Oxygen Mask Fittings and CRU Blocks
Like anything else in military aviation, there are many different items doing a similar job, but each one is specialized for specific applications. Below we will discuss 3 types of "oxygen mask connectors" and 2 types of "oxygen blocks" as used primarily by the Air Force.
When a crewmember ejects, they need to be supplied oxygen in case egress from the aircraft occurs at over 10,000 feet AGL. The modern ejection seats have emergency o2 stored oxygen bottles "Bail-Out Bottle" built into the seat. The crewmember receives the oxygen supply during regular flight from the aircraft o2 system (the Air Force has the regulator built into the aircraft system, the Navy uses crew-mounted regulators [CRU-79/P, CRU-88/P] see the MBU-12/P vs. MBU-14/P article. The Air Force uses oxygen blocks which have "ports" for various fittings.
The CRU-60/P, seen here attached to the PCU-15ejection torso harness (F-4 Phantom, F-15 Eagle). The CRU block (60/P or 94/P) attaches securely to the PCU harness via the metal CRU Bracket, seen at right. The MBU-12/P or 5/P oxygen mask attaches to the CRU-60/P by the 3 Pin Quick Disconnect fitting. The hose from the emergency bottle in the ejection seat attaches to the Bail Out Bottle elbow. The aircraft oxygen hose hooks into the friction fitting at the bottom of the CRU-60/P. This "friction" fitting requires 5 pounds of pull to disconnect- Upon ejection, the aircraft oxygen hose separates from the CRU-60 and the crewmember breathes from the bailout bottle.
The Combat Edge CRU-94/P oxygen block is seen here attached via the CRU Bracket to the PCU-15A/P ejection torso harness (used on the F-16 Fighting Falcon). The MBU-20/P Combat Edge (CE) oxygen mask attaches to the CRU-94/P by the 3 Pin Quick Disconnect fitting, like the masks do above to the CRU-60/P. The only difference between the CRU-60 and the CRU-94 is the addition of one extra port for the CSU-17/P Counter Pressure Vest. It plugs into the 94/P with a 4 Pin Quick Disconnect fitting. The other bail-out bottle & aircraft friction fitting works the same as on the CRU-60/P.