Continuing Ed

Perusing The POH

The pilot's operating handbook (POH) for my airplane is thin - they all were 25 years ago - but I still manage to learn something new each time I read it. Often, it's not easy to spend quality time with the POH because it's kept in the airplane. FBOs understandably are reluctant to let renters borrow POHs to bone up. It's risky to let the operating manual get separated from its airplane. I feel the same way about my airplane's POH. It's not a document required to be in the airplane, but if I leave it at home I don't have a vital reference in the airplane.

A POH is not required for a light aircraft (one that weighs under 6,000 pounds) manufactured before March 1, 1979. The FAA says an explanation of the airplane's operating limitations must be present in the airplane in some fashion, either on placards, markings, or in a manual. This requirement usually is satisfied by posting placards in the cockpit and baggage compartment.

Those of us who fly airplanes at least two decades old use a POH or similar unofficial but highly practical guide. The cover of mine says it's an "Owner's Manual." It has a section on operating limitations, but a disclaimer explains that if anything in the section "contradicts the FAA-approved markings and placards, it is to be disregarded."

(You can buy a POH for the make and model airplane you normally fly. Essco Inc. in Akron, Ohio, sells copies of POH, service, and parts manuals for a wide variety of aircraft, engines, and avionics. Call 330/644-7724 or fax 330/644-0886.)

Light aircraft manufactured after March 1, 1979 must carry an FAA-approved Airplane Flight Manual (AFM). An AFM is issued for a specific airplane, and it's not valid for any other, even if it's the same make and model.

How do you know whether your airplane's manual is an AFM or a POH? Look at the opening page. If it's an AFM it will say so, and the airplane's N-number or serial number is posted, along with the instruction that the AFM must be carried in the airplane at all times. Even if it's not an AFM, the POH may contain the official weight and balance papers and operating limitations for any optional equipment such as avionics or tip tanks. That information must be aboard the airplane at all times.

The last time I paged through my manual I made a list of items that I found interesting for one reason or another. For example, some things hadn't stuck in my memory, probably because I don't need the information except in rare circumstances. In other cases I discovered I'd developed a few bad habits - bad because my technique didn't precisely match that recommended in the handbook.

For example, my manual explains that the navigation light circuit breaker also controls the radio transmitter relay. There's no indication of this on my airplane's modest circuit breaker panel. If the breaker pops, the radios go dead whether the nav lights are on or not. If I didn't know the breaker was tied into the radio relay, I could get mighty confused.

Another interesting fact I gleaned from my review was that the flaps retract from their maximum 40-degree extension to 20 degrees in just two seconds. That's important because 40 degrees is the recommended setting for a short-field landing, and 20 degrees is the initial go-around flap setting.

Normally I fly a final approach with 30 degrees of flaps. I don't often practice go-arounds from a full-flap approach, so the flaps' quick partial-retraction had faded from my memory. I went to the airport and flew a few circuits to check it out, and found it actually takes three seconds to go from 40 degrees to 20 degrees. But I'm not complaining.

The handbook also advises pilots to turn the Fuel Selector switch to the Right or Left Tank position when the airplane is parked or being fueled. If the selector is in the Both position the fuel could crossfeed from one tank to another through the interconnected vent line. Selecting Right or Left Tank closes the vent line to the opposite tank, and isolates the fuel.

Why is this important? If the airplane is parked on a slight slope and the selector is in the Both position - easy to do because Both is the required takeoff and landing position - fuel could flow from the high-side tank to the low side, out the vent tube, and onto the ground. If the airplane is refueled with the selector in the Both position, some gas from a just-filled tank could siphon over into the empty tank before that tank is filled. The result is less-than-full tanks which, as they say, could ruin your whole day.

I knew all of that, but apparently not well enough because I hadn't made a habit of automatically switching to Right or Left Tank position before shutting the engine down.

My list is specific to my airplane, but I think the lesson is universal. You can't always remember everything about the airplane you fly. This is especially true if you fly only occasionally, or fly a variety of aircraft. There's simply too much to know. A periodic review of the POH should serve to dust off those seldom-used items of information, as well as restore the sheen to the things you thought you knew so well.