Air carrier widebody transport altitude deviation excursion from clearance altitude.

Attributes
ACN	126273
Time
Date	198910
Day	Tue
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : sea
State Reference	WA
Altitude	msl bound lower : 34200 msl bound upper : 35000
Environment
Flight Conditions	VMC
Light	Dusk
Aircraft 1
Controlling Facilities	artcc : zse
Operator	common carrier : air carrier
Make Model Name	Widebody, Low Wing, 2 Turbojet Eng
Navigation In Use	Other
Flight Phase	cruise other descent other
Route In Use	enroute airway : zse
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 210 flight time total : 22000
ASRS Report	126273
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 250 flight time total : 6000 flight time type : 1000
ASRS Report	126063
Events
Anomaly	altitude deviation : excursion from assigned altitude
Independent Detector	other controllera
Resolutory Action	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:

Center made transmission with reference to altitude FL330. Transmission was garbled and I thought he had given clearance to descend to FL330. Our flight director profile had us within the top of descent profile for descent. I reset our program altitude on the computer and called the center to confirm descent clearance. After second attempt, center advised crossing traffic was at FL330. The computer, however, had initiated gradual descent. Descent was stopped 500' below FL350 as center asked what our altitude was. Climb back to FL350 was initiated. Supplemental information from acn 126063: I was off center communication radio while listening for sea ATIS.

Original NASA ASRS Text

Title: ACR WDB ALT DEVIATION EXCURSION FROM CLRNC ALT.

Narrative: CENTER MADE XMISSION WITH REF TO ALT FL330. XMISSION WAS GARBLED AND I THOUGHT HE HAD GIVEN CLRNC TO DSND TO FL330. OUR FLT DIRECTOR PROFILE HAD US WITHIN THE TOP OF DSCNT PROFILE FOR DSCNT. I RESET OUR PROGRAM ALT ON THE COMPUTER AND CALLED THE CENTER TO CONFIRM DSCNT CLRNC. AFTER SECOND ATTEMPT, CENTER ADVISED XING TFC WAS AT FL330. THE COMPUTER, HOWEVER, HAD INITIATED GRADUAL DSCNT. DSCNT WAS STOPPED 500' BELOW FL350 AS CENTER ASKED WHAT OUR ALT WAS. CLB BACK TO FL350 WAS INITIATED. SUPPLEMENTAL INFO FROM ACN 126063: I WAS OFF CENTER COM RADIO WHILE LISTENING FOR SEA ATIS.

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.