A look at FAR Part 91.151 and real life.

FAR Part 91.151: Fuel requirements for flight in VFR conditions, sets up minimum fuel requirements for flight in VFR conditions. In other words, it’s telling you, the pilot in command, how much fuel must be on board to fly legally.

Here’s the language:

(a) No person may begin a flight in an airplane under VFR conditions unless (considering wind and forecast weather conditions) there is enough fuel to fly to the first point of intended landing and, assuming normal cruising speed:€”

(1) During the day, to fly after that for at least 30 minutes; or

(2) At night, to fly after that for at least 45 minutes.

(b) No person may begin a flight in a rotorcraft under VFR conditions unless (considering wind and forecast weather conditions) there is enough fuel to fly to the first point of intended landing and, assuming normal cruising speed, to fly after that for at least 20 minutes.

What does this mean?

It’s actually pretty straightforward. It’s saying two things:

• First, it assumes that when you do your flight plan for a flight, you should know how much fuel is required for that flight. For example, if you expect the flight to your first intended landing point (your destination) to take 30 minutes and you burn 12 gallons per hour, that means you’ll need 6 gallons to get to that destination (12÷60×30).
• Second, it’s requiring that you load additional fuel as follows: If you’re flying an airplane during the day time, you’ll need an extra 30 minutes worth of fuel to be legal; in this example, another 6 gallons for a total of 12 gallons. An airplane at night would need 45 minutes worth of extra fuel; 9 gallons (12÷60×45) in this example for a total of 15 gallons. And a helicopter, which often has its own special rules, only needs an extra 20 minutes of fuel day or night; 4 gallons (12÷60×20) in this example for a total of 10 gallons.

The assumptions here are very important. You need to do a flight plan to know how much fuel it will take to get to your destination. A flight plan should take into consideration wind speed and other weather conditions — for example, conditions that may require rerouting around storms or low-visibility areas. This is related to FAR Part 91.103: Preflight Action, which states, in part:

Each pilot in command shall, before beginning a flight, become familiar with all available information concerning that flight. This information must include—

(a) For a flight under IFR or a flight not in the vicinity of an airport, weather reports and forecasts, fuel requirements, alternatives available if the planned flight cannot be completed, and any known traffic delays of which the pilot in command has been advised by ATC;

By flight plan, I mean a real flight plan. Normally, that involves calculations using a whiz-wheel or handheld aviation calculator or the ever-popular Duats online service (my personal favorite). Looking at a chart and guessing doesn’t count.

What Would a Prudent Pilot Do?

Although I don’t like the phrase “a prudent pilot” — primarily because it was used on me by an FAA person who seemed to suggest that I might not be prudent — it is something to consider here. Using the example above, if you had to complete the flight as planned, would you just take the fuel required by the FARs? In other words, 12 gallons for an airplane during the day, 15 gallons for an airplane at night, or 10 gallons for a helicopter during the day?

A prudent pilot wouldn’t if he/she could safely take more. The limitations would depend on max gross weight; performance at high elevations, high temperatures, or high weight; and weight and balance. Performing weight and balance calculations and checking performance charts is part of the responsibilities of every pilot in command before a flight — that’s part of FAR Part 91.103, too. Remember, you need to “become familiar with all available information concerning that flight.” [Emphasis added.]

Why would more fuel be better?

Do I really need to ask?

More fuel means more time in flight. For me, that could mean the difference between taking an in-flight detour to follow a stream or river that’s rarely flowing or flying the boring straight route from point A to point B. Or the difference between successfully navigating around a fast-moving thunderstorm or having to land in the middle of nowhere to wait it out. Or having to pay $4.90/gallon for fuel at my destination rather than $3.47/gallon at my home base.

According to the 2006 Nall Report, 10.5% of aviation accidents in 2005 were due to poor fuel management — pilots running out of fuel or forgetting to switch fuel tanks. This is sheer stupidity by the pilots — something I call “stupid pilot tricks.” By taking on more fuel than you need, you’ll be reducing the chance of becoming one of these stupid pilots. (You can still be another kind of stupid pilot, though.)

You’ll also have one less thing to worry about in flight.

And if that ain’t prudent, I don’t know what is.