Turbine Pilot

The 'baby' King Air goes on steroids

It's become fashionable to publicize the new, much-heralded crop of very light jets (VLJs). But though some may dwell on this phenomenon, let's not lose sight of the benefits that turboprops offer in comparison. For example, on trips of 500 nm or less — the distance of the overwhelming majority of all business flights — turboprops can offer more economical fuel burns than VLJs. That's because their engines are most efficient in the middle altitudes, say, in the 18,000-to-25,000-foot range. VLJs, or any turbofan-powered airplane, for that matter, are most fuel efficient when cruising in the 35,000-to-41,000-foot range. It remains to be seen whether VLJ pilots (especially those flying in busy airspace dominated by airliners) will be cleared to those altitudes, so fuel flows may well be higher than optimal — and higher than those published in sales brochures.

But what about the speed advantages of a jet? True, most business jets have no trouble cruising at speeds better than 300 knots. Most smaller turboprops traditionally top out between 200 and 260 knots. But turboprop manufacturers are addressing this challenge by — what else? — upping engine power.

Power to spare

A prime example is Beechcraft's King Air C90GT, with its new 550-shp (shaft horsepower) Pratt & Whitney PT6A-135A engines. Although this power rating is the same used in previous C90s, the big difference with the GT is that its engines have a power reserve of sorts. Its PT6As are capable of putting out as much as 750 shp. By flat-rating them to 550 shp, the engines are in effect loafing at takeoff. But they can keep on putting out those 550 horsepower right up to 20,000 feet. The result is a maximum cruise speed of 272 knots. That beats its predecessor, the C90B, by 26 KTAS. The C90B's PT6A-21 engines (which top out at 550 shp, and are not flat-rated) begin losing maximum power the moment they climb away from the runway.

The power boost also cuts times-to-climb by almost half, compared with the C90B. The GT will go to its maximum operating altitude of 30,000 feet in 24.5 minutes; the C90B takes 46 minutes.

The C90GT has two other big improvements. The airplane's four-blade propellers have been optimized for cabin noise reduction by limiting them to 1,900 rpm. (Earlier C90 propellers turned as high as 2,200 rpm.) Further noise reduction is achieved by installing 26 dynamic vibration absorbers in the fuselage, all electronically tuned so as to cancel out propeller noise.

The propeller limitation caused challenges during the airplane's development. The slower-turning propellers meant slower takeoff acceleration, and longer takeoff distances. The answer here was to authorize takeoffs using the approach flaps setting, which cuts standard-day takeoff runs to 2,392 feet. Without approach flaps, takeoff distances would be 2,986 feet, a Beechcraft spokesman said. Pilots have the choice of doing either flaps-up or flaps-approach takeoffs.

Then there was the increased maximum torque (1,520 feet/pound versus the C90B's 1,315 foot/pound) exerted on the propeller blades. To accommodate the higher forces, the GT's propellers were shot-peened for greater strength. Shot-peening is a process that blasts metal surfaces with shot, which relieves tensile stresses and hardens the metal.

Climbout King

King Air cockpits are well designed, and the C90GT's is no exception. There's something about the look, feel, and arrangement of the controls, levers, gauges, and switches that inspires confidence and promotes familiarity. Like the rest of the airplane, the cockpit gives the impression of substance and strength. Together with proper training (a week-long pilot initial training course at FlightSafety International is included in the airplane's $2.95 million price) this makes it easy to transition to the left seat of a King Air.

SPEC SHEET

From the cockpit

Engine starts and pretakeoff checks are fairly straightforward, and include checks of the airplane's autofeather and rudder-boost systems. Both systems are standard equipment, but engine fire-detection and extinguishing systems are options. To test the auto-feather system you increase power on both engines, push the autofeather test switch, and then retard power on one engine and then the other. As a power lever is retarded below approximately 260 foot/pounds, the associated propeller will start to feather. To test the rudder boost — a great system that automatically applies force to the "good engine's" rudder pedal in case of a power loss — you set the power levers to high power settings, then push one lever farther forward. When the system detects an asymmetry in bleed-air output, you'll see rudder-pedal movement as the system reacts.

After putting the flaps to the Approach preselect setting, Beechcraft demonstration pilot Casey Davis and I taxied into position for takeoff at Beech Field, located right next to the Hawker Beechcraft Corp. offices in Wichita. Up came the power levers to the maximum torque values, down the runway we went, and soon we were climbing away at 150 knots and 1,800 fpm. The airplane was about 300 pounds shy of its maximum takeoff weight of 10,100 pounds.

