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Aircraft landing gear: “Landing gear overhaul requires a specific trade expertise”

When it comes to maintaining the aircraft landing, skill shortages are a significant challenge currently being experienced by aircraft maintenance, repair and overhaul (MRO) organisations in the context of a growing industry.

“The whole industry is experiencing a shortage of technicians and with the current unemployment rate being so low the micro-industry demand is being exacerbated. Landing gear overhaul requires a specific trade expertise.

“For example, the machinists are focussed on a specific machine type and with the current situation they might be asked to run a different machine. However, they would not be asked to perform a plating operation or to paint a landing gear. This creates functional area experts, which increases the efficiency of the overhaul, thereby reducing turn-times,” says Pastor Lopez, president of MRO services for components, systems, composites and structures at GA Telesis.

Czech Airlines Technics has 18 years of experience in landing gear maintenance and in its experience there is indeed a lack of qualified technical staff, especially during the last few years.

“Based on our practice, it is necessary to realise that training of new candidates lasts approximately 2-3 years. For both B1 and B2 it is of utmost importance to know in detail the procedure of landing gear overhauls according to the relevant component maintenance manuals.

“Our company cooperates with technical secondary schools and universities, this helps to secure graduates with the requested knowledge while the graduates can develop practice in our company’s facilities during their studies,” says Pavel Hales, chairman of the board of directors at Czech Airlines Technics.

“The landing gear business is very labour intense and requires different levels of skills. Some of the most important skills are usually the landing gear inspection and rework processes; especially machinery, plating and non-destructive testing [NDT] operations. The skills are developed through various apprenticeship and internal personal development programmes,” says Tadas Juozonis, sales and marketing executive at Lufthansa Technik Landing Gear Services UK.

He also points out that while it is not easy to recruit the most critical skills, there are currently enough maintenance technicians available in Europe and Asia.

Aircraft landing gear

Technological upgrades

One of the distinctive features of landing gears is that they are complex components and have many parts. While there have not been many major technological advances in landing gears in the past, in recent years some technological enhancements have been witnessed.

“Original equipment manufacturers [OEMs] have been balancing the need to design lighter and more durable landing gears. While some new technology has been embraced, there has not been a breakthrough technological advance since the B707 and the DC8 first rolled out of the factory.

The introduction of titanium first appeared on the B747 gears in the 1970s. Boeing first expanded its use on the B777 by manufacturing large structural components from this material. Aside from that, the electrical part of the gear has been improved with more sensors to increase its operational safety,” says Lopez.

Design falls within the strategy of landing gear producers and is only remotely related to the design of the respective type of aircraft.

“We can expect to see the use of more lightweight materials, which will have impact on the construction and design of new landing gear sets. Landing gear overhauls must be performed in accordance with prescribed rules in the maintenance planning document (MPD) on average every 10 years. According to our experience, operational wear and tear, free play and corrosion of the components are the most frequently found issue,” says Hales.

To simplify landing gear repair, high velocity oxygen fuel spraying (HVOF), a robotic deposition control, is a real step forward. HVOF thermal spray coating is titanium based coating and a replacement for chrome plating. “Lufthansa Technik has already made significant investment in order to use this technology for landing gear parts as well.

“This technology might be new for the landing gear business, with the A380 landing gears being the first where this technology is widely used; however, it is also used in other departments of ours, such as engine overhaul. Therefore, we have enough experience and full capability to step into this market,” says Juozonis.

“The Boeing 787 was the first aircraft to use zinc-nickel as a substitute for cadmium solutions. We will use this technology because the industry has to say goodbye to cad plating. The size of or landing gear services’ plating shop is sufficient to accommodate additional tanks.”

Aircraft landing gear

Indeed new aircraft types are equipped with more durable metals (high steel and titanium alloys) and corrosion-resistant coating are increasingly used for landing gears.

“For example, with Boeing 777 aircraft that already use titanium parts such as the truck beam, torsion link, drag strut and side strut there is already a significantly reduced turnaround time (TAT) and overhaul cost. These parts mainly require non-destructive testing inspection and replacement of bushings. Usually no surface treatment is required,” says Juozonis.

Maintenance frequency

All landing gear components are treated equal when it comes to maintenance. The degree of rework tends to vary for the same aircraft type, even within a single operator.

“For instance, an aircraft operating in harsh conditions will likely experience more degradation when compared to another aircraft operating in dry climates,” says Lopez. “While there is an effort to use more titanium material for the landing gear structure, most landing gears still have steel and aluminium. These remains susceptible to corrosion and cracks, which need to be addressed during the overhaul process.

