Controller failed to hear readback of wrong assigned altitude. Operational deviation.

Attributes
ACN	129443
Time
Date	198911
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : ccv
State Reference	VA
Altitude	msl bound lower : 4000 msl bound upper : 8000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : orf
Operator	common carrier : air carrier
Make Model Name	Medium Transport, High Wing, 2 Turboprop Eng
Flight Phase	descent other
Route In Use	enroute : direct
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Experience	controller radar : 6
ASRS Report	129443
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 240 flight time total : 12000 flight time type : 2500
ASRS Report	129448
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : published procedure
Independent Detector	other controllera
Resolutory Action	none taken : anomaly accepted
Consequence	faa : investigated
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Deviation

Narrative:

I was working 3 sectors combined on 1 scope, working approximately 8 to 10 aircraft. Air carrier X DH8 checked onto the frequency at 10000', requesting to proceed direct phf. I instructed air carrier X to 'descend and maintain 4000', proceed direct phf, amend altitude maintain 8000' direct phf.' in air carrier X's readback I heard 8000' and assumed it was correct. Later I observed air carrier X leaving 6400'. I asked air carrier X to 'say altitude' and he reported 'out of 6000 for 4000'.' I advised air carrier X that his altitude had been amended to 8000', but now he could continue to 4000' direct phf. There were several VFR aircraft in the vicinity as well as one IFR aircraft overflt aircraft at 7000'. At no time did I observe less than standard sep between air carrier and any other aircraft. I reported air carrier X to my supervisor as a possible pilot deviation. After reviewing the tape 4 or 5 times, I was finally able to ascertain air carrier X's readback: 'ok, out of 8000' direct phf and we're down to 4000'.' I had assumed the readback to say 'down to 8000', direct phf.' on the tape the readback was difficult to understand and the lack of standard phraseology may have contributed to the hearback error. Also, at the time the workload was moderate and complex.

Original NASA ASRS Text

Title: CTLR FAILED TO HEAR READBACK OF WRONG ASSIGNED ALT. OPERATIONAL DEVIATION.

Narrative: I WAS WORKING 3 SECTORS COMBINED ON 1 SCOPE, WORKING APPROX 8 TO 10 ACFT. ACR X DH8 CHKED ONTO THE FREQ AT 10000', REQUESTING TO PROCEED DIRECT PHF. I INSTRUCTED ACR X TO 'DSND AND MAINTAIN 4000', PROCEED DIRECT PHF, AMEND ALT MAINTAIN 8000' DIRECT PHF.' IN ACR X'S READBACK I HEARD 8000' AND ASSUMED IT WAS CORRECT. LATER I OBSERVED ACR X LEAVING 6400'. I ASKED ACR X TO 'SAY ALT' AND HE RPTED 'OUT OF 6000 FOR 4000'.' I ADVISED ACR X THAT HIS ALT HAD BEEN AMENDED TO 8000', BUT NOW HE COULD CONTINUE TO 4000' DIRECT PHF. THERE WERE SEVERAL VFR ACFT IN THE VICINITY AS WELL AS ONE IFR ACFT OVERFLT ACFT AT 7000'. AT NO TIME DID I OBSERVE LESS THAN STANDARD SEP BTWN ACR AND ANY OTHER ACFT. I RPTED ACR X TO MY SUPVR AS A POSSIBLE PLT DEVIATION. AFTER REVIEWING THE TAPE 4 OR 5 TIMES, I WAS FINALLY ABLE TO ASCERTAIN ACR X'S READBACK: 'OK, OUT OF 8000' DIRECT PHF AND WE'RE DOWN TO 4000'.' I HAD ASSUMED THE READBACK TO SAY 'DOWN TO 8000', DIRECT PHF.' ON THE TAPE THE READBACK WAS DIFFICULT TO UNDERSTAND AND THE LACK OF STANDARD PHRASEOLOGY MAY HAVE CONTRIBUTED TO THE HEARBACK ERROR. ALSO, AT THE TIME THE WORKLOAD WAS MODERATE AND COMPLEX.

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.