That critical 35-psi diving line
Do you fly an older Cessna Citation with Pratt & Whitney JT15D engines? Then you should know some of the maintenance nuances surrounding an in-flight loss of oil pressure, as well as operations with low oil pressure. As you might suspect, the implications can be serious.
If you encounter an in-flight drop in oil pressure—as long as it isn’t below 35 psi—consult the appropriate checklist. You will have noticed the drop because it causes the master caution warning light to come on. But if the oil pressure drops to 35 psi or below, the engine should be shut down immediately. This is a memory item.
Your job isn’t finished quite yet. Once you land and report the shutdown to a maintenance facility, expect a check of the affected engine’s oil quantity, and a pivotal question: How long did the engine run with oil pressure below 35 psi prior to shutdown?
If the oil quantity is less than 2.5 quarts and metal particles are found in the oil-filter element, the engine has to go an overhaul shop for inspection and possible overhaul. If there are no metal particles, then the engine should be filled with oil and given a dry motoring run to listen for unusual noises. If any are heard, it’s a trip to the overhaul shop. If not, then it’s time for a 15-minute ground run, followed by another check of the filter. Any metal particles? Then it’s off to the shop.
In my experience, JT15D oil pressure usually stays stable in the green zone. If oil pressure is into the yellow after startup or during taxi, this usually is a good indication that oil quantity is low. Check immediately to determine if quantity is low because of normal oil consumption, or something more sinister.
Luis Savigne IV is an executive with the Florida Flight Center of Bradenton, Florida.
Quick quiz
Know your engine ops?
1. What is the maximum allowable oil consumption on JT15D engines?
A. One quart every four hours measured over a 10-hour period.
B. Two quarts within a 10-hour period.
C. Two quarts within a four-hour period.
2. When should the oil level be checked on JT15D engines?
A. Before start.
B. Within 10 minutes of shutdown.
C. Both A and B.
Answers:
1. A.
2. C.
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