Question about ground spoilers and a bounced landing

[Searider]

Sinbad1,

Just a question from an curious bystander.

When the Ground Spoilers are automaticaly deployed with main gear compression, do they stay deployed or in the event of a bounce, do they also automatically retract when the load is taken off of the main gear ?

[Sinbad1]

:ok:
Dear Searider
Your Question below;
When the Ground Spoilers are automatically deployed with main gear compression, do they stay deployed or in the event of a bounce, do they also automatically retract when the load is taken off of the main gear ?

To answer your question you need to understand the basic layout of the system. It is not just the compression of the switch on the R/H leg torsion link, there are other inputs needed to complete the circuit.

The necessary sequence for proper automatic speed brake operation is as follows:
Airplane landed with speed brake control lever in ARMED position.If, with the airplane in air, the speed brake control lever is placed in the ARMED position and then returned to the DOWN position,and the airplane is then landed in this condition (without speed brakes, such as the airplane being used for pilot training and doing touch and go landings), the spoilers will deploy upon the next arming on the ground. Also if thrust reverse is used the spoilers will drive to the up position. The speed brakes will automatically extend during a refused takeoff (RTO) when the thrust levers are moved to idle position and the reverse thrust levers are moved to reverse thrust position, with wheel speed greater than 60 knots.
The system in simple way;
A ground spoiler interlock valve is installed in the hydraulic line between the up ports of the ground spoiler actuators and the ground spoiler control valve. The interlock valve is operated by a push-pull cable from the right main gear upper torsion link. With the airplane airborne, the shock strut is extended and the upper torsion link positions the push-pull cable to close the valve. When the airplane touches down, the shock strut is compressed and the push-pull cable opens the valve to actuate the ground spoilers.
When the main gear wheels begin rotation at touchdown, the (speed brake actuator) positioned under the speed brake lever will move the speed brake control lever to full up position raising the ground and flight spoilers.

If either engine thrust lever is positioned 25 degrees forward from engine idle position, the actuator will move the speed brake control lever into the DOWN detent, lowering the ground and flight spoilers. Indicator lights are provided on the centre instrument panel to verify that the system is properly armed.

The ground spoilers have two positions, fully retracted or fully raised.The fully raised position for all the ground spoilers
to blow down at critical speed. Protection against actuator damage due to thermal expansion of entrapped hydraulic fluid or extreme "up" loads from the flaps is provided by a thermal relief valve and relief check valve.

During a refused takeoff (RTO), application of the reverse thrust levers mechanically lifts the speed brake lever out of the down and locked detent.
With the landing gear in the extended position, the hydraulic pressure remains blocked until the airplane touches the ground and the right main landing gear shock strut is compressed.

As the shock strut inner cylinder is compressed, the upper torsion link moves the push-pull cable to open the interlock valve. The interlock valve then connects hydraulic pressure from the ground spoiler control valve with the up ports of the ground spoiler actuators.

On the ground, the speed brake lever may be rotated aft to the UP position. In this configuration, all the ground spoilers will be raised 60 degrees and all the flight spoilers will be raised 40 degrees.

The speed brake lever actuator will drive the control lever full aft to the UP position when the correct combination of main landing gear wheels rotate at a speed greater than 60 knots or when the right main gear strut is compressed and air sensing switch and ground sensing switch are both in ground mode.



I hope the above is satisfactory:ok:

[Searider]

Very satisfactory !

Thanks.

[Porrohman]

Craig - many thanks for your feedback. I now have a better understanding of these matters.

Thanks also to others who have explained detailed technical aspects about the flaps, spoilers, nose undercarriage and hydraulics systems on the 737-400.

Thanks to PK for providing lots of local knowledge and feedback. I have read many of your posts in recent months with much interest.

In relation to this accident, a picture is building up but there are, unsurprisingly, more questions than answers at this stage; some technical and some human factors. I expect that corporate, commercial, training, regulatory, procedural and other matters will also come under scrutiny.

Something that disturbs me in relation to this accident is that lots of people are being too hasty to blame the aircrew, who at this time are still probably in a state of shock and trying to understand what happened. With the benefit of 20/20 hindsight, I expect the aircrew will be asking themselves what would have happened if they had done x or hadn't done y. That's human nature. We all do it.

Feelings of guilt are unsurprising. By way of an example, the crew of the United Airlines DC-10 that crashed at Sioux City were proved to be heroes but that's not how they felt. So, the fact that the Garuda crew may have expressed remorse or guilt proves absolutely nothing. I'm still inclined to believe they acted professionally throughout. I'm also inclined to believe that each decision they took was made with the best of intentions based on the information that they had available to them at the time and based upon their training, procedures etc. Some of those decisions doubtless had to be made in a split second.

I find it disappointing that so many people have been critical of the aircrew when the full facts are yet to be established. In the fullness of time the aircrew may be fully exonerated and hailed as heroes for averting what could have been a much worse tragedy.

As with most accidents, I expect this one will have been caused by a multitude of factors all coming together at the same time. Those pointing the finger of guilt at the aircrew should remember that they are innocent until proven guilty, not the other way around.

Porrohman.

[Sinbad1]

:ok: Dear porrohman,

I could not have said it better my self. 100% right in every word you have writen.
Well Done