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General Aviation Safety
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.
TO THE FEDERAL AVIATION ADMINISTRATION: Revise 14 CFR Section 25.671 to account for the failure or jamming of any flight control surface at its design-limited deflection. Following this revision, reevaluate all transport-category aircraft and ensure compliance with the revised criteria.
Original recommendation transmittal letter:
Closed - Reconsidered
COLORADO SPGS, CO, United States
Uncontrolled Descent and Collision with Terrain, United Airlines Flight 585, Boeing 737-200, N999UA, 4 Miles South of Colorado Springs Municipal Airport
Addressee(s) and Addressee Status:
FAA (Closed - Reconsidered)
Safety Recommendation History
The Safety Board concludes that transport-category airplanes should be shown to be capable of continued safe flight and landing after a jammed flight control in any position unless the jam can be shown to be extremely improbable. Accordingly, the Safety Board believes that the FAA should amend 14 CFR Section 25.671(c)(3) to require that transport-category airplanes be shown to be capable of continued safe flight and landing after jamming of a flight control at any deflection possible, up to and including its full deflection, unless such a jam is shown to be extremely improbable. Because the Safety Board recognizes that the language of Safety Recommendation A-96-108 may not have adequately expressed this concern, that recommendation is classified "Closed--Reconsidered Superseded."
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.
Letter Mail Controlled 5/18/98 3:54:43 PM MC# 980640: The FAA does not concur with the Board's position that it is necessary to account for a jam in any flight control surface at its "design-limited deflection." Currently, 14 CFR 25.671(c)(3) requires this interpretation, unless it can be shown that such a condition is extremely improbable. For a control surface to jam in its design-limited deflection during flight would require an active system failure to cause the control surface to move to the extreme position and remain there. The FAA allows the applicant to show compliance with the runaway and jam condition by demonstrating, based on a probability analysis, that this condition is an extremely improbable event or that it can be alleviated. A jam condition is more likely to occur in a control position normally encountered. The FAA policy is to require the applicant to demonstrate controllability for this condition. The FAA held a public meeting on December 3, 1996, in Seattle, Washington, to discuss jams in flight controls. At this meeting, the FAA solicited comments from industry on this issue. There was a consensus among manufacturers that a jam in the extreme position is not a realistic condition. The FAA has reviewed industry's comments and considered other factors related to this issue as a basis of its decision not to revise 14 CFR 25.671 as requested by the Board. I consider the FAA's action to be completed on this safety recommendation, and I plan no further action.
A-96-108 ASKED THE FAA TO REVISE 14 CFR SECTION 25.671 TO ACCOUNT FOR THE FAILURE OR JAMMING OF ANY FLIGHT CONTROL SURFACE AT ITS DESIGN-LIMITED DEFLECTION. FOLLOWING THIS REVISION, REEVALUATE ALL TRANSPORT-CATEGORY AIRCRAFT AND ENSURE COMPLIANCE WITH THE REVISED CRITERIA. HOWEVER, BECAUSE THE FAA HAS NOT INDICATED WHAT ACTION IT PLANS TO TAKE, A-96-108 IS CLASSIFIED "OPEN--AWAIT RESPONSE."
CURRENTLY, 14 CFR 25.671, AS REVISED BY AMENDMENT 25-23 ON 4/8/70 , REQUIRES THAT THE AIRPLANE MUST BE SHOWN BY ANALYSIS, TESTS, OR BOTH TO BE CAPABLE OF CONTINUED SAFE FLIGHT AND LANDING AFTER ANY OF THE FOLLOWING FAILURES OR JAMMING IN THE FLIGHT CONTROL SYSTEM AND SURFACES: ANY SINGLE FAILURE OR ANY COMBINATION OF FAILURES NOT SHOWN TO BE EXTREMELY IMPROBABLE; ANY JAM IN A CONTROL POSITION NORMALLY ENCOUNTERED DURING TAKEOFF, CLIMB, CRUISE NORMAL TURNS, DESCENT, AND LANDING UNLESS THE JAM IS SHOWN TO BE EXTREMELY IMPROBABLE OR CAN BE ALLEVIATED. A RUNAWAY OF A FLIGHT CONTROL TO AN ADVERSE POSITION AND JAM MUST BE ACCOUNTED FOR IF SUCH RUNAWAY AND SUBSEQUENT JAMMING ARE NOT EXTREMELY IMPROBABLE. THE EXISTING REGULATIONS, SPECIFICALLY THE LAST PROVISION WHICH CONSIDERS A RUNAWAY CONTROL SURFACE JAMED AT ITS DEFLECTION LIMIT, ADDRESS THE INTENT OF RECOMMENDATION A-96-108, EXCEPT FOR ALLOWING EXTREMELY IMPROBABLE ( ONE IN A BILLION) EVENTS. TO REQUIRE THAT A DESIGNER ACCOUNT FOR CONTROL SURFACE JAMMING AT ITS DESIGN-LIMITED DEFLECTION, REGARDLESS OF THE PROBABILITY OF THE EVENT, IS CONTRARY TO THE BASIC REGULATORY PHILOSOPHY USED THROUGHOUT 14 CFR PART 25. TO EVALUATE THIS ISSUE FURTHER, THE FAA WILL USE DATA DEVELOPED AT A 12/3/96, PUBLIC MEETING. THE FAA HELD THIS MEETING TO DISCUSS THE SUBJECT OF FLIGHT CONTROL JAMS AND TO SEEK COMMENTS FROM THE GENERAL PUBLIC REGARDING CRITERIA THAT COULD BE USED IN SHOWING COMPLIANCE WITH THE REQUIREMENTS OF 14 CFR 25.671(C) (3) RELATIVE TO FLIGHT CONTROL JAMS IN THE NORMALLY ENCOUNTERED POSITION. IN ADDITION, THE PUBLIC WAS ALSO INVITED TO DISCUSS THIS RECOMMENDATION. THE FAA WILL EVALUATE THE COMMENTS RECEIVED AT THE PUBLIC MEETING REGARDING THESE ISSUES AND WILL FURTHER ASSESS THE SAFETY IMPACT OF THIS RECOMMENDATION. I WILL INFORM THE BOARD OF THE FAA'S COURSE OF ACTION TO ADDRESS THIS RECOMMENDATION BY 4/1/97.
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