What if We Legislated Accurate Aircraft Fuel Level

Yes Virginia, Bad Fuel Level Indication Can Lead to Aircraft Fuel Starvation.

If you look at the small aircraft fuel starvation/exhaustion statistics you might make an assumption that aircraft might have poor fuel quantity indication systems and you might be exactly right.  What is more astounding is that the FAA will agree with you and put it in writing.   Three to four aircraft a week find a way of running out of fuel in North America.

But if you ask a pilot - they will probably equivocate and  shift the responsibility for these fuel starvation events elsewhere. 

So let's look at some of the basics:

Every transportation system, save small piston and turboprop aircraft in North America,  when you evaluate fuel starvation from a functional hazard assessment, indicate that a failure or inaccuracy of the fuel indication is a causal factor in fuel starvation.  

Lets look at the closest brethren to small aircraft - our commercial aircraft cousins.

 

In large commercial aIrcraft fuel quantity indication has been determined to be a leading factor in fuel starvation - The example of the Gimli Glider a Air Canada Boeing 767 that suffered fuel exhaustion and glided to a landing was due to erroneous fuel loading calculations and fuel-gauge malfunctions.

The aircraft's fuel gauges were inoperative because of an electronic fault which was indicated on the instrument panel and airplane logs (the pilots believed the flight was legal with this malfunction)

In an Aviation Week Article in Nov 2011 

EASA Proposal Targets Fuel Starvation Risks

Lessons learned from 65 transport aircraft fuel starvation incidents and accidents in the past four decades have prompted the European Aviation Safety Agency (EASA) to propose certification rule modifications designed to mitigate the occurrence of similar incidents. 

The notice of proposed rulemaking (NPA-2011-13) issued this summer would modify EASA's certification specifications for large aeroplanes (CS-25) by requiring the installation of fuel identification systems, replacing the currently required fuel quantity indicators for each fuel tank. The new systems would have to permanently display to the flight crew the total quantity of usable fuel on board as well as in each fuel tank. provide low-level fuel warnings for each tank, and warn the crew of an airplane configuration that, if left uncorrected, would starve one or more engines of fuel.

In this case EASA would like to improve aviation safety by putting in a better fuel quantity indication system in Commercial aircraft to address the Fuel Starvation hazard.

Not so in General Aviation, Let's look at how AOPA handles this same concept.

• Know how much fuel you have onboard. 

• Think of Fuel not in Gallons but in Hours and Minutes.
• Use a calibrated Dipstick and your Fuel Computer (Trip Computer)
• Depart with Full Tanks

• Know your fuel system 
• Know what kind of fuel is in your tank
• Update your status during flight
• Land with adequate reserve

In this helpful Fuel Awareness White Paper somewhere at the end

• Finally "some sort of Fuel indication is provided for the pilot" 

So nowhere in this paper does the AOPA tie the fuel you have onboard your small aircraft to your fuel quantity instrumentation in the aircraft.  Instrumentation that is designed to let you know your remaining fuel quantity, nowhere. 

It is a fact that a working fuel indication system should help you determine how much fuel you have all the way through your flight. 

Why do we tolerate this in General Aviation Aircraft.  

By FAA regulation you are supposed to have Fuel gauge for each and every aircraft tank. When you take delivery of a new aircraft you should expect the following from your fuel indication:  Part 23

• This gauge is to read from Full to Empty 

• Where Empty is the least fuel you can safely use.

• This gauge is to be marked with Numbers and what these Numbers represent i.e. Gallons.

There is no other performance standard for this gauge and even for large commercial aircraft the fuel indication regulation reads exactly the same.

In commercial aircraft the fuel indication system typically meets a TSO Standard which is a numerical quality standard for indication.  Maintenance is required to show that this system is maintaining that standard. 

Here is where it get's lost in the General Aviation world.  There is no quantitative  (numerical)  performance standard in the regulation.   The fuel quantity system does not typically meet a numerical performance TSO standard.  In fact it has been stated, that it only needs to be accurate when you are Empty.   This statement is not folklore its printed FAA policy and guidance. 

The  FAA Position - We don't really have a usable standard, it's up to you. 

The follow on regulations for the pilot and mechanic are equally vague and fuzzy and they are as follows: 

Pilots need to have a working fuel gauge indicating the quantity of fuel in each tank.  Part 91

Mechanics need to insure the following under the aircraft's mandatory yearly maintenance: Part 43

• Check for poor condition

• Check that the gauge is properly secured to the aircraft

• Check to insure the markings are clear 

• Check (where practical) for improper operation 

So we have a  touchy / feely standard for what constitutes a working fuel gauge in general aviation.  

If we peer into the maintenance manuals - this aviation requirement is equally spongy and strangely consistent for every small aircraft manufactured.   

Most aircraft manufacturers have issued Service Bulletins outlining a calibration procedure that could be accomplished to insure the system is somewhat accurate, but is not required.

There is no quantitative standard for for small aircraft fuel gauge accuracy and no quantitative standard in the field to determine if the fuel gauge is providing useful information to the pilot.

 Actually accuracy is left up to the personal discretion of the pilot and their mechanic to a personal definition of "working" and "improper operation".   This is obviously a purely qualitative evaluation.  

Remember:

 If you can't measure it 

you can't manage it.

Let's look at an example of  how small aircraft fuel indication should be handled:

The Australian Civil Aviation Authority came upon this lack of a consistent standard and decided to do something about it.   The Australian fuel quantity performance standard has to be met 4 year intervals.   This testing is mandated by law and very similar in result to an FAA or EASA AD.  You must comply, but it deals with forcing proper maintenance and not addressing a manufactured design defect.

This mandatory repetitive compliance testing has a clear qualitative standard that is traceable back to the FAA requirement and the underlying Society of Automotive Engineering requirements for fuel indication in aircraft.  

The standard is flexible enough to account for aircraft that have rudimentary sight gauge indication systems.   

Even more impressive is that this standard is combined with an element of best practice to insure an aircraft has accurate fuel level indication for the pilot to use.

Basically these standards are :

• That the Fuel Gauge progress smoothly and continuously to empty as fuel is drained.

• The Fuel Gauge reads Empty with the zero usable fuel level in the tank.

• If the Fuel Gauge is marked at major graduations for fuel quantity (Part 23 Aircraft) that the gauge indicate within a few percentage points of that marked value.

• If the Fuel Gauge is marked in 1/4 tank increments (E,1/4.1/2,3/4, F) that a placard be placed along side the instrument to list the numerical volume associated with that mark. 

Simple and straight forward, Why don't we give it a try.