Narrative:

Comments/details: upon entering the FBO's ramp area, there were no less than 3 linemen positioned as follows, to assist us in parking the aircraft: 1) one just beyond where the nose of the aircraft would be when the parking maneuver was complete, 2) one in front of the wingtip of the aircraft we would be parked adjacent to, and 3) one in front of and just a few ft away from the wall we would have to taxi parallel to before making the final 90 degree turn into the parked position. During the parallel-to-the-wall portion of our taxi, the captain asked me to monitor our right wing. I looked back and continued looking back and positioned my l-hand so that I could give him a thumbs up (or down) sign. Though the rain made it difficult to see the wingtip clearly, I estimated that we had adequate clearance -- approximately 10 ft. About 1/2 way through this parallel-to- the-wall taxi, the captain asked me how it looked. I responded, 'looking good,' or 'plenty of room,' or something to that effect, since it appeared that we were maintaining a parallel track over the ramp with reference to the wall and that we still had adequate clearance. Because of the extreme viewing angle and the rain beading and periodically running in rivulets down the side window, I maintained an extremely rapid scan back and forth between the wingtip and the wall and the lineman who was in a much better position to monitor the clearance in question. If our clearance decreased, he would be able to detect it before I could and would given an appropriate signal which I was in the best position to see. A few seconds after the turn away from the wall was commenced, the winglet struck a vertical supporting wall post which extended out from the wall by approximately 1-2 ft. At the time of impact the lineman was still giving us a thumbs up indication that we had adequate clearance and it still appeared to me that we had adequate clearance. Perhaps our track was not perfectly parallel to the wall and we were undetectably inching closer and closer to the wall just prior to making the 90 degree turn, or the geometry of the main and nose gear and the combination of differential braking and nose steering input was such that the wingtip suddenly swung out much closer to the wall than would normally be expected after the turn was initiated. The rain was also a contributing factor as it reduced and distorted visibility. Recommendations: the phenomenon sometimes referred to as 'delta-wing wing-growth' should be formally introduced to both initial and recurrent training programs. A phone call to gulfstream engineering confirmed my suspicion that nowhere do they publish the exact distance that the wing effectively 'grows' under the aforementioned conditions, though they do publish a turning radius diagram from which the information might be deduced. Most of the pilots that I questioned so far have never heard of this phenomena. The few who were aware of it guessed that the distance involved for a g-iv) was between 6-9 inches --in fact, it is approximately twice as much. The engineer I spoke with at gulfstream gave his estimate as 2-3 ft. Aircraft manufacturers should publish applicable data documenting the precise extent of such 'wing-growth' and FBO's should be required to document that their linemen have been trained accordingly. Flight safety should devote at least as much time to this aspect of aircraft ground operations as they do on the effect of flap setting on horizontal stabilizer position and hangar clearance since wing growth is far more insidious and, once underestimated, is almost impossible to recover from due to the accelerated nature of the turn. The extremely disadvantaged viewing angle from the cockpit makes it very difficult to accurately estimate the distance from the wingtip of a swept-wing aircraft to an adjacent ground object under ideal circumstances, much less with rain beading and streaming down the window. Under the latter conditions, the crew is almost completely dependent upon the guidance of linemen 'wing walking' the aircraft. If the lineman is not familiar with the requirements of swept- wing aircraft, he will inevitably mislead the crew.

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Original NASA ASRS Text

Title: GIV CREW ALLOWED R WINGTIP TO CONTACT BUILDING DURING TAXI. TAXI.

