Beechcraft 99 N326CA

Summary

On 19 January 2017 at about 18:48 local time, a Beechcraft 99 registered N326CA, operated by Alpine Aviation Inc, was involved in an accident near Billings, Montana, United States. One person was 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

19 January 2017 at 18:48

Classification

Accident

Location

Billings, Montana, United States

Nearest airport

Billings Logan Intl (BIL)

Coordinates

45.8078, -108.5428

Aircraft

Beechcraft 99

Registration

N326CA

Category

Airplane

Year built

1970

Engines

2

Operator

Alpine Aviation Inc

Operating rule

Part 135: Air Taxi & Commuter

Phase of flight

Not recorded

Route

Glendive → Sidney

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

WPR17LA056

Nobody was injured.

The fatigue failure of the left main landing gear (MLG) actuator piston rod, which prevented the hydraulic system from producing pressure to control the MLG’s position and led to the right MLG collapsing during landing.

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

Read the full NTSB narrative

The commercial pilot reported that, after departing for the cross-country, cargo flight, he retracted the landing gear and heard a "thud" sound. Subsequently, the main landing gear (MLG) "unsafe" light illuminated, and the left MLG light remained illuminated green, indicating that it was still extended despite the landing gear handle being in the retracted position. The pilot returned to the departure airport, and during touchdown, the right MLG collapsed, which resulted in substantial damage to the right aileron and right wing spar. During the postaccident examination of the landing gear, the left MLG actuator's piston rod was found fractured. Metallurgical examination of the piston rod revealed that the rod had failed in its threaded section due to fatigue cracking over about 60% of the cross-section. Contact wear was observed on the faying surface of the retaining nut and piston head and the shoulder of the piston rod. These signatures were consistent with the nut not being tight enough to mitigate sliding of the piston head relative to the piston rod and retaining nut. It could not be determined if the manufacturer required a specific torque to be applied to the nut during assembly. Based on the evidence, it is likely that inadequate torque on the nut reduced the preload on the threaded section of the piston rod and contributed to premature fatigue crack propagation in the rod and its eventual failure. The failure of the piston rod allowed hydraulic fluid to pass freely from the down-side to the up-side of the piston, which prevented the hydraulic system from producing pressure to control the MLG's position.

Quoted verbatim from the NTSB record.