AS350 pilot reported starting a descent too early and passing within less than 300 feet of a ridge.

Attributes
ACN	1574537
Time
Date	201808
Local Time Of Day	1201-1800
Place
Locale Reference	IWA.Airport
State Reference	AZ
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Eurocopter AS 350/355/EC130 - Astar/Twinstar/Ecureuil
Operating Under FAR Part	Part 135
Flight Phase	Descent
Route In Use	VFR Route
Flight Plan	VFR
Person 1
Function	Pilot Flying Single Pilot
Qualification	Flight Crew Air Transport Pilot (ATP) Flight Crew Flight Instructor Flight Crew Instrument
Experience	Flight Crew Last 90 Days 70 Flight Crew Total 17500 Flight Crew Type 2000
Events
Anomaly	Inflight Event / Encounter CFTT / CFIT
Miss Distance	Vertical 200

Narrative:

During descent from mountainous terrain; I descended too early and passed within less than 300 feet AGL of a ridge. This was an unintentional excursion during descent from mountainous terrain into the valley floor. I was leaving a 1000 foot AGL cruise to a planned 1500 foot cruise in lower terrain. During my descent I noticed my radar altimeter decreasing in altitude; I expected it to indicate approximately 300 to 400 feet passing the ridge; but I noticed it actually indicate a low of just above 200 prior to starting its climb back up to indicate approximately 2000 AGL. I never intended to be below 300; but the aicraft indications did show that I was below 300.

Original NASA ASRS Text

Title: AS350 Pilot reported starting a descent too early and passing within less than 300 feet of a ridge.

Narrative: During descent from mountainous terrain; I descended too early and passed within less than 300 feet AGL of a ridge. This was an unintentional excursion during descent from mountainous terrain into the valley floor. I was leaving a 1000 foot AGL cruise to a planned 1500 foot cruise in lower terrain. During my descent I noticed my radar altimeter decreasing in altitude; I expected it to indicate approximately 300 to 400 feet passing the ridge; but I noticed it actually indicate a low of just above 200 prior to starting its climb back up to indicate approximately 2000 AGL. I never intended to be below 300; but the aicraft indications did show that I was below 300.

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.