4F Emergencies - Engine Roughness or Overheat Flashcards
- What are some of the most common operational causes of detonation? (FAA-H-8083-25)
a. Using a lower fuel grade than that specified by the aircraft manufacturer.
b. Operating with extremely high manifold pressures in conjunction with low rpm.
c. Operating the engine at high power settings with an excessively lean mixture.
d. Extended ground operations or steep climbs where cylinder cooling is reduced.
- What is detonation? (FAA-H-8083-25)
Detonation is an uncontrolled, explosive ignition of the fuel/air mixture within the cylinder’s combustion chamber. It causes excessive temperatures and pressures which, if not corrected, can quickly lead to failure of the piston, cylinder, or valves. In less severe cases, detonation causes engine overheating, roughness, or loss of power. It is characterized by high cylinder head temperatures, and is most likely to occur when operating at high power settings.
- What action should be taken if detonation is suspected? (FAA-H-8083-25)
Detonation may be avoided by following these basic guidelines during the various phases of ground and flight operations:
a. Make sure the proper grade of fuel is being used.
b. While on the ground, keep the cowl flaps (if available) in the full-open position.
c. During takeoff and initial climb, use an enriched fuel mixture, as well as a shallower climb angle to increase cylinder cooling.
d. Avoid extended, high power, steep climbs.
e. Develop habit of monitoring engine instruments to verify proper operation.
- What is preignition? (FAA-H-8083-25)
Preignition occurs when the fuel/air mixture ignites prior to the engine’s normal ignition event. Premature burning is usually caused by a residual hot spot in the combustion chamber, often created by a small carbon deposit on a spark plug, a cracked spark plug insulator, or other damage in the cylinder that causes a part to heat sufficiently to ignite the fuel/air charge. Preignition causes the engine to lose power, and produces high operating temperature. As with detonation, preignition may also cause severe engine damage, because the expanding gases exert excessive pressure on the piston while still on its compression stroke.
- What actions should be taken if preignition is suspected? (FAA-H-8083-25)
Detonation and preignition often occur simultaneously and one may cause the other. Since either condition causes high engine temperature accompanied by a decrease in engine performance, it is often difficult to distinguish between the two. Using the recommended grade of fuel, and operating the engine within its proper temperature, pressure, and rpm ranges, reduces the chance of detonation or preignition.
- If the engine begins to run rough when flying through heavy rain, what action should be taken?
During flight through heavy rain, it is possible for the induction air filter to become water saturated. This situation will reduce the amount of available air to the carburetor resulting in an excessively rich mixture and a corresponding loss of power. Carburetor heat may be used as an alternate source of air in such a situation.
- Are there any special considerations necessary when using the auxiliary pump after an engine-driven fuel pump failure? (POH)
In a high-wing, single-engine aircraft, which has sustained an engine-driven fuel pump failure, gravity flow will provide sufficient fuel flow for level or descending flight. If the failure occurs while in a climb or the fuel pressure falls below 0.5 PSI, the auxiliary fuel pump should be used.
- What operating procedure could be used to minimize spark plug fouling?
Engine roughness may occur due to “fouling” of the spark plug electrodes. This condition may occur on the ground or in the air and is usually the result of an excessively rich mixture setting which causes unburned carbon and lead deposits to collect on the spark plug electrodes. A pilot may alleviate this problem to some degree by always using the recommended lean setting for the given condition.
