N35700Cessna 172I · 1968

On June 6, 2017, about 1800 Alaska daylight time, a Cessna 172I (Skyhawk) airplane, N35700, sustained substantial damage following a loss of engine power and a subsequent impact with terrain at the Birchwood Airport (BCV), Chugiak, Alaska. The private pilot and sole passenger sustained minor injuries. The airplane was registered to and operated by the pilot under the provisions of Title 14 Code of Federal Regulations Part 91 as a visual flight rules personal flight when the accident occurred. Day visual meteorological conditions prevailed, and no flight plan had been filed. The flight departed from the Sixmile Lake Airport (AA06), Anchorage, Alaska at about 1700.

The pilot reported the route of the flight went to the Knik Glacier area and was to terminate back at AA06. The purpose of the flight was for sightseeing with a friend. Enroute back to AA06 while flying about one half mile southwest of BCV at 1,200 ft above mean sea level and 100 kts, the engine started "sputtering" and then quit. The pilot reported he adjusted the airspeed to about 65 kts and attempted to restart the engine. In a written statement dated June 11, 2017, he reported he "went through a quick flow" of checking the master switch, the key position, all of the electrical circuit breakers, the throttle, the mixture, the propeller control, and the fuel selector valve. He switched the fuel selector valve from the right position to the left position, turned on the boost pump, and tried to restart the airplane with no success. He then switched the fuel selector valve to the both position and tried another start with no success.

The pilot attempted to conduct a forced landing at the nearest airport and maneuvered the airplane for a landing to runway 02L at BCV. Subsequently, the airplane touched down short of the runway in a flat open field about 20 ft south of the airport. During the landing roll, the airplane impacted the airport perimeter chain-link fence, the nose wheel separated, the propeller impacted terrain, and the airplane came to rest inverted in the grass, about 150 ft to the southeast of the threshold of runway 02L as shown below in figure 1. The airplane sustained substantial damage to both wings, the fuselage, and the empennage. The two occupants egressed from the inverted airplane without further incident.

Figure 1 – View of the inverted airplane at BCV (courtesy of the NTSB).

In a conversation on June 8, 2017 with the NTSB investigator-in-charge (IIC), the pilot reported that the fuel selector valve was in the "left position" when the engine started to cause problems. He initially reported that he was "using the left" fuel tank prior to the accident. He later reported that he was "using the right" fuel tank prior to the accident. He added, he switched the fuel selector valve to "both" after being in the left and right positions. After the airplane impacted terrain and came to rest, he reported that he set the fuel selector valve to the off position.

In the safety recommendation section of the NTSB Accident/Incident Reporting Form 6120.1, the pilot recommended further experience for himself with the inflight restarting procedures for the airplane.

A review of the airplane maintenance records revealed that the originally installed engine, a 150-horsepower Lycoming Engines O-320-E2D, was removed and the accident engine, a 200-horsepower Lycoming Engines IO-360-A1B6 (serial number L-19632-51A), was installed in May 1995. The engine retrofit was completed under Supplemental Type Certificate (STC) SA807CE.

In May 1995, an 18-gallon O&N Aircraft Modifications, Inc., auxiliary fuel tank (kit number 172100, serial number 182) was installed in the aft baggage compartment under STC SA615NE.

A review of the airplane maintenance records revealed that the originally installed engine, a 150-horsepower Lycoming Engines O-320-E2D, was removed and the accident engine, a 200-horsepower Lycoming Engines IO-360-A1B6 (serial number L-19632-51A), was installed in May 1995. The engine retrofit was completed under Supplemental Type Certificate (STC) SA807CE.

In May 1995, an 18-gallon O&N Aircraft Modifications, Inc., auxiliary fuel tank (kit number 172100, serial number 182) was installed in the aft baggage compartment under STC SA615NE.

The NTSB IIC and a Federal Aviation Administration (FAA) aviation safety inspector (ASI) traveled to BCV shortly after the accident occurred on June 6, 2017. The NTSB IIC and the FAA ASI documented the accident site. Both wing fuel tanks remained intact from the accident sequence and no signs of a fuel leak were observed. Both wing fuel tank caps were observed to be correctly installed and secured. The wreckage was recovered and transported to a secure location in Wasilla, Alaska for a future examination of the airframe and engine. During the recovery process, about 1 gallon of fuel was retrieved from the left wing and about 7.5 gallons of fuel were retrieved from the right wing. On August 15, 2017, a wreckage examination and layout were conducted under the direction of the NTSB IIC. Two FAA ASIs along with air safety investigators from the NTSB and Textron Aviation were present.

Airframe control continuity was established. Airframe to engine control continuity was also established.

The fuel selector valve, as shown below in figure 2, was examined and manipulated freely to all four positions (left tank, right tank, both tanks, and off) with no issues noted. Heavy usage marks were observed on the valve, which was intact and connected to the system via a split pin. The placard on the fuel selector valve stated, "Switch to single tank operation immediately upon reaching cruse altitude above 5,000 feet."

