Narrative:

We were aware of the turbulence forecast area near the mountains by den; and that we may be transiting the lower corner of it en route ZZZ1. We were flying econ cruise of mach .78 at FL390 (because of weight; although dispatched at FL410). As we approached; ATC queries and reports indicated only light chop/turbulence with ATC; stating it existed up to FL380 and lasting only a few mins for east/west travel. So; it appeared only 'light' and below us. As we approached slightly northwest of santa flight engineer; NM; the light chop began as the seatbelt sign was put back on. It started to worsen so I sat the flight attendants down. The chop did indeed worsen even more shortly thereafter. Within a min or so; the light chop suddenly and instantaneously turned into moderate turbulence with some mountain wave action. As I started to pull power to slow to mach .76; the airspeed literally jumped to mach .82 with clacker in about 2 seconds. I was stunned at how quickly this happened with only 'light chop' conditions reported at altitudes below us only. I had to further pull power all the way to idle with the speed continuing upward to mach .84 where it stayed for about 10 seconds (while at idle)! The speed then slowly dissipated over the next 15 seconds or so as I gradually added power to intercept mach .76. Within the next min or two; the rough ride went back to light chop; then smooth until; amazingly; about 20 mins later; approaching abeam ama; some slight mountain wave was again encountered for a couple of mins! After the encounter; we looked in the fom to see if reaching vmo +20 KTS or mmo +.02 mach (design limit speeds of 340 KTS; mach .84) required a logbook write-up and maintenance inspection (I thought that they did with recent emphasis on the fact from flight operations). I was also unsure of the potential maintenance inspection timeline requirements (ie; immediate; or within a certain number of days; or... Etc). This maintenance inspection requirement knowledge turns out to be a critical customer service issue inbound to a station after even only touching design limit speeds (also for flap overspds). We found an fom appendix page that talks about 'unscheduled maintenance checks...exceeding design speed (vmo +20 KTS or mmo +.02 mach).' since we did not 'exceed' the design speed; but only 'reached' it; those words convinced us that no maintenance action or inspection delay would be expected reaching destination. We knew a mechanic would be there to confirm our assumption also. It was not until after talking to maintenance control on landing; and their grounding of the aircraft for inspection (approximately 1-2 hours) that I discovered this in the fom on the previous pages. The fom appendix talks about 'items that require guidance from maintenance control' but only an 'information' write-up: operational exceedances that do not require maintenance inspection: 1) vmo exceedance of less than 20 KTS. 2) mmo exceedance of less than .02 mach. This is; apparently; correctly worded regarding real world operations. However; it contradicts the fom page guidance that one must 'exceed' design limit speed to actually trigger the inspection requirement (ie; 361 KTS; mach .85 ). Because of our confusion in thinking no inspection was required; passenger were already boarding as we got the news from maintenance control that the aircraft required an inspection which could take a couple of hours. Since we were a couple of hours from destination when the overspd occurred; we could have informed dispatch via ACARS of the event and inspection requirements well ahead of time for other arrangements and aircraft swap planning to be done to inconvenience our passenger the least. Therefore; I believe that the following changes need to be made to the fom: 1) the page should read; 'reaching and/or exceeding design limits speeds of 360 KTS; mach .84 (vmo +20/mmo +.02). 2) the fom limitations should include; somewhere; the definition of 'design limit speed' and then state that reaching and/or exceeding those speeds 'require' grounding of the aircraft at destination for a maintenance inspection (possibly a couple of hours); so contact dispatch and/or station operations as soon as possible of the overspd so that passenger and aircraft swap planning can commence. (The same is true for flap speed exceedances). Also; why not blatantly state that maximum operating speeds; vmo/mmo (clacker) are 340 KIAS; mach .82; there also?

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Original NASA ASRS Text

Title: A B737-700 AT FL390 EXPERIENCED MODERATE MOUNTAIN WAVE ACTION WITH MACH/AIRSPEED DEV EXCEEDING VMO/MMO LIMITS AND REQUIRING INSPECTIONS.