Apart from using flaps for takeoff, there is very little procedural difference between flying a C90GT and any other recent-model C90. There's a new VMC for the GT — 85 knots, which is 5 knots faster than in previous models — and new markings on the engine gauges that reflect the new engines' performance limits. And that's about it for new cockpit features.

It's in climb and cruise that you see the advantages of the new PT6s. Under standard conditions, climb rates at takeoff are 700 fpm better than in earlier C90s, and the GT will keep on climbing at a healthy rate. Passing through 17,000 feet on our way to 27,000 feet, the vertical speed indicator showed a 1,900-fpm climb. At 21,000 feet, we were still climbing at a respectable 1,600 fpm. More power at higher altitudes is what flat-rating is all about.

Another advantage is the engines' wider operating limits. During climbs, most turboprop engines begin to "temp out" (reach their maximum interturbine temperatures, or ITTs) around 14,000 feet or so — depending on outside temperatures.

This means that pilots must reduce power by pulling back on the power levers to reduce both torque and ITTs. Obviously, this curtails climb performance. But with the GT the engines aren't working at their full, rated power, so you can keep the power levers way up during long climbs — and the ITTs will stay within limits. A bigger oil cooler also helps keep temperatures under control.

As for torque limits, de-rating also provides ham-fisted pilots margins of error. Should you advance the power levers too much and exceed the engines' torque limits, you have a full seven minutes to pull the levers back, save face, and spare the engines damage. That's because the engine components were designed to put out much more power than is actually used in the C90GT installation. With the C90B engines, you have just 20 seconds to correct over-torques.

GT cruising

We reached our cruise altitude of 27,000 feet in 17 minutes, 30 seconds — not bad, but we'd have arrived there in just 11 minutes had it not been for the ATC-induced step climbs. At maximum cruise power we saw an indicated airspeed of 173 knots — just below the V _MO "barber pole" marker on the airspeed indicator. True airspeed with our minus 28 Celsius outside air temperature (international standard atmosphere plus 8 degrees) worked out to be 265 knots.

Our ITTs were at 760 degrees Celsius — well below the 805-degree redline. Were we in a C90B, Davis said, we'd break the ITT redline at our power setting. Our fuel flows were 240 pounds per hour (pph) per side, for a total of 72 gph. Davis said to count on 600 pph (90 gph) for the first hour of flight, then 500 pph (75 gph) for each subsequent hour. With four passengers, Beechcraft says, the airplane will fly 831 nm and have NBAA IFR fuel reserves to fly to an alternate airport 100 nm away from the first intended destination.

Davis said that our fuel burn at 27,000 feet was about the same as would be expected for a C90B flying at 16,000 to 20,000 feet — but the 90B would be some 20 knots slower. The upshot: The C90GT is optimized for flight at higher altitudes. For the same fuel burn as a C90B, it flies higher and faster. Its best speeds are achieved at 20,000 feet; the C90B tops out at 15,000 feet.

During descents, you have to watch the GT's barber pole and be ready to reduce power. Unlike the C90B, it is possible to overspeed in normal, power-on descents. Once in the pattern, however, the GT behaves like any other King Air. Its controls are a tad heavy, but personally I think this enhances the airplane's naturally great handling characteristics by discouraging overcontrolling.

We shot a few different types of visual landings, and for flying an ILS the setup goes as follows: Select approach flaps below 184 knots, gear down upon intercepting the glideslope, reduce power gradually to 400 to 550 foot-pounds per side (depending on the airplane's weight), and fly to short final at 120 KIAS. Then you can go to full flaps, pull power back slightly, and wait for 150 feet agl or so. At that point, begin pulling the power levers all the way back to their flight idle stops. If you time it right, the levers will hit the flight idle gates at touchdown, where airspeed would work out to be 90 knots or so, depending on wind conditions. After that, pull up and back on the power levers to engage reverse thrust, and apply brakes to slow the airplane to a taxi speed.

The ageless favorite

Cognoscenti may call the King Air a dated design, but its appeal is undeniable. The airplane's engineers have simply gotten the design right, right from the start. The 90-series King Airs have always been major hits in the marketplace, with a 43-year production run and more than 2,500 total sales. Since its introduction in 2005, 85 C90GTs had been delivered as of this writing.

The only thing truly dated about the GT is its 1980s-era Collins Pro Line 2 avionics, which, almost certainly, will soon be replaced with a more modern, large-screen suite. In the meantime, the C90GT will continue to draw customers who want the handling, cabin, and midaltitude performance that all King Airs offer, the service network that maintains them, and the easy transition that awaits pilots moving up or down to a C90 cockpit.

E-mail the author at [email protected].