How close will you get to empty?

Ed Haywood

Ed Haywood

Final Approach
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Let's say you have a fuel computer and GPS. You launch day VFR with at least a 30 minute reserve. The winds are a bit worse than predicted, or you have to maneuver more than expected.

What is your personal threshold to divert enroute?
 
Ed Haywood said:
Let's say you have a fuel computer and GPS. You launch day VFR with at least a 30 minute reserve. The winds are a bit worse than predicted, or you have to maneuver more than expected.

What is your personal threshold to divert enroute?
Click to expand...
Landing with at least a 30-minute reserve.
 
Ed Haywood said:
Let's say you have a fuel computer and GPS. You launch day VFR with at least a 30 minute reserve. The winds are a bit worse than predicted, or you have to maneuver more than expected.

What is your personal threshold to divert enroute?
Click to expand...
A heck of alot more conservative than it used to be since that one time in winter, at midnight, with a 50-70 kt headwind when I figured I would be ok, until I reached my destination and discovered the airport had turned off pilot controlled lighting, and I had to divert to my alternate on fumes...
 
I was a young kid when my Dad was doing his instrument rating. I happened to be with him one day when he and the CFII were discussing the “three hour rule”.

I guess it’s the law of primacy - but many, many years later - I still hold it as a hard rule. Three hours, start-up to shut down.

I fly with full tanks (5.5 hours with a 30 min reserve), but 3 hours start-up to shut down.
 
I ask because yesterday I flew to Athens GA. Flight plan penciled out to 3:45. I have 4 hours total fuel at 10 gph ROP, so I figured I would have to stop somewhere.

Enroute, I dialed power back to 65% and leaned to peak at 7 gph. My fuel computer said I would have 45 minutes remaining, so I pressed on. I felt a bit nervous about trusting it. But today the aircraft took 33 gal, so I still had an hour left.
 
Last edited:
Ed Haywood said:
Let's say you have a fuel computer and GPS. You launch day VFR with at least a 30 minute reserve. The winds are a bit worse than predicted, or you have to maneuver more than expected.

What is your personal threshold to divert enroute?
Click to expand...
1+ hour reserve in the plan and divert when it becomes apparent that actual will be some point below that. With just a stopwatch and a chart, that point will be 59 minutes and 59 seconds. Armed to the hilt with hardware, it becomes closer to 31 minutes remaining.
 
Ed Haywood said:
… I felt a bit nervous about trusting it. But today when I filled up it took 33 gal, so I still had an hour left.
Click to expand...
This really is a good lesson. When being conservative turns out to be correct.

In an airplane, I’ve never looked at endurance to be something to challenge, which is the polar opposite from my days as an ALO/JTAC. The difference is the mission. Nothing in GA is worth the push I can make happen for the mission.
 
Ed Haywood said:
I ask because yesterday I flew to Athens GA. Flight plan penciled out to 3:45. I have 4 hours total fuel burning 10 gph ROP, so I figured I would have to stop somewhere.

Enroute, I dialed power back and leaned to peak at 7 gph. My fuel computer said I would have 45 minutes remaining, so I pressed on. I felt a bit nervous about trusting it. But today the aircraft took 33 gal, so I still had an hour left.
Click to expand...
For long-ish flights like that, I plan a couple of cruise settings and pick the one that works out the best.
 
In the RV-6, I trust the analog gauges and fuel burn down to 5 gallons, which is 40 minutes or so. I manage it so all the remaining fuel is in one tank. In the RV-10, I'm uncomfortable if either tank is below 5 gallons, so 5 gallons x 2 tanks = 50 minutes.
 
The only time I will ever have a 30 minute reserve is if it is a local flight near or in the pattern. Anything beyond that, I want to be on the ground with at least an hour on board. If I'm in the Comanche with 6 hours of fuel, that means a 5 hour range. I usually need to stop before the plane does.
 
I wouldn't go under an hour but given my plane's fuel range and my personal endurance I've never even gotten close to that low.
 
TCABM said:
This really is a good lesson. When being conservative turns out to be correct.

