NYC94FA106

After discharging passengers on an island, the S-76 helicopter departed for a return flight to the mainland. One minute after takeoff, at 500 feet above the water, a vibration followed by a loud bang occurred. The main gear box (mgb) chip light illuminated and the number one eng dropped off line. A forced landing was initiated, the emergency floats were inflated and a ditching to water was accomplished. The number one eng was shut down, and the acft was water taxied on the second eng. After a second bang was heard the number two eng was shut down. Examination revealed that the left hand (number one eng) helical gear in the mgb, failed from fatigue cracks across the 12 attaching bolt holes. The torque required on the 12 nuts was 4OO inch pounds. Three nuts had less then 60 inch lbs, the remaining nine had no torque. Both mgb oil pumps were seized from FOD that entered the pumps through an alternate oil path, that by-passed the oil screens. The number two eng pinion gear in the mgb, failed due to overheating from the lack of lubrication. Elapsed time was less than 6 minutes from initial forced landing to second engine shut down.

HISTORY OF FLIGHT On June 30, 1994, at 1940 eastern daylight time, a Sikorsky S-76, N76UT, owned by United Technologies Corporation and piloted by Mr. James A. Williams, was substantially damaged during a forced landing and ditching to the Narragansett Bay near Newport, Rhode Island. The two pilots and passenger were not injured. Visual meteorological conditions prevailed and a visual flight rules flight plan had been filed for the flight operating under 14 CFR 91.

The helicopter had departed Hartford, Connecticut, and proceeded to Goat Island, Rhode Island, with passengers. According to the flight crew, the flight to Goat Island was uneventful. The passengers were discharged at Goat Island and N76UT departed for the return leg over water back to Hartford. The pilot-in-command (PIC) reported that about 1 minute after a normal takeoff, while level at 500 feet above the water, he heard a unusual "hum" from some where in the aircraft. In a statement provided by the PIC, he stated:

"...Within a few more seconds the noise got considerably louder, coupled with noticeable vibrations, followed by a loud bang. I announced we were going down, called for floats to be armed, called for floats to be deployed and subsequently ditched in the water...I secured the left engine that had failed to flight idle and continued to water taxi to safer waters. After approximately 2 minutes there was a loud rumble at which time I secured the right engine..."

According to the Federal Aviation Administration (FAA) Inspector's statement, the PIC stated to him that shortly after the transmission chip detector light illuminated, the transmission low oil pressure light illuminated, followed by an un-commanded reduction of power on the number one engine.

The pilot-not-flying (PNF) reported that shortly after takeoff, he heard a "buzzing" sound that quickly became a rumble, then a severe vibration. Almost simultaneously he heard a muted explosion and the main transmission chip caution light illuminated, followed by an engine out warning tone. He further stated that during the emergency, he had been communicating on the helicopters VHF radio; however, after the water landing he utilized a portable cellular phone, dialed 911, and reported his situation to the police. The police contacted the Coast Guard, who arrived on the scene within several minutes of receiving the call.

The deck of the responding Coast Guard ship was higher then the helicopter. This required the crew of N76UT to exit the helicopter into the sea water before they could be recovered. The Coast Guard ship then took the helicopter in tow and proceeded to a land dock.

The accident occurred during the hours of dusk at approximately 41 degrees, 29 minutes north latitude, and 71 degrees, 22 minutes west longitude.

Personnel information

Pilot-in command

The PIC, Mr. James A. Williams, holds an Airline Transport Pilot Certificate with ratings for airplane multi-engine land and rotorcraft helicopter. He holds a Commercial Pilot Certificate with ratings for airplane single engine land, single engine sea, and glider. Mr. Williams also holds a Flight Instructor Certificate for airplane single and multi-engine land, rotorcraft helicopter, glider, and instrument airplane.

His most recent Federal Aviation Administration (FAA) Second Class Medical Certificate was issued on December 21, 1993.

The pilot operator report indicated that Mr. Williams had accumulated a total of 10,000 flight hours, of which 2,000 hours were in the S-76.

Pilot-not-flying

The PNF, Mr. Wesley A. Smith, holds an Airline Transport Pilot Certificate with ratings for airplane multi-engine land and rotorcraft helicopter. He held a Commercial Pilot Certificate with a rating for airplane single engine land.

His most recent Federal Aviation Administration (FAA) Second Class Medical Certificate was issued on May 27, 1994.

The pilot operator report indicated that Mr. Smith had accumulated a total of 6,500 flight hours, of which 1,000 hours were in the S-76.

Wreckage

The helicopter remained upright on the emergency floatation equipment; however, the fuselage partially submerged and salt water came in contact with the entire lower portion of the main fuselage, cabin floor and tailboom. The remainder of the helicopter was undamaged except for the number one engine and the main gear box (MGB).

The number one engine compressor section displayed small nicks and dents on the compressor blades. The top aft area of the MGB, near the tail rotor take-off, displayed a rupture in the case approximately 4 inches wide by 18 inches long. The two speed sensors, normally mounted in that area, were hanging outside of the case still attached to their electrical harnesses.

Several pieces of the MGB case, and two segments of a helical gear rim, were found on the number one engine deck. There was no indication of debris penetration or damage to any of the surrounding helicopter structure or systems.

Turning the number one input flange in a clockwise direction did not drive the main rotor head, the tail take-off flange, or back drive the number two input flange. Turning the number two input flange in a clockwise direction, also did not drive the main rotor head, the tail take-off flange, or back drive the number one input flange.

The MGB, serial number A231-00072, part number 76351-09600- 042, was removed on July 2, 1994, and transported to the Sikorsky Aircraft Overhaul and Repair Facility for further evaluation.

Tests and research

Main Gear Box (MGB)

On Sunday, July 3, 1994, Sikorsky personnel initiated the disassembly and inspection of the MGB at the Sikorsky Aircraft Facility. The FAA Flight Standards District Office (FSDO) Inspector, David G. O'Donnell, responsible for the on scene investigation, and the NTSB investigator-in-charge (IIC), were not present, and did not learn of the disassembly until July 5, 1994.

A document dated July 8, 1994, with a section labeled "Notes and Observations," was provided to the FAA and NTSB by the Director of Sikorsky Product Safety. This provided the observations made on July 1, 1994, and the disassembly of the MGB on July 3, 1994.

During the disassembly, the right and left side chip detectors were removed, and numerous ferrous debris was found on the magnetic wafers of both detectors. The screen portion of the detectors contained minor debris. The lubrication probe jets were removed and no evidence of debris was found on either screen element. The oil filter assembly was in the by-pass, as indicated by the red button extension. Some metallic debris was identified in the filter element.

In addition to the segments of helical gear found outside of the MGB, the remaining pieces were found inside of the MGB. These segments were determined to be part of the left hand (number one engine) helical gear rim. The center section of the helical gear remained bolted to the tail rotor take-off (TTO) spur pinion. The helical gear rim was separated from the center section of the gear, in the vicinity of the bolt holes where the 12 bolts join the helical gear and the TTO. The self-locking nuts on 2 of the 12 bolts were determined to have 60 inch pounds of torque, and a third had 20 inch pounds of torque. Eight of the remaining nuts had no measurable torque. The 12th nut was missing from the bolt. Sikorsky torque specifications required 400 inch pounds on each of the 12 nuts.

The nuts on each of the main input assemblies were removed, and the torque values were recorded in the tightening direction. The values were found to be as follows:

Number 1 Input Assembly actual reading blue print

part number 76351-09137-101 250 foot pounds 250 ft/lbs part number 76351-09135-101 350 ft/lbs 600 ft/lbs

Number