C-130 Hercules Upgrade
SQNLDR Dane Fea, C-130 LEP OPO explains the Human Machine Interface aspects of the RNZAF’s C-130 Life Extension Programme (LEP) currently underway in Edmonton, Canada.
More often than not, when aircraft undergo major avionics upgrades, a full Human Machine Interface (HMI) programme is not carried out to the extent required by the magnitude of the upgrade.
The magnitude of the upgrade to the RNZAF’s C-130s under the Life Extension Project (LEP) is big. So big that the upgrade has often been termed ‘The most comprehensive upgrade ever carried out on a C-130H’. The structural, mechanical and avionics aspects of this major overhaul have been detailed in other Air Force News articles. For the purposes of this article it is sufficient to say that the scope of the changes demand an extensive HMI programme.
The primary aims of any HMI programme are:
- To ensure that the modified aircraft is compliant with relevant aviation authority (in this case the Federal Aviation Authority - FAA) and military specification standards for certification.
- To ensure that the modified aircraft’s equipment is arranged to provide for optimum mission effectiveness.
- To ensure that the modified aircraft’s equipment is designed to provide for maximum safety in operation.
- To ensure that equipment is located to maximise maintenance access.
To meet the various HMI aims, the prime contractor for the LEP, Spar Aerospace, contracted Stephen Day Consulting (SDC) to prescribe a suitable HMI programme for the project. The prescribed programme, incorporated into the LEP contract as the HMI plan, is a comprehensive process that has tendrils that reach into many of the other processes involved in the project.
A very concise summary of the HMI plan would be:
- Dissect the operating procedures of the RNZAF to extract critical periods of high workload during various phases of flight.
- Set specific project milestone working groups to formally evaluate the aircraft design.
- At these working groups assess the design against certification requirements and run scenarios based on the critical periods of workload obtained previously to isolate any issues.
- Amend the aircraft design to incorporate the findings of the working groups.
The actual HMI process that has been applied to the C-130 LEP design has followed the prescribed programme closely. At all stages Subject Matter Experts (SMEs) from the RNZAF have been consulted as part of the decision making process. RNZAF involvement has primarily been through participation in working groups and indirectly via email and teleconference. In total, the Resident Project Team (RPT) has hosted eleven RNZAF personnel, both aircrew and maintainers, at Spar Aerospace for five HMI working groups.
Probably the most significant working group held to date was the formal evaluation of a Cockpit Mockup. This mockup (depicted) is a full scale cockpit replica assembled by Spar’s engineers.
The mockup was scrutinised by Spar, Spar’s HMI consultant, the NZRPT and RNZAF aircrew over three days. Many HMI changes resulted from the Mockup evaluation which have subsequently been incorporated into the modified aircraft’s design. 
There have been numerous changes to the aircraft’s design produced by the HMI effort. The most significant being:
- Validation of the Copilot’s FMS Multifunctional Control and Display Unit (MCDU) side panel positioning.
- Movement of the pilot’s MCDU to improve access.
- Altering the Fire Control Handles to indicate fire conditions more appropriately.
- Movement of the Hydraulic Control Panel from the Main Instrument Panel (MIP) to a position within reach of the Flight Engineer.
- Centralising the hydraulic pressure indications and trim indications for easier scanning by the front three crew members.
- Changing the Caution Advisory Warning System (CAWS) to a single central panel with associated Master Warning and Master Caution indications for the Pilot and Copilot.
- Rationalising CAWS indications to reduce crew workload.
- Ensuring consistent colours for all warnings, cautions and other indications across the full cockpit.
- Reorganising and relabelling all aircraft circuit breakers for ease of identification.
The HMI process has resulted in many other ‘tweaks’ for the aircraft’s design. The process of design improvement is ongoing and is not formally complete until the end of flight testing. The next major HMI milestone will be a formal evaluation of the System Integration Laboratory 
(SIL) being assembled in Albuquerque by Honeywell. The SIL allows for very comprehensive testing of the entire integrated avionics architecture. The HMI evaluation of the SIL is eagerly anticipated as this will be the first evaluation of actual live equipment.
While it is certainly true that no aircraft design is perfect, the considerable HMI effort on the C-130 LEP will ensure that the final design will not only meet all certification requirements, but will also provide for optimum mission effectiveness and maximum safety in operation.
WGCDR Frank Dyer
The centre wing components to be replaced.
One of the many challenges, and probably the most significant, on the C-130 Life Extension Project (LEP) was how to rebuild the centre wing box on the aircraft.
This is the main structural component on the aircraft and it is the item currently plaguing C-130 operators around the world due to cracking that has been found within this structure. Many operators are facing severe operational restrictions and limitations due to this component and some high-life aircraft are already restricted to very limited cargo loads and/or no passenger loads. So what’s the problem? Just replace the thing Smithers and be damned! Unfortunately replacement with a new item comes at a significant cost and actual availability of the new centre wing is always a concern given that the U.S Air Force have recently embarked on their own programme to replace 155 of their own center wings by 2020.
