Boeing 737 Max Engine Start Procedure

The Boeing 737 MAX aircraft is powered by the CFM International LEAP-1B engines. The LEAP-1B is an environmentally friendly engine that improves fuel consumption, CO2 emissions, and noise compared to previous-generation engines. It also uses lighter, more durable materials and advanced aerodynamic design techniques.

There are four options for starting the engine:

1. Normal Start – Typical start where the starting air pressure is supplied by the APU and the Starter Air Valve (SAV) position is controlled by the Start Switch.
2. Manual Override of Starter Air Valve – This start requires maintenance access under the engine cowl to manually override the Starter Air Valve (SAV) position. This start method can be used to start the engine in the case of a SAV unresponsive to Start Switch command.
3. Engine Cross Bleed Start – This start method uses starting air pressure supplied by bleed air pressure from the cross engine, which was started previously.
4. Ground Start Cart – This start method uses starting air pressure supplied by the ground start cart and Starter Air Valve (SAV) position is controlled by the Start Switch.

For a basic understanding, we will review the Normal Start Procedure.

Engine Start Procedure

• Follow all the safety procedures and aircraft limitations.
• Set the parking brake lever on the control stand to the ON position.
• Ensure that all circuit breakers are closed.
• Start the APU and supply air pressure to the pneumatic system.
• Confirm there is sufficient fuel in Main Tank 1 and Main Tank 2 to cover the heat exchangers for the hydraulic system. A minimum of 760 kg in each of Main Tank 1 and Main Tank 2 is necessary to cool the hydraulic system heat exchangers.
• Check the engine oil level indication in the flight compartment.
• Perform a fire test to ensure the engine’s fire detection system is serviceable.
• Maintain pressure in the “A” and “B” hydraulic systems to ensure full control of the nose gear steering and the main wheel brakes.
• Set the air conditioning PACK switches to OFF.
• Place the engine start switch to the GRD position. This will also power up the EEC, and all engine indications will appear.
• Look for the START VALVE OPEN alert on the engine display indication.
• Monitor N2 to verify engine acceleration. A white MOTORING indication will appear across the middle of the N2 indication at 18% during extended motoring to accommodate bowed rotor starts. Bowed Rotor Motoring (BRM) is active for all ground starts. N2 speed is controlled to approximately 23% during BRM. The dwell time spent at the BRM speed depends on the residual T3 temperature, the duration since engine shutdown, and the sensed core vibration levels during motoring. Once that dwell time is reached, the rest of the start sequence will continue.
• Verify that the oil pressure increases.
• Communicate with ground personnel to confirm that N1 begins to turn counterclockwise.
• Once MOTORING is no longer displayed over the N2 indication, move the start lever from CUTOFF to the IDLE position when N2 reaches 25% or achieves maximum motoring speed (minimum of 20% N2).
  • Note: Maximum motoring occurs when N2 acceleration is less than 1% within approximately 5 seconds.
  • CAUTION: Do not apply rotational force when moving the engine start lever.
• Ensure the fuel flow indication shows a positive reading and that the EGT rises within 10 seconds.
  • During the TCMA/EOS test, the fuel flow indication will be zero, and the ENG VALVE CLOSED light will illuminate bright blue until the test is complete.
• Monitor EGT and N2 increase until starter cutout at 63% N2.
• Verify that the engine start switch returns to the OFF [AUTO] position at 63% N2 and the START VALVE OPEN alert is no longer displayed.
• Monitor all engine parameters (N1, N2, EGT, fuel flow, and oil pressure) as the engine speed increases to idle.
• After the engine is stable at idle, start the other engine.
  • Note: The engine is considered stable at idle when the EGT start limit redline is no longer displayed.

Starter Operation Limits

• Multiple consecutive start attempts are permitted. Each start attempt is limited to 3 minutes of starter usage.
• A minimum of 10 seconds is needed between start attempts.
• Starter usage is limited to 5 minutes for all extended engine motorings. A minimum of 5 minutes is needed between the first two extended engine motorings.
• For the third and subsequent extended engine motoring, a minimum of 10 minutes is needed between each engine motoring.

Normal Engine Start Considerations

• Do not move an engine start lever to IDLE detent early or a hot start can occur.
• Keep a hand on the engine start lever while monitoring RPM, EGT and fuel flow until stable
• If fuel is shutoff accidentally (by closing the engine start lever) do not reopen the engine start lever in an attempt to restart the engine
• Failure of the ENGINE START switch to stay in GRD until the starter cutout RPM can cause a hot start. Do not re–engage the ENGINE START switch until engine RPM is below 20% N2.
• If a fluid leak (other than a continuous stream) from any of the engine drains is discovered during the Exterior Inspection, the engine can be started. If during engine start, the ground crew reports a fluid leak from an engine drain, the engine start may be continued.
• If the fluid leak continues after the engine is stable at idle, do one of the following:
  • Shut down the engine for maintenance action, or
  • Run the engine at idle thrust for up to 5 minutes. If the fluid leak stops during this time, no maintenance action is needed, or
  • Shut down and restart the engine. Run the engine at idle thrust for up to 5 minutes. If the fluid leak stops during this time, no maintenance action is needed.
• For the first flight of the day, at airport elevations at or above 2,000 feet MSL, if the temperature is below 5°C/41°F, consider placing the Ignition select switch to BOTH before starting the engines. This may increase the likelihood of a successful engine start on the first attempt.

Abort Engine Start

Abort the engine start if any of the following conditions occur:

• N1 or N2 does not increase or increases very slowly after the EGT increases.
• No oil pressure indication by the time the engine is stable at idle.
• EGT does not increase within 15 seconds after moving the engine start lever to the IDLE detent.
• EGT quickly nears or exceeds the start limit.

Starting Control

The engine starting is controlled by the EEC. When the ENGINE START switch is set to the GRD position, the EEC commands the Start Air Valve (SAV) to open. This allows compressed air (from the opposite engine, APU, or a ground cart) to flow to the air turbine starter. The starter then drives the accessory, transfer, and inlet gearboxes. Electrical power for controlling the engine start is supplied by the battery bus.

Engine Wet Start

The EEC stops the engine start if the EGT does not increase within 10 seconds after the engine start lever is moved to the IDLE position. The EEC stops fuel flow and turns off the ignition. The engine starter will continue to motor the engine until the ENGINE START switch is moved to OFF.

Engine Hot Start

If the EEC detects a hot start condition or a start stall (hung start) condition during a ground start, the numeric EGT display box will thicken and turn on and off. If the EGT starting limit is exceeded, the EEC stops the fuel flow and ignition. The numeric EGT display will continue to flash until the engine start lever is moved to the CUTOFF position. This feature operates on the ground only.