Accident Details
On November 16, 2017, about 1800 Pacific standard time, a Piper PA-28R-201T (registration N5966V) was substantially damaged during an accident near Nipton, California. The pilot and passenger were not injured. The flight, a personal trip under 14 CFR Part 91, had departed North Las Vegas Airport (VGT) at about 1655, destined for Brackett Field Airport (POC) in La Verne, California.
While cruising at 10,000 ft mean sea level, the pilot began leaning the engine mixture using the JPI-700 engine data monitor. After about five minutes, both occupants noticed abrupt engine roughness. The pilot observed that the No. 5 cylinder head temperature (CHT) had spiked, the airplane began slowing, and altitude could not be maintained. During the descent, a slight acrid odor was noticed in the cockpit for about one minute before dissipating. The pilot set the electric fuel pump to high and switched fuel tanks, but performance did not change.
After losing about 500 ft, air traffic control contacted the pilot, who reported engine trouble. An alternate airport 26 miles west was offered, but the pilot chose a highway as the safest landing point. The propeller was still turning but did not appear to be producing power. The touchdown was hard, and visual references were hindered by dust, vibration, and moonless night conditions. The right main landing gear collapsed, and substantial damage occurred to both wings, with the right main gear strut pushed up through the wing.
Engine Data Analysis
The JPI-700 engine data monitor was downloaded. Data showed a rise in CHT for cylinder No. 5 just after 1740. Exhaust gas temperature (EGT) values for cylinders 1, 3, and 5 diverged at about the same time, and the device calculated a disparity in EGT differential. Engine rpm began dropping from 2,400 about 1743:45, stabilizing near 2,100, then dropping sharply around 1751:03 before the recording ended at 1751:15.
Postaccident Examination
During the engine examination, the crankshaft was rotated by hand with continuity to the accessory section confirmed. Spark was produced on all six top spark plug leads. Thumb compression was obtained on all cylinders except No. 5. The top spark plugs were removed; all but No. 5 exhibited dark combustion deposits. The No. 5 spark plug had a molten, metal-like substance around the electrode.
Borescope examination of the cylinders revealed normal operating signatures in cylinders 2, 4, and 6. The No. 5 cylinder showed signs consistent with detonation/preignition, including material missing from around the piston face circumference, and mechanical damage to the exhaust and intake valves. Cylinders 1 and 3 exhibited minor signs of detonation.