Aircraft mlt X was cleared to 5000', which was occupied by aircraft mlt Y. System error occurred.

Attributes
ACN	112271
Time
Date	198905
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : mcc
State Reference	CA
Altitude	msl bound lower : 4000 msl bound upper : 5000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	other
Make Model Name	Military Trainer
Flight Phase	climbout : intermediate altitude descent other
Route In Use	arrival other enroute airway : mcc
Flight Plan	IFR
Aircraft 2
Operator	other
Make Model Name	Military Transport
Flight Phase	descent other other
Route In Use	arrival other
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Experience	controller radar : 13
ASRS Report	112271
Person 2
Function	controller : approach
Qualification	controller : radar
Events
Anomaly	conflict : airborne less severe non adherence : published procedure other anomaly other other anomaly other
Independent Detector	atc equipment other atc equipment : unspecified
Resolutory Action	none taken : detected after the fact
Consequence	faa : investigated
Miss Distance	horizontal : 6000 vertical : 500
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

I was busy with a military tanker who could not hear my xmissions. The tanker was being vectored to final approach course and had already missed 2 of my xmissions and headed for a higher minimum vectoring altitude (MVA). About the same time as I was having difficulty communicating with the tanker, I accepted handoff on an mlt X whose data block altitude indicated 3300'. The mlt X reported on frequency and I did not hear the pilot report level at 3000'. The position operational manual mandates this aircraft to fly into my airspace at 5000' unless coordinated otherwise. Busy with the tanker, I climbed the mlt X to 5000'. Data block altitude was covered by another data block so in effect data block information was useless. This error would not have taken place if procedures as per the operation manual had been followed, data block offset had worked properly, had I heard the mlt X report level at 3000', and had I not been busy with the tanker. Collision alert system notified myself and supervisor about error. Callback conversation with reporter revealed the following: the reporter stated that the aircraft involved were mlt's. 2 sectors were involved north feeder and mather sector. The positions were decombined. The reporter was working the mather sector. Procedure: when positions are combined aircraft landing at mcc would be handed off at 5000'. When positions are decombined aircraft landing at mcc would be handed off descending to 3000'. Aircraft mlt Y was in handoff status from north feeder to mather sector descending to 5000'.

Original NASA ASRS Text

Title: ACFT MLT X WAS CLEARED TO 5000', WHICH WAS OCCUPIED BY ACFT MLT Y. SYSTEM ERROR OCCURRED.

Narrative: I WAS BUSY WITH A MIL TANKER WHO COULD NOT HEAR MY XMISSIONS. THE TANKER WAS BEING VECTORED TO FINAL APCH COURSE AND HAD ALREADY MISSED 2 OF MY XMISSIONS AND HEADED FOR A HIGHER MINIMUM VECTORING ALT (MVA). ABOUT THE SAME TIME AS I WAS HAVING DIFFICULTY COMMUNICATING WITH THE TANKER, I ACCEPTED HANDOFF ON AN MLT X WHOSE DATA BLOCK ALT INDICATED 3300'. THE MLT X REPORTED ON FREQ AND I DID NOT HEAR THE PLT REPORT LEVEL AT 3000'. THE POSITION OPERATIONAL MANUAL MANDATES THIS ACFT TO FLY INTO MY AIRSPACE AT 5000' UNLESS COORDINATED OTHERWISE. BUSY WITH THE TANKER, I CLIMBED THE MLT X TO 5000'. DATA BLOCK ALT WAS COVERED BY ANOTHER DATA BLOCK SO IN EFFECT DATA BLOCK INFO WAS USELESS. THIS ERROR WOULD NOT HAVE TAKEN PLACE IF PROCS AS PER THE OP MANUAL HAD BEEN FOLLOWED, DATA BLOCK OFFSET HAD WORKED PROPERLY, HAD I HEARD THE MLT X REPORT LEVEL AT 3000', AND HAD I NOT BEEN BUSY WITH THE TANKER. COLLISION ALERT SYSTEM NOTIFIED MYSELF AND SUPVR ABOUT ERROR. CALLBACK CONVERSATION WITH REPORTER REVEALED THE FOLLOWING: THE REPORTER STATED THAT THE ACFT INVOLVED WERE MLT'S. 2 SECTORS WERE INVOLVED NORTH FEEDER AND MATHER SECTOR. THE POSITIONS WERE DECOMBINED. THE REPORTER WAS WORKING THE MATHER SECTOR. PROC: WHEN POSITIONS ARE COMBINED ACFT LNDG AT MCC WOULD BE HANDED OFF AT 5000'. WHEN POSITIONS ARE DECOMBINED ACFT LNDG AT MCC WOULD BE HANDED OFF DSNDING TO 3000'. ACFT MLT Y WAS IN HANDOFF STATUS FROM NORTH FEEDER TO MATHER SECTOR DSNDING TO 5000'.

Data retrieved from NASA's ASRS site as of August 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.