Sunday, April 07, 2019

Beechcraft Bonanza V35B, N777PH: Fatal accident occurred November 04, 2017 near Alva Regional Airport (KAVK), Woods County, Oklahoma

David Thomas Chael

Cortney Lyle (Cory) Washburn 

The National Transportation Safety Board traveled to the scene of this accident.

Additional Participating Entities: 

Federal Aviation Administration / Flight Standards District Office; Oklahoma City, Oklahoma
Textron Aviation; Wichita, Kansas
Continental Motors; Mobile, Alabama
American Bonanza Society; Wichita, Kansas

Aviation Accident Factual Report - National Transportation Safety Board:

Investigation Docket - National Transportation Safety Board:

Location: Alva, OK
Accident Number: CEN18FA023
Date & Time: 11/04/2017, 1728 CDT
Registration: N777PH
Aircraft: BEECH V35B
Aircraft Damage: Destroyed
Defining Event: Miscellaneous/other
Injuries: N/A
Flight Conducted Under: Part 91: General Aviation - Instructional


The private pilot had recently purchased the Bonanza airplane, which he and an experienced flight instructor were using to conduct his first training flight in a Bonanza. During a visual approach, the engine's left cowling opened. According to the pilot, who initially survived the accident, the flight instructor assumed control of the airplane. Based on video from home surveillance cameras, the descent rate for the approach increased to about 1,000 ft per minute about 100 ft above ground level. About 7 seconds later, the airplane impacted trees and a power line located 1/2 mile from the runway threshold.

The airplane was one of three Bonanza airplanes modified with a Robertson Short Takeoff and Landing (STOL) system. The flight characteristics for this modification included a strong pitch-down force while extending the flap from 15° to 30° position, which is greater than in Bonanzas without this STOL system. The investigation could not determine if the pilot or flight instructor was aware of this unique flight characteristic, which was not described in the STOL certification information.

The pilot had compiled a list of airplane discrepancies, which included "cowling latch - pilot's side rear spring." It is likely a latch for the left engine cowling opened in flight because it was not properly secured during the preflight. The flight instructor and pilot were likely distracted by the open engine cowling and did not expect the strong pitch-down force during flap extension, which resulted in a high descent rate on short final.

Probable Cause and Findings

The National Transportation Safety Board determines the probable cause(s) of this accident to be:
The flight instructor's and pilot's failure to recognize that a high descent rate had developed on short final, likely due to their distraction by an open engine cowling, and the unexpected strong pitch-down force during flap extension due to the installation in the airplane of a Short Takeoff and Landing system.


Pitch control - Design (Cause)
Descent rate - Not attained/maintained (Cause)
Aircraft structures - Inadequate inspection (Cause)

Personnel issues
Aircraft control - Instructor/check pilot (Cause)
Aircraft control - Pilot (Cause)
Understanding/comprehension - Pilot (Cause)
Understanding/comprehension - Instructor/check pilot (Cause)
Identification/recognition - Pilot (Cause)
Identification/recognition - Instructor/check pilot (Cause)
Preflight inspection - Pilot

Factual Information

History of Flight

Part(s) separation from AC
Miscellaneous/other (Defining event)

Approach-VFR pattern final
Collision with terr/obj (non-CFIT)

On November 4, 2017, at 1728 central daylight time, a Beech V35B (Bonanza) airplane, N777PH, impacted terrain during approach to Alva Regional Airport (AVK), Alva, Oklahoma. The pilot and flight instructor were fatally injured, and the airplane was destroyed. The airplane was registered to the pilot who was operating it under the provisions of Title 14 Code of Federal Regulations Part 91 . Day visual meteorological conditions prevailed and no flight plan was filed for the local instructional flight, which departed AVK about 1710.

