Warning and Protection systems
The landing gear incorporateds a ground based failsafe system to prevent inadvertent 'up' selection of the landing gear whilst the aircraft is on the ground.
The GEAR switch is wired through the left hand squat switch mounted on the left landing gear leg which prevents the GEAR switch from working whilst on the ground.
The left MLG squat switch
Once the aircraft becomes airborne and the weight is off the wheels, the squat switch will allow power from the GEAR switch to activate the gear control valve and the bypass valve for correct function of the landing gear system.
This safety feature cannot be overridden. If electrical power is lost the gear cannot be retracted.
The table below shows the function of both the left hand and right hand squat switches during operation of the aircraft:
A landing gear warning horn is provided and is used to indicate aurally to the pilot of an abnormal condition.
The warning horn is controlled by the power levers and/or the flap selector and will sound intermittently when either:
- The gear is not down and locked and either power lever is retarded below approx 1/8 inch from the flight idle detent, or
- The landing gear is not down and locked and the flap selector is positioned beyond the APPR position.
The warning horn can be silenced by pressing the HORN DISABLE button on the gear control panel except when the flaps are selected beyond the APPR setting with the gear not down and locked.
The horn will be reset once the power levers are advanced further than 1/8 inch forward of the flight idle detent after being silenced by the HORN DISABLE button.
The HORN DISABLE button
The horn will also sound if the landing gear switch is positioned to the UP position with the aircraft on the ground.
Note: This should not be attempted on the ground and is not part of the preflight walk around procedure.
The warning horn can be tested prior to flight by pressing and holding the PRESS TO TEST button on the annunciator panel with the battery switches on.
Retard the power levers individually to the flight idle detent and then forward of the 1/8 inch position again to ensure that both power lever switches are working correctly.
The flap selector switch will also activate the horn whilst holding the PRESS TO TEST button by lowering the flap selector beyond the APPR flap setting.
Correct function of the landing gear warning horn is a safety item and must be checked prior to flight.
PRESS TO TEST button located on the annunciator panel