Reasons for the runup
The critical checks every pilot should master
Mechanical failure accounts for about 20 percent of all airplane accidents. How can we avoid landing among those counted in that statistic?
Crucial to any preflight is the series of tasks performed in designated runup areas, a feature of almost all airports. The runup is so essential to safe flight that airports have set aside precious real estate for just these few steps on our preflight checklist.
Here are the typical runup tasks and their purpose:
Engine health check: The engine is brought to a specific rpm on the ground to ensure smooth and consistent operation at altitude. This can help detect irregularities potentially indicating fouled spark plugs or other engine malfunctions.
Magnetos: We switch between magnetos during the runup to ensure each operates correctly without a significant rpm drop. A decrease greater than 200 rpm could indicate a magneto timing problem that should be checked, or other problem with the ignition system.
Propeller control: Runup for aircraft with adjustable propellers means cycling the prop to check pitch change and oil system integrity. Verify oil pressure is in the green range and oil temperature is climbing to the green—vital in cold weather to prevent overspeed.
Carburetor heat: For carbureted engines, pull the carb heat on for at least 10 seconds during the runup, and watch for the expected slight dip in rpm. A drop exceeding 300 rpm indicates an exhaust leak, and flying with a suspected leak is unsafe.
Brake reliability: Holding the brakes during the runup verifies brake effectiveness.
Suction gauge: The suction gauge indicates the pressure produced by the vacuum pump and can reveal the vacuum system’s overall health. This check can confirm the suction is within limits. If it reads too low, the suction drawn through the gyroscopes may be insufficient to keep them stable.
Engine instruments: We monitor engine instruments, such as oil pressure, oil temperature, and fuel flow, to verify they’re within specified parameters and that there are no indications of system anomalies.
Ammeter and electrical system: By observing the ammeter at increased rpm, we can ensure the electrical charging system works correctly and that there aren’t any unusual electrical loads or shorts.
System anomalies detection: Besides the specific checks, the runup allows you to detect abnormal noises, vibrations, or smells that might suggest a problem.
Throttle to idle: When we throttle all the way back from our runup rpm, we mimic the power change we initiate during the landing phase, allowing us to make sure the engine is running smoothly at idle.
Meticulous preflight runups are more than routine; they’re our gateway to safe skies. Such diligence fortifies our defenses against in-flight failures, reaffirming the runup’s critical place in our safety arsenal.
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