According to a state trooper who spoke with the pilot at an emergency room, the pilot and flight instructor flew to Cherokee Municipal Airport, Cherokee, Oklahoma, for a practice approach and were returning to AVK when the accident occurred. The pilot stated that he and the flight instructor noticed that the left engine cowling had "popped up" during the approach to AVK. Subsequently, the flight instructor assumed control of the airplane. About 1/2 mile before reaching the runway 18 threshold, the airplane collided with trees and a power line, which were about 40 ft higher than the airport's elevation. The airplane came to rest inverted on its left side, and a postcrash fire ensued.

The pilot and flight instructor egressed the airplane with their clothes on fire. The flight instructor was unable to move away from the wreckage during the postcrash fire and subsequent explosion and died at the accident site. The pilot climbed a hill next to the airplane, and responders helped him extinguish his burning clothes. The pilot was taken to an emergency room near the accident site and subsequently transported to the Integris Burn Center, Oklahoma City, Oklahoma, with burns on over 80% of his body. The pilot died on November 7, 2017, from the injuries he sustained. 

A segment of the final approach was captured by five home surveillance video cameras, and a video study was conducted, which confirmed that the left engine cowling was open during the final approach. During a 12-second period that corresponded to 1,500 ft of ground track, the airplane descended from about 250 ft to about 100 ft above ground level, and the airspeed decreased from 76 ± 4 knots to 71 ± 4 knots. The landing gear was extended and the flap positions could not be determined. At the end of the 12-second period, as the airplane approached the accident site, the descent rate increased to about 1,000 ft per minute.

Flight Instructor

The flight instructor, age 61, held commercial pilot and flight instructor certificates with airplane single- and multiengine land and instrument ratings. On his most recent Federal Aviation Administration (FAA) airman medical application, dated May 15, 2017, the flight instructor reported 2,529 hours of civil flight experience with 110 hours in the previous 6 months. On an insurance application dated May 1, 2017, the flight instructor reported 11,456 hours of total flight experience, which included his military flight experience. The flight instructor owned a Beech Bonanza airplane and frequently trained in them.


The pilot, age 39, held a private pilot certificate with an airplane single-engine land rating. The pilot was issued a third-class medical certificate with no limitations on September 10, 2014. A logbook review revealed that the pilot had accumulated 231 flight hours as of June 1, 2017. The pilot had recently purchased the airplane and chose to receive training from the flight instructor based on the instructor's strong teaching reputation with Bonanza airplanes. The accident occurred during the pilot's first training flight and second flight overall in the accident airplane.


The airplane, serial number D-9544, was issued a standard airworthiness certificate on October 17, 1973. The airplane was equipped with a Continental IO-520-BA10 engine, serial number 241368-R, and a three-bladed McCauley propeller. The airplane's last annual inspection occurred on May 1, 2017, at a total airframe time of 1,927.7 hours. A second control yoke was installed before the accident flight.

In 1979, a Robertson Short Takeoff and Landing (STOL) system was installed in accordance with Supplemental Type Certificate (STC) SA503NW. The modification included removal of the ailerons; installation of full-span, single-slotted flaps; and installation of a spoiler roll control system. Flap positions for the STC modification were 0°, 15°, and 30°. The airplane was one of only three Bonanza airplanes modified by the STC.

A handwritten list of airplane discrepancies, with penmanship matching entries in the pilot's logbook, was found in the pilot's hangar. One of the listed discrepancies was "cowling latch - pilot's side rear spring."

A review of cowling latch part information indicated that each latch had two springs. One spring returned the latch jaws to the closed position when the bayonet fittings were pushed into the latch, and one spring exerted tension on the latch mechanism.

The airplane flight manual contained the following information concerning the engine cowlings:

The Bonanza is equipped with Hartwell latch mechanisms on the right and left upper engine cowling for quick and easy access to the engine compartments without the aid of tools. Each cowl latch (two per cowl) is locked and released by a single recessed handle located in the lower cowling panel on each side of the engine. To close the cowling, lower the cowling to the closed position with the handle in the prelatch position. The handle has three positions: flush with the fuselage is latched; held fully forward is unlatched; approximately 90° to the fuselage is prelatch (ready to close cowl). An audible click denotes the bayonet fittings, located forward and aft on the upper cowl, sliding into the latch safety catch. The cowl is locked by moving the latch handle to the full recessed position. The security of the forward latches can be checked by pulling out on the check tab attached to the lower forward edge of the upper cowling. If the cowling can be moved after latching, open the cowling, check the latch alignment and re-latch.

