November 2012
Improper fuel management, contamination and poor preflight planning cause far too many GA accidents; statistics reveal nearly two accidents per week on average. Whether the result of fuel exhaustion, improper planning or mechanical issues, the majority of these fuel mishaps are easily preventable.
IMPROPER FUEL MANAGEMENT
However basic a fuel system may seem, as pilot in command it is important to know the system’s design and operation. Figures such as unusable fuel and total capacity, what fuel is considered part of the empty weight of the aircraft, and what type and grade of fuel is approved for your aircraft are essential information.
All aircraft fuel tanks must be marked to indicate the fuel capacity, type, and grade of fuel required. Aircraft modified by STC for the use of auto fuel should include this information as well.
There are operational issues specific to a make and model of aircraft to consider when operating an aviation fuel system. What fuel tank will be used for takeoff and landing? Does the center of gravity change with fuel burn? When is an auxiliary fuel pump used? What is the recommended sequence of fuel burn from multiple fuel tanks, and why?
Some aircraft return excess fuel to a single tank and if that fuel tank is full, return fuel will drain overboard. Does a tiptank installation allow for increased gross weight, and what are the restrictions? What would be the maximum imbalance allowed between fuel tanks?
Are there Service Bulletins and/or Airworthiness Directives that apply to the fuel system of the aircraft you operate? Aircraft approved for auto fuels by STC have specific requirements and exclude the use of fuel that contains alcohol.
These details are very important to know before you, as pilot in command, venture out into the wild blue yonder.
FLIGHT PLANNING
Many accidents have occurred over the years, and continue to occur, because an experienced pilot thought that he/she was familiar with the performance figures for the aircraft. These pilots didn’t actually run the numbers, though—and thus, they ran out of fuel.
I once was visiting with some friends at a local airport’s pilot lounge when we saw a couple pushing an aircraft down the active runway. I went out with my friends to investigate and discovered that the pilot had planned 13 gallons of fuel for his trip… and that is what he fueled the aircraft with before he took off. The pilot told me that the engine quit on short final at the destination—and he was “happy” with his excellent planning!
With access to computer programs, accurate weather information, the Internet and good old book numbers from the aircraft operating handbook, it’s easier than ever to obtain satisfactory performance information. It should take only a few minutes to calculate the numbers for a flight and determine if you have sufficient fuel (with reserves) to make the planned trip.
When considering performance figures obtained from an aircraft operating handbook, take into consideration that the published numbers were arrived at when the aircraft was new. It was flown with optimum center of gravity, with its fuel/air mixture leaned, and with a test pilot at the controls. The true performance may differ by a considerable amount for an older, not so perfect, plane.
Air carriers normally operate with a flight plan that includes not only a navigation log, but also incorporates a fuel log with minimum or recommended fuel at each waypoint.
As pilot in command, your interest should be sparked any time there is any deviation from the recommended fuel figures. Is there a fuel leak? Adverse winds? Is the aircraft loaded and trimmed properly? Is the proper cruise power setting and recommended leaning procedure being utilized?
Should there be any deviation from the calculated flight plan information, the safest pilots will contemplate a fuel stop prior to continuing to their destination.
PREFLIGHT VERIFICATION
When you preflight your aircraft, spend some time looking over the fuel system components. Take a look at the area on the wing and tail behind the fuel caps to see if there are any stains that would indicate a fuel leak.
If there are stains, then it is likely that some fuel is being lost—and if fuel can leak out of a cap, then it is likely water can seep into the fuel when the aircraft is parked. Fuel cap gaskets should be pliable and should not have cracks or gaps in the seal.
Should you discover a problem, correct it by obtaining the services of a mechanic. Never replace any fuel system component with anything but an approved aircraft part; proper size, shape and material are critical to the correct operation of the fuel system.
Fuel vents are another component that requires inspection during preflight. Bugs, dirt, ice and snow can obstruct a fuel system vent in a matter of a few hours, rendering one or more fuel tanks unusable.
