sellener

Im just starting some complex training in a 172RG and am studying the hydraulic system for the gear.

My question in short is simply..... With the master switch on with the aircraft on the ground (gear down) what would the gear indicator lights indicate if their was no hydraulic fluid in the system.

sellener

would it be correct to say.... that after hydraulic pressure is used to lower the gear and actuate the downlocks, which would illuminate the gear down light, a complete loss of hydraulic pressure would have no effect on the gear down indicator light.

etflies

I should think so, reading the hydraulic system description for the 172RG it says a series of electrical switches will illuminate one of the indicator lights after the gear reaches the selected position, so I would imagine they are lit by gear position, not by hyd. pressure.

Tail Dragger

You will still see 3 in the green, the lights are activated by the down locks swinging into place and have no conection to the hydraulic fluid. as stated above

elcidflyer04

On the horrible 172rgs i instructed in there was only one green light and not three. What actived the green light was a squat switch on the nose gear. I think thats how it worked but that was a while ago.

nyalex

I will throw in my .02. Once the 3 gear down switches are activated, you get one green light. However, if you were to lose your hydraulic fluid, I think the red unsafe light would come on as well, so both are illuminated. Last week in a 172rg we had the gear down and I pulled the circuit breaker. I then had my student pull the handle to the up position. This released all of the hydraulic pressure in the down line, but because the power pack was un-powered, it did not move the gear. We had both a green and red light. We then put the handle back in the down position and put the breaker in, the motor kicked on for 1/2 a second, and the red light went off. I think this means the pressure switch in the power pack has to be "tripped" as well as all 3 down and locked to turn off the red light. Same thing happens when you hand pump down, there is a short period of time when both lights are on, until you get enough pressure in the system to trip the pressure switch. If you lose hydraulic fluid then obviously there is no pressure in the line, pressure switch isn't activated, and you have both lights on. That is my take, discuss.....

shdw

Right, one light for gear down, wrong with the squat switch part. If the squat switch in the nose caused the light to light up how could you ever get it lit in the air?

A squat switch is nothing more than a switch on the ground which prevents you from retracting the gear, I believe it is in the nose in the RG but don't recall for sure. When your on the ground the circuit is open and thus will not allow the electrical signal to reach the pump, once airborne it is closed and will allow retraction.



For the OP, as others posted, the light is activated by multiple electrical "limit switch" whose circuit is open (light off) when the gear is up or down the circuit is closed (light on). For the RG there is an amber light with its own limit switch indicating up and a green light with a separate switch to indicate gear down.

As for there being switches in each gear, I do not believe that is true. I think all three: up limit switch, down limit switch, and squat switch, are located in the nose. However, without the electrical schematic on hand and no documentation in the POH, I do not remember and therefore cannot verify that.

What I can tell you is there is absolutely no tie to hydraulic pressure and the electrical switches/gear lights in the RG. There will be no way for you to know of a hydraulic leak until you attempt to put the gear up and get nothing or visually see it during preflight. You can check it from inside by the rudder pedals on the pilots side during your preflight.

FlyingPirate

pretty much says it all.

In my experience flying a 210, which has an almost identical system as the 172RG, It is extremely important to look out your window to verify the gear is indeed DOW ALL THE WAY. I have had numerous times when I extended the gear lever to the down position, hydralic pump came on, gear came down, green light illuminated, and hydralic power pack turned off. I look out my window and realize the gear is only partially extended. Double check it everytime!

sellener

my original question stems from my preflight of the RG with an instructor who does not check hydraulic fluid level on preflight. It made me curious if their was any electrical indicator of a hydraulic loss?

It would seem to me that hydraulic fluid level would be an important check? But the POH says to check it every 25 hours or something like that.

In regards to whether or not the nose gear switch lights the green light or whether a combination of nose gear, and main gear switches light the green light, it appears that their are are three switches that need to be traversed by current to light the switch in the electrical schematic.

I am not familiar with reading schematic diagrams but there does appear to be three switches (L main Gear, R main Gear, and Nose gear) depicted on the diagram. This is coming not from the POH but from a 1980 CutlassRG Infromation Manual given out by the instructor (it is a 1980 cutlass we are flying)

When questioning my instructor however, he stated the green light only indicates the nose gear is down and locked?

I have to explain the hydraulic system to him next lesson so I guess we'll find out, but Id have to say based on the information Im looking at the mains and the nose have to be down and locked for the single green indicator to come on.

I do understand the importance of visually checking always.

mmaviator

i remember the poh saying check the hydraulic fluid every 25. what harm would it be to check it everytime? i checked it everytime and one of the main spots to see a fluid leak is on the main gear along the bottom of the strut(dont quote me heard from my instructor). had a dpe tell me that you should have a cane when you fly this aircraft..........cause you can reach out of the window and pull the gear down with 'hook' part of the cane.

what was you question again .