NTSB Identification: CEN16LA043
HISTORY OF FLIGHT
On November 15, 2015, about 0904 central standard time, an amateur built Lancair IV-P airplane, N10UU, was substantially damaged during a forced landing following an inflight loss of engine power near Shawano, Wisconsin. The pilot and flight instructor sustained minor injuries. The airplane was registered to and operated by Fly Fast LLC under the provisions of 14 Code of Federal Regulations Part 91 as an instructional flight. Day visual meteorological conditions prevailed for the local flight, which departed from the Shawano Municipal Airport (EZS), Shawano, Wisconsin about 0841.
The purpose of the flight was to conduct Lancair Owners and Builders Organization (LOBO) transition training for the pilot. While practicing an emergency descent, the pilot stated the engine oversped above the normal operating limit of 2,700 revolutions per minute (rpm). The pilot returned the airplane to level flight and noticed the engine begin to run rough and subsequently lost power. After the pilot and flight instructor unsuccessfully attempted to regain normal engine power, the pilot executed a forced landing into a field with the landing gear and flaps up. After touchdown, the left wingtip contacted a rock wall and the airplane tumbled, damaging both wings and fuselage.
Based on data downloaded from the Chelton electronic flight instrumentation system (EFIS), the airplane began the practice emergency descent from 6,500 ft mean sea level (msl) about 20 minutes after takeoff. With wings level and engine power near idle, the airplane pitched over to a nose low attitude of 22 degrees and encountered a 0.5 G load factor for about 5 seconds. During this low G period, the engine oil pressure decreased from 49 pounds per square inch (psi) to 34 psi, then increased to 44 psi as 1 G flight resumed. The airplane accelerated to 177 knots indicated airspeed (kias) and engine speed increased to 2,800 rpm.
While the airplane continued in a steep descent, a left turn commenced, which reached a bank angle of 55 degrees and a G load factor of 2.79. During this descending left turn, airspeed increased to 195 kias, vertical speed increased to 7,200 ft per minute (fpm), and engine speed peaked at 3,390 rpm. Over the next 15 seconds, the airplane returned to wings level flight and engine rpm dropped to 2,060 rpm, with fuel flow increasing from 6.2 gallons per hour (gph) to 11.1 gph.
Prior to start of the emergency descent, the exhaust gas temperature (EGT) and cylinder head temperature (CHT) of all six cylinders were parallel and consistent with a cylinder making power. Immediately following the engine overspeed, #1, 4, 5, and 6 cylinder EGTs and CHTs started to decrease, and continued to drop for the remainder of the flight. The #2 and #3 cylinder EGTs initially increased from about 700 to 1,100 degrees F. About one minute later, the #2 cylinder EGT decreased to match the other cooling cylinders, while the #3 cylinder EGT ranged from 700 to 1,400 degrees F for the remainder of the flight.
The flight instructor, age 54, held commercial and flight instructor certificates with airplane single-engine land, single-engine sea, multi-engine land, and instrument ratings. He was hired by the airplane owners to conduct transition training using the LOBO FAA and Industry Training Standards (FITS). He reported 1,416 total flight hours, with 32 hours in the make and model of the accident airplane. The instructor completed LOBO flight instructor ground and flight standardization training in September 2014 and completed recurrent ground standardization training in September 2015.
The pilot, age 66, held airline transport pilot and commercial certificates with airplane single-engine land and multi-engine land ratings. He was a retired airline pilot and reported 23,000 total flight hours, with 5 hours in the make and model of the accident airplane.
The accident airplane was an experimental amateur-built aircraft constructed from a kit, whose components were manufactured by the designer, Lancair International, Inc. The airplane was equipped with a Continental Motors TSIO-550E engine and a MT constant-speed four-blade wood propeller.
The pilot operating handbook listed an emergency descent airspeed of 170-274 kias, best glide airspeed of 120 kias, and never exceed airspeed of 274 kias. The normal operating limits for the engine were 38.5 inches of manifold pressure, 30-60 psi of oil pressure, and 2,700 rpm.
According to the engine's type certificate data sheet, the oil sump capacity was 12 quarts, with 6.5 quarts usable at a 14.5 degrees nose down attitude. Several Lancair pilots who had competed in the Reno Air Races stated that low G maneuvering would often result in an engine surge and/or overspeed.
On March 2, 2016, the engine was examined at Continental Motors under the supervision of the NTSB investigator-in-charge (IIC), with technical representatives from Continental Motors and LOBO. The crankshaft was rotated to verify engine drive train continuity. According to the airplane owner, the magnetos were installed on the Continental TSIO-550-E16B engine manufactured in 2009 and had 282 hours of time in service since overhaul. The magnetos were type S6RSC-25P magnetos, Continental Motors part number 10-500556-101.
