Narrative:

Flight xx den-phl on sep/xx/96 diverted to ewr due to WX and delays at phl. Flight time after landing at ewr was 8 hours, 19 mins. Consulted company crew schedule with regard to legality of continuing back to phl after refueling as duty time was currently exceeding 12 hours. Crew desk reminded us of exception to flight time rules for far part 121 carriers during irregular/WX operations. After WX cleared and aircraft was refueled we prepared aircraft for departure to phl. Accomplished normal push back, start-up and taxi to runway. Immediately after takeoff a rapid, intense vibration was felt in both rudder pedals, causing both pedals to deflect approximately 1-2 inches fore and aft alternately and also causing severe shaking/vibration in the cockpit. Suspecting a tire out of balance or wobbling, I twice firmly applied brakes with no change in frequency or intensity resulting. I then directed the first officer to select gear handle from 'up' to 'off,' still no change. Cycled gear completely down then up and off twice, still no help. With recent B737 accidents in mind I selected the yaw damper switch off for approximately 10 seconds then back on, still no help or change in vibration. Directed the first officer to declare an emergency for return ewr and put gear down. Leveled at 2500 ft MSL and once again very firmly applied brakes, problem stopped. Accomplished approach and landing checklists and landed normally. Crash/fire people advised no visible irregularities and taxied to the gate upon completion of inspection. Air carrier has no procedure for this kind of rudder vibration and neither of pilots have ever experienced it before in some 2700 hours of combined experience in B737- 200 and 300 series aircraft. Company maintenance later advised us that this problem is caused by a shuttle valve in hydraulic/brake system slamming back and forth and that problem has occurred once before on another of our company's aircraft and at several other airlines. In addition manufacturer is aware of problem and has been for several yrs. Nothing in our simulator training or our flight manual makes any mention of this. Contributing factorswere a very long scheduled duty day, combined with this irregularity to produce a crew on duty from XA00 am to XQ20 am the following day after completion of maintenance debrief, company reports and insistent calls from FAA and NTSB. First officer and I had discussed insidious small errors/problems that lead to most accidents on a flight earlier in the day's trip which included bos- den, 2 hour situation in den, then den-phl with diversion, etc. Indeed in conferring with crew scheduler prior to this incident I had mentioned we were both tired and concerned about safety. Crew scheduler's only concern seemed to be with getting trip to operate and the fine points of far exception which allowed it. I believe safety should preclude these types of exceptions. Callback conversation with reporter revealed the following information: the reporter was PF and captain of the flight. He was concerned that a hydraulic problem was occurring that would affect the rudder system. He was thinking of the colorado springs and pittsburgh accidents, that this might be leading up to those types of accidents. When safely on the ground, a mechanic diagnosed the problem as a shuttle valve that was oscillating between the main and emergency brake system. He theorized that if a brake pedal was depressed after liftoff it could start the system cycling. Although both pilots are certain they did not depress the brake pedals after liftoff, they all seem to have agreed that one pedal might have been depressed, which was enough to start the system cycling. The captain admitted to having big feet that might have accidentally depressed a brake pedal. That is all it would take to get the system cycling. The aircraft was placed on jack stands and the vibration could be duplicated by depressing slightly on 1 brake pedal as the gear retracted. The aircraft manufacturer was aware that this situation could be inadvertently induced. When the system was repeated on the jack stands, the FAA and NTSB dropped any further interest they had in incident. Supplemental information from acn 346595: the gear was cycled down then up. No change invibrations. Captain mentioned applying pressure to rudder pedals and brakes several times in air to stop vibration. Upon third heavy application vibrations stopped, did not return. Callback conversation with reporter revealed the following information: the first officer on this flight had the same feelings as the captain regarding the seriousness of any rudder problems. When they had the problem stopped and the aircraft safely on the ground, first officer was positive it was a control problem. As they taxied to the gate, everything was normal. When a mechanic told them what he thought the problem was, the reporter was positive the mechanic didn't know what he was talking about. The mechanic happened to remember the same type incident 4 yrs earlier. This was when the mechanic ordered the aircraft to be lifted on some jacks and have the gear retracted. When this was performed, the situation repeated itself several times when the brake pedal was depressed. The FAA and NTSB lost interest in this case when it turned out the problem was brakes and not rudder. Reporter was positive the mechanic did not know what he was talking about, but, this mechanic turned out to be sensational.

