Let’s Talk Fuel: Strategy and Tactics

Let’s Talk Fuel: Strategy and Tactics

Let’s Talk Fuel: Strategy and Tactics

From recent NTSB preliminary reports:

A Piper PA46-310P was substantially damaged during a forced landing while on approach to Poughkeepsie, New York. The pilot and two passengers were seriously injured, and one passenger sustained minor injuries. The airplane came to rest upright among trees and brush. The was no evidence of fuel, no fuel spillage, and no odor of fuel. 

A Beech Baron impacted terrain 0.25 mile north of Chadron Municipal Airport, Nebraska. The pilot, pilot-rated-passenger, and one passenger were fatally injured, and the airplane sustained substantial damage. The fuel tanks breached due to impact, and there was no evidence of a fuel spill underneath the  airplane. About 3 ounces of fuel was found in the right fuel strainer assembly. One ounce of fuel was found in the left engine-driven fuel pump supply line.

The final investigations may determine more about why these airplanes ran out of fuel. Clearly, neither of these pilots took off expecting their airplanes to run out of gas and crash. Both tragedies suggest we take another look at fuel management – both fuel strategy and fuel tactics. 

Fuel Strategy 

Strategy is an overall plan for success. The strategy is to fuel the airplane so that it is within weight and balance limits with enough fuel to arrive at your intended destination with an adequate reserve. There are two major decisions associated with deciding your fuel strategy.

Fuel weight: This does not always mean taking off with the tanks full, or even putting in as much fuel the payload permits to remain below the airplane’s maximum gross weight. For example, the single-engine performance of a twin – even a turbine twin or jet – increases dramatically with a relatively small reduction in airplane weight. As little as 100 pounds reduction in total weight can change a piston twin’s single-engine climb rate from 250 feet per minute to 400 feet per minute or better. That’s a substantial real-world improvement, especially since you’re traveling more than a mile and a half across the ground for every minute of that “blue line” climb. Even in a heavy single, it may be advantageous to load less than the maximum amount of fuel possible to improve takeoff and climb performance.

Reserve fuel: Once you know how much fuel you’ll have aboard the airplane, determine the time you can
remain aloft with an adequate fuel reserve. “Adequate” can range from the barely legal VFR or IFR minima to a more conservative personal minimum. For example, I use one hour of fuel
remaining at destination or alternate – even more if the weather is IMC.

This seems backward from the way most pilots plan a flight, which is to decide on a destination and then plan the fuel load. I agree that’s where fuel planning starts. A necessary crosscheck, though, is to express the fuel aboard in terms of time (not distance) aloft. You’re not looking for a number of miles to tick by as you fly, you’re watching the clock and putting the wheels on the ground before you begin using your fuel reserve. You may have to adjust the destination to the fuel load, not the other way around.

How much fuel does your airplane burn? Most pilots answer by citing the cruise fuel burn, but most airplanes burn a lot more fuel during climb, fuel that you may not make up in descent. A turbocharged piston-twin may cruise at 28 total gallons per hour but burn 70 gallons per hour in climb. The first quarter tank of fuel seems to go by fast in a lot of airplanes. Include this real-world fuel burn in your computed fuel time. 

You’ve developed a strategy: fuel on board, how much fuel reserve you’ll require, and how long you can stay aloft. Confirm the amount of fuel you expect is on board, set your totalizer, crosscheck traditional fuel gauges, and prepare to put your strategy into practice. 

Fuel Tactics

Tactics are the techniques you’ll use to pursue your fuel strategy. The modern cockpit makes it easy to “get tactical” with your fuel. But it also can lull you into a false complacency. To pursue your fuel strategy, use all of the tactical tools at your disposal, old and new.

Fuel burn: Engine monitors provide the means to methodically set power and adjust fuel burn to get desired results. The result is often different from the charts in the Flight Manual, meaning you may have to adjust other performance expectations derived from other charts as well. 

Fuel quantity monitoring: Pilots put great store in digital fuel monitors, or totalizers. Their faith is warranted, but there are also limitations. Fuel totalizers:

  • … are only as good as the data input into them. Many fuel exhaustion events are presaged by the pilot inputting the amount of fuel he/she thought was put into the airplane but was not – a reminder that pilots should personally watch fueling operations whenever possible. 
  • … must be calibrated properly. When you fill the tanks, check the amount the totalizer says should be loaded to check its accuracy. If there’s more than a couple tenths of a gallon difference you may want to have the calibration checked.
  • … display how much fuel is remaining (assuming data input is correct), but not where it is located. Pilots need to track the distribution of fuel between tanks by different means.
  • … tell you how much fuel has gone through the transducer, but they cannot detect if any is leaking out another way such as venting through a poorly sealed fuel cap. 

Old-fashioned fuel gauges are a necessary “sanity check” to monitor fuel level and the distribution of fuel between tanks. Further, if there is a discrepancy between the totalizer reading and the fuel gauges, don’t dismiss the old, analog technology. Only traditional fuel gauges actually sense what is (or isn’t) in the tanks. If the indicated level is lower than expected, believe it and act accordingly. Use a totalizer and fuel gauges together. Can you really believe fuel gauges? See the sidebar within this article.

Time updates: Frequently check not only the current fuel state, but the amount of time left in the tanks before you reach into reserves, and the time to destination. Calculate the amount of time remaining in the tanks when you expect to arrive, and begin making plans to stop for fuel now if the time in the tanks at the end of your flight will be less than your “adequate reserve.”

More considerations for cruise flight fuel tactical review: 

As you pass checkpoints or GPS distances remaining, check actual fuel burn against anticipated. Recalculate fuel remaining at destination if your actual burn exceeds what you predicted to that point. 

As you did during climb, glance out at the fuel caps or fuel vents occasionally if they’re visible from the cockpit, and the wing or structure behind caps and ports to discover if fuel is siphoning overboard in the slipstream. Land if you note any leaks. 

Follow precise mixture leaning procedures to get the best fuel flow for your mission, whether it be a fast trip, an endurance run or some compromise between the two. 

Compare fuel gauges and totalizers to your calculations and a clock in a regular fuel crosscheck. If the fuel gauges read lower than expected, land and reconfirm the fuel onboard.

Recompute reserves often enough you can easily land early if needed. 

Use an alarm or timer to remind you when to switch fuel tanks, if the airplane requires. 

Reduce power and cruise slower for longer endurance, if needed. 

Don’t “hope” the ground speed will improve, or think you’ll “make it up in the descent.” Fuel exhaustion events often end up within a mile or two of the intended destination when the pilot thinks he/she has enough to make it. 

Make the decision early to land for fuel if you cannot determine the amount of fuel remaining, or if your computed reserve at destination slips below your minimums. “I might have been able to make it nonstop” is a much more desirable post-flight reflection than “I almost made it.”

If you think you have enough fuel, you don’t have enough fuel. You need to know. The only way to know for sure is to enact a fuel strategy, then approach it tactically to meet your
strategic goals. 

 

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