Date: 201808
Local time of day: 1201-1800
Location: ZFW.ARTCC, TX
Flight conditions: VMC
Light: Daylight
Aircraft: B737-800
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZFW
ATC / advisory: Center ZFW
Aircraft component: Fuel System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Situational Awareness
Second reporter function: Pilot Not Flying; First Officer
Anomaly: Aircraft Equipment Problem Critical; Flight Deck / Cabin / Aircraft Event Illness / Injury; Flight Deck / Cabin / Aircraft Event Smoke / Fire / Fumes / Odor; Inflight Event / Encounter Fuel Issue
Detector: Person Flight Attendant
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Landed in Emergency Condition
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: At the top of climb/level off/cruise; 22;000 ft; one of the aft cabin flight attendants called the cockpit and complained about an odor that was making her nauseous. I asked what the odor smelled like and she stated she wasn't sure. I then asked her if it smelled like something burning; electrical; or fuel. She stated it was probably more of a fuel smell. I asked her if the smell was throughout the cabin and she wasn't sure. I then called the forward #1 Flight Attendant and asked her if she had any strange odors in the forward cabin. She stated no; she smelled nothing. I then asked the aft cabin Flight Attendant if any passengers could smell the odor and if passengers were becoming nauseated. She did not know. I then asked her to walk forward from the rear of the cabin toward the front to determine where the smell began and where it stopped and to check and see how the passengers in the affected cabin were feeling. At this point the First Officer and I started the Aircraft Odor checklist. Several minutes later the aft cabin Flight Attendant called me back and stated that one passenger thought the odor smelled like hydraulic fluid and several others thought it smelled like fuel. She also stated the smell began around Row 17 and continued all the way back to the aft galley/rear of the aircraft; but that it seemed to be less intense. I then asked her how she was feeling and how the passengers were feeling. She reported that both of them (#2 and #4 flight attendants) and several passengers were now feeling nauseous; light headed and dizzy. I asked if she thought the odor still smelled like fuel and if the odor was getting stronger and she stated yes.At this point; with the number #1 Flight Attendant also on the interphone; I explained to them that I was going to [advise ATC] and get us on the ground as quickly as possible; and that I would get back to them shortly. I quickly gave the aircraft and radio control over to the First Officer and had him [advise ATC]; directing him to proceed direct to the RNAV IAF. I then completed the Aircraft Odor checklist with the assumption being FUEL as the possible source. The difficulty for me in accomplishing this checklist was trying to determine if the odor was classified as strong or as mild/moderate. I chose strong and proceeded to the Smoke; Fire and Fumes checklist. Accomplishing this checklist left me somewhat confused since we had no smoke; fire or fumes; but rather a strong aircraft odor that smelled like fuel. In this case the Smoke; Fire or Fumes Checklist sent me back to the Aircraft Odor Checklist. By this point in the Aircraft Odor Checklist we had started our descent and I then referred to and accomplished the non routine landing checklist; advised dispatch via ACARS; briefed the #1 Flight Attendant on a precautionary landing and emphasizing no ground evacuation anticipated; and then made an address to the passengers regarding our situation. Once I was able to focus my attention back in the cockpit I accomplished the descent checklist and then took back control of the aircraft. The First Officer did an outstanding job getting the aircraft direct and coordinating with ATC. The approach and landing were uneventful. Once we landed and cleared the runway I let the flight attendants know what was occurring and that we were not going to evacuate. I then stopped the aircraft on a taxiway and had the fire chief check our aircraft; in particular for potential fuel leaks and/or heat signatures. Then I made a passenger address further explaining what was occurring outside the aircraft and that everything was ok and safe. The fire chief then gave us an all clear report and we proceeded to our gate with the fire trucks following closely behind. Once at the gate and parked the aft cabin flight attendants called again and reported that the fuel odor/fumes were even stronger than before. Within a minute the fire chief came to the cockpit and report strong fuel fumes outside around the airplane. We quickly deplaned the passengers. Hind sight indicates an obvious fuel leak that penetrated the air conditioning system.According to the QRH Aircraft Odor Checklist; an ODOR is not smoke or fumes associated with a fire source; an odor is any smell; and a fume is dangerous to inhale. So what did I have on my flight an ODOR or a FUME? With so many new; young; and inexperienced flight attendants in our airline today the descriptions; or lack of descriptions; leave Captains unsure of what really is an odor or a dangerous fume. Once on the ground and at the gate it was clear that we had a major fuel leak; fume; or vapor problem. I think we should look at further defining the word FUMES in our Smoke; Fire or Fumes Checklist to include Fuel Fumes. Furthermore; with hindsight as a guide; I think the checklist needs to address passenger electronic equipment; which should be immediately turned off and shut down if fuel fumes exist in the cabin. Numerous cases in the United States have had individuals igniting gasoline fumes at fueling pumps while parked at a gas station; blowing up the entire gas station and killing themselves; all because they answered their cell phone or turned on the light function on their cell phone. Static electricity appears to be the problem with electronic devices; and if fuel fumes are strong enough in the cabin of an airplane; then the subsequent result could be catastrophic.


Second narrative: [Reported narrative contained no additional information.]


Synopsis: B737 flight crew reported fuel fumes/odor in the aft cabin resulted in a direct approach and landing at the planned destination.