Very hard landing Boeing 737-800

[snydersnapshots]

Depending on the design of the auto-speedbrake system I can see that happening.

Assume (and this is totally assuming on my part since I don't know the design of the 737 system) the speedbrake system is designed to deploy when two conditions are met: the throttles are at idle and wheels are spinning faster than some RPM threshold.

So a landing is attempted and the sequence is as follows:

1. Pilot enters flare with throttles above idle. Speedbrake system doesn't deploy because neither condition is met.
2. Aircraft briefly touches down and wheels spin up. Now one condition is met (wheel speed) for the auto-speedbrakes but they don't deploy because the other condition (throttle position) is not met.
3. Airplane becomes airborne again.
4. Pilot moves throttles to idle position while plane is still airborne. The speedbrakes now deploy because both conditions are met: throttles are at idle, and wheels are spinning because they take several seconds to spin down and it's only been 0.5 second since #2.
5. Aircraft begins descending at a rapid rate and BAM!

There is however a tradeoff. The above sequence definitely has the possibility to result in a hard landing, and possible damage to the aircraft but probably not really serious damage. But if the spoiler system were designed to be more conservative in when it deploys, the result could be a long landing that takes the plane off the far end of the runway, which could have disastrous consequences.

Here, as written in the Book of Boeing:

Ground Operation
All flight and ground spoilers will automatically rise to full extend on landing if the speed brake lever is in the ARMED position and both thrust levers are at IDLE. When spin-up occurs on any two main wheels, the speed brake lever moves to the UP position and the flight spoilers extend. When the right main landing gear shock strut is compressed, a mechanical linkage opens the ground spoiler shutoff valve to extend the ground spoilers. If a wheel spin-up signal is not detected, the speed brake lever will move to the UP position and all spoiler panels will deploy automatically, after the ground safety sensor engages in the ground mode (main gear strut compression).

All spoiler panels will extend automatically if takeoff is rejected and the thrust reverse levers are positioned for reverse thrust. Wheel spin-up (60 kts.) must have occurred on any two main wheels in order for the automatic extension to take place.

After an RTO or landing, if either thrust lever is advanced, the SPEED BRAKE lever automatically moves to the DOWN detent and all spoiler panels retract. The spoiler panels may also be retracted by manually moving the SPEED BRAKE lever to the DOWN detent.

A failure in the automatic functions of the speed brakes is indicated by the illumination of the SPEED BRAKE DO NOT ARM light. In the event the automatic system is inoperative, the speedbrake lever must be moved manually to the UP position after landing.