N9876R

On September 15, 2022, about 1202 Pacific daylight time, a Beech M35 airplane, N9876R, was substantially damaged when it was involved in an accident near Henderson, Nevada. The flight instructor and pilot receiving instruction were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight.

The flight instructor reported that they planned to fly from their home airport in Camarillo, California, to satisfy an insurance requirement. The airplane was equipped with a total of 6 fuel tanks: two main fuel tanks, two auxiliary fuel tanks, and two wingtip fuel tanks. The instructor visually checked the main and auxiliary tanks by opening the fuel caps. He verified the fuel quantity of the wingtip tanks by visually observing each tanks’ window gauge. The instructor reported the following main fuel tank levels were observed during his preflight inspection (only the main fuel tanks were used during the accident flight):

Fuel Tank

Fuel Level

Left main (25 gallons total)

3/4

Right main (25 gallons total)

Full

Table 1: Fuel quantities before their departure on the accident flight

According to the instructor, they departed for their destination about 1005 and climbed to a cruise altitude of 7,500 ft mean sea level. The pilot, who was seated in the left seat, stated that about 40 minutes into the flight, and 45 minutes before landing, they switched to the right main fuel tank and confirmed that the fuel quantity displayed FULL on the digital fuel gauge. However, about 25 minutes later, the right main fuel gauge still indicated that the tank was FULL. The instructor and the pilot discussed the abnormality, which they attributed to a faulty sensor, but dismissed the issue after they determined that the tank contained sufficient fuel to complete the flight to their destination. About 15 minutes later, the pilot began a straight-in approach to runway 35L. While on final approach the pilot noticed the airplane’s altitude was low, so he added power but did not receive a response from the engine. The pilot then informed the instructor of the loss of altitude while he advanced the throttle to the full open position. As the pilot continued to fly the airplane, the instructor selected the left main tank on the fuel selector to restore engine power, but he was unsuccessful, and the airplane continued to descend.

The airplane touched down in the dirt, impacted a berm, and came to rest on a road about 0.2 nautical miles south of the runway.

Both pilots co-owned the airplane, which they had purchased together in July 2022.

The airplane received substantial damage to the fuselage and left wing. A Federal Aviation Administration inspector observed the following fuel levels about one hour after the accident:

Fuel Tank

Fuel Level

Left main (25 gallons total)

1/2

Right main (25 gallons total)

Empty

Table 2: Fuel quantities one hour after the accident

Fuel System

According to the pilot’s operating handbook, the airplane was equipped with both main bladder fuel tanks installed at the inboard right and left wing. Outboard of the main fuel tanks are right and left wing auxiliary fuel tanks. The airplane was also equipped with right and left wingtip fuel tanks composed of fiberglass, which were installed in accordance with Federal Aviation Administration Supplemental Type Certificate SA 02722CH.

The capacity of each main fuel tank is 25 gallons (22 gallons usable). Fuel is fed from both tanks to a selector valve before it continues to a fuel strainer, fuel pump and then the engine. The fuel quantity is measured by float-operated sensors that transmit electrical signals to the fuel quantity indicators on the instrument panel. Total capacity of the auxiliary tanks is 20 gallons (19 gallons usable).

A postaccident examination of the fuel system found that the right main fuel tank bladder had collapsed. The inspection did not reveal any blockages in any of the fuel lines and the right main fuel tank vent was clear. When the right main fuel tank was pressurized, no leaks were observed at the fuel cap. A test of the right main fuel tank quantity measurement system found that it reported ½ - ¾ full regardless of the float sensor position in the fuel bladder. No visible breaches were observed in the right main fuel tank.

JPI Data

The airplane was equipped with a JPI 930 engine monitoring system. Data retrieved from the unit that captured the accident flight showed that the airplane departed about 1037, when the manifold pressure was increased to about 23 inches Hg and the engine speed was about 2,500 rpm. The right main fuel level indicated 22 gallons at the time and indicated between 18 and 22 gallons for the remainder of the flight. The left tank fuel level was about 17 gallons at the time and indicated between 8 and 12 gallons when they switched tanks about 45 minutes before their planned landing. Fuel flow was about 22 gph during cruise flight from about 1050 to 1141, at which point the fuel flow decreased to about 17 gph where it remained until the engine lost power. At 1202:26 fuel flow decreased from about 15 gph to 0 gph, accompanied by a rapid reduction in exhaust gas temperature (EGT) at each cylinder from about 1,200 – 1,400° F to about 800 – 1,000° F. During this time, manifold pressure increased to about 25 inches Hg and rpm decreased from 2,500 rpm to 1,800 rpm. In the next 30 seconds the EGTs further decreased to about 250° F, with an increase of manifold pressure to about 28 inches Hg and a decrease of engine speed to about 1,000 rpm.