A Faster King Air

Since 1981, when the B200 series replaced the original King Air 200 in production, the Pratt & Whitney PT6 turboprop engines have been flat rated at 850 shaft horsepower (SHP). The new engines on the B200GT raise that flat rating to a much higher level to deliver the increased speed and climb rates.

As you probably know, turbine engines have a number of operating limitations including rpm, pressure and internal temperature. Each limitation is critical for safe engine operation and long engine life, but in a free turbine engine like a PT6 it is temperature that caps power output. Because the internal temperature of the hot gases flowing over the turbine sets the maximum power output of the engine, it is said to have a certain "thermodynamic rating," meaning that it is capable of delivering that much power at its maximum inter-turbine temperature (ITT).

However, other parts of the engine -- particularly the gearbox that reduces turbine rpm to a value usable by a propeller -- often have a maximum rating lower than the thermodynamic potential of the engine. Limiting power to the propeller to match the capability of the gearbox or to the ability of the airplane to use the power is what is meant by flat-rating an engine. In other words, the full potential of the engine at low altitudes is restrained to suit the gearbox and airframe, but that reserve of power becomes available at higher altitudes for faster climb and cruise.

The venerable PT6 turboprop engine is divided into two main sections, one to generate the hot high-pressure gas stream and another that captures the energy in that gas to turn the propeller. The power producing part of the engine is not coupled directly to the propeller, and that is why it is called a "free turbine" design.

The way a PT6 operates is that air is drawn into the rear of the engine and compressed through multiple stages as the air flows forward. Beyond the compressor is the combustion section where fuel is sprayed into the compressed air and ignited. The rapidly expanding gas caused by the fire surges forward over turbines that are connected to the compressor sections so the whole process of compression, combustion and hot gas generation can be maintained.

The hot exhaust coming out of the gas generator section of a PT6 is analogous to the exhaust blast of a jet engine. But instead of using the exhaust stream to propel the airplane, the gases are forced over a separate turbine in the front of the PT6 engine. That power turbine is connected to the gearbox that reduces the turbine speed down to propeller rpm, and the gases then exit the exhaust stacks at the front of the engine. Because there is no mechanical link between the two sections of the engine a PT6 can idle with its propeller turning very slowly in the feathered position, or the prop can even be braked to a stop while the gas producing section of the engine continues to operate.

The King Air 200 really doesn't need more than the 850 shp that has been delivered to its propellers since the very first model, but it can use as much of that power as possible all the way up to its ceiling of 35,000 feet. The PT6A-42 engine in the previous model of the 200 can deliver maximum cruise power up to altitudes in the high teens, depending on air temperature, but above that, climb rate and cruise speed peak and then begin to slow. The engine in the new B200GT produces maximum power into the high 20s where cruise speed can be 20 or more knots faster and climb rates several hundred feet per minute higher.

To get this improvement at high altitude Pratt took the gas generator part of the PT6A-60A engine that powers the bigger King Air 350 with 1,050 shp rating and mated it to the gearbox section of the Dash 42 engine in the previous model of the 200. The new engine, dubbed a PT6A-52, is still limited, or flat rated, to 850 shp at the propeller, but the engine has the thermodynamic ability to produce well over 1,000 shp.

The reason you need to start with more power potential at takeoff than you can use is that as the air thins at altitude, power drops off. The compressor section of a turbine engine has a finite ability to compress air to the necessary value. With the air becoming less dense as you climb -- the atmosphere loses half of its density by 18,000 feet -- the compressor simply can't deliver as much air by weight to the combustion section. And the air coming out of the compressor is hotter and thus it burns hotter, so the engine temperature limits are reached with less punch from the hot gases out of the combustor. The result is power drops off with altitude.

The bottom line is that the new Dash 52 engine in the B200GT leaves the runway with loads of power potential in reserve, and that potential is converted to airspeed and climb up high. Because both sections of the new engine have long track records in the King Air fleet they can enter service with a full 3,600-hour overhaul interval while an all-new engine would need to demonstrate its reliability over time. The Dash 52 engine was initially reserved for new production, but in the past few weeks Blackhawk has received an STC to install the engine on existing King Air 200s with no requirement for other airframe modifications. A flat-rated Dash 61 engine is also available for retrofit as part of a Raisbeck modification package.