Sump drains need to be checked not only on preflight but after fueling as well to determine if the fuel system has been contaminated by incorrect fuel such as jet fuel instead of Avgas. A transparent container should be used to inspect for contamination; if the sample is clear, cloudy, or mixed with foreign material, suspect the Avgas is contaminated and don’t operate your aircraft until the fuel is checked by a professional and the aircraft is declared safe to operate.
Should you find a sump drain plugged or leaking, don’t ignore it, as either situation suggests that your aircraft may not be airworthy and should not be operated until the problem is corrected.
FUELING
When fueling, it may be very important (on certain models) that the aircraft be level in order to completely fill one or more fuel tanks. If you are expecting maximum range from your aircraft you must be certain that all the fuel tanks are completely full. Fuel gauges must be operational for each fuel tank for an aircraft to be considered airworthy.
Should you turn on the master switch and a nearly empty fuel tank indicates full, then the aircraft is not airworthy and repairs are in order before the next flight.
As aircraft age, the fuel gauges, sending units and wiring suffer from corrosion and deterioration and may require repair or replacement. There are repair facilities that either sell new units or repair fuel gauges and senders. There are several suppliers of digital fuel gauges which are available as direct replacements for the old-style gauges.
PERFORMANCE CONSIDERATIONS
Many aircraft are sensitive to loading, and performance may suffer from other than optimum center of gravity locations. Several General Aviation aircraft respond favorably to an aft CG operation (just be sure that limits are not exceeded) and the use of some properly secured ballast in the aft baggage area of your aircraft may save some fuel.
Ensure that you are using the latest center of gravity information for your aircraft when attempting to optimize fuel burn with CG at or near the limits. Often a lower cruise power setting using the lowest RPM for the associated manifold pressure can save some fuel while adding only a few more minutes of overall flight time.
Leaning of the fuel/air mixture is also important to ensure maximum performance. While there have been a lot of discussions about lean of peak operation to save fuel, in my experience aircraft that are equipped with a carburetor seem not to benefit as much from lean of peak engine operation as do the fuel injection models. Read the engine operation manual for your aircraft and follow the manufacturer-approved procedures for leaning to get the best performance while ensuring a long, trouble-free engine life.
Proper aircraft rigging is also important: if your aircraft takes a lot of rudder trim, or you are holding pressure on the rudder or ailerons during cruise flight, then a check of the rigging should be made so as not to waste fuel.
Aircraft instrumentation is also important as inaccurate tachometer, manifold pressure or airspeed indications don’t allow for optimum performance—and waste fuel.
REPLACEMENT PARTS AND MODIFICATIONS
There are many companies that offer aftermarket parts and modifications that will save fuel or at least allow you the opportunity to get the most fuel efficiency from your plane.
Digital instruments (replacements for standard analog instruments) are available for almost every aircraft. Modern fuel gauges, fuel flow indicators, engine instruments and integrated navigation systems can enhance or allow full performance from your aircraft. These upgrades can be money well spent.
Aircraft fuel quantity indication upgrades or repairs must include, at the very least, verification that each fuel tank sending unit is operating properly through the full range of function. As fuel sender units age, they are often found to be defective or are worn in certain areas. Malfunctions may occur intermittently or infrequently.
If you plan on upgrading to a digital system or are having problems with fuel quantity indications, consider having your airplane’s sender unit(s) repaired or replaced as corrective action.
When considering modifications that claim to increase cruise speed, reduce fuel burn or enhance performance in some way, always verify the results with someone who has actually modified a plane. Does the plane fly the same as it did before the modification, or is there something you should know about how it handles after the mod?
A lot of modifications are costly and may not live up to the claims. It’s also possible that a mod may not be as beneficial for your particular aircraft as it is on others, depending on the other mods installed on your plane.
Before considering airframe modifications, have your plane checked over carefully for issues that reduce performance, such as rigging. Make sure you have accurate and up-to-date center of gravity calculations. Maybe an actual weighing of the aircraft is in order.
