Sikorsky has spent almost three decades polishing its S-76 to address shortfalls and keep it competitive. We spoke to operators to judge how successful it has been.
Demand for Sikorsky's sleek and stylish S-76 is at it highest since the helicopter's launch 30 years ago, but competition in the medium twin market is intensifying. The newly certificated Bell/Agusta Aerospace AB139 is muscling into the S-76's corporate and offshore markets. But Sikorsky has some product improvements in hand and more in prospect, which it believes will keep the S-76 competitive as deliveries pass the 600 mark.
The original 4,770kg (10,500lb) S-76A first flew in March 1977 and was certificated in November 1978. The current 5,320kg S-76C+ first flew in June 1994, and was certificated two years later. The past three decades have been a story of incremental product improvement that continues today. Beginning this year, all S-76C+ helicopters for the corporate and VIP market will be fitted with the Quiet Zone gearbox, which Sikorsky says significantly reduces noise in the cabin and cockpit.
Also this year, the manufacturer will certificate the Turbomeca Arriel 2S2, which was selected in 2002 as the engine for future S-76s. The 2S2 provides 6% more power than the S-76C+'s Arriel 2S1s and features dual-channel electronic engine control. It will be the latest in a series of engine upgrades that have punctuated the helicopter's history.
The Allison (now Rolls-Royce) Model 250 turboshafts in the original S-76A earned a reputation for unreliability, and pilots learned to handle the engines with kid gloves. The switch to Turbomeca Arriels in an "A+" variant turned the helicopter's fortunes around almost overnight. The Arriel 1S turboshafts offered higher reliability, 8% more power and a 483kg increase in maximum weight. The conversion was developed by CGTM - the test arm of Turbomeca - and first flew in April 1986. An upgrade kit was developed, but the S-76A+ never became a production model.
Teething troubles
Offshore operators such as Bond and Bristow Helicopters judged the S-76A to be a good helicopter with poor engines and were behind the A+ upgrade effort. Bristow now operates S-76A+s from Norwich, UK and Den Helder, Netherlands, serving the southern North Sea. CHC Scotia - which evolved from Bond and British International Helicopters - also has three in the same area. The problems with the A model, however, were not replicated onshore. "Two of our five S-76A models have been flying the line for over 14 years; averaging between 130 and 140 flying hours a month, without any real problem," says Morris Forchuck, director of maintenance at Vancouver-based scheduled operator Helijet International.
"Since 1987 we have flown 11 differentS-76A or A+ aircraft for 115,000h. Average utilisation has been around 120h a month and maintenance dispatch reliability has been better than 98%," says Forchuck. "Since we started using the S-76A in 1987, we have accumulated over 200,000h with the 250-C30S. As we have a more than a 1.5 cycle per hour operation, our units always cycle out before they time out. We average about 1,650h between turbine overhauls."
Gordon Jones, an experienced S-76 pilot who served as Helijet's director of flight operations, says: "The S-76A works fine in the cool, sea-level climate of western Canada. But performance quickly drops off as you increase altitude or hit summer temperatures, resulting in lower cruise speeds. Also, OEI [one engine inoperative] ceiling at gross weight is not great. As any A-model pilot will tell you, the flight manual has one set of 'approved' Sikorsky limitations and a second, lower, set of Allison 'manufacturer's recommended settings' that you needed to stick to to conform to its warranty."
Without exception, says Jones, operators that had problems with the A model and converted to the A+ were those that "pulled the snot out of them" regularly. Others, happy to husband the power settings, had fewer problems. "We [Helijet] ended up establishing lower continuous cruise-power settings, below even the Allison settings, and that helped," he says.
Both the A+ and A++ (introduced with the further uprated Arriel 1S1) conversions proved popular onshore and off: the engines and the increases in gross weight offered improved payload and performance. However, it was the launch of the S-76B, in 1982, that marked the next significant stage in the helicopter's evolution. First flight was in June 1984, leading to certification and first deliveries in 1985.
The S-76B offered vastly improved single-engine and hot-and-high performance: the new Pratt & Whitney Canada PT6B-36A engines increased take-off power by 48%. But their higher fuel consumption proved uneconomical over the northern North Sea, and KLM Helicopters, based further south, was the only offshore operator to take theS-76B. Airframe strengthening enabled a further increase in gross weight to first 5,000kg, then 5,180kg and eventually 5,320kg.
