Pilot deviation caused by misunderstood clearance.

Attributes
ACN	296432
Time
Date	199502
Day	Mon
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : irk
State Reference	MO
Altitude	msl bound lower : 31500 msl bound upper : 33000
Environment
Light	Dawn
Aircraft 1
Controlling Facilities	artcc : zkc
Operator	common carrier : air carrier
Make Model Name	MD-80 Super 80
Operating Under FAR Part	Part 121
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	296432
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	altitude deviation : overshoot non adherence : clearance
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

30 mi northeast of irk, we were given a descent to what I heard as FL300. During this transmission, the first officer was leaving the cockpit as I was donning oxygen mask. I acknowledged leaving FL370 for FL300. The sector controller did not reply. A normal descent was initiated. Upon the first officer's return I briefed the descent to FL300. He resumed control of aircraft at approximately 31500 ft. The controller told us we were to maintain FL330. First officer immediately initiated climb to FL330. There was no conflict with other aircraft. I questioned the controller on the FL300 transmission and he said there was no problem.

Original NASA ASRS Text

Title: PLTDEV CAUSED BY MISUNDERSTOOD CLRNC.

Narrative: 30 MI NE OF IRK, WE WERE GIVEN A DSCNT TO WHAT I HEARD AS FL300. DURING THIS XMISSION, THE FO WAS LEAVING THE COCKPIT AS I WAS DONNING OXYGEN MASK. I ACKNOWLEDGED LEAVING FL370 FOR FL300. THE SECTOR CTLR DID NOT REPLY. A NORMAL DSCNT WAS INITIATED. UPON THE FO'S RETURN I BRIEFED THE DSCNT TO FL300. HE RESUMED CTL OF ACFT AT APPROX 31500 FT. THE CTLR TOLD US WE WERE TO MAINTAIN FL330. FO IMMEDIATELY INITIATED CLB TO FL330. THERE WAS NO CONFLICT WITH OTHER ACFT. I QUESTIONED THE CTLR ON THE FL300 XMISSION AND HE SAID THERE WAS NO PROB.

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.