Narrative:

We were on a VFR/MVFR ferry permit for maintenance in VFR conditions in a P2V neptune; restricted category with pilot and copilot aboard only. On the approach check we noticed the main hydraulic system pressure was at 1000 psi in a normally 1700 psi system. I had the first officer check the reservoir quantity and for fluid leaks. Nothing abnormal found at the time I suspected an internal bypass problem or the loss of an engine driven hydraulic pump. The manual and emergency checklists were consulted for procedures; but none were found. I elected to follow the hydraulic system failure emergency checklist. We opened the jet inlet doors and extended the gear (the flaps were already 20 degrees; so we left them alone). I advised tower of what we suspected and told them I will need to stop on the runway; 'pin' the gear and have the company meet me with a tow bar to move the airplane. I asked the tower for priority and stated 'we are not declaring an emergency'. The tower commented later that he had two IFR inbounds and would ask center to slow up the traffic. I was asked how much runway I would require to stop on (I said 2/3). The tower asked if I could delay my landing for the inbound traffic. I told them that if we have lost an engine driven pump; there was danger of a fire. We also stated that if the system pressure held we would exit the runway and shut-down. The tower gave us immediate landing clearance and dispatched fire equipment. We were grateful of that but still had not declared an emergency. The tower was of great assistance in giving us a 'company' frequency to contact maintenance for a tow. A normal 20 degree flap touch down was made with reversing down to less than 50 KTS. The brakes were applied lightly and held at 60 KTS. We used up most of the runway; turning off on the second to last taxiway at an extremely slow speed. The problem was found to be a faulty system pressure regulator. No apparent threat of fire; but at the time; I believed it to be a threat. Also; in correctness; I now realize a pump failure probably would not cause a steady low pressure state; but would supply 1700 psi fluid at a much lower rate. It is true that a failed pump would cause a fire since there is no way to isolate and the neptune has no fire extinguishers either. But rather than take a primer in hydraulics 101 and in lieu of no available procedures; I feel I made a prudent decision.

Related reports:

Google
 

Original NASA ASRS Text

Title: P2V Captain discovered low main hydraulic pressure during the approach check; took appropriate precautions and informed ATC.

Narrative: We were on a VFR/MVFR ferry permit for maintenance in VFR conditions in a P2V Neptune; restricted category with pilot and copilot aboard only. On the approach check we noticed the main hydraulic system pressure was at 1000 PSI in a normally 1700 PSI system. I had the First Officer check the reservoir quantity and for fluid leaks. Nothing abnormal found at the time I suspected an internal bypass problem or the loss of an engine driven hydraulic pump. The manual and emergency checklists were consulted for procedures; but none were found. I elected to follow the hydraulic system failure emergency checklist. We opened the jet inlet doors and extended the gear (the flaps were already 20 degrees; so we left them alone). I advised Tower of what we suspected and told them I will need to stop on the Runway; 'pin' the gear and have the company meet me with a tow bar to move the airplane. I asked the Tower for priority and stated 'we are not declaring an emergency'. The Tower commented later that he had two IFR inbounds and would ask center to slow up the traffic. I was asked how much runway I would require to stop on (I said 2/3). The Tower asked if I could delay my landing for the inbound traffic. I told them that if we have lost an engine driven pump; there was danger of a fire. We also stated that if the system pressure held we would exit the runway and shut-down. The Tower gave us immediate landing clearance and dispatched fire equipment. We were grateful of that but still had not declared an emergency. The Tower was of great assistance in giving us a 'company' frequency to contact maintenance for a tow. A normal 20 degree flap touch down was made with reversing down to less than 50 KTS. The brakes were applied lightly and held at 60 KTS. We used up most of the runway; turning off on the second to last taxiway at an extremely slow speed. The problem was found to be a faulty system pressure regulator. No apparent threat of fire; but at the time; I believed it to be a threat. Also; in correctness; I now realize a pump failure probably would not cause a steady low pressure state; but would supply 1700 PSI fluid at a much lower rate. It is true that a failed pump would cause a fire since there is no way to isolate and the Neptune has no fire extinguishers either. But rather than take a primer in hydraulics 101 and in lieu of no available procedures; I feel I made a prudent decision.

Data retrieved from NASA's ASRS site as of April 2012 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.