Narrative:

Twenty-seven days ago while flying aircraft abc and five days ago while flying a different aircraft; I noticed an unusual thing about the autoflt system. While on an ILS approach (localizer/GS green) there was an 'extra' white LNAV annunciation below the green localizer on the FMA. I fly this plane for the military and we recently received a bulletin addressing a similar (if not the same) problem with the military version of the B737 (C40A). I'd give you an FAA ad but this bulletin doesn't have one; I'll retype what I can fit in here; although boeing has gotten upset in the past about who pays for what and who gets what information; so hopefully there is a similar bulletin sitting on someone's desk at company from boeing addressing the same issue. All that follows is a retyping of the bulletin we got issued in the military. I got it between my flts on the dates I mentioned above. On the first date; I was asking myself what is that white LNAV doing there; saw the bulletin a week later; and then saw it again on the second date mentioned and realized that the military bulletin seems to apply to our latest deliveries here. 'Subject: incorrect implementation of to/GA to LNAV feature of cds blockpoint 06 (BP06) and FMC update U10.5 or U10.5A installed. Reason: this bulletin informs flight crews of incorrect implementation of the optional to/GA to LNAV feature when cda BP06 is installed in conjunction with FMC update U10.5 or U10.5A. Information in this bulletin is recommended by the boeing company but may not be FAA approved at the time of writing. In the event of conflict with the FAA approved airplane flight manual (afm); the afm shall supersede. The boeing company regards the information or procedure described herein as having a direct or indirect bearing on the safe operation of the model airplane. If cds BP06 is installed with FMC updates U10.6; the to/GA to LNAV mode is correctly implemented and is only available if the option has been purchased by an operator. If cds BP06 is installed with FMC update U10.5 or U10.5A; however; the to/GA LNAV mode is armed whenever the leading edge devices are extended to the commanded position; an FMC approach has been selected and the logic for LNAV arm is satisfied. Boeing did not intend for the to/GA to LNAV feature to be enabled with FMC update U10.5 or U10.5A; and this software combination has never been certified by the FAA. Because the function may be confusing to a flight crew when it is inadvertently enabled; boeing recommends operators ensure cds BP06 is not installed with FMC update U10.5 or U10.5A. Operators should install FMC update U10.6 with cds BP06 or install an earlier cds bp with FMS update U10.5A or earlier. Operators should be aware; however; that FMC update U10.6 is required for correct implementation of all short field performance features. Operating instructions: if cds BP06 is installed with FMC update U10.5 or U10.5A: 1) on the ground; if LNAV arm is displaced in white on the ma without selection of LNAV prior to toga; there is no operational effect. The indication is a nuisance display only and will extinguish when to/GA is pressed. No crew action is required. 2) on the ground; if LNAV is selected prior to toga; all FMA indications and LNAV operations are correct. No additional crew action is required. 3) during approach: collins FCC's installed: if LNAV arm is displayed in white on the FMA; the go around roll mode will automatically transition from track hold to LNAV above 50 ft RA during a flight director missed approach. During an autoplt go around; LNAV will engage when the airplane is above 400 ft AGL. Below these transition altitudes; the roll mode will be toga (flight director or autoplt commands track hold). Honeywell 709 fccs installed: if LNAV arm is displayed in white on the FMA; the go around roll mode will automatically transition from track hold to LNAV above 400 ft RA during a flight director or autoplt go around. Below this transition altitude; the roll mode will be in toga (flight director or autoplt commands track hold). With either FCC software installed; the flight crew must be aware the flight directorwill provide roll guidance to the LNAV path. If an alternate missed approach has been assigned; the PF must maintain the correct course manually. A different roll mode can be selected above 400 ft AGL.' I don't think this is a huge deal; but think if might be good to get some guidance from boeing or flight operations. Since it happened to me on 2 very recent deliveries and not on other 700's that I've flown recently; it seems to be a small problem. I can attest that the 'flight crew confusion' part above is true; since we are not used to seeing a white LNAV when on a green localizer. I hope that the above bulletin provides enough information to track down a similar boeing bulletin addressed to company or civilian operations. Military bulletins come with a companion FAA ad number on them. This one did not; presumably because they published before they got one (based on the legalese note below the reason). I'm guessing that there is already something in the works to inform our crews of this issue; but if not; maybe we should get something. I think the last paragraph sums it up. Usually we aren't going into LNAV after a missed until we hit a button but with this glitch; a crew could be inadvertently led down the garden path and maybe follow LNAV on a converging approach when you really need to turn sooner or do something different.

