ENGINE FAILURE Case History

This case history is presented in the interests of economy and safety of flight. Analysis of the GEM datalog provides an excellent educational tool for understanding the complex relationships of engine management.

With the Advanced Graphic Engine Monitoring with Data Logging provided by Insight's GEMINI, Daniel Knopper, an Aerostar Owner, was able to download critical in-flight engine behavior, as described and shown in this 3D graph, when his Aerostar Lycoming Engine failed due to detonation.

Daniel Knopper in his own words says;

"After landing safely, the stored data of Insight's Graphic Engine Monitor provided indisputable proof of proper operation to the overhaul facility for full warranty. Besides the unit showing the detonation of the failed cylinder, it revealed two additional cylinders encountering detonation range temperatures that normally would have gone undetected. Physical evidence was present on inspection of these cylinders and they were replaced by the rebuilder without any question.

Self diagnosis, trend monitoring and cost benefits don't compare to the restored peace of mind I have flying my Aerostar."

Discussion of Factors

Aircraft: Piper Aerostar 602P (Twin engine turbocharged pressurized high-performance six passenger)

Engine: Lycoming TIO-540-AA1A5 290 HP

Background: Maintenance Intensive aircraft.

A history of engine failures and in-flight engine shut-downs preceded installation of two new Engines and a GEMINI 1200 Graphic Engine Monitor.

Abnormal combustion process:

Detonation and Pre-ignition are used to describe the same conditions within an engine. When diagnosing an engine failure, it is vital to know whether detonation or pre-ignition caused the engine failure.

Detonation and pre-ignition are totally separate conditions in terms of what they are and what damage they do. Detonation is caused by the spontaneous combustion of fuel in the combustion chamber verses a normal even desired burn. Detonation causes high cylinder head temperatures and low exhaust gas temperatures creating a pinging noise, that in aircraft engines you cannot hear.

Pre-ignition is premature ignition of the fuel/air mixture before the spark while the compression stroke is occurring, but earlier than desired. Pre-ignition can cause extremely high temperatures in a short time.

Causes of Abnormal combustion process:

Detonation can lead to pre-ignition if hot spots develop in the combustion chamber. Pre-ignition leads to detonation if combustion chamber temperatures raise the gas/air mixture to a high enough temperature to ignite spontaneously.

Detonation is caused by:

• · Too high a compression ratio for the octane of fuel used.
• · Too lean a fuel mixture, which slows the fuel burn and appears as an advance in timing.
• · Hot spots in the combustion chamber.
• · High power settings.
• · Pre-ignition

Pre-ignition is caused by:

• · Using an incorrect spark plug.
• · Hot spots in the combustion chamber.

Symptoms of Detonation/Pre-ignition:

CHT is usually increased, EGT may be decreased. Due to the wide variety of factors affecting CHT and EGT there is no simple or obvious way to detect abnormal combustion process!

Fuel Quality:

A fuels octane rating describes it's ability to resist detonation. Turbocharged engines require high octane fuel to offset the detonation inducing affects of high cylinder pressures and temperatures. Contamination of fuel by alcohol, jet-fuel or a lower grade of gasoline reduces it's octane-rating.

Injector Nozzles:

Restriction of fuel-flow by nozzle clogging increases back-pressure on the fuel system. This causes an increase in indicated fuel-pressure while fuel-flow is actually decreasing!

Pilot Technique:

Normal Aerostar Pilots Operating Handbook (P.O.H) recommended procedures were employed by the flight crew. Crew consisted of pilot/owner and maintenance chief. Both highly experienced on aircraft type.

Aircraft Status:

Fresh premium-rebuilt right engine. Low-time premium-rebuilt left engine. Newly-installed GEMINI 1200 system.

Prelude to Engine Failure

The aircraft departed a sea-level airport and performed a P.O.H. normal climb to 19,000 ft. Both engines appeared to operate normally in the climb. Level cruise flight was established at flight time 0.40. Cruise power was set and the right engine was leaned to P.O.H. recommended fuel-flow. All engine temperatures and pressures indicated well within normal operating ranges.

This datalog shows the subsequent events.