Leftovers. You have to love ’em. Especially if they have been hanging around the ’fridge for a while and they age appropriately—mixing in flavors in on top of flavors. Sometimes the leftovers are wonderfully tasty and you might think it cannot be better.
Or can it?
For aviators, there might be something more wonderful than leftovers in the refrigerator. What could a pilot use more than—?
Gas. And not the kind that irritates one’s stomach—we’re talking about real gas, the kind of stuff that keeps airplanes in the air. Liquid gold, 80 and 100-octane, maybe 100-LL, and for some, jet fuel.
No matter the type of fuel in the tanks and running through the engines, you have to keep in mind there is a legal amount you must have in the tanks when you shut down the engines after landing. The FAA says it is 30 minutes at normal cruise power settings for day VFR flights and 45 minutes for night flights or IFR operations.
Thirty minutes flying time is not much. Forty-five minutes isn’t that much more.
If you have flown an airplane down to these fuel levels, you know how nerve-wracking this situation can become. There is little question a dwindling fuel supply can hamper a pilot’s critical thinking skills.
Many pilots agree these fuel reserves are too low. A Piper Cherokee or Cessna 172 powered by a 150-hp Lycoming with a nominal fuel flow of 8 gph can land from a night or IFR flight with only 6 gallons of fuel. The legal reserves for a VFR fight is only 4 gallons.
The problem with most general aviation airplanes is the lack of precision in the fuel system. The gauges will indicate “empty” long before the tanks reach the reserve levels of 2 gallons a side.
Landing with that low a fuel level requires careful planning and knowledge of actual fuel flows acquired from flying that particular aircraft and engine combination. Additionally, many airplanes will have maneuvering limitations imposed because of the low fuel state. These are some of the reasons many pilots agree flying to so low a fuel capacity is an unsafe practice.
Because there are still many variables a pilot might have to deal with that can eliminate a four-gallon reserve. These variables include weather, the ATC environment near the destination, a miss-rigged or faulty carburetor, or other engine problems causing higher than normal fuel flows. The list can go on and the consequences dire.
An example of a situation involving air traffic control could be something complex, or maybe as simple as the preceding plane in front of you having an incident on the only runway within 50 nm. For a 100-knot airplane, that will virtually eliminate the FAA mandated 30 minute reserve.
You cannot plan for these types of events. You can plan for other, more normal, events. Take weather, for example.
If the weather is questionable, a pilot has many options. The pilot can postpone the flight, the destination can be changed to some other airport nearby, or if the pilot is rated, he or she can choose to file IFR.
Now, here’s the important thing about “leftovers.”
When planning and flying instruments, wise pilots will know exactly how much fuel they will have after landing, regardless of the landing taking place at the destination or the alternate. More importantly, they will know exactly what their options are for the available fuel onboard.
Options? Yes, options.
Take for example, an IFR flight. The options available for the instrument pilot includes two: how many approaches can you shoot at the destination trying to get in, and, how long can you hold waiting for the weather to improve. Now the question becomes, how do you know how many approaches? How much holding time? And most importantly, when do you execute?
Let’s take a look at a typical instrument flight from Montgomery, AL to Orlando Executive, FL flown in a Piper Seminole along the preferred low-altitude airways. Let’s assume a heavy-handed pilot who typically flies at high power settings resulting in a fuel flow of 20 gph. The flight, according to flight planning, will involve 2 hours, 24 minutes and 49 gallons of fuel. If everything goes as it should and the aircraft lands on the first approach, there will remain 53 gallons of fuel out of the 102 gallons useable.
If the weather is below minimums, however, the pilot must make some very important decisions. In most cases, the pilot can try approach after approach in hopes of getting in, or he or she might elect to reduce power to max conserve and wait the weather out. The key is for the pilot to know how many approaches they can make, or how long to hold.
The most important aspect is counting those approaches carefully and not shooting one too many, or knowing exactly what time to depart the hold for the alternate.
If the alternate for this flight is Tampa International, the flight from Orlando Executive to KPA will take 34 minutes and 12 gallons of fuel. Adding the fuel together for the leg from KMGM to KORL (49 gallons) with the fuel required from KORL to KTPA (12 gallons) and the reserve requirement of 15 gallons, the minimum fuel required for the flight is 76 gallons. This includes one approach at KORL and then immediately proceeding to the alternate of Tampa.
Subtracting 76 gallons from the initial useable fuel load of 102 gallons leaves the pilot with 26 gallons of excess fuel, or “leftovers.”
Now the question becomes one of what can a pilot do with the excess fuel.
If the weather at the destination looks as though it will allow a successful approach at some point, the pilot can make multiple approaches trying to get in. How many? Assuming a lower fuel flow of 18 gph and 15 minutes per approach, 26 gallons divided by 18 equals one hour and 26 minutes. Dividing 1.4 by .25 equals a total of five approaches (rounded down).
If this is the intent of the pilot, what he or she needs to do is mark each approach somewhere on their nav card. In other words, there needs to be a tick marked at each missed approach in order to shoot no more approaches than fuel will allow. I had a friend do that once—lose track of the approaches and his fuel—he almost did not make it. In this example, after the fifth approach, the pilot needs to pick up the clearance to the alternate and go. When arriving in Tampa and shooting the approach and landing, the pilot will have exactly 15 gallons (45 minutes) fuel reserve at shutdown.
If the pilot should choose to hold, he or she needs to know a few more numbers. Assuming the flight departs KMGM at 0400Z, and flight time is 2:24, arrival at KORL will be 0624Z. With a fuel surplus of 26 gallons, and assuming an endurance powering setting allowing for a fuel flow of 14 gph, the pilot has the option to hold for one hour 51 minutes.
After entering the hold, the pilot needs to write down the “drop dead time” for departure to Tampa somewhere clearly visible on the nav card. The time to depart for Tampa should be noted both in GMT and local time if needed. Arrival at KORL 0624Z (0242L DST) plus 1:51 in holding means departure for Tampa must happen at 0815Z (0415L DST). After the 34-minute flight to Tampa, the fuel supply will be right at the 45-minute legal reserve.
The bottom line is this: pilots can never have too much fuel. The fuel they do have, they need to know how to use it.
©2012 J. Clark
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