A320 first officer reported being cleared below class B airspace without notice from ATC.

Attributes
ACN	1242462
Time
Date	201502
Local Time Of Day	0601-1200
Place
Locale Reference	IAD.Airport
State Reference	VA
Environment
Flight Conditions	IMC
Aircraft 1
Make Model Name	A320
Operating Under FAR Part	Part 121
Flight Phase	Final Approach
Route In Use	Vectors
Flight Plan	IFR
Person 1
Function	First Officer Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 90 Flight Crew Total 3560 Flight Crew Type 3117
Events
Anomaly	ATC Issue All Types Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance Deviation - Procedural FAR Deviation - Procedural Published Material / Policy

Narrative:

Washington approach was vectoring long down winds for runway 1R. 1L was unprepared and 1R was reported braking action fair. We were at 4000 feet and approach continued us on downwind after the last fix on the HYPER5.01R. ATC told us that they were delaying our turn a bit at 18 DME aml. At 20 DME aml; I told the captain (ca) that we were exiting class B airspace and ATC should have told us according to jo 7110.65V. ATC turned us to 280 and descended us to 3000 MSL (floor of class B from 20-15 DME aml). Just inside 20 DME; ATC told us to descend and maintain 2000 which would put us below class B floor without giving us specific authorization to operate below class B. This is not legal. I told captain I was going to delay descent in an effort to stay above the floor. ATC then repeated the descent clearance at about 17.5 DME; and we told him that we were endeavoring to stay above class B floor which is required. We were then switched to tower without incident or comment. We heard approach tell traffic following us that he was descending them below class B airspace; which is what he should have told us in conjunction with our clearance to 2000 MSL.

Original NASA ASRS Text

Title: A320 First Officer reported being cleared below class B airspace without notice from ATC.

Narrative: Washington approach was vectoring long down winds for runway 1R. 1L was unprepared and 1R was reported braking action fair. We were at 4000 feet and approach continued us on downwind after the last fix on the HYPER5.01R. ATC told us that they were delaying our turn a bit at 18 DME AML. At 20 DME AML; I told the Captain (CA) that we were exiting Class B airspace and ATC should have told us according to JO 7110.65V. ATC turned us to 280 and descended us to 3000 MSL (floor of Class B from 20-15 DME AML). Just inside 20 DME; ATC told us to descend and maintain 2000 which would put us below Class B floor without giving us specific authorization to operate below Class B. This is not legal. I told Captain I was going to delay descent in an effort to stay above the floor. ATC then repeated the descent clearance at about 17.5 DME; and we told him that we were endeavoring to stay above Class B floor which is required. We were then switched to tower without incident or comment. We heard approach tell traffic following us that he was descending them below class B airspace; which is what he should have told us in conjunction with our clearance to 2000 MSL.

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.