Brandy, a pilot mom from Illinois, writes: So now that my daughter is learning to fly, there are a lot of aviation magazines around the house. Being a bit of a nervous type, I can’t help but read the various accident reports and I’m shocked to see how many seem to come about from pilots running out of gas. How is that possible?
While I agree that it sure seems like a lot of airplanes are running out of gas and turning into gliders, to be honest, I’m surprised it doesn’t happen more often. And the reason for that boils down to two issues: First, there’s no way to know how much gas you have in your tanks, and second, there’s no way to know how much gas you’ll need for your flight.
Let me take you through how that’s possible, starting with not having a clue about how much gas we really have.
The first thing to understand here is that, for 99% of all general aviation airplanes, it’s not possible to fill both the seats and the fuel tanks. If you put four people in a four-seat airplane and fill the fuel tanks to the brim, the plane will be too heavy to fly. So, unlike with a car, “filling up” is rarely an option, and most times we fly with a partial fuel load.
OK, you say, so what about the fuel gauges? Surely you can see how much gas you have?
That’s the next dirty little secret.
Traditional airplane fuel gauges are notoriously unreliable and, to make things worse, they are only required to be accurate when reading empty. Yes. You read that right. The only time they are right is right before the engine conks out.
The fuel totalizer found in fancy modern glass cockpit airplanes isn’t much better, as it needs to be updated manually by the pilot each and every time fuel is added. If you get absent minded, key in a wrong number, or if the line person doesn’t put in the amount of fuel you ordered, it’s a case of garbage in, garbage out.
That being the case, wouldn’t it be prudent to, like, take off the gas cap and look into the tank to see how much fuel you have before a flight? Why, yes, yes it would.
But there are problems here, as well. While about half of GA airplanes have their wings on the bottom of the fuselage, where God intended they should be (not that I’m biased), the other half have their wings on top of their fuselages, requiring some serious acrobatics to clamber up and look into the gas hole.
The problems don’t stop there. Even with low-wing planes where it’s easy to walk up and remove the gas cap, it’s not that simple. You are often out on a bright sun-flooded tarmac trying to see down inside a small dark hole in a bright white wing. So naturally you use a flashlight. Or at least you do until you drop one into your gas tank, requiring an expensive rescue.
All of that aside, the pilot’s problems aren’t over, thanks to something called dihedral, which is just a fancy word for the fact that the airplane’s wings are not parallel to the ground. They sweep upward from the fuselage to the wing tips — the airplane’s equivalent to hands raised in prayer. As the fuel tanks are in the wings, the tanks aren’t flat when the plane is parked, meaning the fuel level isn’t flat. Plus, if the ramp is sloped, the fuel may slosh in a way to make the tank appear more full than it really is.
While some airplanes have a “tab” in the tank below the filler neck that gives you a visual indication of a defined percent fuel load, many airplanes have nothing but fuel and air to look at. Is the tank 50% full or 40% full? Or 60%? It’s hard to say.
As eyeballing the fuel level is as notoriously unreliable as the damn fuel gauge is, many of us use a fuel “straw” to dip the tank. This works the same way as the straw in your chocolate milk when you were a kid. Dip it in, hold your finger over the top, remove it and see how much fluid is in the straw.
But, once again, uncertainty rules. For most airplanes you only know how many inches of fluid are in the high end of the not-level tank — and even for those that do have straws calibrated to gallons, you can get a different reading depending on where on the filler neck you hold the straw. Holding the straw at a slight angle can throw off the reading, too.
So I think you can see how difficult it is to determine just how much gas we have.
Now let’s jump to figuring out how much gas we need.
Unlike cars, which can generally go the same distance on a given amount of gas, an airplane’s fuel burn per mile is highly variable. The largest challenge comes in the realm of airspeed vs. ground speed.
A car always travels at ground speed. If you are driving, God forbid, at 55 miles per hour, you are traveling over the ground 55 miles per hour. But for airplanes, it’s different, because airplanes are traveling through air which, itself, is moving over the ground.
The easiest way to understand this is to picture yourself standing on a spit of land between a lake and a river. On the lake two campers are paddling a canoe. The water is still, so they are moving only as fast as they can paddle. But on the river two other campers are going downstream and their canoe zips past you because their travel speed is how fast they can paddle, plus the speed of the river’s flow.
It’s the same in the air. If the air is moving in the same direction as the airplane, the plane’s speed over the ground is its airspeed plus the speed of the wind. Conversely, if you are flying against the wind, your ground speed is slower than your airspeed.
