Crj-200 captain reported that on several occasions A80 controllers have issued descend via clearance...

Narrative:

I have observed a potential safety threat; or at the very least a legal trap; involving the new 'descend via' arrivals into atlanta. During the last week or so I have experienced at least three arrivals during which we were first instructed to 'descend via;' but then later received a vector off the arrival without any sort of amended altitude instruction. This situation renders the vertical clearance ambiguous at best. In each instance we questioned the controller and eventually received an amended and specific altitude instruction. In one case; upon our questioning; the controller responded by saying 'you were instructed to descend via the arrival' instead of giving us a new altitude assignment. I responded: 'you gave us a heading; we are not currently on any arrival.' after a pause; he then agreed to give us an altitude assignment.it would be very helpful if the atlanta center and TRACON controllers could be reminded to please not leave us hanging like that. Any ambiguous ATC clearance is inherently unsafe. If a flight is cleared to 'descend via;' but is then later vectored off the arrival; a new altitude assignment needs to be provided at that time. Any ambiguous ATC clearance is inherently unsafe.

Original NASA ASRS Text

Title: CRJ-200 Captain reported that on several occasions A80 controllers have issued descend via clearances and then a heading off the arrival without an altitude assignment.

Narrative: I have observed a potential safety threat; or at the very least a legal trap; involving the new 'Descend Via' arrivals into Atlanta. During the last week or so I have experienced at least three arrivals during which we were first instructed to 'descend via;' but then later received a vector off the arrival without any sort of amended altitude instruction. This situation renders the vertical clearance ambiguous at best. In each instance we questioned the controller and eventually received an amended and specific altitude instruction. In one case; upon our questioning; the controller responded by saying 'you were instructed to descend via the arrival' instead of giving us a new altitude assignment. I responded: 'You gave us a heading; we are not currently on any arrival.' After a pause; he then agreed to give us an altitude assignment.It would be very helpful if the Atlanta Center and TRACON controllers could be reminded to please not leave us hanging like that. Any ambiguous ATC clearance is inherently unsafe. If a flight is cleared to 'descend via;' but is then later vectored off the arrival; a new altitude assignment needs to be provided at that time. Any ambiguous ATC clearance is inherently unsafe.

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	1407045
Time
Date	201611
Local Time Of Day	1201-1800
Place
Locale Reference	ATL.Airport
State Reference	GA
Environment
Light	Daylight
Aircraft 1
Make Model Name	Regional Jet 200 ER/LR (CRJ200)
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Route In Use	Vectors
Flight Plan	IFR
Person 1
Function	Captain Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	ATC Issue All Types Deviation - Procedural Published Material / Policy

Crj-200 captain reported that on several occasions A80 controllers have issued descend via clearances and then a heading off the arrival without an altitude assignment.