Sofema Aviation Services www.sassofia.com takes a look at Aircraft Landing Gear Overhauls
Introduction
Original equipment manufacturers [OEMs] continue to balance the need to design lighter and more robust landing gears. The use of titanium has been seen for several decades after first appearing on the B747 and in a more significant way on the B777
Landing Gears Are Expensive!
A set of Landing Gears for an Airbus 320 cost around 1.8 million USD increasing to 5.0 million USD for Airbus 330/340 and upwards of 7.0 million USD for B777.
Clearly then a significant cost which needs to be managed, as a rule a Landing Gear Overhaul can cost between 10% & 20% of the price of a full set.
Landing gear overhaul quotations are offered using a variety of pricing formula
NTE (Not To Exceed)
With NTE, you are provided with the maximum quote and an assurance your final bill will not exceed that quote. Often, the final bill is under the NTE price.
Firm Fixed.
With Firm Fixed, you are provided with the final bill regardless of the condition of the gear.
Standard
Standard Pricing includes all labour required to perform the normal inspection or overhaul and required parts.
Any discrepancies found during the inspection that require additional parts and labour will be quoted over and above.
Always consider contract exclusions.
These include
a) Additional customer requests,
b) Optional Service Bulletins,
c) Missing or abused parts,
d) Replacement of life-limited parts,
e) Technical Support Engineering Charges
Questions to ask regarding any received quotation
a) Does it include shipping costs for outsourced components?
b) Are parts or other special programs included in the pricing?
c) What are the contract exclusions?
d) What parts are considered over and above?
e) Are discrepancy and repair costs included in the labour flat rate?
Overhaul Considerations
To overhaul a set of gears can take 6 weeks (or more) so from a maintenance planning perspective the landing gear creates many issues which need to be managed.
A typical overhaul of the landing gear will take place at around 10 Years
The landing gears are thoroughly cleaned and then disassembled into numerous components, which are then individually cleaned.
Paint is then stripped from the components using either mechanical or chemical processes. All components are then inspected using a number of non-destructive test processes, as well as additional optical checks to reveal defects.
As well as checks for corrosion and fractures, checks are performed to ensure the dimensions and chromed surfaces of all components are within limits
Addressing Findings
Any corrosion found is assessed and treated just enough to remove all the affected material without impacting as far as possible the underlying material.
Additional assessments are carried out to ensure within limits, out of limit components will need to be replaced.
Only a certain defined allowable maximum of material may be removed; if more is necessary, then the component must be removed and replaced by a serviceable component.
A repair technique simple to the Plasma Spray used on Engine Hot Section Blades is used called HVOF ( high velocity oxygen fuel spraying). HVOF thermal spray coating is a titanium-based coating and a replacement for chrome plating.
In HVOF application, fuel gas is fed at high pressure into the combustion chamber of a special nozzle, where it burns to produce a hot, high-pressure gas stream. Tungsten carbide powder particles are then injected into this gas stream.
The stream is then directed toward the substrate being coated, to create a dense, durable coating with less than 1 percent porosity.
Re- Assembly and Final Test
After cleaning, inspection and repair, the several thousand components are reassembled into a full working system. Rig testing is performed followed by return to the aircraft.
Sofema Aviation Services offers EASA compliant regulatory training to cover Aircraft Landing Gear Engineering and Maintenance Management Considerations. For details please see www.sassofia.com or email office@sassofia.com
