Air carrier X non adherence to ATC clearance unauthorized descent from assigned altitude.

Attributes
ACN	293078
Time
Date	199501
Day	Sun
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : sak
State Reference	MT
Altitude	msl bound lower : 8100 msl bound upper : 9000
Environment
Flight Conditions	IMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zlc
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	cruise other
Route In Use	enroute : direct
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument pilot : atp
Experience	flight time last 90 days : 178 flight time total : 5560 flight time type : 557
ASRS Report	293078
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance
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:

We were given a heading to intercept the localizer and proceed inbound on the ILS runway 2 approach -- glazier park international. When the GS was alive, my captain asked me if I was going to following the GS, I replied 'yes.' we continued our descent on the GS and at approximately 8100 ft MSL and outside of smith lake NDB (approximately 16 mi from the airport), center told us we were not cleared for the approach and we were to maintain 9000 ft. We leveled off and started a climb toward 9000 ft. We looked at each other and my captain said, 'I thought we were cleared for the approach when he (center) gave us the heading to intercept the localizer.' before we could reply, an aircraft ahead of us on the approach said they were about to land and could cancel IFR. Center replied with 'roger, squawk 1200, frequency change approved,' and immediately told us we were cleared for the approach. Also, we don't recall an instruction to maintain 9000 ft nor were we aware of an aircraft on the approach ahead of us.

Original NASA ASRS Text

Title: ACR X NON ADHERENCE TO ATC CLRNC UNAUTH DSCNT FROM ASSIGNED ALT.

Narrative: WE WERE GIVEN A HDG TO INTERCEPT THE LOC AND PROCEED INBOUND ON THE ILS RWY 2 APCH -- GLAZIER PARK INTL. WHEN THE GS WAS ALIVE, MY CAPT ASKED ME IF I WAS GOING TO FOLLOWING THE GS, I REPLIED 'YES.' WE CONTINUED OUR DSCNT ON THE GS AND AT APPROX 8100 FT MSL AND OUTSIDE OF SMITH LAKE NDB (APPROX 16 MI FROM THE ARPT), CTR TOLD US WE WERE NOT CLRED FOR THE APCH AND WE WERE TO MAINTAIN 9000 FT. WE LEVELED OFF AND STARTED A CLB TOWARD 9000 FT. WE LOOKED AT EACH OTHER AND MY CAPT SAID, 'I THOUGHT WE WERE CLRED FOR THE APCH WHEN HE (CTR) GAVE US THE HDG TO INTERCEPT THE LOC.' BEFORE WE COULD REPLY, AN ACFT AHEAD OF US ON THE APCH SAID THEY WERE ABOUT TO LAND AND COULD CANCEL IFR. CTR REPLIED WITH 'ROGER, SQUAWK 1200, FREQ CHANGE APPROVED,' AND IMMEDIATELY TOLD US WE WERE CLRED FOR THE APCH. ALSO, WE DON'T RECALL AN INSTRUCTION TO MAINTAIN 9000 FT NOR WERE WE AWARE OF AN ACFT ON THE APCH AHEAD OF US.

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.