Fuel Management

Fuel Management

“From an accident prevention perspective, fuel mismanagement is one of the most frustrating problems. The accidents are easy to avoid. The hardpart is reaching the pilots who are most at risk, because they’re not the ones attending safety seminars or taking online courses. A new approach is needed to get pilots to stop and think about the issue. Airing some ‘dirty laundry’? Perhaps, but we think it’s more than justified by the lives, aircraft, and dollars we lose to this problem every year. 

ACCIDENTS do far more damage to GA’s reputation than educational efforts to rectify the situation.

It shows that, the pilot community,  is making a good faith effort to address the problem.”

—Bruce Landsberg, President, AOPA Foundation

Fuel Management Accidents

Fuel management accidents are among the most preventable types of GA mishaps, and yet pilots still manage to turn perfectly good airplanes into impromptu gliders at an alarming rate well over two per week in the US.

The primary way GA pilots manage fuel on board is to do arithmetic.



 You look at the length of your trip, the winds, read some performance charts, then bust out your calculator or whiz wheel  to figure out how long it will take you to get to your destination at what fuel burn. I might get anywhere from 10 to 18 miles per gallon on a flight. And if the headwind is stronger than I expected or I'm routed the long way, it might take more than that. The 30 minute required reserve  is really not enough. 

FAR Part 91-151

Fuel Level Sender Video

Video Overview of Fuel Level History and Retrofit

We will start getting videos together of units in test and evaluation

Aerospace Logic Instrument Panel Interface

Here is the interface for the digital fuel level sender 

History of AMR Fuel Level

Charles Beck, a Navy Veteran, Lawyer, NASA Alumni and Engineer has looked closely at the issue of fuel level reporting and annunciation in aircraft.

Charles had designed and produced, through his company International Avionics,  master caution and annunciation panels and other electrical systems for great number of popular general aviation aircraft.

Charles had a particular interest in the number of aviation accidents regarding fuel in aviation or the lack thereof.  His insight and skills as a pilot and engineer allowed him to look at the problem to see if he could apply his considerable technological skills and spacecraft experiance to mitigating the hazard.

Charles initiated this work at an accurate low fuel warning system - known to most as the annunciation system on the Mooney M20 series aircraft.  This system  has been copied and emulated in software by a majority of the GA industry.  It was not an FAA requirement at that time to have a separate annunciated low fuel warning - It was just a good idea.

Charles ran into a problem however in that the information from the fuel level senders available to the GA fleet did not lend themselves to accurate and reliable output.

At first Charles addressed this with signal conditioning and looked at methods for getting the sensor out of the fuel.   Patents followed these efforts and Charles turned his attention to Hall Effect sensors as a possible opportunity to remotely and accurately measure fuel level.   His experiments with Hall effect did not produce a reliable aviation sensor.   Temperature, magnetic fields and drift over time rendered these Hall Effect efforts to be unsuitable to the aviation application.

About this time an old technology, in a new and compact form became commercially available  -  We may remember the Suunto wristwatch compass as the first consumer application of Anisotropic Magneto Resistive (AMR) technology - an electrical sensor discovered by Lord Kelvin to measure the direction of a magnetic flux.

Combining the remote moving magnet connected to mechanical float or other means and measuring the position  of that magnetic field  remotely and accurately with AMR technology  lead to Charles fuel level patent.

AMR technology allowed an angular measurement potential down to 0.02 degrees -and  provided a  remote, safe and accurate fuel measurement immune from temperature, other magnetic fields, drift or wear.

Charles Beck's relationship with Mooney Aircraft allowed him opportunity to test this system and improve it's output and interface.   As Mooney Aircraft struggled to find firm footing,  first with economic and then competitive issues this system and its advantages was literally left waiting in the wings.

I was encouraged by two Mooney Alumni to take a close look at the system and it's advantages.   Issues with fuel level systems were on the  top ten customer complaints for every major air and rotorcraft OEM  -  there was a clear opportunity for something new, and CIES has captured  that opportunity. 

Float Based Sensors - Accuracy Quality Reliability

Float Based Sensors 

These sensors have been in use for a long period of time.  They have a few advantages that are difficult to overcome.   If they have a less than stellar reputation it is more about the electronics used, than the method  of finding a fluid level.    We will assume that quality and good practice

• The float will find the surface 

• Provides a reliable value for full and empty
• Provides a stable output, even under fluid agitation.

