A system specific to the Gulfstream IV/V aircraft series, the nutcracker switch is located aft of the thrust levers in the cockpit.
The primary function of the Gulfstream nutcracker system is to verify the spoiler deployment mode in which the aircraft is configured to.
Upon extension of the landing gear on approach, the flight crew will press the nutcracker switch. Upon pressing the nutcracker switch, 2 possible indications will illuminate; AIR/AIRBORNE or GROUND mode.
These illuminations will consist of Left and Right (L AND R) indications, one for each set of the main landing gear.
AIRBORNE Mode = spoilers are not configured to extend at IDLE thrust
GROUND Mode = spoilers will deploy automatically upon selection of IDLE thrust
On approach when the landing gear is selected to the DOWN position, the correct, safe indication given on the nutcracker switch will be AIR Mode, in which spoilers will not be deployed if idle thrust is selected prior to landing.
The reason for testing this system prior to landing is for safety purposes, in which GROUND mode while the aircraft is still airborne will lead to full spoiler deployment upon selection of IDLE thrust.
Such an incident occurred in 2002 at KTEB, in which a Gulfstream V was substantially damaged beyond repair. The investigation findings conclude that the nutcracker system was in GROUND mode prior to touchdown, resulting in premature spoiler deployment at approximately 50 feet Above Ground Level (AGL).
This resulted in the aircraft experiencing a hard landing resulting in major structural damage to the landing gear, wings, and undercarriage portion of the fuselage. A full, detailed report can be read here.
The nutcracker system works in conjunction with the WOW landing gear system to determine whether or not spoilers should be deployed. The WOW system, also known as the Weight on Wheels system determines when the aircraft’s landing gear is locked down and in contact with the ground.
The WOW system consists of electrical switches attached to the main landing gear, in which indications of GROUND or AIR status of the aircraft are determined by the compressed or uncompressed status of the switch.
Upon the main landing gear making contact with the ground on landing, the WOW system will communicate with the nutcracker system in order to transition from AIR mode to GROUND mode, in which spoilers will now be deployed upon idle thrust selection.
The automatic deployment of spoilers/speedbrakes upon touchdown will be activated once spoilers have been selected to ARMED mode on the speed brake control panel of the aircraft.
Arming of the spoilers with automatic deployment upon touchdown assists in decelerating the aircraft, along with reverse thrust and the braking system.
The automatic deployment of the speed brakes ensures aircraft deceleration commences promptly upon landing.
The operator’s checklists will provide detail of these procedures.
In newer model Gulfstream aircraft (G550/G650), the nutcracker system has been integrated as part of the WOW system.
This integration has eliminated the requirement for the nutcracker switch and system as an independent unit.