ARTCC radar controller descended a commuter CL65 to FL210, but the pilot read back FL200 instead, re...

Attributes
ACN	355202
Time
Date	199612
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : hv0
State Reference	WV
Altitude	msl bound lower : 20000 msl bound upper : 20000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zid
Operator	common carrier : air carrier
Make Model Name	Challenger CL604
Operating Under FAR Part	Part 135
Flight Phase	descent other
Flight Plan	IFR
Aircraft 2
Operator	general aviation : personal
Make Model Name	Small Transport, Low Wing, 2 Recip Eng
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Experience	controller non radar : 2 controller radar : 10
ASRS Report	355202
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	altitude deviation : overshoot conflict : airborne less severe non adherence : clearance non adherence : published procedure 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	Other
Miss Distance	horizontal : 12600 vertical : 0
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

I was working pkb radar position with light traffic and light complexity. Due to moderate chop at FL240 and above, several aircraft were requesting lower altitudes to get out of the chop. Nga Y, a BE60, was en route from rdu to cmh at FL200. I observed air carrier X being radar handed off to me from ZDC. As I started to accept radar on air carrier X, ZDC took back the handoff and climbed him to FL240 per pilot request. Approximately 8 mins later, air carrier X started experiencing chop at FL240 and requested lower from our 'high' side radar. I accepted radar air carrier X approximately 45 mi east of crw. When air carrier X made initial radio contact with me, I acknowledged for air carrier X to descend to FL210 due to traffic northbound (nga Y) at FL200. As air carrier X started to read back the clearance, several sits occurred simultaneously. Air carrier Z called descending to FL240 and stated his restr could not be met due to reduced airspeed due to the chop. I was attempting to coordinate with all sectors involved to provide information about air carrier Z not making his restr. At the same time another air carrier reported pkb airport insight, and I cleared him for visual approach to runway 21. Then I coordinated his position to pkb tower. Also, a C130 training flight was holding at OM for pkb and requested radar vectors for VOR 21 approach to pkb. I then went back to air carrier Z and reclred him to FL210 as per LOA with ZOB. As air carrier Z and the C130 were acknowledging their clrncs (I was working 3 separate frequencys), air carrier X read back descent to FL200. I did not copy the missed altitude information due to blocked xmissions from other frequencys, so I assumed the correct altitude was received. I was made aware of the problem when conflict alert activated and I observed air carrier X mode C read below FL210 which was in the data block. I advised air carrier X that his assigned altitude was FL210, and he responded 'out of FL200 for FL210.'

Original NASA ASRS Text

Title: ARTCC RADAR CTLR DSNDED A COMMUTER CL65 TO FL210, BUT THE PLT READ BACK FL200 INSTEAD, RESULTING IN LTSS WITH A BE60 AT FL200.

Narrative: I WAS WORKING PKB RADAR POS WITH LIGHT TFC AND LIGHT COMPLEXITY. DUE TO MODERATE CHOP AT FL240 AND ABOVE, SEVERAL ACFT WERE REQUESTING LOWER ALTS TO GET OUT OF THE CHOP. NGA Y, A BE60, WAS ENRTE FROM RDU TO CMH AT FL200. I OBSERVED ACR X BEING RADAR HANDED OFF TO ME FROM ZDC. AS I STARTED TO ACCEPT RADAR ON ACR X, ZDC TOOK BACK THE HDOF AND CLBED HIM TO FL240 PER PLT REQUEST. APPROX 8 MINS LATER, ACR X STARTED EXPERIENCING CHOP AT FL240 AND REQUESTED LOWER FROM OUR 'HIGH' SIDE RADAR. I ACCEPTED RADAR ACR X APPROX 45 MI E OF CRW. WHEN ACR X MADE INITIAL RADIO CONTACT WITH ME, I ACKNOWLEDGED FOR ACR X TO DSND TO FL210 DUE TO TFC NBOUND (NGA Y) AT FL200. AS ACR X STARTED TO READ BACK THE CLRNC, SEVERAL SITS OCCURRED SIMULTANEOUSLY. ACR Z CALLED DSNDING TO FL240 AND STATED HIS RESTR COULD NOT BE MET DUE TO REDUCED AIRSPD DUE TO THE CHOP. I WAS ATTEMPTING TO COORDINATE WITH ALL SECTORS INVOLVED TO PROVIDE INFO ABOUT ACR Z NOT MAKING HIS RESTR. AT THE SAME TIME ANOTHER ACR RPTED PKB ARPT INSIGHT, AND I CLRED HIM FOR VISUAL APCH TO RWY 21. THEN I COORDINATED HIS POS TO PKB TWR. ALSO, A C130 TRAINING FLT WAS HOLDING AT OM FOR PKB AND REQUESTED RADAR VECTORS FOR VOR 21 APCH TO PKB. I THEN WENT BACK TO ACR Z AND RECLRED HIM TO FL210 AS PER LOA WITH ZOB. AS ACR Z AND THE C130 WERE ACKNOWLEDGING THEIR CLRNCS (I WAS WORKING 3 SEPARATE FREQS), ACR X READ BACK DSCNT TO FL200. I DID NOT COPY THE MISSED ALT INFO DUE TO BLOCKED XMISSIONS FROM OTHER FREQS, SO I ASSUMED THE CORRECT ALT WAS RECEIVED. I WAS MADE AWARE OF THE PROB WHEN CONFLICT ALERT ACTIVATED AND I OBSERVED ACR X MODE C READ BELOW FL210 WHICH WAS IN THE DATA BLOCK. I ADVISED ACR X THAT HIS ASSIGNED ALT WAS FL210, AND HE RESPONDED 'OUT OF FL200 FOR FL210.'

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.

ARTCC radar controller descended a commuter CL65 to FL210, but the pilot read back FL200 instead, resulting in less than standard separation with a BE60 at FL200.