3.2 Aircraft Systems and Flight

 Hydraulic Systems

   

    One of the systems that is crucial to aircraft flight and landing is the Hydraulic system. The hydraulic system controls many of the secondary flight control systems as a primary method of use. The systems usually operate wing flaps, spoiler/speedbrakes, landing gear, and aircraft brakes. They are pressurized by pumps driven by accessory gearboxes off an engine, electrical motors, by hand, or air driven. When a hydraulic system fails, it is usually catastrophic, pouring gallons of hydraulic fluid overboard. I have attached a video of what it looks like from inside a KC-135 when catastrophic failure happens to a pressure relief valve in a system. The second picture is what the valve looked like when I removed it.

    One of the biggest fears of losing a hydraulic system is losing the ability to brake once the aircraft has landed. When losing the ability to brake on aircraft, many factors have to be assessed, runways distance, airspeed on approach, and the ability to use the aircraft's natural drag to slow it to a safe speed. In an article from the Australian Government (2020), their Safety Bureau reported an incident of an Airbus A320 with a loss of the green hydraulic system shortly after takeoff. The control tower told the aircraft to go into a holding pattern when they returned to Melbourne Intl. They then discovered what system had failed and that they would be landing without brakes or nose wheel steering. They relaid the information to ATC and briefed the crew and cabin passengers. They lined up for their approach, landed smoothly, and turned off the runway at a safe speed. Everyone was safe and on the ground. After landing, an investigation was launched to find what had caused the failure. They found a chaffing hydraulic line that had ruptured, thus causing the in-flight emergency. The Safety Board launched a fleet inspection to determine if more aircraft had the same problems and found none. 

Could this in-flight emergency been avoid? Sometimes, there is no telling what could cause a system failure, but there are ways to mitigate potential problems. In this situation, it was a hydraulic line rubbing or chafing against a bolt head that was previously unknown that this spot was a chaffing area. If the airline instituted an inspection for known chaffing areas, future mishaps like this could be avoided. The airline could also do a quick inspection when the aircraft lands in the high chaffing areas. The safety board did the right thing in doing a fleet-wide inspection of the area in question. It is a relief to find that the other jets did not have the same issue. For the areas that are known for chaffing, they could wrap the lines in chaff wrap. This plastic material usually goes around the hydraulic line to ensure it has a buffer between components.

   When it comes to component failure like the picture I attached. The Air Force recalls parts like this to run tests in metal fatigue and track how long a component has been on the aircraft. This gives data for scheduled time changes and possible new construction out of different materials. This helps us keep reliable aircraft in the sky. 

Australian Government. (2020, October 9). Hydraulic system failure involving Airbus A320, near Melbourne Airport, Vic., on 11 April 2018. Australian Transportation Safety Bureau. http://www.atsb.gov.au/publications/occurrence-briefs/2018/aviation/ab-2018-057/

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