Start a Boeing 737 cold and dark in a flight simulator: power, IRS, APU, bleed air, engine light-off, after-start checks and common fixes.
To start a Boeing 737 cold and dark in a flight simulator, establish battery or ground power, align the IRS, start the APU, configure the fuel and pneumatic systems, then start each engine at adequate N2 before restoring packs, generators, hydraulics and bleed air. Exact switch positions vary by 737 model and add-on.
Which 737 cold-and-dark procedure should you use?
Use the checklist written for the exact 737 variant and add-on you are flying. The sequence below follows a typical 737NG-style installation, but Classics, MAX aircraft and simplified default models do not all simulate the same switches or system logic.
| Aircraft type | What to expect |
|---|---|
| Default or simplified 737 | Some overhead controls may be decorative, and the simulator's automatic engine-start command may be the intended method. |
| Study-level 737NG or MAX | Electrical buses, bleed pressure, fuel supply, IRS alignment and saved panel states must all be configured correctly. |
| Older FSX or Prepar3D add-on | System depth varies widely; use the manual supplied with that aircraft rather than assuming PMDG-style behaviour. |
For the default FSX aircraft, our FSX 737-800 power-up and engine-start sequence gives the relevant cockpit flow. PMDG users in Microsoft Flight Simulator should follow the separate PMDG 737 panel-state and startup procedure, because that aircraft models details a generic sequence cannot cover.
How do you start the 737 engines from cold and dark?
A normal simulated 737 start proceeds from electrical power to APU power, pneumatic configuration and engine light-off. Do not rush past the indications: each stage confirms that the next one has the power or pressure it requires.
- Secure the aircraft. Set the parking brake or chocks, place both thrust levers at idle and confirm both engine fuel-control or start levers are at CUTOFF. Check that usable fuel is loaded and external doors are closed before engine start.
- Establish electrical power. Switch the battery ON and set standby power to AUTO where fitted. If external power shows available, connect it; otherwise continue on battery power only long enough to start the APU.
- Start the APU. Move the APU switch to START and release it to ON. Watch for APU EGT rise and a stable running indication, then place the APU generator switch or switches on the electrical buses. Our explanation of how the APU supplies electrical and pneumatic power covers why it is needed before the main engines.
- Begin IRS alignment. Move both IRS selectors to NAV on aircraft that model them, then enter or confirm the aircraft's present position through the CDU if required. Alignment can continue while the remaining cockpit preparation is completed, but moving the aircraft may interrupt it.
- Configure fuel and bleed air. Turn on the fuel pumps required for tanks containing usable fuel; do not run centre-tank pumps merely because the switches exist. Set the packs OFF, APU BLEED ON and the isolation valve to AUTO or OPEN as required by the aircraft. Engine bleed switches normally remain ON. Verify that duct pressure is available.
- Complete the before-start items. Switch on the anti-collision beacon, confirm the area is clear and configure the hydraulic pumps according to the aircraft checklist. Ground equipment should be disconnected unless it is deliberately providing power or pneumatic air.
- Start engine 2. Starting the right engine first is the common 737 procedure, although the aircraft can use another order when operations require it. Move its engine start switch to GRD and confirm N2 begins increasing. At approximately 25% N2, or the maximum motoring speed specified by the add-on, move that engine's fuel-control lever to IDLE.
- Monitor the start. Confirm EGT rises, oil pressure appears and N1 and N2 continue increasing. On common 737NG simulations, the starter cuts out automatically around the mid-50% N2 range and the start switch leaves GRD. Move the fuel lever back to CUTOFF if there is no light-off, no oil pressure or an abnormal EGT rise.
- Start engine 1. Once engine 2 is stable at idle, repeat the same GRD, N2, fuel-IDLE and indication checks for the left engine.
- Complete the after-start flow. Put both engine generators on their buses, set packs to AUTO, return the isolation valve to AUTO and confirm engine bleed air is ON. Switch APU bleed OFF and shut down the APU after any cool-down required by the aircraft checklist. Set probe heat, hydraulics and engine start switches for taxi and take-off, then configure flaps and trim.
Can you start a 737 without the APU?
You can start a 737 without its APU only when the simulation provides another source of pneumatic pressure. External electrical power can illuminate and power the aircraft, but it cannot rotate an engine by itself; you need a simulated ground-air cart or a cross-bleed start from an engine already running.
Many default aircraft and add-ons do not model a pneumatic ground cart. In those aircraft, starting the APU is the practical manual-start method even when ground electrical power is connected.
Why will the 737 engines not start?
Most failed 737 starts come from missing bleed pressure, incorrect fuel-lever timing or an electrical source being disconnected too early.
- N2 remains at zero: check that the APU is running, APU BLEED is ON, the packs are OFF and the isolation valve permits air to reach the starter.
- N2 increases but EGT does not: confirm the correct fuel-control lever was moved to IDLE, usable fuel is aboard, the required fuel pumps are running and the ignition/start switch remains in GRD.
- The APU will not start: verify the battery is ON, fuel is available and the APU fire control is in its normal position. A depleted simulated battery may require external power or reloading a valid panel state.
- The cockpit goes dark after APU shutdown: the engine generator switches were probably not placed on the buses. Reconnect APU or ground power, then transfer electrical load to the engine generators.
- IRS ALIGN remains displayed: enter the present position if required and allow the selected alignment time to finish. Restart the alignment if the aircraft was moved during the process.
When is the cold-and-dark startup complete?
The startup is complete when both engines are stable, engine generators power the buses, the normal bleed and pack configuration is restored, the APU is no longer required and the aircraft has passed its after-start checks. That does not yet make it departure-ready: route entry, performance data and flight-control checks remain separate tasks.
If the navigation system is your next obstacle, follow our 737 FMC route and performance programming sequence rather than mixing FMC setup into the engine-start flow.