Of course in the real world, wind is usually at a complex angle, and it changes all the time over the route.
The bottom line is that you never truly know how long it will take to fly somewhere, and thus there is no way to truly know how much fuel you will burn to get there.
Oh, but that’s not all.
Airplanes burn more fuel as they climb to altitude than they do in cruise flight —some as much as double.
Also, fuel burn varies with altitude, pressure, and temperature.
Plus airplanes have something called a mixture control, where the pilot selects the mix of gas and air for the engine. How you set your mixture affects how much gas you burn. Of course we have charts and graphs and all manner of data to help us figure out how much gas we think we’ll burn in advance, and there are ways to check what you are really burning in flight, but all are subject to error.
All of this — never knowing what we have and what we’ll need — is why the FAA has regulations requiring a fuel reserve. But like the low fuel light in your car, the required reserve is pretty paltry.
Of course many pilots — including me — have a higher personal minimum, but given our limited weight carrying abilities that, too, has its limits.
So I try to cut people some slack when they completely run out of gas. I can see how on a bad day, all those uncertainties could add up and bring you out of the sky. It’s probably a miracle we don’t run out of gas more often.
But all of that said… I’ve never run out of gas.
At least, not in an airplane.
I’m glad to see a lot of comments. This IS something we should be talking about. According to the data-crunchers at the Air Safety Institute, there have been 177 crashes due to G.A. pilots running out of gas in just the last six years… and a fair number of the crashes were fatal.
I appreciate you bravery for writing on this subject. Many of the comments are very thoughtful. I would like to point out that aviation took the maritime laws and philosophy that the captain has the responsibility for the ship. In other words, THE CAPTAIN IS ALWAYS AT FAULT. Whatever happens, no matter the circumstance, it’s the captain’s responsibility.
I have a couple of observations on fuel;
– most newer cars use fuel at about 2 gph at freeway speeds [ 30 mpg at 60 mph].
So, a car with a 16 gallon fuel tank can operate for about 8 hours before ‘running out of gas’
– most of our aircraft carry enough fuel for 3-4 hours. Some with long range tanks carry 5-6 hours of fuel.
– So, do pilots not remember, or recognize, that our aircraft are limited to much less time in the air than a car is on the highway ?
Other than some talk in ground school on fuel use and calculations, during my pilot training, the instructor never bothered with fuel use calculations, let alone teaching proper leaning procedures.
The aircraft were [ are] rented ‘wet’, so if you didn’t know how much fuel was used during a flight.
I had insisted on filling the tanks prior to a flight, AND refilling the tanks afterward, so that I could calculate the actual fuel use under the flight conditions.
The POH data is usually close to actual use[ Cessna ], but it can vary a lot depending on how the pilot operates the aircraft ; percent power and leaning.
Of course, the author’s care to maintain a LARGE reserve is wise. But he makes an excellent case for understanding fuel exhaustion as a consequence of many factors a pilot cannot control precisely.
It’s probably wise to spend some time getting a glider rating, since, yeah, stuff happens, especially in general aviation. I prefer to fly with a healthy reserve, but am comforted by the fact that I’ve got hours of experience aloft in aircraft with no engine turning, no fuel aboard, and lots of delightful “dead-stick” landings with them.
Finishing my Line Operating Experience (LOE) as a new MD-80 captain, my check airman arose from the co-pilots seat on his way to first class for the return to ORD. He paused for a moment, then put his hand on my shoulder and said, captain, you’ve got a lot of s..t to remember, but it all boils down to two things: don’t run out of gas, and don’t hit nuthin. Eloquent, that man.
Like density altitude and slowly rising terrain fuel exhaustion can be a silent hazard .
Thoughtful planning and continuous reassessment using “ available information “ as mentioned in this article are crucial: knowing your tanks are full, knowing appropriate fuel burn from previous experience considering head winds duration of flight. Using GPS and foreflight jpi engine monitoring taken all together should improve your calculations.Great article. Thanks Chris
Running out of fuel in an airplane is plane stupidity in the pilots part, plane and simple. Nothing else matters. Any one running out of fuel need to have their ticket taken away, It’s the very easy way of keeping these individuals from killing themselves and possibly others. Nothing else can put a band aid on this stupid act.
So, the real “moral of this story is”…comply with 14 CFR 91.151 & 14 CFR 91.167, whatever it takes…no excuses.
I find the ’30 & 45 minutes’ of reserve fuel to be very inadequate.
This guy departed with 1 hr of reserve fuel, assuming that he accounted for the forecast winds, but there is no mention that he did any wx review.