A video of an exemplar engine cowling being shut and photographs of an exemplar engine cowling, latches, and bayonet fittings, are included in the docket for this investigation.

In 1995, Beechcraft released a Safety Communique, which stated, in part, the following:

Beech Aircraft Corporation continues to receive reports of accidents following the opening of a cabin door, baggage door, engine cowling, or fuel cap during takeoff or flight. In many cases, the pilot failed to make certain the cabin door, baggage door, engine cowling, or fuel cap was properly latched and secured during pre-flight. In each accident, the pilot also failed to properly control the airplane and the airplane stalled at low altitude. 



If a cabin door, baggage door, or engine cowling is not properly latched and secured, it will usually open during takeoff immediately before or at rotation, although there have been reports of unlatched doors and engine cowlings opening in cruise flight. On some models, additional noise is to be expected. Do not permit yourself to be distracted. 


Evidence indicates that the airplane impacted a tree, followed by a power line, before coming to rest inverted in a shallow wash adjacent to a steep hill. Most of the fuselage and the right wing were consumed by fire, and several trees near the accident site were burned.

Examination revealed that the flight control cables were continuous from end to end. The cables had separated from the cockpit controls and empennage flight surfaces due to melting of the structure at the cable ends. The aileron bellcranks were intact with the control cables attached. The elevator trim actuator was not located in the wreckage. The left-wing flap was found extended 30°, and the landing gear were extended. Two control yokes were found in the wreckage.

The engine was lying on its left side with the main wreckage. All six cylinders remained attached to the crankcase, and the magnetos remained attached to their respective mounting positions. The magneto housings and internal components were thermally damaged.

The top spark plugs were removed and exhibited normal wear when compared to the Champion Check-A-Plug chart. The fuel pump exhibited thermal and impact damage. The drive coupling was fractured, and the fuel pump would not turn by hand. The fuel pump was disassembled, and the internal components were thermally damaged. The fuel manifold valve had separated from its mount and exhibited severe thermal damage. The fuel nozzles were removed and were free of debris.

The cylinder combustion chambers were examined with a lighted borescope with no anomalies noted. As the crankshaft was manually rotated, thumb compression was obtained on all six cylinders, and continuity was established to the accessory gears. The muffler did not exhibit any breaches or signs of external sooting.

The propeller governor was removed, and the control arm rotated freely by hand from stop to stop. The propeller governor drive rotated freely, and oil was discharged when rotated by hand. The propeller remained attached to the crankshaft propeller flange and exhibited thermal damage. One blade was relatively straight, the second blade was bent aft near the blade hub, and a third blade exhibited "S" bending. Examination of the engine and flight control system revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation.

Three of the four engine cowling latches and three of the four bayonet fittings were recovered from the wreckage. Both left cowling latches were partially melted by postcrash fire. The right forward cowling latch remained attached to the structure and exhibited minimal fire damage. The rear half of the right cowling access doorframe was consumed by postcrash fire. None of the three cowling latches recovered were engaged by a bayonet fitting.

Two of the recovered bayonet fittings had their mounting brackets attached, but they were not attached to a cowling access door. Based on the design of the brackets, these two bayonet fittings were determined to be the forward bayonet fittings. The third bayonet fitting, an aft fitting, was found attached to a portion of a melted cowling access door. It could not be determined if the third bayonet fitting was from the left or right side of the engine. The exterior handles on both sides of the engine cowlings were found in the latched position.


The Office of the Chief Medical Examiner, Oklahoma City, Oklahoma, performed an autopsy on the flight instructor and attributed his death to "smoke inhalation and thermal burns." The FAA's Bioaeronautical Research Sciences Laboratory Oklahoma City, Oklahoma, performed toxicology tests on the flight instructor. The results were negative for all tests conducted.