The RNZAF C-130 LEP was therefore an ideal opportunity to address this problem. To cut a long story short the decision was made to carry out fatigue improvements on the upper surface of the wing (the least stressed structure when the aircraft is flying) and rebuild the remainder of the centre wing with new structure. As can be seen from the diagram this means rebuilding the U-shaped lower structure and marrying it back up to the fatigue-enhanced upper surface.
The first issue was the upper surface – the structure needed to be improved so it will last to at least the planned withdrawal date of the aircraft. The centre wing has however already accumulated fatigue cycles throughout its service to date. A significant amount of work went in to calculating the fatigue life accumulated considering the different flying profiles the aircraft has undergone during its service. Much of the RNZAF flying data that had been gathered over the years was run through algorithms and programmes to determine the fatigue life expended to date. It was then calculated how much life extension would be required within each area of the structure to reach the planned flying hours at the withdrawal date.
To achieve this extension SPAR Aerospace had to then test the various improvement methods to determine which method would be used in each area of the centre wing. The majority of improvements could be achieved by improving the strength of the fastener hole to inhibit cracking a proven process known as Hole Cold Working (HCW).
The testing of the various fasteners and Hole Cold Worked holes was subcontracted to Fatigue Technologies Incorporated (FTI). Following a design review held at Spar, FTI carried out the testing at their test facility in Seattle using fatigue testing machines that apply hundreds of thousands of calibrated cycles to a test coupon until cracking occurred. 87 test coupons were manufactured and tested in the process which took many weeks to complete.
From this testing it was determined some 6000 holes would be improved (by HCW) in the upper surface and other areas would require strengthening or replacement. This part of the LEP required significant effort and was led by Mr. Victor Zvyagintsev a fatigue expert who has had considerable practical fatigue testing experience on many large aircraft. His extensive knowledge and experience made for some very lively and enlightening discussions during the many design reviews as the fatigue improvement programme was developed. Structural input from RNZAF Engineers and DSTO also assisted during this process.
In parallel with this SPAR and the Resident Project Team (RPT) in Edmonton Canada were also working on the other challenge: How to rebuild the u-shaped centre wing box. While centre wings have been removed and refitted before, this is the first time outside Lockheed Martin that anyone has ever re-built a centre wing.
The centre wing is 36½ feet long, 6 ½ feet deep and 3 feet high. First the tooling had to be made from scratch. The tooling had to be able to lift the wing, move the wing and hold the wing in place while it was being dismantled. The tooling then had to be used to rebuild the lower surface and front and rear spars and marry this assembly back up to the re-worked upper surface. No big deal, except that everything must be accurate to within 0.010 inch (about 1 human hair thickness).
The MoD Project Manager Mr. Ian Gibson and WGCDR Frank Dyer participating at a tooling design review in KUKA's Detroit facility. “ this is the first time outside Lockheed Martin that anyone has ever re-built a centre wing. ”
To achieve this SPAR subcontracted KUKA, a large U.S tooling company who specialise in the use of robotics in aerospace and therefore were used to working to the very accurate tolerances required. A large portion of last year went in to developing the tools, involving both SPAR and the RPT in a number of design reviews at KUKA's Aerospace facility in Detroit. The final tooling has been achieved through a co-operative work environment between the three organisations. It was very satisfying to see the final product of the five main tooling fixtures arrive in January this year at SPAR and the accuracy and quality of the tools were quickly confirmed using the laser tracking tool that automatically measures in three dimensions. The tools are obviously very large to accommodate the wing components however the size belies the minute detail that had to be gone in to in many of the areas to accommodate the hundreds of unique aspects of the wing assembly. Each of the four end plates that bolt to the ends of the wing box in the marriage fixture are over 300kgs each machined from steel plate. A significant proportion of the remainder of the tooling is manufactured and cast from aluminium to match any thermal expansion or reduction of the wing as it is being assembled.
The centre wing from NZ 7003 was removed in December 2006 and it is now located in the tooling with the refurbishment process ongoing. This marks the first time a centre wing has been removed from a C- 130 with the intention of rebuilding it. On the lower surface alone there will be over 40,000 holes drilled and reamed for the fasteners. Individual components such as the 13 main lengthwise beams (stringers) that attach to the skin will be built up, with their accompanying fittings, in separate jigs before bringing them to the main tools. Throughout the rebuild process the wing, and tooling, will be constantly checked using the laser tracking tool which can measure to within four thousandths of an inch over 400 feet. Once the centre wing is fully assembled prior to it being refitted to the aircraft another tool will be attached to each end and the end fittings will be automatically machined to align with the exact reference planes the wing has been built to.
So as C-130 centre wing problems continue for operators worldwide it is heartening to see the encompassing solution developed at SPAR for the RNZAF LEP. As was seen at the 2006 Hercules Operators Conference it is likely other users will continue to have to carry out ongoing piecemeal component replacements to continue operating as further issues arise with this item. While this is not an area of the LEP that will generally be visible to RNZAF servicepersons operating with the Hercules we can rest assured that New Zealand C-130's will be able to continue operating safely well into the next decade.