Air carrier X had less than standard separation from air carrier Y. System error.

Attributes
ACN	179277
Time
Date	199105
Day	Thu
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : hto
State Reference	NY
Altitude	msl bound lower : 19500 msl bound upper : 19500
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zbw
Operator	common carrier : air carrier
Make Model Name	Widebody, Low Wing, 4 Turbojet Eng
Navigation In Use	Other
Flight Phase	descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
ASRS Report	179277
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	conflict : airborne less severe non adherence : clearance non adherence : published procedure non adherence : required legal separation
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance other
Consequence	faa : investigated
Miss Distance	horizontal : 24000 vertical : 0
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

I was working a combined sector (32, 33). I issued air carrier X a crossing restriction, from FL220 to cross an intersection at 110 at 250 KTS. In the next few seconds I observed air carrier Y at FL200 on a converging course with air carrier X. Air carrier Y was also an arrival aircraft. I issued air carrier X a clearance to maintain FL210. I then received a handoff on air carrier Y. I approved air carrier Y descending to 11000 through my airspace. Shortly I observed air carrier X descending through FL200. I issued him headings to try to maintain separation standards, however, the 2 aircraft were within 5 mi. Apparently, when I issued air carrier X FL210, the pilot was making a transmission at the same time, therefore never received the clearance. The only way to avoid these types of errors is to make sure you (the controller) hear exactly what the pilots read back after a clearance to be sure the aircraft will comply with clrncs.

Original NASA ASRS Text

Title: ACR X HAD LTSS FROM ACR Y. SYS ERROR.

Narrative: I WAS WORKING A COMBINED SECTOR (32, 33). I ISSUED ACR X A XING RESTRICTION, FROM FL220 TO CROSS AN INTXN AT 110 AT 250 KTS. IN THE NEXT FEW SECONDS I OBSERVED ACR Y AT FL200 ON A CONVERGING COURSE WITH ACR X. ACR Y WAS ALSO AN ARR ACFT. I ISSUED ACR X A CLRNC TO MAINTAIN FL210. I THEN RECEIVED A HDOF ON ACR Y. I APPROVED ACR Y DSNDING TO 11000 THROUGH MY AIRSPACE. SHORTLY I OBSERVED ACR X DSNDING THROUGH FL200. I ISSUED HIM HDGS TO TRY TO MAINTAIN SEPARATION STANDARDS, HOWEVER, THE 2 ACFT WERE WITHIN 5 MI. APPARENTLY, WHEN I ISSUED ACR X FL210, THE PLT WAS MAKING A XMISSION AT THE SAME TIME, THEREFORE NEVER RECEIVED THE CLRNC. THE ONLY WAY TO AVOID THESE TYPES OF ERRORS IS TO MAKE SURE YOU (THE CTLR) HEAR EXACTLY WHAT THE PLTS READ BACK AFTER A CLRNC TO BE SURE THE ACFT WILL COMPLY WITH CLRNCS.

Data retrieved from NASA's ASRS site as of July 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.