Sikorsky/Orlando S-55 N17754

Summary

On 18 September 2000 at about 15:15 local time, a Sikorsky/Orlando S-55 registered N17754, operated by Papillon Helicopters Inc., was involved in an accident near Hoover Dam, Arizona, United States. 7 people were on board and 7 had minor injuries. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

18 September 2000 at 15:15

Classification

Accident

Location

Hoover Dam, Arizona, United States

Coordinates

36.0304, -112.0192

Aircraft

Sikorsky/Orlando S-55

Registration

N17754

Category

Helicopter

Engines

1

Operator

Papillon Helicopters Inc.

Operating rule

Part 135: Air Taxi & Commuter

Phase of flight

Not recorded

Route

Las Vegas → Grand Canyon

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

LAX00FA342

7 people had minor injuries.

**This report was modified on 2/23/2016. Please refer to the public docket for this accident for more information.** The failure of Papillon maintenance personnel to recognize the significance of the increasing metal in the oil analysis test results and the illumination of the chip detector warning, the combination of which indicated internal engine wear that subsequently resulted in loss of engine drive to the rotor systems during flight. Contributing to the accident was National Flight Services' failure to properly torque the bull and sun gear retaining nut, which resulted in wear and the ultimate disengagement of the bull and sun gear.

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

Read the full NTSB narrative

**This report was modified on 2/23/2016. Please refer to the public docket for this accident for more information.** The helicopter was being operated as a sightseeing flight to the Grand Canyon. The pilot reported that during cruise flight the rotor and engine noise suddenly decreased and the helicopter began a descent. During the ensuing forced landing, the helicopter landed hard. The helicopter was fabricated from an ex-military remanufactured and modified Sikorsky S-55 (UH-19D). The original radial reciprocating engine had been replaced with a Garrett Gas Turbine TPE 331 modified to a TSE 331 IOUA 511 SW. It had a 6,000-hour time between overhaul. According to maintenance records dating back to July 3, 1985, the accident engine P-54083 operated in more than one Fairchild SA226 airplane in Australia and several rotary wing S-55 aircraft during their certification in the United States. Following the accident, the engine was shipped to the modifier for functional testing in a cell. The engine started and idled normally. Increasing the rpm to the certified operating specification of 101.5 percent revealed no abnormal conditions. The test propeller was moved from the start locks and increasing torque load was applied. As the torque was increased, the engine responded normally until approximately 60 percent torque when the indicated engine rpm rapidly decreased and an emergency shutdown was initiated. The process was repeated through 12 cycles, during which the indicated rpm began a sudden rapid decrease when torque was increased. Test cell troubleshooting failed to identify or correct this condition. During manual rotation of the propeller following the final cycle, some "slipping" was noted between the output shaft and the main rotating group. Subsequent examination of the gearbox revealed disengagement of the sun and bull gear assembly. Examination revealed fretting damage to the retaining nut and mating surfaces related to loss of specified torque. Visual examination of the sun and bull gears revealed severe damage to the mating splines of both gears. When the next-to-last and last engine oil samples taken prior to the accident were compared, iron increased 412.5 percent, and magnesium increased 571.6 percent. Just before the accident flight, the engine chip detector warning light illuminated and maintenance personnel removed, cleaned, and reinstalled the chip light sensor.    

Quoted verbatim from the NTSB record.