ANC13LA026

NTSB accident investigation · Isaak Paul G Isaak Super CUB · Sterling, AK · February 28, 2013

Accident · Serious injuriesLimited investigationFinal report
Date
February 28, 2013, 15:10 local (19:10 UTC)
Place
Sterling, AK
Injuries
2 serious
Damage
Substantial damage
Phase of flight
Maneuvering
Aircraft
N130ZIsaak Paul G Isaak Super CUB
Defining event
Maneuvering-low-alt flying: Loss of control in flight
Weather
Visual (VMC) · Day
Status
Completed · report December 11, 2013
Report
Approved by Office Director
NTSB office
Alaska Regional Office
Parties
Federal Aviation Administration
FAA report
20130228003219A
Case key
86349

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

The pilot’s failure to maintain adequate airspeed while maneuvering at low altitude, which resulted in an aerodynamic stall.

Findings · 2

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

A witness familiar with the accident airplane stated that the pilot would typically make a low pass after a flight to let friends or family members know he was back. Due to injuries sustained in the accident, the pilot was unable to remember anything about the accident. According to the passenger, the pilot was making a second low pass over friends just before the accident. Witnesses reported seeing the airplane flying very slowly, about 300 feet above the ground, with the engine at a low power setting. The airplane’s right wing dipped and it subsequently entered a near vertical spiraling descent, collided with a tree and came to rest in a snow bank. The airplane sustained substantial damage to the wings, lift struts, and fuselage. No evidence of any preimpact mechanical anomaly was discovered during the postaccident examination of the airplane and engine. Given the lack of evidence of any mechanical problems, the passenger and witness’s account of the accident, along with the airplane’s near vertical descent, it is likely that the pilot inadvertently stalled the airplane at low altitude and was unable to recover.

Factual narrative

On February 28, 2013, about 1510 Alaska standard time, a ski-equipped, experimental/homebuilt Isaak Super Cub airplane, N130Z, sustained substantial damage when it collided with terrain following an in-flight loss of control, about 2 miles northwest of Sterling, Alaska. The airplane was being operated by the pilot as a visual flight rules (VFR) personal flight, under 14 Code of Federal Regulations, Part 91, when the accident occurred. The certificated private pilot and passenger sustained serious injuries. Visual meteorological conditions prevailed, and no flight plan was filed. During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge on February 29, a witness who was familiar with the accident airplane stated that, typically when the pilot retuned from a flight, he would make a low pass to let friends or family members know he was back. During the accident flight, the witness stated that the engine seemed to be running smoothly, although the engine was operating at low power setting. He said that the airplane was flying very slowly, approximately 300 feet above ground level, and then it “appeared to drop out of the sky.” The airplane entered a nose down, near vertical spiraling descent to the right, collided with a tree, and came to rest in a snow bank adjacent to a house. The witness added that during the vertical descent, the engine rpm increased significantly, which continued until impact. On February 29, 2013, a Federal Aviation Administration (FAA) airworthiness inspector from the Anchorage Flight Standards District Office, traveled to the accident site, and examined the airplane. The inspector reported that his examination revealed no preaccident mechanical anomalies that would have precluded normal operation. Due to injuries sustained in the accident, the passenger was unable to be interviewed until after his recovery. During a telephone conversation with NTSB, IIC on April 19 the passenger seated in the rear seat stated that the purpose of the flight was to go look at a moose kill, and spot for coyotes in the area. The flight departed a remote frozen snow-covered lake near his house. Upon their return they spotted some friends, and made a low pass at approximately 200 feet above the ground. They had come around for a second pass, flaps were set at one notch, and the airplane was running smoothly, when the right wing dipped, and the airplane rolled over impacting the ground. The airplane sustained substantial damage to the wings and fuselage. Due to injuries sustained in the accident, the pilot was unable to be interviewed until after his recovery. During a telephone conversation with the NTSB IIC on April 19, 2013, the pilot reported that he was unable to remember anything about the accident. The pilot did not submit an NTSB Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1).

Aircraft

Registration
N130Z
Reported as
Isaak Paul G Isaak Super CUB
Category
Airplane, amateur-built
Serial number
01
Engine
Lycoming O&VO-360 SER, 180 horsepower, reciprocating
Damage
Substantial damage
Flight
Personal · Part 91
Airworthiness certificate
Special, Experimental (Special)
Departed
Sterling, AK

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
36
Injuries
Serious
Certificate
Private
Airplane ratings
Single-engine land
Medical
Class 3, Unknown
Seat
Front

Weather

Conditions
Visual (VMC) · Day
Wind
10° at 8 knots
Visibility
10 statute miles
Lowest ceiling
7,500 ft broken
Temperature
32 °F, dew point 27 °F
Altimeter
29.34 inHg
Observed at
PAEN, 15 nm away

Docket · 1

The files NTSB released with the investigation on September 28, 2013, on NTSB’s docket system: statements, records, photos and specialists’ reports. 50 KB 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.