B737-700 captain reported deviating from an assigned airspeed on the RNAV (rnp) Z approach to runway...

Narrative:

While flying the frnch 3 arrival into den; initial approach assigned an airspeed of 210. Just prior to handing off to final approach; the airspeed was changed to maintain 190. Upon contact with the final approach controller; the airspeed was reconfirmed to maintain 190. About five miles from himom; the final approach controller gave the following clearance. 'Maintain 190; at himom; cleared the RNAV Z approach to runway 34R.' we continued flying 190 KIAS until reaching himom where we closed the speed intervention window and confirmed we were LNAV and VNAV path commencing the approach. The aircraft began to slow as we began configuring for the landing. After mcmul while arcing left towards kugln; our speed had decreased to approximately 160 KIAS when ATC queried our airspeed. Upon replying; ATC informed us we were assigned 190 KIAS. We were then assigned 'maintain 170 KIAS to corde and contact tower.' we felt ATC failed to clarify their intentions for our airspeed once commencing the approach. Had the clearance stated an expected airspeed past himom we would not have failed to maintain their desired airspeed for our flight. We felt ATC should have stated; 'at himom cleared the RNAV Z 34R approach; except maintain 170 to corde; contact tower.' this type of communication would have prevented our slowing.

Original NASA ASRS Text

Title: B737-700 Captain reported deviating from an assigned airspeed on the RNAV (RNP) Z Approach to Runway 34R at DEN when they misunderstood the clearance.

Narrative: While flying the FRNCH 3 Arrival into DEN; Initial Approach assigned an airspeed of 210. Just prior to handing off to Final Approach; the airspeed was changed to maintain 190. Upon contact with the Final Approach Controller; the airspeed was reconfirmed to maintain 190. About five miles from HIMOM; the Final Approach Controller gave the following clearance. 'Maintain 190; at HIMOM; cleared the RNAV Z Approach to Runway 34R.' We continued flying 190 KIAS until reaching HIMOM where we closed the Speed Intervention window and confirmed we were LNAV and VNAV PATH commencing the approach. The aircraft began to slow as we began configuring for the landing. After MCMUL while arcing left towards KUGLN; our speed had decreased to approximately 160 KIAS when ATC queried our airspeed. Upon replying; ATC informed us we were assigned 190 KIAS. We were then assigned 'maintain 170 KIAS to CORDE and contact Tower.' We felt ATC failed to clarify their intentions for our airspeed once commencing the approach. Had the clearance stated an expected airspeed past HIMOM we would not have failed to maintain their desired airspeed for our flight. We felt ATC should have stated; 'At HIMOM cleared the RNAV Z 34R Approach; except maintain 170 to CORDE; contact Tower.' This type of communication would have prevented our slowing.

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	1605666
Time
Date	201812
Local Time Of Day	0601-1200
Place
Locale Reference	DEN.Airport
State Reference	CO
Environment
Light	Daylight
Aircraft 1
Make Model Name	B737-700
Operating Under FAR Part	Part 121
Flight Phase	Descent
Route In Use	STAR FRNCH3
Flight Plan	IFR
Person 1
Function	Pilot Flying Captain
Qualification	Flight Crew Multiengine Flight Crew Air Transport Pilot (ATP) Flight Crew Instrument
Experience	Flight Crew Last 90 Days 361 Flight Crew Type 14400
Events
Anomaly	ATC Issue All Types Deviation - Procedural Clearance Deviation - Speed All Types

B737-700 captain reported deviating from an assigned airspeed on the RNAV (rnp) Z approach to runway 34R at den when they misunderstood the clearance.