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Friday, April 18, 2014

The "Zero Fuel" Myth - You know, Fuel Gauges only Need to be Accurate when Empty

You don't really need to know what happened after this true Accident Narrative - It is evident from the beginning.

Picture Draw Jerel Draw,  jereldye.com

Prior to the incident, I received an instructional ride and completed my C-172 checkout. I then flew with a passenger and solo, three flights, for a total of 5.3 hours in the bird.

In all three of those flights.
  • I observed erroneous fuel quantity indications,
  • Intermittent cycling of the fuel gauges to zero.
  • LH Fuel Low Level Warning light coming on intermittently. 

An [instructor] told me this condition was well  known, typical for this aircraft and not uncommon for general aviation aircraft.

I discussed the erroneous fuel quantity indications with the Chief Pilot, and asked
him if I should write them up. 


He said no, that the indications were within the spec, which requires only that they
read accurately when empty.

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The statement that fuel gauges only read accurately when empty is repeated so many times in the aviation dialog.

 You would almost have to believe it is true.
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Actually far from it.

  • It is a comment you hear repeated by many pilots, the magazines & AOPA / FAA Safety Briefs.  
  • It is not uncommon to have bad fuel gauges in aviation, it is frighteningly almost the rule.  

What is true: 


  • Fuel gauges are "Required" aircraft instruments for powered aircraft.
  • They are required to be functional by design and in operation on the aircraft   -  Specifically:
    • Read fuel level from FULL to EMPTY.  
    • EMPTY needs to be calibrated at "Zero Usable Fuel"
      • The Zero Usable Fuel is the fuel level,  where in the worst condition - fuel cannot be drawn from the tank.
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Designing, Maintaining or Flying an aircraft with bad or in-operative fuel gauges is illegal.  


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Why is it surprising that so many GA pilots run out of fuel.

I think the answer is obvious.

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