Kicked off in 1989, the S-7C programme united the strengthened B airframe and drive system with a 3% growth version of the Arriel, known as the 1S1. The first S-76C flew in May 1990, leading to certification the following March. The main advantage of the C over the A+ was the extra 227kg of payload, which translated into two more passengers or more comfortable reserves. This is why Bond - now CHC Scotia - bought the aircraft in 1996, initially to operate from Aberdeen, Scotland, but latterly in the southern sector of the North Sea.
CHC Scotia chief technical pilot Steve O'Collard says: "The fuel burn is slightly up, from 640lb/h [290kg/h] to 660lb/h, due to the extra weight and the new engine, so endurance is marginally down as fuel capacity is the same. It's also colder here, which helps, because the C performance falls off rapidly above about +10¡C as the engines aren't man enough for the extra weight."
The S-76C+, the current production version, replaced the Arriel 1S1 with the 2S1. This further increased power, and the digitally controlled engines have a 30s OEI rating, improving single-engine performance while retaining the range of the S-76C. The first S-76C+ flew in June 1994 and was certificated two years later. Offshore Logistics of New Iberia, Louisiana, which last year ordered 15 S-76C+ helicopters and took out a further 24 options, plans to renew its S-76 fleet over five years. The promise of 30-40% higher productivity for the C+ makes this purchase attractive, says chief executive Dru Milke.
Range compromise
In moving from the A to the B model, the helicopter's range had been compromised, admits Sikorsky's S-76 programme manager, Eric Hansen. "In developing the C+, we had to address that. It has the payload capability of the B with the range of the A, which is why Sikorsky stopped manufacturing the B in 1999 - even though there was a market segment that liked it, we decided that if they gave the C+ a chance, they would like it."
However, the C+ has not proved to be the answer for everybody. One UK VIP pilot says he has never been able to get out of confined sites with full fuel and, above 4,000ft (1,200m), the cruise speed was closer to 130kt (240km/h) than 150kt. Eurocopter's more modern EC155, in comparison, retains its 155kt normal operating speed. Adam House, a pilot with UK earth-moving equipment builder JCB, says there is an issue with the endurance of the C+ when operating from confined spaces.
Corporate and offshore pilots alike look forward to the day when they can get Class 1 take-off performance at maximum all-up weight. Only the new generation of rotorcraft like the AB139 make that a realistic goal. At present, with the S-76C+, if they want to use it in a confined area, they are restricted to 4,990kg rather than the maximum 5,300kg. "We are all keeping an eye on the AB139," says House. "It has the airliner-like performance - by the time you rotate, you're safe single-engine."
The Arkansas Children's Hospital at Little Rock has no performance problems with its two S-76C+s, even though summer temperatures regularly exceed 38¡C (100¡F), because they normally stay well within maximum all-up weight and are under fewer restrictions than in the UK. The hospital has flown more than 1,100h on each of the year-old aircraft with few problems. Aviation director Bernard Raysor says his board chose the larger cabin size of the S-76 because of where they are and what they do not do. "We are in the middle of the state and don't attend accidents," he says. "Almost all our work involves fetching critically ill, but stable, children for operations. We can get called out on flights that routinely exceed one hour. We can carry premature twins, each in an incubator, or a child and a 350lb heart-lung machine, plus equipment and four attendants."
Finnish scheduled operator Copterline has passed 10,000h on its two S-76C+s flying passengers to and from Helsinki, Finland and Tallinn, Estonia. Managing director Kari Ljungberg says the 18min flight "saves travellers more than 2h each way over the fixed-wing alternative". The operation is demanding. "We have made more than 35,000 flights since 2000 and passenger demand is leading to our historical average of 200 flight hours a month being increased to more like 220," he says.
If Copterline's experience is a gauge of S-76C+ in-service reliability - the despatch rate is 99.7% over the past four years - then Sikorsky has successfully evolved the S-76 to keep pace with demands. The next chapters in the S-76's history will determine whether the company's first purely commercial helicopter can continue its success.
ANDREW HEALEY / LONDON
Source: Flight International
