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Safety Recommendation Details

Safety Recommendation A-99-024
Details
Synopsis: On 9/8/94, about 1903:23 eastern daylight time, USAir (now US Airways) flight 427, a Boeing 737-3B7 (737-300), N513AU, crashed while maneuvering to land at Pittsburgh Int'l. Airport, Pittsburgh, PA. Flight 427 was operating under the provisions of 14 code of federal regulations (CFR) part 121 as a scheduled domestic passenger flight from Chicago-O'Hare Int'l. Airport, Chicago, Il, to Pittsburgh. The flight departed about 1810, with 2 pilots, 3 flight attendants, and 127 passengers on board. The airplane entered an uncontrolled descent and impacted terrain near Aliquippa, PA. All 132 people on board were killed, and the airplane was destroyed by impact forces and fire. Visual meteorological conditions prevailed for the flight, which operated on an instrument flight rules flight plan.
Recommendation: TO THE FEDERAL AVIATION ADMINISTRATION: Revise Airworthiness Directive 96-26-07 so that procedures for addressing a jammed or restricted rudder do not rely on the pilots' ability to center the rudder pedals as an indication that the rudder malfunction has been successfully resolved, and require Boeing and U.S. operators of Boeing 737s to amend their airplane flight manuals and operations manuals accordingly. (Supersedes Safety Recommendation A-96-107, A-96-109, A-96-112, and A-96-113)
Original recommendation transmittal letter: PDF
Overall Status: Closed - Acceptable Action
Mode: Aviation
Location: ALIQUIPPA, PA, United States
Is Reiterated: No
Is Hazmat: No
Is NPRM: No
Accident #: DCA94MA076
Accident Reports: Uncontrolled Descent and Collision With Terrain, USAir Flight 427, Boeing 737-300, N513AU
Report #: AAR-99-01
Accident Date: 9/8/1994
Issue Date: 4/16/1999
Date Closed: 4/24/2001
Addressee(s) and Addressee Status: FAA (Closed - Acceptable Action)
Keyword(s):

Safety Recommendation History
From: NTSB
To: FAA
Date: 4/24/2001
Response: WITH THE ISSUANCE OF AD-2000-22-02, THE FAA HAS COMPLETED THE ACTIONS RECOMMENDED. HOWEVER, THE SAFETY BOARD NOTES THAT THE FAA HAS NOT SUBMITTED A RESPONSE FOR A RELATED SAFETY RECOMMENDATION, A-99-25, WHICH ASKS THAT 14 CFR PART 121 CARRIERS PROVIDE THEIR FLIGHT CREWS WITH INITIAL AND RECURRENT FLIGHT SIMULATOR TRAINING IN THE "UNCOMMANDED YAW OR ROLL" AND "JAMMED OR RESTRICTED RUDDER" PROCEDURES IN BOEING'S 737 (737) OPERATIONS MANUAL. ALTHOUGH THOSE PROCEDURES HAVE BEEN SIMPLIFIED UNDER AD-2000-22-02, IT REMAINS ESSENTIAL FOR BOEING 737 FLIGHT CREWMEMBERS TO OBTAIN AND MAINTAIN HANDS-ON PROFICIENCY IN DEALING WITH A RUDDER MALFUNCTION, INCLUDING EXPERIENCE IN A FULL-FLIGHT SIMULATOR WITH ALERTING CUES AND THE REQUIRED CONTROL INPUTS AND PROCEDURAL STEPS. THE BOARD IS ALSO CONCERNED THAT NONE OF THE PROCEDURES ESTABLISHED THUS FAR, INCLUDING THOSE IN AD-2000-22-02, WOULD ALLOW FLIGHT CREWS TO READILY MAINTAIN CONTROL OF A 737 (-200 THROUGH -500 MODEL) IN THE EVENT OF A HARD-OVER RUDDER MALFUNCTION OCCURRING AT LOW ALTITUDES WHILE TAKING OFF AND LANDING OR DURING HIGH-SPEED RUNWAY OPERATIONS. THE BOARD WOULD APPRECIATE LEARNING ABOUT THE FAA'S ACTIONS IN RESPONSE TO A-99-25. HOWEVER, BECAUSE THE FAA HAS COMPLETED THE RECOMMENDED ACTIONS FOR THIS RECOMMENDATION, A-99-24 IS CLASSIFIED "CLOSED--ACCEPTABLE ACTION."

