Aircraft Systems and Flight

           In aviation, an aircraft engine, or powerplant, is one of the most essential systems on the aircraft. There are two types of engines in aviation, a reciprocating engine and a gas turbine engine, which converts heat energy into mechanical energy by the flow of some fluid mass (air) through the engine (PHAK, 2016). This occurs from the undergo operation of the four major components that all engines share: an intake, a compression, a combustion (or power) and an exhaust. Gas turbine type engines also require an additional spool or turbine. Regardless of the type, the primary purpose of an aircraft engine is to generate enough thrust to propel the aircraft through the air by creating lift on the wings. The engine also generates power to other various systems that support the operations of the aircraft. This includes the electrical system, the hydraulic system (engine-powered only) and the bleed air system, which provides both air conditioning and pressurization. It is critical for the engine to accelerate at a self-sustaining speed throughout the flight. Failure to operate efficiently may cause internal damages, an engine shutdown and an emergency landing.

         There are many different indications of an engine malfunction during the start sequence or in flight that can lead to an engine failure. Two of those indications is a hot and hung start. A hot start occurs when the Exhausted Gas Temperature (EGT) exceeds the safe limit of an aircraft. This is usually caused by too much fuel entering the combustion chamber or insufficient turbine rpm (PHAK, 2016). A hung start can happen when the engine fails to accelerate to the proper speed after ignition or does not accelerate to idle rpm. A hung start may be caused by an insufficient starting power source or fuel control malfunction (PHAK,2016). Any time an engine has a hot or hung start, refer to the AFM/POH or an appropriate maintenance manual for inspection requirements. Other engine malfunctions and system failures include compressor stalls, engine flameout, severe vibrations, propeller overspeed, overheating, fuel contamination, preignition, high/low oil pressures, high oil temperatures and high oil consumptions, along with EGT, rotational speed (N1 and N2) and fuel flow exceeding its limitation. This can occur from the engine having an imbalance in its vectors or the air intake becoming stagnate. Overall, an engine malfunction can either be intermittent or steady and still fly, but when it becomes severe, the appropriate procedure is shutting down the engine so no further damage can occur.

Reciprocating Engine Diagram (4-Stroke Cycle)

Gas Turbine Engine (Turbofan)

          So, what happens when an engine fails during a flight? Depending on the aircraft, most multi-engine aircrafts are designed to operate with one engine for its calculated performance. Therefore, pilots are trained to undergo special procedures for engine malfunctions, so he/she are aware and competently prepared in the event of this happening. Every aircraft has an AFM/POH for specific information pertaining to the aircraft, the aircraft systems, the limitations and emergency procedure. Understanding the entirety of the aircraft while being flown is critical to its safe operation, situational awareness, proper maintenance and the event of an emergency (PHAK, 2016). The impact of an engine failure will depend on the complexity of the aircraft. A multi-engine aircraft would not be as severe as a single reciprocating engine aircraft in the event of an engine failure, since there is a secondary engine. Nevertheless, there are certain procedures and checklist the pilots must follow to reserve that failed engine and land safely. The impact of a single engine failure can lead to a more detrimental situtation since other various systems including the electrical system, the hydraulic system and the bleed air system can fail prior to an engine failure. This is because the engine is the overall power source for those systems. Failure on those systems can lead to the generator(s) cutting off and losing some of the flight instruments, the loss of hydraulic use in the flight controls, landing gear and brakes, and the bleed air system not providing the air conditioning nor pressurization in the cabin of the aircraft; moreover, it will also not serve its primary purpose of producing enough thrust to stay lifted. This can cause the aircraft to stall and fall out of the sky. Enduring the ultimate life or death decision that any pilot shall make in this situation to either ditch or crash land. So, it imperative for the pilots and the maintenance department to always follow the correct procedures from the AFM/POH when operating or working on the aircraft engine to prevent any mishap, or worst, casualties.

References:

Federal Aviation Administration (FAA). (2016). Pilot’s Handbook of Aeronautical Knowledge (PHAK). Retrieved https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/phak/