Narrative:

On approach to ord we encountered moderate to severe mixed or clear ice in a B737. The ice formed on the underside of the wings (probably due to the high angle of attach while on approach) and created so much drag that the fuel flow required to stay on the glide path almost doubled from normal. 4500 pph as opposed to the normal 2700 pph. Any performance issues, such as the ability of the plane to go around or successfully encounter an engine failure were in serious question. The flight was msy-ord. The conditions were 300 ft and visibility 3/4 mi in fog. Surface temperature 34 degrees F. The cloud tops were uniform at 7000 ft and solid down to 300 ft AGL. No clouds of vertical development. We entered the clouds on a left downwind for runway 9L and flew an estimated 40 mi in the clouds. As soon as we entered the clouds we issued a PIREP for moderate to severe mixed ice and this continued to 300 ft AGL. We turned on the wing heat immediately upon detecting the rapid ice buildup and this kept the leading edges of the wings very clean. A pilot can see this from the cockpit. However, as the approach continued down the glide path, we noticed that we were continually adding power to stay on the glide path. By the time we landed the fuel flow was up to 4500 pph per engine. As soon as we were parked, I went down to look at the plane and as suspected, there was a great deal of clear or mixed ice on the underside of the wings, aft of the limit of the leading edge heat. There was also about 2-3 inches of mixed ice on the leading edges of the horizontal stabilizer. The outside air temperature was 34 degrees F so the ice was melting fast. I went into the terminal and bought a disposable camera and took the enclosed photo. This was at least 20 mins after landing, so much of the ice was melted. However, you can see that much of the ice is still present. When first observed from the ground, the ice was approximately 1/2 inch thick and rough, like a rubber door mat. It covered the entire underside of the wings from the wing root to the wing tip laterally, and from the aft limit of the leading edge heat to the front of the flaps. I believe that the accompanying photo and this narrative establish some significant possibilities. First, the B737 does have a clear aft limit to its leading edge ice protection. Second, when ice forms aft of this limit, on the underside of the wing, the increase in drag is enormous. This calls into question the aircraft's ability to perform (under these conditions) to its full range of certification. For example, I have serious doubts that this airplane could have climbed normally in a go around. I believe a single engine go around would be virtually impossible. I also believe that this situation could result in a hard, or short, landing if the power increases fall behind the drag increases. (Getting behind the power curve.) callback conversation with reporter revealed the following information: reporter suspected extensive ice accumulation while flying approach when the engine power had to be increased to maintain airspeed. A normal fuel flow would be 2700 pounds per hour, but now the requirement was up to 4500 pounds per hour. There was no headwind, so he felt positive the increased fuel flow was because of ice accumulation. His power requirements were so high to fly the approach, he was concerned if he could make a go around if necessary. Worse, he was positive the aircraft could not stay airborne if an engine failed. The landing and touchdown had no problems. After parking at the gate, reporter inspected aircraft and saw much accumulation of ice on the underside of the wing. Wing was clear from the leading edge to about 4 ft aft. Then the ice accumulation showed as rough ice on the wing bottom. Reporter took 20 mins to obtain a camera to illustrate the ice accumulation. With the delay to get a camera, much of ice had melted, but the photo dramatically shows the accumulation of ice on the underside of the wing. There was also an accumulation of ice on the horizontal stabilizer. Reporter's point about all of this is that wing anti-ice isn't sufficient to handle all types of icing.

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Original NASA ASRS Text

Title: B737 ENCOUNTERS SEVERE ICING DURING APCH IN ORD AIRSPACE.

