Narrative:

Flight arrived in mdw with an MEL for an inoperative yaw damper. The forms and the flight release correctly reflected MEL 322-3 and the special procedures were reviewed. The outbound flight to hou was planned at FL370 with a planned arrival fuel of 6.5. The WX packet showed occasional moderate turbulence at the higher altitudes. The release showed a maximum sheer number of 7 over lit. I elected to bump up the departure fuel from 16.1 to 17.1 anticipating the use of a lower cruising altitude for smooth air. The flight attendants were advised about the inoperative yaw damper. The flight departed 30 mins late for hou. The ride deteriorated climbing through FL310 and the flight attendants were told to return to their seats. The fasten seat belt sign was on and passenger were advised to remain seated as we continued our climb to FL370. ATC advised us that the ride at FL370 was intermittent light chop with occasional moderate. Approaching FL370 the ride deteriorated to nearly continuous moderate chop and light turbulence. The dutch roll was noticeably uncomfortable and a lower altitude was requested. We encountered light to moderate turbulence during the descent down to FL280 at .76 mach. The combination of turbulence and the inoperative yaw damper resulted in an extremely uncomfortable ride. At one point during the descent the aircraft dutch roll oscillations reached +/-20 degrees of bank, and +/-5 degrees of yaw with a cycle period of approximately 15 seconds. The autoplt was disconnected and minimal control inputs were used as the dutch roll damped out. The dutch roll took nearly 1 min to damp out. The motion was not violent but it was quite uncomfortable and certainly disconcerting for the passenger. The ride improved as we descended to FL280. Any bumps greater than light chop resulted in noticeable dutch roll. We eventually ended up at FL240 where the ride was generally smooth. The flight attendants in the back of the aircraft reported provisioning supplies were thrown around in the cabinets and some of the wine bottles shattered. There were no injuries or passenger complaints reported. I am seriously concerned about flts in the -700 with an inoperable yaw damper in areas of turbulence or any chop greater than light. In a prior life, I worked as a military aeronautical engineer specializing in aircraft stability and control. I believe the dutch roll event described above could be exacerbated by aggressive pilots attempting to fight the dutch roll. Aggressive pilot inputs could result in a catastrophic pilot induced oscillation. The technique I used to recover the aircraft was to freeze the stick and rudder and allow the aerodynamics to dampen out the oscillations. Although I am not an expert in the B737 dutch roll characteristics, I suggest the company and boeing review the event described above and determine if some changes are needed to the -700 inoperative yaw damper MEL provisos and the QRH procedures. I have 3 suggestions that I feel should be considered for -700 aircraft dispatched under this MEL. 1) flts should be limited to areas with nothing greater than light turbulence and light chop. 2) consideration should be given to a maximum altitude and speed for operation without a yaw damper. 3) the QRH should be modified to include desired recovery procedures from large dutch roll oscillations.

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Original NASA ASRS Text

Title: A B737-700 CAPT RPTED THAT HE DEPARTED MDW WITH AN MEL'ED YAW DAMPER AND ENCOUNTERED TURB THAT CAUSED THE ACFT TO DUTCH ROLL.

