ANC23LA051

NTSB accident investigation · Stinson 108 · Ninilchik, AK · July 13, 2023

Accident · No injuriesClass 3 · LimitedFinal report
Date
July 12, 2023, 16:24 local (Jul 13, 2023, 00:24 UTC)
Place
Ninilchik, AK · road
Injuries
1 uninjured
Damage
Substantial damage
Phase of flight
Enroute
Aircraft
N97719Stinson 108
Defining event
Enroute: Loss of engine power (total)
Weather
Visual (VMC) · Day
Status
Completed
Report
Approved by Office Director
Investigation class
Class 3
NTSB office
Alaska Regional Office
Parties
FAA/FSDO
FAA report
20230712014659A
Case key
192643

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

A partial loss of engine power due to failure of the No. 1 cylinder intake valve head.

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.

Engine (reciprocating): recip eng cyl sectionAircraft › Aircraft power plant · FailureStinson 108: 1 caseAll aircraft: 373 casesProbable cause

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 reported that while en route he noticed a loss of engine power and the oil pressure decreasing. He performed a forced landing to a road. During the landing rollout the right wingtip struck a sign, which resulted in substantial damage. Postaccident examination of the engine revealed the No. 1 cylinder was fractured from the engine and remained partially attached by exhaust tubes and the intake manifold. The intake valve stem was fractured about an inch from the interior base of the valve. The piston and intake valve were destroyed by the internal forces in the engine and the fragments were not located.

Factual narrative

On July 12, 2023, about 1624 Alaska daylight time, a Stinson 108 airplane, N97719, was substantially damaged when it was involved in an accident near Ninilchik, Alaska. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot stated he departed Homer Airport (HOM) destined for Anchorage, Alaska. A few miles northwest of the Ninilchik Airport (NIN) he noticed a loss of engine power and the oil pressure decreasing. The pilot determined he was too far from the NIN airport to return so he elected to perform a forced landing to a road. During the landing roll the right wingtip struck a traffic sign, which resulted in substantial damage to the right wing. Postaccident examination of the engine revealed the No. 1 cylinder was fractured from the engine and remained partially attached by exhaust tubes and the intake manifold. The intake valve head and stem was fractured about an inch from the interior base of the valve. The piston and intake valve were destroyed by the internal forces in the engine and the fragments were not located. The pilot reported the engine had a total time of 626 hours at the time of the accident. The last annual inspection was completed 12 months before the accident at an engine total time of 556.4 hours. The engine logbook showed the manufacturer’s recommended time between overhaul is 1,200 hours.

Aircraft

Registration
N97719
Reported as
Stinson 108
Category
Airplane
Serial number
108-719
Built
1946
Airframe hours
3,211
Engine
Franklin O335-150-B4, 155 horsepower, reciprocating
Damage
Substantial damage
Flight
Personal · Part 91
Airworthiness certificate
Standard, Normal
Last inspection
Annual · July 30, 2022
Departed
PAHO · Homer, AK
Destination
PAEN · Kenai, AK
Airport
NIN · Ninilchik
Equipment
Electronic flight bag or handheld device, Handheld GPS

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
38
Injuries
None
Certificate
Private
Airplane ratings
Single-engine land
Medical
Class 3, Without waivers/limitations
Last flight review
September 25, 2022
Seat
Left
Restraint
4-point
Flight hours
204 total · 130 in this make and model · 149 as pilot in command · 24 in the last 90 days · 10 in the last 30 days

Weather

Conditions
Visual (VMC) · Day
Wind
180° at 3 knots
Visibility
10 statute miles
Lowest ceiling
1,100 ft broken
Temperature
55 °F, dew point 52 °F
Altimeter
30.16 inHg
Observed at
AHO, 24 nm away
METAR
PAHO 121953Z 18003KT 10SM SCT007 BKN011 13/11 A3016 RMK AO2 SLP212 T01280106

Docket · 5

The files NTSB released with the investigation on August 21, 2024, on NTSB’s docket system: statements, records, photos and specialists’ reports. 30.6 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.