Narrative:

Initially had failure of leading edge flaps to extend normally. Accomplished alternate extension of leading edge flaps. This situation was unrelated to the problem that followed, however, in accomplishing the alternate leading edge extension checklist, the flap handle was positioned to 5 degrees. After the leading edge flaps were extended, it was determined that the outboard trailing edge flaps were still at 0 degrees, and the inboard trailing edge flaps were at 5 degrees (as expected). Note: although the flap handle controls both leading edge and trailing edge flaps, the 2 system operate normally by different means -- the leading edge flaps are normally operated by pneumatic air, and the trailing edge flaps are operated by 2 independent hydraulic system -- inboard trailing edge flaps operated by hydraulic system #1 and outboard trailing edge flaps operated by hydraulic system #4. I have enclosed a copy of the abnormal/emergency checklists for 2 procedures that are variously used for problems with trailing edge flaps: 1) alternate trailing edge flap operation, and 2) asymmetrical/split trailing edge flaps. We initially accomplished the split trailing edge flaps procedure down to the point in that procedure that mentions 'for landing, extend operable trailing edge flaps to 25 degrees on flap speed schedule.' at this point, the split trailing edge flaps procedure was abandoned, and the alternate trailing edge flap operation procedure was commenced. In retrospect, it was undoubtedly incorrect to use this procedure due to some of the built-in system protections being compromised. At any rate the outboard te flaps were eventually extended to 25 degrees, but the inboard trailing flaps were only able to be extended to approximately 8 degrees. As this was clearly a split trailing edge flap situation, the split trailing edge flaps procedure was reaccomplished in its entirety. An emergency was declared and subsequent landing was uneventful. For future use, I would recommend that the alternate trailing edge flap operation checklist contain a bold letter caution near the top of the procedure stating something similar to this: 'caution if asymmetrical/split trailing edge flaps exist, do not accomplish the alternate trailing edge flap operation. Accomplish the asymmetrical/split trailing edge flaps procedure.' also, on the asymmetrical/split trailing edge flaps checklist, I would prefer to see less ambivalent language with respect to 'for landing, extend operable trailing edge flaps to 25 degrees on flap speed schedule.' more specific language mandating the use of 'normal means,' ie, hydraulic extension of operable trailing edge flaps with the flap handle would probably clear up any confusion about the means to extend the operable trailing edge flaps.

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Original NASA ASRS Text

Title: A B747-100 ON APCH AT 2000 FT HAD INBOARD TRAILING EDGE FLAPS FAIL TO EXTEND BEYOND 8 UNITS, OUTBOARD FLAPS WENT TO 20 UNITS.

Narrative: INITIALLY HAD FAILURE OF LEADING EDGE FLAPS TO EXTEND NORMALLY. ACCOMPLISHED ALTERNATE EXTENSION OF LEADING EDGE FLAPS. THIS SIT WAS UNRELATED TO THE PROB THAT FOLLOWED, HOWEVER, IN ACCOMPLISHING THE ALTERNATE LEADING EDGE EXTENSION CHKLIST, THE FLAP HANDLE WAS POSITIONED TO 5 DEGS. AFTER THE LEADING EDGE FLAPS WERE EXTENDED, IT WAS DETERMINED THAT THE OUTBOARD TRAILING EDGE FLAPS WERE STILL AT 0 DEGS, AND THE INBOARD TRAILING EDGE FLAPS WERE AT 5 DEGS (AS EXPECTED). NOTE: ALTHOUGH THE FLAP HANDLE CTLS BOTH LEADING EDGE AND TRAILING EDGE FLAPS, THE 2 SYS OPERATE NORMALLY BY DIFFERENT MEANS -- THE LEADING EDGE FLAPS ARE NORMALLY OPERATED BY PNEUMATIC AIR, AND THE TRAILING EDGE FLAPS ARE OPERATED BY 2 INDEPENDENT HYD SYS -- INBOARD TRAILING EDGE FLAPS OPERATED BY HYD SYS #1 AND OUTBOARD TRAILING EDGE FLAPS OPERATED BY HYD SYS #4. I HAVE ENCLOSED A COPY OF THE ABNORMAL/EMER CHKLISTS FOR 2 PROCS THAT ARE VARIOUSLY USED FOR PROBS WITH TRAILING EDGE FLAPS: 1) ALTERNATE TRAILING EDGE FLAP OP, AND 2) ASYMMETRICAL/SPLIT TRAILING EDGE FLAPS. WE INITIALLY ACCOMPLISHED THE SPLIT TRAILING EDGE FLAPS PROC DOWN TO THE POINT IN THAT PROC THAT MENTIONS 'FOR LNDG, EXTEND OPERABLE TRAILING EDGE FLAPS TO 25 DEGS ON FLAP SPD SCHEDULE.' AT THIS POINT, THE SPLIT TRAILING EDGE FLAPS PROC WAS ABANDONED, AND THE ALTERNATE TRAILING EDGE FLAP OP PROC WAS COMMENCED. IN RETROSPECT, IT WAS UNDOUBTEDLY INCORRECT TO USE THIS PROC DUE TO SOME OF THE BUILT-IN SYS PROTECTIONS BEING COMPROMISED. AT ANY RATE THE OUTBOARD TE FLAPS WERE EVENTUALLY EXTENDED TO 25 DEGS, BUT THE INBOARD TRAILING FLAPS WERE ONLY ABLE TO BE EXTENDED TO APPROX 8 DEGS. AS THIS WAS CLRLY A SPLIT TRAILING EDGE FLAP SIT, THE SPLIT TRAILING EDGE FLAPS PROC WAS REACCOMPLISHED IN ITS ENTIRETY. AN EMER WAS DECLARED AND SUBSEQUENT LNDG WAS UNEVENTFUL. FOR FUTURE USE, I WOULD RECOMMEND THAT THE ALTERNATE TRAILING EDGE FLAP OP CHKLIST CONTAIN A BOLD LETTER CAUTION NEAR THE TOP OF THE PROC STATING SOMETHING SIMILAR TO THIS: 'CAUTION IF ASYMMETRICAL/SPLIT TRAILING EDGE FLAPS EXIST, DO NOT ACCOMPLISH THE ALTERNATE TRAILING EDGE FLAP OP. ACCOMPLISH THE ASYMMETRICAL/SPLIT TRAILING EDGE FLAPS PROC.' ALSO, ON THE ASYMMETRICAL/SPLIT TRAILING EDGE FLAPS CHKLIST, I WOULD PREFER TO SEE LESS AMBIVALENT LANGUAGE WITH RESPECT TO 'FOR LNDG, EXTEND OPERABLE TRAILING EDGE FLAPS TO 25 DEGS ON FLAP SPD SCHEDULE.' MORE SPECIFIC LANGUAGE MANDATING THE USE OF 'NORMAL MEANS,' IE, HYD EXTENSION OF OPERABLE TRAILING EDGE FLAPS WITH THE FLAP HANDLE WOULD PROBABLY CLR UP ANY CONFUSION ABOUT THE MEANS TO EXTEND THE OPERABLE TRAILING EDGE FLAPS.

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.