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Kay
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PA28, 0.6 gallons remaining (2.5 liters) of usable fuel at landing

Fri Sep 03, 2021 4:05 pm

I had a long flight flying in a PA28, 1976 Piper Archer II 180PS. The flight included a 23minute climb from 6,000ft to 12,000ft, and staying at 12,000ft for 50 minutes. Total flight time was 4h13 minutes because of a detour and having to avoid a lot of clouds. At 12,000ft, I leaned the mixture.

I was switching tanks religiously every 30 minutes, and thought that the aircraft having 181 liters of usable fuel (24 gallons), I still must have almost an hour of usable fuel at the expected landing time. Now, take-off, and one of the other climbs (mentioned above) were on the right tank. At landing, it so happens that i was also on the right tank. So i was surprised, after landing, when that tank was bone dry when i looked inside (no visible fuel anywhere), and the left tank was also dry when looking straight down, but there was some fuel visible on the side, in the deeper side of the tank. I was livid when at refueling, the right tank took 88 liters (out of 90.5 liters of usable fuel theoretically), and the left one took 77 liters. I landed on the right tank with 2.5 liters of fuel in the tank (if it's correct, that the tank has 24 gallons of usable fuel). At the consumption rate of the flight (10 gallons per hour), that was less than 4 minutes more of flying.

Can this be? If this is true, what was wrong that took me so close to the edge? Now I specify the endurance of the aircraft as 4h30mins in the flight plan instead of 5h.
Total weight was 2,280 pounds.

Thanks!
 
LH707330
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Re: PA28, 0.6 gallons remaining (2.5 liters) of usable fuel at landing

Fri Sep 03, 2021 4:36 pm

Couple questions to help narrow it down:
1. What were your fuel gauges showing?
2. Were you leaning at intermediate altitudes to hit the book fuel burn numbers? Also, how much fudge factor did you bake in? The POH numbers are usually for clean, new aircraft with new engines and proper procedure, so it's good to plan in an extra 5-10%.
3. Were you seeing abnormal fuel flows?
4. What was the fuel state before you took off?
5. Are there any popped rivets with streaks that might indicate a fuel leak?
6. Are there reporting requirements in your jurisdiction for events like this? You might want to look that up to be sure.

Ultimately, I'm glad you made it back safely. I'd strongly recommend going through all aspects of your plan and flight and figuring out what you want to do differently in the future. Fuel starvation is no joke.
 
N1120A
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Re: PA28, 0.6 gallons remaining (2.5 liters) of usable fuel at landing

Fri Sep 03, 2021 6:05 pm

1) You're supposed to start leaning in climb at 5000', maybe higher.

2) Leaning is a science. You need to do more than just lean an inch or two.

3) Tanks may hold more than published
 
IADCA
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Re: PA28, 0.6 gallons remaining (2.5 liters) of usable fuel at landing

Fri Sep 03, 2021 6:44 pm

LH707330 wrote:
Couple questions to help narrow it down:
2. Were you leaning at intermediate altitudes to hit the book fuel burn numbers? Also, how much fudge factor did you bake in? The POH numbers are usually for clean, new aircraft with new engines and proper procedure, so it's good to plan in an extra 5-10%.

Ultimately, I'm glad you made it back safely. I'd strongly recommend going through all aspects of your plan and flight and figuring out what you want to do differently in the future. Fuel starvation is no joke.


These seem like the most obvious things. One thing that seems unanswered is what the intermediate altitude for the rest of the flight was: we have climb, cruise...and a heck of a lot of time at some unspecified altitude. Unless there was an error in initial fueling or a leak, that seems to be the likely culprit.

But this is a better way to find out how one's own flying relates to the POH than does this flight extended by ten minutes, that's for sure.
 
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Starlionblue
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Re: PA28, 0.6 gallons remaining (2.5 liters) of usable fuel at landing

Sat Sep 04, 2021 2:26 am

Light aircraft don't have a lot of margin for error, and the fuel gauges are rather "approximate". As mentioned above, the POH does not account too well for the widely varying conditions you may encounter.

Checking fuel flow periodically against a benchmark is important.

You're alive to talk about it. This is good. Mistakes happen and the important thing is to be honest with oneself and learn.
 
N1120A
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Joined: Sun Dec 14, 2003 5:40 pm

Re: PA28, 0.6 gallons remaining (2.5 liters) of usable fuel at landing

Sat Sep 04, 2021 4:30 am

Where do you get 5 hours endurance in an Archer anyway? Unless you are running reduced power or lean of peak (not likely), Archers burn 10.5-11 GPH. At 48 usable, you have more like 4.4 hours endurance.
 
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zeke
Posts: 16355
Joined: Thu Dec 14, 2006 1:42 pm

Re: PA28, 0.6 gallons remaining (2.5 liters) of usable fuel at landing

Sat Sep 04, 2021 10:08 am

Kay wrote:
I had a long flight flying in a PA28, 1976 Piper Archer II 180PS. The flight included a 23minute climb from 6,000ft to 12,000ft, and staying at 12,000ft for 50 minutes. Total flight time was 4h13 minutes because of a detour and having to avoid a lot of clouds. At 12,000ft, I leaned the mixture.

