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Safety Recommendation Details

Safety Recommendation A-96-109
Details
Synopsis: On March 3, 1991, at 0944 mountain standard time, United Airlines flight 585, a Boeing 737-291 airplane, crashed during an approach to the Colorado Springs, Colorado, airport. The crew of 5 and the 20 passengers were killed. The airplane was destroyed by the impact and a postcrash fire. The weather was clear with unlimited visibility. There were windshear reports during the day. At the time of the accident the surface winds were reported to be out of the northwest at 20 knots gusting to 28. The safety board has not determined the cause(s) of the accident and an investigation of airframe, operational and weather factors is continuing.
Recommendation: TO THE FEDERAL AVIATION ADMINISTRATION: Require the Boeing Commercial Airplane Group to develop and install a cockpit indicator system for all new production B-737 airplanes that indicates rudder surface position and movement. For existing B-737 airplanes, when implementing the installation of an enhanced-parameter flight data recorder, require the installation of a cockpit indicator system that indicates rudder surface position and movement. (Superseded by A-99-20 through A-99-29)
Original recommendation transmittal letter: PDF
Overall Status: Closed - Unacceptable Action/Superseded
Mode: Aviation
Location: COLORADO SPGS, CO, United States
Is Reiterated: No
Is Hazmat: No
Is NPRM: No
Accident #: DCA91MA023
Accident Reports: Uncontrolled Descent and Collision with Terrain, United Airlines Flight 585, Boeing 737-200, N999UA, 4 Miles South of Colorado Springs Municipal Airport
Report #: AAR-92-06
Accident Date: 3/3/1991
Issue Date: 10/18/1996
Date Closed: 4/16/1999
Addressee(s) and Addressee Status: FAA (Closed - Unacceptable Action/Superseded)
Keyword(s):

Safety Recommendation History
From: NTSB
To: FAA
Date: 4/16/1999
Response: Because of the complexity of the 737 rudder system (and the potential for unforeseen failure mechanisms), its lack of redundancy in the event of a single-point failure or a latent failure, and the continued absence of cues to help alert flight crews to latent failures, the safety board concludes that a reliably redundant rudder actuation system is needed for the 737, despite the significant improvements that have been made in the system's design. Accordingly, the board believes that the FAA should require that all existing and future 737's have a reliably redundant rudder actuation system. This redundancy could be achieved by developing a multiple-panel rudder surface or providing multiple actuators for a single-panel rudder surface. Further, A-96-107, -109, -112, and -113 are classified CLOSED—UNACCEPTABLE ACTION/ SUPERSEDED. A-96-107, A-96-109, A-96-112, and A-96-113 are superseded by A-99-20 through A-99-29.

From: NTSB
To: FAA
Date: 2/2/1999
Response: THE ISSUES ADDRESSED IN A-96-107, -108, -109, -112, -113, AND -118 AND A-97-18 WILL BE FURTHER ANALYZED AND DISCUSSED IN OUR FINAL REPORT ON THE USAIR FLIGHT 427 ACCIDENT INVESTIGATION, WHICH THE BOARD WILL CONSIDER IN MARCH 1999. THE FAA'S RESPONSES TO THESE RECOMMENDATIONS WILL BE INCORPORATED IN THE BOARD'S ANALYSIS OF THESE ISSUES. THEREFORE, THESE RECOMMENDATIONS REMAIN AS CURRENTLY CLASSIFIED, PENDING ISSUANCE OF OUR FINAL REPORT.

From: FAA
To: NTSB
Date: 5/13/1998
Response: Letter Mail Controlled 5/18/98 3:54:43 PM MC# 980640 THE FAA HAS REVIEWED ITS PREVIOUS POSITION ON THIS RECOMMENDATION AND CONTINUES TO BELIEVE THAT THERE IS NOT A REQUIREMENT TO INSTALL A COCKPIT INDICATOR SYSTEM IN BOEING 737 AIRCRAFT ON A MANDATORY BASIS. THE YAW DAMPER INDICATOR MOUNTED ON THE CENTER INSTRUMENT PANEL DISPLAYS YAW DAMPER MOVEMENT OF THE RUDDER BUT NOT RUDDER MOVEMENT INPUT BY THE RUDDER PCU. RUDDER MOVEMENTS ARE READILY APPARENT TO THE FLIGHTCREW BY THE MOVEMENT OF THE RUDDER PEDALS, EXCEPT IN THOSE INSTANCES WHERE THE MOVEMENT IS CAUSED BY THE YAW DAMPER. AS STATED IN THE FAA'S RESPONSE DATED 1/16/97, A RUDDER POSITION INDICATOR WOULD HAVE LIMITED VALUE DURING THE ONSET OF A ROLL/YAW DEPARTURE FROM CONTROLLED FLIGHT COMPARED TO A PROMPT AND AGGRESSIVE PILOT RESPONSE. THE BOARD EXPRESSED CONCERN THAT A PILOT, NO KNOWING THE POSITION OF THE RUDDER, MAY TURN OFF A HYDRAULIC SYSTEM INSTEAD OF TAKING THE CORRECT ACTION OF TURNING OFF THE YAW DAMPER SYSTEM. ANY RUDDER MOVEMENT OUTSIDE THE SMALL MOVEMENT OF THE YAW DAMPER SYSTEM WILL BACK-DRIVE THE RUDDER PEDALS AND BE NOTED BY THE PILOTS IF THEIR FEET ARE ON THE PEDALS. IF AN UNCOMMANDED RUDDER MOVEMENT OCCURS, THE FLIGHTCREW WILL TAKE APPROPRIATE, IMMEDIATE ACTION TO MAINTAIN CONTROL OF THE AIRPLANE AND TO FOLLOW THE APPROPRIATE EMERGENCY OR NONEMERGENCY PROCEDURES. THE NONEMERGENCY PROCEDURES DIRECT THE FLIGHTCREW TO APPLY FORCE TO THE RUDDER PEDALS AND SYSTEMATICALLY SELECT THE FLIGHT CONTROL SWITCH TO "STBY RUD" IF THE RUDDER PEDALS REMAIN JAMMED. THE FLIGHTCREW WILL ONLY SELECT "HYDRAULIC SYSTEMS OFF" WHEN FOLLOWING NONEMERGENCY OPERATING PROCEDURES. THE FAA HAS COMPLETED A NUMBER OF ACTIONS TO ADDRESS BOEING 737 RUDDER ISSUES. THE SERIES OF AD'S REFERENCED IN RESPONSE TO A-96-107, -112, AND -113, AND A-97-16 ALSO PRECLUDES THE RUDDER JAM/REVERSAL SCENARIO AND FURTHER SUPPORTS THE CONCLUSION THAT A RUDDER SURFACE POSITION INDICATOR IS NOT A MANDATORY REQUIREMENT. I CONSIDER THE FAA'S ACTION TO BE COMPLETED, AND I PLAN NO FURTHER ACTION ON THIS RECOMMENDATION.

