Engine accessories: starters, pumps, sensors, valves

Engines come with hundreds of different acces­sories―making it all the more com­plex and de­mand­ing a task to main­tain them quickly and reliably.

11.2017 | Text: Denis Dilba

Denis Dilba holds a degree in mechatronics, is a graduate of the German School of Journalism, and founded the “Substanz” digital science magazine. He writes articles about a wide variety of technical and business themes.


If you imagine an aero en­gine—with its com­pres­sors, tur­bi­nes and com­bustor—as a human heart, then its acces­sories could be likened to the coro­nary blood vessels. Just as the human heart is sur­rounded by a net­work of arteries, the engine is sur­rounded by a range of sup­port­ing com­po­nents. The analogy continues: acces­sories are split into numer­ous com­po­nent groups that are critical to the func­tion­ing of the whole, as in the human heart. Should these acces­sories fail, the engine is at risk of suf­fer­ing some­thing akin to a heart attack: the engine can no longer op­er­ate safely and the air­craft must either per­form an emer­gency landing or else remain grounded. Mean­while, the costs in­curred in­crease with every passing minute.

Christian Ludwig and his team are there to do all they can to avoid such a scenario. “And if it does hap­pen, we’re the ones who can get the air­craft back in the air the fastest,” says the Di­rec­tor of Acces­sories Op­era­tions at MTU Main­tenance Canada in Richmond. Here, right on the door­step of Vancouver and its inter­national air­port, MTU has es­tab­lished its Acces­sory Repair Centre of Excel­lence (A.R.C.). Initially, the plan was simply to ag­glom­erate acces­sories activ­ities within MTU but, as the com­pany con­tinued to invest in the per­son­nel and infra­structure required for acces­sories repair, it quickly saw the oppor­tunity to turn it into its own, effective business.


Extreme complexity: engines come with hundreds of different accessories.


Starter for the V2500 and the GE90


Solenoid valve


Bleed valve


Fuel-cooled oil cooler (FCOC)


Main actuator


Hydraulic pump for CF6 engines


Fuel pump for the CF6-80C2


Air-cooled cooler (ACDC)


Air valve


Actuator for active clearance control




Valve for active clearance control


VSV actuator

Extreme complexity

“The biggest challenge when it comes to acces­sories is the enor­mous complexity in­volved,” says Ludwig—a level of com­plexity that only a select few in the market have a handle on. One single en­gine has an aver­age of 80 dif­fer­ent acces­sories, manu­fac­tured by 15 to 20 dif­ferent suppliers. The array of com­po­nents ranges all the way from starter motors, fuel pumps, hydraulic pumps, ac­tua­tors, sensors, and valves all the way to wiring har­nesses and tubing. “When you’re catering to all sorts of dif­ferent engine types, like we are, it quickly amounts to a bewil­dering array of hun­dreds of dif­ferent acces­sories that you have to manage,” says Ludwig. Just the logistics of gath­ering to­gether the individual parts re­quired to re­pair a wide range of acces­sories is an enormous task in itself.

On top of that, you have to factor in the range of geo­graphic and time con­straints that come into play when you have repairs to be carried out, and you need to have ex­perts on hand to do the job. “For in­stance, if an air­line is flying to Hawaii and ex­peri­ences a leaking fuel pump, they will need an opera­tional replace­ment as soon as pos­sible,” says Ludwig. “At the same time, we need to re­serve enough ca­pac­ity to deal with main­tenance and re­pairs on engine acces­sories that come in as part of a sched­uled engine shop visit.” Then there are acces­sories that need to be checked after a set number of hours in ser­vice. “We have to be able to cover all that work at the same time, or else our cus­tomers will lose interest,” says Ludwig.

Accessory expertise and all-inclusive service

MTU Maintenance Canada has developed several test cells to cater to the various accessory subsystems.

450 repair procedures

Accordingly, the accessory repair process has to run like clock­work. “When an acces­sory comes in, an in­coming test shows us what isn’t working. Then we take the unit apart and give it a good clean be­fore we perform visual in­spec­tion and tests on the com­po­nents,” explains Ryan James, who is re­spon­sible for engi­neering at the A.R.C. Repairs are then carried out, followed by reas­sembly and final testing, before the acces­sory is sent back to the customer. Repairs draw on some 450 dif­ferent pro­cedures. And if the re­pair work is taking too long, James’s col­leagues will simply take a com­plete, func­tion­ing unit of the same model from storage, and send that back instead.

As a result, defective acces­sories can be replaced with func­tion­ing ones within be­tween four and 24 hours. “With some air­lines, we have agree­ments to keep replace­ment units for their fleets in central storage. From there, the units are put onto the next air­craft to land at the air­port where the ex­change is due to take place,” says James. “That’s when we achieve the four hour replace­ment rate.” But even the 24-hour turn­around time is often faster than what the com­pe­tition can offer, com­pe­tition that in­cludes com­panies such as Luft­hansa Technik, Allen Air­craft, AJ Walter and Triumph, as well as the manu­facturers of the acces­sories them­selves. The latter in par­ticu­lar often specialize in just a few acces­sories, and are slower in the decision-making process because of the size of their company. This means that they are rarely able to match the service offered by MTU’s A.R.C.

Video: MTU Maintenance Canada: Accessory Repair Centre Article with video

MTU Maintenance Canada: Accessory Repair Centre

Accessories are components such as starters, fuel and hydraulic pumps, actuators, sensors, valves and tubing—all essential to the smooth operation of aircraft fleets. MTU Maintenance Canada has set up an Accessory Repair Centre of Excellence to repair such components quickly and reliably. To the video

All-inclusive service package for accessories

The Canadians are also extremely flexible, offering acces­sory repairs for every­thing from busi­ness jet engines such as the CF34-3 to the mighty GE90 that powers the Boeing 777. “Our all-inclusive service pack­age for acces­sories is par­ticu­larly ­popular,” says Ludwig. This is a compre­hensive service whereby MTU takes care of all an air­line’s acces­sories. This includes the man­age­ment of line replace­able units (LRUs), specific ­acces­sory com­po­nents that can be re­placed on location during routine opera­tions. “This demanding service offering is possible only ­because around half of our em­ployees in this segment work on site with the customer,” says Ludwig.

Everything points to growth. Last year, the A.R.C. repaired 11,000 acces­sories, bringing in busi­ness amounting to 60 million Canadian dollars. The 98 members of the A.R.C. team cur­rently serve 114 customers, which in­clude air­lines, engine manu­facturers and even the U.S. Air Force. “We’ve set our sights on almost doubling our rev­enues by 2020,” says Ludwig. In other words, busi­ness is booming.

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