Narrative: COMMENTS/DETAILS: UPON ENTERING THE FBO'S RAMP AREA, THERE WERE NO LESS THAN 3 LINEMEN POSITIONED AS FOLLOWS, TO ASSIST US IN PARKING THE ACFT: 1) ONE JUST BEYOND WHERE THE NOSE OF THE ACFT WOULD BE WHEN THE PARKING MANEUVER WAS COMPLETE, 2) ONE IN FRONT OF THE WINGTIP OF THE ACFT WE WOULD BE PARKED ADJACENT TO, AND 3) ONE IN FRONT OF AND JUST A FEW FT AWAY FROM THE WALL WE WOULD HAVE TO TAXI PARALLEL TO BEFORE MAKING THE FINAL 90 DEG TURN INTO THE PARKED POS. DURING THE PARALLEL-TO-THE-WALL PORTION OF OUR TAXI, THE CAPT ASKED ME TO MONITOR OUR R WING. I LOOKED BACK AND CONTINUED LOOKING BACK AND POSITIONED MY L-HAND SO THAT I COULD GIVE HIM A THUMBS UP (OR DOWN) SIGN. THOUGH THE RAIN MADE IT DIFFICULT TO SEE THE WINGTIP CLRLY, I ESTIMATED THAT WE HAD ADEQUATE CLRNC -- APPROX 10 FT. ABOUT 1/2 WAY THROUGH THIS PARALLEL-TO- THE-WALL TAXI, THE CAPT ASKED ME HOW IT LOOKED. I RESPONDED, 'LOOKING GOOD,' OR 'PLENTY OF ROOM,' OR SOMETHING TO THAT EFFECT, SINCE IT APPEARED THAT WE WERE MAINTAINING A PARALLEL TRACK OVER THE RAMP WITH REF TO THE WALL AND THAT WE STILL HAD ADEQUATE CLRNC. BECAUSE OF THE EXTREME VIEWING ANGLE AND THE RAIN BEADING AND PERIODICALLY RUNNING IN RIVULETS DOWN THE SIDE WINDOW, I MAINTAINED AN EXTREMELY RAPID SCAN BACK AND FORTH BTWN THE WINGTIP AND THE WALL AND THE LINEMAN WHO WAS IN A MUCH BETTER POS TO MONITOR THE CLRNC IN QUESTION. IF OUR CLRNC DECREASED, HE WOULD BE ABLE TO DETECT IT BEFORE I COULD AND WOULD GIVEN AN APPROPRIATE SIGNAL WHICH I WAS IN THE BEST POS TO SEE. A FEW SECONDS AFTER THE TURN AWAY FROM THE WALL WAS COMMENCED, THE WINGLET STRUCK A VERT SUPPORTING WALL POST WHICH EXTENDED OUT FROM THE WALL BY APPROX 1-2 FT. AT THE TIME OF IMPACT THE LINEMAN WAS STILL GIVING US A THUMBS UP INDICATION THAT WE HAD ADEQUATE CLRNC AND IT STILL APPEARED TO ME THAT WE HAD ADEQUATE CLRNC. PERHAPS OUR TRACK WAS NOT PERFECTLY PARALLEL TO THE WALL AND WE WERE UNDETECTABLY INCHING CLOSER AND CLOSER TO THE WALL JUST PRIOR TO MAKING THE 90 DEG TURN, OR THE GEOMETRY OF THE MAIN AND NOSE GEAR AND THE COMBINATION OF DIFFERENTIAL BRAKING AND NOSE STEERING INPUT WAS SUCH THAT THE WINGTIP SUDDENLY SWUNG OUT MUCH CLOSER TO THE WALL THAN WOULD NORMALLY BE EXPECTED AFTER THE TURN WAS INITIATED. THE RAIN WAS ALSO A CONTRIBUTING FACTOR AS IT REDUCED AND DISTORTED VISIBILITY. RECOMMENDATIONS: THE PHENOMENON SOMETIMES REFERRED TO AS 'DELTA-WING WING-GROWTH' SHOULD BE FORMALLY INTRODUCED TO BOTH INITIAL AND RECURRENT TRAINING PROGRAMS. A PHONE CALL TO GULFSTREAM ENGINEERING CONFIRMED MY SUSPICION THAT NOWHERE DO THEY PUBLISH THE EXACT DISTANCE THAT THE WING EFFECTIVELY 'GROWS' UNDER THE AFOREMENTIONED CONDITIONS, THOUGH THEY DO PUBLISH A TURNING RADIUS DIAGRAM FROM WHICH THE INFO MIGHT BE DEDUCED. MOST OF THE PLTS THAT I QUESTIONED SO FAR HAVE NEVER HEARD OF THIS PHENOMENA. THE FEW WHO WERE AWARE OF IT GUESSED THAT THE DISTANCE INVOLVED FOR A G-IV) WAS BTWN 6-9 INCHES --IN FACT, IT IS APPROX TWICE AS MUCH. THE ENGINEER I SPOKE WITH AT GULFSTREAM GAVE HIS ESTIMATE AS 2-3 FT. ACFT MANUFACTURERS SHOULD PUBLISH APPLICABLE DATA DOCUMENTING THE PRECISE EXTENT OF SUCH 'WING-GROWTH' AND FBO'S SHOULD BE REQUIRED TO DOCUMENT THAT THEIR LINEMEN HAVE BEEN TRAINED ACCORDINGLY. FLT SAFETY SHOULD DEVOTE AT LEAST AS MUCH TIME TO THIS ASPECT OF ACFT GND OPS AS THEY DO ON THE EFFECT OF FLAP SETTING ON HORIZ STABILIZER POS AND HANGAR CLRNC SINCE WING GROWTH IS FAR MORE INSIDIOUS AND, ONCE UNDERESTIMATED, IS ALMOST IMPOSSIBLE TO RECOVER FROM DUE TO THE ACCELERATED NATURE OF THE TURN. THE EXTREMELY DISADVANTAGED VIEWING ANGLE FROM THE COCKPIT MAKES IT VERY DIFFICULT TO ACCURATELY ESTIMATE THE DISTANCE FROM THE WINGTIP OF A SWEPT-WING ACFT TO AN ADJACENT GND OBJECT UNDER IDEAL CIRCUMSTANCES, MUCH LESS WITH RAIN BEADING AND STREAMING DOWN THE WINDOW. UNDER THE LATTER CONDITIONS, THE CREW IS ALMOST COMPLETELY DEPENDENT UPON THE GUIDANCE OF LINEMEN 'WING WALKING' THE ACFT. IF THE LINEMAN IS NOT FAMILIAR WITH THE REQUIREMENTS OF SWEPT- WING ACFT, HE WILL INEVITABLY MISLEAD THE CREW.

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.