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Questions tagged [fuel-systems]

Any question regarding aircraft fuel systems, how they work etc.

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90 votes
5 answers
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Why do we need to starve the engine before turning it off?

This question is for Piper Tomahawk, but I guess applies to any small aircraft. Why do we need to use the fuel mixture to starve the engine before turning it off with the key? Why can't we just turn ...
Cloud's user avatar
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72 votes
6 answers
31k views

Why are fuel tanks in the wings filled first, and why are they used last?

When fueling airliners, why is fuel filled first in the tanks in the wings and then the center tanks? And why do they use fuel from the center tanks first and then from the tanks in the wings? From ...
lemonincider's user avatar
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57 votes
4 answers
13k views

Why do many GA aircraft not have a "Both" fuel selector?

I've been trying to rack my brain around this and asked a few CFI's who couldn't give me more than "because that is how it was done", but a good number of GA aircraft save for Cessna and maybe a few ...
Ron Beyer's user avatar
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55 votes
9 answers
57k views

Why are fuel tanks located in wings?

Passenger aircraft have fuel tanks in the wings. Why? What are the advantages and disadvantages of this location ? examples of disadvantages I would suspect: added weight increases the structural ...
summerrain's user avatar
  • 3,434
41 votes
6 answers
12k views

Is fuel moved around during flight on a passenger or cargo plane? If so why?

Is fuel moved around during flight on a passenger or cargo plane? If so why? Is balance an issue?
Sarah's user avatar
  • 457
31 votes
5 answers
21k views

Why didn’t the Captain of Cathay Pacific flight 780 shut down engine 1 and land with a more reasonable speed?

In the approach phase, engine 1 of Cathay Pacific flight 780 got stuck at about 70% N1 and it forced the crew to do an overspeed landing (230knots). Why didn't they shut it off by turning the fuel ...
xMooo's user avatar
  • 421
27 votes
4 answers
13k views

Why are the center tank pumps deactivated when slats are extended on the A320?

Why are the center tank pumps deactivated when slats are extended on the A320? I researched about this and all I can see is hints. They say it is because of regulations or certifications.
MNKY's user avatar
  • 293
22 votes
6 answers
6k views

Is there a tank priority sequence for using the fuel tanks?

Is there a tank priority sequence for using the fuel tanks, or does the pilot decide?
TestUser's user avatar
  • 323
18 votes
4 answers
13k views

What is the purpose of the fuel shutoff valve?

Most GA planes have a fuel shutoff valve which I don't quite understand the purpose of. Does it cut the fuel flow with the mixture. My theory is to prevent fuel flow at earlier stage for safety ...
Mike no smith 's user avatar
18 votes
1 answer
7k views

How does the fuel pump work in a PA-28 and when should I use it?

Just started flying again after 14 years and I'm taking this to the finish line this time. All my time, up till 10 am today, is in a C172. I did fly a PA 28-151 today and liked it. I do have some ...
user2425931's user avatar
18 votes
2 answers
2k views

How is fuel managed in the Zero-G A310?

There are several Zero-G airplanes to experiment briefly microgravity without going into orbit. One is the A310 from Novespace (F-WNOV): Novespace A310 F-WNOV (source: Jonas Wirz at Airplane-Pictures....
mins's user avatar
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17 votes
5 answers
6k views

Why aren't "fuel polishing" systems removing water & ice from fuel in aircraft, like in cruising yachts?

Should you sump fuel tanks when the fuel system is below freezing? the question should one sump fuel-tanks before flying, if in freezing-conditions? but this implies another question that boggles me:...
BulldozerMind's user avatar
17 votes
1 answer
6k views

Why is fuel used as a hydraulic fluid?

Why is fuel used in some servo-systems as a hydraulic fluid (fueldraulic systems) of modern civil and military aircraft such as the Boeing 777-200/-300 (Pratt & Whitney PW4084) or the Lockheed ...
user avatar
17 votes
1 answer
2k views

When drop tanks (those with external lines) are released, how are the two connections (air and fuel) released?

ww2aircraft.net Say in a P-51 (shown above), when drop tanks (those with external lines) are released, how are the two connections (air and fuel) released? Do they shear off and fall with the tank? ...
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16 votes
4 answers
8k views

Why do jet engine igniters require huge voltages?

Wikipedia's Components of Jet Engines has this to say on the igniters: A high voltage spark is used to ignite the gases. The voltage is stored up from a low voltage (usually 28 V DC) supply provided ...
DrZ214's user avatar
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16 votes
3 answers
12k views

Is excess fuel leaking normal during take off of a B737?

When we look over this video it's noted that some fuel is coming off from the left wing during the rotate. This is the position of the fuel vent within the wing, ...
Germano Sarmento's user avatar
16 votes
2 answers
3k views

What is the appropriate fuel tank selection to land a 172?