• Simple mechanism and controlled motion about a pivot.

• Used everyday in the most critical applications 

• Independent of fluid type or composition

• The singular most popular method for measuring liquid level 

• A float and pivot arm can be maintained for millions of operational cycles 

The typical methodology for finding level is resistance - either in a wound wire or a resistance grid.  The output is simply a distinct resistance value.  However this mechanical method for obtaining an electrical value for fluid level has a few problems.

• This practice introduces a mechanical wear item into the system.  It is this wear on the resistance surface that draws the most criticism.

• The CIES Inc float sensor design has only a pivot to wear - and we can utilize a lighter float as there is limited friction to overcome.

• Resistance needs electrical modification to correlate with volume 

• The CIES Inc. float sensor design is digital output and can be programmed to tank volume 

• Resistance circuits immersed in fluids are susceptible to corrosion from alcohol in gasoline or de sulfered diesel or potentially to the 100LL replacement.

• The CIES Inc. float sensor design sensing element is outside of the fuel compartment no chance for corrosion 

CIES Inc answered the quest  - What if we could combine the simple and effective elements of a pivoted float and replaced the resistance element and its problems from the fuel tank sending system

Only CIES Inc has a patent to combine a sophisticated, reliable and stable sensor technology to a simple float mechanism.

CIES FUELRITE Level Sensor 

Utilizing the patented Anisotropic Magneto Resistive technology allows CIES Inc in an intrinsically safe non contact system.

CIES Inc  effectively married the simplicity and effectiveness of the float based system with a non contact level sensing technology with the following characteristics:

• Effective 
• Accurate
• Sensitive - Measures down to 0.02 Degrees 
• Immune to nearby magnetic fields
• No hysterisis -
• No drift over time or temperature - stable 
• Intrinsically Safe 

A proven system backed by exhaustive testing. 

Let us know your unique application

Contact Us

How Do You Inspire Pilot Confidence

- The Answer is Simple -

You Provide Them with Information They Can Trust 

It seems uncomplicated, ... accurate, reliable and trusted information is key to instilling a conviction that everything is going well.

Imagine a Synthetic Vision System that throws a few imaginary mountains at you, just for fun.   This would not be a system that inspires confidence.    Random false information would make a routine IFR flight more stressful and  stomach clenching even if you knew without a doubt that no mountainous terrain exists at any time in the State of Illinois.

  Conflicting information no matter how outrageous or unbelievable adds to pilot workload.

Cross checking normally reliable sources and getting similar results are the hallmarks of a good pilot.  Minor anomolies in calculation or display can be noted and corrected before a situation occurs.  To make this effective, any display in the cockpit should match what the pilot believes to be true most of the time.

In aircraft fuel level systems - reliable trusted information is hard to come by.

Pilots Trust in Fuel Sight Gauges 

Ignoring the issues of having a flammable substance with clamped connections on transparent and UV susceptible tubing or a fragile glass tube in the cockpit  - pilots trust seeing fuel as the most confidence inspiring  vs. any other method of level gauging.   If I can see it,  I have fuel and I know how much.   If I can't see it,  I don't have fuel in that tank.   I trust it, universally most pilots do.   But the limitations (high wing mostly)  revolve around the visibility of fuel  - Cessna uses a ball on the 162 Skycatcher.  But really these systems are best left in the dark.

Pilots have Faith in Capacitive Fuel Gauges

Professional pilots use them, they are the system of commercial aviation.  I hear from pilots that capacitive systems have no moving parts and are exact and reliable,  these pilots have not taken a careful look at commercial systems or the problems and solutions contained in a commercial or business aircraft system.   Good capacitive systems are expensive - the have extensive compensation for the fuel characteristics,  like temperature, water, entrained air, component corrosion These are all part of the capacitive equation for fuel level.   Good commercial Capacitance level systems compensate for this,  systems that rely on the capacitive reputation and fail to compensate or address these issues leave quite a bit to be desired.

Pilots will Believe in Anisotropic Magneto Resistive 

While more difficult technology to grasp,  digital output for fuel level from a float based system truly represents a real breakthrough in fuel level sensing.  