Narrative: FLT ARRIVED IN MDW WITH AN MEL FOR AN INOP YAW DAMPER. THE FORMS AND THE FLT RELEASE CORRECTLY REFLECTED MEL 322-3 AND THE SPECIAL PROCS WERE REVIEWED. THE OUTBOUND FLT TO HOU WAS PLANNED AT FL370 WITH A PLANNED ARR FUEL OF 6.5. THE WX PACKET SHOWED OCCASIONAL MODERATE TURB AT THE HIGHER ALTS. THE RELEASE SHOWED A MAX SHEER NUMBER OF 7 OVER LIT. I ELECTED TO BUMP UP THE DEP FUEL FROM 16.1 TO 17.1 ANTICIPATING THE USE OF A LOWER CRUISING ALT FOR SMOOTH AIR. THE FLT ATTENDANTS WERE ADVISED ABOUT THE INOP YAW DAMPER. THE FLT DEPARTED 30 MINS LATE FOR HOU. THE RIDE DETERIORATED CLBING THROUGH FL310 AND THE FLT ATTENDANTS WERE TOLD TO RETURN TO THEIR SEATS. THE FASTEN SEAT BELT SIGN WAS ON AND PAX WERE ADVISED TO REMAIN SEATED AS WE CONTINUED OUR CLB TO FL370. ATC ADVISED US THAT THE RIDE AT FL370 WAS INTERMITTENT LIGHT CHOP WITH OCCASIONAL MODERATE. APCHING FL370 THE RIDE DETERIORATED TO NEARLY CONTINUOUS MODERATE CHOP AND LIGHT TURB. THE DUTCH ROLL WAS NOTICEABLY UNCOMFORTABLE AND A LOWER ALT WAS REQUESTED. WE ENCOUNTERED LIGHT TO MODERATE TURB DURING THE DSCNT DOWN TO FL280 AT .76 MACH. THE COMBINATION OF TURB AND THE INOP YAW DAMPER RESULTED IN AN EXTREMELY UNCOMFORTABLE RIDE. AT ONE POINT DURING THE DSCNT THE ACFT DUTCH ROLL OSCILLATIONS REACHED +/-20 DEGS OF BANK, AND +/-5 DEGS OF YAW WITH A CYCLE PERIOD OF APPROX 15 SECONDS. THE AUTOPLT WAS DISCONNECTED AND MINIMAL CTL INPUTS WERE USED AS THE DUTCH ROLL DAMPED OUT. THE DUTCH ROLL TOOK NEARLY 1 MIN TO DAMP OUT. THE MOTION WAS NOT VIOLENT BUT IT WAS QUITE UNCOMFORTABLE AND CERTAINLY DISCONCERTING FOR THE PAX. THE RIDE IMPROVED AS WE DSNDED TO FL280. ANY BUMPS GREATER THAN LIGHT CHOP RESULTED IN NOTICEABLE DUTCH ROLL. WE EVENTUALLY ENDED UP AT FL240 WHERE THE RIDE WAS GENERALLY SMOOTH. THE FLT ATTENDANTS IN THE BACK OF THE ACFT RPTED PROVISIONING SUPPLIES WERE THROWN AROUND IN THE CABINETS AND SOME OF THE WINE BOTTLES SHATTERED. THERE WERE NO INJURIES OR PAX COMPLAINTS RPTED. I AM SERIOUSLY CONCERNED ABOUT FLTS IN THE -700 WITH AN INOPERABLE YAW DAMPER IN AREAS OF TURB OR ANY CHOP GREATER THAN LIGHT. IN A PRIOR LIFE, I WORKED AS A MIL AERO ENGINEER SPECIALIZING IN ACFT STABILITY AND CTL. I BELIEVE THE DUTCH ROLL EVENT DESCRIBED ABOVE COULD BE EXACERBATED BY AGGRESSIVE PLTS ATTEMPTING TO FIGHT THE DUTCH ROLL. AGGRESSIVE PLT INPUTS COULD RESULT IN A CATASTROPHIC PLT INDUCED OSCILLATION. THE TECHNIQUE I USED TO RECOVER THE ACFT WAS TO FREEZE THE STICK AND RUDDER AND ALLOW THE AERODYNAMICS TO DAMPEN OUT THE OSCILLATIONS. ALTHOUGH I AM NOT AN EXPERT IN THE B737 DUTCH ROLL CHARACTERISTICS, I SUGGEST THE COMPANY AND BOEING REVIEW THE EVENT DESCRIBED ABOVE AND DETERMINE IF SOME CHANGES ARE NEEDED TO THE -700 INOP YAW DAMPER MEL PROVISOS AND THE QRH PROCS. I HAVE 3 SUGGESTIONS THAT I FEEL SHOULD BE CONSIDERED FOR -700 ACFT DISPATCHED UNDER THIS MEL. 1) FLTS SHOULD BE LIMITED TO AREAS WITH NOTHING GREATER THAN LIGHT TURB AND LIGHT CHOP. 2) CONSIDERATION SHOULD BE GIVEN TO A MAX ALT AND SPD FOR OP WITHOUT A YAW DAMPER. 3) THE QRH SHOULD BE MODIFIED TO INCLUDE DESIRED RECOVERY PROCS FROM LARGE DUTCH ROLL OSCILLATIONS.

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.