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Original NASA ASRS Text

Title: A B737-700 PLT WHO FLIES BOTH MIL AND CIVIL VERSIONS RPTS THAT AN ANOMALY (LNAV INDICATION IN WHITE SOMETIMES SHOWING DURING ILS APCHS) HAD BEEN ADDRESSED BY THE MIL BUT NOT BY A CIVILIAN EMPLOYER.

Narrative: TWENTY-SEVEN DAYS AGO WHILE FLYING ACFT ABC AND FIVE DAYS AGO WHILE FLYING A DIFFERENT ACFT; I NOTICED AN UNUSUAL THING ABOUT THE AUTOFLT SYSTEM. WHILE ON AN ILS APCH (LOC/GS GREEN) THERE WAS AN 'EXTRA' WHITE LNAV ANNUNCIATION BELOW THE GREEN LOC ON THE FMA. I FLY THIS PLANE FOR THE MIL AND WE RECENTLY RECEIVED A BULLETIN ADDRESSING A SIMILAR (IF NOT THE SAME) PROB WITH THE MIL VERSION OF THE B737 (C40A). I'D GIVE YOU AN FAA AD BUT THIS BULLETIN DOESN'T HAVE ONE; I'LL RETYPE WHAT I CAN FIT IN HERE; ALTHOUGH BOEING HAS GOTTEN UPSET IN THE PAST ABOUT WHO PAYS FOR WHAT AND WHO GETS WHAT INFO; SO HOPEFULLY THERE IS A SIMILAR BULLETIN SITTING ON SOMEONE'S DESK AT COMPANY FROM BOEING ADDRESSING THE SAME ISSUE. ALL THAT FOLLOWS IS A RETYPING OF THE BULLETIN WE GOT ISSUED IN THE MIL. I GOT IT BETWEEN MY FLTS ON THE DATES I MENTIONED ABOVE. ON THE FIRST DATE; I WAS ASKING MYSELF WHAT IS THAT WHITE LNAV DOING THERE; SAW THE BULLETIN A WEEK LATER; AND THEN SAW IT AGAIN ON THE SECOND DATE MENTIONED AND REALIZED THAT THE MIL BULLETIN SEEMS TO APPLY TO OUR LATEST DELIVERIES HERE. 'SUBJECT: INCORRECT IMPLEMENTATION OF TO/GA TO LNAV FEATURE OF CDS BLOCKPOINT 06 (BP06) AND FMC UPDATE U10.5 OR U10.5A INSTALLED. REASON: THIS BULLETIN INFORMS FLT CREWS OF INCORRECT IMPLEMENTATION OF THE OPTIONAL TO/GA TO LNAV FEATURE WHEN CDA BP06 IS INSTALLED IN CONJUNCTION WITH FMC UPDATE U10.5 OR U10.5A. INFORMATION IN THIS BULLETIN IS RECOMMENDED BY THE BOEING COMPANY BUT MAY NOT BE FAA APPROVED AT THE TIME OF WRITING. IN THE EVENT OF CONFLICT WITH THE FAA APPROVED AIRPLANE FLT MANUAL (AFM); THE AFM SHALL SUPERSEDE. THE BOEING COMPANY REGARDS THE INFO OR PROC DESCRIBED HEREIN AS HAVING A DIRECT OR INDIRECT BEARING ON THE SAFE OP OF THE MODEL AIRPLANE. IF CDS BP06 IS INSTALLED WITH FMC UPDATES U10.6; THE TO/GA TO LNAV MODE IS CORRECTLY IMPLEMENTED AND IS ONLY AVAILABLE IF THE OPTION HAS BEEN PURCHASED BY AN OPERATOR. IF CDS BP06 IS INSTALLED WITH FMC UPDATE U10.5 OR U10.5A; HOWEVER; THE TO/GA LNAV MODE IS ARMED WHENEVER THE LEADING EDGE DEVICES ARE EXTENDED TO THE COMMANDED POSITION; AN FMC APCH HAS BEEN SELECTED AND THE LOGIC FOR LNAV ARM IS SATISFIED. BOEING DID NOT INTEND FOR THE TO/GA TO LNAV FEATURE TO BE ENABLED WITH FMC UPDATE U10.5 OR U10.5A; AND THIS SOFTWARE COMBINATION HAS NEVER BEEN CERTIFIED BY THE FAA. BECAUSE THE FUNCTION MAY BE CONFUSING TO A FLT CREW WHEN IT IS INADVERTENTLY ENABLED; BOEING RECOMMENDS OPERATORS ENSURE CDS BP06 IS NOT INSTALLED WITH FMC UPDATE U10.5 OR U10.5A. OPERATORS SHOULD INSTALL