• It is safe, reliable - no wear parts
• There are no electronics in the fluid
• It is compatible with modern cockpit displays
• The fuel flow totalizers will match fuel quantity - giving you a truly redundant system in the cockpit.
• Provides a level output under extreme conditions

Youtube Video of the Sender under Test

How Can a Float Based Sender be so Accurate

Accuracy in Fuel Level Sensing 

Absent the aircraft substantiation that is protected intellectual property at the present time,  it is hard to demonstrate what this system does for the average pilot.  

This fuel system component will generate considerable interest, but fuel level senders of the past have been, an ineffective tool for pilots to utilize.

We can all point to or tell stories of classic flying films where the lead has - tapped the fuel gauge to see if it was reporting correctly.

A technological advancement in this field may not just improve an existing fuel quantity indication system  - but may become a new component with the potential to be disruptive to aviation safety. 

Why? 

In earlier dialogs we discussed the digital aspect of the fuel level sensor output - but what does that mean.

In the diagram above illustrates a distinct position output of the float arm as represented as a ray on the hemisphere.

The middle point being represented by the binary 10000000  - the next ray above is 01111111 the next ray above by the binary 01111110.   Each of these is different.

What this provides is a positive address for the float position for every ray shown on the diagram.

By combining a digital address to a non contact level system.  We allow free motion of the float - no discernible wear - no wear that would affect this digital output.

A measuring system with many discrete addresses over the rise and fall of the float makes it is easier to carefully describe the tank volume into usable information for the pilot.

More information allows complex tank shapes and configurations commonly found in aircraft to be described in more controlled and accurate manner.

The non-contact part of the sensor takes the fuel contents of the tank and it's varying electrical and physical properties out of the equation.  

The controlled float finds the fuel / air boundary in all flight conditions.

Legacy Systems 

Resistive Systems 

So lets compare to a resistive based float system with the resistance trace in the tank  - most general aviation aircraft in the field use this or some variation.

So the manufacturer of the fuel sender will talk about how this resistor card is laser trimmed and it has 50 or 60 precision resistive steps from empty to full when the unit is brand new.  

So that appears to be similar to the example above - yes the digital example has more steps but it is more expensive - yes.  

What is not revealed  is that the resistive steps in output are not distinct or different  - but rather a subtle step increase or decrease in the electrical property when new - after use or wear the subtleties are easily blurred or worn away.  So we in actual practice have a system that now may incur discontinuities in the stepwise output - and provide a less than adequate reading or even deceptive reading for fuel level .   

When we talk about modern general aviation aircraft and the resistance traces become much smaller as shown on the right.   The need for intrinsic safety - explosion proof requirement brought about some subtle changes in aviation fuel systems.  It was no longer acceptable to have wires or traces in the fuel tank proper.  The general aviation industry turned to propane gauges that had the wiper driven by a magnetic couple to an external wiper system enclosed in plastic.


Capacitive Systems

Capacitive Systems - this is the domain of larger aircraft and some small aircraft.  It is the defacto system for aviation.  The designs have no moving parts and are reliable in principle.

Again we are not dealing with distinct positions but an electrical subtlety between one level and another.  So while the fluid provides a good dielectric - the qualities of the fuel become a critical component in how the system works.  Therefore what you add to the tank is a measurable component for the fuel gauge system and is known as the k factor in a capacitance equation.

So what you add - Fuel -  Quality, Temperature, Composition, Entrained Air, Water and Temperature  have a direct bearing on the output of the gauge.

Components of a good Capacitive level systems contain the following:

• Probe Compensators - measure permittivity of the fuel  - ability to carry a charge
• Densitometers  to determine the specific gravity of the fuel
• Temperature compensation - direct though linear effect on k 
• Compensation of tube diameters to provide a linearized output

If your capacitive level system does not have compensation,  it has limited value in aircraft applications. 

Capacitance probes while highly developed and may utilize segregated DC or AC power, can meet requirements for intrinsic safety.   Capacitive systems however will never overcome the fact that we have separated metal tubes connected to external wiring in the aircraft.

Capacitive systems have difficulty with

• Fuel Stratfication - hot fuel added over cold soaked fuel 
• Contamination
• Corrosion 
• Indifferent fuel quality or in non aviation applications alcohol percentages

Capacitance systems in transport aircraft are redundent in that there are two systems for each tank to insure dispatch reliability for transport aircraft.  

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.