Removal of the automatic undercarriage lowering system

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The following describes important changes that have been made to the undercarriage system on G-HALC. It is important that you are familiar with the new mode of operation.

(Information supplied by A. Johnson)

  • Why was the original undercarriage lowering system ripped out and bypassed?
  • What happens now on take off?
  • What happens now on landing?
  • How did the original system work?
  • Theory of Operation after modification
  • Emergency deployment

  • Q. Why was the original undercarriage lowering system ripped out and bypassed?

    What was wrong with it ? Why wasn't it repaired ?

    A. The gear refused to raise on climb out for a few worrying minutes at any speed. Maintenance test flew HALC and found the emergency extend system was not working either. Piper discourage repair of this system and actively recommend replacement with an approved retrofit kit, which is what we have done.

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    Q. What happens now on take off?

    A. There is now no minimum speed limit to raising the gear. The gear will come up and tuck away, however, the gear unsafe and the gear in transit lights will remain lit and the horn will sound until you clean up the flaps. It will be a bit disconcerting at first, but hopefully you will get used to it.

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    Q. What happens now on landing?

    A. There is a micro-switch wired into the flap selector. If flaps 10 or more is selected and the gear is up, the horn will sound, and both the gear in transit light and the gear unsafe red light will illuminate. This is supposed to be a unsubtle reminder to lower the gear.


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    Q. How did the original system work?

    A. Driven by a secondary pitot, it stopped the user from retracting the gear below approx. 85 mph on the climbout and automatically lowered the gear and sounded the horn if the airspeed decayed below approx. 105mph.

    There was also an alarm on the throttle quadrant, it made a noise if power is reduced to near idle with the gear up but did nothing else.

    The bypass lever in the centre console near the flap lever originally had a dual purpose. In its central position, it had no effect on operation of the landing gear. If raised and locked by its slide cross pin it bypassed the pitot landing gear extend/retract system. Useful for those slow climbouts when you really want the gear to retract to clean up .. at around 80-85mph. It could also be used to drop the gear in a emergency, if the normal gear down lever did not produce the desired effect.

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    HALC landing gear - Theory of Operation after modification.

    The slide across pin has been replaced with a bolt, as the bypass function is redundant. You can still lower the gear in an emergency, but you need to understand how the gear system works to be able to use it correctly

    The undercarriage system on our Arrow is hydraulically operated. On command to retract, a hydraulic pump starts to pressurise the system, the wheels come up, and when they hit their stops pressure builds towards the cut out setting on the hydraulic circuit. Once sufficient, the switch operates and cuts the motor off. Thus the gear is held up by hydraulic pressure only. The lower gear command releases the hydraulic pressure and disables the pump. The gear falls assisted by gravity and springs.

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    Emergency deployment

    The problem is that the emergency extend lever releases the hydraulic pressure mechanically, allowing fluid to return to the reservoir. If you try this in the air without disabling the pump, it will turn on once the pressure is released and try to bring the wheels back up again, and they are left part up/down. (This assumes that the gear is selected 'UP', which may be the case in an emergency or malfunction of the selector switch. If the gear is selected 'DOWN', the pump will not try to bring the gear back up) The solution is to either pull the breaker for the hydraulic pump or (Gasp!) turn off all the electrics ! This is the only way to guarantee Wheel deployment. If you turn off the electrics you will obviously lose the three green indicators.

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    This website is intended for use by the members of the G-HALC group. Any information posted on this web site is posted in good faith, but the accuracy can not be guaranteed and should not be used for airborne use.
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