Air Carrier flight crew reported a fuel odor during departure taxi which dissipated and returned during initial climb accompanied with a fuel imbalance indication. After troubleshooting the fuel issue the Captain requested priority handling for an immediate air return where the flight landed safely.
Synopsis
Air Carrier flight crew reported a fuel odor during departure taxi which dissipated and returned during initial climb accompanied with a fuel imbalance indication. After troubleshooting the fuel issue the Captain requested priority handling for an immediate air return where the flight landed safely.
Narrative
Waiting for taxi clearance from ground for an extended amount of time I noticed an unusually strong jet fuel smell. The Captain noticed the same. We called the Flight Attendants to see if they noticed a strong fuel smell in the cabin. They didn't. We had one of the FA's (Flight Attendants) come to the flight deck to see if we had gotten used to the smell or what they noticed. The Flight Attendant didn't notice anything unusual. We reconfigured packs; cycling to see if the smell would dissipate then we started the other engine and the smell seemed to be gone so we were comfortable departing. We took off during the climb out around 10-11;000 ft.; we noticed a fuel imbalance and the number one main tank was indicating approximately 1300 lbs. less than the right. The Captain ran the QRH for a fuel leak- it didn't appear that we had an imbalance after running some numbers and not being able to account for a huge drop in fuel. Thinking about the jet fuel smell based back on the ground in ZZZ was the question - that did we have a fuel leak - so [we advised ATC] and we returned to ZZZ. The QRH says to shut down an engine. Given the close proximity to ZZZ; we did not. The rest of the flight was uneventful Fire and rescue didn't notice anything abnormal upon meeting us once we cleared the runway.
Second reporter narrative
On a single engine taxi out a strong jet fuel odor was noticed by both myself and the first officer; as this is not an uncommon event; we continued the taxi out but the smell seemed to persist longer than is normal. After starting the number 1 engine; the smell seemed to dissipate; so we decided to continue for takeoff. After a normal departure climbing out of 10;000 ft. and accelerating we noticed a fuel imbalance; with the number 1 main tank indicating approximately 1200-1300 lbs. less than the right main tank. I checked the fuel burned numbers to see if this could just be an imbalance because of a lower pressure center tank pump causing us to burn fuel out of the main tank; and found that we could not account for 900 lbs. of fuel. We ran the QRH for a fuel leak; which confirmed a potential fuel leak. The QRH for a fuel leak states 'A change in fuel imbalance of 500 lbs. within 30 minutes or less'. We were less than 15 minutes into the flight; and had a fuel imbalance of 1200 lbs. and could not account for where 900 lbs. of the fuel had gone by checking the fuel used and comparing it to the fuel we left with. We decided to return to ZZZ and [advised ATC] as a precaution. The QRH then leads you to 'go to step 11' which directs a precautionary engine shut down. I utilized my Captains authority to leave the engine running since we were so close to landing; and fuel starvation was not an imminent threat. This part of the QRH should be reviewed; as it seems foolish to shut down an engine based on the guidance from the first part of the checklist; as there is more than one thing that could cause you to get to step 11; such as a faulty indication. I mention the fuel smell during taxi out; because it did lead me to believe that we could be facing a greater threat and made me quicker to make the decision to return; vs continuing longer and seeing if I could identify an actual leak; or if it would stabilize. After landing; we had airport fire and rescue inspect the airplane to see if they saw any fuel leaks; which they did not. We taxied to the gate for an uneventful end to the flight.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.