Worn flap bushings and tracks can decrease performance and tend to deteriorate at an increasing rate after initial wear takes place. Cowl flap rigging (an item that tends to be overlooked) will decrease performance, especially during cruise flight; check the rigging and replace the worn parts.
Check your instruments for accuracy—especially the airspeed indicator and tachometer. When was the last time either of these were checked on your aircraft? Check your logbooks for past repairs and have your mechanic take a look at these repairs to see if they were done properly.
Fly your aircraft and compare the actual numbers to the POH numbers. If the numbers don’t closely match, do your homework; find out why. If there is a problem, then correct it before spending money on modifications.
MAINTENANCE ISSUES
As an aircraft owner you are responsible for the maintenance of your aircraft and as a pilot of any aircraft (including rental or club aircraft) you must ensure prior to every flight that the complete aircraft is in airworthy condition. As aircraft age, parts wear out and don’t function properly, creating an unsafe condition. As an aircraft owner you should know your aircraft better than anyone else, and those seemingly minor problems that you have been deferring can eventually cause a major problem.
Does your fuel selector operate freely, yet have positive stops at each selection? Does the engine stop when you shut off the fuel (check this on the ground only), or does it continue to run for an extended period of time?
Do you smell fuel when you open the door after the plane has been parked for a while? Does fuel transfer from one tank to another when the aircraft is parked for a day or two? Are you finding contamination in a certain fuel tank on a regular basis? Do all the fuel quantity gauges work properly all the time, or is one or more not working? Is there evidence of fuel leaks around the fuel caps or quick drains?
If you answered yes to any of these questions, have a licensed mechanic check the aircraft before the next flight. In addition to correcting deficiencies, scheduled maintenance (such as 100-hour or annual inspection) should confirm that the fuel system is fully operational and that all components are in the original/unmodified condition—if applicable.
Certain routine maintenance actions should be performed during scheduled maintenance, such as cleaning and inspecting the fuel screens and replacing seals or gaskets when reinstalling the fuel screen. Fuel valves should be checked at each annual or 100-hour inspection to verify that not only does the fuel actually stop when selecting “off,” but that the detents for the various positions are positive and properly marked with the fuel capacity and selection such as “left,” “right,” or “off.”
Vent lines should be checked for leaks and continuity, and flexible hoses should be replaced at regular intervals (five years is standard for most fuel and oil lines). The fuel system must be properly maintained in exactly the original configuration as the aircraft was delivered from the factory.
Fuel line routing, heat shields, and even the type and size of the hoses and fittings must duplicate the original design and nothing should be removed, changed or substituted unless specifically allowed by the manufacturer or other official source. Any unapproved changes—however slight—can negatively affect system performance.
A problem often discovered during maintenance of aircraft that are not flown on a regular basis is corrosive water damage in fuel tanks, fuel valves, and gascolators, as well as in carburetors and fuel injection systems.
If an aircraft is not going to be flown for weeks or months, it is important that the manufacturer’s preservation procedure be followed to prevent expensive damage from occurring.
When performing annual inspections I sometimes find that Airworthiness Directives are signed off as complied with, but at some point things changed. For example, placards were removed, fuel caps were replaced with unapproved caps, or flight manual changes (such as additional pages detailing the operation of a new system or part, as applicable) are missing, lost, or were never recorded. It is important that AD notes be reviewed from time to time to ensure that the aircraft continues to be in compliance.
Aircraft accidents involving fuel are preventable if the proper procedures, planning and regulations are followed. Take the time to properly preflight your aircraft, correct deficiencies prior to flight, and operate with a thorough knowledge of the aircraft operating manual. Always operate with the motto “safe, legal and smart” and you will be rewarded with a long life of great flying.
Michael Berry, a former aircraft repair shop owner, is a multi-engine rated ATP (757/727). In addition, he’s a turbo jet flight engineer, an A&P/IA mechanic, airplane owner and 121 air carrier captain. Berry has 15,000-plus pilot hours. Send questions or comments to editor@www.piperflyer.com.
