Controller misjudged A320 climb rate at high altitude resulting in loss of required separation.

Attributes
ACN	568835
Time
Date	200212
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	navaid : den.vortac
State Reference	CO
Altitude	msl single value : 38500
Environment
Flight Conditions	VMC
Light	Dawn
Aircraft 1
Controlling Facilities	artcc : zdv.artcc tracon : n90.tracon
Operator	common carrier : air carrier
Make Model Name	A320
Operating Under FAR Part	Part 121
Flight Phase	climbout : intermediate altitude
Route In Use	departure : other published ifr departure
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zdv.artcc
Operator	common carrier : air carrier
Make Model Name	DC-10 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller radar : 12
ASRS Report	568835
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Events
Anomaly	conflict : airborne less severe non adherence : published procedure non adherence : required legal separation
Independent Detector	atc equipment : conflict alert other controllera
Resolutory Action	none taken : anomaly accepted
Consequence	faa : investigated
Miss Distance	vertical : 1500
Supplementary
Problem Areas	ATC Human Performance
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

The A320 departed den on the way to phx. The A320 checked on frequency from the low altitude sector climbing to FL260. I cleared the A320 to FL390, requested altitude. A couple of mins later, crossing traffic was observed from the west at FL370. I asked the A320 pilot if they could reach FL390 in 4 mins. The pilot stated it would be close. I figured the A320 had 6 mins before separation would be lost. From observing the mode C of the A320, the A320 was climbing at an 1800-2000 FPM rate through FL370. From FL370 to FL380 the A320 climb rate was about 1000 FPM. The A320 climb rate reduced to 500 FPM to FL385. The A320 then leveled off at FL385 for approximately 2 mins. This is when separation was lost. The A320 took about another min or 2 to reach FL390. The very good climb rate through FL380 and adequate climb rate to FL385 gave me a false sense of security. I felt the A320 would reach FL390 before separation would be lost. Therefore, I took no other actions. The fact that the A320 climbs well except for the final few hundred ft to FL390 is one I will definitely remember.

Original NASA ASRS Text

Title: CTLR MISJUDGED A320 CLB RATE AT HIGH ALT RESULTING IN LOSS OF REQUIRED SEPARATION.

Narrative: THE A320 DEPARTED DEN ON THE WAY TO PHX. THE A320 CHKED ON FREQ FROM THE LOW ALT SECTOR CLBING TO FL260. I CLRED THE A320 TO FL390, REQUESTED ALT. A COUPLE OF MINS LATER, XING TFC WAS OBSERVED FROM THE W AT FL370. I ASKED THE A320 PLT IF THEY COULD REACH FL390 IN 4 MINS. THE PLT STATED IT WOULD BE CLOSE. I FIGURED THE A320 HAD 6 MINS BEFORE SEPARATION WOULD BE LOST. FROM OBSERVING THE MODE C OF THE A320, THE A320 WAS CLBING AT AN 1800-2000 FPM RATE THROUGH FL370. FROM FL370 TO FL380 THE A320 CLB RATE WAS ABOUT 1000 FPM. THE A320 CLB RATE REDUCED TO 500 FPM TO FL385. THE A320 THEN LEVELED OFF AT FL385 FOR APPROX 2 MINS. THIS IS WHEN SEPARATION WAS LOST. THE A320 TOOK ABOUT ANOTHER MIN OR 2 TO REACH FL390. THE VERY GOOD CLB RATE THROUGH FL380 AND ADEQUATE CLB RATE TO FL385 GAVE ME A FALSE SENSE OF SECURITY. I FELT THE A320 WOULD REACH FL390 BEFORE SEPARATION WOULD BE LOST. THEREFORE, I TOOK NO OTHER ACTIONS. THE FACT THAT THE A320 CLBS WELL EXCEPT FOR THE FINAL FEW HUNDRED FT TO FL390 IS ONE I WILL DEFINITELY REMEMBER.

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.