Cessna 208 N861MA

Summary

On 22 October 2013 at about 04:45 local time, a Cessna 208 registered N861MA, operated by Mokulele Flight Service Inc, was involved in an accident near Wailea, Hawaii, United States. 10 people were on board and nobody was injured. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

22 October 2013 at 04:45

Classification

Accident

Location

Wailea, Hawaii, United States

Nearest airport

Kahului (OGG)

Coordinates

21.1000, -156.7167

Aircraft

Cessna 208

Registration

N861MA

Category

Airplane

Year built

2000

Engines

1

Operator

Mokulele Flight Service Inc

Operating rule

Part 135: Air Taxi & Commuter

Phase of flight

Not recorded

Route

Kahului → Waimea-Kohala

Aircraft damage

Substantial

Weather

VMC

Light

Dusk

NTSB number

WPR14FA024

Nobody was injured.

Improper maintenance that resulted in contamination of the engine's compressor turbine disc and blade assembly by glass bead remnants, which resulted in a blade failure.

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

Read the full NTSB narrative

According to the flight crew, as the airplane passed through about 8,000 ft mean sea level during climb over open ocean water, they heard a loud bang and a grinding sound, which was followed by a loss of engine power. Sparks were observed coming out of the engine's right exhaust. The flight crew initiated a turn back towards the departure airport, which was about 13 miles north of their position. The crew accomplished the emergency checklists and elected to perform an emergency landing on a highway. During the landing roll, the airplane struck two highway traffic signs, which resulted in substantial damage to the right wing. A postaccident examination of the airplane's engine revealed that all of the compressor turbine (CT) blades had separated near the blade platforms, and the remaining stubs were gouged and battered. The fracture surface of one of the blades displayed smooth features characteristic of fatigue fracture; all other blade fracture surfaces displayed course features characteristic of overload fracture. The fatigue-fractured blade's microstructure in the fracture area was normal, and the blade material and hardness met engineering drawing requirements. The CT hub displayed a frosted appearance over the entire front and aft surfaces, and glass beads and bead fragments were observed between the fir-tree joints of the blade platforms and the CT disc, consistent with the disc assembly having been cleaned by aggressive glass media blasting in the assembled condition. The engine manufacturer specifies that all media blast cleaning be performed with the CT disc and blades disassembled. The glass bead contamination of the fir-tree joints caused the CT blades to be unevenly restrained, and it altered the blades' designed vibration frequency, making them susceptible to the aerodynamic vibrations from the combustor gas flow. Therefore, the fatigue fracture of the blade was most likely due to the glass bead contamination. The CT disc assembly had been removed from the engine for repair about two months before the accident, and this was likely when the glass bead media cleaning occurred and the beads became embedded in the exposed fir tree joints. When the CT disc assembly is installed in the engine, the fir tree joints are protected from exposure; therefore, the glass bead contamination could not have occurred when the engine was installed on the airplane.  

Quoted verbatim from the NTSB record.