Schosanski John H COZY MK IV R N4518S

Summary

On 4 January 2017 at about 22:30 local time, a Schosanski John H COZY MK IV R registered N4518S was involved in an accident near Napa, California, 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

4 January 2017 at 22:30

Classification

Accident

Location

Napa, California, United States

Nearest airport

Napa County (APC)

Coordinates

38.2089, -122.2900

Aircraft

Schosanski John H COZY MK IV R

Registration

N4518S

Category

Airplane

Year built

2012

Engines

1

Operator

Not recorded

Operating rule

Part 91: General Aviation

Purpose of flight

Personal

Phase of flight

Not recorded

Route

Napa → Napa

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

WPR17LA048

Nobody was injured.

A partial loss of power due to missing apex seals. 

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

Read the full NTSB narrative

The commercial pilot reported that he was practicing touch-and-go landings in the experimental, amateur-built airplane. During the final approach, he noted that he would be landing farther down the runway then he desired, so he initiated a go-around. However, when he advanced the throttle, the engine power decreased. The pilot subsequently landed on the remaining runway, but the airplane overran the runway end and came to rest in a marsh, which resulted in substantial damage to the left wing. A Mazda automotive engine had been modified by the pilot for use in the accident airplane. The postaccident engine examination revealed that two park apex seals had been installed in each of the three corners of each rotor to seal their edges. However, the two top seals from one of the rotor sides were missing; they were not recovered after the accident. According to a Mazda rotary engine conversion guide, this engine is susceptible to premature apex seal failures, which can be greatly reduced by lubrication delivered directly by a two-stroke sump designed to burn with a minimum of deposits; the sump was tested and functioned normally. The investigation determined that the absence of these seals would have resulted in low compression and degraded power. Because there were no other mechanical malfunctions or failures noted that could have affected engine performance, it is likely that the engine lost partial power due to the missing apex seals, which likely failed and were expelled from the engine for reasons that could not be determined.

Quoted verbatim from the NTSB record.