Narrative:

Commuting on flight #; sitting in row 18 captain side (just aft of the left wing). Metar XA56Z 310/11 8SM 18BKN 24BKN 60OVC 01/M03 30.23 metar XB25Z 330/10 8SM 18SCT 60OVC 00/MO3 30.24 after pushback the aircraft was deiced for cold soaked fuel frost under the wing. I visually checked the top of the wing for ice or precipitation and saw none. Takeoff was normal; climbing thru broken/ovc 2K-10K with layers above 10000 ft. On climbout (approximately 6000 ft) heard and felt a series of bangs below my feet (left side of aircraft). Assumed it was bags or cargo shifting in the aft cargo compartment. After leveling at cruise (approximately 5 minutes at cruise) heard a series of bangs from the right side of the aircraft. Numerous passenger heard the noise and said they saw something depart the wing area. I called the cockpit via the aft flight attendant interphone. Spoke with captain/first officer about what I observed. I speculated it was ice that formed on the wing root (referring to the rbf). There were no abnormal indications from the cabin and the captain reported no abnormal indications or handling. On descent I observed a large area of clear ice (over 1/4 inch thick) on the wings (left and right). The ice had formed from the white walking area near the wing root; outward approximately 6 ft; where the sheet of ice had broken and shed was easily observable. The ice had formed over the fuel tank outline (black line) on the upper surface of the wing. On the ground I spoke with the captain and first officer about the incident. Both the captain and I spoke with chief pilot about the incident. The most important issue here is that there was no ice or precipitation on the upper surface of the wing prior to departure. The first officer had even used a ladder during preflight to check the upper surface of the wings. My assumption is that the fuel tank temperature was near freezing and as the aircraft climbed thru the moist layers; ice formed over the cold soaked fuel tanks. Anti-icing on the ground would not have stopped this from occurring.supplemental information from acn 815790: this flight was an am orginator. During his preflight walk around inspection; the first officer discovered ice had formed on the underside of both wings. During the exterior inspection he used a baggage loader to get a closer view of the upper surface of the wings. He did not find any evidence of contamination on the upper surfaces of the wings. As part of my preflight I went to the aft galley area; opened both exit doors to get a closer look at the stabilizer and tail area; and found no contamination on those surfaces. After the exterior inspections; we coordinated with ground crew for deicing the underside of both wings. The deicing crew also looked at the wings before pushback to make sure they would be able to remove all the icing. During the rest of the preflight I noted the fuel temperature was -2 degrees celsius. The ATIS weather report was: winds 310/11; visibility 8SM; ceiling 1800 ft; temperature +1 celsius; dew point -3 celsius; altimeter 30.23. Airport surfaces were wet due to an earlier frontal passage but no precipitation was falling at the time. Pushback; deicing; taxi; and takeoff were uneventful. On climbout we passed through broken decks at 1800 ft and 2400 ft MSL. We then climbed through an overcast deck at 6000 ft MSL and exited around 8000 ft MSL. During the rest of the climb to FL220 we passed through a few thin cloud layers. At FL220 and through the rest of the flight we remained in VFR conditions with only a few areas of light haze. Engine anti-ice was used for most of the climbout. As we leveled off; a company jumpseating pilot called the cockpit and stated that just after the 10000 ft he and some passenger heard a noise that sounded like something bouncing off the side of the fuselage. The jumpseating pilot said at first he thought the noise was caused by baggage shifting in the cargo bay; but he and another passenger noticed a flash of light outside one of the windows. The jumpseating pilot then looked at the top of the wings and noticed that ice had formed on top of the wings and was sloughing off. The ice sloughing off and hitting the fuselage probably caused the noise and what seemed to be a flash of light since exterior lights were on during the climb. The jumpseating pilot said it looked like the ice completely sloughed off. Both the first officer and I looked at the leading edges of the wings and did not see any contamination. During the initial descent; I turned on the wing heat for about one minute to ensure the leading edges were clear. Conditions were mostly VFR during our descent. Engine anti-ice was used only briefly; about minute; as we passed through some thin cirrus. Weather at mdw was clear; temperature -9 celsius; dew point -13 celsius; altimeter 30.24. Approach and landing were uneventful. At the gate the jumpseating pilot talked with me about the icing and said he noticed ice forming on the upper surface of the wings during the approach. I then went outside and inspected the wings. The leading edges and underside of the wings were clear; but a thin sheet of clear ice had formed on top of the wings just outboard of the painted exit path next to the fuselage. Refueling had begun by this time and the ice was melting off due to the temperature of the fuel being uploaded. I checked the fuel temperature and the gauge was reading +3 celsius. All wing and flight control surfaces were deiced before our departure. I don't believe any actions by this crew could have prevented the icing. As far as we could tell aircraft performance was not adversely affected. The icing that occurred during approach concerned me the most since we were in VFR conditions. I wonder if conditions were closer to conditions that heavier icing may have occurred.

