- Date
- July 22, 2012, 13:30 local (18:30 UTC)
- Place
- Chicago, IL
- Injuries
- 1 minor
- Damage
- Substantial damage
- Phase of flight
- Enroute
- Aircraft
- N4970YYamokoski William Glastar
- Defining event
- Enroute-cruise: Powerplant sys/comp malf/fail
- Weather
- Visual (VMC) · Day
- Status
- Completed · report December 19, 2012
- Report
- Approved by Office Director
- NTSB office
- Central Region
- Parties
- FAA/FSDO
- FAA report
- 20120722016159A
- Case key
- 84422
From the NTSB’s public API. By law, NTSB reports can’t be used as evidence in lawsuits over the accident.
On this page
Probable cause
Failure of the automotive engine's reduction gearbox while in cruise flight.
Findings · 1
NTSB’s coded findings. Those marked are part of the probable cause; the rest are factors or other findings. Under each, the cases with the same finding.
Sequence of events
The events NTSB coded, in order, by phase of flight. The defining event is the one that best describes the accident. Under each, the cases with the same event anywhere in their sequence.
Analysis
The pilot was on a cross-country flight in an experimental airplane when the engine began to “race.” The pilot tried to reduce power by adjusting the throttle, but the engine and propeller were unresponsive. He then made a forced landing to a soft field, and the airplane nosed over. Examination of the automotive engine revealed that the spline-shaft and adapter gears in the reduction gearbox were worn, which resulted in the gearbox's failure. According to the pilot, the gearbox was not a regularly inspected item for this particular engine/gearbox combination. At the time it failed, the gearbox had accrued 247 total hours since new.
Factual narrative
On June 22, 2012, at 1330 central daylight time, an experimental-amateur built Yamokoski Glastar was substantially damaged after it made a forced landing to a field in Chicago, Illinois. The private pilot/owner/builder sustained minor injuries. No flight plan was filed for the flight that departed Wittman Regional Airport (OSH), Osh Kosh, Wisconsin, around 1200 and was destined for Southwest Michigan Regional Airport (BEH), Benton Harbor, Michigan. Visual meteorological conditions prevailed for the personal flight conducted under 14 Code of Federal Regulations Part 91. The pilot said he was following the shoreline back to Michigan when he heard and felt two "thumps" from the engine compartment. Approximately 10 seconds later, the pilot heard another thump and the engine RPM began to race. The pilot tried to reduce power by adjusting the throttle, but the engine and propeller were unresponsive. The pilot made a forced landing to a soft field and the airplane nosed-over damaging the right wing strut and the vertical stabilizer. Examination of the automotive engine revealed that the spline-shaft and adapter gears in the reduction gearbox were worn, which caused the gearbox to fail. The pilot reported that the gearbox was not a regularly inspected item for this particular engine/gearbox combination. The gearbox was installed new and had only accrued 247 hours at the time of the accident.
Aircraft
- Registration
- N4970Y
- Reported as
- Yamokoski William Glastar
- Category
- Airplane, amateur-built
- Serial number
- 5377
- Airframe hours
- 1,424
- Engine
- Subaru Boxer 2.5L, 400 horsepower, reciprocating
- Damage
- Substantial damage
- Flight
- Personal · Part 91
- Operator
- Yamokoski William
- Registered owner
- Yamokoski William
- Airworthiness certificate
- Special, Experimental (Special); Standard, Normal
- Last inspection
- Condition · October 25, 2011 · 87 hours before
- Departed
- OSH · Osh Kosh, WI
- Destination
- BEH · Benton Harbor, MI
- Airport
- None
Matched to the registry by N-number and the event date; the registry’s history has gaps, so older matches can be wrong. Compare the reported make and model.
Flight crew
As NTSB recorded them. NTSB leaves out names.
- Role
- Pilot
- Age
- 63
- Injuries
- Minor
- Certificate
- Private
- Airplane ratings
- Single-engine land
- Instrument ratings
- Airplane
- Medical
- Class 3, Unknown
- Last flight review
- May 29, 2010
- Seat
- Left
- Flight hours
- 1,515 total · 1,424 in this make and model · 47 in the last 90 days · 25 in the last 30 days
Weather
- Conditions
- Visual (VMC) · Day
- Visibility
- 10 statute miles
- Lowest ceiling
- None
Docket · 3
The files NTSB released with the investigation on October 23, 2012, on NTSB’s docket system: statements, records, photos and specialists’ reports. 1.4 MB in all.
FAA reports on this event · 1
The FAA’s own accident and incident reports, matched to the aircraft by N-number and date.
Other investigations on N4970Y · 1
Matched to the same aircraft by N-number and date.