EMS helicopter descended below assigned al thinking he had been cleared for an approach.

Attributes
ACN	349205
Time
Date	199609
Day	Fri
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : zzz
State Reference	US
Altitude	msl bound lower : 3000 msl bound upper : 5000
Environment
Flight Conditions	IMC
Light	Night
Aircraft 1
Controlling Facilities	tracon : zzz
Operator	common carrier : air taxi
Make Model Name	Helicopter
Operating Under FAR Part	Part 91
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air taxi
Function	flight crew : single pilot
Qualification	pilot : commercial pilot : instrument
Experience	flight time last 90 days : 100 flight time total : 5000 flight time type : 1200
ASRS Report	349205
Person 2
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other flight crewa
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Inbound to ZZZ on IFR flight plan on EMS flight. I was handed off from xyz center to XXX. Approach at 5000 ft on direct leg to YYY NDB. XXX approach advised I was to expect the ILS runway 28 approach to ZZZ. At the time I was 11 mi east of the NDB at 5000 ft, 120 KIAS in and out of the clouds. Without authority/authorized or clearance I descended to 3000 ft for the approach. I simply misinterpreted what XXX approach communicated to me. The fault was totally mine. No extenuating circumstances.

Original NASA ASRS Text

Title: EMS HELI DSNDED BELOW ASSIGNED AL THINKING HE HAD BEEN CLRED FOR AN APCH.

Narrative: INBOUND TO ZZZ ON IFR FLT PLAN ON EMS FLT. I WAS HANDED OFF FROM XYZ CTR TO XXX. APCH AT 5000 FT ON DIRECT LEG TO YYY NDB. XXX APCH ADVISED I WAS TO EXPECT THE ILS RWY 28 APCH TO ZZZ. AT THE TIME I WAS 11 MI E OF THE NDB AT 5000 FT, 120 KIAS IN AND OUT OF THE CLOUDS. WITHOUT AUTH OR CLRNC I DSNDED TO 3000 FT FOR THE APCH. I SIMPLY MISINTERPRETED WHAT XXX APCH COMMUNICATED TO ME. THE FAULT WAS TOTALLY MINE. NO EXTENUATING CIRCUMSTANCES.

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.