Ever think of the engine that powers your aircraft?

When one talks of flying, the first thing that comes to mind is the airline one has chosen. Then comes the flight number and for enthusiasts the next thing is whether it is a Boeing or an Airbus aircraft. Rarely, if ever, does one think of the engine that will fly one to his or her destination even though it is among the most important parts that make a flight possible.

What engine to use in its aircraft is a decision taken by individual airlines and they consider various factors before settling for the right one. The two largest aircraft manufacturers, Airbus and Boeing, maintain that airlines are free to choose the type of engine that they want for their aircraft. That is why IndiGo chose the Pratt & Whitney (PW) engines for its initial order of the New Engine Option (NEO) aircraft.

It is one of the worst-kept secrets that IndiGo went in with the PW engines when it ordered its Airbus A320 aircraft as, during that time, Kingfisher was going down and IndiGo wanted more aircraft to cash in on the demand that would be created by Kingfisher folding up.

However, IndiGo’s choice of engine had disastrous consequences as the variety that it ordered faced major problems, like turnback of aircraft and in-flight shutdown of the engine. The Directorate General of Civil Aviation asked IndiGo to replace the unmodified engines if it wanted to continue flying this variety of aircraft. The airline is now modifying the engines for the safety of its flights and has till May 31 to complete the process.

Fleet factors

“Each airline is unique and it can take the decision that is best for it,” a Boeing spokesman says. Earlier, Boeing offered a choice of engines for its different models but right now, of the commercial passenger aircraft on offer, only the 787 offers a choice of either GE or Rolls-Royce engines.

An Airbus spokesperson adds that an airline or customer may want to select engine types that are common with its existing fleet to fit in with the existing maintenance agreements. “Alternatively, an airline or customer may want to broaden its engine type,” the spokesperson adds.

Generally, CFM International (the Safran-GE consortium) and Pratt & Whitney make engine types for the Airbus A320 family while Pratt & Whitney is the sole engine supplier for the A220 family of aircraft.

However, there are various aspects that airlines need to keep in mind before they select a particular engine. To begin with, the engines are different for narrow body and wide body aircraft so what engines an airline opts for will depend on the mix of its fleet. Then, given that the engine forms such a significant part of an aircraft, there are only a few options that the airline can choose from. Worldwide, GE, Pratt & Whitney and Rolls-Royce are some of the better known engine manufacturers.

Aerodynamics factor

According to Boeing, a plane’s design is done in concert with the engine design. “The design of the airplane influences the engine more than the engine influencing the design of the airplane. Engines must be built and tested in advance of the airframe so that they are ready for the flight test programme,” a spokesperson for the company says.

In addition, each engine type is tested on a test platform (by the engine company) and on the airframe (by Boeing). “As part of the development process, Boeing lays out specific requirements for the engines and the engine companies submit proposals to Boeing demonstrating how they will meet those requirements. We evaluate their proposals and decide which engine (or engines) we will go forward with,” says the spokesperson.

Both Airbus and Boeing are categorical that an airline can place an order for their aircraft before selecting the engine but the manufacturers will not assemble the planes without the engines. Says the Airbus spokesperson, “Each aircraft is designed specifically for a chosen engine and any change to the engine type will affect the aerodynamics of the aircraft.”

This is necessary as an engine plays a very important role in the aerodynamic movement of the aircraft. “That is why each engine offered on a particular model must meet very exacting requirements ranging from thrust to fuel consumption and sizing,” says the Boeing spokesperson.

“The engine housing, which covers the engine, constitutes part of the overall aerodynamics of the aircraft. The shape or look of the engine housing can change slightly depending on the engine type,” adds the Airbus spokesperson.

Further, only engines that are certified with the specific airframe can be installed on that airframe. They cannot be switched to an uncertified model after delivery. Airframes cannot be delivered without engines. On delivery, the individual airplane is certified as being airworthy.

Not just a matter of changing the motor

Airbus officials add that each engine version has its own pylon design attaching it to the wing as well as the engine control systems. “Changing an engine is not simply a matter of changing the motor but also the control system, the engine housing and the pylons. Each aircraft is designed specifically for a chosen engine and any change to engine type will affect the aerodynamics of the aircraft,” the Airbus spokesperson says.

Airbus has modified some test aircraft and changed the engines during the flight test and certification process as, at the end of the day, safety of the aircraft and the fliers it is carrying is of paramount importance and everything that can be done to ensure this is followed by both the aircraft and engine manufacturers.

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