This is an excerpt from a report made to the Aviation Safety Reporting System. The narrative is written by the pilot, rather than FAA or NTSB officials. To maintain anonymity, many details, such as aircraft model or airport, are often scrubbed from the reports.
We noticed an unusually low fuel reading on our left tank for the duration we had flown. Our fuel was topped off prior to flight. Approximately one hour into the flight we were showing half a tank on the left (~13 gallons missing) and a full tank on the right. We would have expected closer to ~5 gallons missing from each tank.
We were able to see fuel leaking from the right tank while in flight, so we diverted to ZZZ and requested priority sequencing due to our fuel loss. We were able to see the fuel gauge dropping in level. We landed at ZZZ with an indication of 5 gallons on the left tank and full on the right tank; both tanks hold 26 gallons.
After landing, we inspected the aircraft and discovered our right tank fuel cap missing. It was present during our preflight.
At our sister flight school at ZZZ, we were able to obtain a temporary replacement fuel cap so that we could return to ZZZ1. We topped off with fuel, taxied to the run-up, and departed for ZZZ1 and returned to ZZZ1 without incident.
Prior to our flight, we had called for a fuel truck and had the tanks filled to full. The student noticed the fuel was very high, to the very top, of the fuel necks after the fueling was completed. Our run-up, departure, and flight were without incident until we discovered the fuel leak.
After returning to ZZZ1, we had learned that Airport Ops had been notified of FOD on taxiway C, which was a fuel cap. We had taxied down taxiway C. Ops returned the fuel cap to our front desk and it looks like it was from our aircraft.
Primary Problem: Human Factors
ACN: 1887185
Whenever I get a plane fueled I have a habit of climbing up and checking that the fuel cap is secure myself. The FBO guy said that maybe half the time pilots double check the cap after they’re done.
I prefer to use the ‘self- fuel’ option, which most airports have.
The fuel is lower cost, and I bring my own 3 step step-ladder, if I need it.
So, I know the tanks are full and can be sure that the caps are on securely.!
[ the rubber gaskets are easily replaced ]
Also, my caps have chains to the filler neck, I can’t lose one.
It’s quite easy on a high wing Citabria type aircraft to have a situation where a fuel cap either isn’t fully tightened by the fuel service guy or the rubber seal in the cap deteriorates to the point of having a weak seal. I have experienced both situations with a corresponding loss of fuel as avgas is sucked out of the filler hole on top of the wing into the airstream. I always carry a spare fuel cap in my plane for this reason and I am obsessive about firmly checking the cap tightness after anyone else touches the cap and about monitoring the fuel level, especially after a fill. If you have the type of cap that simply screws in with a rubber gasket inside, I recommend taking a look at the soundness of the rubber and order a new set if youhave cracks or dry rot developing.
When refuelling my aircraft, I once found a fuel cap from a Cessna on the fuel ramp, and was able to return it to the very shocked pilot who had just topped off before parking. It is quite easy to do and we keep a spare cap in our aircraft.
A little bit of rush as after refueling my aircraft, and doing the preflight one evening as I was trying to get to our hunting site. Taxied out, and while taxiing a thought came to me. “Did I put the fuel cap back?” I shut down on the taxiway and then looked and sure enough, I hadn’t replaced the cap. I was glad I was reviewing what I did before getting too far.
The article was NOT clear or even ‘general’ regarding the aircraft ‘Type’.
However, by deduction, a high wing aircraft can [usually] feed fuel from both wing tanks for relatively equal fuel levels in both… and a low wing aircraft [usually] feeds from one wing-tank at a time, Sooo this is likely a Cessna… C150? C172?
I always found it harder to check high wing tanks without a ladder…. using the built-on step and the strut and balancing at the same time made for sketchy/unsafe[?] upper wing-surface checks… especially in windy/dark condition.
High fuel levels [into the filler-neck?] can be difficult to deal with… but fuel filler-caps demand check, double check and ‘tug[pull]-check’.
Just ‘click’ on the ACN #:
Aircraft
Reference : X
Aircraft Operator : FBO
Make Model Name : Skyhawk 172/Cutlass 172
Crew Size.Number Of Crew : 2
Operating Under FAR Part : Part 91
Flight Plan : None
Mission : Training
Flight Phase : Cruise
Route In Use : Direct
The fuel cap was “present” during the preflight. After the refueling, the student noticed the fuel tank was very full. Well, to see that, the student had to have removed the fuel cap, which later was discovered missing. Sounds to me like the student didn’t secure the fuel cap properly.
Well, at least they were monitoring their fuel and took decisive action well before it was too late.