Friday, July 7, 2017

de Havilland Canada DHC-2 Beaver, N4787C: Accident occurred July 24, 2013 in Thorne Bay, Alaska

The National Transportation Safety Board did not travel to the scene of this accident.

Additional Participating Entity:
Federal Aviation Administration / Flight Standards District Office; Juneau, Alaska

Aviation Accident Final Report - National Transportation Safety Board:

Investigation Docket - National Transportation Safety Board:

Aviation Accident Data Summary - National Transportation Safety Board:

Registered Owner: Dole Enterprises LLC
Operator: Promech Air LLC 

NTSB Identification: ANC13LA068
Nonscheduled 14 CFR Part 135: Air Taxi & Commuter
Accident occurred Wednesday, July 24, 2013 in Thorne Bay, AK
Probable Cause Approval Date: 03/17/2015
Aircraft: DEHAVILLAND BEAVER DHC 2, registration: N4787C
Injuries: 3 Serious, 1 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The pilot reported that, while the float-equipped airplane was in cruise flight about 1,200 ft above ground level, the engine made a loud noise and lost partial power, so he maneuvered the airplane to land on a nearby lake. During the approach, the engine lost total power, and the airplane descended into an area of trees before reaching the lake, which resulted in substantial damage to the wings, fuselage, and empennage. 

The operator reported that the engine had been overhauled (zero-timed) 31 hours before the accident. A postaccident engine examination revealed metal fragments and heavy gouging damage to the rotating components within the crankcase. The bottom portion (crankshaft end) of the No. 1 linkrod and its respective bushing were missing from the No. 1 linkpin; the oil sump contained metal debris consistent with heavily damaged remnants of these (and other) components. The No. 2 cylinder barrel and linkrod and the No. 3 linkrod showed deformation to the left (in the direction of engine rotation). Based on the damage observed in the engine, it is likely that the event that initiated the engine failure involved either the the No. 1 linkrod bushing or the bottom portion of the No. 1 linkrod; however, the extensive damage to these components precluded determination of the failure mode.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
The failure of the No. 1 linkrod bushing or the bottom portion of the linkrod, which resulted in a total loss of engine power.

On July 24, 2013, about 1140 Alaska daylight time, a float-equipped de Havilland DHC-2, N4787C, collided with trees following a loss of engine power near Lake Galea, about 15 miles northwest of Thorne Bay, Alaska, on Prince of Wales Island. The airline transport pilot and two passengers received serious injuries, one passenger was uninjured, and the airplane sustained substantial damage. The on-demand air taxi flight was operated by Promech Air, LLC, under the provisions of 14 Code of Federal Regulations (CFR) Part 135 with a company visual flight rules flight plan filed. Visual meteorological conditions prevailed. The flight departed Ketchikan Harbor Seaplane Base (5KE), Ketchikan, Alaska, at 1100 and was destined for Shipley Bay, Alaska.

According to the pilot, the airplane was in cruise flight at an altitude of about 1,500 feet above mean sea level (msl), which he estimated was about 1,200 feet above ground level (agl) in the area over which he was flying, when he heard a loud "boom" and a series of loud and continuous "pop-pop-pop" noises. The pilot said that he reported to the company via the radio that he had lost an engine cylinder and was going to land. The pilot said that everything was shaking and that he did an immediate 180-degree turn to land on the lake that he had just overflown. The pilot stated that, as he turned the airplane on a base leg for the lake, he put in two pumps of flaps, and, about that time, the engine lost power completely. The pilot estimated that the amount of time that elapsed from when he first heard the loud "boom" to the time that the engine lost power completely was less than 1 minute. The pilot stated that, once the engine lost power completely, the airplane was soon colliding with trees. According to the operator, the airplane came to rest in a wooded area about 300 yards from the lake, sustaining substantial damage to the wing, fuselage, and empennage. 

The pilot stated that he and two passengers were able to exit the airplane but the passenger in the right seat was unable to exit the airplane until more help arrived. The pilot located the airplane's 406-MHz emergency locator transmitter and flipped the switch to the "on" position to be sure that it was transmitting. According to the operator, the Rescue Coordination Center (RCC) telephoned the operator and provided coordinates for the downed airplane. The pilot also located the airplane's survival kit, and he and a passenger positioned a piece of wing wreckage in a marsh area to try to make the accident site visible to overflying aircraft. The pilot established cellular telephone contact with the operator, which had dispatched another company airplane to assist. The pilot said that he heard the other company airplane approaching and used a flare from the survival kit to signal his location. The other company airplane landed on Lake Galea, and company personnel hiked to the accident site to assist the pilot and passengers. A U.S. Coast Guard (USCG) helicopter from Air Station Sitka soon arrived. The USCG transported the pilot and all three passengers from the scene two at a time.

Aircraft recovery personnel who retrieved the wreckage and Federal Aviation Administration (FAA) inspectors who observed reported that engine cylinder damage was visible. According to the operator, the Pratt & Whitney R-985-AN-14B engine had accumulated 31 hours since major overhaul.

