTED Y TO CLB AND MAINTAIN 7000 FT. THE PLT ADVISED THAT THE LAST CTLR HAD ASSIGNED HIM 6000 FT. I THEN INSTRUCTED X TO CLB IMMEDIATELY AND MAINTAIN 7000 FT. THE PLT OF X DID NOT ACKNOWLEDGE THE INSTRUCTION BUT I DID OBSERVE THE ACFT CLBING OUT OF 6000 FT. I THEN ADVISED Y TO MAINTAIN 6000 FT AND CALLED TFC AT HIS '2 O'CLOCK; 2 MI; A TWIN COMMANDER CLBING OUT OF 6000 FT.' I ADVISED Y TO MAINTAIN VISUAL SEPARATION WITH THE ACFT. THE PROB AROSE WHEN I STARTED GETTING BUSY FLOWING TFC TO OAKLAND. WHEN SMF TWR CALLED FOR RELEASE OF 2 ACFT FOR OAKLAND I WAS ALREADY AWARE OF 2 OVERFLTS APCHING MY AIRSPACE ALSO FOR OAKLAND. THEN SAC TWR CALLED FOR RELEASE ON AN ACFT ALSO TO OAKLAND. I ALSO HAD 3 OTHER ACFT ON FREQ AT THE TIME AND WAS WORKING THE POS BY MYSELF. WHEN SMF CALLED AGAIN FOR 2 MORE DEPS TO OAKLAND I TOLD THEM TO HOLD FOR RELEASE. IT WAS AT THIS TIME I CALLED FOR A COORDINATOR. I BELIEVE THAT I CALLED LATE FOR HELP. I WAS PLENTY BUSY FLOWING AND TALKING TO AIRPLANES. HAVING TO TALK TO SMF AND SAC TWRS AND TO SUU APCH CTL DISTRACTED ME LONG ENOUGH TO ALLOW THESE 2 ACFT TO LOSE STANDARD SEPARATION.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.