From: FAA
To: NTSB
Date: 12/20/2000
Response: Letter Mail Controlled 12/26/2000 11:21:32 AM MC# 2001812 ON 8/16/00, THE BOARD STATED THAT ALTHOUGH IT WAS SATISFIED WITH THE RESULTS OF A SIMULATOR EVALUATION OF THE PROCEDURE, THE RESULTS FROM THE PROCEDURAL EVALUATIONS PERFORMED BY THE INDEPENDENT FLIGHT CONTROLS ENGINEERING TEST AND EVALUATION BOARD (ETEB) HAVE HIGHLIGHTED INADEQUACIES IN THE AIRPLANE FLIGHT MANUAL (AFM) PROCEDURE REQUIRED BY AIRWORTHINESS DIRECTIVE (AD) 96-26-07. THE FAA AGREES WITH THE BOARD AND, IN RESPONSE TO THE ETEB'S RECOMMENDATIONS, FORMED A TEAM TO EVALUATE TWO REVISIONS TO THE AFM PROCEDURE REQUIRED BY AD 96-26-07. THE EVALUATION INCLUDED 10 SIMULATOR SESSIONS THAT INVOLVED FLIGHTCREWS FROM ALASKA AIRLINES, SOUTHWEST AIRLINES, UNITED AIRLINES, US AIRWAYS, KLM ROYAL DUTCH AIRLINES, AND SCANDINAVIAN AIRLINES. THE FLIGHTCREWS WERE SUBJECTED TO VARIOUS SIMULATED RUDDER FAILURES AND WERE NOT BRIEFED ON THE NATURE OF THE FAILURES PRIOR TO THE EXERCISE. THE FLIGHTCREWS WERE ONLY TOLD THAT THEY WERE AIDING BOEING IN EVALUATING VARIOUS PROCEDURAL REVISIONS. CERTAIN NONRUDDER FAILURES WERE ALSO SIMULATED SO THAT THE FLIGHTCREWS WOULD NOT ASSUME THAT EACH FAILURE TO WHICH THEY WERE SUBJECTED WAS ASSOCIATED WITH THE RUDDER. FOLLOWING THE FLIGHTCREW EVALUATION, THE BOARD WAS AFFORDED THE OPPORTUNITY TO EVALUATE THE FINAL VERSION OF THE REVISED AFM PROCEDURE. ON 10/11/00, A SAFETY BOARD PILOT PARTICIPATED IN A SIMULATOR SESSION, WHICH WAS A DUPLICATION OF THE AIRLINE FLIGHTCREW SESSION. AS A RESULT OF THE AIRLINE FLIGHTCREW AND SAFETY BOARD EVALUATIONS, THE FAA ISSUED AD 2000-22-02 ON 10/20/00. AD 2000-22-02, WHICH SUPERSEDES AD 96-26-07, REVISES THE EXISTING AFM PROCEDURE TO SIMPLIFY THE INSTRUCTIONS FOR CORRECTING A JAMMED OR RESTRICTED FLIGHT CONTROL CONDITION. AD 2000-22-02 IS AN IMMEDIATELY ADOPTED RULE THAT HAS A 30-DAY COMPLIANCE TIME. I HAVE ENCLOSED A COPY OF AD 2000-22-02 FOR THE BOARD'S INFORMATION. I BELIEVE THAT THE FAA HAS ADDRESSED THE FULL INTENT OF THIS RECOMMENDATION, AND I CONSIDER THE FAA'S ACTION TO BE COMPLETED.

From: NTSB
To: FAA
Date: 8/16/2000
Response: THE SAFETY BOARD AGREES WITH THE FAA THAT, DURING THE EVALUATION, THE TEST SUBJECTS REPORTED THAT THEY IMMEDIATELY KNEW WHEN THE LOSS OF BACK PRESSURE ON THE RUDDER PEDALS INDICATED THAT THE PROBLEM WAS UNDER CONTROL. HOWEVER, SINCE THAT TEST, THE BOARD HAS LEARNED THAT THE ENGINEERING TEST AND EVALUATION BOARD (ETEB), WHICH WAS FORMED BY THE FAA TO EXAMINE THE ENTIRE 737 RUDDER SYSTEM, MAY HAVE ACQUIRED NEW INFORMATION THAT DIRECTLY AFFECTS THIS PROCEDURE. PENDING THE RELEASE OF THE ETEB REPORT, A-99-24 IS CLASSIFIED "OPEN--ACCEPTABLE RESPONSE."