Because the big changes in the B200GT are under the cowling it's very difficult to identify the airplane compared to previous B200 models. The only external clue -- other than the 200GT graphics -- for real King Air experts is the shape of the exhaust stacks, which are now virtually identical to those on the bigger model 350. But inside the B200GT are several important improvements borrowed from the 350, including newly styled seats with more comfort and adjustments; cabin sidewalls with integrated armrests that make the cabin functionally wider; stronger and more durable tables between the seats; and tuned dynamic vibration absorbers and better sound insulation system.

The cockpit houses a fully integrated Collins Pro Line 21 avionics system with three big flat-panel displays, a flight management system (FMS), very capable autopilot with its control panel up high in the glareshield instead of down in the pedestal, and a file server system that contains Jeppesen electronic approach charts, weather data and other information. The Pro Line 21 was in the B200, but traffic and terrain warning systems are now standard. And the airplane is fully compliant with reduced vertical separation minimum (RVSM) requirements so it can fly above 28,000 feet in U.S. airspace.

To see what the new engines do for the B200GT, we filled the main tanks with 2,300 pounds of fuel -- 3,645 pounds is max -- and with two onboard had a takeoff weight of 11,500 pounds, compared to a maximum certified takeoff weight of 12,500 pounds. This B200GT had been newly delivered to a customer and was typically equipped with an empty operating weight of 8,532 pounds. The change to the "GT" model added about 50 pounds to the typical empty weight, leaving a maximum useful load of around 4,059 pounds to be divided between fuel and payload.

Because the maximum takeoff weight on the B200GT is not over 12,500 pounds there are no certification requirements for minimum takeoff performance profile should one engine fail at the worst possible moment. However, all of the information necessary to calculate whether a takeoff and climb can continue safely after an engine failure is in the operating manual and only a fool would ignore it. The airplane has automatic propeller feathering if an engine fails, and there is a rudder boost system that steps on the proper rudder to help keep the airplane flying straight, so pilot workload after a sudden engine failure is minimal. If a pilot considers airport elevation, air temperature, obstacles and takeoff weight, there is no reason the B200GT can't safely complete a takeoff and climb even if the worst happens at the least favorable point, just as jets and larger airplanes are required to do.

Flying the B200GT is no different than any earlier model of the 200 line. You advance the throttles only until the torque -- a measure of horsepower to the propeller -- limits are reached and the airplane flies off with very little back pressure to rotate. But, for some reason that makes no technical sense, the B200GT seems more spirited on takeoff and initial climb. There is the same 850 shp reaching the props, but the airplane has more get up and go. And King Air pilots with tons more time in the airplane than I have agree with this impression. Who knows why, but it is a good thing.

I saw climb rates ranging from 1,500 to 2,000 fpm with an indicated airspeed of 160 knots or so, and that value held through 23,000 feet. Even out of 27,000 feet to our clearance of 28,000 feet the B200GT was going up at more than 1,000 fpm despite outside air temperatures warmer than standard. We couldn't climb above FL 280 because the airplane operator had not yet applied for and received the individual certification necessary to fly in RVSM airspace that begins above that level.

With the propellers set at a low 1700 rpm and engine temperature set at maximum for high speed cruise, the B200GT settled down at a true airspeed of 301 to 305 knots with total fuel burn of 640 to 660 pounds per hour. That was 20 or more knots faster than the previous model and just what the book predicted in terms of performance. We could have held that airspeed at a higher altitude with RVSM approval and cut the fuel flow. Because the new engines burn more fuel to make that extra power, maximum range in the B200GT is about 200 nm less when flown at max cruise. However, if you slow down to the 280 or so knots that is top cruise of the earlier model, range comes out about the same.

