Fuel Starvation — Avoiding the Big Splat

~ Thomas Turner

I leveled at 11,000 feet as Santa Fe slid beneath the left wing. Turning southeast onto the airway that runs the pass between the San Juan de Cristos to the north and the Sandias to the south, I set the Bellanca Super Viking’s power and tweaked the trim for cruise. Reaching to the floorboards I moved the fuel selector to the AUX position, for auxiliary-tank fuel placarded “for use in level flight only.” “Level off checklist complete,” I spoke to myself after completing the level-off “flow pattern.” But then…

The noise didn’t die down much, but airspeed was dropping and it was taking more and more nose-up trim to hold altitude. A quick glance at the Exhaust Gas Temperature (EGT) gauge confirmed that the temperature was off the bottom of the scale. The engine had quit. My first response was the correct one: the problem occurred shortly after I moved the fuel selector, so the logical course of action was to put it back where it had been before. A flip of the wrist and fuel again flowed to the engine. EGTs and airspeed came up, and I was able to trim back to the cruise position. In all, the entire incident took less than a minute, and I never lost more than about 30 feet. Was the tank empty? Was the fuel line blocked, or the tank’s air inlet plugged? Did I simply not get the fuel selector firmly into the AUX position?

FUEL STARVATION
The phrase litters engine-failure accident reports. Unlike fuel exhaustion, the act of running completely out of fuel, fuel starvation means that the engine quit because it ran out of gas — but that there was still fuel available in the airplane. How can this happen? Unless you’re flying one of the smaller, single-engine Cessnas, one of a very few other rare birds that have a single, ON/OFF fuel selector (damn good idea, by the way!), or a larger piston twin with but one fuel tank per engine and subsequently a pair of ON/OFF valves (we’ll talk about crossfeed in a bit), you almost have to switch fuel tanks in flight. Hence, the situation may someday occur when you select a tank with no fuel, contaminated fuel, or fuel delivery system problems and the engine will die. How can you avoid the “big splat” at the end of a fuel starvation event? Here are some quick hints for preventing fuel starvation.

SINGLE-ENGINE AIRPLANES

    1. Start the engine on any tank.

Insider’s Note: Some airplanes may route “return fuel” from injection systems to a single fuel tank regardless of the tank in use. With those systems, to prevent fuel overflow through the pressure relief lines, start these airplanes on the “return fuel” tank.

    1. Taxi to the runup area on the tank you used for start. You now have verified proper function of this fuel tank and its selector.
    2. Upon reaching the run-up area, switch to the auxiliary tank (if installed and fueled). Complete your Before Takeoff checklist items (except for the engine run-up) on the auxiliary tank. If more than one auxiliary tank is installed and fueled, cycle through each during the low-power portion of your Before Takeoff checks. Run the engine no less than a full minute (use a timer) on each aux tank unless prior experience shows that there is enough fuel between the aux tank and the fuel selector to run the engine for more than a minute before power loss. In that case, run on the aux long enough to confirm fuel is feeding from the tank, not just the lines. You have now verified proper function of the aux tank(s) and its/their selector(s).
    3. Before the “run up” portion of your Before Takeoff check, switch to the “other” main tank (do this upon reaching the run-up area if no auxiliary tanks are installed or fueled). Complete your run-up on this tank. You have now verified proper operation of this tank and its selector.
    4. REGARDLESS of whether you completed any of the above steps, ALWAYS TAKE OFF ON THE SAME TANK YOU USED FOR THE RUN-UP. This ensures you have tested proper operation of that tank and your tank selection at a reasonably high power setting just before takeoff.

Do not switch fuel tanks just before taking off.

  1. Make no fuel tank selection changes until at least 1000 feet AGL and in a position to land if the engine quits, higher if over adverse terrain and/or in IMC.
  2. Most auxiliary fuel tanks are placarded for use in straight-and-level flight only. Do not select an auxiliary fuel tank until in level, cruise flight, and select a “main” tank prior to beginning descent or practice maneuvering (anything beyond level, standard-rate turns).