The Office of the Chief Medical Examiner, Oklahoma City, Oklahoma, performed an autopsy on the pilot and attributed his death to thermal injuries. The FAA's Bioaeronautical Research Sciences Laboratory performed toxicology tests on the pilot. Therapeutic levels of morphine, which is commonly prescribed in an emergency medical setting, were detected.


STOL Modification

In 2005, the American Bonanza Society (ABS) published an article describing the characteristics of a Robertson STOL-converted airplane. The owner of a Bonanza airplane with a STOL conversion wrote the article, which stated, in part, the following:

Important handling characteristics: the modification provides a unique blend of speed, climb performance, STOL, and long legs, but the STOL modification brings some important handling characteristics. Most notable are larger trim changes with flap extension, needing full nose up trim, now 21 degrees, for landing at forward CG [center of gravity] with full (30 degrees) flaps.

Following the accident, the author of the ABS article flew his STOL-converted airplane with another experienced Bonanza pilot who had never flown one with a STOL conversion. When the flap position was changed from 15° to 30°, the latter pilot commented that a much more pronounced pitch-down force occurred compared to a conventional Bonanza and that more pitch trim was required to offset the change in flap position. When the flaps were lowered from 15° to 30° without the pilots making a corresponding control input or trim adjustment, the airplane subsequently pitched down to about 20°, and the vertical airspeed increased to more than 1,500 ft per minute in about 5 seconds.

Aircraft and Owner/Operator Information

Aircraft Make: BEECH
Registration: N777PH
Model/Series: V35B
Aircraft Category: Airplane
Year of Manufacture: 1973
Amateur Built: No
Airworthiness Certificate: Utility
Serial Number: D-9544
Landing Gear Type: Retractable - Tricycle
Seats: 4
Date/Type of Last Inspection: 05/01/2017, Annual
Certified Max Gross Wt.: 3400 lbs
Time Since Last Inspection:
Engines: 1 Reciprocating
Airframe Total Time: 1927 Hours as of last inspection
Engine Manufacturer: Continental Motors
ELT: C126 installed, not activated
Engine Model/Series: IO-520-BA10
Registered Owner: Cortney L. Washburn
Rated Power: 285 hp
Operator: On file
Operating Certificate(s) Held: None

Meteorological Information and Flight Plan

Conditions at Accident Site: Visual Conditions
Condition of Light: Day
Observation Facility, Elevation: KWDG, 1167 ft msl
Distance from Accident Site: 48 Nautical Miles
Observation Time: 1750 CDT
Direction from Accident Site: 119°
Lowest Cloud Condition:
Visibility:  10 Miles
Lowest Ceiling: Broken / 20000 ft agl
Visibility (RVR):
Wind Speed/Gusts: 4 knots /
Turbulence Type Forecast/Actual: /
Wind Direction: 20°
Turbulence Severity Forecast/Actual: /
Altimeter Setting: 29.8 inches Hg
Temperature/Dew Point: 17°C / 11°C
Precipitation and Obscuration: No Obscuration; No Precipitation
Departure Point: ALVA, OK (AVK)
Type of Flight Plan Filed: None
Destination: ALVA, OK (AVK)
Type of Clearance: None
Departure Time: 1700 CDT
Type of Airspace: Class E

Airport Information

Airport: ALVA RGNL (AVK)
Runway Surface Type: Concrete
Airport Elevation: 1476 ft
Runway Surface Condition: Dry
Runway Used: 18
IFR Approach: None
Runway Length/Width: 5001 ft / 75 ft
VFR Approach/Landing: Straight-in

Wreckage and Impact Information

Crew Injuries: N/A
Aircraft Damage: Destroyed
Passenger Injuries: N/A
Aircraft Fire: On-Ground
Ground Injuries: N/A
Aircraft Explosion: On-Ground
Total Injuries: N/A
Latitude, Longitude: 36.787778, -98.670556

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