Air carrier flight crew read back and complied with same descent clearance. Busy controller queried.

Attributes
ACN	309991
Time
Date	199507
Day	Fri
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : slc
State Reference	UT
Altitude	msl bound lower : 25000 msl bound upper : 26000
Environment
Flight Conditions	VMC
Light	Dusk
Aircraft 1
Controlling Facilities	artcc : zlc tower : sfo
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent other
Route In Use	enroute other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : instrument pilot : atp pilot : commercial
Experience	flight time last 90 days : 200 flight time total : 14000 flight time type : 6000
ASRS Report	309991
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 250 flight time total : 4700 flight time type : 460
ASRS Report	310080
Events
Anomaly	altitude deviation : overshoot non adherence : clearance
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance other
Consequence	faa : reviewed incident with flight crew
Supplementary
Primary Problem	Ambiguous
Air Traffic Incident	other

Narrative:

We were issued a clearance by ZLC controller to descend to FL260 from our cruise altitude of FL310. While descending, at about FL290, ZLC controller amended our clearance to descend to FL250. All clearance and instructions were acknowledged and read back. After leveling at FL250 the salt lake controller questioned our altitude and told us he had issued FL260 as our clearance. We told him he amended our clearance to FL250. The controller denied this and gave us further descent instructions. The controller was saturated working several other flts during this time. He most likely gave us the wrong clearance. We however, read everything back as given. Supplemental information from acn 310080: initial clearance was 'descend to FL260, expect 17000 ft 40 mi south of slc.' clearance was read back. During descent, altitude was amended to FL250. Clearance was again read back.

Original NASA ASRS Text

Title: ACR FLC READ BACK AND COMPLIED WITH SAME DSCNT CLRNC. BUSY CTLR QUERIED.

Narrative: WE WERE ISSUED A CLRNC BY ZLC CTLR TO DSND TO FL260 FROM OUR CRUISE ALT OF FL310. WHILE DSNDING, AT ABOUT FL290, ZLC CTLR AMENDED OUR CLRNC TO DSND TO FL250. ALL CLRNC AND INSTRUCTIONS WERE ACKNOWLEDGED AND READ BACK. AFTER LEVELING AT FL250 THE SALT LAKE CTLR QUESTIONED OUR ALT AND TOLD US HE HAD ISSUED FL260 AS OUR CLRNC. WE TOLD HIM HE AMENDED OUR CLRNC TO FL250. THE CTLR DENIED THIS AND GAVE US FURTHER DSCNT INSTRUCTIONS. THE CTLR WAS SATURATED WORKING SEVERAL OTHER FLTS DURING THIS TIME. HE MOST LIKELY GAVE US THE WRONG CLRNC. WE HOWEVER, READ EVERYTHING BACK AS GIVEN. SUPPLEMENTAL INFO FROM ACN 310080: INITIAL CLRNC WAS 'DSND TO FL260, EXPECT 17000 FT 40 MI S OF SLC.' CLRNC WAS READ BACK. DURING DSCNT, ALT WAS AMENDED TO FL250. CLRNC WAS AGAIN READ BACK.

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.