FMC UPDATE U10.6 WITH CDS BP06 OR INSTALL AN EARLIER CDS BP WITH FMS UPDATE U10.5A OR EARLIER. OPERATORS SHOULD BE AWARE; HOWEVER; THAT FMC UPDATE U10.6 IS REQUIRED FOR CORRECT IMPLEMENTATION OF ALL SHORT FIELD PERFORMANCE FEATURES. OPERATING INSTRUCTIONS: IF CDS BP06 IS INSTALLED WITH FMC UPDATE U10.5 OR U10.5A: 1) ON THE GND; IF LNAV ARM IS DISPLACED IN WHITE ON THE MA WITHOUT SELECTION OF LNAV PRIOR TO TOGA; THERE IS NO OPERATIONAL EFFECT. THE INDICATION IS A NUISANCE DISPLAY ONLY AND WILL EXTINGUISH WHEN TO/GA IS PRESSED. NO CREW ACTION IS REQUIRED. 2) ON THE GND; IF LNAV IS SELECTED PRIOR TO TOGA; ALL FMA INDICATIONS AND LNAV OPS ARE CORRECT. NO ADDITIONAL CREW ACTION IS REQUIRED. 3) DURING APCH: COLLINS FCC'S INSTALLED: IF LNAV ARM IS DISPLAYED IN WHITE ON THE FMA; THE GAR ROLL MODE WILL AUTOMATICALLY TRANSITION FROM TRACK HOLD TO LNAV ABOVE 50 FT RA DURING A FLT DIRECTOR MISSED APCH. DURING AN AUTOPLT GAR; LNAV WILL ENGAGE WHEN THE AIRPLANE IS ABOVE 400 FT AGL. BELOW THESE TRANSITION ALTS; THE ROLL MODE WILL BE TOGA (FLT DIRECTOR OR AUTOPLT COMMANDS TRACK HOLD). HONEYWELL 709 FCCS INSTALLED: IF LNAV ARM IS DISPLAYED IN WHITE ON THE FMA; THE GAR ROLL MODE WILL AUTOMATICALLY TRANSITION FROM TRACK HOLD TO LNAV ABOVE 400 FT RA DURING A FLT DIRECTOR OR AUTOPLT GAR. BELOW THIS TRANSITION ALT; THE ROLL MODE WILL BE IN TOGA (FLT DIRECTOR OR AUTOPLT COMMANDS TRACK HOLD). WITH EITHER FCC SOFTWARE INSTALLED; THE FLT CREW MUST BE AWARE THE FLT DIRECTORWILL PROVIDE ROLL GUIDANCE TO THE LNAV PATH. IF AN ALTERNATE MISSED APCH HAS BEEN ASSIGNED; THE PF MUST MAINTAIN THE CORRECT COURSE MANUALLY. A DIFFERENT ROLL MODE CAN BE SELECTED ABOVE 400 FT AGL.' I DON'T THINK THIS IS A HUGE DEAL; BUT THINK IF MIGHT BE GOOD TO GET SOME GUIDANCE FROM BOEING OR FLT OPS. SINCE IT HAPPENED TO ME ON 2 VERY RECENT DELIVERIES AND NOT ON OTHER 700'S THAT I'VE FLOWN RECENTLY; IT SEEMS TO BE A SMALL PROB. I CAN ATTEST THAT THE 'FLT CREW CONFUSION' PART ABOVE IS TRUE; SINCE WE ARE NOT USED TO SEEING A WHITE LNAV WHEN ON A GREEN LOC. I HOPE THAT THE ABOVE BULLETIN PROVIDES ENOUGH INFO TO TRACK DOWN A SIMILAR BOEING BULLETIN ADDRESSED TO COMPANY OR CIVILIAN OPS. MIL BULLETINS COME WITH A COMPANION FAA AD NUMBER ON THEM. THIS ONE DID NOT; PRESUMABLY BECAUSE THEY PUBLISHED BEFORE THEY GOT ONE (BASED ON THE LEGALESE NOTE BELOW THE REASON). I'M GUESSING THAT THERE IS ALREADY SOMETHING IN THE WORKS TO INFORM OUR CREWS OF THIS ISSUE; BUT IF NOT; MAYBE WE SHOULD GET SOMETHING. I THINK THE LAST PARAGRAPH SUMS IT UP. USUALLY WE AREN'T GOING INTO LNAV AFTER A MISSED UNTIL WE HIT A BUTTON BUT WITH THIS GLITCH; A CREW COULD BE INADVERTENTLY LED DOWN THE GARDEN PATH AND MAYBE FOLLOW LNAV ON A CONVERGING APCH WHEN YOU REALLY NEED TO TURN SOONER OR DO SOMETHING DIFFERENT.

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.