I was switching tanks religiously every 30 minutes, and thought that the aircraft having 181 liters of usable fuel (24 gallons), I still must have almost an hour of usable fuel at the expected landing time. Now, take-off, and one of the other climbs (mentioned above) were on the right tank. At landing, it so happens that i was also on the right tank. So i was surprised, after landing, when that tank was bone dry when i looked inside (no visible fuel anywhere), and the left tank was also dry when looking straight down, but there was some fuel visible on the side, in the deeper side of the tank. I was livid when at refueling, the right tank took 88 liters (out of 90.5 liters of usable fuel theoretically), and the left one took 77 liters. I landed on the right tank with 2.5 liters of fuel in the tank (if it's correct, that the tank has 24 gallons of usable fuel). At the consumption rate of the flight (10 gallons per hour), that was less than 4 minutes more of flying.

Can this be? If this is true, what was wrong that took me so close to the edge? Now I specify the endurance of the aircraft as 4h30mins in the flight plan instead of 5h.
Total weight was 2,280 pounds.

Thanks!


What speed were you flying ?
 
Kay
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Joined: Fri Mar 01, 2002 3:41 pm

Re: PA28, 0.6 gallons remaining (2.5 liters) of usable fuel at landing

Sat Sep 04, 2021 12:28 pm

LH707330 wrote:
Couple questions to help narrow it down:
1. What were your fuel gauges showing?

Since at the club the fuel gauges are not considered accurate, i was focused on my calculations and didn’t look very much at them, definitely a lesson there. They were consistent, the right fuel gauge was showing completely empty and the left one having a bit left.

2. Were you leaning at intermediate altitudes to hit the book fuel burn numbers? Also, how much fudge factor did you bake in? The POH numbers are usually for clean, new aircraft with new engines and proper procedure, so it's good to plan in an extra 5-10%.

Yes i leaned at the intermediate altitude of the flight. Most of the flight was at 6,000 and 7,000 feet. I wasn’t leaning to reach the peak or the ultimate efficiency precisely, but leaning i would say 3/4 of the way there.

3. Were you seeing abnormal fuel flows?
In fact the fuel flow was at one point at high altitude actually lower than usual but still green, towards the bottom of the green. The rest of the flight, normal. I have a lot of hours on that aircraft, somehow i know it was where it is meant to be.

4. What was the fuel state before you took off?
I filled it completely the day before.

5. Are there any popped rivets with streaks that might indicate a fuel leak?
My understanding is that the aircraft is very very well maintained by the club, same as all their aircraft.


6. Are there reporting requirements in your jurisdiction for events like this? You might want to look that up to be sure.
I spoke about it to my examiner at the club.

Ultimately, I'm glad you made it back safely. I'd strongly recommend going through all aspects of your plan and flight and figuring out what you want to do differently in the future. Fuel starvation is no joke.
Indeed, thanks!
 
Kay
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Re: PA28, 0.6 gallons remaining (2.5 liters) of usable fuel at landing

Sat Sep 04, 2021 12:31 pm

N1120A wrote:
1) You're supposed to start leaning in climb at 5000', maybe higher.
I do remember that i have.

2) Leaning is a science. You need to do more than just lean an inch or two.
Yes, I didn’t go all the way scientifically, another lesson here.


3) Tanks may hold more than published

I’m really glad to read that. Especially that the aircraft holds 9liters of unusable fuel according to the POH. What that means I don’t know. Like when i refuel 165 total litres, should I consider that the aircraft had 16 litres left (total being 181 litres), or 189 litres, which is the actual size of the space in there..


Interestingly, when i drained the next day before refuelling, there wasn’t any fuel that came out of the drainer under the engine!
 
Kay
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Re: PA28, 0.6 gallons remaining (2.5 liters) of usable fuel at landing

Sat Sep 04, 2021 12:35 pm

IADCA wrote:
LH707330 wrote:
Couple questions to help narrow it down:
2. Were you leaning at intermediate altitudes to hit the book fuel burn numbers? Also, how much fudge factor did you bake in? The POH numbers are usually for clean, new aircraft with new engines and proper procedure, so it's good to plan in an extra 5-10%.

Ultimately, I'm glad you made it back safely. I'd strongly recommend going through all aspects of your plan and flight and figuring out what you want to do differently in the future. Fuel starvation is no joke.


These seem like the most obvious things. One thing that seems unanswered is what the intermediate altitude for the rest of the flight was: we have climb, cruise...and a heck of a lot of time at some unspecified altitude. Unless there was an error in initial fueling or a leak, that seems to be the likely culprit.

But this is a better way to find out how one's own flying relates to the POH than does this flight extended by ten minutes, that's for sure.


Definitely this is a better way indeed!... i was on the right tank, that i had switched to 13 minutes ago, so i was planning to stay on it 17 minutes more, yet it had less than 4 minutes left. On my next flights i skipped switching tanks to the right at one point, and kept it on the left, because the left seems to have much more fuel, since take off is on the right.

Intermediate altitude was 6,000-7,000 feet and i was leaning close to ideally but not ideally. I haven’t included fudge in my calculations. (Well, i thought 35 litres per hour is a high estimate. Now i calculate 40 litres per hour!)
 
Kay
Topic Author
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Re: PA28, 0.6 gallons remaining (2.5 liters) of usable fuel at landing

Sat Sep 04, 2021 12:35 pm

zeke wrote:
Kay wrote:
I had a long flight flying in a PA28, 1976 Piper Archer II 180PS. The flight included a 23minute climb from 6,000ft to 12,000ft, and staying at 12,000ft for 50 minutes. Total flight time was 4h13 minutes because of a detour and having to avoid a lot of clouds. At 12,000ft, I leaned the mixture.

