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Safety Recommendation Details

Safety Recommendation A-99-027
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: Evaluate the Boeing 737's block maneuvering speed schedule to ensure the adequacy of airspeed margins above crossover airspeed for each flap configuration, provide the results of the evaluation to air carrier operators of the Boeing 737 and the NTSB, and require Boeing to revise block maneuvering speeds to ensure a safe airspeed margin above crossover airspeed.
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: THE SAFETY BOARD APPRECIATES RECEIVING THE INFORMATION THAT THE FAA SUBMITTED. ALTHOUGH THE BOARD HAS RESERVATIONS ABOUT WHETHER THE REVISED BLOCK MANEUVERING SPEEDS PROVIDE A SUFFICIENT SAFETY MARGIN AT ALL AIRCRAFT WEIGHTS AND FLAP CONFIGURATIONS, THE FAA HAS COMPLETED THE ACTIONS RECOMMENDED. ACCORDINGLY, A-99-27 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 3/24/99, THE FAA ISSUED FLIGHT STANDARDS INFORMATION BULLETIN FOR AIR TRANSPORTATION 99-02, MANEUVERING SPEEDS AND RECOVERY PROCEDURES FOR BOEING 737 AIRPLANES. THE BULLETIN RECOMMENDED AN ACROSS-THE-BOARD INCREASE OF 10 KNOTS TO THE PUBLISHED B-737 MANEUVERING SPEED SCHEDULES FOR FLAP SETTINGS OF "FLAPS UP, 1, 5, AND 10." SUBSEQUENTLY, ON 4/5/99, THE BOEING COMPANY ISSUED FLIGHT OPERATIONS FLIGHT CREW INFORMATION BULLETIN 99-1, MANEUVERING SPEEDS FOR BOEING 737-100/200/300/400/500. THE BULLETIN REVISED ALL MANEUVERING SPEEDS FOR "FLAPS UP, 1, 5, AND 10" BY AT LEAST 10 KNOTS (AND AS MUCH AS 20 KNOTS FOR CERTAIN CONDITIONS WITH FLAP SETTINGS OF "FLAPS 5") AND ADDED NEW INFORMATION FOR AIRPLANES OPERATING AT WEIGHTS LOWER THAN 103,000 POUNDS. SINCE THE ISSUANCE OF THESE BULLETINS, BOEING HAS ALSO INCLUDED THIS INFORMATION IN ITS 737 OPERATIONS MANUALS. THE FAA CONSIDERED ITS ACTION TO BE COMPLETED WITH THE ISSUANCE OF FLIGHT STANDARDS INFORMATION BULLETIN FOR AIR TRANSPORTATION 99-02. ON 8/16/00, THE BOARD ASKED THAT THE FAA PROVIDE DETAILED INFORMATION ON THE EVALUATION IT CONDUCTED OF THE BOEING 737'S BLOCK MANEUVERING SPEED SCHEDULE. THE BOARD FURTHER STATED THAT IT BELIEVED THAT THE REVISED BLOCK MANEUVERING SPEED SCHEDULES SHOULD BE PROVIDED FOR THE BOEING 737 "NEXT GENERATION" AIRPLANES (BOEING 737-600, -700, -800, AND -900). PENDING FURTHER INFORMATION FROM THE FAA, THIS SAFETY RECOMMENDATION WAS CLASSIFIED IN AN "OPEN ACCEPTABLE" STATUS. I HAVE ENCLOSED A COPY OF BOEING LETTER B-H200-17054-ASI DATED 9/18/00, WHICH PROVIDES THE SUBSTANTIATING INFORMATION THAT THE BOARD IS REQUESTING. THE ENCLOSED INFORMATION ALSO INCLUDES THE REVISED BLOCK MANEUVERING SPEED SCHEDULES FOR THE BOEING 737 "NEXT GENERATION" AIRPLANES. 