NTSB Factual Report

HISTORY OF FLIGHT

On October 1, 1998, at 1005 hours Pacific daylight time, an Aero Commander 680 FPL, N5YZ, was destroyed during a forced landing at Palm Springs, California. The pilot was fatally injured. Visual meteorological conditions prevailed for the personal flight and no flight plan was filed. The flight, operated by Desert Aircraft Sales, originated at Palm Springs as a local area flight under the provisions of 14 CFR Part 91. After a northbound departure from runway 31L, the pilot stayed low and reported a fuel problem. The aircraft collided with power lines and terrain about 1.5 miles north of the airport.

PILOT INFORMATION

The pilot's logbook was not recovered. According to Federal Aviation Administration (FAA) records, the pilot held a private pilot's certificate for airplane single and multiengine land airplanes. He also held an instrument airplane rating. The pilot reported a total of 3,200 flight hours at his third-class flight physical on October 23, 1996.

AIRCRAFT INFORMATION

No aircraft records were recovered. The aircraft had been modified by installation of higher horsepower engines and turbochargers with manual wastegates. An aircraft sales specification sheet was obtained and represented the aircraft as having a Mr. RPM Turbo 800 Conversion. The conversion replaces the Lycoming IGSO-540-B1A 380 horsepower supercharged engines with Lycoming IO-720-B1B 400 horsepower engines. Turbochargers are installed with manual exhaust bypass valves. There are no manifold pressure overboost protection systems.

The aircraft had been fueled twice the day before the accident with aviation grade 100LL fuel in preparation for a trip.

The specification sheet stated that the total aircraft time was 5,420 hours, and that both engines had 1,390 total hours since new. The left engine had zero hours since major overhaul, and the right engine had 70 hours since top overhaul.

Aircraft information was obtained from a prospective buyer who had declined the purchase because, according to him, 10 years of aircraft records were missing.

METEORLOGICAL CONDITIONS

At 0953, Palm Springs weather was reporting: clear, 10 miles visibility; wind calm; temperature 79 degrees Fahrenheit; dew point 52 degrees Fahrenheit; altimeter 29.89 inHg.

WRECKAGE AND IMPACT INFORMATION

The wreckage was located 1.5 miles north of the Palm Springs Regional Airport in an area of sand dunes. The heading of the aircraft was measured about 230 degrees magnetic. Witnesses reported seeing the aircraft rotate about 360 degrees during collision with the power lines and ground. A section of right outer wing leading edge was found under the wire location with wire imprints. A postcrash fire nearly consumed the aircraft structure.

The on-scene examination of the wreckage revealed engine oil trailing across both the right and left horizontal stabilizers and elevators. Preliminary examination of the engines revealed mild peening of the No. 6 cylinder top and bottom spark plugs from the left engine. The engine manual wastegates were found partially closed.

MEDICAL AND PATHOLOGICAL INFORMATION

On October 2, 1998, the Riverside County Medical Examiner performed an autopsy on the pilot. During the course of the procedure samples were obtained for toxicological analysis by the FAA Civil Aeromedical Institute in Oklahoma City, Oklahoma.

The analyses were negative for cyanide and ethanol; carbon monoxide measured 18 percent; Diphenhydramine (Benedril) was detected in the liver, blood, and urine; and Acetaminophen (Tylenol) was detected in the urine. Details of the analysis are attached to this report.

TESTS AND RESEARCH INFORMATION

Postaccident engine examination revealed evidence of over-temping (see note 1 regarding detonation under Additional Information) within the engine cylinders. Examination of the left engine cylinders revealed holes burnt through six pistons; the right engine had four pistons with holes burnt through. Valve and ring damage was also noted in the cylinders.

A fuel sample was obtained from the right wing fuel tank cell and was taken to a fuel-testing laboratory for analysis. The report confirmed that the fuel was uncontaminated 100LL-aviation fuel. The refueling FBO also tested their fuel to specification. The fuel sample tests are attached to this report.

Both RSA Fuel Injection Servos were sent to Precision Airmotive Corporation for examination and testing. One servo was functional tested and one was not due to damage. Both were disassembled and examined and there were no conditions or discrepancies found.

During postaccident examination of the aircraft systems the manual wastegates were found partially closed; a position that can provide additional manifold pressure. The engines are restricted to a maximum manifold pressure of 29.5 inHg.

Postaccident propeller examination revealed that both propellers were rotating at the time of impact and were not feathered. According to the Hartzell Propeller Company report, no preimpact discrepancies were noted on either propeller that would have precluded normal operation.

ADDITIONAL INFORMATION

1) Detonation (a reciprocating engine condition). An explosion or uncontrolled burning inside the cylinder or cylinders of a reciprocating engine. Detonation occurs when the pressure and temperature inside the cylinder becomes higher than the critical pressure and temperature of the fuel, and may be caused by using fuel that has a lower octane rating, or performance number, than is specified for the engine.

The pressure rise inside the cylinder caused by the fast-moving flame front can heat and compress the unburned fuel-air mixture enough for it to explode, or release its energy faster than the engine can accept it. This causes a rapid rise in cylinder pressure, excessive cylinder head temperature, and a decrease in engine power.

NTSB Probable Cause

The pilot's failure to properly use the manual turbocharger wastegates and to monitor the manifold pressure during takeoff.