Personally, I plan for 2 hrs min. fuel at my destination. I have 5 hrs of fuel and I usually need a break at 3 hrs., so it works for me. !
While all those points are mostly true, I believe the leading cause of fuel exhaustion is “Get there-itis “.
I am a CFII. I tell all my students and those who I conduct Flight Reviews for they can make flying as safe as they want to make it. It’s that simple.
As for as where the wings are located, one has to appreciate a high wing when it’s raining. High wings also provide built in shade in flight. Last but not least, the wheels and belly will absorb a lot of energy before the wings contact the ground in an off field emergency landing, Think about it.
I have wondered about the high number of airplanes that seem to run out of gas also. I will never forget being at Oshkosh in the 1980’s, a Cessna Cardinal was ditched in Lake Winnebago. The pilots statement was “I had six hours of fuel on board, and had only flown five and a half hours, so I had plenty of gas, that is not what caused the engine to fail!”
Being in aviation for over 40 years, the objective is ALWAYS be conservative and make sure you do one thing…one thing right and that is to have enough fuel on board! No speculation, just ensure you have enough fuel on board. And that really isn’t hard to do. I get it – not very many airplanes can fill the seats and fill the tanks, but most flights don’t involve a gross weight concern. ADD ENOUGH FUEL TO MAKE IT!
Airplanes don’t run out of gas, pilots run the tanks dry.
We just flew a commercial plane yesterday from SNA to EWR. I was staring out the window of our airplane wondering whether airplanes ever run out of fuel. I convinced myself that there must be many redundant checks before a commercial plane takes off. Two hours later, the pilot made an announcement: “I have bad news. We’re running low on fuel. We have to make a stop in Cleveland.” I’ve never heard of this before. I wonder how often this happens, given the challenges you innumerate. Ugh!!!
Look up Gimli glider.
So, just to be clear, you are saying we can never be sure how much gas we have on board, how much gas we burn and nothing is reliable enough to give us this information. Hmmmm… I guess in my years of flying I forgot how to calculate fuel burn based on multiple sources, including the history of experience, that I am unaware of the fuel capacity of the tanks when they are visibly full, and I can’t calculate in any reasonable way, using many available methods to determine within 2 gallons(100lbs) how much fuel I have at any given time. I have flown many different aircraft, prop and jet and am always using multiple methods and resources to determine fuel used, on board, needed to next point of landing and reserves. No, fuel gauges, measuring devices and methods as well as calculations are not exact. However if you use all available resources, (a term the FAA loves to use in regulation and enforcement )
You will have a quite accurate estimate of the fuel used, on board and needed. Having run out of fuel and made a safe off airport landing, (in the woods of Alaska in January), I always use aforesaid all available resources and am never caught unaware of my fuel state and have multiple responses available. In defense of NOT running out of gas.
Dont’ know about where you fly, but where I fly the winds and weather are notoriously unpredictable — and intense. Very careful preflight planning sometimes just goes up in smoke when 10-knot northerly breezes suddenly (without no frontal action, nor forecaster prediction) turn into howling 40-knot southern gales. On occasion, waves off the Rockies, 500 miles away, surprise us with harsh turbulence and severe downdrafts, and wreck our smooth, efficient flight.
Unpredicted pop-up thunderstorms, or unexpectedly thick stratus with heavy rain or snow, force long diversions that drain the tank, as we struggle to reach an adequate alternate in the dark, while the carb, prop and wings ice up, or we dodge hail strikes.
I agree that careful preflighting is important, and hefty reserves are life-saving. Sometimes, though, they’re just not enough. This article helps explain why. GA is not the safest thing to do, no matter the caution of the pilot.
God created birds to fly. Every one I’ve seen has high wings and retractable landing gear. I can barely stand it when I fly a low wing airplane.
When the author slammed the high wing aircraft, I quit reading the article. High wing aircraft have numerous advantages over low wing aircraft.
It has everything to do with the price of fuel, people don’t want to see those $100.00 bills go into their fuel tanks, so they try to estimate approx. how much fuel they can get away from not putting in to their furl tanks, remember when fuel was priced accordingly ?? You didn’t hear of anyone running out of fuel, because people could afford to fill up their tanks.. Greed has become and is a very dangerous way of living, and will continue, mainly because greed has grown to an uncontrollable way of life…
After reading all the negative reviews, I will say I do agree with the author of this piece, but a little thought and wisdom needs to be applied to truly understand the message. I guess this not written for common folk to understand.
