Monday, May 27, 2019

Loss of Control in Flight: Kolb Twinstar Mk III, N9123R, fatal accident occurred April 20, 2018 at Collegedale Municipal Airport (KFGU), Apison, Hamilton County, Tennessee

The National Transportation Safety Board did not travel to the scene of this accident.

Additional Participating Entity:

Federal Aviation Administration / Flight Standards District Office; Nashville, Tennessee

Aviation Accident Factual Report - National Transportation Safety Board:

Investigation Docket - National Transportation Safety Board: 

Location: Collegedale, TN
Accident Number: ERA18LA134
Date & Time: 04/20/2018, 1830 EDT
Registration: N9123R
Aircraft Damage: Destroyed
Defining Event: Loss of control in flight
Injuries: 1 Fatal
Flight Conducted Under: Part 91: General Aviation - Personal 

On April 20, 2018, at 1830 eastern daylight time, an experimental amateur-built Kolb Mark III, N9123R, was destroyed when it collided with terrain shortly after takeoff from Collegedale Municipal Airport (FGU), Collegedale, Tennessee. The private pilot was fatally injured. Visual meteorological conditions prevailed near the accident site, and no flight plan was filed for the local personal flight conducted under the provisions of Title 14 Code of Federal Regulations Part 91.

The airplane's owner reported that the pilot was supposed to be performing high-speed taxi testing of the airplane and that he did not know the pilot intended to take off. He stated that the pilot completed two high-speed taxis and "crow-hops" in the airplane (that is, he would "taxi, lift off, climb the airplane to about 10 ft above ground level [agl], and then land"). During the third taxi, the owner heard the pilot apply "full power," and the airplane then took off from the runway, turned right "above the trees" adjacent to the runway, and entered the traffic pattern. The airplane then "leveled, banked left, and dove into the ground." The owner added that it did not appear that the pilot attempted to correct the dive.

Another witness, who was located on the northeast end of the runway, reported seeing the airplane above the departure end of the runway about 500 ft agl when it "turned left…and dove straight" into the side of a hill. He said that it sounded as though the pilot reduced power before the turn but increased power during the descent and that the engine was "screaming" as the airplane descended to ground impact.

The owner provided a video recording of the airplane that was oriented in the direction of flight and which captured the ground taxi and takeoff and ended before the airplane's descent into terrain. A review of the video revealed that the takeoff roll was about 400 ft long. The engine sound was smooth, continuous, and remained unchanged throughout the takeoff roll and the 45 seconds of the climb that was recorded. The video showed that, after takeoff, the airplane had a high angle of attack and a steep angle of climb, and the tops of each wing were visible. The airplane drifted right of the runway centerline but remained flat in the roll axis.

The pilot held a private pilot certificate with airplane single-engine land and instrument airplane ratings. His most recent Federal Aviation Administration (FAA) second-class medical certificate was issued on November 1, 1999, at which time, he reported 71 total hours of flight experience.

The Office of the Hamilton County Medical Examiner, Chattanooga, Tennessee, performed the autopsy on the pilot and determined the cause of death as multiple blunt force injuries.

The FAA Bioaeronautical Sciences Research Laboratory, Oklahoma City, Oklahoma, performed toxicological testing on the pilot and the test yielded results for the presence of a sedating over-the-counter antihistamine cetirizine in blood (0.012 (ug/ml, ug/g) and liver samples. According to the NTSB Medical Officer, the levels detected were below the therapeutic range, and assuming normal dosage at the time of ingestion, the levels suggested the pilot was within the FAA's recommended period for the performance of airman duties.

A review of photographs of the pilot's logbook revealed that the pilot had accrued about 248 total hours of flight experience. The low number and poor quality of the photographs prevented a determination of the total, type, and recency of his flight experience; however, the most recent entry and endorsement indicated that the pilot flew a tail-wheel equipped ultralight airplane on July 9, 2016, and an unidentified aircraft on September 10, 2016.

The airplane was manufactured in 1995 and registered to the owner on January 4, 2017. It was powered by a Suzuki 1.3 liter, 4-cylinder automobile engine.

According to the owner, he purchased the airplane disassembled and "half restored" from what appeared to be accident damage. He and the pilot completed the repairs and assembly of the airplane using a "build manual" and a set of plans. The owner did not have airframe or engine logbooks for the airplane, and a condition inspection had not been completed. The owner said the condition inspection was supposed to have been completed "before the first flight."

At 1853, the weather reported at Chattanooga Lovell Field, located 9 miles from the accident site, included few clouds at 25,000 ft, 10 miles visibility, winds from 010° at 10 knots, temperature 20°C, dewpoint -4°C, and an altimeter setting of 30.28 inches of mercury.

Examination of photographs of the wreckage provided by the FAA revealed that the airplane came to rest uphill of the initial ground scar, and the wreckage path was oriented along a magnetic heading of about 300°. Impressions in the grass on either side of the scar were of the same approximate dimensions as the leading edge and span of each wing.

Both wings were uniformly crushed aft in compression, and the fabric covering of each wing was shredded. The empennage remained largely intact. Control continuity could not be established due to the extent of the damage to the remainder of the airframe and the entanglement of structure and control cables. Examination of breaks and fractures in the cables and bellcranks revealed that they were consistent with overload failure.

The cockpit area was destroyed, and the instrument panel was separated. The engine cradle was separated and only remained attached by wires and cables. A nylon cargo strap was found entangled with the wreckage. According to the owner, the strap secured sand bags and a board used for ballast.