On a recent checkout on a C172 I was told to select "fullest tank" as opposed to "both" that I have been doing for years. Given the aircraft is high wing (gravity feed) with no auxiliary fuel pump ...
3GREENS's user avatar
  • 163
16 votes
2 answers
4k views

How is fuel mass measured in airliners?

Large airliners display the amount of fuel in each tank as a mass (usually in kg or lbs) and not as a volume. This makes sense since mass is important for weight&balance considerations and the ...
Bianfable's user avatar
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15 votes
5 answers
7k views

What could the fuel pump failure have been that my flight experienced?

I was on an Easyjet flight (I think an A320), when mid-flight, I overheard a member of cabin crew tell another passenger there was a 'technical' issue with the aircraft, that might make us slightly ...
Cloud's user avatar
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14 votes
2 answers
4k views

Why nitrogen generation system is only present in centre tank only?

I was going through FCOM of A320 and it mentioned that nitrogen generation system is only there for centre tank and not for wing tanks what is the reason for the same?
Sourabh Jain's user avatar
13 votes
5 answers
11k views

Why is mixture lean recommended on the ground?

Mixture lean is typically recommended during the ground operations at sea-level pressure in the POHs of most small aircraft equipped with a carburetor system. Why is it? I heard some people saying it'...
lemonincider's user avatar
  • 7,565
12 votes
6 answers
6k views

Does this fuel leak from the carburetor of a Cessna 172E need immediate maintenance?

Consider: I'm concerned with a fuel leak I've developed on my Cessna 172E in the past three weeks and appears to be coming from the carburetor. There is even some fuel in the air breather near the ...
Ron Davis's user avatar
  • 121
12 votes
2 answers
5k views

Why fuel left/right when C172 is secured?

The C172 POH checklists say to set the fuel selector to "right" or "left" when securing the plane but "both" while operating the plane. What is the point of changing the fuel selector when the engine ...
StephenS's user avatar
  • 27.7k
12 votes
1 answer
566 views

How do fuel trim and air bubbles prevention work in inverted flight?

I was reading Why do many GA aircraft not have a "Both" fuel selector? and voretaq7's excellent answer got me to thinking. He cites the regulations noting that the plane must only draw fuel from one ...
hildred's user avatar
  • 1,281
11 votes
4 answers
3k views

Is there any work on improving fuel tanks so they could store hydrogen?

I think that hydrogen is among the best fuels for use in supersonic and hypersonic flight, is there any work on improving fuel tanks so they could store hydrogen? What would be the best state to ...
securitydude5's user avatar
11 votes
1 answer
3k views

Why is the refueling point of this A320 on the left wing instead of the right?

Every other A320 I've seen has the refueling done in the right wing but not this one. Why? Registration YL-LDN
Otto Broman's user avatar
11 votes
3 answers
2k views

Why don't all cylinders have priming lines?

Questions about the primer for carburetor engines. Why does the primer only spray fuel to three (sometimes just one) of four cylinders. (Like Piper Cherokee or Seminole) And is it true that priming ...
Denji's user avatar
  • 133
11 votes
2 answers
1k views

What are possible explanations for fuel being expelled in this video?

In another question, I asked about whether or not a fuel spill would be reportable or not. The answer was "no", because the aircraft was not in flight. What are the possible causes of the spill ...
Steve's user avatar
  • 2,218
10 votes
1 answer
4k views

Why would the outer tanks fuel on the A320 be colder than the inner tanks?

I have noticed in a number of instances during long flights typically over 5 hours the fuel in the outer tanks on the A320 are colder than the fuel in the inner tanks. This goes against the system ...
Jai's user avatar
  • 1,502
9 votes
3 answers
3k views

Do pilots need a fuel pressure/temperature gauge?

Fuel pressure gauge allows you to monitor the fuel pressure while the engine is under a load. However, since the fuel pressure requirement is listed by the engine manufacturer, do pilots even need a ...
Faito Dayo's user avatar
9 votes
4 answers
3k views

How do you know which fuel an aircraft uses?

Other than the decals on the plane, how would you know what fuel to use in an aircraft? Where is this limitation documented? For some aircraft, does this limitation include some sort of substitute ...
Amirul Syamim's user avatar
9 votes
2 answers
2k views

How common were (are?) hydraulically driven fuel pumps?

The XB-70 had a large number of fuel transfer pumps (something like 25) to transfer fuel from the 10 other tanks into the sump tank, and then three fuel "boost" pumps to pump it from that to ...
tml's user avatar
  • 756
9 votes
1 answer
3k views

Why does fuel vaporize in the carburetor?

So I get that a carb vaporizes fuel and mixes it with the air intake for the engine. But my question is what is the explanation for what causes the fuel to vaporize after it exits the fuel nozzle?
BDeFreitas's user avatar
9 votes
1 answer
4k views

Why not leave an electric fuel pump on all the time?

This question is related to single-engined piston airplanes equipped with an electric fuel pump like the Piper Dakota/Arrow etc. The POH states that the fuel pump should be switched on for takeoffs/...
Prashant Saraswat's user avatar
9 votes
2 answers
2k views

Why does a fuel-injected engine have a mixture control?

