Flight Instructors will always stress the Preflight - and for good reasons. All pilots should do a thorough preflight, although there are a few more cocky pilots who believe they can glance at the airplane, remove the chocks and cowl plugs and start 'er up. Doing a proper preflight is also a part of every student pilot's check ride. The Preflight is always the responsibility of the Pilot-in-command. Not so coincidentally, anything that goes wrong with the plane is usually his or her responsibility also.

A preflight can catch things that could easily kill you in flight or in an attempt to take flight. There have been quite a few NTSB reports dealing with cowl plugs, tools in the cowl, and other careless mistakes. Completing the preflight inspection can save lives.

After being a student pilot for a while, I got used to running through the preflight checklist. The point is to get proficient and efficient, but not careless. A basic checklist for a preflight on a small aircraft (a Cessna 172 in this example, but it works for most of it's kind) is as follows:

• Check your Required Documents:


• Airworthiness Certificate     - Means the aircraft was inspected not to fall apart
• Registration     - Just like a car
• Pilot Operating Handbook     - Tons of info on the plane, procedures, and specs.
• Weight and Balance     - Calculates how much weight the plane can carry and where it can be placed
• Set the Parking Brake   - To keep the plane from moving, possibly rolling over you.
• Check the Fire Extinguisher is Charged   - Fires happen.
• Record the time on the Hobbs and Tachometer  - To record length of flight.
• Remove the Control Wheel Lock   - So you can move the controls; make sure they move freely.
• Ensure Ignition Switch is at OFF   - If this is on, the magnetos can be hot. When you turn the prop, it could easily start and take your hands off... or more.
• Ensure Avionics Switch is OFF   - If everything is on when you flip on the master, you might blow a fuse
• Master Switch ON   - This turns on power to all electronics.
• Put Flaps at 10 - 30°   - When flaps are down you can check them easier.
• Avionics Power Switch ON
• Listen for Avionics Cooling Fan  - If the fan isn't on, your equipment will overheat in flight and fail.
• Avionics Power Switch OFF   - No need to keep them running.
• Check Low-Vacuum Light is ON   - Your plane shouldn't be making a vacuum yet, it's not moving.
• Check Fuel Quantity Indicators   - Not foolproof, but helps to double check everything. If they're showing full when your tanks are empty, that's a problem.
• Check Exterior Lighting (Anti-Collision lights, nav, etc.)   - You want these to work
• Master Switch OFF   - Keep the Hobbs meter from running during your check.
• Fuel Selector Value set to BOTH   - Evenly takes fuel from both tanks, this way.
• Static Pressure Alternate Source Value pushed OFF   - You don't need an alternate source, your primary should be good.
• Baggage Door LATCHED and LOCKED  - To keep your goodies from leaving you midflight.

Now for the Exterior:

At the Empennage:

• If Necessary, remove the Rudder Gust Lock  - Keeps wind from moving your rudder when parked. You want to be able to move it.
  
• If Necessary, remove the Tail Tie Down  - You don't want your plane tied to the pavement.
• Check Tail Control Surfaces for moveability   - If these don't move, you can't control the pitch of the plane.

At the Right Wing:
• Check (now extended) Flap   - look for bad bends and dings that could effect performance
• Check Aileron   - Same check as flap
• Remove Wing Tie Down
• Check Main Wheel, Tire and Brake   - Not flat? No brake fluid leaking?
• Drain Fuel Sump, & Check for Water / Debris   - You dispense a little fuel into a cup, and look for water bubbles or debris. Both of these can effect the performance greatly, and could even cause stalls.
• Visually Check Fuel Quantity in Tank   - Meters aren't fool proof
• ReSecure the Fuel Filler Cap   Watching fuel streaming from your wing, in-flight, isn't a happy sight.

Moving to the Nose:
• Check Engine Oil Quantity is in acceptable range
• Resecure the Oil Filler Cap
• Drain the Fuel Strainer and Check Visually for Water or Debris   - Again, water in the fuel is bad.
• Close the Oil Access Door
• Drain the Fuel Selector Drain   - Once more looking for water/debris in another section of the fuel system.
• Walk to the front and check the propeller leading edge for nicks and cracks   - These can cause problems in flight.
• Check spinner to be on securely   - You don't want the spinner to fly off at 2600 RPMs...
• Check Engine Cooling Air Inlets are clear of animals, birds (yes, this is quite common in cowlings... nice and warm for the birdies), or tools left by a mechanic. ***Starting engine with objects here can cause serious damage
• Check the Carburetor Air Filter screen is relatively unobstructed   - You don't want to block airflow to the carb.
• Check the Nose Wheel; Tire for pressure, and strut is showing some strut.   - If the strut is totally down, it means there's no pressure, thus no cushion when you land.
• Remove the nose tie down if necessary
• Check the Static Source opening is clear   - This works with vacuum instruments, and in calculating airspeed. It should always be clear.

Moving to the left wing of your aircraft:

• Visually check the fuel quantity in the left wing tank.   - Again, gauges can lie or fail.
• Resecure the fuel filler cap
• Remove the Pitot Tube cover and inspect pitot tube is clear.   - This is also used in calculating altitude and airspeed. With it plugged, it can cause you many problems.
• Check Fuel Tank Vent Opening
• Check Stall Warning Opening   - If this is blocked, you won't hear the warning buzzer when you're about to stall. Bad.
• Test Stall Warning by sucking in over opening through shirt, or omit if you prefer.   - This simulates vacuum over wing created by stall. You should hear the buzzer.
• Remove the wing tie down, if necessary
• Check the Main Wheel Tire
• Drain the fuel sump and check for water and debris

Move the the Left Wing Trailing Edge:
• Check the Aileron and Flap
• Feel safe to enter the aircraft and begin the Engine Start Checklist. :o)

At this point, you're airplane is basically safe to fly - as far as a pilot could determine. This doesn't mean things can break or fail anyways, but it can catch quite a few things before the flight occurs. You can always delay a flight if you find something broken on the ground, but once you're in the air it can become a competely different story. Takeoffs are optional, landings are mandantory.

Sources:
- Personal Knowledge and from my time at the US Air Force Auxiliary Flight Academy.