N6841QBeech 35-B33 · 1964

On April 13, 2013, about 1221 mountain standard time, a Beech 35-B33, N6841Q, collided with a ditch during a forced landing near San Manuel Airport, San Manuel, Arizona. The pilot was operating the airplane under the provisions of 14 Code of Federal Regulations Part 91. The airline transport pilot sustained serious injuries. The airplane sustained substantial firewall and fuselage damage just aft of the cabin, as well as both wings during the accident sequence. The cross-country flight departed Pegasus Airpark, Queen Creek, Arizona, about 1150, with a planned destination of San Manuel. Visual meteorological conditions prevailed, and no flight plan had been filed.

The pilot reported that the flight was part of a round-robin trip initiating from Tucson International Airport, and then onwards to Pegasus Airpark, with a stop at San Manuel for fuel, and a return to Tucson. He stated that the flight was uneventful, and upon approaching San Manuel he overflew the airport heading north at an elevation of 5,000 feet, and initiated a left turn to enter the right downwind leg for runway 29. He reduced engine power, and descended to 4,100 feet, extended the landing gear, and deployed full flaps. He initiated the base turn while increasing engine power, but the engine did not respond. He immediately turned on the auxiliary fuel pump with no effect. The airplane was not sufficiently high enough to reach the runway, so he performed a forced landing in rough rising terrain short of the field.

The pilot reported that the left fuel tank quantity indicator gauge was inoperative, and that it was his understanding that the left fuel tank contained more fuel than the right during the landing approach. He surmised that fuel flow may have been restored if he had switched to the right fuel tank when the engine lost power.

The left wing sustained a leading edge gouge 24 inches outboard of the root, which had breached the fuel tank bladder. Recovery crew stated that at the accident site the right fuel tank contained about 12 gallons of fuel, and the left tank contained about 10 gallons.

The engine and airframe were examined at a recovery facility by the NTSB investigator-in-charge, with engine assistance provided by a representative from Continental Motors, Incorporated.

The following is a partial summary of the airframe, engine, and fuel pump/metering unit examinations. No anomalies were noted to any of the engine, airframe, or fuel control components that would have precluded normal operation. See the public docket for full examination reports.

The fuel selector valve was examined, and moved through the "OFF", "LEFT TANK", and "RIGHT TANK" positions. The detents were positive, with an audible click heard as the selector handle was rotated through each position. The fuel lines from the firewall through to each wing fuel tank were free of obstruction, and about 8 ounces of fuel was drained from the selector valve sump. Disassembly of the valve revealed that its screen was free and clear of debris and corrosion. Blue-colored fuel was present in the line from the selector valve to the engine driven and auxiliary fuel pumps.

The engine sustained minimal damage, and remained partially attached by its mounts on the right side. The inlet air filter and box were crushed, and the fuel injection control assembly had broken away from the sump and throttle control body.

The fuel lines between the pump and metering unit, along with the metering unit through to the manifold valve, had broken off at their respective fittings. The flow divider was opened, and its diaphragm was pliable and free of cracks. No fuel was observed within the divider cavity, or any fuel lines forward of the engine driven fuel pump.

The engine driven fuel pump was removed, and the drive shaft was intact. The pump's input drive was rotated by hand, was stiff to turn, and made a squeaking sound.

The engine driven fuel pump and fuel injection control assembly were subsequently retained and examined at the facilities of Pacific Continental Engines (PCE), Pacoima, California, in the presence of the NTSB investigator-in-charge.

Disassembly of both units revealed no internal blockages, or debris to be present within any internal cavity or passage, and all internal components were free of corrosion. The inner walls of the fuel pump body assembly were shiny and free of gouges. The fuel pump shaft, and associated plate end and blades were intact, and the blade contact surfaces and plate end exhibited light scoring, which according to representatives from PCE was consistent with normal service. The representative further stated that rotational resistance by hand at the input shaft was not unusual, and there were no indications of a catastrophic internal failure.