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Original NASA ASRS Text

Title: DEADHEADING CREW MEMBER REPORTS ICE FORMING AND SHEDDING ON THE WING UPPER SURFACE OF B737NG DURING CLIMB OUT.

Narrative: COMMUTING ON FLIGHT #; SITTING IN ROW 18 CAPTAIN SIDE (JUST AFT OF THE LEFT WING). METAR XA56Z 310/11 8SM 18BKN 24BKN 60OVC 01/M03 30.23 METAR XB25Z 330/10 8SM 18SCT 60OVC 00/MO3 30.24 AFTER PUSHBACK THE ACFT WAS DEICED FOR COLD SOAKED FUEL FROST UNDER THE WING. I VISUALLY CHECKED THE TOP OF THE WING FOR ICE OR PRECIPITATION AND SAW NONE. TAKEOFF WAS NORMAL; CLIMBING THRU BKN/OVC 2K-10K WITH LAYERS ABOVE 10000 FT. ON CLIMBOUT (APPROX 6000 FT) HEARD AND FELT A SERIES OF BANGS BELOW MY FEET (LEFT SIDE OF ACFT). ASSUMED IT WAS BAGS OR CARGO SHIFTING IN THE AFT CARGO COMPARTMENT. AFTER LEVELING AT CRUISE (APPROX 5 MINUTES AT CRUISE) HEARD A SERIES OF BANGS FROM THE RIGHT SIDE OF THE ACFT. NUMEROUS PAX HEARD THE NOISE AND SAID THEY SAW SOMETHING DEPART THE WING AREA. I CALLED THE COCKPIT VIA THE AFT FLT ATTENDANT INTERPHONE. SPOKE WITH CAPTAIN/FIRST OFFICER ABOUT WHAT I OBSERVED. I SPECULATED IT WAS ICE THAT FORMED ON THE WING ROOT (REFERRING TO THE RBF). THERE WERE NO ABNORMAL INDICATIONS FROM THE CABIN AND THE CAPTAIN REPORTED NO ABNORMAL INDICATIONS OR HANDLING. ON DESCENT I OBSERVED A LARGE AREA OF CLEAR ICE (OVER 1/4 INCH THICK) ON THE WINGS (LEFT AND RIGHT). THE ICE HAD FORMED FROM THE WHITE WALKING AREA NEAR THE WING ROOT; OUTWARD APPROX 6 FT; WHERE THE SHEET OF ICE HAD BROKEN AND SHED WAS EASILY OBSERVABLE. THE ICE HAD FORMED OVER THE FUEL TANK OUTLINE (BLACK LINE) ON THE UPPER SURFACE OF THE WING. ON THE GROUND I SPOKE WITH THE CAPTAIN AND FO ABOUT THE INCIDENT. BOTH THE CAPT AND I SPOKE WITH CHIEF PLT ABOUT THE INCIDENT. THE MOST IMPORTANT ISSUE HERE IS THAT THERE WAS NO ICE OR PRECIPITATION ON THE UPPER SURFACE OF THE WING PRIOR TO DEPARTURE. THE FO HAD EVEN USED A LADDER DURING PREFLIGHT TO CHECK THE UPPER SURFACE OF THE WINGS. MY ASSUMPTION IS THAT THE FUEL TANK TEMPERATURE WAS NEAR FREEZING AND AS THE ACFT CLIMBED THRU THE MOIST LAYERS; ICE FORMED OVER THE COLD SOAKED FUEL TANKS. ANTI-ICING ON THE GROUND WOULD NOT HAVE STOPPED THIS FROM OCCURRING.SUPPLEMENTAL INFO FROM ACN 815790: THIS FLIGHT WAS AN AM ORGINATOR. DURING HIS PREFLIGHT WALK AROUND INSPECTION; THE FO DISCOVERED ICE HAD FORMED ON THE UNDERSIDE OF BOTH WINGS. DURING THE EXTERIOR INSPECTION HE USED A BAGGAGE LOADER TO GET A CLOSER VIEW OF THE UPPER SURFACE OF THE WINGS. HE DID NOT FIND ANY EVIDENCE OF CONTAMINATION ON THE UPPER SURFACES OF THE WINGS. AS PART OF MY PREFLIGHT I WENT TO THE AFT GALLEY AREA; OPENED BOTH EXIT DOORS TO GET A CLOSER LOOK AT THE STAB AND TAIL AREA; AND FOUND NO CONTAMINATION ON THOSE SURFACES. AFTER THE EXTERIOR INSPECTIONS; WE COORDINATED WITH GROUND CREW FOR DEICING THE UNDERSIDE OF BOTH WINGS. THE DEICING CREW ALSO LOOKED AT THE WINGS BEFORE PUSHBACK TO MAKE SURE THEY WOULD BE ABLE TO REMOVE ALL THE ICING. DURING THE REST OF THE PREFLIGHT I NOTED THE FUEL TEMPERATURE