Engine Breakup

Editor Joe Escobar highlights the NTSB recommendations released Aug. 28, 2006.


On Aug. 28, the NTSB issued the following recommendations:

(A-06-60) Urgent. Require that all CF6-80A and -80C2 high pressure turbine (HPT) stage 1 disks and applicable -80E1 HPT stage 1 disks that have more than 3,000 cycles since new (CSN) and have not been reworked in accordance with General Electric Service Bulletins (SB) 72-0788 or 72-1089 or have not yet been inspected in accordance with SB 72-0779 or Alert Service Bulletin 72-A1026 be immediately removed from service for inspection and rework in accordance with these SBs. Those CF6-80A and -80C2 HPT stage 1 disks and applicable -80E1 HPT stage 1 disks that have fewer than 3,000 CSN and have not been reworked or inspected in accordance with these SBs can remain in service until reaching the 3,000 CSN threshold, at which time they should also be removed from service for inspection and rework.

(A-06-61) Urgent. Require that all CF6-80A and -80C2 high pressure turbine (HPT) stage 1 disks and applicable -80E1 HPT stage 1 disks that have not been reworked in accordance with General Electric Service Bulletins (SB) 72-0788 or 72-1089 but have been inspected in accordance with SB 72-0779 or Alert Service Bulletin (ASB) 72-A1026 and have more than 3,000 cycles since the inspection be immediately removed from service for reinspection and rework in accordance with these SBs. Those CF6-80A and -80C2 HPT stage 1 disks and applicable -80E1 HPT stage 1 disks that have not been reworked in accordance with SBs 72-0788 or 72-1089 but have been inspected in accordance with SB 72-0779 or ASB 72-A1026 and have fewer than 3,000 cycles since the inspection can remain in service until reaching the 3,000 cycles-since-inspection threshold, at which time they should also be removed from service for reinspection and rework.

(A-06-62) Revise the engine-related airworthiness directive process to ensure that the compliance timelines are appropriately established.

(A-06-63) Require a design review of CF6-80 series high pressure turbine (HPT) stage 1 disks that incorporate chamfered blade slot bottom aft corners that includes a stress analysis and finite element model emphasizing the blade slot bottom aft corner to determine whether sufficient material property margin exists to ensure that cracks do not occur. If the design review of chamfered HPT stage 1 disks finds that this design does not provide sufficient material property margin, then a redesign or material change should be implemented.

On another topic, when the NTSB went to review the flight data recorder (FDR) and cockpit voice recorder (CVR) it noted that although playback of the FDR provided data of the engine failure event as well as the engine performance problem reported by the flight crew of the previous flight, there was nothing on the CVR concerning the maintenance run. This was due to the common practice of maintenance personnel pulling the CVR circuit breaker prior to a maintenance run.

The NTSB has advocated disabling CVRs as soon as possible after landing after a reportable incident or accident has occurred to preserve data that could be used to assist with the event investigation. Due to the recent incident the NTSB is recommending the following:

(A-06-64) Require that maintenance personnel ensure that an aircraft's cockpit voice recorder (CVR) is operating before conducting any engine ground tests. If an airplane has been involved in a reportable event, the incident CVR should be removed to preserve the event data and any subsequent ground test should be delayed until a suitable replacement CVR can be installed in the aircraft.

This article is based on the NTSB Aug. 28 report. These are NTSB recommendations and not regulatory. To read the full report, visit www.ntsb.gov. Additional images of the June engine failure can be viewed on www.amtonline.com.

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