Air carrier altitude deviation results in less than standard separation with corp aircraft.

Attributes
ACN	97026
Time
Date	198808
Day	Fri
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : cys
State Reference	WY
Altitude	msl bound lower : 20400 msl bound upper : 21000
Environment
Flight Conditions	VMC
Light	Dusk
Aircraft 1
Controlling Facilities	artcc : zdv
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other
Flight Phase	climbout : intermediate altitude cruise other descent other
Flight Plan	IFR
Aircraft 2
Operator	general aviation : corporate
Make Model Name	Small Transport, Low Wing, 2 Turboprop Eng
Flight Phase	cruise other cruise other
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
ASRS Report	97026
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : airborne less severe inflight encounter : weather non adherence : required legal separation
Independent Detector	other other : unspecified atc
Resolutory Action	flight crew : returned to intended course or assigned course other
Consequence	faa : investigated
Miss Distance	horizontal : 24000 vertical : 600
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Air carrier X was stopped at FL200 for traffic (corp Y was at FL210). Traffic was issued to Y as 7 O'clock, 5 mi, type, FL200. Both aircraft had recently departed from denver approach's airspace. My next scan of the sector I observe air carrier X at FL205 and 4 mi from Y (loss of standard sep). X was instructed to maintain FL200 and say altitude. Mode C indicated FL204, X reported level FL200. When X was clear of Y, he was climbed to FL230 and informed of the pilot deviation. X requested a second readback of the pilot deviation. Readback given, only then did X mention he had been getting bounced around a lot at FL200. Corp Y pilot said he would vouch for air carrier X being in chop. Pilots should inform the controller of chop/rough rides if they are unable to hold altitude, so additional measures for providing sep can be taken.

Original NASA ASRS Text

Title: ACR ALT DEVIATION RESULTS IN LESS THAN STANDARD SEPARATION WITH CORP ACFT.

Narrative: ACR X WAS STOPPED AT FL200 FOR TFC (CORP Y WAS AT FL210). TFC WAS ISSUED TO Y AS 7 O'CLOCK, 5 MI, TYPE, FL200. BOTH ACFT HAD RECENTLY DEPARTED FROM DENVER APCH'S AIRSPACE. MY NEXT SCAN OF THE SECTOR I OBSERVE ACR X AT FL205 AND 4 MI FROM Y (LOSS OF STANDARD SEP). X WAS INSTRUCTED TO MAINTAIN FL200 AND SAY ALT. MODE C INDICATED FL204, X REPORTED LEVEL FL200. WHEN X WAS CLEAR OF Y, HE WAS CLBED TO FL230 AND INFORMED OF THE PLT DEV. X REQUESTED A SECOND READBACK OF THE PLT DEV. READBACK GIVEN, ONLY THEN DID X MENTION HE HAD BEEN GETTING BOUNCED AROUND A LOT AT FL200. CORP Y PLT SAID HE WOULD VOUCH FOR ACR X BEING IN CHOP. PLTS SHOULD INFORM THE CTLR OF CHOP/ROUGH RIDES IF THEY ARE UNABLE TO HOLD ALT, SO ADDITIONAL MEASURES FOR PROVIDING SEP CAN BE TAKEN.

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.