B737NG Landing Roll

[Capt. Greaseon]

Question for you 73 drivers. What is required for ground spoiler deployment, auto brakes, and reverse thrust ? Is it wheel spinup, weight on wheels etc.......

[R Rafferty]

Here's how they work.

Automatic Speed Brake:
- SPEED BRAKE lever in "Armed"-position
- SPEED BRAKE ARMED light illuminated
- Radio Altitude less than 10ft
- Landing Gear strut compresses on touchdown
- Both Thrust levers are retarded to IDLE, and
- Main Landing Gear spin up more than 60kts (if spin up is not detected, the Air/Ground-sensor will activate the system and Flight Spoilers will deploy)

Any Landing Gear compression will enable Flight Spoilers to deploy. When Right Main Gear-strut compressed, the Ground Spoilers deploy.


Auto Brake:
First select Auto Brake 1,2,3 or MAX.
Auto Brake begins when a) Both forward Thrust levers are retarded to IDLE, and b) the Main Wheels spin up

Reverse Thrust:
Can be deployed when either Radio Altimeter senses less than 10ft Radio Alt, or when Air/Ground sensor is in the Ground mode.


I hope you will find this info useful, and will be able to land and stop a little bit quicker....

R Rafferty

[alexban]

1 If the speedbrakes are in armed position they are independent of autobrake or reverse thrust.
When thrust levers are retarded to idle,spin up >60kts detected or any gear strut compression will deploy the flight spoilers.
Right gear compression will deploy the ground spoilers also.
2 If the speedbrakes lever is in down position during landing or rejected take-off,the auto-speedbrakes sys is also independent of autobrakes and operates when spin-up is more than 60kts,thrust levers are retarded to idle and reverse thrust levers are positioned for reverse thrust.
If you advance any thrust levers the spoiler panels will retract.

[Mike Dornheim]

I'm writing this for Aviation Week and would like to understand the 737-700 retarding systems.
Would like to clarify:

1) For autobrakes, is wheel spinup (means >60 kt.?) required? Is there an air-ground sensor backup if wheels don't spinup on icy runway, like the autospoilers have?

2) What does it take for the manual brakes and/or antiskid to work? If the wheels haven't spun up to >60 kt., does pressing the brake pedal actually clamp the brakes, or does it do nothing?
Is there an on-ground (squat switch) indication required for the brakes to work?
Is there any difference between the brakes working, and the antiskid working? That is, can the brakes clamp but the antiskid is not yet alive, perhaps because wheel spinup hasn't been sensed?

3) The sensors for weight-on-wheels in the autospoiler logic is curious -- the description provided by Mr. Rafferty suggests 3 separate things: a) air/ground sensor, b) any landing gear compression, and c) R MLG compression.
Are those really 3 different things?
What does it take for the air/ground logic to think it's on the ground?

Thanks,
-- Mike Dornheim

[FCS Explorer]

hope this helps.

Autobrake System

The autobrake system uses hydraulic system B pressure to provide maximum deceleration for rejected takeoff and automatic braking at preselected deceleration rates immediately after touchdown. The system operates only when the normal brake system is functioning. Antiskid system protection is provided during autobrake operation.
Rejected Takeoff (RTO)

The RTO mode can be selected only when on the ground. Upon selection, the AUTO BRAKE DISARM light illuminates for one to two seconds and then extinguishes, indicating that an automatic self–test has been successfully accomplished.

To arm the RTO mode prior to takeoff the following conditions must exist:

* airplane on the ground
* antiskid and autobrake systems operational
* AUTO BRAKE select switch positioned to RTO
* wheel speed less than 60 knots
* forward thrust levers positioned to IDLE.

With RTO selected, if the takeoff is rejected prior to wheel speed reaching 90 knots autobraking is not initiated, the AUTO BRAKE DISARM light does not illuminate and the RTO autobrake function remains armed. If the takeoff is rejected after reaching a wheel speed of 90 knots, maximum braking is applied automatically when the forward thrust levers are retarded to IDLE.

The RTO mode is automatically disarmed when both air/ground systems indicate the air mode. The AUTO BRAKE DISARM light does not illuminate and the AUTO BRAKE select switch remains in the RTO position. To reset or manually disarm the autobrake system, position the selector to OFF. If a landing is made with RTO selected (AUTO BRAKE select switch not cycled through OFF), no automatic braking action occurs and the AUTO BRAKE DISARM light illuminates two seconds after touchdown.
Landing

When a landing autobrake selection is made, the system performs a turn–on– self–test. If the turn–on–self–test is not successful, the AUTO BRAKE DISARM light illuminates and the autobrake system does not arm.

Four levels of deceleration can be selected for landing. However, on dry runways, the maximum autobrake deceleration rate in the landing mode is less than that produced by full pedal braking.

After landing, autobrake application begins when:

* both forward thrust levers are retarded to IDLE
* the main wheels spin–up.

NOTE: Landing autobrake settings may be selected after touchdown prior to decelerating through 60 kts of ground speed. Braking initiates immediately if the above conditions are met.

To maintain the selected landing deceleration rate, autobrake pressure is reduced as other controls, such as thrust reversers and spoilers, contribute to total deceleration. The deceleration level can be changed (without disarming the system) by rotating the selector. The autobrake system brings the airplane to a complete stop unless the braking is terminated by the pilot.
Autobrake – Disarm

The pilots may disarm the autobrake system by moving the selector switch to the OFF position. This action does not cause the AUTO BRAKE DISARM light to illuminate. After braking has started, any of the following pilot actions disarm the system immediately and illuminate the AUTO BRAKE DISARM light:

* moving the SPEED BRAKE lever to the down detent
* advancing the forward thrust lever(s), except during the first 3 seconds after touchdown for landing
* applying manual brakes.

[Mike Dornheim]

FCS Explorer -- thank you very much!

-- Mike