Turbine Pilot: King Air C90GTI: More Power, More Panel

Spec Sheet

Routings: Flying High

By Doug Turner

All year long, mountains provide passengers with uninterrupted scenery. But it’s the pilot’s view out the front windshield that is unparalleled. Equally impressive are the challenges and rewards to pilots operating at high-elevation airports.

Last winter, I flew into the Eagle County Regional Airport in Colorado, which serves the Vail and Beaver Creek ski areas. The weather was ski-country perfect with overcast skies at about 2,500 feet with five miles visibility in light snow. For us flatlanders, that’s pretty good VFR weather, but for Eagle, it is pretty close to minimums. I was flying a Twin Commander 690 turboprop, a great airplane for mountain flying.

Arriving from the east we receive a series of step-downs from flight level 280, first to FL240, then to FL200. ATC had cleared us direct to the Kremmling VORTAC. Then, when 20 miles out, we were cleared direct to VOAXA, and told to cross VOAXA at or above 14,000 feet, then cleared for the LDA/DME Runway 25 approach. If you look at the approach plate, you will see lots of brown in varying shades. That means lots of rocks, which will make one sit up and pay close attention!

LDA stands for localizer-type directional aid. It is similar to a regular localizer, but it is not aligned with the runway centerline. This LDA has a glideslope, and the approach chart shows a 3.8-degree slope. The first thing I do is slow down. This arrival will require a couple of turns, steep descents, and, like all approaches in instrument meteorological conditions, concentration. I know there will be icing in the descent, so all the “heat” switches come on: nacelle, generator inlet, propeller, pitot, rudder, and high windshield heat. In times like this, turbine airplanes really shine because their engines provide plenty of welcome power and electricity. Entering the clouds, I select continuous ignition and coach myself to include visual observation of the leading-edge boots frequently.

The miles to VOAXA decrease on the GPS as the altimeter unwinds. Level at 14,000 for the first three miles, then two, one, and the autopilot dutifully turns us southbound and we join the Kremmling 184 radial. The GPS sequences to AQULA, six miles ahead.

Now, it’s down to 12,900 feet, a gentle but determined descent and level-off. Up to now, the autopilot has been flying the lateral navigation via the GPS, while I fly the vertical with the autopilot pitch wheel. We make a smooth team, and the autopilot has given me space and time to carefully monitor our progress and set up for the approach.

Level at 12,900, I engage the altitude hold, and the localizer comes alive. We are just below the glideslope, and I engage the approach mode of the autopilot. AQULA arrives, and we turn inbound, the DME dutifully reading 17.2 miles. It all checks. Down with the gear, select approach flaps, and I look outside at the wings. I energize the boots and pop off a layer of crusty rime. We’re coming down.

The autopilot balloons slightly, then pushes over the nose, creating a hefty descent rate. As we go slightly through the glideslope, I tense. When you are in the mountains and in the soup, and you go below glideslope—even a little—you had better take notice, and I do. Before I can complain, the autopilot shows it shares my concern, and it faithfully joins the glideslope from a half dot below. We are passing WEHAL at 12,200 and everything checks out fine. I sit up straight, like Momma told me to.

The windshield wiper, although motionless, shows a light crust of ice, reminding me to look at the wings again. They show only a light crust, and I elect to wait before energizing the boots again. The cabin is down. I extend and turn on the landing lights. We are lit up like a 747.

Landing checklist is complete, except for flaps. Here comes AIGLE, and we’re now in and out of the clouds. The rocks left and right look eerie, so I quit looking and check on our progress. I pop the boots, and away goes a thin layer of ice. Descending through 10,000 feet and out of the bottom of the clouds, we arrive at WASHI. I know that this is actually the final approach fix, but by choice I have been flying the aircraft as though it was all a final approach, as far back as AQULA. At 9,000 feet and 7.4 DME the runway comes into view. The airplane is not aligned with the runway, and I remind myself, that’s normal on an LDA approach.

Visual now, I incrementally work the flaps down to full and the airplane slows without departing the glideslope. All in trim now, I touch the autopilot disconnect switch and gently maneuver the airplane onto a two-mile final, then slow to 120 knots across the fence. Intentionally, I carry some extra speed since I don’t know how much ice remains on the unprotected surfaces of the airplane. It’s a long runway, and I use reverse sparingly. We’re down. Taxi in, clean up the airplane, and shut down. It’s another perfect day in ski country.