I was switching tanks religiously every 30 minutes, and thought that the aircraft having 181 liters of usable fuel (24 gallons), I still must have almost an hour of usable fuel at the expected landing time. Now, take-off, and one of the other climbs (mentioned above) were on the right tank. At landing, it so happens that i was also on the right tank. So i was surprised, after landing, when that tank was bone dry when i looked inside (no visible fuel anywhere), and the left tank was also dry when looking straight down, but there was some fuel visible on the side, in the deeper side of the tank. I was livid when at refueling, the right tank took 88 liters (out of 90.5 liters of usable fuel theoretically), and the left one took 77 liters. I landed on the right tank with 2.5 liters of fuel in the tank (if it's correct, that the tank has 24 gallons of usable fuel). At the consumption rate of the flight (10 gallons per hour), that was less than 4 minutes more of flying.

Can this be? If this is true, what was wrong that took me so close to the edge? Now I specify the endurance of the aircraft as 4h30mins in the flight plan instead of 5h.
Total weight was 2,280 pounds.

Thanks!


What speed were you flying ?


Average speed around 100kts. Indicated airspeed was 110, 120, however, something that surprised me is that my airspeed was very low at altitude (12,000feet), like maybe 95 or 90.
 
Kay
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Re: PA28, 0.6 gallons remaining (2.5 liters) of usable fuel at landing

Sat Sep 04, 2021 12:37 pm

Starlionblue wrote:
Light aircraft don't have a lot of margin for error, and the fuel gauges are rather "approximate". As mentioned above, the POH does not account too well for the widely varying conditions you may encounter.

Checking fuel flow periodically against a benchmark is important.

You're alive to talk about it. This is good. Mistakes happen and the important thing is to be honest with oneself and learn.



I need to be more careful at the meaning of what i see on the fuel flow, in that case. Lots of lessons here.
 
Kay
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Re: PA28, 0.6 gallons remaining (2.5 liters) of usable fuel at landing

Sat Sep 04, 2021 12:40 pm

N1120A wrote:
Where do you get 5 hours endurance in an Archer anyway? Unless you are running reduced power or lean of peak (not likely), Archers burn 10.5-11 GPH. At 48 usable, you have more like 4.4 hours endurance.



If we calculate 11, yes. At 10.5, it’s 4 hours and 34 minutes. The switching of tanks adds another complexity of the possibility of drying up because the fuel is in the other tank. In the future i will skip switching to keep them exactly matched.
 
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Aaron747
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Re: PA28, 0.6 gallons remaining (2.5 liters) of usable fuel at landing

Sat Sep 04, 2021 2:13 pm

Kay wrote:
IADCA wrote:
LH707330 wrote:
Couple questions to help narrow it down:
2. Were you leaning at intermediate altitudes to hit the book fuel burn numbers? Also, how much fudge factor did you bake in? The POH numbers are usually for clean, new aircraft with new engines and proper procedure, so it's good to plan in an extra 5-10%.

Ultimately, I'm glad you made it back safely. I'd strongly recommend going through all aspects of your plan and flight and figuring out what you want to do differently in the future. Fuel starvation is no joke.


These seem like the most obvious things. One thing that seems unanswered is what the intermediate altitude for the rest of the flight was: we have climb, cruise...and a heck of a lot of time at some unspecified altitude. Unless there was an error in initial fueling or a leak, that seems to be the likely culprit.

But this is a better way to find out how one's own flying relates to the POH than does this flight extended by ten minutes, that's for sure.


Definitely this is a better way indeed!... i was on the right tank, that i had switched to 13 minutes ago, so i was planning to stay on it 17 minutes more, yet it had less than 4 minutes left. On my next flights i skipped switching tanks to the right at one point, and kept it on the left, because the left seems to have much more fuel, since take off is on the right.

Intermediate altitude was 6,000-7,000 feet and i was leaning close to ideally but not ideally. I haven’t included fudge in my calculations. (Well, i thought 35 litres per hour is a high estimate. Now i calculate 40 litres per hour!)


Some conservative margin for error is never a bad idea in a GA aircraft. Better safe than sorry, even more so if you have passenger weight and it's not just you.
 
m007j
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Re: PA28, 0.6 gallons remaining (2.5 liters) of usable fuel at landing

Sat Sep 04, 2021 3:31 pm

Depending on density altitude, you should start leaning in climb, even before hitting 5,000'. Leaning in climb gives you better performance, reducing the time spent in climb and thus your overall fuel burn. My likely guess is that you may have waited too long to lean and spent too much fuel there.
Kay wrote:
N1120A wrote:
Where do you get 5 hours endurance in an Archer anyway? Unless you are running reduced power or lean of peak (not likely), Archers burn 10.5-11 GPH. At 48 usable, you have more like 4.4 hours endurance.

If we calculate 11, yes. At 10.5, it’s 4 hours and 34 minutes. The switching of tanks adds another complexity of the possibility of drying up because the fuel is in the other tank. In the future i will skip switching to keep them exactly matched.


Fuel burn math is done at 14 gph in climb and 9.5 gph in cruise at the company I teach for. I've seen a 5.2 flight at 11,000 before with 30 minutes reserve, it requires careful leaning and cruise climbs to happen but it is possible. Your last sentence confused me Kay, just making sure you'll continue to switch tanks at timed intervals.

Kay wrote:
Average speed around 100kts. Indicated airspeed was 110, 120, however, something that surprised me is that my airspeed was very low at altitude (12,000feet), like maybe 95 or 90.

Let's get the speeds straight here. Are you sure your indicated was 120, because that seems a little high for cruising at 12k and could have caused your fuel burn problems (you need a fair bit of throttle to keep going that fast up there, indeed I'm skeptical that you can even do 120 indicated at 12k)? Or is your indicated 100 and true airspeed 120? If this, then was your groundspeed 95 (so now you effectively have a 30+ kt headwind, increasing fuel burn)?
 