Narrative: WE WERE AWARE OF THE TURB FORECAST AREA NEAR THE MOUNTAINS BY DEN; AND THAT WE MAY BE TRANSITING THE LOWER CORNER OF IT ENRTE ZZZ1. WE WERE FLYING ECON CRUISE OF MACH .78 AT FL390 (BECAUSE OF WT; ALTHOUGH DISPATCHED AT FL410). AS WE APCHED; ATC QUERIES AND RPTS INDICATED ONLY LIGHT CHOP/TURB WITH ATC; STATING IT EXISTED UP TO FL380 AND LASTING ONLY A FEW MINS FOR E/W TRAVEL. SO; IT APPEARED ONLY 'LIGHT' AND BELOW US. AS WE APCHED SLIGHTLY NW OF SANTA FE; NM; THE LIGHT CHOP BEGAN AS THE SEATBELT SIGN WAS PUT BACK ON. IT STARTED TO WORSEN SO I SAT THE FLT ATTENDANTS DOWN. THE CHOP DID INDEED WORSEN EVEN MORE SHORTLY THEREAFTER. WITHIN A MIN OR SO; THE LIGHT CHOP SUDDENLY AND INSTANTANEOUSLY TURNED INTO MODERATE TURB WITH SOME MOUNTAIN WAVE ACTION. AS I STARTED TO PULL PWR TO SLOW TO MACH .76; THE AIRSPD LITERALLY JUMPED TO MACH .82 WITH CLACKER IN ABOUT 2 SECONDS. I WAS STUNNED AT HOW QUICKLY THIS HAPPENED WITH ONLY 'LIGHT CHOP' CONDITIONS REPORTED AT ALTS BELOW US ONLY. I HAD TO FURTHER PULL POWER ALL THE WAY TO IDLE WITH THE SPEED CONTINUING UPWARD TO MACH .84 WHERE IT STAYED FOR ABOUT 10 SECONDS (WHILE AT IDLE)! THE SPD THEN SLOWLY DISSIPATED OVER THE NEXT 15 SECONDS OR SO AS I GRADUALLY ADDED PWR TO INTERCEPT MACH .76. WITHIN THE NEXT MIN OR TWO; THE ROUGH RIDE WENT BACK TO LIGHT CHOP; THEN SMOOTH UNTIL; AMAZINGLY; ABOUT 20 MINS LATER; APCHING ABEAM AMA; SOME SLIGHT MOUNTAIN WAVE WAS AGAIN ENCOUNTERED FOR A COUPLE OF MINS! AFTER THE ENCOUNTER; WE LOOKED IN THE FOM TO SEE IF REACHING VMO +20 KTS OR MMO +.02 MACH (DESIGN LIMIT SPDS OF 340 KTS; MACH .84) REQUIRED A LOGBOOK WRITE-UP AND MAINT INSPECTION (I THOUGHT THAT THEY DID WITH RECENT EMPHASIS ON THE FACT FROM FLT OPS). I WAS ALSO UNSURE OF THE POTENTIAL MAINT INSPECTION TIMELINE REQUIREMENTS (IE; IMMEDIATE; OR WITHIN A CERTAIN NUMBER OF DAYS; OR... ETC). THIS MAINT INSPECTION REQUIREMENT KNOWLEDGE TURNS OUT TO BE A CRITICAL CUSTOMER SVC ISSUE INBOUND TO A STATION AFTER EVEN ONLY TOUCHING DESIGN LIMIT SPDS (ALSO FOR FLAP OVERSPDS). WE FOUND AN FOM APPENDIX PAGE THAT TALKS ABOUT 'UNSCHEDULED MAINT CHKS...EXCEEDING DESIGN SPD (VMO +20 KTS OR MMO +.02 MACH).' SINCE WE DID NOT 'EXCEED' THE DESIGN SPD; BUT ONLY 'REACHED' IT; THOSE WORDS CONVINCED US THAT NO MAINT ACTION OR INSPECTION DELAY WOULD BE EXPECTED REACHING DEST. WE KNEW A MECH WOULD BE THERE TO CONFIRM OUR ASSUMPTION ALSO. IT WAS NOT UNTIL AFTER TALKING TO MAINT CTL ON LNDG; AND THEIR GNDING OF THE ACFT FOR INSPECTION (APPROX 1-2 HRS) THAT I DISCOVERED THIS IN THE FOM ON THE PREVIOUS PAGES. THE FOM APPENDIX TALKS ABOUT 'ITEMS THAT REQUIRE GUIDANCE FROM MAINT CTL' BUT ONLY AN 'INFO' WRITE-UP: OPERATIONAL EXCEEDANCES THAT DO NOT REQUIRE MAINT INSPECTION: 1) VMO EXCEEDANCE OF LESS THAN 20 KTS. 2) MMO EXCEEDANCE OF LESS THAN .02 MACH. THIS IS; APPARENTLY; CORRECTLY WORDED REGARDING REAL WORLD OPS. HOWEVER; IT CONTRADICTS THE FOM PAGE GUIDANCE THAT ONE MUST 'EXCEED' DESIGN LIMIT SPD TO ACTUALLY TRIGGER THE INSPECTION REQUIREMENT (IE; 361 KTS; MACH .85 ). BECAUSE OF OUR CONFUSION IN THINKING NO INSPECTION WAS REQUIRED; PAX WERE ALREADY BOARDING AS WE GOT THE NEWS FROM MAINT CTL THAT THE ACFT REQUIRED AN INSPECTION WHICH COULD TAKE A COUPLE OF HRS. SINCE WE WERE A COUPLE OF HRS FROM DEST WHEN THE OVERSPD OCCURRED; WE COULD HAVE INFORMED DISPATCH VIA ACARS OF THE EVENT AND INSPECTION REQUIREMENTS WELL AHEAD OF TIME FOR OTHER ARRANGEMENTS AND ACFT SWAP PLANNING TO BE DONE TO INCONVENIENCE OUR PAX THE LEAST. THEREFORE; I BELIEVE THAT THE FOLLOWING CHANGES NEED TO BE MADE TO THE FOM: 1) THE PAGE SHOULD READ; 'REACHING AND/OR EXCEEDING DESIGN LIMITS SPDS OF 360 KTS; MACH .84 (VMO +20/MMO +.02). 2) THE FOM LIMITATIONS SHOULD INCLUDE; SOMEWHERE; THE DEFINITION OF 'DESIGN LIMIT SPD' AND THEN STATE THAT REACHING AND/OR EXCEEDING THOSE SPDS 'REQUIRE' GNDING OF THE ACFT AT DEST FOR A MAINT INSPECTION (POSSIBLY A COUPLE OF HRS); SO CONTACT DISPATCH AND/OR STATION OPS ASAP OF THE OVERSPD SO THAT PAX AND ACFT SWAP PLANNING CAN COMMENCE. (THE SAME IS TRUE FOR FLAP SPD EXCEEDANCES). ALSO; WHY NOT BLATANTLY STATE THAT MAX OPERATING SPDS; VMO/MMO (CLACKER) ARE 340 KIAS; MACH .82; THERE ALSO?

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.