Less than standard separation between two air carrier aircraft. Operational error.

Attributes
ACN	106021
Time
Date	198903
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : har
State Reference	PA
Altitude	msl bound lower : 24500 msl bound upper : 25000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zny
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other
Route In Use	enroute airway : j220
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller radar : 15
ASRS Report	106021
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
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance none taken : unable
Consequence	faa : investigated
Miss Distance	horizontal : 21000 vertical : 500
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Air carrier X northbound bwi to buf level FL250. Air carrier Y eastbound ord to phl FL270 was cleared to FL110. Both aircraft turned 20 degrees when the descent of air carrier Y was observed to be slower than normal. Traffic was issued and an additional 20 degrees turns were applied. Although air carrier Y saw the traffic no increase in descent rate was noted. System error occurred in part due to air carrier Y's less than standard rate of descent.

Original NASA ASRS Text

Title: LESS THAN STANDARD SEPARATION BETWEEN TWO ACR ACFT. OPERATIONAL ERROR.

Narrative: ACR X NBOUND BWI TO BUF LEVEL FL250. ACR Y EBND ORD TO PHL FL270 WAS CLRED TO FL110. BOTH ACFT TURNED 20 DEGS WHEN THE DSCNT OF ACR Y WAS OBSERVED TO BE SLOWER THAN NORMAL. TFC WAS ISSUED AND AN ADDITIONAL 20 DEGS TURNS WERE APPLIED. ALTHOUGH ACR Y SAW THE TFC NO INCREASE IN DSCNT RATE WAS NOTED. SYS ERROR OCCURRED IN PART DUE TO ACR Y'S LESS THAN STANDARD RATE OF DSCNT.

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.