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zeke
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Re: PA28, 0.6 gallons remaining (2.5 liters) of usable fuel at landing

Sat Sep 04, 2021 7:50 pm

Kay wrote:
Average speed around 100kts. Indicated airspeed was 110, 120, however, something that surprised me is that my airspeed was very low at altitude (12,000feet), like maybe 95 or 90.


Sounds like you were around 65% power

Working the flight backwards (253 minutes total)
Circuit time - 5 minutes 1 gallon
Descent - 12000 ft to 1000 ft 22 minutes (500 fpm) (5.5 gal)
12000 ft cruise - 50 minutes
6000 ft cruise ??
Climb from sea level to 12000 ft (ISA) - 30 minutes/9 gal (POH)

So your cruise at 6000 ft was 253-5-22-50-30=146 min

Climb from SL to 12000 ft (30 min it does not matter if you level off at 6000 ft first and climb later the total climb will be 20 min) 9 gal
65% power is 9.5 gph (146 [email protected] ft, 50 [email protected] ft) = 31.03 gal
Descent - 5.5 gal (22 min)
Circuit - 1 gal (5 min)
Total - 46.53 gal

Total Useable 24 gal per side, you should have landed with 1.47 gal

I would strongly advise you to have a good look at the difference between the PA28-181 Archer II POH (1976) and the PA28-181 Archer III POH (1994 https://s3.amazonaws.com/atp-program-do ... /pa-28.pdf ), using the Archer II POH will result in lower fuel burn (eg 65% in the Archer II is 9 gph, Archer III 9.5 gph). I would encourage you to plan using the later data (Archer III), and plan to land with 5 gal.

An aircraft from 1976 will not be straight, the prop will not be new, the engine will not be new, the paint will not be new, the bugs on the airframe and window will be new, this all reduces performance.
 
Kay
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Re: PA28, 0.6 gallons remaining (2.5 liters) of usable fuel at landing

Sat Sep 04, 2021 7:57 pm

m007j wrote:
Depending on density altitude, you should start leaning in climb, even before hitting 5,000'. Leaning in climb gives you better performance, reducing the time spent in climb and thus your overall fuel burn. My likely guess is that you may have waited too long to lean and spent too much fuel there.
Kay wrote:
N1120A wrote:
Where do you get 5 hours endurance in an Archer anyway? Unless you are running reduced power or lean of peak (not likely), Archers burn 10.5-11 GPH. At 48 usable, you have more like 4.4 hours endurance.

If we calculate 11, yes. At 10.5, it’s 4 hours and 34 minutes. The switching of tanks adds another complexity of the possibility of drying up because the fuel is in the other tank. In the future i will skip switching to keep them exactly matched.


Fuel burn math is done at 14 gph in climb and 9.5 gph in cruise at the company I teach for. I've seen a 5.2 flight at 11,000 before with 30 minutes reserve, it requires careful leaning and cruise climbs to happen but it is possible. Your last sentence confused me Kay, just making sure you'll continue to switch tanks at timed intervals.

Kay wrote:
Average speed around 100kts. Indicated airspeed was 110, 120, however, something that surprised me is that my airspeed was very low at altitude (12,000feet), like maybe 95 or 90.

Let's get the speeds straight here. Are you sure your indicated was 120, because that seems a little high for cruising at 12k and could have caused your fuel burn problems (you need a fair bit of throttle to keep going that fast up there, indeed I'm skeptical that you can even do 120 indicated at 12k)? Or is your indicated 100 and true airspeed 120? If this, then was your groundspeed 95 (so now you effectively have a 30+ kt headwind, increasing fuel burn)?


Regarding switching tanks, yes i will continue to switch, but if i know that the right tank took a hit because of a long climb or a take-off, and if the right tank is trailing, then the next slot when i would switch to the right tank, I’d keep it on the left 30minutes more, and then start switching again. This would bring the two tanks closer together (and the 30minutes interval will stay all along except when I skip once if needed).

Because the main problem was that i had 24 minutes of fuel left when i landed, but only 4 of those were on the right tank, which i was on! This severe lack of fuel in the right tank puzzled me (maybe the take off, climbs, staying at 12,000 feet hit the right tank more, and poor leaning).

Regarding the airspeeds, it was showing at low altitudes and even 5 or 6,000 maybe 110, 115 airspeed (not ground speed). At altitude, no, it was significantly slower (and lower fuel flow), now i only have the record of the ground speed, which was the whole duration in the mid-80s knots. I’m pretty sure the airspeed was also low, maybe in the 90s.
 
LH707330
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Re: PA28, 0.6 gallons remaining (2.5 liters) of usable fuel at landing

Sun Sep 05, 2021 7:33 pm

Kay wrote:
Since at the club the fuel gauges are not considered accurate, i was focused on my calculations and didn’t look very much at them, definitely a lesson there. They were consistent, the right fuel gauge was showing completely empty and the left one having a bit left.

Well, there's an old joke that you shouldn't trust a fuel gauge unless it shows empty. I'd try to figure out how accurate those gauges are, either by getting a measuring stick when filling it, or trying some other approach to get a calibration. Then use that information to plan fuel stops. As you fly along, I'd make a rule that says "we're not going to keep going to point C unless we cross B with at least X amount. Brief this with passengers so they can hold you to it as well from a planning standpoint.
Kay wrote:
Yes i leaned at the intermediate altitude of the flight. Most of the flight was at 6,000 and 7,000 feet. I wasn’t leaning to reach the peak or the ultimate efficiency precisely, but leaning i would say 3/4 of the way there.

