Williams UH-1H N502AW

Summary

On 15 November 2011 at about 15:37 local time, a Williams UH-1H registered N502AW, operated by Airwest Helicopters, was involved in an accident near Grand Canyon, Arizona, United States. One person was on board and one was seriously injured. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

15 November 2011 at 15:37

Classification

Accident

Location

Grand Canyon, Arizona, United States

Nearest airport

Valle Airport (40G)

Coordinates

35.7106, -112.2136

Aircraft

Williams UH-1H

Registration

N502AW

Category

Helicopter

Engines

1

Operator

Airwest Helicopters

Operating rule

Part 91: General Aviation

Purpose of flight

Other Work Use

Phase of flight

Not recorded

Route

Grand Canyon → Supai

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

WPR12LA039

1 person was seriously injured.

The loss of main rotor power due to a main rotor transmission failure from a lack of lubrication.

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

Read the full NTSB narrative

According to the pilot, the helicopter was about 500 ft above ground level (agl) when he saw the master caution warning light illuminate; he then saw that the low transmission oil pressure light was also illuminated. He immediately maneuvered away from power lines and set up an approach to land. While descending, the helicopter yawed left and right, and, about 10 ft agl with the airspeed almost at 0, the main rotor speed slowed and then stopped, and the helicopter subsequently fell to the ground. The pilot reported that the engine continued to operate for about 15 seconds after impact. An on-scene examination revealed that both main rotor blades remained intact with no leading edge damage. Examination of the helicopter revealed a band of discoloration around the circumference of the transmission case near the main rotor reduction gear assembly; localized paint peeling was also noted. There were no oil stains or residue on the transmission case. During the subsequent transmission disassembly, the mast was found coated in metal debris along its length, and the mast bearing was found coated in oil. Molten metal pieces were found in the upper planetary gears, ring gear, and sun gear, consistent with insufficient lubrication. The lower planetary gears sustained significant damage from the molten metal pieces. There was no damage to the transmission oil pump, oil was present in the oil pump cavity, and some debris and scoring were evident on the housing. Examination of the passages within the transmission oil manifold revealed medium-to-high density particles in several of the passages, but none of the passages were blocked; particles were also found in the chip detector. The particles were identified as being generally composed of metals commonly used in gears, housings, and bushings. The damage to the transmission indicated that it likely seized as a result of an overtemperature condition due to a lack of lubrication. Due to the severity of the damage, the reason for the lack of lubrication could not be determined.

Quoted verbatim from the NTSB record.