Less than standard separation between mlt and another aircraft. Operational error. Hearback problem.

Attributes
ACN	167125
Time
Date	199012
Day	Mon
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : iso
State Reference	NC
Altitude	msl bound lower : 31000 msl bound upper : 32500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdc
Operator	other
Make Model Name	Military Transport
Flight Phase	descent other
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller radar : 8 controller supervisory : 3
ASRS Report	167125
Person 2
Affiliation	government : military
Function	flight crew : captain oversight : pic
Qualification	pilot : military
Events
Anomaly	conflict : airborne less severe non adherence : clearance non adherence : published procedure non adherence : required legal separation
Independent Detector	atc equipment other atc equipment : unspecified
Resolutory Action	controller : issued new clearance
Consequence	faa : investigated
Miss Distance	horizontal : 26250 vertical : 1700
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Mlt X checked on at FL350. I cleared the aircraft to FL330. Mlt X read back, 'out of 35 for 31.' (I missed the readback; i.e., I thought he said, '35 for 33,' or 'FL330.') about 3 mins later the C/a activated and I asked X to say altitude. He responded, 'passing 325.' I reclred mlt X to FL330 and reported the problem to the area supervisor in charge.

Original NASA ASRS Text

Title: LESS THAN STANDARD SEPARATION BETWEEN MLT AND ANOTHER ACFT. OPERATIONAL ERROR. HEARBACK PROBLEM.

Narrative: MLT X CHKED ON AT FL350. I CLRED THE ACFT TO FL330. MLT X READ BACK, 'OUT OF 35 FOR 31.' (I MISSED THE READBACK; I.E., I THOUGHT HE SAID, '35 FOR 33,' OR 'FL330.') ABOUT 3 MINS LATER THE C/A ACTIVATED AND I ASKED X TO SAY ALT. HE RESPONDED, 'PASSING 325.' I RECLRED MLT X TO FL330 AND RPTED THE PROB TO THE AREA SUPVR IN CHARGE.

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.