Descent rate not in accordance with the aim and the controllers expectations.

Attributes
ACN	85727
Time
Date	198804
Day	Mon
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : psp
State Reference	CA
Altitude	msl bound lower : 31000 msl bound upper : 35000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zla
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 210 flight time total : 7560 flight time type : 3000
ASRS Report	85727
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : atp
Experience	flight time last 90 days : 240 flight time total : 4700 flight time type : 1000
ASRS Report	86010
Events
Anomaly	non adherence other other anomaly other
Independent Detector	other controllera
Resolutory Action	other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	other

Narrative:

En route at FL350 we received a clearance to descend FL310 for traffic, cross psp at FL240. We started a descent for FL310 at a rate of 1200 FPM thinking that this was sufficient in that ATC did not request to expedite or be at FL310 by a certain time. Out of approximately FL330, ATC informed us that our descent was not in accordance with the aim, and not to slow our descent. We expedited the descent out of FL310 and continued a normal descent to FL240. We had assumed that a descent over 1000 FPM was all that was required. Now looking back at the aim it requires optimum rate consistent with operating characteristics of the aircraft. Optimum rate would have been about twice as fast. We could have presented a situation for less than minimum sep.

Original NASA ASRS Text

Title: DESCENT RATE NOT IN ACCORDANCE WITH THE AIM AND THE CTLRS EXPECTATIONS.

Narrative: ENRTE AT FL350 WE RECEIVED A CLRNC TO DSND FL310 FOR TFC, CROSS PSP AT FL240. WE STARTED A DSCNT FOR FL310 AT A RATE OF 1200 FPM THINKING THAT THIS WAS SUFFICIENT IN THAT ATC DID NOT REQUEST TO EXPEDITE OR BE AT FL310 BY A CERTAIN TIME. OUT OF APPROX FL330, ATC INFORMED US THAT OUR DSCNT WAS NOT IN ACCORDANCE WITH THE AIM, AND NOT TO SLOW OUR DSCNT. WE EXPEDITED THE DSCNT OUT OF FL310 AND CONTINUED A NORMAL DSCNT TO FL240. WE HAD ASSUMED THAT A DSCNT OVER 1000 FPM WAS ALL THAT WAS REQUIRED. NOW LOOKING BACK AT THE AIM IT REQUIRES OPTIMUM RATE CONSISTENT WITH OPERATING CHARACTERISTICS OF THE ACFT. OPTIMUM RATE WOULD HAVE BEEN ABOUT TWICE AS FAST. WE COULD HAVE PRESENTED A SITUATION FOR LESS THAN MINIMUM SEP.

Data retrieved from NASA's ASRS site as of August 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.