Narrative:

On may/xa/97 I was the captain of base flight (service from lgw to ein). The 2 previous flts (fmo to ein and ein to lgw) were normal and free of problems. Immediately after takeoff from lgw, however, the aircraft experienced sudden uncommanded violent roll tendencies, both left and right. The flight controls were very ineffective in controling the aircraft. The aircraft as well as the flight controls were jerking rapidly back and forth (mostly left and right). I knew we had an extreme flight control problem, but I could not determine the cause. My thoughts at the time were that perhaps a ground vehicle had struck an aileron and bent it. My first officer, xyz, performed an aircraft exterior inspection accompanied by a base pilot in training on the ground in lgw. As part of the new pilots training xyz explained in detail the preflight procedures. They observed nothing unusual about the aircraft at that time. After gear and flap retraction the problem got more severe. Shortly after passing 1000 ft I instructed xyz to declare an emergency and inform lgw tower that we were going to enter a l-hand visual pattern for runway 26L and we wanted to land as soon as possible. The aircraft was not responding very well to any flight control inputs, the ailerons were particularly unresponsive. We leveled off at 2000 ft and reduced the power setting so as not to exceed 180 KTS. During the turn to downwind and most of the downwind leg the aircraft repeatedly rolled quickly to the left and right at times exceeding 60 degrees of bank and causing a subsequent loss of altitude of approximately 250 ft. Keeping the aircraft flying required 100% of my attention. Abeam the field on the downwind leg we extended the flaps to 15 degrees and the aircraft became somewhat more stable. Xyz completed the after takeoff and both descent and approach checklists whilst communicating with ATC. At that time we were cleared for the visual approach and cleared for landing. Our checklists were completed and I was concentrating on keeping the aircraft stable. During the base leg the aircraft's sudden rolling tendency became stronger again. We lowered the landing gear and extended flaps to 25 degrees. The aircraft was still exhibiting land right rolling tendencies but these were less pronounced, probably due to the flap position and our slower airspeed. I increased the threshold target speed by 20 KTS. The landing was firm but remarkably smooth. After notifying the fire brigade that the emergency was over we parked the airplane at the gate. Upon visual inspection of the airplane we found a crack in the upper right wing surface, parallel and just behind the ice boots. This was located directly in front and in the middle of the right aileron (and aileron trim tab). This crack in the fiberglas covering of the wing was approximately 1 1/2 ft long and about 2 inches wide. On the ground (with no airflow over the wings) it was protruding above the wing only about 1/3 of an inch. In-flight, however (with airflow over the wing holding it open), it protruded a full 2 inches effectively becoming an air brake and distorting the flow of air over the right wing and aileron. Not only was a 2-3 ft section of the wing not flying but the turbulent air produced by the protruding surface was moving the right aileron violently up and down resulting in the violent rolling movements the aircraft experienced. The aileron was rendered ineffective for controling the aircraft due to the decreased abnormal air flowing over it. I believe that somehow (I don't know how) a small crack occurred on top of the wing. The flow of air over the wing got in between the crack making it grow ever larger during our short (6 min) flight. I think that if the airspeed was increased or the flight had lasted any longer the crack would rapidly have grown from the engine nacelle to the wingtip. That situation would have resulted in a complete stall of the right wing and aileron from which recovery would be impossible. The aircraft was only marginally ctlable as it was. In order to insure that this situation does not occur again, I recommend a thorough, detailed maintenance inspection of the top of all EMB120 wings, directly between the deicing boots and the wing surface. All EMB120 pilots and technicians should be made aware of the possible catastrophic consequences of any surface cracks discovered in that area. Procedures relating to the maintenance of the wing deicing boots including installation and inspection procedures should also be reviewed to insure that they have not contributed to the creation of such cracks.

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Original NASA ASRS Text

Title: AN EMB120 DECLARED AN EMER AND RETURNED TO THE FIELD DUE TO SUDDEN UNCOMMANDED VIOLENT ROLL TENDENCIES CAUSED BY AN 18 INCH CRACK IN THE UPPER R WING LEADING EDGE SURFACE AFT OF THE DEICER BOOT.

