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What are the most important parts of a commercial aircraft?

Chris Kjelgaard ponders the question: what are the most important parts of a commercial aircraft?

This may seem a chicken-and-egg notion, but recently the question of just which parts of a commercial aircraft are the most important for its functionality and operation has exercised my mind.

It is clear that only the entire aircraft – the airframe together with its engines, its fuel system, and its electronic, electrical, pneumatic, hydraulic and mechanical systems – is capable of operating its passenger- or cargo-carrying mission to the certificated standard of safety, operational efficiency and comfort.

One may argue that some parts and systems – those not required by an aircraft’s minimum equipment list for the aircraft to be dispatched – are not highly important. An in-flight entertainment (IFE) system might fall into this category.

However, few airlines would wish to dispatch aircraft – particularly those operating long-haul sectors – with inoperative IFE systems. On long-haul flights without any IFE to divert their attention, many passengers might become bored and fractious.

Not only would such passengers create a lot more work for harried cabin crews, they might also create ‘air rage’ problems for the flight attendants. This eventuality is all the more likely given the trend for airlines to pack greater numbers of passengers into ever thinner and less comfortable seats, so passengers increasingly feel like sardines in a tin.

Also, accidents are known not to have single causes. Every major commercial-aircraft accident results from a combination of causative factors, some accidents representing extremely unlikely and unfortunate combinations of a series of very rare events.

So it is impossible to say with certainty that seemingly innocuous minor glitches, not vital to the minimum equipment list, will never represent causative factors in a commercial-aviation accident.

Of course, the airframe – the fuselage, wings and control surfaces – is an absolutely integral part of every commercial aircraft. This is an incontrovertible fact.

Every commercial aircraft’s avionics, air-to-ground communication systems and flight controls are vital too. No commercial aircraft can operate in today’s increasingly complex air traffic management environment and increasingly crowded skies without the use of sophisticated navigation, flight management, situational awareness and communications systems.

All these systems require the use of computers; and nowadays, millions of lines of software code.

All the equipment on the flight deck, a space always as small as a manufacturer can make it without hampering the pilots’ ability to do their job, is there for a good reason. It provides the pilots with all the information they need to fly the aircraft safely, to control it in flight and to reach the destination in as fuel-efficient and comfortable a manner as possible without compromising the safety of the flight.

The aircraft’s other major systems are vital too. No modern commercial turbine aircraft can operate reliably and properly without cabin air pressurisation, or without its control surfaces and landing gear operating smoothly.

But every aircraft system, whether those used only by the pilots or those systems present for the necessary or convenient use of every person on board, needs to have a source of power to be able to operate – particularly electrical power.

In modern aircraft, some power may be provided by large, rechargeable batteries installed deep in the fuselage. During in-flight electrical emergencies, sufficient power to ensure that pilots can control aircraft down to safe landings may be provided by ram air turbines which deploy automatically, though these systems aren’t installed on every commercial-aircraft type.

On the ground and sometimes in flight, most aircraft obtain much or all of the electrical power they need for cabin and other systems from their auxiliary power units. These are small turbine engines operated specifically to generate electrical power.

Almost invariably, however, modern commercial aircraft obtain most or all of the electrical, pneumatic and hydraulic power they need for the operation of their systems from their engines.

Most aircraft designs call for compressed air to be bled from the engines’ compressors to power cabin air and other systems, but the Boeing 787 – the first ‘bleedless’ aircraft – draws only electrical power from its turbofans.

A very strong argument may be made that any commercial aircraft’s engines are its most crucial assets. Without them, no commercial aircraft would be able to take off or operate any mission. Its engines represent from one-third to one-half of every new commercial aircraft’s net price.

In addition to providing the propulsive power which enables a commercial aircraft to fly, its engines also provide almost all its other power requirements. Modern turbofans and turboprops are enormously sophisticated items of capital equipment which embody the latest technological advances – in terms of materials, coatings, aerodynamic design and computerised operation – much more than do any other parts of an aircraft.

The aircraft part-out market bears this out. There are many instances on record of young commercial aircraft being retired and parted out because the market values of their engines (as parts or whole engines) exceed the economic value of keeping the aircraft in service.

As someone who writes frequently about turbine aero engines, who enjoys finding out about the amazing technological advances each new generation of commercial-aircraft engines introduces, and who loves the powerful whooshes or fan-drone sounds of modern turbofans operating at high power, I personally reckon the engines of commercial aircraft are their most important parts. To me they’re certainly the most interesting ones.

TAGS: Airframes
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