B737-800 captain experiences confusion during the anthm RNAV to bwi due to the late runway transitio...

Narrative:

Descending on the anthm STAR under washington center control; we were cleared to descend 'via the anthm' arrival. We had the ATIS; but because washington does not assign the runway transition; we set 11;000 in the MCP; which is the lowest we can go without a runway assignment. When we were switched over to potomac approach; reporting altitude passing; descending via to 11;000; and the ATIS; the response we got was '33 left'. No 'continue descent via 33 left transition'; or 'maintain 11;000 ; expect 33 left'; or 'continue descent to X thousand; expect 33 left'(or some variation thereof). After a few moments; I queried the controller if we were cleared to continue descent via the 33 left transition; at which point he responded; 'continue via the 33 left transition'. We continued without further incident. To me this exchange was confusing and could lead to a misinterpretation of the approach clearance. This is the second time this has happened to me and on advice from the chiefs I am filing this report because this confusion needs to be addressed. Standardized phraseology needs to be used. I think the controllers are assuming that we will fly the transition because the ATIS has the active runway information. But I don't think this is correct. The controllers need to be specific.

Original NASA ASRS Text

Title: B737-800 Captain experiences confusion during the ANTHM RNAV to BWI due to the late runway transition assignment by PCT Approach; and their reluctance to issue the transition on the initial check in.

Narrative: Descending on the ANTHM STAR under Washington Center Control; we were cleared to descend 'via the ANTHM' arrival. We had the ATIS; but because Washington does not assign the runway transition; we set 11;000 in the MCP; which is the lowest we can go without a runway assignment. When we were switched over to Potomac Approach; reporting altitude passing; descending via to 11;000; and the ATIS; the response we got was '33 Left'. No 'continue descent via 33 Left transition'; or 'Maintain 11;000 ; expect 33 Left'; or 'continue descent to X thousand; expect 33 Left'(or some variation thereof). After a few moments; I queried the Controller if we were cleared to continue descent via the 33 Left transition; at which point he responded; 'Continue via the 33 Left transition'. We continued without further incident. To me this exchange was confusing and could lead to a misinterpretation of the approach clearance. This is the second time this has happened to me and on advice from the Chiefs I am filing this report because this confusion needs to be addressed. Standardized phraseology needs to be used. I think the Controllers are assuming that we will fly the transition because the ATIS has the active runway information. But I don't think this is correct. The Controllers need to be specific.

Data retrieved from NASA's ASRS site 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.

Attributes
ACN	1235213
Time
Date	201501
Local Time Of Day	1201-1800
Place
Locale Reference	BWI.Airport
State Reference	MD
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	B737-800
Operating Under FAR Part	Part 121
Flight Phase	Descent
Route In Use	STAR ANTHM ONE
Flight Plan	IFR
Person 1
Function	Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 178
Events
Anomaly	ATC Issue All Types Deviation - Procedural Published Material / Policy

B737-800 captain experiences confusion during the anthm RNAV to bwi due to the late runway transition assignment by pct approach; and their reluctance to issue the transition on the initial check in.