After administering about a dozen Twin Commander transition courses and twice as many currency courses in the last two years, I have concluded that the three most important things to consider when moving up from a piston aircraft to a turbine Twin Commander are:
I subscribe to the adage that “movement is life” and most of the time speed also equates to life, but too much speed can also work against you. Speed (a noun) is a way of measuring how quickly something is moving or being done.
The first speed consideration is the engines. Whether your new Twin Commander has the Dash 5 or the Dash 10 version of the TPE-331 engine, it probably turns faster (speed) and produces more horsepower than previous engines you have flown behind. One of the single most critical and necessary items in transition training is learning the proper care and feeding of these great Garrett (Honeywell now, but I’ll use the old-school name) engines.
The second speed consideration is airspeed control, which we achieve by applying some operational tips and tricks during all phases of flight. From takeoff to landing, instrument procedures or visual flying, speed control, and therefore time management, is a most important item to be considered when transitioning to a faster turbine Twin Commander. These great airplanes are known for their superior speed, aren’t they? So how do we best manage that greater speed? By first recognizing that faster is not always better.
The third speed consideration is about respecting and understanding the structural limitations of this airplane’s design as relates to airspeed. The very reason you are transitioning to a turbine airplane is probably related to wanting more speed. We all want faster, higher, farther, don’t we? The turbine Twin Commander is known as a speed demon, and an efficient one at that. Understanding the “why” as well as the “how” of staying within the structural limits of this great aircraft is a vital and necessary element of transition training to a turbine Twin Commander.
Let’s look at each of the three speed considerations in more detail.
SPEED 1: THE ENGINES
We start with the speed of the turbine section, which is approximately 41,340 rpm (this is not a typo). The front end of the engine (propeller) only turns at 1590 rpm at 100%. Hence, we have a reduction gearbox ratio of 26:1. That is, while your prop does one revolution, your turbine section just did 26 revolutions per minute. Much of the efficiency of this engine comes from very high rpm (and low torque) in the turbine section that is converted to low rpm (and high torque) and sent to the propeller though a big reduction gearbox.
Much has been said and written about starting a Garrett engine, and this is also where pilots used to Pratt turboprops must realize that the Garrett is an animal of a different design. Try not to understand a Garrett engine based on your knowledge of a Pratt. Do a memory dump and start fresh. Piston-engine pilots are easier to train on the Garrett engine than are Pratt pilots.
A tip about keeping the start normal: temperature is not the only thing you must monitor during a Garrett engine start; you must also monitor the speed, that is, the engine rpm and start time. It typically takes between 20-40 seconds to start a Garrett engine under normal circumstances and temperatures. Monitoring your rpm (speed) during this phase is almost as critical as monitoring temperature. Speed is life in this case—if your rpm ceases to continue to rise, you will more than likely get a hot start. Therefore, your first indication of a potential hot start is not temperature, but speed or rpm.
Do not rely on hearsay or so-called educated guesswork to operate the Garrett engines. This is not an engine to experiment with; you must know how to properly manage this much speed and horsepower. Only use approved training materials sanctioned by the engine or airframe manufacturer, and experienced and approved training instructors. In other words, slow down and take the time required to learn the engine.
SPEED 2: AIRSPEED CONTROL
One of the most appealing aspects of the turbine Twin Commander is its awesome speed. Often while administering a transition training course, I find myself spending considerable time giving the new Twin Commander pilot instruction on how not to use all this wonderful speed.
Take VFR pattern work, for example. We typically want to use maximum available horsepower for any takeoff. So, we execute a beautiful takeoff roll, liftoff and climbout, clean the airplane up, and turn downwind to practice our landings. Problem is, we never decreased our power setting and now we are indicating 180-200 kts. This is not a safe airspeed for pattern work. Decreasing your power setting by well over 50% of your takeoff power is a little counterintuitive to most piston-engine pilots, yet that is what you need to do. If, for example, you were indicating 600 hp per engine on takeoff, you would need to reduce to about 300 hp per side upon reaching a safe altitude and entering the traffic pattern.
Another example related to speed that seems to be unique to the turbine Twin Commander happens during the landing phase. An interesting aspect of flying the Twin Commander is that there seemingly is an absence of the sensation of speed. The sound and feel of the airplane is much the same at 80 knots as it is at 180 knots. When maneuvering at low altitude and low airspeed, it is very easy to allow the airplane to slow to a stalling speed without realizing you are doing so, or being way too fast and not realizing it. Consequently, the first few landings with a new Twin Commander pilot usually are either too fast or too slow. Most new pilots seem to want to err on what they consider the safe side of the equation, and end up doing the approach and the landing much too fast.
During an instrument approach procedure, speed control is critical. If you start too fast you will more than likely end up too fast. You could overshoot altitudes, bust minimums, and even pass up the airport (I have seen this done), or at least pass up a good portion of the airport (runway behind you) while on rollout. Teaching transition pilots how not to fly an instrument approach (meaning not too fast), is one of the areas we emphasize in transition training for Twin Commanders. Slow down so you can stay ahead of the airplane during an approach and landing.
SPEED 3: STRUCTURAL LIMITATIONS
Every turbine Twin Commander comes with a maximum turbulence-penetration speed. These speeds relate directly to the structural strength of the airframe design, with the empennage usually being the weakest link. Excessive speed is the quickest way to bend or break your new turbine Twin Commander airplane.
With most Twin Commander models there is a big 180-kt IAS placard on the windshield post, applicable to flying in light-to-moderate turbulence. This same placard directs you to fly no faster than Va (maneuvering speed) if encountering severe turbulence. Depending on your operating weight this can be 40 kts or more less than the 180-kt limit. Many transition pilots seem to be surprised these airspeeds are so low, considering how fast the Twin Commander can go. The lighter the airplane’s weight, the lower the Va speed. This also seems to be counterintuitive to some transition pilots, who think that the lighter the airplane the faster I can go, right? Wrong! The lighter you are, the slower you must go in any kind of turbulence to keep from bending your airplane.
This caution is especially true, and maybe much more so, in the 690A, B and C model Twin Commanders converted to Dash 10T engines. These airplanes still have all the same airspeed limitations as the original design, but now with a Dash 10T engine you have an aircraft that is capable of cruising at FL270 at or very near MMO. While not a concern in and of itself, if you do not slow the airplane down to published turbulence-penetration speeds in turbulence you could exceed the structural limits of the fuselage, empennage or wing, causing major damage, or worse. If you are already cruising close to max speed, or MMO, and you begin a descent without a reduction in engine power first, you will be over MMO is a few seconds. So, reduce power prior to nose-over for a descent.
To review, the three most important things about transitioning into a turbine Twin Commander are:
Speed 1: Know your engine and manage this great powerplant’s speed and horsepower. Slow down and learn the engine.
Speed 2: Faster is not always better. Slow down in the pattern and on an instrument approach. Speed control (usually means slower) is key to a successful flight. Slow down to stay ahead.
Speed 3: Respect the airframe design limitations, especially in turbulence and descents from altitude. Slow down to save the airplane and your day.
Most of all, enjoy your new turbine Twin Commander.
J.R. Bob Huskey has been flying for more than 40 years, has more than 10,000 total flight hours with 3500 hours in turbine Twin Commanders. He’s also worked full-time in aircraft maintenance for 15 years. Since 1998 he has been a professional pilot, and is currently flying a 695B/1000 Twin Commander. Since 2012 he has been administering insurance-approved transition and currency courses with larryyorkaviation.com.