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Original NASA ASRS Text

Title: B737-300 EXPERIENCES RUDDER VIBRATION SHORTLY AFTER TKOF.

Narrative: FLT XX DEN-PHL ON SEP/XX/96 DIVERTED TO EWR DUE TO WX AND DELAYS AT PHL. FLT TIME AFTER LNDG AT EWR WAS 8 HRS, 19 MINS. CONSULTED COMPANY CREW SCHEDULE WITH REGARD TO LEGALITY OF CONTINUING BACK TO PHL AFTER REFUELING AS DUTY TIME WAS CURRENTLY EXCEEDING 12 HRS. CREW DESK REMINDED US OF EXCEPTION TO FLT TIME RULES FOR FAR PART 121 CARRIERS DURING IRREGULAR/WX OPS. AFTER WX CLRED AND ACFT WAS REFUELED WE PREPARED ACFT FOR DEP TO PHL. ACCOMPLISHED NORMAL PUSH BACK, START-UP AND TAXI TO RWY. IMMEDIATELY AFTER TKOF A RAPID, INTENSE VIBRATION WAS FELT IN BOTH RUDDER PEDALS, CAUSING BOTH PEDALS TO DEFLECT APPROX 1-2 INCHES FORE AND AFT ALTERNATELY AND ALSO CAUSING SEVERE SHAKING/VIBRATION IN THE COCKPIT. SUSPECTING A TIRE OUT OF BAL OR WOBBLING, I TWICE FIRMLY APPLIED BRAKES WITH NO CHANGE IN FREQ OR INTENSITY RESULTING. I THEN DIRECTED THE FO TO SELECT GEAR HANDLE FROM 'UP' TO 'OFF,' STILL NO CHANGE. CYCLED GEAR COMPLETELY DOWN THEN UP AND OFF TWICE, STILL NO HELP. WITH RECENT B737 ACCIDENTS IN MIND I SELECTED THE YAW DAMPER SWITCH OFF FOR APPROX 10 SECONDS THEN BACK ON, STILL NO HELP OR CHANGE IN VIBRATION. DIRECTED THE FO TO DECLARE AN EMER FOR RETURN EWR AND PUT GEAR DOWN. LEVELED AT 2500 FT MSL AND ONCE AGAIN VERY FIRMLY APPLIED BRAKES, PROB STOPPED. ACCOMPLISHED APCH AND LNDG CHKLISTS AND LANDED NORMALLY. CRASH/FIRE PEOPLE ADVISED NO VISIBLE IRREGULARITIES AND TAXIED TO THE GATE UPON COMPLETION OF INSPECTION. ACR HAS NO PROC FOR THIS KIND OF RUDDER VIBRATION AND NEITHER OF PLTS HAVE EVER EXPERIENCED IT BEFORE IN SOME 2700 HRS OF COMBINED EXPERIENCE IN B737- 200 AND 300 SERIES ACFT. COMPANY MAINT LATER ADVISED US THAT THIS PROB IS CAUSED BY A SHUTTLE VALVE IN HYD/BRAKE SYS SLAMMING BACK AND FORTH AND THAT PROB HAS OCCURRED ONCE BEFORE ON ANOTHER OF OUR COMPANY'S ACFT AND AT SEVERAL OTHER AIRLINES. IN ADDITION MANUFACTURER IS AWARE OF PROB AND HAS BEEN FOR SEVERAL YRS. NOTHING IN OUR SIMULATOR TRAINING OR OUR FLT MANUAL MAKES ANY MENTION OF THIS. CONTRIBUTING FACTORSWERE A VERY LONG SCHEDULED DUTY DAY, COMBINED WITH THIS IRREGULARITY TO PRODUCE A CREW ON DUTY FROM XA00 AM TO XQ20 AM THE FOLLOWING DAY AFTER COMPLETION OF MAINT DEBRIEF, COMPANY RPTS AND INSISTENT CALLS FROM FAA AND NTSB. FO AND I HAD DISCUSSED INSIDIOUS SMALL ERRORS/PROBS THAT LEAD TO MOST ACCIDENTS ON A FLT EARLIER IN THE DAY'S TRIP WHICH INCLUDED BOS- DEN, 2 HR SIT IN DEN, THEN DEN-PHL WITH DIVERSION, ETC. INDEED IN CONFERRING WITH CREW SCHEDULER PRIOR TO THIS INCIDENT