Doug Turner is an aviation consultant. He flies a Beechcraft Baron B-55.

Turbine Talk: Specific Range

By Barry Schiff

Listen to pilots discussing jet operations and you inevitably will hear them mentioning specific fuel consumption (SFC) and specific range.

Simply stated, the SFC of a turbofan engine is the amount of fuel (in pounds) required to produce a pound of thrust at a given thrust setting under a given set of conditions. It is a measure of engine efficiency. (The SFC of a reciprocating engine is pounds of fuel per brake horsepower being developed.)

Specific range, however, should be of great interest to pilots. It expresses how many air miles an airplane can fly while burning a pound of fuel. It also can be expressed in nautical air miles per 100 pounds of fuel. Specific range is a measure of the efficiency of the airplane.

An easy way to determine specific range is to divide true airspeed during cruise by fuel flow. For example, during long-range cruise in a Cessna Citation CJ3 with a true airspeed of 351 knots at FL450 and a fuel flow of 618 pph, specific range is 0.568 nm per pound of fuel (or 56.8 nm per 100 pounds).

During high-speed cruise at 415 knots at FL350 and a fuel flow of 1,198 pph, specific range is reduced to 0.346 nm per pound of fuel (or 34.6 nm per 100 pounds). This reflects a 39 percent reduction in cruise range when operating at high speed. To include the effect of wind, divide groundspeed by fuel flow to determine specific range in nautical ground miles per pound of fuel.

• Routings: Flying High
• Turbine Talk: Specific Range

All the attention given to the burgeoning light and very light business jet market obscures a significant fact: Turboprops are alive and well. Just look at Hawker Beechcraft’s King Air line of turboprop twins. King Airs have dominated the turboprop market since their introduction in 1964, racking up more than 7,000 sales and 50 million flight hours. The 2007 delivery numbers from the General Aviation Manufacturers Association (GAMA) list 157 King Air sales. Compare that to the numbers for the only other turboprop twin being manufactured today—Piaggio Aero’s P.180 Avanti, with 21 sales in 2007.

For many, the C90 King Airs (the so-called “baby” King Airs, even though their max takeoff weights hover at around 10,000 pounds) retain their appeal as step-up airplanes for those coming from top-of-the-line complex piston singles and twins, or as alternatives to turboprop singles and light jets. Boosting that appeal has been a priority over the past two years.

GT power

First came an engine upgrade. In 2006, Hawker Beechcraft (then under the ownership of Raytheon) replaced the C90B’s 550-shaft-horsepower Pratt & Whitney PT6A-21 engines with PT6A-135A powerplants. Thus was born the C90GT. The -135A engines are thermodynamically capable of 750 shp, but for the C90 application they’re derated to 550 shp—the airplane’s originally specified power rating. Why change engines if the power rating is the same? Because that extra thermodynamic horsepower means the engines are capable of producing the full 550 shp under high and hot conditions, and at higher altitudes. This is a result of the -135A’s higher ITT (interturbine temperature, as measured between two turbine wheels) redline of 805 degrees Celsius; the -21 engines have 695-degree ITT redlines. That extra 110 degrees of redline margin means more torque and power at altitude, and under other conditions that would have limited the smaller engine. Simply put, the -135As loaf in situations where the -21s “temp out.”

This all boils down to faster times to climb than C90 models prior to the GTs, better takeoff performance, and faster cruise speeds at higher altitudes. Hawker Beechcraft says that the C90GT is 26 knots faster than plain-Jane C90Bs, coming in with max cruise speeds up to 272 knots at 20,000 feet or slightly higher. The C90B tops out at 247 knots at 16,000 feet. As for time to climb, the GTi can reach 30,000 feet in 25 minutes. A C90B takes a whopping 46 minutes to climb to that altitude.

During my demonstration flight with Hawker Beechcraft’s Trevor Blackmer and Brady Stewart, the C90GTi was still climbing at 1,300 fpm passing through 14,000 feet, and it took us just 16 minutes to reach FL240.

Pro Line glass

Last December, Hawker Beechcraft added Rockwell Collins’ Pro Line 21 avionics suite to the C90GT. This latest improvement is just as significant as the engine upgrade, in that it modernizes the panel, cleans it up, and offers plenty of workload-saving capabilities. The system includes three eight-by-10-inch liquid crystal displays; a glareshield-mounted autopilot/flight guidance mode control panel; a flight management system (FMS); and a dedicated radio-tuning unit (VHF radios can also be tuned via the center pedestal-mounted FMS).

