Fleet commonality

Southwest Airlines has operated a pure Boeing 737 fleet since 1971, operating nearly every variant of the type.

Aviation commonality describes the economic and logistic benefits of operating a standardized fleet of aircraft that share common parts, training requirements, or other characteristics.

Different types of commonality

Commonality policies may be defined in a variety of ways, depending on the operator:

• for civilian aircraft:
  • By model, same generation (e.g. Boeing New Generation 737-700, 737-700ER, 737-700C)
  • By model, different generations (e.g. Boeing New Generation 737-700 and MAX 737-7)
  • By family (e.g. Boeing 737)
  • By manufacturer (e.g. Boeing)
  • By engine (e.g. Rolls-Royce RB211)
  • Any combination of the above

• for military aircraft, the same can be said:
  • By model, same generation (e.g. General Dynamics F-16A, F-16B)
  • By model, different generations (e.g. General Dynamics F-16A/B, multirole F-16C/D)
  • By family (e.g. General Dynamics F-16)

More detailed examples, for civilian and military aircraft

Airbus, within and across families commonality

In order to get significant market shares, the emerging Airbus company had to compete with american giants, like Boeing or Mc Donell Douglas. The only way to succeed was to cumulate significant competitive advantages like fuel savings (first wide-body twinjet -A300-), noise and pollution reduction, numerous innovations (first two crew cockpit-A310-, first production fly-by-wire airliner -A320- after (and from) Concorde, more and more composites, etc.), but also production costs reduction, and, last but not least, other operational costs savings for companies, in maintenance, spare parts, crew training and certification, and aircraft scheduling.

A key success factor was to drastically develop commonality within a family (A300 - A310) and also between families of aircraft (A300-A320-A330-A340-A380-A350). "The extent of cockpit commonality within and across families of aircraft is a unique feature of Airbus that, in Management’s opinion, constitutes a sustainable competitive advantage."

"Cockpit commonality has been the cornerstone for cockpit design in Airbus aircraft, and the gargantuan A380 will be no exception."

The first completed A380, in Toulouse, France, 2005

"Fifteen of the company’s aircraft models, from the 100-seat A318 to the double-deck A380 – including the three new A350 XWB Family members – feature nearly identical flight decks and similar handling characteristics", which is a challenge, since innovation has been strong from the very begining of Airbus.

"This commonality philosophy to reduce development costs and also permits aircraft operators to realise significant cost savings in crew training, spare parts, maintenance and aircraft scheduling."

The transition training from A320 Family aircraft to the A380 takes 13 working days, from A330/A340 Family aircraft it takes 12 working days, while a pilot with no Airbus FBW experience requires 24 working days to complete the A380 standard type rating course. These time savings lead to lower training costs for airlines and considerably increased crew productivity.

"The annual savings in training and payroll expenses through improved productivity from the reduced transition time can be up to US$ 300,000 for each new Airbus aircraft added to the fleet. It also is more economical for an airline to recruit new pilots who already are Airbus-qualified."

Same cabin cross-section (A300, A310, A330, A340), maximum commonality of airframe spares within the A300, A310, A330, A340. Physical commonality

This Airbus focus began with physical commonality, as Airbus’ derivative of A300 – the A310 – shared a common airframe configuration and systems.

Airbus A300 fuselage cross-section, showing the passenger compartment above and the baggage area below.

And from the first plane (A300), the fuselage diameter has been carefully chosen, for a more spacious, comfortable cabin on a genuine twin-aisle widebody jetliner, and optimized for freight LD3 containers), in order to be kept for the future variants (310, 300-600) and families (330, 340). This was a key factor for freight companies, and a security for airlines: they new they could resell their planes to them.

This same cabin cross-section helped to decrease the number of spare parts (there are as many common elements between the A300 and the A330 as between the 340-200 and 340-600), and to reduce the production and maintenance costs.

The A300-600 and A310 share systems, engines, flight decks, cabin interiors and major structural items. Plus, the same choice of engines was available for the A300-600 and A310: the General Electric CF6-80C2 and Pratt & Whitney's PW4000.

