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Safety Recommendation Details

Safety Recommendation A-91-077
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, AIR PORT. THE CREW OF 5 AND THE 20 PASSENGERS WERE KILLED. THE AIRPLANE WAS DESTROYED BY THE IMPACT & A POSTCRASH FIRE. THE WEATHER WAS CLEAR WITH UNLIMITED VISIBILITY. THERE WERE WINDSHEAR REPORTS DURING THE DAY. AT THE TIME OF THE ACCI DENT 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, & AN INVESTI GATION OF AIRFRAME, OPERATIONAL, AND WEATHER FACTORS IS CONTINUING.
Recommendation: THE NTSB RECOMMENDS THAT THE FEDERAL AVIATION ADMINISTRATION: ISSUE AN AIRWORTHINESS DIRECTIVE REQUIRING A CHECK ON ALL BOEING 737 AND 727 MODEL AIRPLANES WITH THE P/N 1087-23 INPUT SHAFT IN THE RUDDER AUXILIARY ACTUATOR UNIT FOR THE FORCE NEEDED TO ROTATE THE INPUT SHAFT LEVER RELATIVE TO THE P/N 1087-22 BEARING OF THE AUXILIARY ACTUATOR UNIT. DURING THIS CHECK, THE BEARING SHOULD BE INSPECTED TO DETERMINE IF IT ROTATES RELATIVE TO THE HOUSING. ALL SHAFT ASSEMBLIES IN WHICH ROTATION OF THE BEARING OCCURS, OR IN WHICH EXCESSIVE FORCE IS NEEDED TO MOVE THE INPUT LEVER, SHOULD BE REMOVED FROM SERVICE ON AN EXPEDITED BASIS AND THE ASSEMBLIES SHOULD BE REPLACED WITH A P/N 1087-21 SHAFT ASSEMBLY THAT HAS A REDUCED DIAMETER ON THE UNLUBRICATED PORTION OF THE SHAFT IN ACCORDANCE WITH REVISION G OF THE P/N 1087-23 ENGINEERING DRAWING. ALL ASSEMBLIES MEETING THE FORCE REQUIREMENT SHOULD BE RECHECKED AT APPROPRIATE INTERVALS UNTIL REPLACED WITH A P/N 1087-21 SHAFT ASSEMBLY CONTAINING A P/N 1087-23 SHAFT THAT HAS A REDUCED DIAMETER ON THE UNLUBRICATED PORTION OF THE SHAFT.
Original recommendation transmittal letter: PDF
Overall Status: Closed - Acceptable Alternate Action
Mode: Aviation
Location: COLORADO SPGS, CO, United States
Is Reiterated: Yes
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: 8/20/1991
Date Closed: 11/15/1993
Addressee(s) and Addressee Status: FAA (Closed - Acceptable Alternate Action)
Keyword(s):

