It was more than a decade ago when Sikorsky began developing a solution to counter the possibility of loss of main gearbox lubricating oil pressure on its large-cabin S-92 helicopter. The impetus behind the project was the 2009 crash of an S-92 about 50 miles off the Canadian Atlantic Coast after mounting studs on the helicopter’s oil filter failed in flight, causing a complete loss of gearbox lubrication.

While the OEM swiftly remedied that particular situation, it self-initiated a system-wide redesign process to ensure any future S-92s encountering that highly rare instance would be safe.

After an investment of more than $100 million, that aspiration has been met with the unveiling of the Phase IV main gearbox, the central feature of the airframer’s new S-92A+ evolution. An independent, auxiliary oil lubrication system has its own three-gallon reservoir that will kick in if the oil pressure in the primary system fails.

“It’s not very likely; it doesn’t happen very often, but it basically lets you fly the aircraft without having any concern with respect to the gearbox and land anywhere you need to,” explained Leon Silva, the Connecticut-based airframer’s v-p of global commercial and military systems. “You don’t need to land in the water; you don’t have a 30-minute restriction. Whatever fuel they have, it will let them essentially stick with the original plan and have a full spectrum of alternatives.”

Thus far, the company has assembled four of the Phase IV gearboxes. As part of the program testing, Sikorsky twice ran the upgraded gearbox via the auxiliary system in a test stand for 7.5 hours—a span that far outlasts the endurance of an S-92.

“We could have kept going from what we saw in the data,” said Kevin Wittke, a lead engineer on the program, during a pre-Verticon media briefing at Sikorsky’s Stratford headquarters. “By all means, the gearbox is still operational; we didn’t see any significant degradation to the internal parts.”

Overall, the company has reached 800 hours of testing, including 200 flight hours on the Phase IV gearbox that has been installed in one of its test S-92s. “We’re projecting finishing [certification] this year, and we’re taking orders,” said Silva. “We’ve done the demonstrations; the rest of it is mostly paperwork.”

Considerations are still being weighed for pricing of the Phase IV, which—in addition to becoming standard equipment on all new-build S-92s going forward—will also be available as part of a retrofit package for existing S-92As. Part of the value equation could include allowances for taking the old Phase III gearboxes as trade-ins, according to Silva.

From the outset, the Phase IV gearbox was designed to be a drop-in replacement for the earlier Phase III version. “Yes, there’s wiring and harnesses and extra things, but you can take the Phase III gearbox out through the existing maintenance procedure and drop this gearbox right in,” said Wittke.

This conversion process can be done right at the customer’s facility. “An important design criterion was not to have to bring it back to the factory because that’s very disruptive to the customers,” added Silva.

In addition to the safety benefits, the move to the Phase IV gearbox carries other benefits, starting with its construction. “One of the significant changes we made is it will actually be made out of aluminum versus magnesium,” Silva said, noting that magnesium is a harder material to work with. “When we start making the Phase IV in aluminum, we anticipate that it will be easier to do.”

While heavier, aluminum has a higher strength capacity than magnesium and there are more suppliers who work with it, thereby expanding the potential suppliers. Given that aluminum is easier to work with, the company expects the acceptable part yield to also increase. That, according to Sikorsky, will foster shorter lead times and make the units more affordable.

Another part of the A+ package benefits is a 1,200-pound increase in the helicopter’s capability, which will translate to extra fuel capacity, extended range, and/or extra load weight. In addition, Sikorsky’s engineers anticipate a higher TBO than the previous Phase III gearbox.

“We expect that the Phase IV will stay on-wing longer, and we have some projections for that, but we want to finish the certification before we publish that,” explained Silva. “The objective is that the overhaul interval and the replacement interval on a lot of these components, especially the big one being the main housing, is to be substantially longer.”

The S-92 entered service in 2004, and there are presently 276 in service in 28 countries in roles ranging from offshore oil and gas support to search-and-rescue to head-of-state transport.  Notably, the fleet has accumulated more than 2.4 million flight hours, adding approximately 13,000 hours every month.

“Even if we didn’t introduce any more S-92s, the current fleet is not even halfway through its usage,” said Silva, adding that helicopters such as this tend to last up to 30 years. He pointed to the major investment in the gearbox as proof of Sikorsky’s commitment to the airframe. “Why would we be doing this if we didn’t have plans for the long term?”