The moral of this story is that, if you want the incidence of aircraft running out of fuel and crashing to go down, pilots need to learn to be skeptical of both their perception of how much fuel they have in the aircraft and how much will be required for flight. That will improve their chances of not running out of fuel. Particularly in our aging (and at times scrappily maintained) GA fleet.
People who run out of fuel in the air either 1.- Thought they had more fuel in their tanks than they really had and/or 2.- Needed more fuel than they thought they needed to complete the flight and/or 3.- Just plain forgot that they needed fuel to fly (forgetfulness or incompetence). I don’t think people run out of fuel because they want to so #3 is low in my list of probable causes.
So in my personal flying endeavors I follow Mr. Dubois way of thinking and carry extra fuel to cover such variability. I have two planes, one with a fairly accurate fuel indication system and another that sometimes is not quite perfect. On the good one I like to land with one hour of fuel. On the not so good one I like to land with 1.5 hours left. Both airplanes are very efficient low fuel consumptions ones so not had to carry the extra fuel. And yes, as an ex-airline pilot I have flown with tighter reserves in jet aircraft but that is another category not applicable to this discussion.
One last bit of personal experience: I have extensive time flying Lancair IVs. Try to know how much fuel you have on that one unless you fill the tank to the top. I can tell you that unless you want to become the Space Shuttle landing on a cow pasture you better make sure you have enough fuel to complete the flight. It is then Mr. Dubois words come into perspective.
So I do think Mr. Dubois is correct. And besides, he didn’t get all those impressive credentials he holds by not knowing what he’s talking about. His words do deserve some careful attention.
Best,
Chris
The article gave me situations to consider when flying or preparing to fly. Most I think about, some I did not.
In my case, Bonanza, the aux tanks 19 usable, don’t feed at the same rate even though they both feed at the same time. One will always take more than the other. What happens when one is basically empty and the other has some usable left, I don’t know and don’t want to find out. I run aux tanks for no more than 45 minutes.
Here’s another, on some Bonanza models.
Left tank, 17 usable, say 11 GPH with the return 3 GPH going back to the left tank. True 11 GPH from the left tank.
Now right tank. 17 usable, same 11GPH, return, 3 GPH to left tank. How fast are you removing fuel from the right tank.. 14 GPH. 3 usable gallons left, hope. Left tank now has 9 gallons, hope. You used the aux tank for one hour, theoretically, so the left tank now has 12 gallons, hope
All this and remember the left tank is filling up at a rate of 3GPH.
You better remember to be on the left tank for landing. Especially for right patterns, no steep turns either.
You might say, I would not use the tanks for that time period. Say switching tanks more often. More things to remember.
Whew, that gives me a headache thinks about it, but I do think about it
Now add tip tanks and W&B.
I sometimes wonder why we punish ourselves with this joy of flying.
Another perspective to consider, starting a cross-country flight in 2022, the safety added by flying with a GPS-based flight app moving map is priceless. One hundred dollars a year can keep a device updated with current maps and approach charts. With ADSB-IN data the device can show weather, NOTAMS, TFRs, etc. Maybe sometimes stale data (10 minutes?) but still updates that can enhance pre-flight/pre-takeoff briefing information.
With a moving map, knowing aircraft position and nearby airport locations & details within 3 meters is priceless. Safety is increased and fuel starvation can be avoided with a mindset that diverting to pick up more gas, avoid weather, etc. is very easy!
Flying VFR cross-country by non-professional pilot like me, my goal at takeoff is a safe landing. And that safe landing may be at the planned destination, but may also be anywhere along the expected route.
While I have never run out of fuel, I could see a situation where the chances would increase exponentially. From personal experience – relying on a fuel totalizer. I bought fuel at an FBO and let the fellow dispensing the fuel re-install the caps. One cap was reversed and did not seal properly. Yes I did check after he was done, but did not catch the reversal since the cap was flush and latched. Long story short, I was relying on the totalizer for fuel remaining and neglected to look at the gages. I lost over 15 gallons from the low pressure drawing the fuel out. This was on a 30 minute flight.
Second occurrence was returning from Sedona (with full fuel ) and encountering a 45 knot head wind that I could not find respite from. Luckily I had my tip tanks to transfer fuel from but it could have been close. So good article for getting a discussion going. Yes, there are bone heads out there that don’t plan, and yes there are unplanned events human error or not that occur. Leave a big fuel margin and don’t be in a hurry.
Sir, you must be confused. It’s September 1st, not April 1st. The only time I can see “cutting someone slack” is if the event was totally out of the pilot’s control, such as a fuel leak or a seriously blown weather forecast. If this piece is serious, you should be ashamed. I hope no fledgling pilots read it and take your foolish opinion to heart.
