B737-700
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 75; Flight Crew Type 11000
Other / Unknown; Communication Breakdown
Aircraft Equipment Problem Critical
Air Traffic Control Provided Assistance; Flight Crew Diverted; Flight Crew Landed As Precaution; General Maintenance Action; General Declared Emergency
Aircraft
My First Officer and I discussed two previous logbook write-ups for hydraulic servicing before we departed on an originating flight. The aircraft seemed to be losing A hydraulic fluid but no leaks had been detected. We monitored hydraulic level closely on the flight. Small loss was noted. When we landed; I walked around the aircraft and again no leaks were detected. We departed; and during cruise; we noticed A hydraulic level decreasing at a steady rate; approximately 10% per hour. We sent a request for Maintenance and Maintenance serviced hydraulics; reviewed previous write-ups; and called Maintenance Control. We then performed checks of all primary flight controls while mechanics watched for leaks and none were found. We then decided to run the engines and check there and once again none were detected. My First Officer and I were observing the quantity on climbout and it appeared to be holding. During an intermediate level off; we noticed the A hydraulic level decreasing at an increasing rate. Within a few seconds; we received a Master Caution flashing and saw that A Engine Driven Pump Low Pressure light was starting to flicker. Without consulting the QRH; I shut off the pump and I did not inform my First Officer why I was doing it and then reached over and turned off the A autopilot and switched it to his side; (B autopilot). Again I failed to tell him what I was doing and why. He was surprised by my actions and 'firmly' asked me what I was doing and I told him that I was trying to stop the complete loss of A system hydraulics and suspected that we would be losing A autopilot and was trying to avoid another distraction.The situation happened very quickly and I reacted out of instinct. In retrospect I feel that I was wrong for not keeping him informed of my thoughts and actions. That small interruption of procedures seemed to cause a brief breakdown of crew coordination. We resolved the issue quickly and then referred to the QRH. The remaining quantity was approximately 17% and we did not get a low pressure light from the engine driven pump and we were holding A system pressure. We notified Dispatch and established a patch with Maintenance Control. It appeared that I may not have adequately explained the situation to maintenance because they felt we were dealing with an A system failure. We were not. We still had A system pressure and the quantity was holding steady at 17%. After a few more minutes of explaining the situation; they understood what failures we were dealing with and the initial thought from Maintenance and Dispatch was for us to continue. Twice I reconfirmed their desire for us to continue. My First Officer and I did not feel that we had an emergency; but we knew that the aircraft would need significant maintenance and our destination seemed the likely place for us to land. Several minutes later; Dispatch informed us that it was decided that we should divert. We had already informed ATC that we had a problem but did not declare an emergency. All flight controls were operational at that time but my First Officer and I were already discussing the possibility that we may lose pressure when flaps and gear were extended for landing so we spent the extra time reviewing the QRH for A System Failure. We read it aloud to one another several times. A long final was requested in case the gear did not extend normally and we had to revert to manual extension. The gear extended very slowly and we had a momentary loss of pressure but it stabilized. During taxi into the ramp area; the nose wheel steering seemed sluggish so we shut down and were towed into the gate. The crew and passengers were kept informed during the entire event. Maintenance had me come down to the ramp to look at the damage to the pump. They felt that the pump was actually burning hydraulic fluid internally which led to its complete failure.First of all I commend the mechanics for being so diligent in looking for a possible problem. I don't know how often this type of failure occurs; but if it is not uncommon; then it may be prudent to take an aircraft out of service and the pumps checked if there has been a history of hydraulic servicing with no apparent leaks. My First Officer and I were confident that we were taking an airworthy aircraft. We knew there was a leak but never considered that it could lead to a complete failure. I think both of us will reconsider the situation if we are ever faced with it again. During approach I became aware of the fact that my First Officer and I had stopped communicating as effectively as we had been and we were concentrating on two separate issues. I feel that if I had continued to verbalize my thoughts to him then he would have realized that I may not have been concentrating on the same thing that he was. I was concerned with the possibility of having to go around and entering into a low fuel situation and he was concerned with getting configured very early. Once I told him of my concerns with fuel and an early configuration; we started communicating much more effectively. I do feel that I may have over tasked my First Officer a few times while we were working the problem. While I was talking with Dispatch and Maintenance; he was left flying single pilot and was also trying to review the QRH and answer the Flight Attendant's questions. Before making contact with Dispatch; we had arrived at a list of things we needed to do and I should have suggested that he hold off with those things until I could participate with him uninterrupted. What I did realize is that my First Officer's experience/knowledge of the aircraft and his willingness to question my thoughts and actions led to both of us coming up with a lot of other options that we individually had not seen. Apparently ATC had declared an emergency on our behalf. My First Officer and I had discussed the need to declare an emergency and we concluded that it was not necessary. In retrospect I think that by ATC declaring on our behalf it actually helped us as a crew by decreasing our workload. Their interaction helped keep us from fixating and increased our situational awareness throughout the remainder of the flight.
B737-700 Captain experiences a loss of A hydraulic system quantity and pressure in cruise and turns off the A system engine driven pump without consulting the QRH or informing the First Officer. Maintenance directs the crew to divert to a suitable airport where they are able to land normally with the A system pressurized although the nose wheel steering fails during taxi in.