For example, in a C172S fuel injected type, what does the mixture control lever control exactly in the fuel system? They have a fuel air control unit which regulates fuel flow based on air passing ...
Jimmy's user avatar
  • 101
9 votes
1 answer
252 views

How is the fuel quality monitored/assured for jetliners?

With tens of thousands of flights daily, many out of smaller and perhaps 'sketchy' airports, it would seem that serious incidents caused by contaminated fuel should happen a lot more often (in a quick ...
GregT's user avatar
  • 261
8 votes
1 answer
1k views

Does the mixture and throttle setting affect the quality of priming of fuel prior to start?

This question is a generality. For airplanes with small reciprocating engines, does the mixture and throttle setting at the time of priming affect the quality of the priming or the engine start, or ...
Ryan Mortensen's user avatar
8 votes
1 answer
532 views

Why was the Graf Zeppelin's endurance when fully fuelled with both fuels less than the sum of its endurances with each fuel separately?

The LZ-127 Graf Zeppelin used a unique dual-fuel system, with both a gasoline tank and a set of gas cells filled with blau gas; the airship could be flown using either fuel or both. The purpose of ...
Vikki's user avatar
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8 votes
2 answers
1k views

How can the fuel decrease evenly from both wing tanks when an A320 is running on APU only?

I stumbled over this sentence in a training material about fuel leak: "If the fuel quantity symmetrically decrease in both wing tanks and the fuel quantity in the center tank decrease, the fuel leak ...
Stefan C's user avatar
8 votes
1 answer
386 views

Can IPA be used as a FSII with MoGas, particularly with a Peterson STC?

This question established a basis for the use of 100% Isopropyl Alcohol (IPA) as a Fuel System Icing Inhibitor (FSII) in aviation gasoline systems. However, this Cessna Service Letter documents that ...
J W's user avatar
  • 16.6k
7 votes
3 answers
1k views

United’s 787-9 upgrade [duplicate]

I read this article about United increasing their performance of the 787-9. More specifically increasing thrust and range, But it says this will be done over software. How do you make an engine burn ...
Tylerb's user avatar
  • 93
7 votes
1 answer
3k views

How does the FAA define fuel capacity for ultralights?

Ultralights under FAR 103 are regulated to a capacity of 5 gallons. I'm wondering how exactly fuel capacity is defined, does it include fuel in the lines, and in the carburetor bowl or elsewhere or ...
Nile River's user avatar
7 votes
5 answers
2k views

Why is alcoholic gasoline such a showstopper for aviation?

One of the main reasons the common avgas grades are still full of 3-plumba-3,3-diethylpentane is the incompatibility of many aircraft fuel systems with the oxygenates (primarily ethanol, with some ...
Vikki's user avatar
  • 28.4k
7 votes
2 answers
2k views

What is the role of HP & LP fuel pumps in aircraft?

What is the role of HP (high pressure) and LP (low pressure) fuel pumps in aircraft like the A320? Why are two different ones needed?
Sachin Chaudhary's user avatar
7 votes
1 answer
3k views

What is the freezing point of 100LL Avgas?

Does anyone knows the exact freezing point of Avgas (100LL) ? I found that Jet A-1 freezes at −47 °C / −53 °F (wikipedia), but didn't manage to find any info on Avgas.
Jimy's user avatar
  • 2,152
7 votes
1 answer
633 views

Can you safely operate a 777 with diesel?

Is it possible to safely operate a Boeing 777 on diesel instead of Jet-A? Are there any regulations that prevent this? Would it cause any damage?
TayE's user avatar
  • 6,595
7 votes
3 answers
2k views

Why do we turn on fuel pump before descent in Diamond DA40?

The checklist procedure is: Electric fuel pump ............. on Mixture ............. rich MAP ............. 15 in of Hg RPM ............. 2300 Why the AFM says to turn on fuel pump during descent ...
Krishna Kanth's user avatar
6 votes
2 answers
4k views

Why does pulling the mixture to idle cutoff increase the RPM slightly?

When adjusting fuel control on a reciprocating engine, why is there a slight RPM rise (50-RPM rise) when pulling the mixture control to idle cutoff? Why if more than a 50-RPM rise, carburetor is set ...
StevenH88's user avatar
6 votes
1 answer
1k views

The fuel shut-off valve was left in over night. Is it dangerous for the plane?

I forgot to pull the shut-off valve in my plane (PZL-110 Koliber 150) while I was trying to start an engine. Will this have any effect on the plane? It has a mixture supply knob and is a pull/push ...
Kamil1598's user avatar
6 votes
2 answers
3k views

How does a fuel density sensor work? (densitometer, cadensicon)

While some fuel volume sensors use ultrasonic measurements this answer to How is fuel mass measured in airliners? says: The FCOM lists the sensors involved in this measurement: The FQI system ...
uhoh's user avatar
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