MULTIENGINE AIRPLANES

    1. Start engines on main tanks. Taxi to the runup area on the main tanks. You now have verified proper function of these fuel tanks and selectors.
    2. Upon reaching the run-up area, switch to the auxiliary tanks (if installed and fueled). Continue your Before Takeoff checklist items (except for the engine run-up) on the auxiliary tanks. If more than one auxiliary tank per engine is installed and fueled, cycle through each during the low-power portion of your Before Takeoff checks. Run the engine no less than a full minute (use a timer) on each tank. If prior experience shows there is enough fuel between the aux tank and the fuel selector to run the engine for more than a minute before power loss you’ll need to adjust your timing accordingly (run on the aux long enough to confirm fuel is feeding). You have now verified proper function of the aux tank(s) and selectors.
    3. Before the “run up” portion of your Before Takeoff check, switch to back to the main tanks. Complete your run-up on these tanks. You have now re-verified proper operation of these tanks.
    4. ALWAYS TAKE OFF ON THE MAIN TANKS. This ensures you have tested proper operation of those tanks and tank selections at a reasonably high power setting just before takeoff. If you forgot to switch from the aux tanks to mains before runup, switch to the mains and run the engines up again to re-check proper main tank operation.

Do not switch fuel tanks *just before* taking off.

  1. Make no fuel tank selection changes until at least 1000 feet AGL and in a position to land if the engine(s) quit(s), higher if over adverse terrain and/or in IMC.
  2. Most auxiliary fuel tanks are placarded for use in straight-and-level flight only. Do not select an auxiliary fuel tank until in level, cruise flight, and select “main” tanks prior to beginning descent or practice maneuvering (anything beyond level, standard-rate turns). After landing and reaching the ramp, switch to the crossfeed position on both engines. In most twins there are no sump drains in the fuel crossfeeds, and this is the only way to verify these lines are operable and free of contamination. Return the fuel selectors to MAIN for the next flight before shutting down.

Warning: if flying a multiengine airplane that has not had the crossfeeds checked recently, or if flying a training mission where use of the crossfeeds is planned, perform the crossfeed check before takeoff. BE CERTAIN TO RETURN THE TANK SELECTORS TO THE MAINS before takeoff.

ALL AIRPLANES

PERFORM THESE CHECKS BEFORE ANY FLIGHT WHEN

  • You intend to use multiple fuel tanks or (in twins) the crossfeed system.
  • You include auxiliary-tank fuel in your planning for alternates.
  • The airplane has been sitting outside in precipitation or freezing temperatures.
  • You make the first flight after aircraft maintenance, modification or inspections.
  • At least a month has passed since the last time you’ve done such checks at any other time you feel the checks are a good idea.
  1. Thoroughly check all fuel tank vent lines for obstructions before flight. Be especially wary if outside temperatures have been at or below freezing (possible ice in the vent lines), or if insects are swarming near your airplane (possible obstruction by “mud dauber” nests or similar).
  2. Thoroughly “sump” ALL fuel drains prior to flight. Remove ALL contamination. Inability to obtain a fuel sample from a drain is grounds for investigation — it may indicate contaminated fuel tanks and/or the presence of ice crystals suspending in the fuel.
  3. Always visually inspect fuel levels before assuming a tank is fueled.
  4. When switching fuel tanks in flight, keep an eye on the fuel pressure, EGT or other reliable engine power gauges to ensure fuel flow and combustion continue. Don’t let go of the fuel selector handle until the engine has run several, reliable seconds on the newly selected tank…and be spring-loaded to put it back where it was if switching tanks does cause a power interruption.
  5. Before approach or landing, make your final fuel tank selection change when at least 1000 feet above terrain (higher over adverse terrain and/or in IMC). I personally like to make my final tank selection, if needed, just prior to descent from cruise. Use a tank that has sufficient fuel for the approach, missed approach/go-around, and climb to at least 1000 ft AGL (higher over adverse terrain and/or in IMC) without need for changing the tank selection. “GUMP” (for Gas, Undercarriage, Mixture, Prop) checks should NOT encourage switching fuel tanks at too low an altitude to recover if the engine stops.
  6. USE YOUR CHECKLISTS for ALL phases of flight so you don’t forget these checks, or attempt taking off with an improper tank selection.
  7. Know and follow all handbook limitations for your fuel system, and practice the steps to restarting a failed engine in flight … just in case.

THE BOTTOM LINE: Do not crash a good airplane because you deprived its engines of fuel. Make sure you’ve got good, usable fuel in the tanks you plan to use, and manage your fuel load wisely.

Published by Thomas Turner