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Safety Recommendation Details

Safety Recommendation A-96-116
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: Define and implement standards for in-service hydraulic fluid cleanliness and sampling intervals for all transport-category aircraft.
Original recommendation transmittal letter: PDF
Overall Status: Closed - Acceptable Action
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: 2/2/1999
Addressee(s) and Addressee Status: FAA (Closed - Acceptable Action)
Keyword(s):

Safety Recommendation History
From: NTSB
To: FAA
Date: 2/2/1999
Response: A-96-116 ASKED THE FAA TO DEFINE AND IMPLEMENT STANDARDS FOR IN-SERVICE HYDRAULIC FLUID CLEANLINESS AND SAMPLING INTERVALS FOR ALL TRANSPORT-CATEGORY AIRCRAFT. BECAUSE THE FAA'S ACTIONS MEET THE INTENT OF A-96-116, IT IS CLASSIFIED "CLOSED--ACCEPTABLE ACTION."

From: FAA
To: NTSB
Date: 6/29/1998
Response: Letter Mail Controlled 7/7/98 3:54:45 PM MC# 980844 THE FAA HAD DETERMINED THAT STANDARD NAS 1638 WAS ADEQUATE FOR CLARIFYING THE PARTICULATE CONTAMINATION LEVELS FOR AIRCRAFT HYDRAULIC FLUID. TO EXAMINE THIS ISSUE FURTHER, THE FAA REQUESTED THAT SAE A-6 COMMITTEE FORM AN INDUSTRY TASK FORCE TO STUDY FLUID CONTAMINATION ISSUES FROM OCTOBER 1995 TO APRIL 1997. THE TASK FORCE CONCLUDED THE FOLLOWING: FLIGHT CONTROL SERVO ACTUATORS DEMONSTRATED OPERATION AT CONTAMINATION LEVELS UP TO NAS 1638 CLASS 17 AND HIGHER; AN IN-SERVICE LIMIT OF NAS 1638 CLASS 9 PRESCRIBED BY A MAJORITY OF CURRENT AIRFRAME MANUFACTURERS WAS CONSERVATIVE, ADEQUATE, AND THE MAXIMUM RECOMMENDED LIMIT. THE TASK FORCE ALSO STUDIED CHEMICAL CONTAMINATION EFFECTS AND PROVIDED THE FOLLOWING IN-SERVICE LIMITS FOR FLUID PROPERTIES, SUCH AS SPECIFIC GRAVITY, MOISTURE CONTENT, VISCOSITY, AND CHLORINE CONTENT: CHEMICAL SENSITIVITY: ACUTATION SYSTEMS ARE INSENSITIVE TO CHEMICAL CONTAMINATION WITHIN NORMAL IN-SERVICE OPERATIONAL LIMITS. GROSS CONTAMINATION WITH OTHER FLUIDS IS PROHIBITED. CHEMICAL QUALITY RECOMMENDATIONS FOR IN-SERVICE HYDRAULIC FLUID: (CHART PROVIDED) CHEMICAL CONTAMINATION ALLOWABLE: CHEMICAL CONTAMINATION IS MORE AN ECONOMIC ISSUE THAN A SAFETY ISSUE AS SHOWN IN THE ABOVE CHART. THE RECOMMENDED LIMITS REFLECT THE MAXIMUM IN-SERVICE LIMITS ESTABLISHED BY MOST AIRFRAME MANUFACTURERS FOR SAE AS1241 HYDRAULIC FLUID. SENSITIVITY METHODS: THE SAE AEROSPACE RECOMMENDED PRACTICE 219, RECOMMENDED METHOD FOR PARTICULATE SENSITIVITY TESTING IS THE BEST AVAILABLE. HOWEVER, THE ONGOING EVALUATION OF TEST METHODS SHOULD RESULT IN AN IMPROVED STANDARD. CONSEQUENTLY, SAE ANTICIPATES REPLACING AEROSPACE RECOMMENDED PRACTICE 219 WITH AN APPROVED STANDARD. BOEING HAS EXPRESSED CONCERN THAT THE INCONSISTENCIES IN THE CURRENT HYDRAULIC FLUID SAMPLING PROCEDURES USED IN INDUSTRY CAN GIVE WIDE VARIATIONS IN THE MEASURED LEVELS OF PARTICULATE CONTAMINATION. BASED ON THE SAE CONCLUSIONS AND RECOMMENDATIONS AND BOEING'S CONCERN, THE FAA REQUESTED THAT THE SAE A-6 COMMITTEE PROVIDE ADDITIONAL INFORMATION NECESSARY TO STANDARDIZE FLUID SAMPLING AND PROCEDURES REGARDING HYDRAULIC CONTAMINATION LEVELS. THE TASK FORCE RECOGNIZED THAT THE INCONSISTENCIES RESULT IN WIDE VARIATIONS IN THE MEASURED LEVELS OF PARTICULATE CONTAMINATION. THERE ARE ONGOING EFFORTS IN THE SAE A-6 COMMITTEE TO DEVELOP A STANDARDIZED PROCEDURE FOR SAMPLING AND TESTING. THE RESULT OF THIS EFFORT IS THE DRAFT DOCUMENT AEROSPACE RECOMMENDED PRACTICE 5376, FLUID SYSTEMS AND COMPONENTS--METHODS, LOCATIONS AND CRITERIA FOR SYSTEM SAMPLING AND MEASURING THE SOLID PARTICLE CONTAMINATION OF HYDRAULIC FLUIDS, WHICH HAS BEEN CIRCULATED FOR SAE A-6 COMMITTEE BALLOT AND IS EXPECTED TO BE ISSUED BY OCTOBER 1998.

