ARTCC radar controller issued clearance to FL230 which should have been FL220.

Attributes
ACN	90010
Time
Date	198806
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : jhw
State Reference	NY
Altitude	msl bound lower : 22000 msl bound upper : 22300
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zob
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
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 155 flight time total : 11800 flight time type : 1375
ASRS Report	90010
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : atp pilot : cfi pilot : instrument pilot : flight engineer
Experience	flight time last 90 days : 180 flight time total : 8000 flight time type : 1100
ASRS Report	89947
Events
Anomaly	other anomaly other
Independent Detector	other controllera
Resolutory Action	other
Consequence	Other
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	other

Narrative:

At approximately XA40Z, clearance was received from the cle ARTCC on frequency 125.2 to climb to and maintain FL230. Clearance was acknowledged with no response from center controller. As we were climbing out of FL220 at approximately FL223 center controller asked to confirm our altitude of FL220. We said we had been cleared to FL230. Controller said we were only cleared to FL220. We descended immediately to FL220. Air carrier about 5 mins behind us on same route had same problem understanding controller and in fact climbed to FL230 before error was rectified. Controller was very hard to understand due to excessive background noise and lack of clarity when pronouncing numbers (her 2 sounded like a 3). Recommendations: that controllers continue to be made aware of the importance of listening carefully to clearance acknowledgements, and that a study be made on the use of the type of microphone that is conducive to excessive background noise (not an uncommon problem with ATC).

Original NASA ASRS Text

Title: ARTCC RADAR CTLR ISSUED CLRNC TO FL230 WHICH SHOULD HAVE BEEN FL220.

Narrative: AT APPROX XA40Z, CLRNC WAS RECEIVED FROM THE CLE ARTCC ON FREQ 125.2 TO CLB TO AND MAINTAIN FL230. CLRNC WAS ACKNOWLEDGED WITH NO RESPONSE FROM CENTER CTLR. AS WE WERE CLBING OUT OF FL220 AT APPROX FL223 CENTER CTLR ASKED TO CONFIRM OUR ALT OF FL220. WE SAID WE HAD BEEN CLRED TO FL230. CTLR SAID WE WERE ONLY CLRED TO FL220. WE DSNDED IMMEDIATELY TO FL220. ACR ABOUT 5 MINS BEHIND US ON SAME ROUTE HAD SAME PROB UNDERSTANDING CTLR AND IN FACT CLBED TO FL230 BEFORE ERROR WAS RECTIFIED. CTLR WAS VERY HARD TO UNDERSTAND DUE TO EXCESSIVE BACKGROUND NOISE AND LACK OF CLARITY WHEN PRONOUNCING NUMBERS (HER 2 SOUNDED LIKE A 3). RECOMMENDATIONS: THAT CTLRS CONTINUE TO BE MADE AWARE OF THE IMPORTANCE OF LISTENING CAREFULLY TO CLRNC ACKNOWLEDGEMENTS, AND THAT A STUDY BE MADE ON THE USE OF THE TYPE OF MIC THAT IS CONDUCIVE TO EXCESSIVE BACKGROUND NOISE (NOT AN UNCOMMON PROB WITH ATC).

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.