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Here is what I know at this time regarding my accident with N15EG at the La
Junta, CO airport, LHX.
The evidence strongly suggest that the gear up circuit must have activated
on final AFTER my GUMP check and the wheels are partially retracted when we
touch down. The following are the facts pertinent to the accident.
FACTS:
1.-The runway markings, gear door damage and lack of damage to the gear
leave little doubt that the gear was moving up at the time of touchdown. The
inboard main gear doors suffered the most damage and are the last to
retract, when the gear opens a sequence valve.
2.-There is little or no damage to the gear. The gear came down, as it
should when the hydraulic pressure dump valve was operated while held by the
crane used to lift the plane from the trailer.
3.-Before lifting the plane from the trailer, I turned on the master
switch, to remove gasoline from the wing tanks using the pumps and forgot to
pull the gear circuit breaker. The battery drain was excessive, so I decided
to disconnect the battery terminals. In doing so I found that the UP RELAY
was very hot to the touch even though the gear switch was in the down
position.
4.-The airspeed squat switch and the gear switch in the down position
should have prevented any power going to the UP RELAY. The hydraulic motor
was not running at this time, but may have been shut off by the pressure
switch?!
5.-With the plane on jacks and the inboard gear doors removed, gear
retraction tests were run many times. Operation was normal!
6.-The airspeed squat switch had to be bypassed to allow these tests.
7.-The gear, flap, starter, and power wiring passes between the seats and
is tie wrapped to the hydraulic lines on the fuselage floor.
8. A pile of chewed up paper towel was found in this console on the floor
and around the wiring, (obviously a start of a mouse nest). The wiring will
have to be pulled to determine if a short occurred at this point.
9.-Full gear up requires 8.6 sec. The gear was only partially retracted.
10.-Using 7 seconds from activation and a descent rate of 300 to 600 ft/min
results in a height above the runway of 35 to 70 feet at activation of gear
up.
11.-At an average airspeed of 80 mph for 7 seconds the plane traveled 830
ft. after initiation of the gear up, placing the plane well over the
runway. Actual touchdown was 1800 ft from the East end of the runway. (The
first 1000' of runway 26 is decidedly uphill and I intended to land past
this rise). The runway length is 6852 ft.
12.-Difficulty with the relays has been previously reported. However, no
accidents were caused by the reported failures.
INITIAL CONCLUSIONS.
1.-At this point in landing, this pilot is certainly not touching anything
except the throttle, stick and rudders and is completely focused on the
runway. Additionally the airspeed squat switch would have prevented an
inadvertent operation of the gear up. It requires 95+ mph to raise the gear.
2.-An electrical failure in either the wiring or the relays caused the gear
to retract at a very unfortunate time. Possibly initiated by changes in
vibrations from the engine or flaps.
3.-More investigation will require removal of all of the wiring under the
center console, disassembly of the relays, and possibly some testing of the
hydraulic motor. This will be done.
QUESTIONS TO BE ANSWERED:
1.-Can the up gear cycle be initiated by any short from a 12v line to the
up relay?
2.-Will the gear down relay pressure switch stay open due to pressure from
the movement of the hydraulic cylinders? Thus allowing the gear up cycle to
continue.
3.-What happens if current is supplied to both windings of the hydraulic
motor. I had thought that this motor would be reversed by reversing
polarity, but that doesn't seem to be the case since they have a common
ground and both leads have the same resistance to ground.
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LML website: http://www.olsusa.com/mkaye/maillist.html
LML Builders' Bookstore: http://www.buildersbooks.com/lancair
Please send your photos and drawings to marvkaye@olsusa.com.
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