<< >> NASA ASRS Report 553874, July 2002

ZDC radar controller misjudges descent rate of aircraft #1 resulting in a loss of separation when aircraft #2, at the higher altitude, descended at a greater rate.

Attributes
ACN	553874
Time
Date	200207
Day	Wed
Local Time Of Day	1201 To 1800
Place
Locale Reference	navaid : ccv.vortac
State Reference	VA
Altitude	msl bound lower : 25000 msl bound upper : 29000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdc.artcc
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	descent : intermediate altitude
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zdc.artcc
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	descent : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller radar : 13
ASRS Report	553874
Person 2
Affiliation	company : air carrier
Events
Anomaly	conflict : airborne critical non adherence : published procedure non adherence : required legal separation other anomaly other
Independent Detector	atc equipment : conflict alert atc equipment other atc equipment : radar/mode c other controllera other flight crewa other flight crewb
Resolutory Action	controller : issued new clearance flight crew : took evasive action
Consequence	faa : investigated
Miss Distance	horizontal : 27000 vertical : 600
Supplementary
Problem Areas	ATC Human Performance
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

I took control of aircraft #1 at FL270, aircraft #2 at FL290. I descended aircraft #1 to FL240. 1 1/2 mins later, observing aircraft #1 at FL260, I descended aircraft #2 to FL250. I thought both aircraft would descend at the same rate, but aircraft #2 descended much quicker. I tried to stop the descent of aircraft #2 and expedite the descent of aircraft #1.

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Original NASA ASRS Text

Title: ZDC RADAR CTLR MISJUDGES DSCNT RATE OF ACFT #1 RESULTING IN A LOSS OF SEPARATION WHEN ACFT #2, AT THE HIGHER ALT, DSNDED AT A GREATER RATE.

Narrative: I TOOK CTL OF ACFT #1 AT FL270, ACFT #2 AT FL290. I DSNDED ACFT #1 TO FL240. 1 1/2 MINS LATER, OBSERVING ACFT #1 AT FL260, I DSNDED ACFT #2 TO FL250. I THOUGHT BOTH ACFT WOULD DSND AT THE SAME RATE, BUT ACFT #2 DSNDED MUCH QUICKER. I TRIED TO STOP THE DSCNT OF ACFT #2 AND EXPEDITE THE DSCNT OF ACFT #1.

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.