GPS and Turn Performance

The airplane was equipped with a Garmin GPSMap handheld GPS receiver. The unit was configured to record track data, which was downloaded by the NTSB investigator-in-charge. Examination of the data revealed that after departing Pegasus Airpark the airplane began a gradual 25-minute climb from airport elevation (1,450 feet) to 6,067 feet while continuing on a southeast heading. Having reached this altitude about 9 miles northwest of San Manuel, the airplane immediately began a descent, overflying the airport about 3 minutes later at an altitude of 5,246 feet (1,975 feet agl). Over the course of the next 3 minutes, the airplane began a series of four segmented left turns ultimately resulting in one complete circle north of the airport. The airplane then joined the right downwind leg for runway 29 about midfield at an altitude of 4,200 feet. Having reached the end of the downwind leg, the airplane began a descending right turn through base to final, with the last position report occurring at an elevation of 3,192 feet, about 2,600 feet short of the runway 29 threshold.

The airplane's turning performance as it circled north of the airport was calculated utilizing the GPS data in conjunction with Aerodynamics for Naval Aviators (NAVWEPS 00-80T-80), Figure 2.29, General Turning Performance (Constant Altitude, Steady Turn). The most aggressive turn was to the left, lasted about 35 seconds, and occurred about 45 seconds before the airplane joined the right downwind leg. The radius of the turn was about 2,500 feet, with an average ground speed of 140 knots. Utilizing these values, the bank angle during the turn would have been about 35 degrees.

The limitations section of the Beechcraft Pilot's Operating Handbook applicable to the accident airplane model defined the following maneuvering limits with respect to certain flight operations:

This is a utility category airplane. Spins are prohibited. No acrobatic maneuvers are approved except those listed below. Maximum slip duration is 30 seconds for airplanes with baffled main fuel cells in both wings and 20 seconds for airplanes with unbaffled main fuel cells in either wing.

Chandelle 128 kts/147 mph

Steep Turn 128 kts/147 mph

Lazy Eight 128 kts/147 mph

Stall (Except Whip) Use slow deceleration

Minimum fuel for above maneuvers - 10 gallons each main tank."

Emergency Procedures

The Emergency Section of the pilot's operating handbook calls for the following procedure during an in-flight loss of engine power:

1. Fuel Selector Valve - SELECT OTHER MAIN TANK (Check to feel detent)

2. Auxiliary Fuel Pump - ON

3. Mixture - FULL RICH, then LEAN as required

4. Magnetos - CHECK LEFT and RIGHT, then BOTH

Fuel Tanks

The airplane was equipped with two "baffled" wing-cell fuel tanks, each with a 37 gallons usable capacity, installed in December 2011.

Engine Monitor

The airplane was equipped with an Electronics International UBG-16 engine monitor, which was capable of displaying and recording exhaust (EGT) and cylinder head temperatures (CHT). The unit was sent to the NTSB Vehicle Recorder Division for data extraction. The unit had been configured to record EGT and CHT temperatures for all six cylinders at 1-minute intervals. The entire flight segment was recorded. Analysis of the data revealed that EGT's for cylinder one and three were between 300 and 600 degrees F lower than all other cylinders for both the accident flight and all flights in the prior 12 months. The lack of a corresponding reduction in CHT's for the respective cylinders meant that the EGT reduction was most likely an error in the monitoring system rather than an actual temperature reduction in the cylinders.

The data for the remaining cylinders presented an average EGT and CHT rise to about 1,600 degrees F and 400 degrees F, respectively, across all cylinders for the first 5 minutes of flight, with a reduction to 1,500 degrees F and 350 degrees F for most of the remaining flight. The last 3 minutes of recorded data displayed a precipitous drop in EGT to 400 degrees F, with a corresponding drop of EGT to 250 degrees F.

Seat Belts

The airplane was equipped with lap-belt restraints, which did not have provisions for a shoulder harness. During the impact sequence, the pilot's upper body pivoted forwards, and he sustained a concussion along with multiple lacerations and punctures to his face and forehead as a result of him striking the instrument panel. As the airplane continued into the terrain, the control yoke moved forwards, striking his chest and breaking his right hand.