C402 pilot reported misunderstanding an altitude clearance; resulting in a descent toward terrain.

Attributes
ACN	1686484
Time
Date	201909
Local Time Of Day	0601-1200
Place
Locale Reference	ZLC.ARTCC
State Reference	UT
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Make Model Name	Cessna 402/402C/B379 Businessliner/Utiliner
Operating Under FAR Part	Part 135
Flight Phase	Descent
Flight Plan	IFR
Person 1
Function	Pilot Flying
Events
Anomaly	Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance Inflight Event / Encounter CFTT / CFIT

Narrative:

On salt lake center and level at 11;000. Thought I was told to contact salt lake center and descend 10;000. I had previously requested 10;000 because I had reached more than 30 min above 10;000. So I swapped frequencies and began descending. At 10;500 center advised of a low altitude warning; and I climbed back up to 11;000.

Original NASA ASRS Text

Title: C402 pilot reported misunderstanding an altitude clearance; resulting in a descent toward terrain.

Narrative: On Salt Lake Center and level at 11;000. Thought I was told to contact Salt Lake Center and descend 10;000. I had previously requested 10;000 because I had reached more than 30 min above 10;000. So I swapped frequencies and began descending. At 10;500 Center advised of a low altitude warning; and I climbed back up to 11;000.

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.