Accident Overview
On November 15, 2015, at approximately 0904 central standard time, an amateur-built Lancair IV-P, registration N10UU, was substantially damaged during a forced landing after an inflight loss of engine power near Shawano, Wisconsin. The aircraft was operated by Fly Fast LLC under 14 CFR Part 91 as an instructional flight. The pilot and a flight instructor sustained minor injuries. Day visual meteorological conditions prevailed for the local flight, which had departed Shawano Municipal Airport at about 0841.
Flight History
The flight was intended to provide Lancair Owners and Builders Organization (LOBO) transition training for the pilot. During a practice emergency descent, the engine oversped beyond its normal operating limit of 2,700 rpm. After returning to level flight, the engine began running rough and subsequently lost power. Despite attempts by both the pilot and instructor to restore power, a forced landing was executed with the landing gear and flaps retracted into a field. After touchdown, the left wingtip struck a rock wall, causing the aircraft to tumble and damaging both wings and fuselage.
Data from the Chelton electronic flight instrumentation system showed the emergency descent began from 6,500 ft msl about 20 minutes after takeoff. With wings level and power near idle, the aircraft pitched down 22 degrees and encountered a 0.5 G load factor for about 5 seconds. During this low-G period, engine oil pressure dropped from 49 psi to 34 psi, then recovered to 44 psi. Airspeed increased to 177 knots indicated, and engine speed reached 2,800 rpm. As the descent continued, a left turn with 55 degrees of bank and 2.79 G load factor occurred, during which airspeed peaked at 195 kias, vertical speed at 7,200 fpm, and engine speed at 3,390 rpm. Over the next 15 seconds, the aircraft returned to wings level, engine rpm dropped to 2,060 rpm, and fuel flow increased from 6.2 to 11.1 gph.
Prior to the emergency descent, exhaust gas temperatures (EGT) and cylinder head temperatures (CHT) for all six cylinders were consistent with normal power. Following the overspeed, EGT and CHT for cylinders #1, #4, #5, and #6 began decreasing and continued to drop. Cylinders #2 and #3 initially showed increased EGT before #2 decreased; #3 EGT fluctuated between 700 and 1,400 degrees F for the remainder of the flight.
Personnel Information
The flight instructor, aged 54, held commercial and flight instructor certificates with ratings in single-engine land and sea, multi-engine land, and instruments. He had 1,416 total flight hours, including 32 hours in the accident make and model. He completed LOBO standardization training in September 2014 and recurrent ground training in September 2015.
The pilot, aged 66, held airline transport pilot and commercial certificates with single- and multi-engine land ratings. A retired airline pilot, he reported 23,000 total flight hours, with 5 hours in the accident airplane.
Aircraft Information
The accident airplane was an experimental amateur-built Lancair IV-P, powered by a Continental Motors TSIO-550E engine driving an MT constant-speed four-blade wood propeller. The pilot operating handbook listed an emergency descent airspeed of 170-274 kias, best glide at 120 kias, and never exceed speed of 274 kias. Normal engine operating limits included 38.5 inches manifold pressure, 30-60 psi oil pressure, and 2,700 rpm. The engine's oil sump capacity was 12 quarts, with 6.5 quarts usable at 14.5 degrees nose-down attitude.
Engine Examination
On March 2, 2016, the engine was examined at Continental Motors under NTSB supervision. The crankshaft rotated with continuity. Magnetos installed on the engine (Continental TSIO-550-E16B, manufactured 2009, 282 hours since overhaul) were type S6RSC-25P. Examination revealed fractured nylon gear teeth: 8 on the left magneto and 16 on the right. The left magneto distributor gear showed missing teeth aligning with #6 and #3 cylinder electrodes; the right magneto showed missing teeth for #4. Both magnetos had permanent magnets rotated from their manufactured positions (left 2°, right 12°), with fractured aluminum casting bosses. No contact between stationary and rotating components was observed. Impulse couplings exhibited pronounced wear. After replacement magnetos were installed, the engine ran successfully to full power in a test cell without anomalies.
Magneto and Propeller Governor Findings
The fractured distributor gears were sent to the NTSB Materials Laboratory. Fractures initiated on both contact and noncontact sides, with smooth areas and curving crack fronts consistent with progressive failure. Fourier-transform infrared spectroscopy identified the gear material as Nylon 6,6.
The propeller governor (McCauley C290D3-M/T13) was examined at McCauley Propeller Systems. The top cover was sheared off, aft low pitch stop post cracked, and bearing loose. Due to accident damage, pump capacity, leakage, relief, and rpm settings could not be verified.
A practice emergency descent in another Lancair IV-P with the same engine did not produce an overspeed. The test airplane was equipped with a counterweighted propeller, unlike the standard (non-counterweighted) propeller on the accident airplane.
Additional Circumstances
During the forced landing approach, the instructor considered lowering flaps but decided not to interrupt the pilot flying. The landing gear and flaps remained retracted at touchdown. The instructor later noted he thought he should have taken control but deferred due to the pilot's extensive experience. No designation of pilot-in-command had been made before the flight; such designation is not required under 14 CFR Part 91.
Following the accident, LOBO flight instructors held a training review session. Topics included recommendations to practice emergency descents above 10,000 ft AGL with conservative profiles, identify pilot-in-command before flight, and remain within gliding distance of an airport during such maneuvers.