Software helps engineers replace aircraft parts

Delta Air Lines' Technical Operations Centre is a key part of the airline's activities, providing a comprehensive maintenance service to the company, as well as to other airlines.

With a fleet of over 500 aircraft that need to be kept fully airworthy, Delta Air Lines' Technical Operations Centre is a key part of the airline's activities, providing a comprehensive maintenance service to the company, as well as to other airlines.

To ensure spare parts are available when needed, it uses ICEM Surf software in the reverse engineering of parts for in-house manufacture.

Back in 1924, when Huff Daland Dusters was founded as the world's first aerial crop dusting organisation, maintenance and overhaul of the firm's aircraft was something that got done only when absolutely necessary.

But that situation began to change when, in 1928, the company became Delta Air Service and on 17th June 1929, inaugurated airline services with the first passenger flights, over a route stretching from Dallas, Texas, to Jackson, Mississippi, via Shreveport and Monroe, Louisiana.

From that point on, aircraft maintenance and repair climbed to the top of the ladder of priorities.

Today, Delta Air Lines is the world's second-largest airline in terms of passengers carried and the leading US carrier across the Atlantic, offering daily flights to 490 destinations in 85 countries through its various airline operations and partners.

And ever since those very early days of its life, the company has put safe and reliable air transport at the heart of its operations.

The key to ensuring that safe and reliable air transport can be found in the work carried out by Delta TechOps, Delta's Technical Operations Division.

Delta TechOps' Technical Operations centre (TOC) is located at Hartsfield-Jackson Atlanta International Airport and is one of the largest and most modern aircraft restoration facilities in the world.

The TOC is a true one-stop-shop that provides a comprehensive range of aircraft maintenance services designed to keep Delta Air Lines' fleet of over 500 aircraft fully airworthy at all times.

It also makes its services available to other aircraft operators on a commercial basis.

The services provided by the TOC include airframe maintenance for both wide-body and narrow-body aircraft; engine maintenance, including full overhaul, repair and support capabilities for engine parts and components; component maintenance, including repair, overhaul and test facilities for electromechanical components and avionics; line and GSE maintenance, for a full range of ground services; and technical support and technical operations training.

Without the wide range of on-site engineering expertise and support provided by Delta TechOps, Delta Air Lines would need to purchase from third-party suppliers more spare parts and components for its aircraft fleet in order to meet its flight schedules.

And while many airlines contract all part overhauls to third-party stations, Delta limits its need for out-sourced composite overhauls by engineering its own in-depth, in-house overhaul procedures.

The Shop Support Engineering office is where the responsibility lies for ensuring that these procedures can be undertaken in a cost-effective and timely manner.

It supports all requests for repairs to Delta's and other commercial airlines' aircraft structural components, including slats, spoilers, flaps, engine cowls, composite skin panels, doors, elevators, rudders, tabs and ailerons.

It is also where the reverse engineering facilities within the ICEM Surf surface modelling, surface model analysis and design visualisation software suite are used.

This software enables design engineering teams to create and analyse complex 3D digital surface models to the highest possible quality, in the shortest possible time.

This model data is then used in the tooling development process to design the mould tools and dies required for manufacturing.

ICEM Surf also offers special functionality to enable the easy input and manipulation of data digitised from physical items, such as an existing aircraft component.

Digital surface models can be developed quickly and automatically from ordered or non-ordered (point cloud) digitised data in a fraction of the time required by other methods.

Special diagnostics tools in the software guide the user to getting the correct balance between surface smoothness and adherence to the digitised data.

This enables users to develop the best fit to the data, based on their own criteria - not the software's internal algorithms.

The main focus at Delta in the use of ICEM Surf is on reducing the need to scrap and replace components as well as reducing the need to out-source composite component overhauls and repairs.

In practice, ICEM Surf is used to generate the data needed by Delta maintenance personnel to CNC-machine special tooling in order to maintain complex surface geometries during elevated pressure and temperature cure cycles for composite components.

In special cases, where contour information on the component is not available from the OEM, Delta's engineers need to reverse engineer the contour of an existing airworthy spare part, using ICEM Surf.

In general, this is used only to design composite flat pattern ply templates, using a sophisticated ply design software suite in conjunction with ICEM Surf.

