S76 helicopter pilot has loss of transmission oil pressure, declares emergency.

Attributes
ACN	563749
Time
Date	200210
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	msl single value : 5000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : zzz.tracon tower : lax.tower
Operator	common carrier : air taxi
Make Model Name	S-76/S-76 Mark II
Operating Under FAR Part	Part 135
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air taxi
Function	flight crew : single pilot
Qualification	pilot : commercial pilot : cfi
Experience	flight time last 90 days : 50 flight time total : 10500 flight time type : 2200
ASRS Report	563749
Person 2
Affiliation	government : faa
Function	controller : departure
Events
Anomaly	aircraft equipment problem : critical other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : transmission oil press other flight crewa
Resolutory Action	controller : provided flight assist flight crew : landed as precaution flight crew : declared emergency
Consequence	faa : reviewed incident with flight crew other other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

During cruise flight (IMC in and out) at 5000 ft, main transmission oil pressure started a continual, slow drop. When pressure reached the yellow (cautionary) range, an emergency was declared and a descent was started. Oil pressure continued to drop to low yellow. ATC advised ZZZ airport was at 190 degrees and 5 mi. Decision was made not to proceed to ZZZ, but rather land in a field as soon as the aircraft encountered VMC. ATC also advised that the last reported ceiling was 1500 ft. Aircraft broke out at 1500 ft and landed on a dirt road. Somewhere between 1500 ft and landing, the oil pressure recovered to the low green. Maintenance could not find a mechanical cause for this occurrence. All transmission oil filters were changed. The aircraft was run up and leak checked. Pressure was normal, aircraft was returned to service.

Original NASA ASRS Text

Title: S76 HELI PLT HAS LOSS OF XMISSION OIL PRESSURE, DECLARES EMER.

Narrative: DURING CRUISE FLT (IMC IN AND OUT) AT 5000 FT, MAIN XMISSION OIL PRESSURE STARTED A CONTINUAL, SLOW DROP. WHEN PRESSURE REACHED THE YELLOW (CAUTIONARY) RANGE, AN EMER WAS DECLARED AND A DSCNT WAS STARTED. OIL PRESSURE CONTINUED TO DROP TO LOW YELLOW. ATC ADVISED ZZZ ARPT WAS AT 190 DEGS AND 5 MI. DECISION WAS MADE NOT TO PROCEED TO ZZZ, BUT RATHER LAND IN A FIELD AS SOON AS THE ACFT ENCOUNTERED VMC. ATC ALSO ADVISED THAT THE LAST RPTED CEILING WAS 1500 FT. ACFT BROKE OUT AT 1500 FT AND LANDED ON A DIRT ROAD. SOMEWHERE BTWN 1500 FT AND LNDG, THE OIL PRESSURE RECOVERED TO THE LOW GREEN. MAINT COULD NOT FIND A MECHANICAL CAUSE FOR THIS OCCURRENCE. ALL XMISSION OIL FILTERS WERE CHANGED. THE ACFT WAS RUN UP AND LEAK CHKED. PRESSURE WAS NORMAL, ACFT WAS RETURNED TO SVC.

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.