You must have a lot of pilots that agrre with You, for sure, Mr. Mike
This is an irresponsible article. There are all sorts of challenges in flying. To fly safely you must be willing and able to meet those challenges every time. If you can’t, or won’t, you should not be in the aviation community. There are lots of reasons a pilot might run out of fuel, none of them excuse the event. Flight instructors should offer solutions that promote aviation safety not excuses for bad ADM.
To those who replied that the article was a waste of time, I think you missed the preamble…the question from Brandy, who asked, “How is that (running out of fuel) possible?”
I don’t think the author was defending running out of gas, he was justifying just how many factors are involved in keeping the proper amount of go-go juice in an airplane.
Personally, I have yet to run out of fuel on a flight. However, more than once I have been surprised at how little fuel I have remaining. Fuel is a variable and never a constant and, as such, requires constant monitoring and appropriate action.
Wow – rough crowd! Although, after flying over 50 years now, I find that pilots are the most critical of each other than any other profession…
That’s a couple of minutes I’ll never get back…
Between dropping a flashlight into the tank, not watching the fueler fuel
the airplane to ensure the correct amount,
not being aware of how to properly use
a fuel stick and carelessly entering data into the fuel computer, perhaps your “pilot example” ought to find another hobby.
Reading this was a total waste of time … no meaningful advice
There is no defense, all variables are covered in training as are the corrective procedures.
There is ignorance and tech dependency, and assuming that’s even correct in the moment.
Since birds are all high wing, didn’t God intend for the wings to be on top? I also have to say this is the first article I remember reading where the term, “gas hole” is used.
This would have been a great article on April FOOLS day. Absurd comes to mind.
I calibrated my 15 (actually 16 gallon) tanks on my experimental Zenith Cruzer using a glass dipstick. I filled the header tank first so as not to confuse the actual wing tank measurements. With the airplane level I added one gallon at a time, checking both the gauge and the dipstick. I never even got a measurement on the dipstick until I had 7 gallons of fuel in the tank (dihedral?!!??) and no measurement on the vertical fuel gauge until 5 gallons.
Surprised that you continue to pass the urban legend/myth that the gauges only have to be accurate when empty. No. The CFR says the gauge must read zero when there is zero useable fuel (there’s still fuel in the tank – not empty) so that there’s a common certification standard/baseline and understanding of zero zero fuel indicated. Does not say that’s the only time they need to be accurate. I find it remarkable that so many people believe the that the FAA would create a certification standard that basically says the first indication you are in trouble is after it’s too late.
For all practical purposes, if fuel is unusable, the tank should be considered empty.
Exactly. So all the CFR says is the certification standard for zero is zero usable not zero fuel in the tank. It does not say that is the only time the indicator has to be accurate.
b) Fuel quantity indicator. There must be means to indicate to the flight crewmembers, the quantity, in gallons or equivalent units, of usable fuel in each tank during flight. In addition –
(1) Each fuel quantity indicator must be calibrated to read “zero” during level flight when the quantity of fuel remaining in the tank is equal to the unusable fuel supply determined under § 25.959;
I have owned a 1981 Cessna Sklyane for 35 years. I can fill the tanks (92 gal – 88 useable) to the brim and put four people in the seats and fly. I have flown 50 years, and have never come close to running out of gas. Go figure.
Yup..! That’s the beauty of the Skylane..!!
I have to comment that I don’t agree on both points.
1. a fuel stick that is calibrated for the aircraft is accurate to about 1 gallon.
So, sticking the tanks will give a fairly accurate number on the fuel in the tanks.
2. Aircraft can only fly for a certain number of hours, depending on the power setting, taking into account the climb, cruise and descend fuel required.
So, calculating the fuel needed for a flight must take also take into account the winds, which are usually not as forecast, so check points should be used to measure progress.
Today, a GPS unit will give ground speed, so a pilot will know the time to destination vs hours of fuel onboard.
There no good reason for a pilot running out of fuel.
[ I prefer my high wing Cessna, which has a ‘both’ position on the fuel selector, so no having to switch tanks…and gravity feed so no fuel pump to fail .
Oh, and 2 doors, so not climbing over the right seat.]
Good piece. Late model 210s have little dihedral and you can burp 11 more gals of avgas into the tanks if you rock the wings during fuel up. Also, the blue fuel stains we used to see at minor fuel weeps and seeps no longer leave a telltale stain due to changes in fuel composition and evaporation rates. This can deteriorate the level of fuel assumed to be in the tank after longer periods of time.