The two primary flight displays (PFDs) show airspeed, altitude, and vertical velocity using the now-familiar vertical-tape display format and, using the FMS and flight guidance system, you can put V-speeds, altitude, airspeed, and navigation preselect information on the screens. The flight guidance panel is intuitive to operate, and its location under the glareshield promotes more heads-up time. Earlier King Airs had autopilot and flight guidance controls far aft on the center pedestal, which meant looking down each time an input was made.

Starting from the top of the MFD, you see first the engine indicating system (EIS) information, consisting of analog and digital formats for propeller torque and speed, and engine ITT, turbine speed, fuel flow, and oil temperature and pressure. Next on the screen is a list of flight plan waypoints, along with the time and distance to each. Also posted is fuel remaining in terms of both pounds and flight endurance.

A range of information can be presented on the lower segment of the MFD, including views of the flight planned route, traffic collision avoidance system targets from the ship’s L-3 SkyWatch; ground proximity information from the TAWS (terrain awareness and warning system); datalink weather from XM WX Satellite Weather; airborne weather radar imagery from the airplane’s own Collins WXR-800 weather radar; and electronic Jeppesen arrival, approach, airport, taxi, and departure charts. Victor and Jet airways can be called up on the MFD’s map displays, as can checklists. You scroll through checklists with a yoke-mounted pushbutton switch as you complete each item. Again, another design aimed at keeping the pilot heads-up, and not fumbling for printed checklists.

Flight insights

Like all King Airs, the C90GTi exudes a sense of substance. It’s a big, sturdy airplane that stands tall on the ramp and turns heads. Once up the airstair door, hang a left at the aft lavatory and make your way forward.

The first time in the cockpit you’re sure to be overwhelmed by the Pro Line 21, but anyone familiar with a King Air front office will certainly recognize the rest of the switchology. After all, most of the entire subpanel and center pedestal are unchanged from those in King Airs many years older. Those flying the Pro Line 21 say that it takes about 20 hours to become completely familiar with working its FMS (a second FMS is optional), programming the flight control system, and setting up the PFD views.

Although the C90GTi is a big airplane, its V speeds are similar to those of big singles. V ₁ (takeoff decision speed), for example, is between 83 and 86 knots. Similarly, V _Y (all-engine best rate of climb speed) is 101 knots.

As an example of the effects of the -135A’s flat-rating, with climb power set and passing through 14,000 feet, our ITTs were showing 718 degrees Celsius. ITT redline is 805 degrees. That extra 87 degrees means that you can safely add power (by advancing the power levers to obtain higher torque values) without causing any engine damage. Climbing through FL210, our torque was a hefty 1,300 foot/pounds, but our ITTs were at 776 degrees—still below redline. In a straight C90B, we would have had to cut back on torque (to about 900 foot/ pounds) to keep from busting that airplane’s 695-degree ITT redline.

At max cruise power at FL230, our numbers confirmed book promises. Our torques were 1,260 foot/pounds (redline is 1,520 foot/pounds), ITTs were a comfortable 760 degrees, and fuel flows were 270 pph (about 40 gph) per side. True airspeed was 269 knots—not bad, given the minus-16-degree Celsius free air temperature, which is 10 degrees C above standard. Compared to a typical light jet, we were flying some 70 to 80 knots slower, sure, but the C90GTi’s fuel flows are about 100 pph lower. On a typical trip of, say, less than 400 nm, the King Air comes in as the more fuel thrifty.

As for landings, all King Airs are pilot-friendly. Target V speeds for the GTi’s final approach segment (V _REF) run from 99 to 101 knots, depending on weight. Again, a familiar and easily memorized speed for those new to the type. Pull the power levers to flight idle at about 10 feet above the runway, hold the nose off, and the result is usually a graceful arrival. Reverse thrust can be used to substantially shorten the rollout.

In all, the C90GTi is a winner. With standard safety features such as auto-feather and rudder bias (to apply rudder pressure in case of an engine failure), the extra engine power, the Pro Lines, and a cabin that’s comfortable and spacious, this newest King Air maintains a strong tradition. So far, 35 C90GTis have been delivered, and in 2008 Hawker Beechcraft expects 90 more to go out the door. Add those to the 7,000 King Airs already in service and you can see that the market likes the brand.

E-mail the author at [email protected].