ANALYSIS: S-92 helicopter flight test

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Sikorsky's S-92A reaches two major milestones this year. In January, the fleet surpassed 500,000 flight hours, many offshore oil operators having flown S-92s an average of 90-110h per month. The second milestone is 200th delivery, due in the second quarter.

In 2000, Flightglobal was given an exclusive flight test of the S-92, then Sikorsky Global Helicopters' latest helicopter. I flew the No 3 prototype when total flying hours had only passed 300h of a 1,400h programme. Now the highest-time aircraft has more than 13,000h, with many topping 10,000h. It seemed time to revisit the multimission type.

There are over 160 S-92s operating in 25 countries, mostly offshore. Sikorsky is expecting operating hours to total 150,000 this year. The latest markets are Ireland and Korea for search and rescue, and Alaska and Thailand for offshore. In 2000 the estimated range with fuel reserves in the demanding environment of the UK's North Sea was 400nm (740km). This is now 472nm, sea level standard, with 30min reserve fuel. Average fuel flow is 1,270lb/h (576kph).

Direct operating costs, estimated at $2,200 per hour in 2000, are now circa $1,630, says one operator. Thanks to a health and usage monitoring system (HUMS), aircraft availability has improved from 91.5% in 2007 to 96% in 2012. It detects degraded components for removal. Sikorsky is also using HUMS to extend the life of major components based on condition rather than hours, reducing direct operating costs and maintenance hours.

SHARING BENEFITS

Operators do their own basic monitoring of HUMS information but can send it to Sikorsky for in-depth analysis. The resultant information is shared among other operators.

The S-92 has a range of proactive and reactive safety equipment: cockpit voice and flight-data recorder with underwater pinger, enhanced ground proximity warning, traffic collision advisory systems and external automatically deployable emergency locator transmitter (ELT). Sikorsky can also provide a helicopter operating programme/flight-data monitoring system. For offshore operations, the S-92 has other onboard ELTs, plus one in each life-raft. The ELTs have a GPS broadcast system.

A major proactive safety feature is the dual-redundant main and tail rotor primary servos. In the unlikely event of a loss of tail rotor control, there is a centring quadrant to allow the pilot to carry out a safe landing.

Maximum gross take-off weight has stayed at 26,500lb (12,000kg) since first delivery, although Sikorsky has successfully tested the aircraft at 27,700lb. The S-92 can take off at maximum weight with full fuel and a full complement of passengers, even in North Sea operating conditions and standards, with all the required fuel reserves, and operate with Category A performance.

During Flight International's previous visit, the aircraft had not undergone hot, high and heavy trials. Sikorsky has now done these, with impressive results. The S-92 will hover at maximum weight out of ground effect up to 6,900ft (2,100m) on a standard day; in ground effect, 8,300ft. It will maintain a single-engine rate of climb of 150ft per minute at maximum weight on a standard day, up to 4,000ft.

Production is running at 36 aircraft per annum. Sikorsky plans to boost this to 40.

For my flight, the weather was clear but cold with a light wind - a pity as I like to test helicopters in strong winds, which can limit performance and controllability and test the tail rotor's authority. But I did fly the prototype up to 46kt (85km/h) sideways to the right before running out of tail rotor pedal control.

My co-pilot was production test pilot Stacy Sheard and in the back was chief pilot Steve Schellberg. The aircraft permits efficient pre-flight inspection. There is no need for a ladder stand to inspect the tail rotor. You climb on to the platform over the sponsons and walk over the tail rotor drive shaft. There are retractable steps up the side of the vertical stabiliser to check the tail rotor. All other components and fluid levels are easily accessible.

For refuelling, there is a single pressure refuelling and defuelling receptacle which does both sponson tanks. There is a standard fuel cap on each tank for gravity refuelling. During the external inspection, I reached at full stretch to try to touch the lowest tail rotor blade. Happily, it was much too high.

ICING PROTECTION

The S-92 is well protected against icing conditions with heated windscreens, engine intake de-icing and, as an optional extra, ­anti-icing main and tail rotors. Since our aircraft was destined for offshore operations, life-rafts with emergency locator transmitters and other equipment had been installed at the front of both sponsons. They can be launched by the pilots or externally. In sea states 4 to 5, there is a three-bag flotation system. Through sea state 6, there is a five-bag installation.

All seats are crash attenuating and fire retardant. In a heavy landing or crash, the undercarriage would take the major impact, then the aircraft belly, then the seats. Sikorsky has designed the S-92 so that the heavy main gearbox behind and above the cabin would not penetrate the cabin in a heavy landing. The fuel system is also crash-worthy.

The 19 passenger seats - with 32in (81cm) pitch and upper-body restraints - offer easy access to the three emergency exits, 10 jettisonable wide windows and wide front door. Cabin height is 6ft (1.83m).

Sheard offered me my choice of cockpit seat. I chose the right-hand one. It was comfortable with lumbar, cushion and other adjustments, and a five-point harness. I was pleased to see logical and pilot-friendly equipment and presentations, and that the original flight instruments in the prototype I flew in 2000 had been replaced with simpler, quicker-to-interpret Rockwell Collins round dials.

