Mid Air Failure of One Engine in a Multi-Engine Aircraft

Have you ever wondered what if one, two or three engines of the four-engine flight carrying you from New Delhi to Texas fails in mid-air? What would happen? Will the pilot keep flying the aircraft or it will give rise to some catastrophic landing? The answer is right here in the article.

You would be amazed to know that you may have flown in a flight having one engine failed in mid-air or on the ground while take-off or landing without your knowing. Though engine failures are accompanied by huge noise or vibrations sometimes they are not very much noticeable, but it is required that the pilot gets to know about the failure very quickly.

A Quantas Airways Flight 32 faced a three-engine failure but still, it managed to land safely with all the crew members and passengers on board safely. Before discussing what actually happens when we face an engine failure in mid-air let me tell you about basic aerodynamic terms that would be used later in this article.

The V speeds

The term V-Speed is derived from the French word VITESSE, meaning speed.

In the world of aviation V-speed is the term used to define airspeed important and useful for an aircraft in different flying conditions. These V-speeds are calculated using the performance testing data.

Some V speeds that are required in the engine failure situation are as follows-

V1- The speed after which take-off should not be aborted.

V2- The speed at which the aircraft may safely be climbed even if one engine is inoperative.

Vmc- The minimum control speed is the speed at which the aircraft is still controllable even if one of the engines is inoperative. The Vmc speed is further divided into two categories Vmca and Vmcg, Vmca is the minimum speed at which aircraft can be controlled even if one engine goes down in mid-air. Similarly, Vmcg is the minimum speed at which the aircraft can be controlled even if one engine goes down at or near the ground.

Vcl- The minimum control speed of an aircraft at which the aircraft is controllable even if one engine goes down in landing configuration i.e. the landing gear is deployed and the aircraft is descending.

Working of the Rudder

The rudder is a control surface which is used to control the yawing action of the aircraft, the rudder is present on the vertical stabilizer present at the tail section of the aircraft. The working of the rudder is based on the principle that when the rudder moves towards left the airflow across the vertical stabilizer is affected and the tail of the aircraft moves towards the right.

Now we will discuss about the aerodynamic consequence of one engine failure in a two engine aircraft, but this concept is easily applicable to aircrafts having more than two engines.

Before jumping on the core concept consider two of your friends holding your hand and pulling you to run with them. Now consider one of them leaves your hand you will get a sudden jerk and yawing motion towards your friend who left your hand, the same situation happens in an aircraft when the thrust from one engine goes off suddenly the aircraft gets a sudden yawing motion towards the engine which is failed.

If this unbalanced thrust is not compensated the aircraft would yaw very rapidly and will get out of control in seconds. Now here comes the skills of the pilot you all have read about rudder earlier which is a control surface used to control the yawing motion of an aircraft. These rudders are used very carefully by the pilot and they are turned in the direction of the operative engine so that they can provide a balancing action to compensate the action of unbalanced thrust produced due to the failure of one engine.

For example the left engine of two the engine aircraft fails then we would get an unbalanced moment acting on the aircraft in a counterclockwise direction as seen from the top. Then the rudder must be deployed in the direction of the operative engine so that we get a moment acting in the clockwise direction. This counterbalancing action would make the aircraft stable even on a single engine.

Effects of engine failure

1. On the Runway

If the engine failure occurs during the take-off then the aircraft would get a yawing moment in the direction of the failed engine. This yawing moment can be controlled with help of rudders if the airspeed is at or above Vmcg, if not then the thrust produced by the operative engine must be reduced before using the aerodynamic control. If the airspeed is below V1 then the takeoff should be aborted. For more details check this article

2. Mid-Air failure

Apart from the yawing action produced by the engine failure discussed earlier there are two more effects produced by the engine failure one is the roll moment induced by the yawing action. This is the result of continuous yawing action toward the failed engine, which causes a decrease of lift in the retreating wing. The second penalty is the arriving from engine failure is the drag produced by the failed engine.

Now the drag produced in the turbojet engine is less as compared to that produced in a turboprop engine due to the wind milling propellers. The drag produced in turboprop engines is reduced by adjusting the propellers blades in the position so that minimum drag is produced by the failed engine.

In the conclusion, I would like to say that it is very much possible to fly a multi-engine aircraft with one, two or three engines failed. According to the new standards set by the FAA the aircraft prior to its usage undergoes a testing procedure in which it is tested to fly even if only 50% of the thrust is available while in mid-air or during the time of take-off or landing. As per the new guidelines the pilot has to land the aircraft to the nearby airport with the consent of ATC in case of an engine failure.

Thanks for reading!

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Mid Air Failure of One Engine in a Multi-Engine Aircraft