Less than standard separation when a bmb and medium large transport converge on the same route at th...

Attributes
ACN	86143
Time
Date	198804
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : sea
State Reference	WA
Altitude	msl bound lower : 18000 msl bound upper : 18000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zse
Operator	other
Make Model Name	Military Transport
Flight Phase	descent other
Route In Use	enroute : direct
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 : direct enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
ASRS Report	86143
Person 2
Function	flight crew : captain oversight : pic
Qualification	pilot : military
Events
Anomaly	conflict : airborne less severe non adherence : required legal separation
Independent Detector	atc equipment other atc equipment : unspecified other controllera
Resolutory Action	controller : issued new clearance none taken : insufficient time
Consequence	faa : investigated
Miss Distance	horizontal : 12000 vertical : 0
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Bmb X was northbound to whidbey NAS east of the sea 158 degree right which is the inbound route for jets landing at seattle from the south. Medium large transport Y was inbound on the sea 158 degree right from lax. Medium large transport Y was vectored west of the radial for sequencing. When sequencing was reestablished, medium large transport Y was vectored back to the right to reintercept the sea 158 degree radial. Bmb X had been converging slightly the whole time. When I realized that the medium large transport would not be below bmb X when the rtes crossed, I turned bmb X, but not in time to avoid loss of separation. I had believed bmb X had been on a jet route, when in fact he had been previously cleared direct which eventually placed him approximately 2 mi west of the airway when the error occurred.

Original NASA ASRS Text

Title: LESS THAN STANDARD SEPARATION WHEN A BMB AND MLG CONVERGE ON THE SAME ROUTE AT THE SAME ALT.

Narrative: BMB X WAS NBOUND TO WHIDBEY NAS EAST OF THE SEA 158 DEG RIGHT WHICH IS THE INBOUND RTE FOR JETS LNDG AT SEATTLE FROM THE SOUTH. MLG Y WAS INBOUND ON THE SEA 158 DEG RIGHT FROM LAX. MLG Y WAS VECTORED WEST OF THE RADIAL FOR SEQUENCING. WHEN SEQUENCING WAS REESTABLISHED, MLG Y WAS VECTORED BACK TO THE RIGHT TO REINTERCEPT THE SEA 158 DEG RADIAL. BMB X HAD BEEN CONVERGING SLIGHTLY THE WHOLE TIME. WHEN I REALIZED THAT THE MLG WOULD NOT BE BELOW BMB X WHEN THE RTES CROSSED, I TURNED BMB X, BUT NOT IN TIME TO AVOID LOSS OF SEPARATION. I HAD BELIEVED BMB X HAD BEEN ON A JET RTE, WHEN IN FACT HE HAD BEEN PREVIOUSLY CLRED DIRECT WHICH EVENTUALLY PLACED HIM APPROX 2 MI WEST OF THE AIRWAY WHEN THE ERROR OCCURRED.

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.

Less than standard separation when a bmb and medium large transport converge on the same route at the same altitude.