How much do you trust sight gauges?

Discussion in 'Hangar Talk' started by asicer, Feb 8, 2019.

  1. asicer

    asicer En-Route

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    You are on your way home VFR on a CAVU day in an airplane (single engine land) equipped with marked sight gauges. 15 minutes out, your timer expires indicating that you hit your fuel reserves. However, your sight gauges are showing about 20 minutes of fuel remaining plus reserves. You tip the wings/nose and verify the readings against the AI. There is an airport directly below you, another halfway home and a straight non-busy freeway connecting them all.

    Do you press on? Or do you divert?

    EDIT: My answer is in post #63
    https://www.pilotsofamerica.com/com...trust-sight-gauges.116775/page-2#post-2679962
     
    Last edited: Feb 14, 2019
  2. Dave Arata

    Dave Arata Pre-Flight

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    Divert! I trust my watch far more than I would the fuel gauges. Especially with an airport directly below. What's the old joke, the only time you can have too much fuel is when you're on fire? I'm a BIG fan of having more than necessary.
     
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  3. Ryanb

    Ryanb Final Approach PoA Supporter

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    I go by time elapsed and nothing else.

    36 gals useable @ 8 gals/hr

    I theoretically have 4.5hrs endurance, but I’ll throw on my own conservatism and say 4hrs and I’m finding an airport to refuel. In this case, I’d divert.
     
  4. falconkidding

    falconkidding Line Up and Wait

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    Sight gauges I'd trust and continue. Regular cessna style gauges everything is based on time.
     
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  5. idahoflier

    idahoflier Pre-takeoff checklist

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    I think to answer your question you need to tell us what our AGL altitude is...
     
  6. asicer

    asicer En-Route

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    Isn't your timer ultimately based on a reading you got from when you sticked the tanks? How is a graduated sight gauge different from a pipette? (Assuming smooth air and unaccelerated straight and level flight)
     
  7. Ryanb

    Ryanb Final Approach PoA Supporter

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    I can’t answer that because I don’t fly anything with sight gauges, but I suppose it would be the same readout bearing you have smooth air.
     
  8. asicer

    asicer En-Route

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    At what altitude would you choose not to divert? :)
     
  9. JOhnH

    JOhnH Touchdown! Greaser! PoA Supporter

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    I will believe whichever one gives me the worst case scenario. I am not sure exactly how the sight glass works, but I'd hate to run my tanks dry while a plugged up sight glass still has some fuel in it.
     
  10. cgrab

    cgrab Pattern Altitude

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    Sight gauges are the most accurate form of fuel gauge (assuming they were installed and marked properly) so I would go with the sight gauge. That said, my plane has Cessna gauges so I dip the tanks, write down what is in each tank on my knee board and calculate when I will have 10 gal in my tank flying at 7.5 gal/hr. I start the clock at engine start and keep an eye on the time in my tanks. When I have 10 gal I will land at an airport with fuel.
     
  11. MooneyDriver78

    MooneyDriver78 Pattern Altitude

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    15 vs 20 minutes?
    I’d assume it’s 15 or less. But I always flight plan for 90 minutes of fuel reserves.
    I don’t trust any fuel gauges to that accuracy.

    Tom
     
  12. Skip Miller

    Skip Miller En-Route

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    In order of decreasing reliability:

    1) most reliable: stick the tanks before takeoff and start the timer on takeoff.
    2) sight gauge - glass tube with fuel visible in a calibrated tube.
    3) mechanical float type gauge such as used on the PA-32-301.
    4) 40 year old POS factory electric gauges.

    -Skip
     
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  13. Heftiger

    Heftiger Pre-takeoff checklist

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    What’s your reserve? If you planned an IFR reserve but everything turned out VFR, then you have plenty of reserve.
     
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  14. Tantalum

    Tantalum En-Route

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    a safe bet is to always go with whatever is giving you the lower indication, if that's the sight gauge then go with that, or if that's your calculation then go with that

    With fuel exhaustion being one of the main causes of forced landings and such an easy thing to fix this is the safest bet
     
  15. dtuuri

    dtuuri En-Route

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    What if you sprung a leak?
     
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  16. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

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    On a plane that I don't know and haven't been flying in much, I take the most conservative measure.

    If I know the plane and have learned how accurate the sight gauges are vs. my (conservative) time estimates, then I might trust the sight gauges. After a while you can develop pretty accurate time estimate of fuel burn on a piston, though.
     
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  17. Skip Miller

    Skip Miller En-Route

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    VFR pilot here. Reserve time varies based on location, hard minimum 45 minutes. I just don't push it. -Skip
     
  18. James331

    James331 Touchdown! Greaser!

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    I trust the one that gives me the lowest indication.
     
