Air carrier medium large transport altitude deviation excursion from clearance altitude.

Attributes
ACN	176643
Time
Date	199104
Day	Thu
Local Time Of Day	0001 To 0600
Place
Locale Reference	airport : atl
State Reference	GA
Altitude	msl bound lower : 10500 msl bound upper : 11000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	tracon : atl
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : commercial pilot : cfi pilot : atp pilot : flight engineer pilot : instrument
Experience	flight time last 90 days : 100 flight time total : 10000 flight time type : 3000
ASRS Report	176643
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance other
Consequence	Other
Supplementary
Primary Problem	Ambiguous
Air Traffic Incident	Operational Deviation Pilot Deviation

Narrative:

Inbound to atl, approach controller cleared flight, 'descend to 6000',' with our call sign. This was very clear and unmistakeable to both pilots and was read back. Subsequent gentle descent initiated by first officer passing 10500' from 11000', controller asked altitude. Told 10500' for 6000'. He said, 'you're not cleared; that was for another aircraft.' controller told us to level at 10000'. The call sign for our call was very clear. If indeed it was for another aircraft, then our readback should have stopped the apparent problem; but, readbacks aren't good enough. If 2 aircraft read back simultaneously, then they both think it has been heard, when probably neither has, but the controller should be alert for a squeal. Only when controllers acknowledge your readback affirmatively with your call sign will you be 100% certain of correct receipt of clearance. That is seldom done by an overloaded ATC. However, this event was early in morning and there was no overload, nor did we even hear other aircraft in pattern.

Original NASA ASRS Text

Title: ACR MLG ALT DEVIATION EXCURSION FROM CLRNC ALT.

Narrative: INBND TO ATL, APCH CTLR CLRED FLT, 'DSND TO 6000',' WITH OUR CALL SIGN. THIS WAS VERY CLR AND UNMISTAKEABLE TO BOTH PLTS AND WAS READ BACK. SUBSEQUENT GENTLE DSNT INITIATED BY F/O PASSING 10500' FROM 11000', CTLR ASKED ALT. TOLD 10500' FOR 6000'. HE SAID, 'YOU'RE NOT CLRED; THAT WAS FOR ANOTHER ACFT.' CTLR TOLD US TO LEVEL AT 10000'. THE CALL SIGN FOR OUR CALL WAS VERY CLR. IF INDEED IT WAS FOR ANOTHER ACFT, THEN OUR READBACK SHOULD HAVE STOPPED THE APPARENT PROB; BUT, READBACKS AREN'T GOOD ENOUGH. IF 2 ACFT READ BACK SIMULTANEOUSLY, THEN THEY BOTH THINK IT HAS BEEN HEARD, WHEN PROBABLY NEITHER HAS, BUT THE CTLR SHOULD BE ALERT FOR A SQUEAL. ONLY WHEN CTLRS ACKNOWLEDGE YOUR READBACK AFFIRMATIVELY WITH YOUR CALL SIGN WILL YOU BE 100% CERTAIN OF CORRECT RECEIPT OF CLRNC. THAT IS SELDOM DONE BY AN OVERLOADED ATC. HOWEVER, THIS EVENT WAS EARLY IN MORNING AND THERE WAS NO OVERLOAD, NOR DID WE EVEN HEAR OTHER ACFT IN PATTERN.

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.