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Safety Recommendation Details

Safety Recommendation A-90-091
Details
Synopsis: The National Transportation Safety Board's investigation of the United Airlines DC-IO accident in Sioux City, Iowa, on July 19, 1989, has revealed that the separation of the fan Stage I rotor disk of the No. 2 engine (a General Electric CF6-6D engine) initiated from a metallurgical anomaly (hard alpha) on the inside diameter surface of the disk bore near its forward corner. As a result of the accident, the Federal Aviation Administration issued Airworthiness Directive (AD) 89-20-01, effective October 7 , 1989.This AD required that certain CF6-6 engine fan Stage I rotor disks be inspected in accordance with General Electric Aircraft Engines (GEAE) Service Bulletin 72-947, dated September 15, 1989. Both the service bulletin and the AD were issued before the pieces of the separated disk were recovered in October, 1989. Titanium metal is processed in batches, referred to as "heats", that have the composition of the final alloy. The raw material that goes into a given heat can consist of processed ore (primarily pure titanium), alloying elements, scrap, and portions of other heats. Each heat of metal is homogenized and purified by repeatedly arc melting the heat in a vacuum furnace. Many of the CF6-6 engine fan disks were made from heats that had been melted twice (the double vacuum melting process). After 1971, General Electric changed their specifications to require three vacuum meltings (the triple vacuum melting process). The AD and service bulletin identify those CF6-6 engine fan Stage I rotor disks that records indicate are from the same heat of metal as the separated disk (Category I disks), those that have raw material in common with the separated disk (Category I1 disks), and those that were made with the double vacuum melting process instead of the triple vacuum melting process (Category I11 disks). The service bulletin also describes a contact ultrasonic inspection, which can be accomplished on-wing, and an immersion ultrasonic inspection, which requires that the disk be removed from the engine. The disks listed in AD 89-20-01 as being in Category I have been removed from service.1 In accordance with AD 89-20-01, all Category I1 and 111 disks should have been subjected to an initial contact ultrasonic inspection, and all Category II disks should have received an immersion ultrasonic inspection by April 1, 1990. The immersion ultrasonic inspection of Category 111 disks can be postponed until December 31, 1990, as long as the disks are subjected to the contact ultrasonic inspection at intervals of 500 cycles or less.
Recommendation: THE NTSB RECOMMENDS THAT THE FEDERAL AVIATION ADMINISTRATION: REQUIRE TURBINE ENGINE MANUFACTURERS TO PERFORM A SURFACE MACROETCH INSPECTION OF THE FINAL PART SHAPE OF CRITICAL TITANIUM ALLOY ROTATING COMPONENTS DURING THE MANUFACTURING PROCESS.
Original recommendation transmittal letter: PDF
Overall Status: Closed - Acceptable Action
Mode: Aviation
Location: SIOUX CITY, IA, United States
Is Reiterated: No
Is Hazmat: No
Is NPRM: No
Accident #: DCA89MA063
Accident Reports: United Airlines Flight 232 McDonnell Douglas DC-10-10‚Äč
Report #: AAR-90-06
Accident Date: 7/19/1989
Issue Date: 6/18/1990
Date Closed: 10/6/1992
Addressee(s) and Addressee Status: FAA (Closed - Acceptable Action)
Keyword(s):

Safety Recommendation History
From: NTSB
To: FAA
Date: 10/6/1992
Response: THE TRCRT RECOMMENDED THAT AN ETCH INSPECTION BE PERFORMED ON FINISH-MACHINED PARTS TO ENSURE THE OPTIMUM OPPORTUNITY TO DETECT SEGREGATION. ALSO, YOUR LETTER INDICATED THAT THE APPROPRIATE AIRCRAFT CERTIFICATION OFFICE WILL WORK WITH ITS MANUFACTURERS TO IMPLEMENT THIS RECOMMENDATION. THE FAA ACTIONS HAVE SATISFIED RECOMMENDATION A-90-91, WHICH IS CLASSIFIED AS "CLOSED--ACCEPTABLE ACTION."

From: FAA
To: NTSB
Date: 5/21/1992
Response: THE TITANIUM ROTATING COMPONENTS REVIEW TEAM (TRCRT) RECOMMENDED THAT A FINAL PART ETCH BE PERFORMED DURING MANUFACTURING, AND THE APPROPRIATE AIRCRAFT CERTIFICATION OFFICE WILL WORK WITH ITS MANUFACTURERS TO IMPLEMENT THIS RECOMMENDATION.

From: NTSB
To: FAA
Date: 3/4/1991
Response: Safety Recommendation A-90-91 asks that the FAA require turbine engine manufacturers to perform a surface macroetch inspection of the final shapes of critical titanium- alloy rotating components during the manufacturing process. The Safety Board notes that the FAA has formed a Titanium Rotating Components Review Team that is studying this issue and that the FAA will apprise the Board of their course of action after evaluating the review team's report. Pending further information, Safety Recommendation A-90-91 is classified "Open--Acceptable Response."

From: FAA
To: NTSB
Date: 7/31/1990
Response: The specifics of this safety recommendation is being addressed by the Titanium Rotating Components Review Team as discussed in response to Safety Recommendation A- 90-90. I will apprise the Board of the FAA's course of action to address this safety recommendation by the end of 1990.