Once in the air, I could tell with a glance at the multi-function display (MFD) panel where we were in space and where we were going. As with all computer-generated MFDs, there is a huge amount of information available for the crew to access, including the state of all major systems and any malfunctions. One nice touch is lighted approach plate holders for both pilots. Once, during an instrument landing system (ILS) approach at night into Aberdeen with the weather at minimum, my hand-held approach plate flew out of the side window. The industry has learned from such events.

There have been accidents with older-generation helicopters, including the S-61, when the crew have fired the extinguisher into the wrong engine because of confusion after an engine fire warning. The procedure shuts down the engine, leaving crew with a single engine on fire. The S-92 system and procedure preclude this from happening. The many other warnings are logical and obvious.

ROTOR START

The S-92 has the luxury of an onboard 90hp (67kW) auxiliary power unit, so we dispensed with the external power cart. Sheard carried out the straightforward pre-start checks, including full and free control checks using the auxiliary power unit to energise the hydraulics and other systems. The engine and rotor start was simple - fuel on, press the start button, wait for the engine to start winding up, select idle on the overhead full-authority digital engine control lever, sit back and watch. Then both FADEC levers were set to "Fly" and we were ready to go. The vital instruments change colour as start-up progresses. We started our flight with everything in the green.

I taxied out, careful to keep the main rotor level. My first hover was uneventful and easy. Little control motion was required in the slight downwind. Power required and power available were easy to interpret with a glance at the small torque gauge at the bottom of the PFD panel. Hover manoeuvres were easy to accomplish; handling qualities, benign.

All usual Category A take-off procedures are available. I came to the hover, added 10% torque while lowering the nose 10˚ down, accelerated to decision point (in our case 40kt), then added 15kt to climb over any obstructions. Sheard programmed the autopilot to take us up to 2,500ft at 120kt on a specific heading for the chase aircraft to take photos.

So we sat back, hands and feet off the controls. On arrival at the photo-shoot area, I hovered the aircraft manually for several minutes at 2,500ft. The aircraft is highly stable, but of course it has lots of automation to keep it so. I later flew it with all these systems taken out and it was still easy to fly. After some practice, I would have been competent and confident enough to carry out a steep approach and land on an offshore platform in this condition.

Photo-shoot over, we went to maximum continuous power in level flight and got to 152kt indicated airspeed. However, we were some 5,500lb below maximum weight and at a low-density altitude - the altitude which the rotors and engines feel. Sheard says operators usually cruise between 135kt and 145kt, but I noted from the performance information that fuel flow at 135kt true airspeed is 1,300pph at ISA +20˚C at 4,000ft, but only 1,100pph at 150kt true airspeed on a standard day.

A slight dive took us to the never-exceed speed (Vne) of 165kt. On my previous visit, the level of vibration was noticeable at this speed, almost uncomfortable, but on this occasion there was only a slight increase.

BENIGN NOISE

There is a complex anti-vibration system, which Sheard switched off. The result was a level of vibration that would be unpleasant on a long flight but acceptable for a shorter get-you-home. I took off my headset to check noise levels. They were benign.

Sheard dropped us into autorotation. At the best rate of descent speed of 80kt, I noted 2,800ft/min (14.2m/s). If you had to carry out a both-engines-out landing at this speed and rate of descent, you would have to begin the flare early to reduce these parameters to zero, level the aircraft, and use the extensive rotor inertia to land it level. But double engine failures in modern helicopters are rare and usually caused by human error.

Sheard put us on to one engine using training mode, presenting all the symptoms of engine failure/single-engine flight. To save engine life in the training mode, 30s and 2min power are fabricated. But the pilot sees and feels what would happen, including slight rotor droop at the moment of failure.

In this condition, Sheard set up the autopilot to carry out a coupled ILS approach back at base. The system flies the aircraft down the approach to 50ft above the runway, gradually reducing the airspeed to 60kt. On short finals, Sheard disconnected the autopilot. I took manual control and carried out a single-engine-running landing. The General Electric CT7-8A engines provide 2,740shp (2,043kW) 30s power and 2,523shp 2min power. With autopilot managing the approach, there is a "go around" button on the cyclic stick.

The S-92 has enough single-engine power for a safe offshore deck landing, provided the pilot has been sufficiently trained and tested to do so and is current. Type rating is done on one of the three full-motion, visual simulators, with some 40h of hands-on flying.

Sikorsky aims to provide an automatic, hands-off offshore rig approach procedure down to the missed approach point (MAP), plus a go-around facility if the platform is not seen. The airframer is looking at a MAP as low as half a mile and minimum visibility as low as one-eighth of a mile.

There was no available slope on which to plant the S-92, but Sheard said she had, elsewhere, landed on one of about 10˚. Since the cockpit is so user-friendly, Sheard did not need a checklist to shut down the aircraft.

The latest S-92 is modern and safe, with all its proactive and reactive systems. Plus, it is both passenger- and pilot-friendly.