Air carrier large transport overshot altitude on descent. Clearance interpretation.

Attributes
ACN	93491
Time
Date	198808
Day	Wed
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : vld
State Reference	GA
Altitude	msl bound lower : 36200 msl bound upper : 37000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zjx
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	descent other
Route In Use	enroute airway : j91
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : flight engineer
Experience	flight time last 90 days : 150 flight time total : 25000
ASRS Report	93491
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 125 flight time total : 10000 flight time type : 600
ASRS Report	93492
Events
Anomaly	altitude deviation : overshoot non adherence : clearance
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance flight crew : returned to intended course or assigned course other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Flight from atl to mco. Numerous thunderstorms over fl and south GA. Our cruising altitude of 41000' with clearance to cross 55 mi northwest eugene at 27000'. ATC said to descend and maintain 37000'. We had programmed the FMC for the crossing restriction. Copilot and I both thought he wanted our 41000' altitude and the aircraft was leaving 41000' at that time. As we were going through about 36200' the controller said to turn to 90 degree heading and maintain 37000'. We immediately climbed back to 37000'. In retrospect, I'm sure his--clearance was correct, but my thought process was not the same as his I'm not sure that he said to maintain 37000', maybe just descend to 37000', but after programming the crossing restriction and the airplane beginning its descent my thoughts were on the restriction. I feel that if a new clearance is issued that is superceding the previous one, they should specifically cancel the previous one--it sure would be safer. We could have very easily maintained 37000' west/O reprogramming the FMC.

Original NASA ASRS Text

Title: ACR LGT OVERSHOT ALT ON DESCENT. CLRNC INTERP.

Narrative: FLT FROM ATL TO MCO. NUMEROUS TSTMS OVER FL AND S GA. OUR CRUISING ALT OF 41000' WITH CLRNC TO CROSS 55 MI NW EUGENE AT 27000'. ATC SAID TO DSND AND MAINTAIN 37000'. WE HAD PROGRAMMED THE FMC FOR THE XING RESTRICTION. COPLT AND I BOTH THOUGHT HE WANTED OUR 41000' ALT AND THE ACFT WAS LEAVING 41000' AT THAT TIME. AS WE WERE GOING THROUGH ABOUT 36200' THE CTLR SAID TO TURN TO 90 DEG HDG AND MAINTAIN 37000'. WE IMMEDIATELY CLBED BACK TO 37000'. IN RETROSPECT, I'M SURE HIS--CLRNC WAS CORRECT, BUT MY THOUGHT PROCESS WAS NOT THE SAME AS HIS I'M NOT SURE THAT HE SAID TO MAINTAIN 37000', MAYBE JUST DSND TO 37000', BUT AFTER PROGRAMMING THE XING RESTRICTION AND THE AIRPLANE BEGINNING ITS DSCNT MY THOUGHTS WERE ON THE RESTRICTION. I FEEL THAT IF A NEW CLRNC IS ISSUED THAT IS SUPERCEDING THE PREVIOUS ONE, THEY SHOULD SPECIFICALLY CANCEL THE PREVIOUS ONE--IT SURE WOULD BE SAFER. WE COULD HAVE VERY EASILY MAINTAINED 37000' W/O REPROGRAMMING THE FMC.

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.