In an airplane, I’ve never looked at endurance to be something to challenge, which is the polar opposite from my days as an ALO/JTAC. The difference is the mission. Nothing in GA is worth the push I can make happen for the mission.
Click to expand...
Well stated.
 
It reminds me of the old story of a king who was looking for a new driver for his carriage. He took the three best candidates out an asked each of them the same question: "How close could you drive me to the edge of this cliff?" The first responded, "Your majesty, I could get within a foot of that cliff." Not to be outdone, the second answered, "I could get you within 6 inches of the edge." When the question was posed to the final candidate, he looked at the king and said, "Your majesty, your life is far to valuable. I would not go anywhere near the edge of the cliff." Guess who got the job?

Personally, VFR or IFR, I try to never exceed 3.5 hrs en route, and generally try for under 3. With 5 hours of fuel, that allows for the possibility that I didn't get as many gallons in as I thought, headwinds are stronger than I planned, or any other number of variables. If I'm going to Oshkosh, my planned stops are usually legs of 255NM, 172NM, 174NM, and then whatever it ends up being from Dodge County to KOSH with the full arrival. The longest leg of that usually ends up being about 2.5 hours or less. On our trip to the Bahamas, I stretched it to 3.5 HOBBS hours on 3 separate legs, but with a pregnant wife in a 172, options are limited.
 
I never want to plan to be airborne with < 300 lbs. That’s about 1 hr at reasonable power.
 
I always plan to land with an hour of fuel remaining. Now, my plane holds 6 hours worth of fuel, and I can only sit in one spot for about 3 hours, so... easy for me to say.

I have a totalizer, digital fuel gauges, and float gauges in the tanks that i can kinda read in flight. I believe whichever of those is the most pessimistic.

On my recent flight to Tulsa, I had planned a fuel stop, but with friendly tailwinds, I decided to skip it. When I landed, my most pessimistic gauges showed 5 gallons each side (i burn 14-15 in cruise), and I was sweating bullets, wishing I had stopped. Of course, when the fuel bill arrived, I had more like 20 on board.
 
Jim K said:
When I landed, my most pessimistic gauges showed 5 gallons each side (i burn 14-15 in cruise), and I was sweating bullets, wishing I had stopped. Of course, when the fuel bill arrived, I had more like 20 on board.
Click to expand...
What did your least pessimistic readout say?
 
asicer said:
What did your least pessimistic readout say?
Click to expand...
The totalizer showed me having a little more... I think a little under 15. It's usually the most accurate, especially if you top off the tanks every time. I had done a couple partial fills previous to that, which added to my uncertainty.
 
Not as low as I'd go on a car. I plan at least an hour reserve, but will go lower than that if I'm close. Precautionary fuel stops are prudent, but everything in aviation requires risk analysis. That fuel stop is not costless; it adds a takeoff and a landing, statistically the most dangerous phases of flight.
 
My JPI is extremely accurate as far as what it says I've burned and what I put back into the tanks when I fill up. Having said that, I seldom go below an hours reserve.

And as others have said, once I get into the 4+ hours on a long XC, I'm ready for a stop at the FBO.
 
Ed Haywood said:
Let's say you have a fuel computer and GPS. You launch day VFR with at least a 30 minute reserve. The winds are a bit worse than predicted, or you have to maneuver more than expected.

What is your personal threshold to divert enroute?
Click to expand...
I might land with a 30 minute reserve, but I am not doing takeoff with a 30 minute fuel reserve.
 
birdy has 5.5 hours of range, i generally go 3 hours but will stretch to 3.5 hours.

that really means i've used 1 hour of fuel in tank one, consumed all the fuel in tank 2 and am now switching back to tank 1 as i'm inbound to land.
 
Soon to be student pilot here with a question.

How much of the reserve is actually accessible?
Is this information available in the PoH?

I'm looking at the specs for a C172, 8 gph burn means a 1 hour reserve leaves you 4 gallons in each wing tank.
In a wide flat tank that doesn't seem like much to me, at what point is the suction uncovered?

Is this more critical in a low wing? Or is every manufacturer different?
 
anyone remember the story (I believe the story to be non-fiction) of the guy flying an arrow, planned a fuel stop but have favorable winds. So he pressed on to his destination. He landed and the engine quit on roll out.
 
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