Learjet 31
Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Flight Instructor
Flight Crew Last 90 Days 90; Flight Crew Total 2250; Flight Crew Type 790
Situational Awareness
Aircraft Equipment Problem Critical
Flight Crew Diverted; Flight Crew Inflight Shutdown; Flight Crew Landed in Emergency Condition
Aircraft
There were build ups in the area and [we] were getting vectors around weather. Once we started climbing into the teens; we noticed the left engine's oil pressure gauge was indicating slightly low; on the border between the green and yellow; approximately 38 psi. The needle was bobbing a bit. We took note of it and were monitoring it as we weren't sure if the gauge was getting ready to fail or if we had an impending issue developing. All other engine indications were normal; including oil temperature. I asked the First Officer to get out the checklist for low oil pressure for review in case we needed it. In the meantime; knowing the gauge was AC; I checked the inverter for proper indications; and everything was normal; as well as all other AC items. The red low oil pressure annunciator light is separate from the gauge; so we decided to wait and see if that light would come on (confirming an actual low pressure situation versus a failed gauge) before commencing any checklists. We reviewed the checklist; and it said for oil pressure between 25-38 psi; to reduce power if necessary to maintain oil temperature; if the pressure dropped below 25 psi (which the annunciator would come on); to perform an engine shutdown in flight. We advised ATC we had a potential oil pressure problem and that we were monitoring and would advise. At that moment the pressure dropped below 25 psi and the annunciator came on. I brought the power to idle on the left engine; leveled at FL260 and we did the engine shutdown in flight checklist. [We] advised Center and requested closest airports. I told the First Officer that I wanted an airport with a control tower; trucks; and at least a 5;000 foot runway. We decided to divert to [an appropriate alternate] for the single engine landing. We broke out about 2;500 feet and had the runway in sight. We were able to do a visual approach and landed uneventfully. Maintenance found a damaged aneroid in the oil pressure relief valve.
LR31A Captain reported diverting to an alternate airport after a precautionary shutdown of the left engine following a low oil pressure indication.