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 BOARD REQUESTS THAT THE FAA PROVIDE DETAILED INFORMATION ON THE EVALUATION IT CONDUCTED OF THE BOEING 737'S BLOCK MANEUVERING SPEED SCHEDULE. THIS INFORMATION WILL ASSIST THE BOARD IN EVALUATING THE CHANGES IN THE FSIB, AND THE REVISIONS TO THE BOEING 737 AFM. ADDITIONALLY, THE SAFETY BOARD BELIEVES THAT REVISED BLOCK MANEUVERING SPEED SCHEDULES SHOULD BE PROVIDED FOR THE BOEING 737 "NEXT GENERATION" AIRPLANES (737-600, -700, -800, AND -900) IN THE EVENT OF A FAILURE OF THE RUDDER PRESSURE REDUCER SYSTEM. PENDING RECEIPT OF THIS INFORMATION, A-99-27 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 AS PREVIOUSLY STATED, ON 3/24/99, THE FAA ISSUED FLIGHT STANDARDS INFORMATION BULLETIN FOR AIR TRANSPORTATION 99-02, MANEUVERING SPEEDS AND RECOVERY PROCEDURES FOR BOEING 737 AIRPLANES. THE BULLETIN RECOMMENDED AN ACROSS-THE-BOARD INCREASE OF 10 KNOTS TO THE PUBLISHED B-737 MANEUVERING SPEED SCHEDULES FOR FLAP SETTINGS OF "FLAPS UP, 1, 5, AND 10. SUBSEQUENTLY, ON 4/5/99, THE BOEING COMPANY ISSUED FLIGHT OPERATIONS FLIGHT CREW INFORMATION BULLETIN 99-1, MANEUVERING SPEEDS FOR BOEING 737-100/200/300/400/500. THE BULLETIN REVISED ALL MANEUVERING SPEEDS FOR "FLAPS UP, 1, 5, AND 10 BY AT LEAST 10 KNOTS (AND AS MUCH AS 20 KNOTS FOR CERTAIN CONDITIONS WITH FLAP SETTINGS OF "FLAPS 5) AND ADDED NEW INFORMATION FOR AIRPLANES OPERATING AT WEIGHTS LOWER THAN 103,000 POUNDS. BOEING HAS COMPLETED ITS REVISION TO ITS BOEING 737 AFM TO REFLECT THE NEW MANEUVERING SPEEDS. I HAVE ENCLOSED A COPY OF PERTINENT PAGES FROM THE BOEING 737-300 AFM FOR THE BOARD'S INFORMATION. BOEING WILL COMPLETE ITS REVISIONS TO THE OTHER BOEING 737 CLASSIC MODELS OVER THE NEXT FEW MONTHS. ALTHOUGH THE BOARD HAS NOT YET RESPONDED TO THE FAA'S INITIAL LETTER DATED 6/25/99, ITS STAFF HAS EXPRESSED CONCERN THAT THE FAA DID NOT INCLUDE INCREASED MANEUVERING SPEEDS FOR BOEING 737-600/700/800/900 SERIES. IN RESPONSE TO THIS CONCERN, THE FAA OFFERS THE FOLLOWING. ALL BOEING 737NG MODELS (BOEING 737-600/700/800) WERE CERTIFIED WITH THE RESPACED SPOOL VALVE AND THE RUDDER PRESSURE REDUCER AS PART OF THE BASIC DESIGN. THE BOEING 737-900 SERIES WILL HAVE AN IDENTICAL FLIGHT CONTROL CONFIGURATION AND WILL BE CERTIFIED IN A SIMILAR MANNER TO OTHER NG MODELS. FURTHER, THE RUDDER PRESSURE REDUCER ON THE NG MODELS DIFFERS FROM THE ONES ON THE CLASSIC MODELS IN THAT IT OPERATES SOLELY ON AIRSPEED (AIRSPEED GREATER THAN 137 KNOTS ACTIVATES THE PRESSURE REDUCTION). THERE IS NO ALTITUDE FOR ACTIVATION, THEREFORE, NO LOW ALTITUDE EXPOSURE LIKE THERE IS ON THE CLASSICS THAT USE -1,000 FEET AS THE ACTIVATION ALTITUDE. THERE IS SOME EXPOSURE IN THE RARE CASE OF A VERY LIGHTWEIGHT AIRPLANE WHOSE APPROACH SPEED COULD BE LESS THAN 137 KNOTS. IN THAT CASE, THE EXPOSURE WOULD BE ABOUT THE SAME AS ONE OF THE CLASSIC MODELS. ADDITIONALLY, THE RUDDER PRESSURE REDUCER IS NOT ON THE MASTER MINIMUM EQUIPMENT LIST, WHICH MEANS THAT IT MUST BE OPERATIVE AT DISPATCH. A FAILURE OF THE RUDDER PRESSURE