If you plan to be cruising at altitudes for a while, I'd definitely spend the time learning how to lean it optimally. Same in the climbs, let the CHT/EGT be your guide with that.
Kay wrote:
In fact the fuel flow was at one point at high altitude actually lower than usual but still green, towards the bottom of the green. The rest of the flight, normal. I have a lot of hours on that aircraft, somehow i know it was where it is meant to be.

How large are the numbers on the display? Could you tell if it were, say, 8.3 GPH vs 8.7?
Kay wrote:
My understanding is that the aircraft is very very well maintained by the club, same as all their aircraft.

That doesn't stop it from breaking. I'd check the underside of the wing before each flight, looking for popped rivets or stains running aft.
 
Kay
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Re: PA28, 0.6 gallons remaining (2.5 liters) of usable fuel at landing

Tue Sep 07, 2021 7:58 am

LH707330 wrote:
Well, there's an old joke that you shouldn't trust a fuel gauge unless it shows empty.


That's so applicable here, exactly! :)

LH707330 wrote:
If you plan to be cruising at altitudes for a while, I'd definitely spend the time learning how to lean it optimally


That's the first thing here, the second being the bad luck that so much more work was put on the right tank (insidiously), making it a risky situation.

LH707330 wrote:
That doesn't stop it from breaking. I'd check the underside of the wing before each flight, looking for popped rivets or stains running aft.


yes but i checked fuel before take-off, from the previous night's refill, and it was still filled to the top.

LH707330 wrote:
How large are the numbers on the display? Could you tell if it were, say, 8.3 GPH vs 8.7?


This i'll need to check the aircraft more closely to know.


But in summary, the main mistery is how the right tank was almost depleted and the left tank had still much more. Maybe simply because of key moments of the flight being on the right tank, and this is why this situation was reached (so frustrating to reach such a risky point, without knowing really why there was so little fuel in the right tank in the end. Next time, use the left more).
 
CRJockey
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Re: PA28, 0.6 gallons remaining (2.5 liters) of usable fuel at landing

Tue Sep 07, 2021 10:54 am

I am glad you live to tell the tale. And find it highly respectable that you share your story which surely won’t be in your memory as your happiest flying moments. And most people would keep to themselves.

Nothing valuable to add from my side, as many excellent replies are above. And while I agree as well with the remarks regarding the mostly useless fuel gauges, they tend to be correct when empty. Have you had a look on them at any point during the flight?

By the way: I find the fact of a nearly empty right tank no mystery at all. After all, the left was all but depleted as well. And takeoff (not using much fuel in the grand scheme of things) but especially climb will suck your tanks dry fast, be it a SEP or a jet. So if that portions was predominantly on the right…

Anyway, as general remark: I find that the tank switcheroo on SEPs one of the largest design deficits and largest threats of small plane flying.
 
LH707330
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Re: PA28, 0.6 gallons remaining (2.5 liters) of usable fuel at landing

Tue Sep 07, 2021 7:59 pm

Kay wrote:
But in summary, the main mistery is how the right tank was almost depleted and the left tank had still much more. Maybe simply because of key moments of the flight being on the right tank, and this is why this situation was reached (so frustrating to reach such a risky point, without knowing really why there was so little fuel in the right tank in the end. Next time, use the left more).


I think you answered your own question there. Although the climb segments are short in terms of time, climbing at WOT chews up a lot of fuel. If you like to cycle, I highly recommend finding a hill that's about 1000 feet/300m with a flat at the top. Ride up it, then compare how easy it is to cruise on the flat. Then imagine doing that 12 times with a 1-ton backpack, that's what your plane did the other day. Fighting gravity is a lot of work....

CRJockey wrote:
By the way: I find the fact of a nearly empty right tank no mystery at all. After all, the left was all but depleted as well. And takeoff (not using much fuel in the grand scheme of things) but especially climb will suck your tanks dry fast, be it a SEP or a jet. So if that portions was predominantly on the right…

Anyway, as general remark: I find that the tank switcheroo on SEPs one of the largest design deficits and largest threats of small plane flying.


Agreed, that's something that could and should be automated out by now.
 
m007j
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Re: PA28, 0.6 gallons remaining (2.5 liters) of usable fuel at landing

Tue Sep 07, 2021 8:26 pm

Kay wrote:

Regarding switching tanks, yes i will continue to switch, but if i know that the right tank took a hit because of a long climb or a take-off, and if the right tank is trailing, then the next slot when i would switch to the right tank, I’d keep it on the left 30minutes more, and then start switching again. This would bring the two tanks closer together (and the 30minutes interval will stay all along except when I skip once if needed).

Because the main problem was that i had 24 minutes of fuel left when i landed, but only 4 of those were on the right tank, which i was on! This severe lack of fuel in the right tank puzzled me (maybe the take off, climbs, staying at 12,000 feet hit the right tank more, and poor leaning).

Regarding the airspeeds, it was showing at low altitudes and even 5 or 6,000 maybe 110, 115 airspeed (not ground speed). At altitude, no, it was significantly slower (and lower fuel flow), now i only have the record of the ground speed, which was the whole duration in the mid-80s knots. I’m pretty sure the airspeed was also low, maybe in the 90s.


Yes but the problem now is that even if you keep it on the tank that you didn't use for climb longer during cruise by 30 minutes, you would still not have come close to equalizing since your fuel burn at cruise is less than climb. To put numbers on it, if you cruise at 9.5 for another 30 minutes, you've burned an extra 4.75 gal from that tank. But, in climb at an extra 30 minutes, that's 6 gal that was burned. Add this over a 4 hour flight and your difference is accounted for. In practice on the Archer II and III, it burns closer to 14gph in climb so the difference is more pronounced.

