Plane & Pilot
Tuesday, December 25, 2012

Transition To A Turboprop

MidWay between Piston Singles and Jets

If you're planning to own a turboprop, it's always a good idea to get professional instruction. Training will likely be insurance mandated and will include initial and recurrent simulator training, as well as type-specific in-aircraft training along with mentor time.
In flight training, and as we move from one piston airplane to another, we memorize certain airspeeds (or, at least, learn how to find them on the airspeed indicator): stall (clean and with flaps), best glide, never exceed, etc. In all airplanes, V-speeds are weight and temperature dependent, but in bigger airplanes such as turboprops, the variation in weight is enough to matter so that values are often computed before each flight. The one exception to this is Vne, which we'll get to later.

With GPS pretty much standard in these airplanes, the route can sometimes be direct from the departure airport (or a nearby navigational aid) to the first fix on an arrival procedure. Altitude is usually selected by comparing winds at several altitudes above FL 200. Any lower, and the turboprop isn't very efficient. Turboprops typically go as high as possible for the best economy. With climb rates of nearly 1,000 fpm at FL 270, most turboprop singles will have no trouble "popping up" to an altitude above FL 200 on all but the shortest flights.

A two-pilot cabin will be a big adjustment—and potentially for the pilot you're flying with. This isn't like flying as a student with an instructor—for one thing, you'll start in the seat on the right, rather than the left, and the captain's job is to complete the mission as efficiently as possible, rather than just to prevent a student under instruction from doing something terminally dumb. You'll probably start out observing the pilot and helping with radio work and charts. If that works out well and the pilot is impressed with your diligence (you've actually read most of the AFM, asked intelligent questions, participated in the preflight and flight planning, and didn't make any major mistakes with the radio) you may be invited to do some of the flying. Take that opportunity when and if it's offered. And, you might want to look up some references on "crew resource management."

Let's Go Flying!
Probably the biggest surprise I had initially as a turboprop copilot came at engine start. Up to that time, the pilot—a CFII who taught me most of what I know about instrument flying—had been a stickler for detailed checklists, someone who never did anything in a rush: but not now. Turboprop pilots use a combination of "flow" (a memorized series of steps that move smoothly from one part of the flight deck to the next) and a much more limited set of checklist items to get the job done as efficiently as possible. You don't want to waste time on the ground, because even at idle, a turboprop engine might be drinking well over a gallon of Jet A every two minutes. Expect some checks to be completed while taxiing, with the goal of being ready for takeoff when you reach the runway threshold. If you've studied the AFM enough to help, you can back the pilot up by reading checklist items to confirm nothing was missed during the flow checks.

It's important to know how to operate the quick-donning oxygen mask. At FL 180, time of useful consciousness is 20 to 30 minutes; at FL 220, it's five to 10 minutes. (Above FL 400, it's a matter of seconds.)
While taxiing, you'll probably see (and later, have the opportunity to do) one of the coolest things about flying a turboprop: reverse thrust. It's done using the Power Control Lever (PCL), which most of the time works like the throttle on a piston airplane—but pull it past idle (usually after operating some sort of protective guard, much like putting a car transmission into reverse), and the prop pitch will reverse, slowing you down. The sound is impressive. It's used on the ground (never in the air) to save wear on the brakes to shorten your ground run.

The next coolest thing on a turboprop flight deck is the Flight Director— although it took me a while to understand why. A function of the autopilot, the flight director makes a visual presentation with one or more "command bars" on the altitude and direction indicator (ADI) in older round-gauge airplanes, or the primary flight display (PFD) on newer glass panels. Basically, the autopilot uses the command bar to show you what it thinks you should be doing, and you function as the servo, translating that command into action with the aircraft yoke. Why not just engage the autopilot—or leave it turned off and hand-fly (without command bars) in climb? By following the flight director, you'll learn how best to control the airplane—follow the command bars, and you'll find yourself controlling the airplane much more smoothly and precisely than you otherwise would. That pays off when you need to hand-fly.

The pilot will probably set the cruise altitude (or an intermediate altitude as instructed by ATC) and arm the autopilot for altitude capture before you leave the ground—and there's one more thing to set: the target altitude for the cabin. That's a function of the cabin pressurization system, usually driven by bleed air from the gas generator section of the engine. This is yet another topic I haven't space to cover in detail; suffice it to say that in most modern turboprops, it's necessary only to set the altitude climbing (or descending) to. But it's really important to do that—if you don't, the results can be embarrassing and potentially dangerous.

Labels: Turboprops


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