The Super King Air is by no means a fingertip airplane to fly, but control forces are reassuringly firm and consistent. The airplane is extremely stable in pitch, so stable in fact that every little change in airspeed requires a slight change in pitch trim to keep control forces neutral. The definition of stability is an airplane that just doesn't want to deviate from its trimmed airspeed, and this one meets that standard. Every time I fly a 200 I at first think I'm doing something wrong because I am always trimming to stay exactly on altitude, but then I engage the autopilot and watch the trim wheel and see that it does the same thing -- only it is better at nailing the target altitude 100 percent of the time than I will ever be.

The B200GT cockpit has new crew seats adopted from the 350, and they are very comfortable and adjustable to suit individual desires. The cockpit is roomier than those of most light business jets with loads of headroom. And the cockpit insulation is superior with no problem of your outboard arm getting cold against the sidewall, and that is an issue in some jets and turboprops.

But it is the cabin much more than the cockpit that has sold more than 2,000 Super King Air 200s, and in the B200GT the cabin is an even better place in its furnishings and sound level. The private potty in the rear with its wood sliding doors and the in-cabin baggage in the rear have always been crucial to passenger comfort. The new seats are a nice improvement, and the "square oval" shape of the cabin maximizes head and shoulder room. The "tuning fork" vibration dampers also help control noise from the propellers. The dampers are tuned to the vibration produced at 1700 rpm and are firmly bolted to the fuselage structure at key points around the cabin. When the noise energy traveling through the metal skin, frames and stringers reaches the damper, much of it is converted soundlessly into vibration by the tuning fork. The dampers require no maintenance, add only a little weight and really do work. The best seats are away from the propellers, but even in the cockpit sound levels are good.

The environmental system also now has the important features of the 350 including automatic temperature control for the cockpit separate from the cabin. The air conditioning system is now more efficient and environmentally friendly, and the B200GT has a 20,500 BTU electric heating system that supplements normal bleed air heat for quick cabin heating on the ground and comfort on long flights on dark, cold nights.

The airplane I flew was fitted with the Raisbeck wing locker modification where lifting hatch-type doors are installed on the aft part of the nacelles, allowing baggage to be carried in the otherwise empty space. The nacelle lockers are great for bulky items such as snow skis or fishing gear, but they have been recently redesigned, increasing the thickness of the locker at the trailing edge so larger luggage fits in as well.

The Super King Air is fully approved for flight in icing conditions with pneumatic boots protecting the leading edges, while electrical heating elements keep ice off the propellers and windshields. Inertial ice separator doors swoosh ice particles out of the rear of the nacelle instead of into the engines, and hot exhaust is routed through the engine air inlet lips to keep them ice free at all times. Main wheel brake heat is also available to keep ice from forming on the brakes after takeoff from a wet or slushy runway. With an excellent Collins weather radar in the nose, XM Weather piped into the Pro Line 21 displays and a super strong airframe that has no life or cycle limits, the Super King Air is as close to an "all weather airplane" as you can get. And if the runway at your destination is slippery, full prop reverse can get you stopped when wheel brakes can't do the job alone.

There was one more pleasant surprise waiting when I landed the B200GT. In earlier models you have to be careful not to pull power all the way to idle in the landing flare because the propellers will go to flat pitch, generating enormous drag, thus ensuring a very firm landing unless you are only inches above the pavement when you chop the power. Again, for some reason nobody can explain, the new engines don't do that, even though they have the same propeller gearbox as the earlier version. Instead of feeling for both neutral thrust and the pavement at the same time as before, you can gradually reduce the throttles to idle in the flare and the B200GT won't fall out from under you.

Beech and Pratt have also taken most of the guesswork out of what it will cost to fly a new B200GT with the Support PLUS+ program that can be tailored to cover maintenance and engine renewal costs by the hour. For around $340 per flight hour you can prepay for maintenance parts and labor costs, and engine overhaul averaged over five years. That leaves fuel as the big variable in operating expenses, but at $5 per gallon for jet-A, Beech estimates the overall direct hourly costs of flying the B200GT at $987.86, or around $3.45 per nautical mile. And the Super King Air has always enjoyed excellent value retention in the used market, so much of the $5.238 million new price tag will be returned a few years down the road.

Can there be demand for another 2,000 Super King Airs? Who knows. But the kind of improvements Beech has made in the B200GT are exactly what has made the airplane so popular for 35 years.