A second departure aircraft overtakes the first aircraft, resulting in less than standard separation...

Attributes
ACN	124713
Time
Date	198910
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : mke
State Reference	WI
Altitude	msl bound lower : 4000 msl bound upper : 4200
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : mke tower : mke
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	climbout : initial
Route In Use	departure other
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	climbout : initial
Route In Use	departure other
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : departure
Qualification	controller : radar
Experience	controller radar : 6
ASRS Report	124713
Person 2
Affiliation	government : faa
Function	controller : local
Qualification	controller : non radar
Events
Anomaly	conflict : airborne less severe non adherence : published procedure non adherence : required legal separation
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance
Consequence	Other
Miss Distance	horizontal : 9000 vertical : 200
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Use of departure sep of the 2 jets did not provide airborne standard sep because of the second jet's higher performance. Due to runway confign and noise abatement procedures, I waited approximately 5 mi to turn second jet to 140 degree heading. Both jets departed 170 degrees with first jet climbing to 5000', second jet to 4000'. I needed to get the first jet over the top and over traffic to avoid adjacent airspace and a time consuming point-out. I turned the first jet to 100 degrees. I then noticed the second jet flying considerably faster. I turned the second jet to 110 degrees, then stopped the first jet at 140 degrees and climbed expeditiously to 6000'. The first jet was always higher than the second jet, and the second jet was still mins from actually catching the first jet, but I assumed the first jet would have out-climbed and kept distance because of like aircraft. I learned a valuable lesson: 'never assume anything.' this was a chasing situation that allowed for approximately 1 1/2 mi horizontal sep and 200' vertical.

Original NASA ASRS Text

Title: A SECOND DEP ACFT OVERTAKES THE FIRST ACFT, RESULTING IN LESS THAN STANDARD SEPARATION.

Narrative: USE OF DEP SEP OF THE 2 JETS DID NOT PROVIDE AIRBORNE STANDARD SEP BECAUSE OF THE SECOND JET'S HIGHER PERFORMANCE. DUE TO RWY CONFIGN AND NOISE ABATEMENT PROCS, I WAITED APPROX 5 MI TO TURN SECOND JET TO 140 DEG HDG. BOTH JETS DEPARTED 170 DEGS WITH FIRST JET CLBING TO 5000', SECOND JET TO 4000'. I NEEDED TO GET THE FIRST JET OVER THE TOP AND OVER TFC TO AVOID ADJACENT AIRSPACE AND A TIME CONSUMING POINT-OUT. I TURNED THE FIRST JET TO 100 DEGS. I THEN NOTICED THE SECOND JET FLYING CONSIDERABLY FASTER. I TURNED THE SECOND JET TO 110 DEGS, THEN STOPPED THE FIRST JET AT 140 DEGS AND CLBED EXPEDITIOUSLY TO 6000'. THE FIRST JET WAS ALWAYS HIGHER THAN THE SECOND JET, AND THE SECOND JET WAS STILL MINS FROM ACTUALLY CATCHING THE FIRST JET, BUT I ASSUMED THE FIRST JET WOULD HAVE OUT-CLBED AND KEPT DISTANCE BECAUSE OF LIKE ACFT. I LEARNED A VALUABLE LESSON: 'NEVER ASSUME ANYTHING.' THIS WAS A CHASING SITUATION THAT ALLOWED FOR APPROX 1 1/2 MI HORIZ SEP AND 200' VERT.

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.