An E120 crew in descent to slc, slowed 45 KTS below the speed ATC thought they were maintaining.

Attributes
ACN	531690
Time
Date	200112
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	navaid : ffu.vortac
State Reference	UT
Altitude	msl single value : 16000
Environment
Flight Conditions	IMC
Weather Elements	Turbulence
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zlc.artcc
Operator	common carrier : air carrier
Make Model Name	Brasilia EMB-120 All Series
Operating Under FAR Part	Part 121
Flight Phase	descent : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : multi engine pilot : commercial pilot : instrument
Experience	flight time last 90 days : 150 flight time total : 1700 flight time type : 400
ASRS Report	531690
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Events
Anomaly	inflight encounter : weather inflight encounter : turbulence non adherence : published procedure non adherence other other anomaly
Independent Detector	other controllera
Resolutory Action	none taken : detected after the fact
Consequence	faa : reviewed incident with flight crew
Supplementary
Problem Areas	Flight Crew Human Performance Weather
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

On the spone arrival into slc from gjt we were experiencing light turbulence at our cruising altitude. Just as we were going to ask for higher we were instructed to cross spone intersection at 16000 ft. Instead of asking for higher we started a more gradual descent. Shortly after, while in the descent, ATC queried our speed. The captain reported '210 KTS in the descent.' before he asked us he had reported to another aircraft to expect light to moderate turbulence through the entire descent. The controller told us that he knew it was turbulent and that if we could maintain best forward speed. We continued to descend at approximately 210 KTS which is slower than normal, because of both the light turbulence we were in and because of potential moderate. The descent continued for awhile and as I leveled I inadvertently allowed the aircraft to slow from 210 KTS to about 165-170 KTS (vb 175 KTS) since I had not added power soon enough this happened. After a short time I noticed the speed and added the power for cruise at that altitude. When speed reached 185 KTS ATC queried our speed. After reporting 185 KTS he recommended that if we were going to slow we needed to let them know and that if we are assigned 210 KTS (we were not) we need to tell them if we can't. I am not sure why, but he was very rude from the beginning. The captain told him we were in turbulence however she did not realize the error on my part and must have assumed I was slowing for the bumps.

Original NASA ASRS Text

Title: AN E120 CREW IN DSCNT TO SLC, SLOWED 45 KTS BELOW THE SPD ATC THOUGHT THEY WERE MAINTAINING.

Narrative: ON THE SPONE ARR INTO SLC FROM GJT WE WERE EXPERIENCING LIGHT TURB AT OUR CRUISING ALT. JUST AS WE WERE GOING TO ASK FOR HIGHER WE WERE INSTRUCTED TO CROSS SPONE INTXN AT 16000 FT. INSTEAD OF ASKING FOR HIGHER WE STARTED A MORE GRADUAL DSCNT. SHORTLY AFTER, WHILE IN THE DSCNT, ATC QUERIED OUR SPD. THE CAPT REPORTED '210 KTS IN THE DSCNT.' BEFORE HE ASKED US HE HAD REPORTED TO ANOTHER ACFT TO EXPECT LIGHT TO MODERATE TURB THROUGH THE ENTIRE DSCNT. THE CTLR TOLD US THAT HE KNEW IT WAS TURBULENT AND THAT IF WE COULD MAINTAIN BEST FORWARD SPD. WE CONTINUED TO DSND AT APPROX 210 KTS WHICH IS SLOWER THAN NORMAL, BECAUSE OF BOTH THE LIGHT TURB WE WERE IN AND BECAUSE OF POTENTIAL MODERATE. THE DSCNT CONTINUED FOR AWHILE AND AS I LEVELED I INADVERTENTLY ALLOWED THE ACFT TO SLOW FROM 210 KTS TO ABOUT 165-170 KTS (VB 175 KTS) SINCE I HAD NOT ADDED PWR SOON ENOUGH THIS HAPPENED. AFTER A SHORT TIME I NOTICED THE SPD AND ADDED THE PWR FOR CRUISE AT THAT ALT. WHEN SPD REACHED 185 KTS ATC QUERIED OUR SPD. AFTER REPORTING 185 KTS HE RECOMMENDED THAT IF WE WERE GOING TO SLOW WE NEEDED TO LET THEM KNOW AND THAT IF WE ARE ASSIGNED 210 KTS (WE WERE NOT) WE NEED TO TELL THEM IF WE CAN'T. I AM NOT SURE WHY, BUT HE WAS VERY RUDE FROM THE BEGINNING. THE CAPT TOLD HIM WE WERE IN TURB HOWEVER SHE DID NOT REALIZE THE ERROR ON MY PART AND MUST HAVE ASSUMED I WAS SLOWING FOR THE BUMPS.

Data retrieved from NASA's ASRS site as of July 2007 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.