In other cases, where data files are available for OEM sheet metal parts, Delta Engineering uses ICEM Surf to pursue parts manufacturing authority (PMA).

It does this by taking a sample of OEM parts, digitally scanning them and then using ICEM Surf to establish tolerances based on the dimensional range of the parts.

These are then sent for material testing to determine the alloy and heat treatment in order to prove that Delta can meet all strength and dimensional requirements during the manufacturing of the PMA part.

In addition, by using ICEM Surf's advanced surface analysis and diagnosis capabilities, repetitive inspections of tool surfaces can be performed on a periodic schedule using portable coordinate measuring machines (CMMs).

The raw data obtained from these machines is imported into ICEM Surf and then compared with nominal mould tool models.

With a typical ideal maximum deviation of 0.025 cm, ICEM Surf enables Delta's engineers to easily and accurately monitor tool surface integrity over time.

In fact, the primary use for scan data with ICEM Surf at the moment is in checking the final surfaces of a component against a master data set.

The ability that ICEM Surf gives Delta's engineers to adjust the surface models that they generate to the original scan data makes it a logical choice for this purpose.

For most reverse engineering projects at Delta, the geometries with which they are dealing are relatively simple.

For example, if they are dealing with an inlet scoop on an engine cowl, the engineers know that the basic shape is going to be around 3rd order.

So they can start a project by using ICEM Surf to sketch the basic shapes of all loft lines on top of the imported scan data and create profiles or surface patches by four curves to give them a starting point.

Using the surface analysis and diagnosis facilities in ICEM Surf, they can then start adjusting the surface model to the scan data.

Once all the basic surface patches have been created, they can then go through the model and start filleting all corners and use the edges of the scan data to trim the surface patches to the digital edge-of-part.

"Actually, we use only a small portion of ICEM Surf's capabilities to do what we need to do", said Todd Herrington, who is responsible for reverse engineered surface modelling at Delta.

"However, to do these same operations with other CAD software products would be much more cumbersome and time consuming".

"We feel that ICEM Surf gives us the best opportunity to maintain complete control during our decision-making process".

Understandably, it is essential that Delta's engineers achieve the original manufacturer's specifications and tolerances and meet any applicable US Federal Aviation Authority (FAA) guidelines.

As far as parts manufactured in-house from the reverse engineering process are concerned, ICEM Surf's deviation diagnosis functions are the most important aspect of the software's use here.

The software provides facilities for interrogating the created surfaces in order to identify any deviation from the original scan data.

A coloured contour plot shows the difference, in millimetres, between nominal and actual values.

Out of position and partly scanned data can also rapidly be positioned using a 'register' function.

This capability is the key to convincing the engineers that their surfaces and tolerances are correctly specified.

Other surface diagnosis functions in ICEM Surf that help Delta's engineers reduce design time are the ability to create sections and to examine surface-to-surface intersections.

Since most commercial aircraft components have only gentle blends, the ability to approximate a cross-section quickly with a Bezier curve and to arrive quickly at the most likely surface patch structure that will suit the specific requirements are important capabilities.

Further, while the exterior structural components of commercial aircraft do not generally require Class A surfaces (the highest quality of surface), ICEM Surf's surface highlights and zebra striping analysis capabilities are used by Delta to ensure surface continuity for ease of machining.

In cases of severely damaged components, without the reverse engineering and surface modelling and analysis facilities provided by ICEM Surf, Delta Air Lines would have little choice other than to purchase new assemblies or to send parts out to third-party repair providers.

This would inevitably increase the overall cost of replacement parts and through loss of control over the manufacturing process, could also affect Delta's ability to meet its flight schedules.

However, the use of ICEM Surf has enabled the Shop Support Engineering office to provide Delta's Technical Operations centre with the surface model data it needs to keep the majority of the manufacturing of replacement parts in house and as a result, to deliver the quality and cost-effective maintenance and repair service needed to keep the airline's fleet of over 500 aircraft fully airworthy.

And from the point of view of the Shop Support Engineering office, it also enables them to keep control of the design-to-manufacture process in order to ensure that in-house manufactured replacement parts pass all regulatory and product quality requirements.

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