Separation was lost when an aircraft deviating around WX was caught by trailing aircraft.

Attributes
ACN	151830
Time
Date	199007
Day	Sat
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : slt
State Reference	PA
Altitude	msl bound lower : 21000 msl bound upper : 21000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zob
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	cruise other
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Experience	controller military : 1 controller radar : 5
ASRS Report	151830
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	conflict : airborne less severe non adherence : published procedure non adherence : required legal separation
Independent Detector	other controllera
Resolutory Action	none taken : unable
Consequence	faa : investigated
Miss Distance	horizontal : 24600 vertical : 200
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Large transport X departed roc. Large transport Y departed buf. Both aircraft climbing level FL210. Large transport Y turned to a 110 degree heading for spacing (both aircraft landing iad) and sep behind large transport X. Large transport Y then turned to a 140 degree heading. When 15 mi had been established between aircraft, large transport Y was given direct slt VORTAC. Large transport X which had been restr to 280 KTS indicated airspeed by a previous controller was given normal airspeed. Large transport Y then restr not to exceed 280 KTS. Large transport X asked to deviate around a buildup. I asked if he could go west and he complied. When I noticed the problem, large transport X looked as if it now headed 240 degrees (from an original 180 degrees) and large transport Y catching up direct slt. Large transport Y was vectored behind large transport X. Large transport X's ground speed, which was the same as large transport Y before large transport Y was restr, was now 60 KTS slower. Large transport Y was given a 110 degree heading to go behind large transport X. Large transport X was given a 180 degree heading to ensure sep--no response. Large transport Y was given FL200. Large transport X was given 180 degree heading. Large transport X said he would be unable to comply because of WX. In 10-15 more seconds radar sep would be lost. No other action would be taken as large transport Y was already behind large transport X and heading 110 degrees.

Original NASA ASRS Text

Title: SEPARATION WAS LOST WHEN AN ACFT DEVIATING AROUND WX WAS CAUGHT BY TRAILING ACFT.

Narrative: LGT X DEPARTED ROC. LGT Y DEPARTED BUF. BOTH ACFT CLBING LEVEL FL210. LGT Y TURNED TO A 110 DEG HDG FOR SPACING (BOTH ACFT LNDG IAD) AND SEP BEHIND LGT X. LGT Y THEN TURNED TO A 140 DEG HDG. WHEN 15 MI HAD BEEN ESTABLISHED BTWN ACFT, LGT Y WAS GIVEN DIRECT SLT VORTAC. LGT X WHICH HAD BEEN RESTR TO 280 KTS INDICATED AIRSPD BY A PREVIOUS CTLR WAS GIVEN NORMAL AIRSPD. LGT Y THEN RESTR NOT TO EXCEED 280 KTS. LGT X ASKED TO DEVIATE AROUND A BUILDUP. I ASKED IF HE COULD GO W AND HE COMPLIED. WHEN I NOTICED THE PROB, LGT X LOOKED AS IF IT NOW HEADED 240 DEGS (FROM AN ORIGINAL 180 DEGS) AND LGT Y CATCHING UP DIRECT SLT. LGT Y WAS VECTORED BEHIND LGT X. LGT X'S GND SPD, WHICH WAS THE SAME AS LGT Y BEFORE LGT Y WAS RESTR, WAS NOW 60 KTS SLOWER. LGT Y WAS GIVEN A 110 DEG HDG TO GO BEHIND LGT X. LGT X WAS GIVEN A 180 DEG HDG TO ENSURE SEP--NO RESPONSE. LGT Y WAS GIVEN FL200. LGT X WAS GIVEN 180 DEG HDG. LGT X SAID HE WOULD BE UNABLE TO COMPLY BECAUSE OF WX. IN 10-15 MORE SECS RADAR SEP WOULD BE LOST. NO OTHER ACTION WOULD BE TAKEN AS LGT Y WAS ALREADY BEHIND LGT X AND HDG 110 DEGS.

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.