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  19. Stewartb

    Stewartb Final Approach

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    Who's sight gauges? I have some in my Cub that I don't trust at all when they get low. I use sight gauges to validate other indicators, like what my expected burn is based on time. Sight gauges aren't perfect.
     
  20. Tom-D

    Tom-D Taxi to Parking PoA Supporter

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    When you are worried about fuel levels stop and get more. ( it doesn't matter which type of gauge you have) That's a lot easier than dealing with the State police, FAA, NTSB. and another group that will have questions
     
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  21. IK04

    IK04 Pre-takeoff checklist

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    If you are within five minutes of your estimated fuel range and you still have a 30 minute reserve, why would you not continue?

    That's the purpose of fuel reserves. You may land with very little fuel in your tanks with no drama as long as you planned for contingency and carried that extra fuel to ensure an arrival with a safe margin.

    Some pilots have been trained to never use their planning reserve. Plans don't always work out, though...
     
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  22. Tom-D

    Tom-D Taxi to Parking PoA Supporter

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    And when you get to your destination and the runway is closed, then what?
     
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  23. IK04

    IK04 Pre-takeoff checklist

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    That would be an example of inadequate preflight planning.
     
  24. Huckster79

    Huckster79 Pre-takeoff checklist

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    Airport below me? Land... Whats the time penalty in landing? You'll need gas at home so you can't count the fill up time. Just the extra time to do the pattern, land, taxi and reverse it. That is a small small time penalty to pay vs being in a field or short final or anywhere but terra firma when they run dry. I don't want to be a statistic. If there wasn't an aiport right below me, then that is what your reserve is for. But I would never use my reserve a single drop if I have another option, those reserves are there if you don't have another option... Just my theology of it...
     
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  25. idahoflier

    idahoflier Pre-takeoff checklist

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    I re-read your question and I misinterpreted it the first time. With the scenario given I would stop and get fuel because something isn't right. Better to figure it out on the ground...
     
  26. DaleB

    DaleB En-Route

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    Or something else happened to close a runway after you departed. Gear-up landing, whatever.
     
  27. Huckster79

    Huckster79 Pre-takeoff checklist

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    I try to be an optimist in all of my life, but when I get to the airport I try to become a pessimist...
     
  28. Tom-D

    Tom-D Taxi to Parking PoA Supporter

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    Runway close in a moments notice.. that aircraft 2 minutes ahead of you blew a tire/crashed, and you can't land.

    Now what?
     
  29. Tom-D

    Tom-D Taxi to Parking PoA Supporter

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    Oh how I wish I could tell what's 5 minutes ahead of me.
     
  30. lancie00

    lancie00 Pre-takeoff checklist

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    Land, get fuel, continue your day. I consider my reserves emergency fuel. I would NEVER use reserves for convenience. Besides, that wouldn't make the news. Land 100' short with dry tanks and you'll be on the cover of every newspaper and the lead story at 6:00 and 10:00. "Local firefighters called to the scene to save inept pilot that refused to purchase fuel! Life threatening flight completed without a flight plan!"
     
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  31. MooneyDriver78

    MooneyDriver78 Pattern Altitude

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    If I have a Cirrus, put the chute and land as normal ;-)


    Tom
     
  32. wanttaja

    wanttaja En-Route

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    The sight gauge on my airplane is a metal rod sticking up through the fuel cap with a cork at the bottom.
    It actually tends to stick; the slipstream will pin the rod to the tube until the gas level goes down low enough that the weight overcomes the friction.
    [​IMG]
    So I tend to go more by the clock.....

    Ron Wanttaja
     
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  33. Tom-D

    Tom-D Taxi to Parking PoA Supporter

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    then it becomes a question is it cheaper to gas up or re-pack a chute? reposition an aircraft from some field. :)
     
  34. Ryanb

    Ryanb Final Approach PoA Supporter

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    This.
     
  35. EdFred

    EdFred Touchdown! Greaser! PoA Supporter

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    land anyway. Never done a spot landing 1500' down ghe runway?
     
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  36. asicer

    asicer En-Route

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    No. You are 15 minutes from your destination and you have 20 minutes of fuel plus reserves if you go by the sight gauges and 0 plus reserves if you go by the timer. It boils down to the question in the thread title.
     
  37. Wheels

    Wheels Pre-takeoff checklist PoA Supporter

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    Ok, I misread the original post.
     
  38. Timbeck2

    Timbeck2 Final Approach

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    <----- or that guy..just kidding..;)
     
  39. idahoflier

    idahoflier Pre-takeoff checklist

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    Join the club! ;-)
     
  40. Dan Thomas

    Dan Thomas Final Approach

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    1) Most reliable: when the engine quits, the fuel is all gone.
     
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