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!

"... But in common sense ... should actuate when ... conditions all exist at the same time~ Is this a Boeing intentional design? But it caused so many hard landings!..."
There are two subjects (at least) that may be of interest to you, in understanding the evolution of these systems.

Pilots sometime make the big difference in MODIFICATIONs to aircraft systems. One such case is B737 air/ground sensing:"Boeing 737 Overruns, A Case History", by Harold Marthinsen and Keith Hagy, _Air Line Pilot_, October/November'93 (Part One) pgs 27-31, and Dec'93 (Part Two) pgs 25-27.
There were cases in the 1980s and early '90's where ALL three (Auto Grnd Spoilers, ThRevrs, AutoBrks) were inhibited during a post-Ldng slide on a wet rwy. Manufacturer's testing was unable to reproduce any cause for all three systems failing simultaneously. The case history built-up over years, TBC could finally no longer dispute the problem. Industry didn't want to pay costs of modifications (even though the cost of just one such accident was more expensive).

RE = Rwy Excursion. More discussion:
slot 304, http://www.pprune.org/rumours-news/399798-aa-crash-jamaica-16.html
entries after slot 344, http://www.pprune.org/rumours-news/438003-american-airlines-jet-goes-off-runway-jackson-hole-wyoming-18.html"... a rare mechanical/ hydraulic interaction in the ... the thrust reversers were locked in transit instead of continuing to deploy. Further, an unrelated defect in the automatic speedbrake mechanism prevented the speedbrakes from automatically deploying...."
Regarding the "hard landing" topic -- that fits into a family of A&L (approach and landing) mishaps that all embrace similar variables: Abnormal Runway Contact (ARC), which also includes Tailstrike, Tip-scrape, crown-buckling (NLG-impact).

Investigative authorities are still struggling to make sense of the factors involved -- often NTSB will simply blame the pilot (eg, 21Mar06, DEN06IA051 (http://www.ntsb.gov/aviationquery/brief.aspx?ev_id=20060330X00368&key=1), which is a perfect exemplar of investigator-err, where management-pilots had encouraged Reduced-drag low-RPM "unspooled" approaches for cost savings).
See slot #43 in http://www.pprune.org/tech-log/373290-nw-a320-tailstrike-den-possible-w-o-3.html#post5645707

More ARC discussion:
Slot 11, http://www.pprune.org/rumours-news/451705-american-md-83-lga-wing-tip-contact-may-5-2011-a.html
http://www.pprune.org/rumours-news/385893-sata-brand-new-a320-hard-landing-lisbon.html
slot #58, http://www.pprune.org/tech-log/350693-vref-landing-3.html
Slot #15, http://www.pprune.org/tech-log/446935-ups-a306-hard-landing-kabq.html
B767-300, ARC at Narita, NLG-impact with crown buckling http://www.youtube.com/watch?v=Xpl3l7OskFU&feature=player_embedded

MD-11, ARC at Narita, 23Mar09:
http://www.youtube.com/watch?v=V6cMK9LUnzI

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°?

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:

But it caused so many hard landings!


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