Fuel leaked into the cabin of an small transport.

Attributes
ACN	277928
Time
Date	199407
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : cdv
State Reference	AK
Altitude	agl bound lower : 0 agl bound upper : 700
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	common carrier : air taxi
Make Model Name	Twin Otter DHC-6
Operating Under FAR Part	Part 91
Flight Phase	cruise other ground : preflight other
Flight Plan	VFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 210 flight time total : 10100 flight time type : 9000
ASRS Report	277928
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	other other : unspecified
Resolutory Action	none taken : unable other
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

Captain and copilot personally refueled aircraft with full fuel in rear host tank of the twin otter (DHC6-200). 12 passenger were boarded. Aircraft departed eastbound straight out and leveled off at approximately 700 ft AGL. Almost immediately, 9 passenger came forward to the cockpit and alerted the copilot of fuel smell in rear of cabin. We acknowledged her comment and began to discuss potential causes of problem. Passenger immediately re-entered the cockpit while showing her hand wetted by fuel from placing it on rear cabin floor by the airstair. I immediately turned back towards the airport and landed approximately 5 mins later. Aircraft taxied in, shutdown and unloaded passenger without event. Crew inspected aircraft and found carpet at top of airstair (approximately 2 square ft) wet with fuel, and fuel dripping from rear belly of aircraft. Fuel caps were inspected and found to be secured and locked approximately in place. However, as rear cap was removed, it was noted that it felt 'loose' while removing. Fuel was noted to still be standing in fuel filler neck -- indicating full tank. On closer inspection, the backing lock nut on cap which controls the 'locked-on' pressure of the cap appeared to have possibly loosened, resulting in a less than ideal tight seal of 'O' ring on cap. (Not compressing adequately) cap was switched, with front cap and tightened with both caps 'feeling' tighter in their new respective filler necks. Carpet was removed and cabin cleared and deodorized. Passenger complained initially of slight headaches from fuel odor and 2 rear nest passenger seated on aft bulkhead had light fuel spray on shoes. The fuel apparently flowed out of aft tank around cap and infiltrated cabin through gasket around rear airstair door frame. The problem appeared to be caused by a combination of full fuel in tank, loosened lock nut on cap and poor gasket seal around door. This problem has been noted before in our twin otter operations. Permanent cure could include better fail-safe cap seal design or 'spoiler' mounted aft of fuel filler to cause fuel to flow off fuselage in flight.

Original NASA ASRS Text

Title: FUEL LEAKED INTO THE CABIN OF AN SMT.

Narrative: CAPT AND COPLT PERSONALLY REFUELED ACFT WITH FULL FUEL IN REAR HOST TANK OF THE TWIN OTTER (DHC6-200). 12 PAX WERE BOARDED. ACFT DEPARTED EBOUND STRAIGHT OUT AND LEVELED OFF AT APPROX 700 FT AGL. ALMOST IMMEDIATELY, 9 PAX CAME FORWARD TO THE COCKPIT AND ALERTED THE COPLT OF FUEL SMELL IN REAR OF CABIN. WE ACKNOWLEDGED HER COMMENT AND BEGAN TO DISCUSS POTENTIAL CAUSES OF PROB. PAX IMMEDIATELY RE-ENTERED THE COCKPIT WHILE SHOWING HER HAND WETTED BY FUEL FROM PLACING IT ON REAR CABIN FLOOR BY THE AIRSTAIR. I IMMEDIATELY TURNED BACK TOWARDS THE ARPT AND LANDED APPROX 5 MINS LATER. ACFT TAXIED IN, SHUTDOWN AND UNLOADED PAX WITHOUT EVENT. CREW INSPECTED ACFT AND FOUND CARPET AT TOP OF AIRSTAIR (APPROX 2 SQUARE FT) WET WITH FUEL, AND FUEL DRIPPING FROM REAR BELLY OF ACFT. FUEL CAPS WERE INSPECTED AND FOUND TO BE SECURED AND LOCKED APPROX IN PLACE. HOWEVER, AS REAR CAP WAS REMOVED, IT WAS NOTED THAT IT FELT 'LOOSE' WHILE REMOVING. FUEL WAS NOTED TO STILL BE STANDING IN FUEL FILLER NECK -- INDICATING FULL TANK. ON CLOSER INSPECTION, THE BACKING LOCK NUT ON CAP WHICH CTLS THE 'LOCKED-ON' PRESSURE OF THE CAP APPEARED TO HAVE POSSIBLY LOOSENED, RESULTING IN A LESS THAN IDEAL TIGHT SEAL OF 'O' RING ON CAP. (NOT COMPRESSING ADEQUATELY) CAP WAS SWITCHED, WITH FRONT CAP AND TIGHTENED WITH BOTH CAPS 'FEELING' TIGHTER IN THEIR NEW RESPECTIVE FILLER NECKS. CARPET WAS REMOVED AND CABIN CLRED AND DEODORIZED. PAX COMPLAINED INITIALLY OF SLIGHT HEADACHES FROM FUEL ODOR AND 2 REAR NEST PAX SEATED ON AFT BULKHEAD HAD LIGHT FUEL SPRAY ON SHOES. THE FUEL APPARENTLY FLOWED OUT OF AFT TANK AROUND CAP AND INFILTRATED CABIN THROUGH GASKET AROUND REAR AIRSTAIR DOOR FRAME. THE PROB APPEARED TO BE CAUSED BY A COMBINATION OF FULL FUEL IN TANK, LOOSENED LOCK NUT ON CAP AND POOR GASKET SEAL AROUND DOOR. THIS PROB HAS BEEN NOTED BEFORE IN OUR TWIN OTTER OPS. PERMANENT CURE COULD INCLUDE BETTER FAIL-SAFE CAP SEAL DESIGN OR 'SPOILER' MOUNTED AFT OF FUEL FILLER TO CAUSE FUEL TO FLOW OFF FUSELAGE IN FLT.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.