Narrative:

B737-700 not meeting production (boeing) nominal reverse N1 at detent 2 or maximum reverse thrust and as a result less stopping margin being available than is calculated by performance computer for slippery runway operations. Aircraft numbers meet production nominal values. Aircraft numbers yield approximately detent 2 values in maximum reverse. Occasions of N1 between detent 2 and maximum values or one engine at detent 2 N1 and the other engine at maximum N1 with the same reverse lever position on both engines. Verification from boeing operations engineering that boeing production nominal values are correct and utilized in boeing performance module in the performance computer. (If so; display detent 2 and maximum values as appropriate on landing output page.) check in fadap for fleet reverse values to identify aircraft not meeting those values. Liaison maintenance as to cause and remedy.callback conversation with reporter revealed the following information: the reporter stated that questions about the reliability and consistency of the B737-ng reverse system. The ng engine fuel control system is fadec with eec limitations. In the reporter's experience the detent defining the physical position of the reverse detent 2 is not always detectable by a pilot. Additionally; when detent 2 is detectable the N1 achieved is a variable and at times different between both engines on the same aircraft. The reporter has also had the experience when at maximum reverse an engine may produce some N1 between detent 2 and maximum while the other engine produces maximum allowable reverse which could be somewhere around 72%. The reporter is concerned that with the wet WX approaching and the history of B737 operations on wet/ice/snow covered runways full reverse thrust may not be present when needed and contribute to an unsafe event.

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Original NASA ASRS Text

Title: B737-700 ENGINE AT MAX OR DETENT 2 REVERSE DO NOT MEET PERFORMANCE SPECIFICATIONS AND MAY NOT PROVIDE THE DESIRED WET RWY STOPPING MARGIN.

Narrative: B737-700 NOT MEETING PRODUCTION (BOEING) NOMINAL REVERSE N1 AT DETENT 2 OR MAX REVERSE THRUST AND AS A RESULT LESS STOPPING MARGIN BEING AVAILABLE THAN IS CALCULATED BY PERFORMANCE COMPUTER FOR SLIPPERY RWY OPS. ACFT NUMBERS MEET PRODUCTION NOMINAL VALUES. ACFT NUMBERS YIELD APPROX DETENT 2 VALUES IN MAX REVERSE. OCCASIONS OF N1 BETWEEN DETENT 2 AND MAX VALUES OR ONE ENGINE AT DETENT 2 N1 AND THE OTHER ENGINE AT MAX N1 WITH THE SAME REVERSE LEVER POSITION ON BOTH ENGINES. VERIFICATION FROM BOEING OPS ENGINEERING THAT BOEING PRODUCTION NOMINAL VALUES ARE CORRECT AND UTILIZED IN BOEING PERFORMANCE MODULE IN THE PERFORMANCE COMPUTER. (IF SO; DISPLAY DETENT 2 AND MAX VALUES AS APPROPRIATE ON LNDG OUTPUT PAGE.) CHECK IN FADAP FOR FLEET REVERSE VALUES TO IDENTIFY ACFT NOT MEETING THOSE VALUES. LIAISON MAINT AS TO CAUSE AND REMEDY.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THAT QUESTIONS ABOUT THE RELIABILITY AND CONSISTENCY OF THE B737-NG REVERSE SYSTEM. THE NG ENGINE FUEL CTL SYSTEM IS FADEC WITH EEC LIMITATIONS. IN THE RPTR'S EXPERIENCE THE DETENT DEFINING THE PHYSICAL POSITION OF THE REVERSE DETENT 2 IS NOT ALWAYS DETECTABLE BY A PLT. ADDITIONALLY; WHEN DETENT 2 IS DETECTABLE THE N1 ACHIEVED IS A VARIABLE AND AT TIMES DIFFERENT BETWEEN BOTH ENGINES ON THE SAME ACFT. THE RPTR HAS ALSO HAD THE EXPERIENCE WHEN AT MAX REVERSE AN ENGINE MAY PRODUCE SOME N1 BETWEEN DETENT 2 AND MAX WHILE THE OTHER ENGINE PRODUCES MAX ALLOWABLE REVERSE WHICH COULD BE SOMEWHERE AROUND 72%. THE RPTR IS CONCERNED THAT WITH THE WET WX APCHING AND THE HISTORY OF B737 OPS ON WET/ICE/SNOW COVERED RWYS FULL REVERSE THRUST MAY NOT BE PRESENT WHEN NEEDED AND CONTRIBUTE TO AN UNSAFE EVENT.

Data retrieved from NASA's ASRS site as of January 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.