The results of the T-45 main landing gear uplock investigation and the effect that organization stucture had on them

by Stack, Christina Marie

The T-45, a military jet trainer aircraft for the Navy, recently experienced two cases of an uncommanded main landing gear extension during high airspeed and high g conditions. These events resulted in an investigation to understand the cause. The initial response to the mishaps was to limit the fleet to lower airspeeds since both mishaps occurred at high speeds. This limitation was not extensively restrictive for fleet operations; however, it was limiting for acceptance flights and functional check flights of aircraft. During the investigations, two different mechanical problems were discovered in the main landing gear uplock mechanism. This mechanism is designed to physically hold the landing gear in the “up” position. The proposed fixes for the identified problems resulted in a new smaller diameter spring pin to remove mechanical interference between the wing structure and the spring pin. The second change was a new material bushing that was designed to remove the friction in the system and allow the latch that holds the uplock in place to move freely. During the investigation, it became evident that there was a lack of knowledge about the landing gear environment among the T-45 community. As a result of this lack of knowledge, the flight test group was asked to conduct a flight test and gather the data needed to ensure that the proposed fixes would completely solve the causal factors of the mishap. The flight clearance for the proposed flight test required the incorporation of Naval Aviation Depot (NADEP) engineer’s proposed corrections into the system. This mandate was met with confusion from the flight test community, due to the desire to investigate the initial configuration to determine the cause of the original mishap. The flight test ii was performed with the corrections and no problems were identified, leaving a question as to the original casual factors. This course of events exemplifies a lack of communication between the flight clearance authority and the flight test community. An attempt was made to reverse some of the initial changes and return the uplock to the original state. It was finally determined that structural interference did create motion in the system, which could possibly result in the landing gear extension that had occurred. The flight test did not result in a full understanding of the original system; however, the test indicated that the new proposed system had no motion that would indicate that a future problem would exist. The new procedures and hardware were released to the fleet allowing the fleet to return to a full flight envelope. This thesis investigates the problem of the uplock mechanism and the flight test that was designed and executed to assist in correcting these problems. It also investigates how organizational structure influenced this engineering investigation and affected the outcome of this test. The flight test community, flight clearance community, maintenance engineering and program offices need to balance the risk inherent to flight test, and the level of understanding of the system under test against the potential knowledge gained by flight testing to determine a path of execution. There are times that flight test results may not enable engineers to understand the causal factors to a problem or define a correction to the problem. In this case, it is the author’s opinion that there may have been information iii lost due to the process used to perform the test. However, the proposed fixes did solve the majority of the fleet’s problems. iv