I would suggest that you reduce the time between tank switches. We generally use 10-15 minute timers but no more than 15 between changing tanks.
 
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BawliBooch
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Re: PA28, 0.6 gallons remaining (2.5 liters) of usable fuel at landing

Tue Sep 07, 2021 9:53 pm

At my club, this would be grounds for a 6 month suspension. At the very Least!

"Margin of Error" is a lesson that was hammered into us in Flying School. When you are down to your reserves you should be thinking of diverting somewhere?
 
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Starlionblue
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Re: PA28, 0.6 gallons remaining (2.5 liters) of usable fuel at landing

Tue Sep 07, 2021 11:41 pm

BawliBooch wrote:
At my club, this would be grounds for a 6 month suspension. At the very Least!

"Margin of Error" is a lesson that was hammered into us in Flying School. When you are down to your reserves you should be thinking of diverting somewhere?


No one is denying that errors were made, but blanket punitive measures for unintentional and non-negligent mistakes tend to lead to people hiding incidents instead of reporting them openly.

It would be one thing if the OP had just been winging it, and then trying to hide what happened, but he did have a considered fuel management plan in place, albeit with some erroneous assumptions.

Now everyone can learn from this through an open discussion instead of the incident being covered up.

This process of deconstructing an incident in order to learn lessons and potentially improve overall safety is similar to what happens at many airlines. "No pilot goes to work intending to make a mistake."
 
N1120A
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Re: PA28, 0.6 gallons remaining (2.5 liters) of usable fuel at landing

Wed Sep 08, 2021 6:09 am

Kay wrote:
zeke wrote:
Kay wrote:
I had a long flight flying in a PA28, 1976 Piper Archer II 180PS. The flight included a 23minute climb from 6,000ft to 12,000ft, and staying at 12,000ft for 50 minutes. Total flight time was 4h13 minutes because of a detour and having to avoid a lot of clouds. At 12,000ft, I leaned the mixture.

I was switching tanks religiously every 30 minutes, and thought that the aircraft having 181 liters of usable fuel (24 gallons), I still must have almost an hour of usable fuel at the expected landing time. Now, take-off, and one of the other climbs (mentioned above) were on the right tank. At landing, it so happens that i was also on the right tank. So i was surprised, after landing, when that tank was bone dry when i looked inside (no visible fuel anywhere), and the left tank was also dry when looking straight down, but there was some fuel visible on the side, in the deeper side of the tank. I was livid when at refueling, the right tank took 88 liters (out of 90.5 liters of usable fuel theoretically), and the left one took 77 liters. I landed on the right tank with 2.5 liters of fuel in the tank (if it's correct, that the tank has 24 gallons of usable fuel). At the consumption rate of the flight (10 gallons per hour), that was less than 4 minutes more of flying.

Can this be? If this is true, what was wrong that took me so close to the edge? Now I specify the endurance of the aircraft as 4h30mins in the flight plan instead of 5h.
Total weight was 2,280 pounds.

Thanks!


What speed were you flying ?


Average speed around 100kts. Indicated airspeed was 110, 120, however, something that surprised me is that my airspeed was very low at altitude (12,000feet), like maybe 95 or 90.


At 12000, you aren't making anything close to the 75% benchmark. When you say your airspeed was "95 or 90," do you mean your indicated airspeed or your ground speed? What was the OAT?

Based on the performance charts, at 12000', on a standard day, you MIGHT make 65% power if leaned to absolute peak EGT and you have a factory standard engine. With wheel fairings, that gets you a best case cruise of about 114 KTAS, 111-112 without them.

Winds tend to be stronger in the middling attitudes, say 10000-15000, compared to something like 5000-6000. You could easily see ground speeds of 90-95 knots.

Also, it sounds like you were flying VFR. Why would you be at an even altitude?

Further, you mentioned something about the engine cowl sump. That sump may not always have much fuel in it, especially if the airplane has been sitting and cold. The fuel would return to the wing tank. Hence why you often need to prime a Cherokee before starting after it has been sitting, either with the primer or by pumping the throttle.
 
Kay
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Re: PA28, 0.6 gallons remaining (2.5 liters) of usable fuel at landing

Thu Sep 09, 2021 12:28 pm

N1120A wrote:
At 12000, you aren't making anything close to the 75% benchmark. When you say your airspeed was "95 or 90," do you mean your indicated airspeed or your ground speed? What was the OAT?
Based on the performance charts, at 12000', on a standard day, you MIGHT make 65% power if leaned to absolute peak EGT and you have a factory standard engine. With wheel fairings, that gets you a best case cruise of about 114 KTAS, 111-112 without them.
Winds tend to be stronger in the middling attitudes, say 10000-15000, compared to something like 5000-6000. You could easily see ground speeds of 90-95 knots.

At 12,000 feet, i was getting mid-80's ground speed. Airspeed must have been lower than 100, or max around 100.

N1120A wrote:
Also, it sounds like you were flying VFR. Why would you be at an even altitude?

It was maneuvers avoiding weather, I didn't want to go any higher and i was granted that altitude.


m007j wrote:
In practice on the Archer II and III, it burns closer to 14gph in climb so the difference is more pronounced. I would suggest that you reduce the time between tank switches. We generally use 10-15 minute timers but no more than 15 between changing tanks.