Safety Recommendation History
From: NTSB
To: FAA
Date: 3/27/2001
Response: From the accident report concerning the uncontrolled descent of a Boeing 737-200 four miles south of Colorado Springs Municipal Airport (adopted 3/27/2001): Because of its concern about galled standby rudder actuator bearings on other B-737s and B-727s, on August 20, 1991, the Safety Board issued the following Safety Recommendation to the FAA: A-91-77 Issue an Airworthiness Directive requiring a check on all Boeing 737 and 727 model airplanes with the P/N 1087-23 input shaft in the rudder auxiliary actuator unit for the force needed to rotate the input shaft lever relative to the P/N 1087-22 bearing of the auxiliary actuator unit. During this check, the bearing should be inspected to determine if it rotates relative to the housing. All shaft assemblies in which rotation of the bearing occurs, or in which excessive force is needed to move the input lever, should be removed from service on an expedited basis and the assemblies should be replaced with a P/N 1087-21 shaft assembly that has a reduced diameter on the unlubricated portion of the shaft in accordance with revision G of the P/N 1087-23 engineering drawing. All assemblies meeting the force requirement should be rechecked at appropriate intervals until replaced with a P/N 1087-21 shaft assembly containing a P/N 1087-23 shaft that has a reduced diameter on the unlubricated portion of the shaft. The FAA's response to this recommendation, dated October 9, 1991, stated that it agreed with the intent of the safety recommendation and that it was considering the issuance of a notice of proposed rulemaking (NPRM) to address the problem. On November 21, 1991, the Safety Board responded to the FAA's letter, indicating that it was pleased with this response. Pending notification of progress on the NPRM, the Safety Board classified Safety Recommendation A-91-77 as “Open—Acceptable Response.” On January 3, 1992, the FAA issued an NPRM (Docket No. 91-NM-257-AD) proposing to adopt an airworthiness directive (AD) applicable to all Boeing Model 727-series airplanes and certain Model 737-series airplanes. This NPRM proposed to require inspection of the input shaft in the auxiliary (standby) rudder power control unit and to require reporting to the FAA on units that fail the inspection test procedure. In a letter dated March 27, 1992, the Safety Board expressed its concern to the FAA that the second part of the Safety Board's recommendation regarding inspection of the bearing was not included in the NPRM. The Safety Board believes that inspection of the bearing for rotation in the housing and for the integrity of the safety wire is an essential part of the entire inspection. Further, the Safety Board advised the FAA that it believed the proposed time frame for compliance with the inspection (4,000 flight hours) might be excessive. The letter stated that the proposed AD, if it included the modifications described above, would fulfill the intent of Safety Recommendation A-91-77. Pending notification of progress on the NPRM, the Safety Board classified A-91-77 as “Open—Acceptable Response.” In its December 8, 1992, report on this accident, the Safety Board stated that because there had been no further action taken by the FAA on its proposed rulemaking and because another airline had found galled bearings during an inspection, it reiterated Safety Recommendation A-91-77 and urged the FAA to expedite action on its AD. In that report, the Safety Board classified A-91 77 as “Open—Unacceptable Action.” On April 19, 1993, the FAA issued a notice in the Federal Register to withdraw the NPRM. In an August 5, 1993, letter to the Safety Board, the FAA explained that it had reevaluated the design of the rudder control system on 727 and 737 airplanes and determined that fighters would be capable of detecting a galled condition by (1) increased force necessary to move the rudder pedal; (2) erratic nose gear steering with the yaw damper engaged; (3) rudder yaw damper kick back or yaw damper back drives on the rudder pedals during flight; and (4) erratic operation of the rudder yaw damper or erratic rudder oscillations with the yaw damper engaged. On November 15, 1993, the Safety Board noted it had no further evidence that galling could result in uncommanded rudder deflections of a significant magnitude and classified Safety Recommendation A-91-77 “Closed—Acceptable Alternate Action.”

From: NTSB
To: FAA
Date: 11/15/1993
Response: THE BOARD IS PLEASED TO NOTE THAT THE FAA'S EVALUATION OF THE DESIGN OF THE RUDDER CONTROL SYSTEM ON BOTH AIRPLANES HAS INDICATED THAT THE GALLING BETWEEN THE INPUT SHAFT AND BEARING IS DETECTABLE BY THE PILOT AND IS NOT AN UNSAFE CONDITION. NONETHELESS, THE BOARD REMAINS CONCERNED THAT THE GALLING CAN RESULT IN ERRATIC FLIGHT CONTROL THAT COULD DISTRACT A FLIGHCREW AND, UNDER SOME CIRCUMSTANCES, COULD POTENTIALLY BE HAZARDOUS. HOWEVER, THE BOARD HAS NO FURTHER EVIDENCE THAT THE GALLING CAN RESULT IN UNCOMMANDED RUDDER DEFECTIONS OF A SIGNIFICANT MAGNITUDE. THEREFORE, RECOMMENDATION A-91-77 IS CLASSIFIED "CLOSED--ACCEPTABLE ALTERNATE ACTION."

