Aircraft Spare Parts Pooling: Art Or Science?

Pooling Puzzles

Flip a coin 10 times and it might come up heads two, three, seven or eight times, rather than the expected five times. Flip the same coin a thousand times, and it will come up heads much closer to the expected 50% of flips.

This also occurs when stocking parts to deal with unexpected breakdowns. The rate of mean time between unscheduled removals (MTBUR) provides the average interval between breakdowns. In small fleets, actual intervals vary according to the Poisson distribution, statistician-speak for “much sooner or later.” Airlines concerned with sticking to schedules must plan for the worst case: “much sooner.” As fleets grow, required stocks can be based more closely on average expectations, so purchases are more affordable.

That is the simple case for airlines accessing parts pools: economizing by sharing risks with other airlines. The practical choice among owned stocks, pools and other options is more complicated. Even airlines with large fleets may have outstations with few flights that need parts for aircraft on the ground (AOG). Flight-hour maintenance programs backed by pools can help carriers economize on infrastructure and repair management staff, not just pool efficiencies. Outsourcing part management saves money, and flight-hour payments conserve capital.

On the other hand, pooling means reduced control of assets. Some carriers want the tight control over part quality, configuration and documentation they believe ownership requires.

Dedicated pools that serve one airline satisfy its control needs but lead to decreases in the efficiency that wider pools provide. They are really rented stocks, not pools. If a dedicated pool is replenished by other airlines’ stocks, there is a gain in efficiency but loss of control.

Pure Outstation Pools For AOGs
Francesco Tetti is business manager of the Luxembourg-based International Airlines Technical Pool (IATP), a nearly 70-year-old alliance that enables 104 airlines to share parts, equipment, line maintenance and aircraft recovery kits at 400 airports. Four staffers at the non-profit IATP manage a pool of 7,500 no-go parts, or those required for departures, valued at $200 million. IATP has about 30 guest and equalized participants, many of them new and smaller airlines.

At each airport, members contribute parts, IATP assigns a value—generally much below market—and then each member there pays an equal share of 20% of this value per year. In return, a member can borrow a needed part, if available, for 14 days, plus a seven-day grace period for returning it.

Tetti says IATP’s part pool is increasing slightly for Boeing 737s, 767s and 777s and Airbus types and declining for Boeing 747s as their use decreases. The pool is just starting for Boeing 787s and generally declining for avionics components. IATP’s annual survey indicates carriers consider all stocking options: owning inventories, borrowing parts and exchanges with OEMs and MROs. “Owned inventories are generally at home bases, and flight-hour pools are expensive, especially with OEM logistics,” he notes. “It’s hard to have inventory at so many airports.” 

Due to system redundancies and improved reliability, there are now only a few no-go items that prevent an aircraft from returning to its home base.

Most airlines carry minimum stocks; financially stronger ones tend to have larger inventories. Tetti argues that economics favor pools for outstations. And IATP offers the skills and tools to install needed parts, another attraction for many carriers.

Pool-Backed Flight-Hour Plans

Spairliners manages component pools, repairs and support for Airbus A380s and Embraer E-Jets. Fabrice Dumas, head of sales and marketing for the Hamburg-based 50-50 joint venture between Lufthansa Technik and Air France Industries, says pool-supported programs have grown more popular in the past 20 years for several reasons:

▪ Modern-day repairs require more investment in equipment. 

▪ Finances encourage tighter control of costs. 

▪ Airlines are reluctant to put cash into part stocks. 

▪ Pool-supported flight-hour maintenance turns fixed costs into charges that vary with schedules and thus revenue.

Most Spairliners pools support flight-hour programs. They include line-replaceable units (LRU) common to many operators but exclude carrier-specific consumables and cabin equipment. Very inexpensive LRUs may be treated as consumables and excluded, as they may be slow-moving and noncritical rotables. The longer a repair turnaround time, the more attractive pooling becomes.

Perhaps 70% of E-Jets depend on pools, including those of Spairliners. Dumas reckons operators of Airbus A320 and older aircraft depend less on pools. Despite small fleets that should favor pooling, only 60% of A380 operstors use it, less than Dumas expected. The largest, Emirates, carries its own stocks.

Owning stocks for many models may be plausible for a fleet of 40-50 aircraft. But Dumas notes that some of the largest low-cost carriers choose pools because they do not want to deal with inventories or repairs.


Spairliners tailors flight-hour programs around airline needs and may include home-base stocks as well. As customer counts grow, Spairliners can offer better pools and prices. An increase in pool and flight-hour providers means more competition, and Dumas says pooling is becoming less expensive.

Airlines still need critical stocks at main bases for no-go items but need fewer spares if supported by a pool. For example, Spairliners can guarantee delivery of a part in a few hours for an AOG or a few days to replenish a stock. Otherwise, an airline might wait 20-40 days for a repair. Carriers choose the appropriate delivery interval according to needs and other arrangements.

Dumas says this model differs from and complements IATP’s pool, which loans a no-go part so an airline can get an AOG back from an outstation for repair. “Carriers subscribed to IATP part by part and station by station do not get guarantees and do not get repairs,” he says.

Financially strong, larger airlines once relied more on in-house stocks, but Dumas says this tendency is eroding. He notes that Republic Airways has 200 aircraft but pools. And pooling is attractive for new aircraft, when fleet size is small, reliability unknown, OEM parts expensive and used parts unavailable. Although less pool-oriented in the past, “U.S. carriers are at least considering pooling,” he notes.

EasyJet Owns And Outsources

EasyJet sometimes accesses pools on an ad hoc basis but has its own stocks, about $100 million in airframe LRUs alone—not including engine, auxiliary power unit and undercarriage components, explains Gary Smith, the airline’s business lead for Neo and futureCabin aircraft. The carrier used pools when it was small and young, but for more than a decade it has bought parts.

EasyJet chose this strategy for several reasons:

▪ With more than 250 aircraft, it had the scale to become its own pool. 

▪ It is strong enough to buy, not pay by the hour. 

▪ The use of pools has the risk of loss of control over assets. 

EasyJet’s young fleet has high and modern standards, and it wants excellent traceability of components when it releases aircraft to lessors. “As soon as you enter a pool, you risk diluting quality,” Smith notes.

He says young carriers pool to reduce cost and investment and increase availability. Having about 50 aircraft of the same model might be necessary to make stock ownership efficient, but “you could . . . pool some parts and own others.” 

EasyJet shed many personnel and infrastructure burdens of in-house repairs. AMOS software tracks parts locations; in-house models, spreadsheets and experience tell EasyJet where stocks should be. For a flight-hour payment, AJW manages logistics for delivering parts and manages repairs, which are outsourced. A tight network and reliable aircraft make this strategy work. “We probably operate to 100 locations that don’t have any specific stocks,” Smith notes. But short-haul routes mean no outstation is more than 5 hr. away. And the highly reliable A320 has many redundant systems. “So the number of times we [have] AOG in remote locations with no spares is small.”

Setting up pooling arrangements in all these outstations would be onerous. So EasyJet relies on AJW to ship spares to AOGs, ad hoc arrangements with other airlines, and its casualty recovery team, which has a dedicated high-speed light aircraft. 

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