Air carrier overtook the aircraft in front of him, resulting in less than standard separation.

Attributes
ACN	121976
Time
Date	198909
Day	Mon
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : ogd
State Reference	UT
Altitude	msl bound lower : 22000 msl bound upper : 22500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zlc
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	climbout : intermediate altitude
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	climbout : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller radar : 15
ASRS Report	121976
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	conflict : airborne less severe non adherence : required legal separation non adherence : published procedure
Independent Detector	atc equipment other atc equipment : unspecified other controllera
Resolutory Action	controller : issued new clearance
Consequence	Other
Miss Distance	horizontal : 27000 vertical : 500
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

I was working the R31 (ogden low sector) and was given a handoff on air carrier and air carrier Y from slc approach control. Air carrier X was approximately 8 mi in front of air carrier Y and both aircraft were on a heading of 020 degrees. Air carrier X checked on frequency and was given a clearance to FL310 and turned to a heading of 330 degrees for its destination airport. Air carrier Y then checked on frequency and was given a clearance to FL310 and turned to a heading of 345 degrees for its destination airport. At this time, I noticed about a 20 KT overtake in ground speed in the 2 aircraft. It appeared that air carrier Y was overtaking air carrier X at sufficient speed that a loss of sep would occur shortly. Therefore, I attempted to stop air carrier Y below air carrier X by issuing a clearance to air carrier Y to maintain FL220. This was done since I had observed a mode C readout on air carrier X of FL231. However, apparently I misread the data on air carrier X. Air carrier Y leveled off at FL220 and picked up ground speed as it did so. Shortly after this, a C/a was initiated and showed air carrier X leaving FL227. The cause of the error was my failure to read the data return properly. The center run dart shows a mode C readout on air carrier X of FL213, not FL231. I do not know what to attribute this error in reading the radar data to. I had a great deal of outside stress due to medical problems occurring with my son, my wife and my mother. However, at the time, I did not feel that these problems were causing me any distrs.

Original NASA ASRS Text

Title: ACR OVERTOOK THE ACFT IN FRONT OF HIM, RESULTING IN LESS THAN STANDARD SEPARATION.

Narrative: I WAS WORKING THE R31 (OGDEN LOW SECTOR) AND WAS GIVEN A HDOF ON ACR AND ACR Y FROM SLC APCH CTL. ACR X WAS APPROX 8 MI IN FRONT OF ACR Y AND BOTH ACFT WERE ON A HDG OF 020 DEGS. ACR X CHKED ON FREQ AND WAS GIVEN A CLRNC TO FL310 AND TURNED TO A HDG OF 330 DEGS FOR ITS DEST ARPT. ACR Y THEN CHKED ON FREQ AND WAS GIVEN A CLRNC TO FL310 AND TURNED TO A HDG OF 345 DEGS FOR ITS DEST ARPT. AT THIS TIME, I NOTICED ABOUT A 20 KT OVERTAKE IN GND SPD IN THE 2 ACFT. IT APPEARED THAT ACR Y WAS OVERTAKING ACR X AT SUFFICIENT SPD THAT A LOSS OF SEP WOULD OCCUR SHORTLY. THEREFORE, I ATTEMPTED TO STOP ACR Y BELOW ACR X BY ISSUING A CLRNC TO ACR Y TO MAINTAIN FL220. THIS WAS DONE SINCE I HAD OBSERVED A MODE C READOUT ON ACR X OF FL231. HOWEVER, APPARENTLY I MISREAD THE DATA ON ACR X. ACR Y LEVELED OFF AT FL220 AND PICKED UP GND SPD AS IT DID SO. SHORTLY AFTER THIS, A C/A WAS INITIATED AND SHOWED ACR X LEAVING FL227. THE CAUSE OF THE ERROR WAS MY FAILURE TO READ THE DATA RETURN PROPERLY. THE CENTER RUN DART SHOWS A MODE C READOUT ON ACR X OF FL213, NOT FL231. I DO NOT KNOW WHAT TO ATTRIBUTE THIS ERROR IN READING THE RADAR DATA TO. I HAD A GREAT DEAL OF OUTSIDE STRESS DUE TO MEDICAL PROBS OCCURRING WITH MY SON, MY WIFE AND MY MOTHER. HOWEVER, AT THE TIME, I DID NOT FEEL THAT THESE PROBS WERE CAUSING ME ANY DISTRS.

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.