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March 3, 2008 · Raytheon Aircraft B36TC · N234MT

Mammoth, CA

Overview

Report Status
Final with probable cause
Event Type
Accident
Date
March 3, 2008
Injury Outcomes
2 injuries (1 serious injury, 1 minor injury)
Location
Mammoth, CA
Aircraft
Raytheon Aircraft B36TC
Tail Number
N234MT
Operator
Michael S Thesman
Injuries
Serious
Aircraft Damage
Substantial
NTSB Number
SEA08LA084

About three minutes after takeoff, the airplane's engine experienced a complete loss in power, but the propeller kept turning. Since the pilot could not get the engine restarted, he configured the airplane for a normal landing, and touched down in what appeared to him to be level snow-covered terrain. Upon touchdown, the airplane sank through about three feet of dense snow, which resulted in a rapid deceleration. Both the airplane's belly and the inboard portion of its wings suffered crushing damage. Inspection of the airplane's fuel storage and delivery systems, and the teardown inspection of the components of the turbocharger system did not reveal any evidence of an anomaly that would have kept the engine from producing full rated horsepower. The engine was successfully test run at various power settings up to a maximum of 2,400 rpm and 30 inches of manifold pressure.

NTSB Probable Cause

A loss of engine power for undetermined reasons. Contributing to the accident was dense snow covering the level terrain.

Full Narrative

On March 2, 2008, about 1620 Pacific standard time, a Beechcraft B36TC, N234MT, collided with snow that was covering level terrain about three miles south of Mammoth Yosemite Airport, Mammoth Lakes, California. The private pilot received minor injuries, his passenger received serious injuries, and the airplane, which was owned and operated by the pilot, sustained substantial damage. The 14 Code of Federal Regulations (CFR) Part 91 personal cross-country flight, which departed Mammoth Yosemite Airport about five minutes prior to the accident, had a planned destination of Van Nuys, California. The pilot had not filed a flight plan. According to the pilot, three or four minutes after takeoff, the engine experienced a "major loss in power." He therefore turned back toward the airport and began to take action to try to restore full power. During this process he switched fuel tanks, checked the magnetos, activated the fuel boost pump to the prime position, and switched to alternate induction air. Ultimately, although the propeller kept turning, the engine lost all power, and the pilot began to look for what he thought would be a safe place to land. He elected to execute a forced landing on level snow-covered terrain in what appeared to be an open field. He then configured the airplane for a normal landing, and touched down in about three feet of dense snow with the landing gear extended. Upon touchdown, the landing gear broke through the surface of the snow, and as the airplane sank into the snow it decelerate rapidly. The accident sequence resulted in crushing damage to the airplane's belly and to the inboard portion of both wings. During the investigation it was determined that at the time of takeoff, the airplane contained about 65 gallons of aviation fuel, which was evenly distributed between the right and left fuel systems. The wreckage was recovered to the facilities of Air Transport, of Phoenix, Arizona, where an FAA-directed inspection of the airframe and engine was performed. That inspection did not reveal any anomalies in the airframe, its air induction system, or its fuel delivery system. After a visual inspection, the engine was successfully run at various power settings up to 2,400 rpm and 30 inches of manifold pressure. As part of the investigation the turbocharger turbine/compressor assembly, pressure relief valve, variable absolute pressure controller, and exhaust bypass valve assembly were sent to Kelly Aerospace Power Systems, where an FAA-monitored teardown inspection was performed. That inspection did not reveal any evidence of anomalies or malfunctions that would have prevented these components from operating in accordance with field serviceable standards.

Flight

Event TypeAccident
Event Time16:20 PST
Nearest Airport0nm
Flight Plan FiledNone
Aircraft FireNo
Aircraft ExplosionNo

Aircraft

AircraftRaytheon Aircraft B36TC
Tail NumberN234MT
Aircraft CategoryAir
DamageSubstantial
OperatorMichael S Thesman
Operating RulePart 91
Engines1
Engine TypeReciprocating
Engine DetailsCont Motor · TSIO-520-UB · Reciprocating · 300
Seats6

People & Injuries

Injury Summary2 injuries (1 serious injury, 1 minor injury)
Fatal0
Serious1
Minor1
Uninjured0
Total2
Crew 1Age 48 · Third Class · Minor

Conditions

ConditionsVMC
LightDaylight
WindCalm
Visibility10 sm
CeilingNone
Temperature / Dew Point39 C / 0 C
Altimeter0
Weather SourcePILO

Appendix: Source Data