The Flight
On August 31, 2012, at approximately 1630 eastern daylight time, a Cessna 402C registered as N769EA, operated by Hyannis Air Service, Inc. doing business as Cape Air as Flight 775, sustained a nose landing gear collapse during the landing roll at Nantucket Memorial Airport (ACK), Nantucket, Massachusetts. The aircraft was operating under 14 Code of Federal Regulations Part 135 as a scheduled domestic passenger flight from Barnstable Municipal Airport-Boardman/Polando Field (HYA), Hyannis, Massachusetts, to ACK. Visual meteorological conditions prevailed, and a visual flight rules flight plan had been filed. The airplane departed HYA about 1608. The airline transport pilot reported normal landing gear extension and indications (three green lights, no red light, no gear warning horn) during the approach. After touching down on the main landing gear, the nose wheel lowered until contact with the runway. The pilot notified air traffic control and evacuated the nine passengers. The aircraft sustained minor damage, and there were no injuries.
Post-Incident Inspection
Examination of the nose landing gear revealed a fracture in the nose landing gear drag brace part number (P/N) 5142002-5 near the actuator attachment lug. The NTSB Materials Laboratory analyzed the drag brace. The fracture occurred aft of the actuator attachment clevis. The rod end fitting for the actuator was also fractured, with features consistent with ductile overstress. A portion of the drag brace fracture surface showed a fatigue crack covering approximately 40 percent of the cross section. Fatigue origins were near the upper inboard corner, an area reworked during a repair in July 2012; however, no tightly curving crack arrest marks consistent with an origin were seen adjacent to the surface. The blend radius at the aft side of the lug measured 0.12 inch, and no paint was evident on the fracture surface.
Repair History
The nose landing gear drag brace had been repaired on June 19, 2011, by an FAA Certificated Repair Station. According to FAA Form 8130-3, the part was cleaned, repaired, inspected, and approved for return to service. The repair included replacement of four bearings and repair of a crack in accordance with Cessna Service Bulletin MEB91-11 Revision 1. The part was then assigned serial number T35119. After installation on another aircraft (N68391) on June 29, 2011, it accumulated 473.4 hours before removal on November 11, 2011. It was installed on N26514 on December 22, 2011, and removed on July 24, 2012, after about 530 hours, totaling 1,003 hours since the June 2011 repair. The drag brace was sent again to the same repair station, where a 1/8-inch shallow crack near the actuator attach lugs was blended per Service Bulletin MEB91-11 Revision 1. A fluorescent dye penetrant inspection revealed no further crack, and the part was returned to service on July 26, 2012.
On August 3, 2012, during a Phase 5 inspection at an airframe total time of 27,968.1 hours, the drag brace was installed on the incident airplane. Subsequently, during Phase 6 (August 15, 2012) and Phase 1 (August 27, 2012) inspections, the part was visually inspected in-situ. At the time of the incident, the airframe total time was 28,098.6 hours. The drag brace had accumulated about 131 hours and 286 cycles since installation. The operator reported that the drag brace total time since June 2011 was approximately 1,134 hours. The operator was complying with Cessna Multi-Engine Service Bulletin MEB91-11R1, which required removal and inspection of the drag brace every 400 hours.
Maintenance Records
Cessna Service Bulletin MEB91-11, Revision 1, dated February 24, 2003, reported cracking of the nose landing gear drag brace near the actuator attach lugs. It required inspection within 250 landings or 12 months, and repetitive inspections every 250 landings for drag braces that had been reworked. On April 1, 2009, Cessna incorporated Supplemental Inspection Number 32-20-00 into the maintenance manual, which specified visual and fluorescent liquid penetrant inspection and prohibited repair of cracked drag braces. This supplemental inspection was revised on September 30, 2011, requiring visual and eddy current inspection and explicitly disallowing repairs. The operator had not incorporated this supplemental inspection and continued to comply with MEB91-11R1.
A review of FAA Service Difficulty Reports from 1995 to March 12, 2014, excluding the incident, revealed 13 reports of cracking or failure of the nose landing gear drag brace P/N 5142002-5, five of which were submitted by the operator. Between 2002 and March 2014, there were three reports (two by the operator) involving cracking or failure of this part, including one May 2010 report of nose landing gear collapse due to drag brace failure. In 2011 and 2012, the operator or the repair station did not submit any Malfunction or Defect Reports for cracking of these drag braces. Records from the repair station that last inspected the failed drag brace showed that from 2002 to 2012, the operator submitted 1,216 drag braces for inspection per MEB91-11R1. Of those, 1,102 were repaired and 114 were cracked beyond the allowable repair limit. In 2010, 24 of 161 inspected were beyond repair; in 2011-2012, 51 of 687 were beyond repair.