Insights

Take Time To Study The POH

My patience grows thin when I conduct a stage check with a student who does not know the airplane. My patience evaporates when I remind myself that if the student doesn't know the plane, neither does the flight instructor.

Flight instructors and students must find time to slow down and study the material that relates to what they are teaching or learning. I understand the instructor's problem, because at one time I was in the same situation - maintaining a heavy student load, taking night classes to complete my education, and worrying about moving onward and upward.

For an example, I'll use a Cessna 172 RG, a complex airplane that is widely used for commercial pilot training. If instructors and students would slow down and take time to carefully read the pilot's operating handbook, they would make some interesting discoveries.

How many fuel drains does the airplane have? Most individuals tell me three, but four is the answer. Like all older single-engine Cessnas, each tank has a drain under the wing; and there's a fuel strainer drain that, in most cases, is activated by a knob in the engine compartment next to the oil dipstick. On some 172 RGs, however, the fuel strainer drain is located on the lower left side of the engine cowl, similar to the fuel strainer drain found on Piper Cherokees. The fourth, hard-to-see fuel drain is located on the bottom of the fuselage under the fuel selector valve. It is depicted in the POH's fuel system schematic.

Do you pump the throttle before you engage the starter? With the Cessna 172 RG you should. I know that you were taught to never pump the throttle in most Cessnas until the engine is rotating because the fuel delivered by the carburetor's accelerator pump will fall out of the carburetor and down into the engine cowl where it becomes a fire hazard if the engine backfires. However, the 172 RG has a sidedraft carburetor, not the updraft carburetor that's common in fixed-gear airplanes. Fuel discharged by the accelerator pump falls into the air plenum beneath the carburetor, and for that reason the POH instructs you to pump the throttle a couple of times before you crank the engine. The engine starts quickly when you follow the manufacturer's advice.

Why does the 172 RG have a sidedraft carburetor? So that there's room for the nosewheel assembly to retract into the engine compartment.

Do you know the significance of the large rubber gasket that fits between the fuel cap and the wing, and of the small rubber disc at the bottom of the fuel cap?

The large gasket prevents fuel from being sucked out of the tank in flight because of the reduced pressure atop the wing, and it keeps water out of the tank when the airplane is on the ground sitting in the rain or being washed. The small rubber disc must be soft and pliable because it, too, prevents fuel from being sucked out of the tank through the fuel-cap vent in flight. Its main purpose, however, is to allow air into the fuel tank through the fuel cap vent if the fuel system's main fuel vent becomes plugged. If the fuel cap vent doesn't work when needed, a vacuum will occur in the tank as the engine uses fuel, and the fuel flow - and engine - will eventually stop.

What is the face of the propeller and what is the back? The face is the side that faces the engine cowling and meets the air when the propeller is rotating. The back is the side of the propeller that faces forward. Check the face of each blade for gouges just like you check the leading edges for nicks. The face takes a real beating from pebbles and other debris.

Do you check the gear-up warning horn before flying? To do this, press the green gear-down light when the master switch is turned on during the initial power-on cockpit check. What else should come on during this check? The low voltage light.

How do you configure the airplane for a short-field takeoff? If you position the flaps to 10 degrees, you may fail the stage check. The POH is very specific. Flaps up for short-field takeoffs and soft-field takeoffs if you are within 100 pounds of the maximum gross weight. If below that weight, 10 degrees of flaps are used for a soft-field takeoff.

How do you know your tires are in good shape? I am amazed at the number of pilots who preflight an airplane but never move it forward or backward in order to check the bottom of the tires. The airplane may be sitting on a bald spot.

Pilots and flight instructors must be inquisitive. Take time to carefully study the POH, including the system schematics. It may make the difference between an accident and a safe flight.

Ralph Butcher, a retired United Airlines captain, is the chief flight instructor at a California flight school. He has been flying for 43 years and has 25,000 hours in both fixed- and rotary-wing aircraft.