Small transport was descended through altitude of an medium large transport.

Attributes
ACN	106769
Time
Date	198903
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : mfd
State Reference	OH
Altitude	msl bound lower : 25000 msl bound upper : 26000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zid
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	cruise other
Route In Use	departure other
Flight Plan	IFR
Aircraft 2
Operator	general aviation : corporate
Make Model Name	Small Transport, Low Wing, 2 Turbojet Eng
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : developmental
ASRS Report	106769
Person 2
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Events
Anomaly	conflict : airborne less severe non adherence : published procedure non adherence : required legal separation
Independent Detector	atc equipment other atc equipment : unspecified other controllera
Resolutory Action	controller : issued new clearance other
Consequence	faa : investigated
Miss Distance	horizontal : 6000 vertical : 100
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

Air carrier X, a cvg departure, was climbed to FL250 for traffic at FL260 swbnd. A higher altitude would not be available for air carrier X until approximately ZOB/ZID boundary. I told rav sector that air carrier X was at FL250 and would be their control for climb. At the same time I requested small transport Y stopped at FL240. Small transport Y altitude readout showed the aircraft at FL230. This coordination took place while air carrier X was 15 mi from ZOB boundary. A short time later I noticed small transport Y mode C at FL260 descending. Having released control for rav sector to climb air carrier X and not being sure what was happening with small transport Y, I did not switch air carrier X until I could ensure some sep. Realizing the altitude readout was not in error and that small transport Y was actually descending back to FL240 through the altitude of air carrier X at FL250, I turned air carrier X to a 090 degree heading. I did not talk to small transport Y until the aircraft was in the day high sector. I asked his altitude and he reported level at FL260.

Original NASA ASRS Text

Title: SMT WAS DESCENDED THROUGH ALT OF AN MLG.

Narrative: ACR X, A CVG DEP, WAS CLBED TO FL250 FOR TFC AT FL260 SWBND. A HIGHER ALT WOULD NOT BE AVAILABLE FOR ACR X UNTIL APPROX ZOB/ZID BOUNDARY. I TOLD RAV SECTOR THAT ACR X WAS AT FL250 AND WOULD BE THEIR CTL FOR CLB. AT THE SAME TIME I REQUESTED SMT Y STOPPED AT FL240. SMT Y ALT READOUT SHOWED THE ACFT AT FL230. THIS COORD TOOK PLACE WHILE ACR X WAS 15 MI FROM ZOB BOUNDARY. A SHORT TIME LATER I NOTICED SMT Y MODE C AT FL260 DSNDING. HAVING RELEASED CTL FOR RAV SECTOR TO CLB ACR X AND NOT BEING SURE WHAT WAS HAPPENING WITH SMT Y, I DID NOT SWITCH ACR X UNTIL I COULD ENSURE SOME SEP. REALIZING THE ALT READOUT WAS NOT IN ERROR AND THAT SMT Y WAS ACTUALLY DSNDING BACK TO FL240 THROUGH THE ALT OF ACR X AT FL250, I TURNED ACR X TO A 090 DEG HDG. I DID NOT TALK TO SMT Y UNTIL THE ACFT WAS IN THE DAY HIGH SECTOR. I ASKED HIS ALT AND HE RPTED LEVEL AT FL260.

Data retrieved from NASA's ASRS site as of August 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.