Civil jet misunderstands communication with ZAU ARTCC controller and descends through an air carrier...

Attributes
ACN	404902
Time
Date	199806
Day	Fri
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : dbq
State Reference	IA
Altitude	msl bound lower : 28000 msl bound upper : 29000
Environment
Flight Conditions	Marginal
Light	Night
Aircraft 1
Controlling Facilities	artcc : zau tower : sju
Operator	general aviation : corporate
Make Model Name	Learjet 24
Operating Under FAR Part	Part 91
Flight Phase	descent other
Route In Use	arrival other enroute : on vectors
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller radar : 16
ASRS Report	404902
Person 2
Affiliation	Other
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 35 flight time total : 9500 flight time type : 800
ASRS Report	405027
Events
Anomaly	conflict : airborne less severe non adherence : far non adherence : required legal separation other anomaly other
Independent Detector	atc equipment other atc equipment : unspecified aircraft equipment other aircraft equipment : unspecified other controllera
Resolutory Action	controller : issued new clearance none taken : unable other
Consequence	Other
Miss Distance	horizontal : 9000 vertical : 350
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Aircraft X came on frequency east of dbq with routing over jvl and points east. I offered routing over rfd (to the south, slightly) which he accepted. I cleared him to FL290, aircraft Y was already at or near FL280 on northwest heading. These 2 aircraft would have to pass at altitude. I mentioned to aircraft X that with this procedure (over rfd), we usually try to have the aircraft cross rfd at 9000 ft and I would probably have to s-turn him to get him to where he could comfortably make the crossing -- at no time did I use the words 'maintain' or 'expect' during this exchange. I suppose he took the advisory as a clearance, for as he requested to deviate, I cleared him to do so and maintain FL290. By the time he read it back, he was already at or above FL280. My data block showed FL290 then nothing for actual altitude. Aircraft Y called with a TCASII RA to climb. By this time, since they were head on, they had already passed and I guess aircraft X went down in front of aircraft Y.

Original NASA ASRS Text

Title: CIVIL JET MISUNDERSTANDS COM WITH ZAU ARTCC CTLR AND DSNDS THROUGH AN ACR'S ALT.

Narrative: ACFT X CAME ON FREQ E OF DBQ WITH ROUTING OVER JVL AND POINTS E. I OFFERED ROUTING OVER RFD (TO THE S, SLIGHTLY) WHICH HE ACCEPTED. I CLRED HIM TO FL290, ACFT Y WAS ALREADY AT OR NEAR FL280 ON NW HDG. THESE 2 ACFT WOULD HAVE TO PASS AT ALT. I MENTIONED TO ACFT X THAT WITH THIS PROC (OVER RFD), WE USUALLY TRY TO HAVE THE ACFT CROSS RFD AT 9000 FT AND I WOULD PROBABLY HAVE TO S-TURN HIM TO GET HIM TO WHERE HE COULD COMFORTABLY MAKE THE XING -- AT NO TIME DID I USE THE WORDS 'MAINTAIN' OR 'EXPECT' DURING THIS EXCHANGE. I SUPPOSE HE TOOK THE ADVISORY AS A CLRNC, FOR AS HE REQUESTED TO DEVIATE, I CLRED HIM TO DO SO AND MAINTAIN FL290. BY THE TIME HE READ IT BACK, HE WAS ALREADY AT OR ABOVE FL280. MY DATA BLOCK SHOWED FL290 THEN NOTHING FOR ACTUAL ALT. ACFT Y CALLED WITH A TCASII RA TO CLB. BY THIS TIME, SINCE THEY WERE HEAD ON, THEY HAD ALREADY PASSED AND I GUESS ACFT X WENT DOWN IN FRONT OF ACFT Y.

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.

Civil jet misunderstands communication with ZAU ARTCC controller and descends through an air carrier's altitude.