B737-800 flight crew reported they did not comply with an ATC assigned speed.

Attributes
ACN	1489271
Time
Date	201710
Local Time Of Day	0601-1200
Place
Locale Reference	ATL.Airport
State Reference	GA
Environment
Light	Daylight
Aircraft 1
Make Model Name	B737-800
Operating Under FAR Part	Part 121
Flight Phase	Descent
Route In Use	Vectors
Flight Plan	IFR
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Type 519
Person 2
Function	Pilot Not Flying First Officer
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Type 7000
Events
Anomaly	ATC Issue All Types Deviation - Procedural Clearance Deviation - Speed All Types

Narrative:

We were on downwind at an assigned speed of 210 knots while in the descent to 7;000 feet. Speed brake was already out. ATC asked for best rate of descent. We slowed to 200 knots and put out flaps 10. Speed fluctuation was too close to flaps 10 limit for me; so I slowed to 190 for flap 10 speed buffer. At the same time; we are hearing on the busy radios of precision runway monitoring (prm) approaches being conducted. We hadn't previously briefed prm approaches and confirmed that wasn't on the ATIS; so we were working on that now as well. Passing somewhere around 5;000 feet; we were queried on what the airspeed was. We responded with speed of 185 and were subsequently scolded for slowing down without permission and given a phone number to call.I think the combination of busy radios; probable prm approach clearance coming; slow to 210 knots; and go down faster resulted in non-compliance with speed clearance. Upon landing I called the company FAA representative who called atl ATC and said he had talked to the controller about the above situation who understood our concern.

Original NASA ASRS Text

Title: B737-800 flight crew reported they did not comply with an ATC assigned speed.

Narrative: We were on downwind at an assigned speed of 210 knots while in the descent to 7;000 feet. Speed brake was already out. ATC asked for best rate of descent. We slowed to 200 knots and put out flaps 10. Speed fluctuation was too close to flaps 10 limit for me; so I slowed to 190 for flap 10 speed buffer. At the same time; we are hearing on the busy radios of Precision Runway Monitoring (PRM) Approaches being conducted. We hadn't previously briefed PRM Approaches and confirmed that wasn't on the ATIS; so we were working on that now as well. Passing somewhere around 5;000 feet; we were queried on what the airspeed was. We responded with speed of 185 and were subsequently scolded for slowing down without permission and given a phone number to call.I think the combination of busy radios; probable PRM Approach clearance coming; slow to 210 knots; and go down faster resulted in non-compliance with speed clearance. Upon landing I called the company FAA representative who called ATL ATC and said he had talked to the Controller about the above situation who understood our concern.

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.