Same cabin cross-section (A318, A319, A320, A321), maximum commonality of airframe spares within the A320 family

The same advantages are noted for the best seller A320 family: optimised cabin layouts- the widest single-aisle fuselage on the market -, better baggage and unmatched cargo capability. "Capitalising on the launch of the A318, Airbus has introduced and revised a number of aircraft systems, which improves overall reliability and reduces maintenance and spares costs, these are now standard on all newly ordered A320 Family aircraft." And Leahy (Airbus) pointed out that A320s have logged some 95 million flight hours with 99.7% dispatch reliability.

The cockpit of the A321 is similar to that of the A318, A319 and A320. This layout would later be incorporated to the A330, A340, A380, and the upcoming A350. This "commonality" saves airlines money due to the short transition time for pilots. Note the side-stick controller, a first for a commercial aircraft, along with the digital fly-by-wire technology.

The A330/A340 cockpit used the A320's six-screen design.

Same flight deck design, fly-bywire controls and handling characteristics (A320, A330, A340, A380).

Pilots can transfer among any aircraft within the Airbus family with minimal additional training. Cross-crew qualification (“CCQ”) across families of aircraft provides airlines with significant operational flexibility. "With Airbus’ CCQ concept, fly-by-wire qualified pilots are positioned for an easy transition between the A320 Family and Airbus’ larger A330, A340 and A380 aircraft through straightforward and rapid differential training".

Another advantage is Mixed Fleet Flying, which "enables a pilot rated on an A340 to switch from very long-haul operations to short- or medium-haul flights at the controls of the A320 Family".

Similar systems, control panels and procedures (all Airbus aircraft)

Airbus commonality extends from the flight deck into the passenger cabin as well, with a maximum use of similar systems, control panels and procedures within the various aircraft families. As a result, cabin personnel benefit from the familiarity of aspects on various Airbus types, while aircraft maintenance also is facilitated with the high inter-changeability of systems and parts.

Maximum commonality between A330 and A340. Operational commonality

These two planes were conceived together, with maximum commonality of airframe spares between them. Despite the fact A330 is a twinjet, and A340 a four-engine, initial A340 versions share the A330 wings. This has reduced the costs, and also the risks for Airbus, since an aircraft launch is very risky. Commonality could have been applied to other aircraft functions. But "in this case, it was implemented at the aircraft systems level and changed the way the crew operate the aircraft. This was the beginning of operational commonality."

As an example of the benefits, unexpected, is the ease to create the military A330 MRTT, the refueling pods replacing two engines on the A340 wings.

Same CFM 56-5B for the whole A320 family

The CFM56-5B engine, specifically developed for the A320 family, has been selected to power more than 55% of all A318 / A319 / A320 / A321 aircraft currently in service or on order, and with the same bill of materials, giving airlines a significant commonality advantage.

95% commonality between existing A320 and A320 NEO

There is 95% commonality of airframe spares between the A320 and the A320neo, with 91% commonality in tooling. And airline customers would be offered new ‘sharklet’ wing tips that would produce fuel savings and improved take-off performance on all A320s from 2012.

And pilots will require only about 2 hours of self-conducted training to transition to the A320neo, mainly to get used to the new power settings associated with the new P&W 1100G or CFM Leap-X engines.

Commonality between future A350-900 and A350-800

The A350-800's concept was revamped in 2009 to be developed as a simple shrink of the A350-900, incorporating minor changes to the systems and structure, rather than as an optimised variant. "We had been planning to optimise the -800 design a lot for its lower take-off weight with a different structure, landing gear and so on," says A350 chief engineer Gordon McConnell. "We were chasing economics to provide the lightest possible aircraft." However, there was pressure from airlines to rethink this plan because of commonality concerns and the wish for additional range - the original A350-800 was designed to fly around 15,360km (8,300nm).

New solutions to four basic questions and tasks

A380 flight deck

"Beyond fly-by-wire architecture, beyond the location of the different controls, we have built our aircraft philosophy around the four main pilot's tasks: to fly, to navigate, to communicate and to manage the aircraft systems," explains Jean-Michel Roy, Airbus pilot.

