B737ng speed brake operation after bounced landing
 

Good evening，everyone~
I am flying B737NGs, and there is question bothers me for a long time.
Hope you guys can give me the right answer! Thanks in advance!
I almost made a landing couple years ago.
I was flying a flap 40 landing, from 50ft to 20ft, the sink was too fast, but i didn`t notice that till 20ft RA, and i pitch hard for saving this situation, when reducing the decent rate ,the aircraft touched down. At that time, the throttle was in the MID position, cause it sank fast, i didn`t retard it at all. with the thottle in there and the aircraft just flew in to the air again.
now is the cytical time, the aircraft was in the air again, my first instinctive action was retard the throttle to land again. I heard the sound of speed brake deployment, and pushed forward on the throttle and restorted the speed brake, and then landed.
after the landing, I checked the QAR data the other day,that landing had a air G load at 1.7G before the first touch down. that was danerous!
My question are:
1/ why the speed brake can deploy even the aircraft is in the air after the first touch down? I heard that 3 seconds after the first touch down even in the air, the aircraft is still in the landing mode, the speed brake will deploy when throttle retard to idle, I don`t know if this is correct or not?
2/ after the first touch down and bounce, the throttle retard to which position, then the speed brake will deploy?
It`s a long story and long question.Thank a lot!

Hi there,

The ground spoliers will deploy as soon as the right main gear compresses or wheel spins AND thrust levers idle.
The bounce came as you had thrust during touchdown and possibly some rate of descent.

What buggs me is that you didnt realise your sink rate until 20ft.
Are you looking outside?the runway should rise at the aiming point about 40 feet in a standard rate of descent and about 30 feet at the 2/3 runway point.
If you didnt realized your sink,it only means you need to force yourself looking outside(rather than flying with feel of pants) and to initiate the flare as the runway rises...just follow the rise with an increase in pitch as you close the thrust levers.

If you ever get in a hard bouce i suggest you go around and do practice it in the sim before...

thanks for your reply de facto!
i was flying flap 40 on a very stable air, and you know sometimes in this very nice condition, your mind and vision will freeze for a little while, but that was critical. and you know that sometimes happens when you fly for a long time.
but my question is when the aircraft bounced in the air，the landing gear struct should extend again, the air ground senser is rerurn to air mode. but when you retard the throttle, the speed brake will still deploy!

The AUTO speedbrake is what you need to look into not only the air /ground logic.
As you ARM the speedbrake,the auto speedbrake will need a few things to operate such as weight on right wheel(air/ground),thrust lever angle,RA less than 10 feet and thrust lever at idle.

Now once you touch down(first time:E),the speedbrake actuator will command the lever to extend UNLESS you have thrust (TRA>44 degr).
Now you are in the air again with the speed brake lever already having got the command to extend via the initial touch and is now waiting for you to be below 10 feet and close the thrust levers:E

You may be in air mode again but you activated the actuator at first touch..and your speedbrake is still on ARM mode.

In any case ,remember a light bounce increases your landing distance,a big bounce requires a go around.

thank you de facto
but i still want to make this clearer~
after the first touch down with TLA ＞44°, the speedbrake will not deploy.
but it is kind of actuated just not moving, just like loading the bullet into the gun waiting for pulling the trigger, which here means the TLA ＜44°?

But in common sense, the aircraft should actuate when all the required conditions all exist at the same time~
Is this a Boeing intendtional design? But it caused so many hard landings!

Yes.
The wheel spin > 60kts is enough (airground logic does not need to be in ground mode)
Therefore if you bounce,the wheels would be spinning, THAT would be your bullet:sad:

No,pilots not appreciating the importance to touch with thrust idle or and late flare do.

sounds like a very exprienced idea! Good to know, thx for sharing. When you say the wheel spins and with throttle idle, do you mean the right wheel spins?Or any wheel spins with the throttle idle can enable the ground spoiler deploys?
My idea is only with the left wheel spins and throttle idle, the ground spoiler will not deploy untill the right strut or the right wheel spin?
Am I right?

That is correct. Only flight spoilers deploy in your example.

You need to dive into this much further...once the ac bounced, you had weight on wheels, and the ac is now in land mode, thus shutting off many systems...that being said.

Speed brakes and spoilers are secondary systems, but in land mode, extend full to optimize braking...thus in the balked landing you describe, the ac is in land mode.

Back in the last century when I flew the B737 this was known as the "bounce augment mode".
It let you squish the oleos all the way down and then dramatically increase the lift to become airborne again!

Terry - was that when the dinosaurs were around, or....?! :8

(Pun intended re your name. Sorry all, couldnt resist)

Came across this piece of info in the FCTM bounced landing recovery

If higher than idle thrust is maintained through initial touchdown, the automatic
speedbrake deployment may be disabled even when the speedbrakes are armed.
This can result in a bounced landing. During the resultant bounce, if the thrust
levers are then retarded to idle, automatic speedbrake deployment can occur
resulting in a loss of lift and nose up pitching moment which can result in a tail
strike or hard landing on a subsequent touchdown.

pretty much covers what the OP Describes.

Auto speedbrake operates when:
Armed and speedbrake armed light illuminates
Thrust retarded to idle
Any gear strut compresses (for flight spoiler, right gear strut for ground spoilers)
Wheel speed greater than 60kts.
Probably after the bounce the system detected the wheel spin and as thrust was retarded that made the spoilers deploy.
If a shallow bounce were to occur it is important not to close the thrust but mantain the landing attitude and tocuhdown.
Hard bounce- go around