From: FAA
To: NTSB
Date: 2/4/2000
Response: Letter Mail Controlled 02/11/2000 3:36:56 PM MC# 2000220 ON 6/8/99, REPRESENTATIVES FROM THE FAA, THE BOEING COMPANY, AND THE BOARD MET TO EVALUATE THE EXISTING AIRPLANE FLIGHT MANUAL (AFM) PROCEDURE MANDATED BY AIRWORTHINESS DIRECTIVE (AD) 96-26-07 TO DETERMINE IF A REVISION TO THE AFM WAS NECESSARY. THE EVALUATION WAS CONDUCTED IN THE BOEING M-CAB SIMULATOR, UTILIZING A BOEING 737-300 SIMULATION MODEL. THE SIMULATION MODEL WAS MODIFIED TO CONSIDER THE EFFECT OF A RUDDER POWER CONTROL UNIT (PCU) SECONDARY SLIDE JAM AND OVERTRAVEL OF THE PRIMARY SLIDE, COMMONLY IDENTIFIED AS A RUDDER REVERSAL. OF PARTICULAR CONCERN TO THE BOARD WAS THE PHENOMENON OF RUDDER PEDAL REVERSAL IN RESPONSE TO A PILOT INPUT. DURING A RUDDER REVERSAL, THE FORCES REQUIRED TO CENTER THE PEDALS COULD BE HIGH ENOUGH TO DEFORM THE COMPONENTS ELASTICALLY IN THE RUDDER SYSTEM. THE DEFORMATION WOULD ALLOW THE PEDALS TO BE CENTERED WITHOUT CAUSING AN ASSOCIATED CENTERING OF THE RUDDER ITSELF. DURING THE EVALUATION, ALL OF THE PARTICIPANTS (PILOTS AND NON-PILOTS) WERE PROVIDED AN OPPORTUNITY TO EXPERIENCE RUDDER REVERSALS DURING CRUISE AND APPROACH PHASES OF FLIGHT AND OVER A RANGE OF AIRSPEEDS AND AIRPLANE CONFIGURATIONS. FOR EACH SCENARIO, THE EXISTING AFM PROCEDURE WAS EVALUATED TO DETERMINE IF IT WAS EFFECTIVE IN REGAINING CONTROL OF THE RUDDER AND IF IT PROVIDED SUFFICIENT CUES TO THE PILOT DURING EACH STEP OF THE PROCEDURE TO KNOW IF THE RUDDER WAS EITHER FUNCTIONING NORMALLY (I.E., THE MALFUNCTION HAD CLEARED) OR THAT THE MALFUNCTION WAS STILL PRESENT. IF THE FORCE REQUIRED TO MOVE THE RUDDER PEDAL REDUCED AND THE PILOT WAS ABLE TO MAINTAIN STRAIGHT AND LEVEL FLIGHT WITH ALL CONTROLS CENTERED, IT WAS IMMEDIATELY OBVIOUS THAT THE MALFUNCTION HAD CLEARED. CONVERSELY, IF THE MALFUNCTION HAD NOT BEEN CLEARED AFTER ACCOMPLISHING ANY PROCEDURAL STEPS, THE CONTINUING EXISTENCE OF THE MALFUNCTION WAS INDICATED BY CONTINUATION OF HIGH RESIDUAL RUDDER FORCES, SIGNIFICANT CONTROL WHEEL DEFLECTIONS (TO NEGATE THE RUDDER-INDUCED ROLL), AND CHANGES IN RUDDER PEDAL FORCES AND DEFLECTIONS ASSOCIATED WITH SPEED CHANGES. IT WAS NOT NECESSARY TO KNOW THE POSITION OF THE RUDDER PEDALS (I.E., WHETHER THEY HAD BEEN CENTERED) TO DETERMINE THE STATUS OF THE MALFUNCTION OR WHETHER OR NOT THE RUDDER ITSELF WAS STILL DEFLECTED. THE HIGH PEDAL FORCES AND THE POSITIONS OF THE OTHER COCKPIT CONTROLS PROVIDED SUFFICIENT CUES TO RECOGNIZE THE STATUS OF A RUDDER MALFUNCTION. AT THE CONCLUSION OF THE EVALUATION, THE GROUP AGREED THAT ENHANCEMENTS IN FLIGHT CREW TRAINING RELATIVE TO THE PILOT CUES ASSOCIATED WITH A RUDDER MALFUNCTION COULD MAKE A REVISION TO THE PROCEDURE UNNECESSARY. CONSEQUENTLY, THE FAA WILL ADDRESS THE NEED TO ENHANCE FLIGHT CREW TRAINING IN RESPONSE TO A-99-25. THE FAA HAS TAKEN MEASURES OVER THE PAST 2 YEARS TO REDUCE OR ELIMINATE