Narrative: ON APCH TO ORD WE ENCOUNTERED MODERATE TO SEVERE MIXED OR CLR ICE IN A B737. THE ICE FORMED ON THE UNDERSIDE OF THE WINGS (PROBABLY DUE TO THE HIGH ANGLE OF ATTACH WHILE ON APCH) AND CREATED SO MUCH DRAG THAT THE FUEL FLOW REQUIRED TO STAY ON THE GLIDE PATH ALMOST DOUBLED FROM NORMAL. 4500 PPH AS OPPOSED TO THE NORMAL 2700 PPH. ANY PERFORMANCE ISSUES, SUCH AS THE ABILITY OF THE PLANE TO GO AROUND OR SUCCESSFULLY ENCOUNTER AN ENG FAILURE WERE IN SERIOUS QUESTION. THE FLT WAS MSY-ORD. THE CONDITIONS WERE 300 FT AND VISIBILITY 3/4 MI IN FOG. SURFACE TEMP 34 DEGS F. THE CLOUD TOPS WERE UNIFORM AT 7000 FT AND SOLID DOWN TO 300 FT AGL. NO CLOUDS OF VERT DEVELOPMENT. WE ENTERED THE CLOUDS ON A L DOWNWIND FOR RWY 9L AND FLEW AN ESTIMATED 40 MI IN THE CLOUDS. AS SOON AS WE ENTERED THE CLOUDS WE ISSUED A PIREP FOR MODERATE TO SEVERE MIXED ICE AND THIS CONTINUED TO 300 FT AGL. WE TURNED ON THE WING HEAT IMMEDIATELY UPON DETECTING THE RAPID ICE BUILDUP AND THIS KEPT THE LEADING EDGES OF THE WINGS VERY CLEAN. A PLT CAN SEE THIS FROM THE COCKPIT. HOWEVER, AS THE APCH CONTINUED DOWN THE GLIDE PATH, WE NOTICED THAT WE WERE CONTINUALLY ADDING PWR TO STAY ON THE GLIDE PATH. BY THE TIME WE LANDED THE FUEL FLOW WAS UP TO 4500 PPH PER ENG. AS SOON AS WE WERE PARKED, I WENT DOWN TO LOOK AT THE PLANE AND AS SUSPECTED, THERE WAS A GREAT DEAL OF CLR OR MIXED ICE ON THE UNDERSIDE OF THE WINGS, AFT OF THE LIMIT OF THE LEADING EDGE HEAT. THERE WAS ALSO ABOUT 2-3 INCHES OF MIXED ICE ON THE LEADING EDGES OF THE HORIZ STABILIZER. THE OUTSIDE AIR TEMP WAS 34 DEGS F SO THE ICE WAS MELTING FAST. I WENT INTO THE TERMINAL AND BOUGHT A DISPOSABLE CAMERA AND TOOK THE ENCLOSED PHOTO. THIS WAS AT LEAST 20 MINS AFTER LNDG, SO MUCH OF THE ICE WAS MELTED. HOWEVER, YOU CAN SEE THAT MUCH OF THE ICE IS STILL PRESENT. WHEN FIRST OBSERVED FROM THE GND, THE ICE WAS APPROX 1/2 INCH THICK AND ROUGH, LIKE A RUBBER DOOR MAT. IT COVERED THE ENTIRE UNDERSIDE OF THE WINGS FROM THE WING ROOT TO THE WING TIP LATERALLY, AND FROM THE AFT LIMIT OF THE LEADING EDGE HEAT TO THE FRONT OF THE FLAPS. I BELIEVE THAT THE ACCOMPANYING PHOTO AND THIS NARRATIVE ESTABLISH SOME SIGNIFICANT POSSIBILITIES. FIRST, THE B737 DOES HAVE A CLR AFT LIMIT TO ITS LEADING EDGE ICE PROTECTION. SECOND, WHEN ICE FORMS AFT OF THIS LIMIT, ON THE UNDERSIDE OF THE WING, THE INCREASE IN DRAG IS ENORMOUS. THIS CALLS INTO QUESTION THE ACFT'S ABILITY TO PERFORM (UNDER THESE CONDITIONS) TO ITS FULL RANGE OF CERTIFICATION. FOR EXAMPLE, I HAVE SERIOUS DOUBTS THAT THIS AIRPLANE COULD HAVE CLBED NORMALLY IN A GAR. I BELIEVE A SINGLE ENG GAR WOULD BE VIRTUALLY IMPOSSIBLE. I ALSO BELIEVE THAT THIS SIT COULD RESULT IN A HARD, OR SHORT, LNDG IF THE PWR INCREASES FALL BEHIND THE DRAG INCREASES. (GETTING BEHIND THE PWR CURVE.) CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR SUSPECTED EXTENSIVE ICE ACCUMULATION WHILE FLYING APCH WHEN THE ENG PWR HAD TO BE INCREASED TO MAINTAIN AIRSPD. A NORMAL FUEL FLOW WOULD BE 2700 LBS PER HR, BUT NOW THE REQUIREMENT WAS UP TO 4500 LBS PER HR. THERE WAS NO HEADWIND, SO HE FELT POSITIVE THE INCREASED FUEL FLOW WAS BECAUSE OF ICE ACCUMULATION. HIS PWR REQUIREMENTS WERE SO HIGH TO FLY THE APCH, HE WAS CONCERNED IF HE COULD MAKE A GAR IF NECESSARY. WORSE, HE WAS POSITIVE THE ACFT COULD NOT STAY AIRBORNE IF AN ENG FAILED. THE LNDG AND TOUCHDOWN HAD NO PROBS. AFTER PARKING AT THE GATE, RPTR INSPECTED ACFT AND SAW MUCH ACCUMULATION OF ICE ON THE UNDERSIDE OF THE WING. WING WAS CLR FROM THE LEADING EDGE TO ABOUT 4 FT AFT. THEN THE ICE ACCUMULATION SHOWED AS ROUGH ICE ON THE WING BOTTOM. RPTR TOOK 20 MINS TO OBTAIN A CAMERA TO ILLUSTRATE THE ICE ACCUMULATION. WITH THE DELAY TO GET A CAMERA, MUCH OF ICE HAD MELTED, BUT THE PHOTO DRAMATICALLY SHOWS THE ACCUMULATION OF ICE ON THE UNDERSIDE OF THE WING. THERE WAS ALSO AN ACCUMULATION OF ICE ON THE HORIZ STABILIZER. RPTR'S POINT ABOUT ALL OF THIS IS THAT WING ANTI-ICE ISN'T SUFFICIENT TO HANDLE ALL TYPES OF ICING.

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.