Narrative:

A321 was on a flight to ZZZ. The pilot called the tower to report a loss of yellow hydraulic system indication. The pilot reported they needed to land immediately. Thankfully with the proper procedure of QRH in his manual; the pilot shut the system off as per procedure and landed safely. That day the aircraft was removed from service and brought to the hangar for maintenance. I worked on the aircraft and was afraid to find out what I found. The inner o-ring on the drain valve for the yellow reservoir system had failed and leaked all the hydraulic fluid during flight. Maintenance action was taken and removed and replaced the drain valve as per the amm (aircraft maintenance manual). I also reported this to maintenance control and they responded that the investigation was already on going and an engineering order was going to be issued. It has been three months and no response or change has been made.the event occurred because of airbus engineers testing the A321 did not notice the failed o-ring on the drain valve of the hydraulic systems. The drain valve does not have a cap or a very strong shut-off valve as the 737 does (which is safety wired). The reason for the failed o-ring is because amts drain the hydraulic system when the system is overfilled in the servicing procedure. The constant draining of the reservoirs causes the inner o-ring to fail over time and with the residual head pressure of the hydraulic system causes the o-ring to break at any given time. This is nobody's fault but the aircraft engineers who might have missed the failed testing of hydraulic fluid pressure system. There is a temporary fix for leaking valves under a company repair document; but does not fix the ongoing problem. This can be fixed but has not been brought up or supported enough to fix it. My suggestions to relieve the problem or prevent the airbus hydraulic system from losing all the fluid during flight or taxi is to change all drain valves to a shut off valve (spring-loaded closed) like the 737 hydraulic system; or install a cap and safety cable to the cap to prevent the loss of fluid if the drain valve inner o-ring fails. If the cap is installed; there should be a periodic check on the valve performance and leak detection as per the maintenance card. As an a&P mechanic for over a decade I have heard the term from FAA inspectors that 'the far rules are written in blood.' I believe that this is the time in this day in age that we need to right the far rules without the use of blood as ink. It is a new generation of aircraft and a new set of qualified amts in the field of aviation. It is my job to help the industry be safe and compliant with rules and regulations given in the world of aircraft as the safest transportation of travels. I would like and need help from the proper set of engineers and team members to support me on the awareness of this drain valve issue on the airbus 321.

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Original NASA ASRS Text

Title: Maintenance Technician reported that the inner O-ring for the hydraulic reservoir drain valve on the A321 continues to fail.

Narrative: A321 was on a flight to ZZZ. The pilot called the tower to report a loss of Yellow Hydraulic system indication. The pilot reported they needed to land immediately. Thankfully with the proper procedure of QRH in his manual; the pilot shut the system off as per procedure and landed safely. That day the aircraft was removed from service and brought to the hangar for maintenance. I worked on the aircraft and was afraid to find out what I found. The inner O-ring on the drain valve for the yellow reservoir system had failed and leaked all the hydraulic fluid during flight. Maintenance action was taken and removed and replaced the drain valve as per the AMM (Aircraft Maintenance Manual). I also reported this to Maintenance Control and they responded that the investigation was already on going and an Engineering Order was going to be issued. It has been three months and no response or change has been made.The event occurred because of Airbus engineers testing the A321 did not notice the failed O-ring on the drain valve of the hydraulic systems. The drain valve does not have a cap or a very strong shut-off valve as the 737 does (which is safety wired). The reason for the failed O-ring is because AMTs drain the hydraulic system when the system is overfilled in the servicing procedure. The constant draining of the reservoirs causes the inner O-ring to fail over time and with the residual head pressure of the Hydraulic system causes the O-ring to break at any given time. This is nobody's fault but the aircraft engineers who might have missed the failed testing of hydraulic fluid pressure system. There is a temporary fix for leaking valves under a Company Repair Document; but does not fix the ongoing problem. This can be fixed but has not been brought up or supported enough to fix it. My suggestions to relieve the problem or prevent the Airbus hydraulic system from losing all the fluid during flight or taxi is to change all drain valves to a shut off valve (spring-loaded closed) like the 737 Hydraulic system; or install a cap and safety cable to the cap to prevent the loss of fluid if the drain valve inner O-ring fails. If the cap is installed; there should be a periodic check on the valve performance and leak detection as per the maintenance card. As an A&P Mechanic for over a decade I have heard the term from FAA inspectors that 'the FAR rules are written in blood.' I believe that this is the time in this day in age that we need to right the FAR rules without the use of blood as ink. It is a new generation of aircraft and a new set of qualified AMTs in the field of aviation. It is my job to help the industry be safe and compliant with rules and regulations given in the world of aircraft as the safest transportation of travels. I would like and need help from the proper set of engineers and team members to support me on the awareness of this drain valve issue on the Airbus 321.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.