From: NTSB
To: FAA
Date: 7/15/1997
Response: THE BOARD AGREES WITH THE FAA'S ASSERTION THAT A RUDDER POSITION INDICATOR WOULD BE OF LITTLE VALUE IN THE INITIAL MOMENTS OF AN UPSET DURING WHICH IMMEDIATE PILOT REACTION MAY BE NEEDED TO PREVENT A LOSS OF CONTROL. HOWEVER, THE BOARD DISAGREES WITH THE FAA'S POSITION THAT RUDDER POSITION INDICATOR WOULD PROVIDE NO PRACTICAL INFO TO THE PILOT. IT HAS BEEN NOTED THAT IN SEVERAL CASES THE PILOTS DID NOT PLACE THEIR FEET ON THE RUDDER PEDALS DURING THE RECOVERY & THEREFORE WERE UNAWARE OF THE RUDDER POSITION BY THE OFFSET OF THE PEDALS. THE BOARD'S INVESTIGATION OF NUMEROUS YAW/ROLL UPSET EVENTS HAS FOUND THAT PILOTS ARE OFTEN UNCERTAIN ABOUT THE POSITION OF THE RUDDER IN THE MOMENTS AFTER REGAINING CONTROL WHEN THEY ARE TRYING TO TROUBLE SHOOT THE PROBLEM. FOR INSTANCE, THE BOARD IS CONCERNED THAT WITHOUT KNOWING THE POSITION OF THE RUDDER, PILOTS MAY TURN OFF A HYDRAULIC SYSTEM WHEN TURNING OFF THE YAW DAMPER SYSTEM WOULD BE THE APPROPRIATE RESPONSE. THEREFORE, THE BOARD REQUESTS THAT THE FAA RECONSIDER ITS POSITION ON THIS ISSUE. PENDING FURTHER CORRESPONDENCE, A-96-109 IS "OPEN--UNACCEPTABLE RESPONSE."

From: FAA
To: NTSB
Date: 1/16/1997
Response: BOEING 737 SERIES AIRPLANES HAVE A YAW DANPER INDICATOR LOCATED ON THE CENTER INSTRUMENT PANEL. THIS INDICATOR SHOWS YAW DAMPER MOVEMENT OF THE RUDDER BUT NOT RUDDER MOVEMENT INPUT BY THE RUDDER PCU. RUDDER INDICATORS IN THE COCKPIT ARE PRIMARILY USED FOR GROUND MAINTENANCE. ALL RUDDER MOVMENTS ON THE BOEING 737, EXCEPT THOSE CAUSED BY THE YAW DAMPER, ARE DIRECTLY APPARENT TO THE FLIGHTCREW THROUGH THE MOVEMENT OF THE RUDDER PEDALS. CONSEQUENTLY, THE FAA BELIEVES THAT AN ADDITIONAL INDICATOR IN THE COCKPIT WOULD ADD NO PRACTICAL INFO TO THE PILOT. A RUDDER POSITION INDICATOR WILL HAVE VERY LITTLE VALUE DURING THE IMMEDIACY OF A ROLL/YAW DEPARTURE FROM CONTROLLED FLIGHT. AN EVENT INVOLVING A ROLL/YAW DEPARTURE FROM CONTROLLED FLIGHT REQUIRES PROMPT & AGGRESSIVE LOT RESPONSE DEPENDING ON THE ATTITUDE, RATE, & ACCELERATION EXPERIENCED. THE FLIGHTCREW CANNOT LOOK FOR, FIND, & REACT TO A RUDDER INDICATOR IN THIS CRITICAL TIME PERIOD. THE USE OF VISUAL & ORAL ALERTS, SUCH AS A HORN OR A LIGHT, IS NOT PERMITTED AS A SINGLE SOURCE OF IDENTIFICATION FOR A SERIOUS EVENT SUCH AS AN AIRCARAFT STALL & YET THESE ALARMS ARE MORE LIKELY TO PRODUCE A PROPER PILOT RESPONSE THAN A RUDDER INDICATOR. THE BOARD'S OWN RECOMMENDATION ON MAKING THE YAW DAMPER FAILURE RESPONSE A LEARNED RESPONSE BY THE FLIGHTCREW SEEMS TO SUPPORT THE FAA BELIEF THAT PROMPT & AGGRESSIVE PILOT RESPONSE IS NEEDED IN THESE EVENTS & NOT ANOTHER INDICATOR IN THE COCKPIT. I PLAN NO FURTHER ACTION ON THIS RECOMMENDATION, & I CONSIDER THE FAA'S ACTION TO BE COMPLETED.