Why Don't They Just Fix It

What is the Aviation Market for Fuel Level Sensing Technology

• Fuel Level Sensing is a very large market for other vehicle types or stationary fuel storage, aviation is a minuscule percentage of sales.

• The following companies are big players in these markets and are protective of their market share:

• Textron Kautex      -TI Group
• Wallbro                  - Robert Bosch
• Hyundai Mobis      - Delphi
• VDO                      - Toyota
• Bourns                    - Methode  
• Rochester Gauge    - Wema, Isspro, S-W

• Most of these companies are not interested in or will actively avoid the aviation market 
• Business interest to license is minimal and no interest in government controlled production
• Exposure to litigation  

• Fuel Level Sensor industry is protective of its Intellectual Property. 

• Hotly Contested Territory (It has been termed a patent minefield) 
• A thorough  patent search is required, prior to initiating a design process.
• Interest in sharing and licensing intellectual property is limited at best.

• Fuel Level Sensing in aircraft needs to be "Intrisically Safe".

• Explosion Proof 
• Limited Spark or Heat energy in the fuel tank
• TWA 800 Disaster brought about changes in FAA policy / regs.
• SFAR 88 - Wire separation from fuel system.
• Electronic Wiring Inspection System - EWIS.  

• Fuel Level Sensing in aircraft is complex. 
• Fuel can contain dissolved air - ie. Jet A 14% by volume 
• This will outgas like soda at altitude.
• This will influence simple capacitive level systems
• Aviation fuel will contain water
• The changes in altitude due to descent will suck ambient air into the fuel tank, that air will contain water vapor that will condense and mix with the fuel. 
• This will  influence simple capacitive level systems
• Aviation fuel will support biological growth and water in fuel will initiate corrosion
• Metallic or resistive components in the tank will be adversely effected and fuel level output in turn will be adversely effected.
• Fuel in aircraft is more dynamic.
• A vehicle with three dimensions of motion allows for a very dynamic fuel environment. 
• This movement will wear away resistance senders of all types and require mechanical complexities to capacitive sensors to stabilize the local fuel level.
• Replacements to 100 LL Avgas may not be so friendly to existing resistance senders in the fuel tank.

• Non-Contact Fuel Level Sensing, which meets the requirement for "Intrinsically Safe" is actively pursued and "IP" accumulated in the Fuel Sender Industry for functional and business reasons.

• Current best sensor system for Multi-Fuel vehicles
• Best sensor system for 100% alcohol fueled vehicles 
• Solves issues with partial alcohol content - corrosion
• Solves issues with de-sulfered diesel 
• Required for LNG -  LPG
• Future vehicle systems with long term fuel storage i.e.. Chevrolet Volt

• Aviation specific fuel system suppliers are not actively interested in the Non-Commercial, Non-Business aircraft application of their products or product lines.

So designing, building and certifying an aviation specific fuel level sender for aircraft under 12,500 lb is like most things in aviation. difficult, challenging and more involved than a cursory examination suggests.   It was however, not impossible.