From: "Sven Jerlhagen" <svenjerlhagen@home.com>
To: <lancair.list@olsusa.com>
Subject: RE: LNC2 GEAR UP
Date: Mon, 30 Jul 2001 23:49:53 -0700
Message-ID: <ENEBKFGHGAOIHPPGCCBFAEJBCBAA.svenjerlhagen@home.com>
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A friend had this happen to his 360: On final one of the greens suddenly
went out, and then on again. He made a go around, and after some thinking
pulled the gear circuit breaker to deactivate the electrics, made sure there
was 3 greens, and landed. Unfortunately, while he was taxiing in, he
reactivated the circuit breaker and the gear retracted. The problem was that
the gear up circuit was connected to a warning horn, which was also
connected (via a separate input) to the header fuel low switch. When the
header fuel low horn activated when dipping the nose on final there was a
creep current through the horn activating the gear up circuit for short
moments. Do you have anything else connected to the gear up circuit ?

So a short to +12V definitely will cause the gear to go up. The way the
hydraulic system is built, the fluid is released to the tank via a pressure
valve, so there will be a pressure generated in the down side by the
retracting cylinders. This is possibly enough to open the down pressure
switch.

Since the squat switch closes as you slow through 95 mph, a short will
activate the gear up circuit at a time when the pilot is concentrated on
final approach, or initiating flare, and certainly not checking the green
lights. Increasing this to 110 mph would visualize a problem while you were
looking at the lights, but would not allow you to retract during a Vy climb
after start, if you ever need that, so I think the squat switch should not
be changed.

Another possibility is of course the mouse, or vibration abrasion.

I wired the gear warning circuit of my 320 by connecting the NC terminal of
all 3 gear microswitches together, and via a flap position switch to the
gear warning horn. This way I will get an audible indication if any gear
momentarily becomes unsafe.

Something else to consider is the orientation of the relays, even if this
shouldn't be the problem here. Sometimes the spring breaks, so they should
be mounted to give the desired function in this case, i.e. main on, starter
off, gear relays off. This can also happen when you fly into turbulence, you
can get a couple positive G that will overpower the spring, and you don't
want this to power on your starter!

Sven Jerlhagen
LNC2 SE-XOP

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