From: NTSB
To: FAA
Date: 7/15/1997
Response: A-96-116 ASKED THE FAA TO DEFINE & IMPLEMENT STANDARDS FOR IN-SERVICE HYDRAULIC FLUID CLEANLINESS REQUIREMENTS & SAMPLING INTERVALS FOR ALL TRANSPORT-CATEGORY AIRCRAFT. PENDING FURTHER DISCUSSION ON THESE ISSUES & REVIEW OF THE FAA'S FINAL ACTION, A-96-114 & -116 ARE CLASSIFIED "OPEN--ACCEPTABLE RESPONSE."

From: FAA
To: NTSB
Date: 1/16/1997
Response: IN AUGUST 1995, THE FAA REQUESTED THE SOCIETY OF AUTOMOTIVE ENGINEER (SAE) A-6 COMMITTEE--AEROSPACE FLUID POWER, ACTUATION, & CONTROL TECHNOLOGIES--TO DEVELOP AEROSPACE STANDARDS FOR HYDRAULIC SYSTEM CLEANLINESS LEVELS, COMPONENTS SENSITIVITY, & CHIP SHEAR CAPABILITY. SPECIFICALLY, THE FAA REQUESTED THE DEVELOPMENT OF THE FOLLOWING FOR TRANSPORT CATEGORY AIRPLANES: MINIMUM ACCEPTABLE HYDRAULIC FLIGHT CONTROL SYSTEM & COMPONENT SENSITIVITY (JAM POTENTIAL & ACTUATOR PERFORMANCE) TO PARTICULATE & CHEMICAL CONTAMINATION, AS WELL AS METHODS TO DETERMINE THE SENSITIVITY. MAXIMUM ALLOWABLE PARTICULATE & CHEMICAL CONTAMINATION LEVELS OF HYDRAULIC FLUID. MINIMUM ACCEPTABLE ACTUATOR CHIP SHEAR CAPABILITY. IN OCTOBER 1995, THE SAE ESTABLISHED A HYDRAULIC FLUID CONTAMINATION TASK FORCE CONSISTING OF ONE FAA REPRESENTATIVE & SEVERAL REPRESENTATIVES FROM THE AIRLINES, FLUID SUPPLIERS, AIRCRAFT MANUFACTURERS, ACTUATOR/SERVO VALVE MANUFACTURERS, PUMP MANUFACTURERS, & FILTER MANUFACTURERS. SEVEN SUBTASK GROUPS WERE IDENTIFIED TO WORK ON THE FOLLOWING ISSUES: (1) JAMS DUE TO PARTICLE CONTAMINATION; (2) JAMS DUE TO CHEMICAL CONTAMINATION; (3) PERFORMANCE DEGRADATION DUE TO PARTICLE CONTAMINATION; (4) PERFORMANCE DEGRADATION DUE TO CHEMICAL CONTAMINATION'; (5) SENSITIVITY TO PARTICLE CONTAMINATION; (6) SENSITIVITY TO CHEMICAL CONTAMINATION; & (7) CHIP SHEAR FORCE LEVELS & THEIR RELEVANCE TO SERVO VALVES/ACTUATORS. THE SAE TASK FORCE PLANS TO SUBMIT ITS RECOMMENDATIONS TO THE FAA IN THE JANUARY-FEBRUARY 1997 TIMEFRAME. THE FAA WILL REVIEW THE SAE RECOMMENDATIONS & TAKE APPROPRIATE ACTION. I WOULD ASK THAT THE BOARD PARTICIPATE IN THE VARIOUS SAE ACTIVITIES SO THAT THE BOARD'S POSITIONS ARE PROPERLY REFLECTED IN THE OVERALL EFFORT. IN ADDITION TO THIS ACTIVITY, THE FAA WILL CLOSELY REVIEW THE CHIP SHEAR CAPABILITY OF THE NEWLY DESIGNED RUDDER PCU SLIDE VALVES DURING THE TYPE CERTIFICATION WITH AN OBJECTIVE OF IMPROVING THE CHIP SHEAR CAPABILITY OF THE NEW DESIGN. I WILL KEEP THE BOARD APPRISED OF THE FAA'S PROGRESS ON THESE RECOMMENDATIONS.