See how Boeing 737 automatic speedbrakes deploy on landing and rejected take-off, what triggers them, and why they may fail in a flight simulator.
On a Boeing 737, automatic speedbrakes deploy the spoiler panels after touchdown when the lever is armed, both thrust levers are at idle and wheel-spin or ground sensing confirms the landing. They dump lift, put more weight on the wheels and improve braking; rejected-take-off logic can also deploy them automatically.
In Aviation & Real-World Flying, these are also called automatic ground spoilers or autospoilers. They are not an airborne system that continuously regulates speed.
What do automatic speedbrakes actually do?
Automatic speedbrakes raise the available flight and ground spoiler panels after the aircraft lands. This destroys much of the wing’s remaining lift, transfers weight onto the landing gear and lets the wheel brakes produce more effective stopping force.
The raised panels add aerodynamic drag too, but lift dumping is their most important landing function. Flight-spoiler panels can also assist roll control and provide manually selected speedbraking in the air; dedicated ground-spoiler panels remain retracted until the aircraft is on the ground.
When do Boeing 737 automatic speedbrakes deploy?
On a normal landing, deployment requires the speedbrake lever to be in the ARMED detent, both forward thrust levers at idle and a valid touchdown signal.
| Situation | Normal lever position | Main triggers | System response |
|---|---|---|---|
| Landing | ARMED | Both thrust levers at idle and main-wheel spin-up at about 60 knots; ground-sensing logic provides backup on applicable variants | Lever travels to UP and the available ground spoilers deploy |
| Rejected take-off | DOWN | Wheel speed above approximately 90 knots and both thrust levers retarded to idle | Lever travels to UP and the spoilers deploy automatically |
| Balked landing or go-around after touchdown | UP after deployment | Forward thrust is advanced again | Spoilers retract and the lever returns towards DOWN |
The wheel-speed figures are representative of common 737 logic. Exact sensing, backup inputs and annunciations differ across Original, Classic, Next Generation and MAX aircraft, so the applicable flight crew manual takes precedence.
The SPEED BRAKE ARMED light confirms that the system is armed; it does not mean the panels are already extended. After touchdown, the cockpit lever should physically move to UP. Depending on the 737 version, selecting reverse after wheel spin can also provide backup deployment when the lever was not armed, but that is not the normal landing technique.
Does arming the speedbrake deploy it in flight?
No. Selecting ARMED places the automatic landing system in standby without raising the panels.
Airborne speedbrake extension is commanded manually by moving the lever out of DOWN towards the flight detent. Crews normally stow it before final approach and then arm it for landing according to their checklist; our practical 737 descent and approach sequence explains where in-flight speedbrake use fits into the wider energy-management task.
Are speedbrakes, autobrakes and reverse thrust the same?
No. They are separate systems that contribute to the same landing rollout:
- Automatic speedbrakes dump lift and add aerodynamic drag.
- Autobrakes command wheel-brake pressure to achieve a selected deceleration.
- Thrust reversers redirect engine thrust to provide additional deceleration.
Normal automatic spoiler deployment does not require reverse thrust. For the separate engine system, see our explanation of how 737 thrust reversers produce and control reverse thrust.
Flap selection does not trigger the automatic speedbrakes either. It changes approach drag, speed and landing performance; our comparison of Flaps 30 and Flaps 40 landing configurations covers that decision separately.
Why did the automatic speedbrakes not deploy in my simulator?
The most common simulator cause is that one of the required inputs never reached the value expected by the aircraft model.
- The lever was not fully in ARMED. Verify the detent and the SPEED BRAKE ARMED indication rather than relying on the lever’s approximate visual position.
- A throttle axis remained above idle. Noise, an incorrect idle calibration or two unequal throttle axes can prevent the system from seeing both thrust levers closed.
- Touchdown logic was not satisfied. A bounce, one main gear remaining airborne or simplified wheel-spin modelling can delay deployment.
- The rejected take-off was below the trigger speed. Automatic RTO deployment is not expected during a low-speed rejection.
- Control assignments conflict. A spoiler axis, toggle command and hardware lever can repeatedly overwrite one another.
- The aircraft has simplified systems. Some simulator aircraft omit wheel-spin backups, automatic lever movement or individual ground-spoiler logic.
Check the cockpit lever immediately after touchdown. If it remains in ARMED, a trigger was probably missing; if it moves to UP but the panels remain down, suspect a control conflict, hydraulic-system simulation or visual-model problem. In a simulator, command the lever manually to UP if automatic deployment fails rather than assuming autobrakes or reverse thrust will compensate.