Approach controller trainee descended an MD80 to alt that a B737 had just left. The B737 was changed to another approach controller frequency and slowed his rate of descent which caused a less than standard separation incident and activated the TCASII on the MD80.

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Attributes
ACN	324371
Time
Date	199508
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : sfo
State Reference	CA
Altitude	msl bound lower : 9000 msl bound upper : 9600
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : oak
Operator	common carrier : air carrier
Make Model Name	MD-80 Series (DC-9-80) Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	B737-200
Operating Under FAR Part	Part 121
Flight Phase	descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
ASRS Report	324371
Person 2
Affiliation	government : faa
Function	controller : approach
Qualification	controller : developmental
Events
Anomaly	conflict : airborne less severe non adherence : required legal separation
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : took evasive action
Consequence	Other
Miss Distance	vertical : 600
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Trainee assigned MD80 9000 ft after observing B73S leave 9000 ft. B73S was frequency changed to another sector and slowed down. MD80 was clean and descended at high rate, causing TCASII RA. Separation decreased to 600 ft. The B73S rate of descent tapered off to little or nothing. Combination of high rate of descent (MD80) and low rate (B73S) caused loss of separation.

Original NASA ASRS Text

Title: APCH CTLR TRAINEE DSNDED AN MD80 TO ALt THAT A B737 HAD JUST LEFT. THE B737 WAS CHANGED TO ANOTHER APCH CTLR FREQ AND SLOWED HIS RATE OF DSCNT WHICH CAUSED A LTSS INCIDENT AND ACTIVATED THE TCASII ON THE MD80.

Narrative: TRAINEE ASSIGNED MD80 9000 FT AFTER OBSERVING B73S LEAVE 9000 FT. B73S WAS FREQ CHANGED TO ANOTHER SECTOR AND SLOWED DOWN. MD80 WAS CLEAN AND DSNDED AT HIGH RATE, CAUSING TCASII RA. SEPARATION DECREASED TO 600 FT. THE B73S RATE OF DSCNT TAPERED OFF TO LITTLE OR NOTHING. COMBINATION OF HIGH RATE OF DSCNT (MD80) AND LOW RATE (B73S) CAUSED LOSS OF SEPARATION.

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.