ARTCC radar controller descended a military DC9 from FL350 to FL310, expect FL180 with a crossing intersection, when cleared of en route traffic at FL290. DC9 descended through FL310, came in conflict with crossing traffic. Military pilot thought he was assigned FL180.

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Attributes
ACN	408650
Time
Date	199807
Day	Sun
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : sie
State Reference	NJ
Altitude	msl bound lower : 29000 msl bound upper : 29000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdc
Operator	other
Make Model Name	DC-9 Undifferentiated or Other Model
Operating Under FAR Part	Part 91
Flight Phase	descent other
Route In Use	arrival other enroute : on vectors enroute airway : zdc
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : developmental
Experience	controller radar : 13
ASRS Report	408650
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 : required legal separation other anomaly other
Independent Detector	atc equipment other atc equipment : unspecified other controllera
Resolutory Action	none taken : detected after the fact
Consequence	faa : investigated
Miss Distance	horizontal : 25200 vertical : 700
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

I was working the sie H1 radar position of ZDC in leesburg, va. I had an aircraft (aircraft #3) at FL290 nebound on J174. I had aircraft #1, C9, at FL390 landing adw. I descended aircraft #1 to FL310 because of the nebound FL290 traffic. Aircraft #1 started a real slow descent and I advised pilot to expect to cross zizzi intersection at FL180. Pilot acknowledged with a 'roger,' further clarifying that this was just an expect (in order for aircraft to plan his descent). I immediately advised aircraft #1 that his assigned altitude was FL310, which he acknowledged. I then gave clearance for aircraft #2 to cross zizzi intersection at FL180. Aircraft #2 read back correctly. Approximately 20 seconds later, I observed conflict alert activated with aircraft #1 and my nebound aircraft at FL290. I advised aircraft #1 that his assigned altitude was FL310, to which he replied, 'negative, we were cleared to FL180.'

Original NASA ASRS Text

Title: ARTCC RADAR CTLR DSNDED A MIL DC9 FROM FL350 TO FL310, EXPECT FL180 WITH A XING INTXN, WHEN CLRED OF ENRTE TFC AT FL290. DC9 DSNDED THROUGH FL310, CAME IN CONFLICT WITH XING TFC. MIL PLT THOUGHT HE WAS ASSIGNED FL180.

Narrative: I WAS WORKING THE SIE H1 RADAR POS OF ZDC IN LEESBURG, VA. I HAD AN ACFT (ACFT #3) AT FL290 NEBOUND ON J174. I HAD ACFT #1, C9, AT FL390 LNDG ADW. I DSNDED ACFT #1 TO FL310 BECAUSE OF THE NEBOUND FL290 TFC. ACFT #1 STARTED A REAL SLOW DSCNT AND I ADVISED PLT TO EXPECT TO CROSS ZIZZI INTXN AT FL180. PLT ACKNOWLEDGED WITH A 'ROGER,' FURTHER CLARIFYING THAT THIS WAS JUST AN EXPECT (IN ORDER FOR ACFT TO PLAN HIS DSCNT). I IMMEDIATELY ADVISED ACFT #1 THAT HIS ASSIGNED ALT WAS FL310, WHICH HE ACKNOWLEDGED. I THEN GAVE CLRNC FOR ACFT #2 TO CROSS ZIZZI INTXN AT FL180. ACFT #2 READ BACK CORRECTLY. APPROX 20 SECONDS LATER, I OBSERVED CONFLICT ALERT ACTIVATED WITH ACFT #1 AND MY NEBOUND ACFT AT FL290. I ADVISED ACFT #1 THAT HIS ASSIGNED ALT WAS FL310, TO WHICH HE REPLIED, 'NEGATIVE, WE WERE CLRED TO FL180.'

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.