“The only time you have too much fuel is when you’re on fire” is often said to be a pilot’s axiom or aviation adage. The saying is sometimes credited to Australian aviator Charles Kingsford-Smith (1897-1935), but there’s no evidence that the saying was used during his lifetime.
 
Aviator and author Ernest K. Gann (1910-1991) wrote in Ernest K. Gann’s Flying Circus (1974):
 
“What happens if one engine quits?”
According to my recollection most DC-3s eventually arrived at their destination if they carried enough fuel. In my private manual I firmly believed the only time there was too much fuel aboard any aircraft was if it was on fire.
 
Gann possibly coined the saying. Shell Aviation News (1976) explained, “Some domestic pilots contend that the only time too much fuel is aboard the aircraft is when it’s on fire.” P.C. Bryant, of Birmingham, Alabama, wrote to Flying magazine in 1981, “Landsberg might want to add one of my principles to his collection: ‘The only time you can have too much fuel in an airplane is when you’re on fire.’”
 
[This entry adds additional research to the original investigation on this quotation made in 2011 by the Quote Investigator—ed.]
 
 
Wikipedia: Charles Kingsford Smith
Sir Charles Edward Kingsford Smith MC, AFC (9 February 1897 – 8 November 1935), often called by his nickname Smithy, was an early Australian aviator. In 1928, he earned global fame when he made the first trans-Pacific flight from the United States to Australia. He also made the first non-stop crossing of the Australian mainland, the first flights between Australia and New Zealand, and the first eastward Pacific crossing from Australia to the United States. He also made a flight from Australia to London, setting a new record of 10.5 days.
 
Wikipedia: Ernest K. Gann
Ernest Kellogg Gann (October 13, 1910 - December 19, 1991) was an American aviator, author, filmmaker, sailor, fisherman and conservationist.
 
Google Books
Ernest K. Gann’s Flying Circus
By Ernest Kellogg Gann
New York, NY: Macmillan
1974
Pg. 191:
“What happens if one engine quits?”
According to my recollection most DC-3s eventually arrived at their destination if they carried enough fuel. In my private manual I firmly believed the only time there was too much fuel aboard any aircraft was if it was on fire.
 
Google Books
Shell Aviation News
Issues 433-444
1976
Pg. XXIII:
Some domestic pilots contend that the only time too much fuel is aboard the aircraft is when it’s on fire.
     
Google Books
April 1981, Flying magazine, pg. 10, col. 2:
Landsberg might want to add one of my principles to his collection: “The only time you can have too much fuel in an airplane is when you’re on fire.”
P. C. BRYANT
Birmingham, Alabama
 
Google Books
Cadillac Flight:
A Novel
By Marshall Harrison
Novato, CA: Lyford Books
1991
Pg. 199:
He reiterated one of his quotes for them: “The only time you can have too much fuel is when your aircraft is on fire.”
 
Google Books
Mastering the Systems:
Air Traffic Control and Weather
By Richard L. Collins
New York, NY: Macmillan
1991
Pg. 240:
The old saw about the only time you have too much fuel is when you are on fire is one way to look at it.
 
Google Books
The Sword of Orion
By Robin A. White
New York, NY: Crown Publishers
1993
Pg. 100:
“I remember being told the only time you have too much fuel is when you’re on fire.”
 
Google Books
February 1998, Flying magazine, pg. 103, col. 1:
It is joked that the only time you can have too much fuel is when you’re on fire. However, there are occasions in large aircraft when it is desirable, and sometimes imperative, to get rid of the weight in the quickest way.
 
Global Wit & Worldly Wisdom
99. Fear of Flying (apologies to Erica Jong)
Flight truths:
1. Every takeoff is optional.  Every landing is mandatory.
2. The only time you have too much fuel is when you’re on fire.
3. You start with a bag full of luck and an empty bag of experience.  The trick is to fill the bag of experience before you empty the bag of luck.
4. A “good” landing is one from which you can walk away.  A “great” landing is one after which they can use the plane again.

Taken from CIO (December 1, 2000, p.46) which in turn stole it from Austrailian Aviation.
 
Google Books
The Military Quotation Book, Revised and Expanded:
More Than 1,200 of the Best Quotations About War, Leadership, Courage, Victory, and Defeat
By James Charlton
New York, NY: St. Martin’s Press
2002
Pg. 108:
The only time an aircraft has too much fuel on board is when it is on fire.
SIR CHARLES KINGSFORD SMITH
 
26 June 2006, Roswell (NM) Daily Record, “Parade request; a little humor” by John Taylor, pg. A5, cols. 2-3:
Air Force Rules of the Air:
1. Every takeoff is optional. Every landing is mandatory.
2. Flying isn’t dangerous. Crashing is what’s dangerous.
3. The only time you have too much fuel is when you’re on fire.
 
Google Books
Stealth Fighter:
A Year in the Life of an F-117 Pilot
By William B. O’Connor
Minneapolis, MN: Zenith Press
2012
Pg. 103:
Pilot’s axiom: The only time you have too much fuel is when your plane is on fire.