That sounds like the thing to do! Reducing the time between switching. I'll go for 15minutes from now on. May I ask where you take the 14gph from? This seems documented nowhere.

zeke wrote:
Sounds like you were around 65% power
Working the flight backwards (253 minutes total)
Circuit time - 5 minutes 1 gallon
Descent - 12000 ft to 1000 ft 22 minutes (500 fpm) (5.5 gal)
12000 ft cruise - 50 minutes
6000 ft cruise ??
Climb from sea level to 12000 ft (ISA) - 30 minutes/9 gal (POH)
So your cruise at 6000 ft was 253-5-22-50-30=146 min

Climb from SL to 12000 ft (30 min it does not matter if you level off at 6000 ft first and climb later the total climb will be 20 min) 9 gal
65% power is 9.5 gph (146 [email protected] ft, 50 [email protected] ft) = 31.03 gal
Descent - 5.5 gal (22 min)
Circuit - 1 gal (5 min)
Total - 46.53 gal

Total Useable 24 gal per side, you should have landed with 1.47 gal

I would strongly advise you to have a good look at the difference between the PA28-181 Archer II POH (1976) and the PA28-181 Archer III POH (1994 https://s3.amazonaws.com/atp-program-do ... /pa-28.pdf ), using the Archer II POH will result in lower fuel burn (eg 65% in the Archer II is 9 gph, Archer III 9.5 gph). I would encourage you to plan using the later data (Archer III), and plan to land with 5 gal.
An aircraft from 1976 will not be straight, the prop will not be new, the engine will not be new, the paint will not be new, the bugs on the airframe and window will be new, this all reduces performance.


I have done a calculation, laid out on Excel, of each section of the flight, to the minute, whether it's climbs or descends same as you did above. Now I see how i am was way-off, because the figures i used were lower than the consumption at climb you use (how i stand corrected!). My calculation indicated that i would have 7.55 usable gallons remaining at landing.

Am I wrong or does reading the POH, other than the graphs in section 5 (which are referred to of course in the text), and which i have read back to back years ago and referred to before this flight, give an impression that consumption stays within this range and not the wild figures if you use the graphs? Adding to the danger, I have spoken about this and had confirmation by my instructor that 9.5gph is a good benchmark to predict endurance, i used 10.5 instead, and was still way off.
I looked at the C172N POH just now as well, and it is also difficult to know the climb fuel consumption. I understand the graphs, but what would it take to have a section on consumption clearly spelling out the typical extreme consumption of every flight phase? People are dying out there and there isn't a single quote of these figures except cruise consumption of 8.4gph, or 7.4gph, which is practically useless and actually most often incorrect as well.
 
N1120A
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Re: PA28, 0.6 gallons remaining (2.5 liters) of usable fuel at landing

Thu Sep 09, 2021 12:45 pm

Switching every 15 minutes is not a great idea, until you are perhaps at the point where you only have an hour of fuel.

14 GPH in climb is prior to leaning - usually under 5000' in a continuous climb or then wherever you stop your climb for a longer period. That's WOT, full rich.
 
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glen
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Re: PA28, 0.6 gallons remaining (2.5 liters) of usable fuel at landing

Thu Sep 09, 2021 7:55 pm

N1120A wrote:
Switching every 15 minutes is not a great idea, until you are perhaps at the point where you only have an hour of fuel.

That's right, switching in short intervalls makes no sense. Some imbalance is no problem.

If you get into the situation of needing your reserves by whatever mistakes it's getting even more important not to switch to much and not to try to balance the two tanks.
If you come as close to zero like described in the event here, it is even more important to have the right tactic: As long as you are at a good altitude you fly one tank empty, i.e. until fuel starvation. Then you finish the flight on the other tank.
Why?
You better start your approach on a tank where all your available fuel is in. Otherwise you have two tanks with an uncertain amount of fuel - maybe 10 minutes, maybe 15, maybe 20 minutes? Maybe more, maybe less? But how much in which tank? You have no idea. And this increases the risk of fuel starvation just in the approach, while there would be still some fuel in the other tank.

Understand me right. That's not a tactic one should plan for. I hope never to come in this situation and I do everything I can to avoid it. But if things go bad, don't make it worse. Then you have to know where the risks are. Emptying a tank at a safe altitude is no risk compared to running dry during approach while there was still fuel available in the other tank.
 
m007j
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Re: PA28, 0.6 gallons remaining (2.5 liters) of usable fuel at landing

Fri Sep 10, 2021 6:35 am

Kay wrote:
That sounds like the thing to do! Reducing the time between switching. I'll go for 15minutes from now on. May I ask where you take the 14gph from? This seems documented nowhere.

That's been my experience over several hundred hours learning to fly in the Archer and a few hundred more teaching in it across the western US. Granted our airframes may have slight differences and our engines aren't quite as efficient thanks to students going full rich on 3+ hour flights daily. I've seen it between 12.5-14 all the way up to 8000' DA leaned as far as possible in some our most worn out planes (2013 model, but the airframe has 14,000 hours on it).
Regarding the timing, I understand that there are some different techniques other posters are advocating for, I encourage you to try out different intervals to see what works for you. Just be careful about running a tank completely dry as the POH does have a limitation on doing that in flight. (see section 4)
 
FlyingElvii
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Re: PA28, 0.6 gallons remaining (2.5 liters) of usable fuel at landing

Mon Sep 13, 2021 3:02 pm

Kay wrote:
I had a long flight flying in a PA28, 1976 Piper Archer II 180PS. The flight included a 23minute climb from 6,000ft to 12,000ft, and staying at 12,000ft for 50 minutes. Total flight time was 4h13 minutes because of a detour and having to avoid a lot of clouds. At 12,000ft, I leaned the mixture.

