Flight crew of an air carrier medium large transport descended from assigned altitude when ATC cleared them to fly a transition. Approach radar controller intervened to advise that they had not been cleared to a lower altitude and the flight crew informed them that they believed that they were automatically cleared to the lower altitude of the transition.

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Attributes
ACN	411450
Time
Date	199808
Day	Thu
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : iad
State Reference	VA
Altitude	msl bound lower : 4600 msl bound upper : 5000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	tracon : iad
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	descent other
Route In Use	arrival other arrival star : star
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Experience	flight time last 90 days : 150 flight time total : 2800 flight time type : 820
ASRS Report	411450
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	controller : issued new clearance other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

We were at 4600 ft descending as specified on the barin transition when ATC asked us what altitude we were at. We said 4600 ft. At this point he told us we had not been cleared to descend as per the transition, but that we were only cleared to 'fly the transition.' when he gave us our initial clearance to fly the transition, we thought that included descending as per the transition. After he did give us our clearance he also said to cross barin at 5000 ft. This complied with the approach chart, so we thought he gave us that altitude for our initial descent point. It seems that in this instance, the clearance was misleading to us. The difference in the clrncs 'cleared for the barin transition' and 'fly the barin transition' can be very small, especially when normally you're cleared for the whole procedure. After ATC did query us as to our altitude, he did clear us for the remainder of the transition. There was no traffic conflict. Contributing factors included fatigue, and unfamiliarity with the procedure.

Original NASA ASRS Text

Title: FLC OF AN ACR MLG DSNDED FROM ASSIGNED ALT WHEN ATC CLRED THEM TO FLY A TRANSITION. APCH RADAR CTLR INTERVENED TO ADVISE THAT THEY HAD NOT BEEN CLRED TO A LOWER ALT AND THE FLC INFORMED THEM THAT THEY BELIEVED THAT THEY WERE AUTOMATICALLY CLRED TO THE LOWER ALT OF THE TRANSITION.

Narrative: WE WERE AT 4600 FT DSNDING AS SPECIFIED ON THE BARIN TRANSITION WHEN ATC ASKED US WHAT ALT WE WERE AT. WE SAID 4600 FT. AT THIS POINT HE TOLD US WE HAD NOT BEEN CLRED TO DSND AS PER THE TRANSITION, BUT THAT WE WERE ONLY CLRED TO 'FLY THE TRANSITION.' WHEN HE GAVE US OUR INITIAL CLRNC TO FLY THE TRANSITION, WE THOUGHT THAT INCLUDED DSNDING AS PER THE TRANSITION. AFTER HE DID GIVE US OUR CLRNC HE ALSO SAID TO CROSS BARIN AT 5000 FT. THIS COMPLIED WITH THE APCH CHART, SO WE THOUGHT HE GAVE US THAT ALT FOR OUR INITIAL DSCNT POINT. IT SEEMS THAT IN THIS INSTANCE, THE CLRNC WAS MISLEADING TO US. THE DIFFERENCE IN THE CLRNCS 'CLRED FOR THE BARIN TRANSITION' AND 'FLY THE BARIN TRANSITION' CAN BE VERY SMALL, ESPECIALLY WHEN NORMALLY YOU'RE CLRED FOR THE WHOLE PROC. AFTER ATC DID QUERY US AS TO OUR ALT, HE DID CLR US FOR THE REMAINDER OF THE TRANSITION. THERE WAS NO TFC CONFLICT. CONTRIBUTING FACTORS INCLUDED FATIGUE, AND UNFAMILIARITY WITH THE PROC.

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.