WAS -2 DEGREES CELSIUS. THE ATIS WEATHER REPORT WAS: WINDS 310/11; VISIBILITY 8SM; CEILING 1800 FT; TEMPERATURE +1 CELSIUS; DEW POINT -3 CELSIUS; ALTIMETER 30.23. AIRPORT SURFACES WERE WET DUE TO AN EARLIER FRONTAL PASSAGE BUT NO PRECIPITATION WAS FALLING AT THE TIME. PUSHBACK; DEICING; TAXI; AND TAKEOFF WERE UNEVENTFUL. ON CLIMBOUT WE PASSED THROUGH BROKEN DECKS AT 1800 FT AND 2400 FT MSL. WE THEN CLIMBED THROUGH AN OVERCAST DECK AT 6000 FT MSL AND EXITED AROUND 8000 FT MSL. DURING THE REST OF THE CLIMB TO FL220 WE PASSED THROUGH A FEW THIN CLOUD LAYERS. AT FL220 AND THROUGH THE REST OF THE FLIGHT WE REMAINED IN VFR CONDITIONS WITH ONLY A FEW AREAS OF LIGHT HAZE. ENGINE ANTI-ICE WAS USED FOR MOST OF THE CLIMBOUT. AS WE LEVELED OFF; A COMPANY JUMPSEATING PILOT CALLED THE COCKPIT AND STATED THAT JUST AFTER THE 10000 FT HE AND SOME PAX HEARD A NOISE THAT SOUNDED LIKE SOMETHING BOUNCING OFF THE SIDE OF THE FUSELAGE. THE JUMPSEATING PILOT SAID AT FIRST HE THOUGHT THE NOISE WAS CAUSED BY BAGGAGE SHIFTING IN THE CARGO BAY; BUT HE AND ANOTHER PAX NOTICED A FLASH OF LIGHT OUTSIDE ONE OF THE WINDOWS. THE JUMPSEATING PILOT THEN LOOKED AT THE TOP OF THE WINGS AND NOTICED THAT ICE HAD FORMED ON TOP OF THE WINGS AND WAS SLOUGHING OFF. THE ICE SLOUGHING OFF AND HITTING THE FUSELAGE PROBABLY CAUSED THE NOISE AND WHAT SEEMED TO BE A FLASH OF LIGHT SINCE EXTERIOR LIGHTS WERE ON DURING THE CLIMB. THE JUMPSEATING PILOT SAID IT LOOKED LIKE THE ICE COMPLETELY SLOUGHED OFF. BOTH THE FO AND I LOOKED AT THE LEADING EDGES OF THE WINGS AND DID NOT SEE ANY CONTAMINATION. DURING THE INITIAL DESCENT; I TURNED ON THE WING HEAT FOR ABOUT ONE MINUTE TO ENSURE THE LEADING EDGES WERE CLEAR. CONDITIONS WERE MOSTLY VFR DURING OUR DESCENT. ENGINE ANTI-ICE WAS USED ONLY BRIEFLY; ABOUT MINUTE; AS WE PASSED THROUGH SOME THIN CIRRUS. WEATHER AT MDW WAS CLEAR; TEMPERATURE -9 CELSIUS; DEW POINT -13 CELSIUS; ALTIMETER 30.24. APPROACH AND LANDING WERE UNEVENTFUL. AT THE GATE THE JUMPSEATING PILOT TALKED WITH ME ABOUT THE ICING AND SAID HE NOTICED ICE FORMING ON THE UPPER SURFACE OF THE WINGS DURING THE APPROACH. I THEN WENT OUTSIDE AND INSPECTED THE WINGS. THE LEADING EDGES AND UNDERSIDE OF THE WINGS WERE CLEAR; BUT A THIN SHEET OF CLEAR ICE HAD FORMED ON TOP OF THE WINGS JUST OUTBOARD OF THE PAINTED EXIT PATH NEXT TO THE FUSELAGE. REFUELING HAD BEGUN BY THIS TIME AND THE ICE WAS MELTING OFF DUE TO THE TEMPERATURE OF THE FUEL BEING UPLOADED. I CHECKED THE FUEL TEMPERATURE AND THE GAUGE WAS READING +3 CELSIUS. ALL WING AND FLIGHT CONTROL SURFACES WERE DEICED BEFORE OUR DEPARTURE. I DON'T BELIEVE ANY ACTIONS BY THIS CREW COULD HAVE PREVENTED THE ICING. AS FAR AS WE COULD TELL AIRCRAFT PERFORMANCE WAS NOT ADVERSELY AFFECTED. THE ICING THAT OCCURRED DURING APPROACH CONCERNED ME THE MOST SINCE WE WERE IN VFR CONDITIONS. I WONDER IF CONDITIONS WERE CLOSER TO CONDITIONS THAT HEAVIER ICING MAY HAVE OCCURRED.

Data retrieved from NASA's ASRS site as of May 2009 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.