MD-83
Aircraft Equipment Problem Critical
Flight Crew Inflight Shutdown; Flight Crew Landed in Emergency Condition; Flight Crew Returned To Departure Airport; General Flight Cancelled / Delayed; General Maintenance Action
Aircraft
[Returned] to [departure airport] due to oil quantity dropping to zero. An overweight landing was not performed. We landed at approximately 138;000 pounds.During climb my First Officer (FO) noticed oil quantity on the right engine (number 2) was at 7 quarts. At the gate before start; the quantity was 12 quarts. I was the flying pilot and asked my FO to run the QRH checklist for loss of oil. QRH was run for 'oil quantity decreasing'.  Our right engine oil quantity did not stabilize between 4-6 quarts as QRH indicated it would if the issue was related to the oil tank cap. We decided to pull the right engine throttle to idle. Our oil quantity continued to drop until it reached zero. Then our oil pressure dropped to 35 psi. I asked my FO to run the engine shut down QRH. I [notified] Center and asked for a return. Center cleared us to do a right turn and down to FL210. I was on the number one radio; my FO was running checklists and informing the FAs and passengers of what was happening.We shut down engine 2 according to QRH 'ENGINE FLAMEOUT / FAILURE / SHUTDOWN'. I monitored; my FO performed. I then asked for 'SINGLE ENGINE APPROACH & LANDING' QRH. Our APU started and took the electrical load on the right side; so a 'LANDING SINGLE GENERATOR' QRH was not required. A complication arose due to MEL on our number 1 engine. We had to leave the left air conditioning supply switch in the off position. Without it; and with number 2 engine shutdown; we lost pressurization. Our 'cabin alt' red annunciator lighted up. Cabin altitude reached approximately 13;800 feet. The oxygen masks in the cabin did not deploy.We landed without further incident. Passengers did not brace. We pulled off the runway into a holding area for fire [crew] to inspect our right engine. They indicated there were no hot spot areas for our right engine temperatures.  My FO made an announcement letting the passengers know they were inspecting the plane. We taxied to gate with the fire trucks following. We were not asked to continue the flight and were released from duty.  I asked the maintenance tech if they were going to run an analysis on the removed oil filter. He said they would do that. When talking with Maintenance Control after we were back at the gate; they wanted to know how long the engine had windmilled without oil pressure. [Maintenance] had asked my FO to monitor oil pressure during our return. I have not heard this before. Apparently; this is for them to know whether the engine has to be replaced or not. Of course; my opinion is to replace the engine and figure out what happened to our engine's loss of oil. It seems it was not simply related to the oil cap being left off; cracking; or malfunctioning somehow else.
A MD-83 Captain reported returning to departure airport after inflight shut down of number 2 engine because of low oil quantity.