Robinson R44 II N61NM

Summary

On 26 August 2017 at about 01:50 local time, a Robinson R44 II registered N61NM was involved in an accident near El Dorado Hills, California, United States. 2 people were on board and 2 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

26 August 2017 at 01:50

Classification

Accident

Location

El Dorado Hills, California, United States

Coordinates

38.7239, -121.0703

Aircraft

Robinson R44 II

Registration

N61NM

Category

Helicopter

Year built

2006

Engines

1

Operator

Not recorded

Operating rule

Part 91: General Aviation

Purpose of flight

Personal

Phase of flight

Not recorded

Route

Auburn → El Dorado Hills

Aircraft damage

Substantial

Weather

VMC

Light

Dusk

NTSB number

WPR17LA188

2 people had minor injuries.

Maintenance personnel's inadequate routine maintenance on the helicopter engine, which led to low cylinder compression, improper magneto timing, and camshaft lobe wear, which subsequently resulted in degraded engine performance.

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

Read the full NTSB narrative

The commercial pilot and passenger departed in the helicopter on a personal flight to a nearby lake, but decided to change course during the flight to meet a friend at his home. They approached from the north with the intention of landing in the backyard. After entering an out of ground effect hover, the pilot received a low rotor rpm indication and the helicopter began to descend. The pilot was able to restore the rotor rpm to normal momentarily, but after completing a 360° right pedal turn to search for a suitable landing site, the helicopter started to sink again. The helicopter's right skid then impacted the ground, which resulted in a dynamic rollover and substantial damage to the fuselage. The property owner stated that he saw intermittent puffs of dark gray smoke coming from the tailpipe that turned into a steady stream after the helicopter completed the pedal turn.  According to maintenance logs, verification of engine-to-magneto timing, a differential compression check, and confirmation of valve movement using a relevant service bulletin were completed during the most recent 100-hour inspection (about 104 flight hours before the accident); however, postaccident examination found that the magnetos were improperly timed by 10o, cylinder compression was low, and a camshaft lobe was severely worn and spalled, which would have inhibited two intake valves from operating normally during the accident flight and resulted in a reduction in the effectiveness of two cylinders. These anomalies resulted in a reduction in the engine's available power, and the absence of this power precluded the helicopter from maintaining an out of ground effect hover. The presence of dark smoke from an operating engine can be the result of an excessively rich mixture; however, the origin of the dark gray smoke in this case could not be determined. A flight instructor who regularly flew the helicopter stated that, despite his repeated reports of degraded engine performance, one of the multiple mechanics responsible for servicing the helicopter justified the performance issues as the result of age, as the engine was nearing its next major overhaul. This likely encouraged the instructors who flew the helicopter to dismiss the problem as well and to "manage" the lack of power instead. Additionally, the mechanic responsible for the helicopter's most recent inspection stated that he did not comply with the manufacturer's service bulletin to inspect the valves for adequate movement, which likely would have prompted an inspection of the camshaft and discovery of the lobe wear.

Quoted verbatim from the NTSB record.