Subsequent disassembly examination of the engine under the authority of the NTSB revealed that the No. 1 cylinder head showed both vertical and horizontal cracks, and the top of the No. 1 piston was visible through the cracks. The No. 1 piston was positioned abnormally high within the cylinder barrel. The vertical crack in the No. 1 cylinder head extended over the top of and bisected the cylinder head, and a horizontal crack extended around the circumference, such that the bisected halves of the cylinder head could be lifted off by hand, exposing the piston top.

Internal damage to the engine precluded the removal of any cylinders using typical engine disassembly techniques. The No. 1 cylinder barrel and the No. 1 piston could not be removed. Removal of the Nos. 2, 3, 6, 7, 8, and 9 cylinders (accomplished by prying the cylinder barrels and applying force) and removal of their respective pistons allowed for a view inside the crankcase. The top (piston end) of the No. 1 linkrod was attached to the piston pin (established by feel), but the bottom portion (crankshaft end) of the linkrod and its respective bushing were missing. The linkpin for the No. 1 linkrod was attached to the crankshaft assembly.

The remaining visible linkrods (Nos. 2, 3, 6, 7, 8, and 9) all exhibited gouging damage. The No. 2 linkrod and No. 2 cylinder barrel showed pronounced deformation to the left (in the direction of engine rotation). The No. 3 linkrod also showed deformation to the left. The underside of the removed pistons (Nos. 2, 3, 6, 7, 8, and 9) all showed heavy gouging damage, and the No. 2 piston also was cracked on the bosses for the piston pin. A piece of a separated crankshaft counterbalance weight was found inside the crankcase with fragments of its attachment bolts present in the separated piece. The separated counterbalance weight piece showed heavy gouging damage. Metal fragments and heavy gouging damage were visible inside the crankcase. The oil sump contained metal debris, including fragments that appeared visually consistent with the color of bushing material, fragments that appeared visually consistent with the shape of piston ring pieces, and other metal debris. 

A maintenance record for the airplane dated July 16, 2013, recorded the installation of engine SN JP206275 at an engine time since overhaul of 0.0 hours, an engine total time of 6,029.5 hours, and an airframe total time of 33,326.1 hours. The engine's authorized release certificate and airworthiness approval tag from the FAA-certificated repair station that performed the overhaul was dated June 6, 2013. A record dated May 28, 2013, documented that the engine's ground test run was 5 hours. A repair station record dated May 15, 2013, (which documented the engine's "inspection, reconditioning, and assembly in accordance with Pratt & Whitney Manual No. 123440") noted that the engine's linkrods were serviceable, and the linkpin bushings were replaced. A record dated January 23, 2013, documented the magnetic inspection of the linkrods. During a telephone interview, a representative from the facility that had performed the engine overhaul stated that the facility had experienced no changes in its linkpin bushing supplier and no differences in its techniques or procedures for performing engine overhauls with regard to the overhaul of the accident engine compared to others.

A floatplane crash injured four people Wednesday on Prince of Wales Island in Southeast, according to Alaska State Troopers.

The de Havilland DHC-2 Beaver, operated by Ketchikan-based Promech Air, went down in some trees near Thorne Bay and Lake Galea, troopers said. The crash occurred about 11:40 a.m. and triggered an emergency locator transmitter, according to the Coast Guard. Promech Air personnel -- who had received radio communication from the pilot saying the plane's engine was dying -- also called for help, the Coast Guard said.

A Coast Guard helicopter crew rescued two of the plane's four occupants and returned to get the final two just before 5 p.m., a Coast Guard spokesman said. All were expected to survive.

The pilot was identified as Charlie Kenlin, 65, of Florida. The passengers were Martin Lakey, 37, Michael D. Lakey, 65 and Rich Webster, 65, all of Washington, according to an online dispatch.

Promech Air offers flight-seeing and charter service. A woman who answered the phone at the company's office said the plane that crashed was not providing either service but declined to comment further.

ANCHORAGE, Alaska— Two people were seriously injured Wednesday when a flightseeing plane with four people on board crashed on Prince of Wales Island in Southeast Alaska, according to Alaska State Troopers.

The U.S. Coast Guard told AST at about noon Wednesday that an emergency locator transmitter from a de Havilland Beaver -- flown by Ketchikan-based tour operator Promech Air -- had been activated near Thorne Bay, troopers wrote in a Wednesday dispatch.

“Investigation determined (the plane) went down in the trees near the southern end of Lake Galea due to engine complications,” troopers wrote. “Two of the four people on board were flown via a USCG helicopter to the Ketchikan General Hospital for treatment of non-life threatening injuries.”

AST spokesperson Beth Ipsen says troopers weren’t immediately aware of the extent of the injuries Wednesday afternoon. She says the helicopter crew had to leave the plane’s other two occupants with minor injuries at the crash site, with a return flight planned to pick them up.

“It was at capacity, because it was a helicopter and they had weight restrictions, so they flew the two injured and came back for the other two,” Ipsen said.

Promech Air didn’t have immediate comment on the incident Wednesday afternoon.

Troopers say the National Transportation Safety Board has been notified of the crash.

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