From: FAA
To: NTSB
Date: 8/5/1993
Response: ON JANUARY 3, 1992, THE FAA ISSUED A NOTICE OF PROPOSED RULEMAKING (NPRM) WHICH PROPOSED TO REQUIRE INSPECTION OF THE INPUT SHAFT IN THE AUXILIARY RUDDER POWER CONTROL UNIT AND TO REQUIRE REPORTING TO THE FAA ON UNITS THAT FAIL THE INSPECTION TEST PROCEDURE. SINCE THE ISSUANCE OF THIS NPRM, THE FAA HAS REEVALUATED THE DESIGN OF THE RUDDER CONTROL SYSTEM ON THE MODEL 727 AND 737 SERIES AIRPLANES AND HAS DETERMINED THAT THE GALLING IS NOT AN UNSAFE CONDITION AND THAT THE FLIGHTCREW WOULD BE CAPABLE OF DETECTING THIS CONDITION. CONSEQUENTLY, ON APRIL 19, 1993, THE FAA ISSUED A NOTICE IN THE FEDERAL REGISTER TO WITHDRAW THE NPRM. THE FAA CONSIDERS THIS ACTION TO BE COMPLETED ON THE PROPOSED RECOMMENDATION.

From: NTSB
To: FAA
Date: 3/27/1992
Response: The Safety Board is pleased to note that on January 3, 1992, the FAA issued a Notice of Proposed Rulemaking (NPRM) (Docket No. 91-NM-257-AD) proposing to adopt an AD that requires inspection of the input shaft in the auxiliary rudder PCU and to require reporting to the FAA on units that fail the inspection. However, the Safety Board is concerned that the second part of the recommendation, regarding inspection of the bearing, is not included in the NPRM. Because looseness of the bearing in the body of the actuator is an additional indication of the galling problem, the Safety Board believes that inspection of the bearing for rotation in the housing and for the integrity of the safety wire is an essential part of the entire inspection. The Safety Board is also concerned that the proposed time for compliance for these inspections (4,000 flight hours) may be excessive. As indicated in the NPRM, the tests and inspections would take only about 6 hours. Because the components affected could cause an uncommanded rudder input, the Safety Board believes that these inspections should be performed as soon as possible or at the very least at the next available inspection of the airplane. The proposed AD, if it includes the modifications described above, will fulfill the intent of Safety Recommendation A-91-77. Pending notification of progress on the rulemaking action, Safety Recommendation A-91-77 remains classified as "Open--Acceptable Response."

From: FAA
To: NTSB
Date: 2/24/1992
Response: ON JANUARY 3, 1992, THE FAA ISSUED A NOTICE OF PROPOSED RULEMAKING (NPRM) (DOCKET NO. 91-NM-257-AD) PROPOSING TO ADOPT AN AIRWORTHINESS DIRECTIVE APPLICABLE TO ALL BOEING MODEL 727 SERIES AIRPLANES AND CERTAIN MODEL 737 SERIES AIRPLANES. THIS NPRM PROPOSES TO REQUIRE INSPECTION OF THE INPUT SHAFT IN THE AUXILIARY (STANDBY) RUDDER POWER CONTROL UNIT (PCU) AND TO REQUIRE REPORTING TO THE FAA ON UNITS THAT FAIL THE INSPECTION TEST PROCEDURES.

From: NTSB
To: FAA
Date: 11/21/1991
Response: This safety recommendation concerns the rudder auxiliary actuator units in the Boeing 737 and 727 model airplanes. We are pleased to note that the Federal Aviation Administration agrees with the intent of this safety recommendation and is considering the issuance of a notice of proposed rulemaking requiring a check for the force needed to rotate the input shaft lever relative to the corresponding bearing. Pending notification of progress on the rulemaking action, Safety Recommendation A-91-77 is classified as "Open--Acceptable Response."

From: FAA
To: NTSB
Date: 10/9/1991
Response: THE FAA AGREES WITH THE INTENT OF THIS SAFETY RECOMMENDATION AND IS CONSIDERING THE ISSUANCE OF A NOTICE OF PROPOSED RULEMAKING TO ADDRESS THIS ISSUE.