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' retracted, a warning horn sounds to alert the pilot that the gear is retracted. If installed
' a CHECK GEAR caution is indicated on the PFD additionally. The same warning appears if the flaps move into position LDG (fully extended) while the gear is retracted.
Page 7 - 14 Rev. 5 15-Nov-2007 Doc. No. 7.01.05-E
To test the gear warning system (refer to 4A.6.1 - PRE-FLIGHT INSPECTION) push the test button close by the gear selector switch. The aural gear alert should appear.
CAUTION
If the aural alert does not appear, an unscheduled maintenance is necessary.
To prevent inadvertent gear retraction on ground, an electric squat switch prevents the hydraulic valve from switching if the master switch is on and the gear extension switch is placed in the “UP” position.
After take-off, the gear should be retracted before an airspeed of 156 KIAS is exceeded. The landing gear may be extended at any speed up to194 KIAS.
The landing gear is designed to be manually operated in the event of failure. Since the gear is held in the retracted position by hydraulic pressure, gravity will allow the gear to extend if the system fails for any reason. To extend and lock the gears in the event of failure, it is only necessary to relieve the hydraulic pressure by means of the emergency gear extension lever, which is located under the instrument panel to the left of the center console. Pulling this lever releases the hydraulic pressure and allows the gear to fall free. Before pulling the emergency gear extension lever, place the gear selector switch in the “DOWN” position.
NOTE
If the emergency gear extension has been pulled due to an emergency, the system has to be checked before pushing the lever in again.
The nose gear is steerable by the use of full rudder pedal travel. A gear damping element, incorporated in the nose gear steering system, prevents shimmy tendencies. When the gear is retracted, the nose wheel centers as it enters the wheel well, and the steering linkage disengages to reduce pedal loads in flight.
Hydraulic gear extension system schematic
The main landing gear of the DA 42 is extended with three hydraulic cylinders. The following schematic figures show the system conditions for each operating mode.
In figure 1 the extension of the landing gear is shown. To reduce the amount of pumped hydraulic fluid during this operation, the return flow is partly led into the feeding flow of
the system.
The figure below shows the system status when the landing gear is extended. All hydraulic cylinders are under high pressure.
The operating mode for the retraction of the landing gear is shown in the next figure. While energizing the right hydraulic valve, the fluid flow in the hydraulic system is started due to different piston areas of the landing gear cylinders although the pressure on both sides of the system is equal.
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本文链接地址：钻石40系列飞机维护手册 DA 40 SERIES AIRPLANE MAINTENANCE MANUAL 4(17)
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