I was switching tanks religiously every 30 minutes, and thought that the aircraft having 181 liters of usable fuel (24 gallons), I still must have almost an hour of usable fuel at the expected landing time. Now, take-off, and one of the other climbs (mentioned above) were on the right tank. At landing, it so happens that i was also on the right tank. So i was surprised, after landing, when that tank was bone dry when i looked inside (no visible fuel anywhere), and the left tank was also dry when looking straight down, but there was some fuel visible on the side, in the deeper side of the tank. I was livid when at refueling, the right tank took 88 liters (out of 90.5 liters of usable fuel theoretically), and the left one took 77 liters. I landed on the right tank with 2.5 liters of fuel in the tank (if it's correct, that the tank has 24 gallons of usable fuel). At the consumption rate of the flight (10 gallons per hour), that was less than 4 minutes more of flying.

Can this be? If this is true, what was wrong that took me so close to the edge? Now I specify the endurance of the aircraft as 4h30mins in the flight plan instead of 5h.
Total weight was 2,280 pounds.

Thanks!

I haven’t seen anyone mention this….
It is summer, check your tank vents….

Filling the tank to the top in the summer heat can be problematic. The fuel comes out of the ground at a cool temp. As it heats in the sun and ambient air, such as sitting on the ramp for a while or a long taxi in the sunshine, the fuel expands as its temp rises. Topping the tanks can cause fuel to be lost through the tank vents as the pressure in the tank increases. On some aircraft, the tank vents can be positioned in a way that you would never notice it while flying.

Ask me how I know this…..
I now ONLY fill to the tabs to allow expansion space, especially in summer heat, and plan appropriately.

Also check for any leaks at the sumps. Sometimes after draining, the sump may not return to the original position due to some obstruction such a dirt. My aircraft had an SB about this, due to the wrong kind of sealant being used on replacement sumps.
 
Kay
Topic Author
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Re: PA28, 0.6 gallons remaining (2.5 liters) of usable fuel at landing

Sun Sep 19, 2021 10:39 am

N1120A wrote:
14 GPH in climb is prior to leaning - usually under 5000' in a continuous climb or then wherever you stop your climb for a longer period. That's WOT, full rich.


According to this chart (fuel to climb from the POH)https://fliegen.ch/pdf/afm/Archer_2/ArcherIISection5.pdf?m=1547476536&, the consumption on climb to 12,000 feet is completely off the charts, impossible to determine, but can be estimated, at 30 degrees temperature at take-off, to need around 15 gallons and less than an hour therefore the rate of consumption will be much higher than 14gph in any circumstance?
So if you mean 14gph is before leaning, this chart, is indicating that the best case scenario is around 15 (must be with leaning then).

LH707330 wrote:
How large are the numbers on the display? Could you tell if it were, say, 8.3 GPH vs 8.7?

I looked again, at 12,000feet it was less than 5, the rest of the flight it was maybe 7 or 8.

zeke wrote:
Iwould strongly advise you to have a good look at the difference between the PA28-181 Archer II POH (1976) and the PA28-181 Archer III POH (1994 https://s3.amazonaws.com/atp-program-do ... /pa-28.pdf ), using the Archer II POH will result in lower fuel burn (eg 65% in the Archer II is 9 gph, Archer III 9.5 gph). I would encourage you to plan using the later data (Archer III), and plan to land with 5 gal.


Definitely. I will add a huge margin from now on and keep a super close eye on how much climbing i do. Many pilots assume that climbs are compensated by the descent, which as the numbers indicate is not true at all. In fact the pa28-181 can deplete its tanks in less than 2.5 hours!!! By just climbing to 12,000 feet in a hot environment, descending and climbing again.
 
chimborazo
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Re: PA28, 0.6 gallons remaining (2.5 liters) of usable fuel at landing

Sun Sep 19, 2021 7:05 pm

If planning max range flights and actually having usable fuel at destination, I’d consider fuel planning one tank dry when cruising at 12,000’.
The half hour each way works pretty well to maintain balance, but one can never know what the actual values are in the tanks (gauges are pretty useless). I’d aim for a dry (say, left tank if you’re single pilot) with 1.5h to go. Then you know everything is in the other tank. No worries about running dry at 1000ft height on an approach etc. Many will disagree but if you run a tank dry at 12k you have loads of altitude to deal with it (and should only take a few seconds to rectify when one tank runs dry). Better than an emergency tank change at low level. You will at least know all your remaining fuel is in the tank last time you select it (whether you actually have enough or not is a different matter).
Another option is to plan a long climb at same throttle setting across two tanks, really work the detail.
My club works on a demonstrated burn rate (averaged out over a “normal” flight): if you’re doing lots of circuits for example and it just so happens from timing you get more on one tank, it’s covered by conservative figures. But when going long range, actual burn is more important.
 
N1120A
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Re: PA28, 0.6 gallons remaining (2.5 liters) of usable fuel at landing

Sun Sep 19, 2021 8:00 pm

Kay wrote:
N1120A wrote:
14 GPH in climb is prior to leaning - usually under 5000' in a continuous climb or then wherever you stop your climb for a longer period. That's WOT, full rich.


According to this chart (fuel to climb from the POH)https://fliegen.ch/pdf/afm/Archer_2/ArcherIISection5.pdf?m=1547476536&, the consumption on climb to 12,000 feet is completely off the charts, impossible to determine, but can be estimated, at 30 degrees temperature at take-off, to need around 15 gallons and less than an hour therefore the rate of consumption will be much higher than 14gph in any circumstance?
So if you mean 14gph is before leaning, this chart, is indicating that the best case scenario is around 15 (must be with leaning then).


The mixture becomes leaner as you fly higher.

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