“Therefore, the overhaul process as dictated by each OEM must be strictly adhered to in order not to induce any additional stresses that may cause a failure in the future. Most landing gears are overhauled on a ten-year interval as mandated by the FAA. Recently, the B777 gears were extended to 12 years based on their condition during the first overhauls.”

For types of parts like torsion links steering components, such as the steering collar, repairs and overhauls are usually performed with shorter frequency than 10 years.

“Intervals of landing gear overhauls are defined by MPDs, with great impact on the landing gear condition by operational wear and tear in connection with the quality of technical maintenance arranged by each airline,” says Hales.

The extent of repair and damage also depends on whether the landing gears are undergoing the first or second overhaul. “During the second overhaul, the repair work can vary considerably. Previous repairs are often found on these legs, which also have to be checked for structural integrity,” says Juozonis.

Specialised organisations

Landing gear overhaul is a very complex business and therefore special departments are required to cope with this complexity.

“Airlines are better off using companies that are solely dedicated to gear overhauls to draw from these companies’ economies of scale. The business of overhauling and repairing gears requires high investment on equipment and people that need to be managed to achieve high efficiencies, therefore producing an acceptable level of return on the investment,” says Lopez.

Lufthansa Technik has three landing gear service locations to support customers globally: Hamburg (Germany), London (UK) and Sun Valley (California). Both Hamburg and London serve Europe, Asia, the Middle East and Africa.

The workload is currently divided between the two locations by aircraft type; Hamburg serves Airbus customers whereas London supplies Boeing customers. Sun Valley supports a mixed fleet of Boeing, Airbus, E-jets in the Americas market.

“Our landing gear product division is currently undergoing a restructuring programme to adapt to the changes in the MRO market. This is because a landing gear combines hundreds of large and small parts, so the work on those parts requires a process chain with excellent coordination between the parties involved. A main advantage of ours is that all these processes can be carried out in-house at all locations,” says Juozonis.

“Our landing gear services facility in London is an example of all activities taking place under one roof. The purpose built facility was opened in 1998 and currently handles around 300 legs a year. The facility is equipped with paint removal equipment, a machine shop, a hydraulics shop, an electrics shop, NDT, a paint shop and a full plating shop.

“A large plating shop has full size tanks that can accommodate landing gears of any size and enables Cadmium plating for corrosion prevention; nickel plating for repair solutions and chrome plating for surfaces exposed to high heat and wear.”

In addition to dedicated equipment and machinery, spare assets and specially dedicated landing gear documentation teams are critical for the landing gear overhaul business.

“This is one of the specific products of the aircraft maintenance industry. An MRO must be qualified by the relevant authorities, certified and approved to ensure the correct performance of all prescribed technologies and able to provide the required training of technical staff. In addition, it must meet all airline requirements. MROs should therefore be able to perform all work in-house. A plating shop is a must,” says Hales.

“For landing gear maintenance, it is necessary to be able to provide airlines with spare landing gear sets. MRO customers should also be able to use spare landing gear sets provided by the MRO for the time of duration of the overhaul.

“Czech Airlines Technics has a total of four own complete landing gear sets and is capable to perform overhauls of three sets simultaneously. Moreover, we can offer to perform in-house all related services, such as landing gear replacements (in our hangars located directly at Václav Havel Airport Prague), which saves costs and time to airlines resulting from the need of grounding the aircraft.”

“In order to reduce aircraft downtime, Lufthansa Technik can provide advanced direct exchange landing gear that meet the customers’ technical specifications. We have a large spare asset pool. An additional complexity when exchanging landing gears is that one and the same aircraft type can have several different maximum take of weight (MTOW) configurations. For example, the Boeing 777 aircraft has at least four weight classes, and we are equipped with exchange landing gears and conversion kits to support any of the weight classes,” says Juozonis.

In landing gear maintenance operations, especially when exchange landing gears are involved, two main areas of documentation management require special attention. These are the traceability of back to birth documentation and the total landing gear cycles.

“The industry now sees increased requirements to documentation quality, which are mainly influenced by leasing companies. We have a dedicated documentation engineering team that works directly with customers and leasing companies to solve any documentation related problems.

For older aircraft types such as Boeing 757 or Boeing 767 and in particular, for a second or third landing gear overhaul with several operators, difficulties are more likely with full back-to-birth documentation,” says Juozonis.

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