Sikorsky S-64F N165AC

Summary

On 1 September 1994 at about 18:10 local time, a Sikorsky S-64F registered N165AC was involved in an accident near Libby, Montana, United States. 3 people were on board and 2 had minor injuries. The aircraft was destroyed. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

1 September 1994 at 18:10

Classification

Accident

Location

Libby, Montana, United States

Coordinates

48.3197, -115.3606

Aircraft

Sikorsky S-64F

Registration

N165AC

Category

Helicopter

Engines

2

Operator

Not recorded

Operating rule

Part 91: General Aviation

Purpose of flight

Unknown

Phase of flight

Not recorded

Aircraft damage

Destroyed

Weather

VMC

Light

Day

NTSB number

SEA94LA228

2 people had minor injuries.

THE FLIGHT CREW ALLOWED THE HELICOPTER'S WEIGHT AND BALANCE TO BE EXCEEDED, AND THE EXTERNAL LOAD (TANK) JETTISON SYSTEM FAILED TO OPERATE. A FACTOR RELATED TO THE ACCIDENT WAS: THE FALSE INDICATION ON THE RETARDANT QUANTITY INDICATOR.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

THE HELICOPTER WAS ON A MAINTENANCE TEST FLIGHT TO TEST A RETARDANT TANK SYSTEM THAT WAS USED TO CARRY AND DISPENSE WATER. AFTER ARRIVING AT A LAKE, THE FLIGHT CREW HOVERED THE HELICOPTER WHILE LOWERING THE SNORKEL TO ONLOAD WATER. HOWEVER, THE QUANTITY INDICATOR WAS MALFUNCTIONING, AND THE CREW MEMBERS WERE UNSURE IF WATER WAS BEING ONLOADED. THE PILOT OPTED TO FLY OUT OF THE HOVER AND DUMP THE WATER FROM THE RETARDANT TANK. AS THE FLIGHT BEGAN TO DEPART THE AREA, THE PILOT NOTED THAT THE HELICOPTER WAS LACKING RESPONSE TO THE COLLECTIVE AND THE RATE OF CLIMB WAS SLOW. WHEN THE WATER WOULD NOT DUMP FROM THE TANK, THE FLIGHT CREW TRIED TO JETTISON THE TANK. NEITHER SYSTEM WOULD WORK. THE ROTOR RPM BEGAN TO DECREASE AND THE HELICOPTER SETTLED INTO THE WATER AND SANK. DURING AN INVESTIGATION, NO MECHANICAL FAILURE OR MALFUNCTION OF EITHER ENGINE WAS FOUND. WHEN CHECKED, THE RETARDANT (WATER) QUANTITY INDICATOR SYSTEM WAS INOPERATIVE AND WOULD ONLY SENSE THAT THERE WAS NO WATER IN THE TANK. TO RELEASE WATER, THE SYSTEM NEEDED TO SENSE THAT THERE WAS ENOUGH WATER FOR THE SELECTED SETTING; THEREFORE, THE TANK DOORS WOULD NOT OPEN TO DUMP WATER WITH THIS MALFUNCTION. NO EVIDENCE WAS FOUND TO DETERMINE WHY THE EMERGENCY TANK DROP SYSTEM DID NOT FUNCTION. USING ESTIMATES, PERFORMANCE DATA INDICATED THE HELICOPTER WAS ABOVE THE MAXIMUM GROSS WEIGHT AND WAS POWER LIMITED FOR THE ENVIRONMENTAL CONDITIONS. ELEVATION OF THE LAKE WAS ABOUT 6500 FEET; AIR TEMPERATURE WAS ABOUT 63 DEGREES.

Quoted verbatim from the NTSB record.