LOW FUEL L-R warning light

[unicom]

Just two questions for clarification:

1. When the procedure calls for an adjustment of the pots where "low fuel" lamps turn on for left and right tanks... Should I understand that the procedure is mentioning some kind of potentiometer located on the annunciator assembly ?

2. The procedure curiously does not ask the aircraft to be positioned in level flight. Is it because it does not matter much ?

Thanks for your feedback  !!!

 

 

[carusoam]

Good questions...

The Maintenace Manual details the annunciator panel.  It has some complexity.

there is no 'legal' level that is being defined by the low level light...  If you have two lights on, it pretty much means land immediately....

Using a fuel totalizer is pretty much the reliable mechanism pilots use to avoid running out of fuel.  The lights are a safety when the totalizer has not worked...

On the ground, Mooneys are pointed skywards.

on short final, fuel runs away from the pick-up. It will be many seconds before FF is reestablished after switching tanks...

i am just a PP, not a mechanic.

Best regards,

-a-

[unicom]

On 13 octobre 2014 at 2:46 PM, turbotrk said:

This is what is in the POH. Warning light is connected to televel, so not really reliable on my advise.

As I stated before it says that light comes on when there is less than 2-1/2 , 3 gallon of usable fuel in the respective tanks.

Fuel flow is adjustable as I have a Shadin Miniflow L and I can change it with any K factor but at the moment 85000 in accordance with the STC seems to be working pretty well.

Hi Turbotrk

The note on the attached extract of your POH is quite interesting. I checked thoroughly the POH of my 1980 M20J (manual number 1223) and there is no such note ?!?

Your annunciator panel might be a different version. Would you have a picture by chance ?

Cheers,

 

Philippe

 

 

[turbotrk]

Just now, unicom said:

Hi Turbotrk

The note on the attached extract of your POH is quite interesting. I checked thoroughly the POH of my 1980 M20J (manual number 1223) and there is no such note ?!?

Your annunciator panel might be a different version. Would you have a picture by chance ?

Cheers,

 

Philippe

 

 

Hi, the note is not from the POH but from the Maintenance Manual.

[unicom]

I had the opportunity today to conduct a few more tests regarding the - Low Fuel - on the annunciator panel. As my left reservoir was empty to start with, I was curious to understand the logic behind the low fuel warning light.

Battery ON: NO low fuel steady light on the annunciator panel despite a completely empty left wing ???

After holding the annunciator panel test button for a few seconds, the light finally comes ON since the low fuel warning circuit is now activated (thanks again turbotrk for pointing the maintenance Manual on that matter)

If you lift momentarily the floating mechanism in the tank (as if there is more fuel), the lamp extinguishes which is very logical...BUT now, release the floating mechanism and the low fuel warning light will not illuminate automatically...unless you hold again the annunciator test button a few seconds !!!

This situation could arise if you encounter turbulence with low fuel in a tank.

Anyway, I am very surprised that the M20J  POH (v.1223) does not clearly state that holding the test button for a few seconds on the annunciator panel is of paramount importance to activate the low fuel warning light.

Never to late to learn and mooneyspace is definitely a good place to get the right feedback from people with knowledge and experience 

 

Edited January 4, 2016 by unicom

[carusoam]

That sounds like the low level warning is inop unless somebody remembers to test the annunciator panel.

That would typically get a warning decal to remind everyone to test it or it will not work...

An example of this type of decal is for the stall warning horn.  It will not work when the master is shut off for emergency landings...

These details get harder to remember under the stress that is present when you need the system to work.

Best regards,

-a-

[ArtVandelay]

I can't believe that's the way it's supposed to work.

Did you do this test in bright daylight?

It's possible your dim switch,function is broken and on causing the low fuel lights to be on, see POH page 7-23

The test light is just resetting it to full brightness, see service manual page

24-39-05; Q3-Q5 or U2 is defective. unfortunately I don't know anyone who has a schematic, see service instruction SI M20-74 for a partial one.

[unicom]

On 4 janvier 2016 at 11:18 AM, teejayevans said:

 

I can't believe that's the way it's supposed to work.

Did you do this test in bright daylight?

It's possible your dim switch,function is broken and on causing the low fuel lights to be on, see POH page 7-23

The test light is just resetting it to full brightness, see service manual page

24-39-05; Q3-Q5 or U2 is defective. unfortunately I don't know anyone who has a schematic, see service instruction SI M20-74 for a partial one.

As surprising as it is, the maintenance manual leaves very little doubt (see below).

I did the test in a hangar...so it was rather dark.

Now, the POH clearly states in the Before Take Off Check List:

CHECK WITH PRESS TO TEST & THROTTLE RETARDED (no time reference)

However, I would be quite interested to get the feedback from J owners who actually got the Low Fuel warning in flight, and how many of them were aware of the procedure below.

 

[carusoam]

Wow...  That detail is something that may be forgotten after a few days...

Thanks for refreshing the memory,

-a-

[CaptainRon]

Hi Mooniacs, would point out the maintenance manual on the m20J talks about calibrating the low fuel level annunciator when replaced. It's under WARNING CIRCUITS. And thanks for sharing about the test button, will check my POH.

[Will.iam]

I think y’all are reading the low fuel press-to-test note wrong. The note is saying when testing you need to press and hold the test button for 2-3 seconds before the low fuel light will come on, not that you need to test it before it will work to show you when you are low on fuel. I base this on the fact i have a 252 TSE and when i press the test switch my low fuel lights do not immediately come on they are out until 2 to 3 seconds pass and then come on. Plus i have ran a tank down and the light came on and i had not press to test at anytime before or during the flight and the system still worked. 
i think the OP of this thread instead of wanting to know how much fuel he had when the light is on, i think the more pressing question would be how many mins left before the engine quits! 
mine at 5500ft 10d above standard temp flying level at 7.1 fuel flow LOP i got 32 mins from the time the low light came on until the engine quit. Fuel totalizer showed 3.9 gallons consumed.