Overnight - The world of aviation fuel level measurement changed

Just like the classic instrument six pack.

Seemingly while you weren't looking  -   The days of simple capacitive and resistive fuel senders disappeared and were relegated to history. 

 You need only to look at the parts manuals for the latest Cirrus SR20, SR22 or Cessna 172, 182 & 206 single engine aircraft.     Take a real close look and  you will see terms like AMR and TDR  (Anisotropic Magneto Resistive & Time Domain Reflectometry).  And instead of a voltage or resistance output to be checked in the maintenance manual - you will see terms like CANBUS and Digital Frequency.  

So what changed ...... well quite a lot ...... the digital age hit fuel level.

• First ---- The FAA requires there to be working fuel gauges in aircraft.  

Fuel gauges that are accurate throughout the range.   Yes the FAA really wants accurate gauges in the aircraft not just at "Empty"

• The FAA in their regulations makes that clear -

• The pilot is required by Part 91.205 to have working fuel gauges
• The definition of working is:   Provide accurate fuel level through the  tank range.

• The aircraft manufacturer is required  by Parts 23.963, 23.1305, 23.1337, 23.1555 to provide working fuel gauges.

• These regulations very clearly indicate that the installed fuel gauges must give accurate fuel level through the whole tank range.
• Note:  Some of these requirements were recently revised.

• Second ----- The rate of fuel starvation events remained unchanged.
•  2 to 3 per week in the US 

For a long time,  excuses have been made for fuel level reporting systems in General Aviation aircraft.   

General aviation fuel gauges were (insert your own adjective) bad, pilots didn't trust them and pilots did not rely on the information they provided.   Plain and Simple 

Uncharacteristically,  the FAA turned a blind eye to the fuel level regulations they provided, tacitly acknowledging in their own documents and publications, that the state of the art was not up to the task.  

Pilots sought and effectively utilized "work arounds" - pilots relied on wristwatches only and aircraft manufacturers and avionic shops installed or incorporated fuel totalizer equipment in the aircraft.  

Iphone App showing fuel level 

Contrary to popular belief totalizers are not required equipment. but they will give pilots confidence in their fuel level.   They have proven to be accurate while in flight and provide a reliable cross check of the wristwatch fuel calculations  at any time.   You will find a fuel totalizer or range graph is on virtually every piece of modern avionic equipment.

Fuel leaking from an aircraft fuel pump

The posting on the web (pictured right) of illustrates succinctly the common complacency of having accurate gauges in the cockpit.   The particular pilot shows his "trusted" iPhone App illustrating a half tank - this app standing in stark contrast to the values depicted on the aircraft fuel gauge.

So why did the FAA really want working fuel gauges in the aircraft.  

Nothing but an actual working fuel gauge .... can tell you exactly what you actually have onboard the aircraft.   

Case in point --- Fuel leaks at a pump are one of the hazards a working gauge will detect.

You would believe that somewhere in the digital age and the era of MFD avionics, the simple fuel gauge would be relegated to the trash heap.   

However 

--- No Pilot Calculation -- 

--- No Totalizer ----

--- No Stop Watch ----

--- No Range Map ----

Only a working aircraft fuel gauge will let you know what you have in your tank and modern technology can give you that information .  

Welcome to the digital age in fuel level reporting