THE EFFECTS OF ANY RUDDER SYSTEM MALFUNCTION, INCLUDING SCENARIOS INVOLVING RUDDER REVERSAL. ON 6/23/97, THE FAA ISSUED AD 97-14-03 TO MANDATE DESIGN CHANGES ADDING A RUDDER LIMITING DEVICE THAT REDUCES THE RUDDER AUTHORITY AT FLIGHT CONDITIONS WHERE FULL RUDDER AUTHORITY IS NOT REQUIRED AND A REDESIGNED, MORE RELIABLE YAW DAMPER SYSTEM. THE RUDDER LIMITER ALLOWS THE FLIGHT CREW TO USE LATERAL CONTROL TO COUNTER ANY COMMANDED OR UNCOMMANDED RUDDER POSITION. COMPLIANCE TIME FOR AD 97-14-03 IS 8/4/00, AND FLEET RETROFIT HAS BEGUN. THE INSTALLATION OF THE RUDDER PRESSURE REDUCER WILL REDUCE THE SEVERITY OF ANY UNCOMMANDED RUDDER DEFLECTION. ON 6/23/97, THE FAA ALSO ISSUED AD 97-14-04 TO MANDATE DESIGN CHANGES TO THE BOEING 737 MAIN RUDDER PCU TO REDUCE OR ELIMINATE THE EFFECTS OF ANY RUDDER MALFUNCTION THAT COULD RESULT IN UNCOMMANDED RUDDER MOVEMENT. THE DESIGN CHANGE TO THE PCU SEVOS ELIMINATES THE POSSIBILITY OF REVERSALS RESULTING FROM A JAMMED SECONDARY SLIDE AND SUBSEQUENT PRIMARY SLIDE OVERTRAVEL, WHICH IS THE ONLY ESTABLISHED MOANS FOR A RUDDER REVERSAL TO OCCUR. IN ADDITION, AD 97-14-04 MANDATES A PERIODIC INSPECTION TO TEST THE MAIN RUDDER PCU FOR INTERNAL LEAKAGE AND TO ENSURE THAT THE RUDDER PCU IS PRODUCING AN ACCEPTABLE HINGE MOMENT. THE INTERNAL LEAKAGE TEST WILL DETECT CERTAIN SERVO VALVE SLIDE JAMS. THE INTERNAL LEAKAGE TEST PROVIDES GREATER SAFETY MARGINS THAN A HARD-TIME REPLACEMENT OF THE MAIN RUDDER PCU BECAUSE IT ENSURES THE PCU IS FUNCTIONING WITHIN ACCEPTABLE LIMITS AT MORE FREQUENT INTERVALS THAN A HARD-TIME INTERVAL. ANY DESIGN CHANGE TO MONITOR THE SERVO VALVE SLIDES WOULD INCREASE THE COMPLEXITY OF THE SERVO VALVE AND MOST LIKELY INCREASE THE PROBABILITY OF JAMMING OF A SLIDE. THE COMPLIANCE TIME FOR AD 97-14-04 WAS 8/4/99, AND FLEET RETROFIT IS COMPLETED. WITH INCORPORATION OF THIS AD, THE NEED FOR U.S. OPERATORS TO ADDRESS RUDDER REVERSAL EXPLICITLY IS ELIMINATED. THE FAA BELIEVES THAT THE ACTIONS REQUIRED BY AD 97-14-03 AND AD 97-14-04 FURTHER REDUCE THE NEED FOR A REVISION TO THE AFM PROCEDURE MANDATED BY EXISTING AD 96-26-07. CONSEQUENTLY, I CONSIDER THE FAA'S ACTION TO BE COMPLETED ON THIS RECOMMENDATION, AND I PLAN NO FURTHER ACTION.

From: FAA
To: NTSB
Date: 6/25/1999
Response: Letter Mail Controlled 6/30/99 3:02:35 PM MC# 990699: The FAA started an initiative, with participation from the Boeing Company and the Board's staff, to determine the scope and appropriate revision to the procedures for addressing a jammed or restricted rudder. It is anticipated that this project will result in a formal evaluation of the current procedures using the Boeing 737 M-cab engineering simulator. Based on the results of the evaluation, an appropriate revision to existing procedures and Airworthiness Directive (AD) 96-26-07 will be made. I will keep the Board informed of the FAA's progress on this safety recommendation.