I HAD MENTIONED WE WERE BOTH TIRED AND CONCERNED ABOUT SAFETY. CREW SCHEDULER'S ONLY CONCERN SEEMED TO BE WITH GETTING TRIP TO OPERATE AND THE FINE POINTS OF FAR EXCEPTION WHICH ALLOWED IT. I BELIEVE SAFETY SHOULD PRECLUDE THESE TYPES OF EXCEPTIONS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR WAS PF AND CAPT OF THE FLT. HE WAS CONCERNED THAT A HYD PROB WAS OCCURRING THAT WOULD AFFECT THE RUDDER SYS. HE WAS THINKING OF THE COLORADO SPRINGS AND PITTSBURGH ACCIDENTS, THAT THIS MIGHT BE LEADING UP TO THOSE TYPES OF ACCIDENTS. WHEN SAFELY ON THE GND, A MECH DIAGNOSED THE PROB AS A SHUTTLE VALVE THAT WAS OSCILLATING BTWN THE MAIN AND EMER BRAKE SYS. HE THEORIZED THAT IF A BRAKE PEDAL WAS DEPRESSED AFTER LIFTOFF IT COULD START THE SYS CYCLING. ALTHOUGH BOTH PLTS ARE CERTAIN THEY DID NOT DEPRESS THE BRAKE PEDALS AFTER LIFTOFF, THEY ALL SEEM TO HAVE AGREED THAT ONE PEDAL MIGHT HAVE BEEN DEPRESSED, WHICH WAS ENOUGH TO START THE SYS CYCLING. THE CAPT ADMITTED TO HAVING BIG FEET THAT MIGHT HAVE ACCIDENTALLY DEPRESSED A BRAKE PEDAL. THAT IS ALL IT WOULD TAKE TO GET THE SYS CYCLING. THE ACFT WAS PLACED ON JACK STANDS AND THE VIBRATION COULD BE DUPLICATED BY DEPRESSING SLIGHTLY ON 1 BRAKE PEDAL AS THE GEAR RETRACTED. THE ACFT MANUFACTURER WAS AWARE THAT THIS SIT COULD BE INADVERTENTLY INDUCED. WHEN THE SYS WAS REPEATED ON THE JACK STANDS, THE FAA AND NTSB DROPPED ANY FURTHER INTEREST THEY HAD IN INCIDENT. SUPPLEMENTAL INFO FROM ACN 346595: THE GEAR WAS CYCLED DOWN THEN UP. NO CHANGE INVIBRATIONS. CAPT MENTIONED APPLYING PRESSURE TO RUDDER PEDALS AND BRAKES SEVERAL TIMES IN AIR TO STOP VIBRATION. UPON THIRD HVY APPLICATION VIBRATIONS STOPPED, DID NOT RETURN. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE FO ON THIS FLT HAD THE SAME FEELINGS AS THE CAPT REGARDING THE SERIOUSNESS OF ANY RUDDER PROBS. WHEN THEY HAD THE PROB STOPPED AND THE ACFT SAFELY ON THE GND, FO WAS POSITIVE IT WAS A CTL PROB. AS THEY TAXIED TO THE GATE, EVERYTHING WAS NORMAL. WHEN A MECH TOLD THEM WHAT HE THOUGHT THE PROB WAS, THE RPTR WAS POSITIVE THE MECH DIDN'T KNOW WHAT HE WAS TALKING ABOUT. THE MECH HAPPENED TO REMEMBER THE SAME TYPE INCIDENT 4 YRS EARLIER. THIS WAS WHEN THE MECH ORDERED THE ACFT TO BE LIFTED ON SOME JACKS AND HAVE THE GEAR RETRACTED. WHEN THIS WAS PERFORMED, THE SIT REPEATED ITSELF SEVERAL TIMES WHEN THE BRAKE PEDAL WAS DEPRESSED. THE FAA AND NTSB LOST INTEREST IN THIS CASE WHEN IT TURNED OUT THE PROB WAS BRAKES AND NOT RUDDER. RPTR WAS POSITIVE THE MECH DID NOT KNOW WHAT HE WAS TALKING ABOUT, BUT, THIS MECH TURNED OUT TO BE SENSATIONAL.

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.