Set Boeing 737 autopilot speed with the MCP, autothrottle, SPEED, LVL CHG and VNAV, plus fixes for blank windows and missed targets.
In a Boeing 737 flight simulator, arm the autothrottle, rotate the MCP IAS/MACH selector to the desired speed, then choose a compatible pitch mode. Use SPEED with altitude hold, LVL CHG for a pitch-controlled climb or descent, or VNAV for FMC-managed speed. Confirm the active mode on the PFD.
“Autopilot speed” is convenient shorthand, but the 737 does not always control speed with the autothrottle. Depending on the selected mode, speed can be maintained by changing thrust, changing pitch, or combining both. The labels and available functions vary between simplified 737s and study-level add-ons.
How do I select a speed on the 737 MCP?
- Arm the autothrottle. Move the A/T ARM switch to ARM. Arming it does not necessarily activate speed control; an appropriate autothrottle or vertical mode must also engage.
- Set the target speed. Rotate the IAS/MACH selector on the Mode Control Panel. The window displays indicated airspeed in knots or Mach—not GPS groundspeed.
- Choose how the aircraft will maintain it. In level flight, use ALT HOLD and press SPEED if MCP speed mode is not already active. For a climb or descent, select LVL CHG or use VNAV when the FMC should manage the profile.
- Engage CMD if required. Autothrottle can operate separately, but the autopilot must be in CMD for it to change pitch automatically.
- Check the Flight Mode Annunciator. The FMA at the top of the primary flight display is the final authority. Look for modes such as MCP SPD, FMC SPD, N1, LVL CHG, V/S, ALT HOLD or a VNAV mode, depending on the phase of flight and aircraft model.
Which speed mode should I use?
| Mode combination | How speed is controlled | Best use |
|---|---|---|
| ALT HOLD and MCP SPD | Autothrottle varies thrust while the autopilot holds altitude | Level flight at a manually selected speed |
| LVL CHG | Autopilot varies pitch to hold MCP speed; autothrottle normally commands climb thrust or idle | Simple climbs and descents to a selected altitude |
| V/S and MCP SPD | Autopilot holds vertical speed while autothrottle changes thrust | Small, controlled altitude changes where vertical rate matters |
| VNAV | FMC targets are maintained through the aircraft's programmed thrust and pitch logic | Managed climbs, cruise and profile descents |
LVL CHG is often the clearest manual option because the aircraft gives priority to the selected airspeed and allows the climb or descent rate to vary. With V/S, the chosen vertical rate has priority; the aircraft can still become too slow in a climb or too fast in a descent after reaching its thrust limit.
Why is the 737 speed window blank in VNAV?
A blank MCP speed window usually means VNAV has authority and the FMC is supplying the target speed. This is normal on 737 simulations that reproduce Boeing's VNAV logic.
To override it temporarily, push the speed selector for speed intervention if the aircraft models that function, then dial the required speed. If speed intervention is unavailable, select another suitable vertical mode and command the speed through the MCP. If VNAV refuses to engage or behaves unexpectedly, use our 737 LNAV and VNAV troubleshooting checks before changing the route or FMC data.
Why is the autopilot not holding the selected speed?
- The autothrottle is only armed: ARM by itself does not prove that thrust is being controlled. Read the FMA rather than relying on the switch or illuminated MCP button.
- LVL CHG is using pitch: Seeing N1 during a climb or idle thrust during a descent is expected. The autopilot should control the selected speed by adjusting pitch.
- VNAV has control: The FMC target may take precedence unless speed intervention is active.
- The aircraft has reached a limit: A steep V/S climb can demand more than maximum thrust, while a steep descent can overspeed even at idle. Reduce the commanded vertical rate or use LVL CHG.
- A hardware throttle is fighting the autothrottle: Noisy axes, duplicate bindings or moving physical levers can overwrite simulated servo commands. Remove duplicate throttle assignments and increase the dead zone only when axis noise is visible.
- IAS and Mach are being confused: Use the IAS/Mach changeover control where provided. The selected value is never groundspeed.
What speed should I set during each flight phase?
Set speeds from the FMC performance data and the procedure being flown, not from one fixed number. Before take-off, many 737 procedures place V2 in the MCP window. VNAV normally manages later climb and cruise targets, including the common 250-knot restriction below 10,000 feet where that limit applies.
During descent, select speeds that allow the aircraft to meet restrictions and decelerate before flap extension; our 737 descent and approach setup explains how LVL CHG, V/S and VNAV fit into that process. Do not command a speed below the appropriate flap manoeuvring speed or above a flap placard limit.
On final, use the calculated VREF plus the correction required by the procedure and conditions rather than guessing. See our guidance on choosing a Boeing 737 landing speed, then follow the ILS configuration and autothrottle sequence when flying an instrument approach.