Can an aircraft overspeed?

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Can an aircraft overspeed?

Aircraft overspeed Airbus A350

An incident took place with a Ryanair flight EL-EBW on Jan 2017. It was Boeing 737-8AS. As the aircraft was descending into a high altitude jet stream, there was an associated increase or rise in the headwind which caused the aircraft to overspeed. In order, to control the aircraft's overspeeding, the pilot switched the autopilot to manual, which eventually led to a nose-up pitch input at the control column. This incident caused few crew members to collapse and undergo severe injury.

Overspeed is that situation or condition of an aircraft in which it's engine is made or forced to operate beyond it's designed limits. However, the consequences that arise when a particular engine is made to run too fast vary depending upon the engine type and the model used. Other factors that determine the type of failure or consequence on the engine on overspeeding are judged mainly by the duration of the overspeeding condition and the speed reached. Few engines can be affected severely by reducing their engine life or cause catastrophic failures even by momentary overspeeding. The engine overspeed is measured in revolutions per minute.

HOW DOES IT HAPPEN?

Overspeed conditions arise when an aircraft exceeds the Never Exceed speed or the Vne of the airframe. Although the speed level doesn't bother the engines used in an aircraft, it is preferable for the pilot to stay within the indicated limits.

An aerodynamic phenomenon, commonly known as Mach tuck, which is too involved to get into in a forum is experienced by Jets and speeding aircraft. But generally, it is observed that it's the aerodynamic regime that results to uncontrollability of the aircraft after the published speed has been exceeded, usually with a fraction or percent of margin.

Induced drag, parasite drag, skin friction drag and many other kinds of drag are created on an airframe as the aircraft flies through the atmosphere, few of them resulting to the point of uncontrollability or complete or partial failure when exceeded. These values are usually determined by the manufacturers of the aircraft. Regardless of being an aerodynamic failure or a structural failure, it is not often published in the POH when the speed is exceeded. To avoid these failures it is best expected for the pilot to stay within the published limits.

EPR or N1 and the EGT temperature present on the engine stack are used to monitor the overspeed factor of an engine.The limits for various flight conditions like take-off and cruise is provided in the POH, which includes the temperature and density altitude at standard conditions.

Aircraft overspeed


PREVENTION OF FAILURE FROM OVERSPEEDING

In most aircraft, designed to avoid overspeeding failures a governor or a regulator is often used to make the overspeeding condition impossible or very less likely to be attained and hence giving no chance for failure due to the same reason. For instance, Some of the aircraft are embedded with constant - speed units which have the capability to change the propeller pitch without any human intervention. This helps the aircraft or the engine to run at the optimal speed.

Aircraft overspeed prevention


Overspeed condition

In propeller driven aircrafts, overspeed conditions are attained when the propeller which is ordinarily connected directly to the engine of the aircraft, has been made or forced to operate at a very fast pace with high-speed airflow during the aircraft performing dive, or in case it moves to a flat pitch in cruising flight due to failure of the governor or any feathering failure from/in the engine.

Coming to jet driven aircraft, overspeed conditions are attained when the maximum operating speed has been exceeded by the axial compressor of the engine. As a result, we notice mechanical failures of the turbine blades or flameouts or even complete destruction of the engine.




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