Reverse engineering saves in jet engine repair

Edited by the Engineeringtalk editorial team Mar 31, 2004

Brookhouse Patterns has helped British Airways achieve an in-house, cost-effective repair of a damaged Boeing 777 engine at its London Heathrow workshops.

By reverse engineering a full bond and support tool for a GE-90 D-duct, Brookhouse Patterns has helped British Airways' Aircraft Component Services Group to achieve an in-house, cost-effective repair of a damaged Boeing 777 engine at its London Heathrow workshops.

Aircraft Component Services (ACS) is the main support workshop at Heathrow and undertakes complex approved repair of many aircraft components.

This avoids sending parts back to original manufacturers for repair, which would incur higher costs and longer repair lead times.

The facilities of ACS were recently challenged, when they were faced with repairing a GE-90 thrust-reverser translating cowl, which had been severely damaged by a collision with another company's fuel truck in Boston.

Although minor repairs to these cowls, or D-ducts as they were known, had been carried out by the workshops previously, a repair of this magnitude had never been attempted.

Essentially, the cowl consists of an acoustic panel of sandwich structure construction, which is attached to an outer panel.

The collision had cause significant damage to the acoustic panel and, faced with a bill of some $250,000, for a complete replacement panel, ACS decided to investigate the repair possibilities.

One of the chief problems facing the repair team was the fact that, to meet Boeing specifications, the panel would have to be cured at a temperature of 350F at the original autoclave curing pressure.

To achieve this, it was realised that a full bond tool would be necessary, to maintain the panel profile and prevent any distortion during the repair cycle.

Having worked previously with Brookhouse, notably in rebuilding damaged Boeing 747 radomes, ACS decided to entrust the building of the support and bonding tool to the Darwen company.

In the absence of any design documentation, Brookhouse agreed to manufacture the new tool by reverse engineering.

Consequently, the damaged acoustic panel was despatched to Darwen, where Brookhouse expertise was first applied to effect a temporary repair of the damaged area to restore the panel to its original surface geometry.

The panel was then used as the original pattern for the support saddle of the tool and was located in a specially manufactured, holding fixture while it was laid up with carbon fibre.

The saddle was then cured on the component in an autoclave.

Having established the correct tool geometry, the carbon fibre, support and backing structure was then attached to the saddle and the complete, rigid assembly was located on a steel handling trolley.

This was used both to hold the tool during transport back to Heathrow and also to wheel the tool around the workshops.

Final repair of the damaged panel, incorporating the use of a specially manufactured honeycomb core, was effected at ACS and the complete assembly was successfully cured on the support and bond tool at elevated temperature and pressure, with no distortion or damage to any part of the structure.

Moreover, ACS now possesses a tool to carry out similar repair jobs, which would normally cost in excess of GBP 1million if sent back to the manufacturer.