Figure 2 – Fuel selector valve (courtesy of the NTSB).

The fuel strainer screen was observed to be clean and free from debris. The fuel strainer bowl was observed to have light corrosion and free from debris.

Upon examination of the auxiliary tank, residual fuel was observed, but it was located below the fuel pickup port in the auxiliary tank. Fuel samples from the left wing tank, the right wing tank, the auxiliary tank, and the gascolator were tested using water-finding paste. No presence of water was detected in all the fuel samples. All the fuel samples had similar appearance and smell to 100 low lead fuel.

The engine was functionally tested on the airframe as shown below in figure 3. A fuel can, containing about 2 gallons of fuel that had been recovered from the wing tanks, was plumbed directly to the boost pump. The engine was started normally and operated at idle for about 5 minutes. The throttle was advanced to 1,700 RPM and a magneto check was performed; both magnetos dropped about 100 RPM. The throttle was advanced to a higher power momentarily and then power was reduced to further stabilize the airframe. The engine was shut down by pulling the mixture lever to cutoff.

Figure 3 – View of the engine operating (courtesy of the NTSB).

The airframe was secured, and a second engine run was attempted. The second attempt to start the engine was unsuccessful. The fuel line from the fuel servo to the flow divider was disconnected and the boost pump was operated to verify fuel system continuity. Fuel was observed exiting from the disconnected servo fuel line. The line was reconnected. The fuel injector lines were disconnected, and the boost pump was operated again to verify fuel system continuity through the manifold valve. Fuel was observed exiting from all four injector lines. The magneto P-leads were disconnected, and the engine was restarted. The engine started roughly and exemplified a rich mixture. After about 15-20 seconds the engine cleared and stabilized at an idle speed. The engine was operated at idle for several minutes and then at full power momentarily. The engine was then shutdown and the magneto P-leads were reconnected. The engine was started again and operated normally when the mixture lever was pulled out about 2 inches to lean the engine. Refer to the engine test video in the public docket.

The fuel injector servo (Bendix, model RSA-5AD1, serial number 69450) was removed from the engine after the test runs for further examination and testing.

The examination revealed no preimpact mechanical malfunctions or failures with the airframe and engine. An examination of the airplane's maintenance records revealed no evidence of uncorrected mechanical discrepancies with the airframe, engine, and propeller.

Cessna 172I Fuel System

The Cessna 172I Owner's Manual discusses the fuel system and starts in part:

Fuel is supplied to the engine from two tanks, one in each wing.

Fuel from each wing tank flows by gravity to a selector valve.

Fuel Management

The Cessna Pilot Safety and Warning Supplements (D5139-13) discusses the importance of fuel management and states in part:

Poor fuel management is often the cause of aircraft accidents.

Pilots should be thoroughly familiar with the airplane fuel system and tank switching procedures.

Fuel Selector Valves

The FAA Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25B) discusses how a fuel selector valve works and states:

The fuel selector valve allows selection of fuel from various tanks. A common type of selector valve contains four positions: LEFT, RIGHT, BOTH, and OFF. Selecting the LEFT or RIGHT position allows fuel to feed only from the respective tank, while selecting the BOTH position feeds fuel from both tanks. The LEFT or RIGHT position may be used to balance the amount of fuel remaining in each wing tank.

Fuel placards show any limitations on fuel tank usage, such as "level flight only" and/or "both" for landings and takeoffs.

Regardless of the type of fuel selector in use, fuel consumption should be monitored closely to ensure that a tank does not run completely out of fuel. Running a fuel tank dry does not only cause the engine to stop but running for prolonged periods on one tank causes an unbalanced fuel load between tanks. Running a tank completely dry may allow air to enter the fuel system and cause vapor lock, which makes it difficult to restart the engine. On fuel-injected engines, the fuel becomes so hot it vaporizes in the fuel line, not allowing fuel to reach the cylinders.

Fuel Injection Systems

The FAA Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25B) discusses the basic components of a fuel injection system works and states in part:

A fuel injection system usually incorporates six basic components: an engine-driven fuel pump, a fuel-air control unit, a fuel manifold (fuel distributor), discharge nozzles, an auxiliary fuel pump, and fuel pressure/flow indicators.

This document also discusses the disadvantages of using fuel injection and states in part:

Difficulty in starting a hot engine.

Problems associated with restarting an engine that quits because of fuel starvation.

The airplane did not carry, nor was required to carry, a crashworthy flight data recorder.

Fuel Injector Servo

On November 28, 2017, an examination and flow check of the fuel injector servo were conducted under the direction of the NTSB IIC at Precision Airmotive in Arlington, Washington. The examination revealed no preimpact mechanical malfunctions or failures with the fuel injector servo. The fuel servo successfully passed the flow check.

Global Positioning System

An undamaged Garmin Aera 660 hand-held global positioning system (GPS) was recovered from the airplane and downloaded by the NTSB. The flight track data showed the airplane descended in a left turn toward BCV before it impacted terrain just short of runway 02L. Refer to the NTSB GPS Factual Report in the public docket for additional information.