REDUCER MEANS THAT THE HYDRAULIC SUPPLY TO THE RUDDER SYSTEM IS ALWAYS AT FULL PRESSURE--AS IF THE RUDDER PRESSURE REDUCER DID NOT EXIST. IF A FAILURE AFTER DISPATCH IS ANNUNCIATED AND THE AIRPLANE IS STILL ON THE GROUND, IT SHOULD NOT TAKE OFF. IF THE FAILURE OCCURS IN FLIGHT, THE SINGLE FLIGHT EXPOSURE TO THE RUDDER PRESSURE REDUCER FAILURE, WHEN COUPLED WITH ANOTHER RUDDER SYSTEM FAILURE THAT WOULD CAUSE AN UNCOMMANDED RUDDER MOVEMENT TO BLOWDOWN DURING A CRITICAL PHASE OF FLIGHT, IS SO LOW THAT IT IS IN THE EXTREMELY IMPROBABLE CATEGORY. THE BOARD'S STAFF ALSO EXPRESSED CONCERN REGARDING HOW THE FLIGHT TESTS WERE CONDUCTED TO DETERMINE THE INCREASED MANEUVERING SPEEDS. IN RESPONSE, AS A FOLLOW-ON TO THIS ACCIDENT INVESTIGATION, BOEING TEST FLEW NEARLY ALL OF THE BOEING 737 MODELS. THE 737-200 ADVANCED AND THE 737-300/400/500 MODELS WERE TEST-FLOWN IN 1996 AND 1997 AT SPECIFIC WEIGHTS AND CG'S. THE BOARD'S STAFF PARTICIPATED IN SOME OF THESE EARLY PHASES OF TESTS ON THE CLASSIC MODELS. ONCE THE TEST FLIGHTS WERE FINISHED, THIS INFORMATION WAS USED TO UPDATE THE SIMULATIONS. THE SIMULATIONS WERE VALIDATED THEN FLOWN AT THE CRITICAL CG THROUGH A RANGE OF WEIGHTS TO ESTABLISH THE NECESSARY MARGINS. THE RESULTS OF THIS EFFORT WERE THE REVISED MANEUVERING SPEEDS. THE SAME EXERCISE WAS PERFORMED FOR THE RUDDER PRESSURE REDUCER. THE BOEING 737-100 WAS NOT TESTED BECAUSE THERE ARE VERY FEW LEFT IN THIS COUNTRY, AND THE BOEING 737-200 NON-ADVANCED WAS NOT TESTED BECAUSE FROM A FLIGHT CONTROLS CHARACTERISTICS STANDPOINT, THE AIRPLANE'S PERFORMANCE IS PREDICTABLE BY THE BOEING 737-200 ADVANCED. IN SUMMARY, THE SAME TYPE OF EVALUATION WAS PERFORMED FOR ALL THE NG MODELS, BUT THE TEST MATRIX WAS NOT QUITE AS EXTENSIVE BECAUSE IT WAS OBVIOUS THAT THE NG MODELS ALWAYS HAD SUFFICIENT MARGIN ABOVE THEIR CROSSOVER SPEEDS. 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: On March 24, 1999, the FAA issued Flight Standards Information Bulletin for Air Transportation 99-02, Maneuvering Speeds and Recovery Procedures for Boeing 737 Airplanes. The bulletin recommended an across-the-board increase of 10 knots to the published B-737 maneuvering speed schedules for flap settings of "Flaps UP, 1, 5, and 10." Subsequently, on April 5, 1999, the Boeing Company issued Flight Operations Flight Crew Information Bulletin 99-1, Maneuvering Speeds for Boeing 737-100/200/300/400/500. The bulletin revised all maneuvering speeds for "Flaps UP, 1, 5, and 10" by at least 10 knots (and as much as 20 knots for certain conditions with flap settings of "Flaps 5") and added new information for airplanes operating at weights lower than 103,000 pounds. The FAA will revise the 737 Airplane Flight Manual to reflect the new maneuvering speeds by July 1999. I will provide the Board with a copy of the revised Airplane Flight Manual change as soon as it is issued.