Engine Starting and Operation
The following instructions cover the starting procedures for reciprocating, turboprop, turbofan, and APU. These procedures are presented only as a general guide for familiarization with typical procedures and methods. Detailed instructions for starting a specific type of engine can be found in the manufacturer’s instruction book.
Before starting an aircraft engine:
- Position the aircraft to head into the prevailing wind to ensure adequate airflow over the engine for cooling purposes.
- Make sure that no property damage or personal injury occurs from the propeller blast or jet exhaust.
- If external electrical power is used for starting, ensure that it can be removed safely, and it is sufficient for the total starting sequence.
- During any and all starting procedures, a “fireguard” equipped with a suitable fire extinguisher shall be stationed in an appropriate place. A fireguard is someone familiar with aircraft starting procedures. The fire extinguisher should be a CO2 extinguisher of at least 5-pound capacity. The appropriate place is adjacent to the outboard side of the engine, in view of the pilot, and also where he or she can observe the engine/aircraft for indication of starting problems.
- If the aircraft is turbine-engine powered, the area in front of the jet inlet must be kept clear of personnel, property, and/or debris (FOD).
- These “before starting” procedures apply to all aircraft powerplants.
- Follow manufacturer’s checklists for start procedures and shutdown procedures.
Reciprocating Engines Starting Procedure
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. Do not attempt 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, flight deck, wheel, and so forth) protecting the aircraft must be removed before attempting to turn the engine. Use external sources of electrical power when starting engines equipped with electric starters, if possible or needed. This eliminates an excessive burden on the aircraft battery. Leave all unnecessary electrical equipment 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 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 direction opposite to normal rotation. This tends to inject the liquid from the cylinder into the intake pipe. The liquid is 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:
- Turn the auxiliary fuel pump on, if the aircraft is so equipped.
- Place the mixture control to the position recommended for the engine and carburetor combination being started. As a general rule, put the mixture control in the “idle cut-off” position for fuel injection and in the “full rich” position for float-type carburetors. Many light aircraft are equipped with a mixture control pull rod that has no detent 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 cut-off” or “full lean” position. The operator can select unmarked intermediate positions between these two extremes to achieve any desired mixture setting.
- Open the throttle to a position that provides 1,000 to 1,200 rpm (approximately 1⁄8" to 1⁄2" from the “closed” position).
- Leave the pre-heat or alternate air (carburetor air) control in the “cold” position to prevent damage and fire in case of backfire. These auxiliary heating devices are 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.
- Move the primer switch to “on” intermittently (press to prime by pushing in on the ignition switch during the starting cycle), or prime with one to three strokes of priming pump, depending on how the aircraft is equipped. The colder the weather, the more priming is needed.
- Energize the starter and after the propeller has made at least two complete revolutions, turn the ignition switch on. On engines equipped with an induction vibrator (shower of sparks, magneto incorporates a retard breaker assembly), turn the switch to the “both” position and energize the starter by turning the switch to the “start” position. After the engine starts, release the starter 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 start switch to the “start” position. When the engine starts, release the start switch. 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 (starter duty cycle) between successive attempts. Otherwise, the starter may be burned out due to overheating.
- After the engine is operating smoothly, move the mixture control to the “full rich” position if started in the “idle cutoff” position. Carbureted engines are already in the rich mixture position. Check for oil pressure.
- Instruments for monitoring the engine during operation include a tachometer for rpm, manifold pressure gauge, oil pressure gauge, oil temperature gauge, cylinder head temperature gauge, exhaust gas temperature gauge, and fuel flow gauge.
Hand Cranking Engines
If the aircraft has no self-starter, start the engine by turning the propeller by hand (hand propping the propeller). The person who is turning the propeller calls: “Fuel on, switch off, throttle closed, brakes on.” The person operating the engine checks these items and repeats the phrase. The switch and throttle must not be touched again until the person swinging the prop calls “contact.” The operator repeats “contact” and then turns on the switch. Never turn on the switch and then call “contact.”
A few simple precautions help to avoid accidents when hand propping the engine. While touching a propeller, always assume that the ignition is on. The switches that 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. This condition could allow the engine to start when the switch is off.
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 when 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 a fall into the blades when the engine starts.
In swinging the prop, always move the blade downward by pushing with the palms of the hands. 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 after the engine has fired is the principal cause of backfiring during starting. Gradual opening of the throttle, while the engine is cold, reduces the potential for backfiring. Slow, smooth movement of the throttle assures correct engine operation.
Avoid over priming the engine before it is turned over by the starter. This can result in fires, scored or scuffed cylinders and pistons, or engine failures due to hydraulic lock. If the engine is inadvertently flooded or over primed, 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.
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. Warm-up rpm is usually between 1,000 to 1,300 rpm.
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. Closely monitor the engine instruments at all times. Do not close the cowl flaps for engine warm-up, they need to be in the open position while operating on the ground. When warming up the engine, ensure that personnel, ground 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. The fireguard must be familiar with the induction system of the engine so that in case of fire, he or she 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 then extinguishes the fire using the available equipment. The fireguard must observe all safety practices at all times while standing by during the starting procedure.
Auxiliary Power Units (APUs)
APUs are generally smaller turbine engines that provide compressed air for starting engines, cabin heating and cooling, and electrical power while on the ground. Their operation is normally simple. By turning a switch on and up to the start position (spring loaded to on position), the engine starts automatically. During start, the exhaust gas temperature must be monitored. APUs are at idle at 100 percent rpm with no load. After the engine reaches its operating rpm, it can be used for cooling or heating the cabin and for electrical power. It is normally used to start the main engines.
Unsatisfactory Turbine Engine Starts
Hot Start
A hot start occurs when the engine starts, but the exhaust gas temperature exceeds specified limits. This is usually caused by an excessively rich fuel/air mixture entering the combustion chamber. This condition can be caused by either too much fuel or not enough airflow. The fuel to the engine must be shut off immediately.
False or Hung Start
False or hung starts occur when the engine starts normally, but the rpm remains at some low value rather than increasing to the normal starting rpm. This is often the result of insufficient power to the starter or the starter cutting off before the engine starts self-accelerating. In this case, shut the engine down.
Engine Fails to Start
The engine failing to start within the prescribed time limit can be caused by lack of fuel to the engine, insufficient or no electrical power to the exciter in the ignition system, or incorrect fuel mixture. If the engine fails to start within the prescribed time, shut it down.
In all cases of unsatisfactory starts, the fuel and ignition must be turned off. Continue rotating the compressor for approximately 15 seconds to remove accumulated fuel from the engine. If unable to motor (rotate) the engine, allow a 30-second fuel draining period before attempting another start.