According to the Kolb Aircraft website, "Although Kolb aircraft are easy to fly and have gentle flight characteristics, they are also high-performance aircraft. We recommend training or some transition training before attempting flight in our aircraft."

FAA Advisory Circular (AC) 90-89B, "Amateur-Built Aircraft and Ultralight Flight Testing Handbook," was issued to make amateur-built aircraft pilots aware that "test flying an aircraft is a critical undertaking," which should be approached with "thorough planning, skill, and common sense" and to provide recommendations and suggestions that could be combined with other sources on test flying (such as, the aircraft plan/kit manufacturer's flight testing instructions, other flight testing data) that would assist amateur owners to "develop a detailed flight test plan, tailored for their aircraft and resources."

The AC also provided guidance on developing a plan for each phase of an amateur-built airplane's production, including preparing for the airworthiness inspection, determining weight and balance, conducting taxi and flight testing, and developing emergency procedures. The suggested flight-testing regimen was separated into 10-hour segments for the 40-plus-hour flight testing requirement.

The AC also included guidelines for the experience level of the test pilot, which included, in part, the following:

The test pilot should be experienced and competent. He/she should have made a minimum of 100 solo flights in similar make, model, and type of ultralight and must follow the FLIGHT-TEST PLAN exactly. The FLIGHT-TEST PLAN should examine the ultralight and its performance capability, beginning with the pre-flight inspection and ending only after the test pilot has explored the ultralight's published flight envelope as described in the flight manual.

The owner reported that he was not familiar with FAA AC 90-89B. 

Pilot Information

Certificate: Private
Age: 62, Male
Airplane Rating(s): Single-engine Land
Seat Occupied: Left
Other Aircraft Rating(s): None
Restraint Used: 4-point
Instrument Rating(s): None
Second Pilot Present: No
Instructor Rating(s): None
Toxicology Performed: Yes
Medical Certification: Class 3 Without Waivers/Limitations
Last FAA Medical Exam: 11/01/1999
Occupational Pilot: No
Last Flight Review or Equivalent:
Flight Time:  71 hours (Total, all aircraft), 1 hours (Total, this make and model)

Aircraft and Owner/Operator Information

Registration: N9123R
Model/Series: KOLB MARK III
Aircraft Category: Airplane
Year of Manufacture:
Amateur Built: Yes
Airworthiness Certificate: Experimental
Serial Number: 4317477E
Landing Gear Type: Tricycle
Seats: 2
Date/Type of Last Inspection:  Unknown
Certified Max Gross Wt.: 1100 lbs
Time Since Last Inspection:
Engines: Reciprocating
Airframe Total Time:
Engine Manufacturer: Suzuki
ELT: Not installed
Engine Model/Series: LY8
Registered Owner: On file
Rated Power: 95 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: KCHA, 688 ft msl
Distance from Accident Site: 9 Nautical Miles
Observation Time: 2253 UTC
Direction from Accident Site: 265°
Lowest Cloud Condition: Few / 25000 ft agl
Visibility:  10 Miles
Lowest Ceiling:
Visibility (RVR):
Wind Speed/Gusts: 7 knots /
Turbulence Type Forecast/Actual: / None
Wind Direction: 10°
Turbulence Severity Forecast/Actual: / N/A
Altimeter Setting: 30.28 inches Hg
Temperature/Dew Point: 20°C / -4°C
Precipitation and Obscuration: No Obscuration; No Precipitation
Departure Point: Collegedale, TN (FGU)
Type of Flight Plan Filed: None
Destination: Collegedale, TN (FGU)
Type of Clearance: None
Departure Time:  EDT
Type of Airspace: Airport Information
Runway Surface Type: Asphalt
Airport Elevation: 860 ft
Runway Surface Condition: Dry
Runway Used: 03
IFR Approach: None
Runway Length/Width: 4986 ft / 75 ft
VFR Approach/Landing: Forced Landing 

Wreckage and Impact Information

Crew Injuries: 1 Fatal
Aircraft Damage: Destroyed
Passenger Injuries: N/A
Aircraft Fire: None
Ground Injuries: N/A
Aircraft Explosion: None
Total Injuries: 1 Fatal
Latitude, Longitude: 35.044444, -85.020000 (est)


  1. I have read the controls can become non effective because the prop only blows over 50% of the control surface. Also, the manufacture claims should not fly one without a rudder trim tab yet that isn't in the kit plans of older aircraft. When you fly them without rudder trim tab it requires 5-10lbs of rudder pressure. Maybe after he took off wasn't ready for these control issues.

  2. Report says:
    "A nylon cargo strap was found entangled with the wreckage. According to the owner, the strap secured sand bags and a board used for ballast."

    If only a single strap secured multiple sand bags, they probably were not adequately and properly secured. In the event of a stall (which appears to have happened), when the plane noses over, some loose items may slide forward, changing the aircraft's center-of-gravity (CG).

    If, in the process, a sand bag slides forward, and is torn by contact with an exposed sharp surface, it might dump a bunch of sand into the downward nose of the aircraft, radically changing the CG, to the point that no amount of up elevator will counter the nose-down attitude.

    While it may be argued that a rapid descent from a stall results in seeming "zero-G", the reality is that a certain amount of air drag will arguably keep at least SOME small bit of gravity force on the contents of the cockpit, permitting the sandbag(s), and loose sand, to flow towards the nose. Whether, under these circumstances, within the brief time of the incident, enough mass can move forward enough to cause unrecoverable CG change, is, of course, debatable. But loose ballast is a potentially lethal hazard on almost any flight.