The following procedures are typical of those used to start reciprocating engines. There are, however, wide variations in the procedures for the many reciprocating engines. No attempt should be made to use the methods presented here for actually starting an engine. Instead, always refer to the procedures contained in the applicable manufacturer's instructions.
Reciprocating engines are capable of starting in fairly low temperatures without the use of engine heating or oil dilution, depending on the grade of oil used.
The various covers (wing, tail, cockpit, wheel, etc.) protecting the aircraft must be removed before attempting to turn the engine. External sources of electrical power should be used when starting engines equipped with electric starters. This eliminates an excessive burden on the aircraft battery. All unnecessary electrical equipment should be left off until the generators are furnishing electrical power to the aircraft power bus.
Before starting a radial engine that has been shut down for more than 30 minutes, check the ignition switch for off; turn the propeller three or four complete revolutions with the starter, or it may be pulled through by hand to detect a hydraulic lock if one is present.
Any liquid present in a cylinder is indicated by the abnormal effort required to rotate the propeller, or by the propeller stopping abruptly during rotation. Never use force to turn the propeller when a hydraulic lock is detected.
Sufficient force can be exerted on the crankshaft to bend or break a connecting rod if a lock is present.
To eliminate a lock, remove either the front or rear spark plug from the lower cylinders and pull the propeller through. Never attempt to clear the hydraulic lock by pulling the propeller through in the opposite direction to normal rotation. This tends to inject the liquid from the cylinder into the intake pipe. The liquid will be drawn back into the cylinder with the possibility of complete or partial lock occurring on the subsequent start.
To start the engine, proceed as follows:
1. Turn the auxiliary fuel pump on, if aircraft is so equipped.
2. Place the mixture control to the position recommended for the engine and carburetor combination being started. As a general rule, the mixture control should be in the "idle cutoff" position for pressure type carburetors and in the "full rich" position for float type carburetors.
Many light aircraft are equipped with a mixture control pull rod which has no detented intermediate positions. When such controls are pushed in flush with the instrument panel, the mixture is set in the "full rich" position. Conversely, when the control rod is pulled all the way out, the carburetor is in the "idle cutoff" or "full lean" position. Unmarked intermediate positions between these two extremes can be selected by the operator to achieve any desired mixture setting.
3. Open the throttle to a position that will provide 1,000 to 1,200 rpm (approximately 1/8 to 1/2 inch from the "closed" position).
4. Leave the preheat or alternate air (carburetor air) control in the "cold" position to prevent damage and fire in case of backfire. These auxiliary heating devices should be used after the engine warms up. They improve fuel vaporization, prevent fouling of the spark plugs, ice formation, and eliminate icing in the induction system.
5. Energize the starter after the propeller has made at least two complete revolutions, and turn the ignition switch on. On engines equipped with an induction vibrator, turn switch to the "both" position. When starting an engine that uses an impulse coupling magneto, turn the ignition switch to the "left" position. Place the ignition switch to "start" when the magneto incorporates a retard breaker assembly. Do not crank the engine continuously with the starter for more than 1 minute. Allow a 3 to 5 minute period for cooling the starter between successive attempts. Otherwise the starter may be burned out due to overheating.
6. Move the primer switch to "on" intermittently, or prime with one to three strokes of priming pump, depending on how the aircraft is equipped. When the engine begins to fire, hold the primer on while gradually opening throttle to obtain smooth operation.
After the engine is operating smoothly on the primer, move the mixture control to the "full rich" position. Release the primer as soon as a drop in rpm indicates the engine is receiving additional fuel from the carburetor.
If the aircraft has no selfstarter, the engine must be started by swinging the propeller. The person who is turning the propeller calls, "fuel on, switch off, throttle closed, brakes on." The person operating the engine will check these items and repeat the phrase. The switch and throttle must not be touched again until the person swinging the prop calls "contact." The operator will repeat " contact" and then turn on the switch. Never turn on the switch and then call "contact."
When swinging the prop, a few simple precautions will help to avoid accidents. When touching a propeller, always assume that the ignition is on. The switches which control the magnetos operate on the principle of short circuiting the current to turn the ignition off. If the switch is faulty, it can be in the "off" position and still permit current to flow in the magneto primary circuit.
Be sure the ground is firm. Slippery grass, mud, grease, or loose gravel can lead to a fall into or under the propeller. Never allow any portion of your body to get in the way of the propeller. This applies even though the engine is not being cranked. Stand close enough to the propeller to be able to step away as it is pulled down. Stepping away after cranking is a safeguard in case the brakes fail.
Do not stand in a position that requires leaning toward the propeller to reach it. This throws the body off balance and could cause you to fall into the blades when the engine starts.
In swinging the prop, always move the blade downward by pushing with the palms of the hand. Do not grip the blade with the fingers curled over the edge, since "kickback" may break them or draw your body in the blade path.
Excessive throttle opening and intermittent priming after the engine has fired are the principal causes of backfiring during starting. Gradual opening of the throttle while priming continuously will reduce the initial "over rich" mixture to a smooth running, best power mixture as the engine picks up speed. An engine operating on an "over rich" mixture is sluggish but will not backfire.
When starting an engine using a priming pump, move the mixture control into "full rich" position, if not previously placed there, when the engine begins to fire. If the engine fails to start immediately, return the mixture control to "idle cutoff" position. Failure to do so will create an excessive amount of fuel in the carburetor air scoop, constituting a fire hazard.
Avoid priming the engine before it is turned over by the starter. This can result in fires, scored or scuffed cylinders and pistons, and, in some cases, engine failures due to hydraulic lock. If the engine is inadvertently flooded or overprimed, turn the ignition switch off and move the throttle to the "full open" position. To rid the engine of the excess fuel, turn it over by hand or by the starter. If excessive force is needed to turn over the engine, stop immediately. Do not force rotation of the engine. If in doubt, remove the lower cylinder spark plugs. If very serious overloading has occurred, it may be necessary to remove the lower cylinder intake pipes. To reduce the likelihood of damage to the engine due to overpriming on some medium and large aircraft, the engine blower drain valves should be checked frequently for fouling or sticking.
Immediately after the engine starts, check the oil pressure indicator. If oil pressure does not show within 30 seconds, stop the engine and determine the trouble. If oil pressure is indicated, adjust the throttle to the aircraft manufacturer's specified rpm for engine warmup. Warmup rpm will usually be in the 1,000 to 1,300 rpm range.
Most aircraft reciprocating engines are air cooled and depend on the forward speed of the aircraft to maintain proper cooling. Therefore, particular care is necessary when operating these engines on the ground.
During all ground running, operate the engine with the propeller in full low pitch and headed into the wind with the cowling installed to provide the best degree of engine cooling. The engine instruments should be monitored closely at all times. Do not close the cowl flaps for engine warmup; closing of the cowl flaps may cause the ignition harness to overheat. When warming up the engine, make sure that personnel, ground installations, equipment that may be damaged, or other aircraft are not in the propeller wash.
Extinguishing Engine Fires
In all cases a fireguard should stand by with a CO2 fire extinguisher while the aircraft engine is being started. This is a necessary precaution against fire during the starting procedure. He should be familiar with the induction system of the engine so that in case of fire he can direct the CO2 into the air intake of the engine to extinguish it. A fire could also occur in the exhaust system of the engine from liquid fuel being ignited in the cylinder and expelled during the normal rotation of the engine. If an engine fire develops during the starting procedure, continue cranking to start the engine and blow out the fire. If the engine does not start and the fire continues to burn, discontinue the start attempt. The fireguard should extinguish the fire using the available equipment. The fireguard must observe all safety practices at all times while standing by during the starting procedure.