History of Flight
On March 12, 2012, about 2055 central daylight time, the pilot of a Beechcraft 1900D airplane, registration N178YV, discovered a hydraulic leak on the nose landing gear (NLG) during a post-flight inspection. The airplane was registered to Raytheon Aircraft Credit Corporation and operated by Great Lakes Airlines as a 14 Code of Federal Regulations Part 121 scheduled passenger flight. The flight had just completed a trip from Denver, Colorado, to Hays, Kansas.
Damage to Airplane
The pilot’s inspection revealed a crack in the NLG actuator end cap, part number 25703-4, serial number 512. The end cap was removed from the actuator and shipped to the NTSB for examination.
Actuator Information
The NLG actuator had accumulated 29,308.7 hours and 39,838 cycles since new. It had been overhauled in 2009 and had accumulated 3,509.9 hours and 4,083 cycles since overhaul. Great Lakes Airlines had performed an ultrasonic inspection in accordance with the Model 1900D Airliner Maintenance Manual three cycles prior to the incident.
Examination of the End Cap
The end cap was examined at the NTSB Materials Laboratory. A visible crack extended circumferentially from the primary extend port on one side, around the diameter, to the secondary extend port on the other side. The fracture faces revealed a relatively flat, smooth zone and ratchet marks originating at the intersection of a radius with an inner diameter, consistent with fatigue. The fatigue zone extended nearly uniformly through the wall thickness, with a preference toward the shuttle valve bore, and had propagated entirely through the thickness near the aft side. The remaining fracture surface displayed a rough, grainy texture consistent with overload.
Metallurgical examination showed a longitudinal grain structure oriented parallel to the shuttle valve bore. The surface finish and machined radius met drawing requirements. Scanning electron microscopy counted approximately 22,563 fatigue striations along the crack propagation path, though this is a minimum value due to unknown full crack length.
Previous Similar Findings
Fatigue cracking on NLG end caps had been found on three other Beechcraft 1900D airplanes operated by Great Lakes Airlines, documented in NTSB investigations CEN11IA341, ENG12IA013, and ENG12IA014.
Maintenance Actions
Following earlier incidents, Hawker Beechcraft revised the Model 1900D Airliner Maintenance Manual on August 1, 2010, adding a recommended overhaul of the NLG assembly every 10,000 cycles or 5 years. On May 1, 2011, instructions for ultrasonic inspection of the NLG actuator end cap were added, along with a recommended repetitive inspection every 1,200 cycles after 8,000 cycles since new or overhaul. On November 1, 2011, a Temporary Revision adjusted the inspection interval to every 600 cycles if overhaul or replacement could not be completed by that date.
The end cap drawing 25703, revision N (approved February 2010), added a specified longitudinal grain direction. This change was initiated by the raw material supplier through the purchasing department and was not related to the fatigue failures, according to APPH, Inc. APPH also stated that since at least 2004, their standard practice was to stamp the actuator serial number in the recessed area between ports on the end cap.
The NTSB issued recommendations A-13-04, 05, and 06 to Hawker Beechcraft on February 13, 2013, addressing fatigue cracking of NLG end caps on Beechcraft 1900D airplanes.