NTSB Identification: CEN11FA193
14 CFR Part 91: General Aviation
Accident occurred Monday, February 14, 2011 in Appleton, WI
Probable Cause Approval Date: 01/30/2014
Aircraft: Gulfstream Aerospace Corp. GV-SP, registration: N535GA
Injuries: 3 Uninjured.
NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.
While the airplane was inside the final approach fix, an amber left side hydraulic quantity low crew alerting system (CAS) message illuminated. The pilot flying (PF) noticed the hydraulic fluid quantity decreasing. Subsequently, an amber left hydraulic system fail CAS message appeared. The pilot not flying (PNF) pulled out the checklist to accomplish the left hydraulic system failure procedures and then suggested a go-around because the landing runway was about 500 feet shorter than the recommended minimum runway length indicated in the checklist. The PF decided to land due to the hydraulic quantity indications, prior autopilot problems, and the airplane's landing configuration. The PNF turned on the auxiliary pump about 500 feet above ground level, and both the PF and PNF thought the auxiliary hydraulic system could support normal spoilers, brakes, and nosewheel steering. The PF selected right thrust reverser aft and began pressing the brakes, but he felt no braking action. He reached for the emergency brakes; however, he did not immediately apply them to slow the airplane because he decided that there was not enough distance remaining to stop the airplane on the runway. Therefore, he attempted to go around with insufficient runway remaining by advancing the throttles to the maximum continuous thrust setting. The PNF did not see the airspeed increase and believed that not enough runway remained to get airborne, so he pulled the throttles back to avoid a runway overrun. The airplane exited the runway and sustained substantial damage. A review of the cockpit voice recorder transcript indicated that, before the emergency, the flight crew did not maintain a disciplined cockpit environment that focused on operationally relevant discussion but instead repeatedly made reference to and discussed objects on the ground and other operationally irrelevant topics. The lack of a sterile cockpit did not promote crew coordination and communication and adherence to procedures, which would have helped mitigate this emergency.
A postaccident examination of the airplane revealed that the nose landing gear swivel assembly, which had passed an acceptance test procedure before its installation on the airplane, was seized and bound and had a fracture on its inboard connecting tube, which was the site of the hydraulic fluid leak. The swivel assembly had galling wear scars on the outside diameter of the spool and the inside diameter of the housing; both the spool and housing were made from similar aluminum alloys that have a propensity to gall and adhere to each other when rubbed together. The connecting tube fracture was consistent with a single bending and torsional overload event associated with high opening forces or seizure in the center swivel due to galling wear. The center housing/spool seizure was consistent with a misalignment of the swivel, which led to the binding together of the similar aluminum alloys of the spool and housing. Further examination showed that the nose landing gear hydraulic system did not have a volumetric hydraulic fuse designed to minimize the loss of hydraulic fluid in the event of a line break downstream of such a device.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The pilot flying's (PF) decision to land on a shorter-than-recommended runway with a known left hydraulic system failure rather than go around as suggested by the pilot-not-flying, his failure to immediately apply emergency brakes following the detection of the lack of normal brakes, and his attempt to go around late in the landing roll with insufficient runway remaining. Contributing to the accident was the nose landing gear swivel assembly failure, the lack of a hydraulic fuse before this critical failure point, and the design of the swivel using two similar alloys with a propensity to adhere to each other when rubbed together. Also contributing to the accident was the lack of a disciplined cockpit environment. Full narrative available
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