"To answer those four basic functions we have brought in new solutions:

• the fly-by-wire system to fly the plane and the side-stick controllers to control the aircraft
• an enhanced flight management system to navigate
• new communication means, with data link, to communicate
• and our electronic centralized aircraft monitoring system to manage the aircraft systems."

The benefits of the Airbus commonality are safety, efficiency and comfort. The protection included into the fly-by-wire system is obviously a factor in enhancing the safety. The efficiency improvement comes from the drastic reduction of training times. On average, an airline pilot changes aircraft type every five years. During that transition phases that lasts around five weeks, he is not flying commercially.

And "contrary to the purely physical commonality that tends to freeze the introduction of new technologies, the Airbus operational commonality doesn't introduce constraints and doesn't prevent from introducing new technologies or new functions."

Dassault, three extremely similar variants of Rafale

Dassault's approach and challenges at the beginning of the 80's are somehow similar to Airbus in the late 60's : France requirements were to replace seven military aircraft in the French Air Force and Navy:

• air-to-air combat: Mirage 2000 RDI and Mirage 2000-5
• air-to-ground/air-to-surface attack: Super Etendard Modernisé (plus the venerable F-8P Crusader), Mirage 2000D and Mirage F1 CT
• reconnaissance: Mirage F1 CR
• deterrence:Mirage 2000N,

A French Navy Rafale M performing a touch-and-go landing on the deck of the carrier USS John C. Stennis (CVN-74).

and to develop one single light to medium swing-role aircraft, and at the lowest development, production and maintenance costs. To minimize the Total cost of ownership (TCO) for French Defence), for budget reasons (later reinforced by the Defence cuts after the end of the Cold War ). And also because the reduction of the electromagnetic signature (stealth) leads to increased fixed cost per aircraft.

While, before the fall of the Berlin Wall and the subsequent end of the Cold War, United Kingdom and Germany wanted to build and use an air superiority, heavier and not a carrier-borne aircraft. Which became the Typhoon Eurofighter.

The (significant) difference with Airbus' challenges was that Airbus could, and had to, conceive different planes, of different sizes and ranges, while Dassault was asked to produce one single aircraft for different roles, and to enable this aircraft to carry out simultaneously different roles.

What Dassault names a "true omnirole" fighter, and results in one aircraft, in three extremely similar variants : Rafale B, C and M.

Commonality between Navy's Rafale M and Air Force's Rafale C

Rafale B, C and M

The first challenge was to get quite the same aircraft for the Navy and for the Air Force. Dassault resolved it (after the Rafale A, "Technology demonstrator", in July 1986) by:

1. building an Air Force prototype "C01" (May 1991)
2. building two Navy prototypes "M01" (December 1991) and "M02"
3. freezing the Rafale M, the reinforced and more complex aircraft
4. lightening it to get Rafale C for the Air Force.

Compared to Rafale C, Rafale M featured greatly reinforced undercarriage to cope with the phenomenal stress on landing; an arrestor hook and "jump strut" nosewheel, which only extends as the aircraft takeoff during a catapult launch; a built-in ladder, carrier-based microwave landing system; and the new fin-tip Telemir system which enables its inertial navigation system to communicate with the aircraft carrier.

Altogether, the modifications and additions makes it 500 kilograms (1,100 lb) heavier than the Air Force's variants.

But Rafale M still retains high commonality with the other variants: the Rafale M and C have for 80% the same structural design and for 95% the same systems.

Commonality between double-seater Rafale B and single-seater Rafale C

The double-seater Rafale B is a fighter and attack variant which can carry out all the roles of the single-seater Rafale C, and which is also used to train the crew. The Rafale B has the same characteristics as variant C, because, unlike many fighters, the fuselage length is exactly identical to the single-seater Rafale C.

That has been enabled by the reduction of the fuel capacity, in the fuselage. As a result, the Rafale B weighs 350 kg more with its internal fuel capacity reduced to 400 liters. For that reasons, the commonality is extremely high between these Air Force variants B and C.

It can be seen that the highest commonality was a top priority, and a full success, of this Rafale programme.