Examination of the magneto distributor gears revealed that numerous nylon gear teeth had fractured, 8 teeth on the left magneto and 16 teeth on the right magneto. The fractured distributor gear teeth were clocked on an exemplary distributor gear in an exemplary magneto. The magneto drive shaft was rotated in a clockwise direction until the area of the separated teeth aligned with the drive gear. Doing so with the left magneto revealed a large arc of separated gear teeth that placed the distributor gear electrode between the #6 and #3 cylinders' distributor block electrodes, as well as a smaller arc of separated gear teeth corresponding to the #4 cylinders' distributor block electrodes. Doing so on the left magneto revealed an arc of missing teeth that placed the distributor gear electrode between the #6 and #3 cylinders' distributor block electrodes.
The permanent magnets cast onto both magneto armatures had been rotated on the armature shaft and the aluminum casting boss on both armatures was fractured. The left magneto permanent magnet was rotated about two degrees from its manufactured position; the right magneto permanent magnet had rotated about 12 degrees from its manufactured position. Neither magneto exhibited evidence of contact between the stationary and rotating components. The impulse coupling of both magnetos exhibited pronounced wear and hammering on the flyweight noses. Scrubbing was visible along the flyweight outer diameters.
Replacement magnetos were installed on the engine, which was successfully test run to full power in a test cell, with no anomalies noted.
MAGNETO DISTRIBUTOR GEAR EXAMINATION
The magneto distributor gears and separated teeth were sent to the NTSB Materials Laboratory for further investigation. Tooth fractures of the left and right distributor gears initiated at both the contact and noncontact sides of the teeth. Fracture features of the gear teeth generally showed a relatively smooth area at the fracture initiation side of the tooth covering about ¼ to ½ of the fracture area. Curving lines representing the fracture front were observed at the boundary of the smooth area. Hackle features and multiple curving crack front lines were present between the smooth area and the fracture termination.
The left and right distributor gears were analyzed using a 1Varian IR600 Fourier-transform infrared (FTIR) spectrometer with a diamond attenuated total reflectance accessory. Each distributor gear had an FTIR spectrum consistent with Nylon 6,6, consistent with the specified material for the distributor gear. The full NTSB Materials Laboratory report is available in the official docket of this investigation.
PROPELLER GOVERNOR EXAMINATION
The McCauley propeller governor, model number C290D3-M/T13, was shipped to McCauley Propeller Systems for examination and testing, with oversight by Federal Aviation Administration (FAA) inspectors. No anomalies were noted with the piston, O-rings, or retaining rings. The top cover sheared off near the control shaft and the aft side of the low pitch stop post was cracked and missing. After removal of the top cover, the bottom half of the bearing was loose inside of the body. Due to accident damage, the pump's capacity, internal leakage rate, pressure relief, and maximum rpm settings could not be verified.
TESTS AND RESEARCH
Australian Civil Aviation Safety Authority Airworthiness Bulletin (AWB) 17-005, Issue 3, dated October 20, 2014, lists a number of potential causes for nylon magneto drive distributor gear failures, including propeller strikes, kick back during starting before fire events, and any other event that can cause shock on the gear train driving the distributor gear.
Inspectors from the FAA Aircraft Evaluations Group, FAA Airworthiness Certification Office overseeing Continental Motors, and NTSB Material Laboratory personnel conducted a review of service difficulty reports, NTSB Materials Laboratory examinations, and manufacturer reports of distributor gear failures in dual magneto failures. Results of the review did not reveal any conclusive pattern related to engine or propeller type. The manufacturer noted that manufacturing of the distributor gears has not changed significantly in the last 20 years.
A practice emergency descent profile was flown in a Lancair IV-P airplane equipped with the same model engine as the accident airplane. An engine overspeed did not occur during the descent and recorded data paralleled the accident airplane's recorded data until level off from the practice emergency descent. Although both airplanes were equipped with the same model MT wood propeller, the accident airplane was equipped with a standard (non-counterweighted) propeller, whereas the testing airplane was equipped with a counterweighted propeller, which is designed to prevent overspeed during a loss of oil pressure.
As the pilot flew the airplane toward the selected forced landing field, the flight instructor stated he considered lowering the flaps, but did not want to interrupt or change the airplane's configuration for the pilot flying. The landing gear and flaps were in the retracted position at touchdown, which occurred at the far end of the selected field.
The flight instructor stated he thought that he should have assumed the flying duties for the forced landing, but deferred to the pilot he was instructing due to his considerable aeronautical experience. The two pilots had not discussed who would be pilot in command or who would fly the airplane if an in-flight emergency occurred. There is no requirement in 14 Code of Federal Regulations Part 91 to designate a pilot in command prior to flight.
Following the accident, LOBO flight instructors met for a flight training review session. Topics included a recommendation to conduct practice emergency descent maneuvers above 10,000 ft above ground level using conservative flight profiles, as well as the need to identify the pilot in command prior to flight. Also discussed was a recommendation to remain within gliding distance of an airport during practice emergency descents.