Gear Motor & Light

[djarrett]

what we found. left main gear squatswitch was loose and sometimes gave indication or flickered. switch was tightened and properly positioned. the hyd pump was working properly and turning off when it reached 1500 psi and then a short cycle and turned off. When your head was lowered to attempt to hear the pump the cooling fan sounded different when you head was lower than the dash. The cost of figuring out the bugs and time and no parts, was a little over $300. the shop ate the cost for the cleaning of the cockpit and scrubing the carpet.

Thanks again

Dave Jarrett

[Learjetter]

Gang,

Ran across a neat blurb in a Cessna Pilot Assn Tech Note (#337-T02) that relates to this issue. The Tech Note advises installation of a "HYD WARN" or "HYD PACK ON" annunciator.

Here is a summary of the relevant text:

Adding a gear motor running warning light, your option

The addition of a warning light connected to the control coil circuit of the gear motor contactor can help in determining proper gear operation. This light is connected in parallel with the contactor and would be on whenever the closing coil of the contactor was energized. With the high noise levels in the cabin and the invention of noise canceling headsets, it is difficult to hear the powerpack running.

The normal gear retraction cycle takes 12 to 16 seconds and gear extension cycle 10 to 14 seconds. Timing the light on and off cycles can check these times. The normal cycling of the gear motor in flight that occurs once every 20 minutes would cause the light to come on momentarily. This event
is usually observed by the pilot as a flash of the discharge light or a negative short time duration pulse in the ammeter. The pump motor contactor can fail to close preventing power to be directed to the pump motor. The warning
light on and no gear movement would indicate this condition. A failed pump motor or open circuit breaker would give the same indication. A failure in the gear down switch circuit, a faulty switch, or broken wire, will stop the gear
system from completing the cycle. The gear will be down, the doors will not close, the green light will be off, and the pump will continue to run. In this example, the pilot would be alerted to a problem with the absence of the green light and the warning light staying on past the normal 10 to 14
seconds. Pulling the 30-amp breaker can shut off the pump motor and a landing with the doors open can be made. A little troubleshooting and repair and gear function should be normal again. This light is not a cure all but can help in determining the difference between a problem or just normal operation.

The part number for the light is MS 25041-4; this is the same light as the amber gear up light installed in the aircraft now. It is available from Aircraft Spruce & Specialty Co. www.aircraft-spruce.com (800-824-1930), (877-477-7823), (fax 714-870-7551), and sells for about $26 ($45 in 2021).

The bulb is the standard GE-327 lamp used for all the post lights. This light has the press-to-test feature so it can be checked any time to be sure the lamp is not burned out. The light should be installed where it can be seen easily and not buried down by the powerpack in the lower quadrant. A
placard with the lettering, HYD WARN, or some other similar worded statement should work. The wire size should be 20 gage, which is the same as all the other indicator light circuits, and connections made as per AC 43.13-1A. Pin 2 on the light connects to the small closing coil terminal on
the power pack contactor, and pin 3 on the light connects to the gear indicator 5-amp circuit breaker for the test circuit. Pin 1 of the light connects to a good ground point. The current draw of the lamp is .04 amperes, which has no effect on the charging system total load. This installation would
be considered a minor alteration and weight and balance change negligible. An entry in the aircraft logbooks by an appropriately rated mechanic would return the aircraft to service. Check with your mechanic to get his feeling on the light installation.

We installed a blue annunciator light in my aircraft just under the cowl flap switches and left of the gear down light. Works as advertised.

[kbecker]

I had this HYD WARN light installed a couple of years ago. I have a copy of the 337 form we filed with the FAA if anyone would like a copy. It works as advertised. 1977G

Kevin