Narrative: ON MAY/XA/97 I WAS THE CAPT OF BASE FLT (SVC FROM LGW TO EIN). THE 2 PREVIOUS FLTS (FMO TO EIN AND EIN TO LGW) WERE NORMAL AND FREE OF PROBS. IMMEDIATELY AFTER TKOF FROM LGW, HOWEVER, THE ACFT EXPERIENCED SUDDEN UNCOMMANDED VIOLENT ROLL TENDENCIES, BOTH L AND R. THE FLT CTLS WERE VERY INEFFECTIVE IN CTLING THE ACFT. THE ACFT AS WELL AS THE FLT CTLS WERE JERKING RAPIDLY BACK AND FORTH (MOSTLY L AND R). I KNEW WE HAD AN EXTREME FLT CTL PROB, BUT I COULD NOT DETERMINE THE CAUSE. MY THOUGHTS AT THE TIME WERE THAT PERHAPS A GND VEHICLE HAD STRUCK AN AILERON AND BENT IT. MY FO, XYZ, PERFORMED AN ACFT EXTERIOR INSPECTION ACCOMPANIED BY A BASE PLT IN TRAINING ON THE GND IN LGW. AS PART OF THE NEW PLTS TRAINING XYZ EXPLAINED IN DETAIL THE PREFLT PROCS. THEY OBSERVED NOTHING UNUSUAL ABOUT THE ACFT AT THAT TIME. AFTER GEAR AND FLAP RETRACTION THE PROB GOT MORE SEVERE. SHORTLY AFTER PASSING 1000 FT I INSTRUCTED XYZ TO DECLARE AN EMER AND INFORM LGW TWR THAT WE WERE GOING TO ENTER A L-HAND VISUAL PATTERN FOR RWY 26L AND WE WANTED TO LAND ASAP. THE ACFT WAS NOT RESPONDING VERY WELL TO ANY FLT CTL INPUTS, THE AILERONS WERE PARTICULARLY UNRESPONSIVE. WE LEVELED OFF AT 2000 FT AND REDUCED THE PWR SETTING SO AS NOT TO EXCEED 180 KTS. DURING THE TURN TO DOWNWIND AND MOST OF THE DOWNWIND LEG THE ACFT REPEATEDLY ROLLED QUICKLY TO THE L AND R AT TIMES EXCEEDING 60 DEGS OF BANK AND CAUSING A SUBSEQUENT LOSS OF ALT OF APPROX 250 FT. KEEPING THE ACFT FLYING REQUIRED 100% OF MY ATTN. ABEAM THE FIELD ON THE DOWNWIND LEG WE EXTENDED THE FLAPS TO 15 DEGS AND THE ACFT BECAME SOMEWHAT MORE STABLE. XYZ COMPLETED THE AFTER TKOF AND BOTH DSCNT AND APCH CHKLISTS WHILST COMMUNICATING WITH ATC. AT THAT TIME WE WERE CLRED FOR THE VISUAL APCH AND CLRED FOR LNDG. OUR CHKLISTS WERE COMPLETED AND I WAS CONCENTRATING ON KEEPING THE ACFT STABLE. DURING THE BASE LEG THE ACFT'S SUDDEN ROLLING TENDENCY BECAME STRONGER AGAIN. WE LOWERED THE LNDG GEAR AND EXTENDED FLAPS TO 25 DEGS. THE ACFT WAS STILL EXHIBITING LAND R ROLLING TENDENCIES BUT THESE WERE LESS PRONOUNCED, PROBABLY DUE TO THE FLAP POS AND OUR SLOWER AIRSPD. I INCREASED THE THRESHOLD TARGET SPD BY 20 KTS. THE LNDG WAS FIRM BUT REMARKABLY SMOOTH. AFTER NOTIFYING THE FIRE BRIGADE THAT THE EMER WAS OVER WE PARKED THE AIRPLANE AT THE GATE. UPON VISUAL INSPECTION OF THE AIRPLANE WE FOUND A CRACK IN THE UPPER R WING SURFACE, PARALLEL AND JUST BEHIND THE ICE BOOTS. THIS WAS LOCATED DIRECTLY IN FRONT AND IN THE MIDDLE OF THE R AILERON (AND AILERON TRIM TAB). THIS CRACK IN THE FIBERGLAS COVERING OF THE WING WAS APPROX 1 1/2 FT LONG AND ABOUT 2 INCHES WIDE. ON THE GND (WITH NO AIRFLOW OVER THE WINGS) IT WAS PROTRUDING ABOVE THE WING ONLY ABOUT 1/3 OF AN INCH. INFLT, HOWEVER (WITH AIRFLOW OVER THE WING HOLDING IT OPEN), IT PROTRUDED A FULL 2 INCHES EFFECTIVELY BECOMING AN AIR BRAKE AND DISTORTING THE FLOW OF AIR OVER THE R WING AND AILERON. NOT ONLY WAS A 2-3 FT SECTION OF THE WING NOT FLYING BUT THE TURBULENT AIR PRODUCED BY THE PROTRUDING SURFACE WAS MOVING THE R AILERON VIOLENTLY UP AND DOWN RESULTING IN THE VIOLENT ROLLING MOVEMENTS THE ACFT EXPERIENCED. THE AILERON WAS RENDERED INEFFECTIVE FOR CTLING THE ACFT DUE TO THE DECREASED ABNORMAL AIR FLOWING OVER IT. I BELIEVE THAT SOMEHOW (I DON'T KNOW HOW) A SMALL CRACK OCCURRED ON TOP OF THE WING. THE FLOW OF AIR OVER THE WING GOT IN BTWN THE CRACK MAKING IT GROW EVER LARGER DURING OUR SHORT (6 MIN) FLT. I THINK THAT IF THE AIRSPD WAS INCREASED OR THE FLT HAD LASTED ANY LONGER THE CRACK WOULD RAPIDLY HAVE GROWN FROM THE ENG NACELLE TO THE WINGTIP. THAT SIT WOULD HAVE RESULTED IN A COMPLETE STALL OF THE R WING AND AILERON FROM WHICH RECOVERY WOULD BE IMPOSSIBLE. THE ACFT WAS ONLY MARGINALLY CTLABLE AS IT WAS. IN ORDER TO INSURE THAT THIS SIT DOES NOT OCCUR AGAIN, I RECOMMEND A THOROUGH, DETAILED MAINT INSPECTION OF THE TOP OF ALL EMB120 WINGS, DIRECTLY BTWN THE DEICING BOOTS AND THE WING SURFACE. ALL EMB120 PLTS AND TECHNICIANS SHOULD BE MADE AWARE OF THE POSSIBLE CATASTROPHIC CONSEQUENCES OF ANY SURFACE CRACKS DISCOVERED IN THAT AREA. PROCS RELATING TO THE MAINT OF THE WING DEICING BOOTS INCLUDING INSTALLATION AND INSPECTION PROCS SHOULD ALSO BE REVIEWED TO INSURE THAT THEY HAVE NOT CONTRIBUTED TO THE CREATION OF SUCH CRACKS.

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.