The aircraft run-up is a mandatory procedure performed by the pilot before flight to ensure the engine and related systems are operating correctly at higher power settings. This pre-takeoff safety check verifies the health of the propulsion system under a load that simulates the demands of flight, confirming operational status before the aircraft commits to the runway. It is designed to identify potential mechanical issues that could lead to an engine malfunction immediately following takeoff.
Defining the Aircraft Run-Up
The run-up involves deliberately increasing engine power while the aircraft remains stationary on the ground. Pilots secure the aircraft, typically by setting the parking brake firmly or placing chocks around the wheels, to prevent any forward movement as engine speed increases. This high-stress test verifies the power plant and its supporting components before the pilot commits to the takeoff roll.
Increasing the engine’s revolutions per minute (RPM) allows the pilot to observe how the entire system responds to a significant power demand. The run-up is conducted at a specific, elevated RPM—often between 1,700 and 2,000 RPM in general aviation aircraft—that is high enough to stress the systems but low enough to maintain control. This phase ensures the engine transitions smoothly from low to high power settings without hesitation. The check confirms that all engine accessories function as designed under operationally relevant power output.
Why the Run-Up Is Essential for Flight Safety
The run-up is a regulatory requirement established to test components that cannot be properly evaluated at idle or taxi power settings. For instance, the ignition system’s redundancy is checked under a load that reveals issues like fouled spark plugs or weak magneto performance. This test prevents engine failure during the initial climb after takeoff, the most demanding phase of flight, where a loss of power leaves minimal time for recovery.
The procedure also confirms the operation of systems like the propeller pitch mechanism, engine cooling, and lubrication. The heat and pressure generated during the high-power run-up verify that oil is circulating effectively and that temperatures and pressures remain within acceptable limits. By proactively identifying mechanical problems on the ground, the run-up drastically reduces the risk of an airborne emergency.
Context: Where and When the Run-Up Occurs
The run-up is performed immediately prior to takeoff, after the taxi procedure is complete and the pilot has received clearance to proceed toward the runway. Most busy airports feature designated run-up areas, often marked with painted lines and signs, located near the active runway holding point. These locations are used to position the aircraft so its propeller wash does not affect other aircraft, ground personnel, or terminal buildings.
Pilots orient the aircraft into the wind during the run-up to improve engine cooling and minimize the impact of the prop wash. Performing the checks at a designated holding point ensures the aircraft is not obstructing the taxiway traffic flow while the pilot systematically works through the pre-takeoff checklist.
Step-by-Step: The Piston Engine Run-Up Procedure
The run-up for piston-powered aircraft, common in general aviation, follows a specific checklist designed to test all engine-dependent systems. After setting the brakes and establishing the required engine RPM, the pilot moves through a series of checks. This procedure reflects the air-cooled, reciprocating design of these engines. Each step isolates a specific component to confirm its operational readiness before the flight begins.
Magneto Check
The magneto check confirms the operational integrity of the aircraft’s dual, independent ignition system. Piston engines use magnetos, which generate electricity for the spark plugs, providing reliable ignition separate from the aircraft’s electrical system. The pilot switches the ignition from “Both” to “Left” and then “Right” while monitoring the tachometer for an RPM drop. Operating on a single magneto naturally causes a slight power reduction.
The maximum allowable RPM drop is typically specified by the manufacturer, often not exceeding 150 to 175 RPM on either magneto. The difference in RPM drop between the left and right magnetos must also be within a narrow tolerance, usually no more than 50 RPM. An excessive drop or a rough engine indicates a problem such as a fouled spark plug or incorrect timing, requiring maintenance. No drop at all suggests a dangerous issue with the magneto’s grounding wire.
Propeller Control Cycle
Aircraft equipped with a constant-speed propeller require a propeller control cycle during the run-up. The pilot momentarily moves the propeller control from the high RPM/low pitch setting to the low RPM/high pitch setting and then back. This action forces the viscous engine oil to circulate through the propeller hub mechanism.
Cycling the propeller ensures the oil is warm and the pitch change mechanism is functioning smoothly. Observing a positive drop and subsequent recovery in engine RPM confirms that the propeller governor is capable of making the necessary adjustments. A failure to see a proper response indicates a problem with the control system that could compromise climb performance.
Carburetor Heat Check
The carburetor heat check verifies that the system can supply heated, unfiltered air to the engine’s induction system to prevent or melt ice formation. Applying carburetor heat causes a noticeable decrease in engine RPM, typically a drop of 75 to 100 RPM, because the heated air is less dense. The pilot confirms this RPM drop and then ensures the RPM returns to the original setting when the control is returned to the cold air position.
Successful completion confirms that the carburetor heat valve is fully opening and closing, directing hot air from a shroud around the exhaust manifold into the engine. A failure to observe the specified RPM drop indicates the system is inoperative, which is a hazard in conditions conducive to carburetor icing.
Instrument and Pressure Checks
The final part of the piston run-up involves scanning the engine instrumentation. The pilot checks gauges for:
- Oil temperature
- Oil pressure
- Cylinder head temperature
- Fuel pressure
These values must be within the manufacturer’s specified operating range. The oil pressure gauge should show a steady reading, confirming sufficient lubrication is reaching all moving parts under the higher power setting. The oil temperature must be warm enough to circulate properly, but not exceed its upper limit. These checks confirm cooling efficiency immediately before takeoff.
Key Differences for Jet Engine Run-Ups
The run-up procedure for turbine-powered (jet) aircraft differs significantly from that of piston engines. Jet engines do not have magnetos or constant-speed propellers to cycle, simplifying the pre-takeoff check. The focus shifts to ensuring stable engine performance parameters and confirming the functionality of complex electronic controls.
Modern jet engines often rely on a Full Authority Digital Engine Control (FADEC) system, which automatically monitors and manages most engine functions. The jet run-up involves briefly increasing the thrust levers to a moderate setting while verifying that the engine parameters stabilize within limits. Pilots monitor the rotational speeds of the engine’s spools, designated as N1 (low-pressure fan speed) and N2 (high-pressure compressor speed), and the Exhaust Gas Temperature (EGT). N1 is the primary thrust-setting parameter. The pilot ensures all readings are stable, with no excessive fluctuations, before receiving final takeoff clearance.