CF34 Engines Summer 2006

• In-Flight Shutdowns & Your Oil System
• Your Duncan Contact

In-Flight Shut Downs & Your Oil System

— Bill Walker

In recent months, Duncan Aviation technicians have found a number of in-flight shutdowns due to oil system problems. These problems have all been related to improper installations and servicing, which include improper servicing of the oil system, omitting packings, cutting packings during installation of components and improper functional leak checks. There are steps that mechanics can take to eliminate these leaks.

Ideally servicing the CF34 engine should be done 15–45 minutes after shutdown when using the Oiler System. If this is done before the first start of the day, fluctuating oil pressure and a wet oil covered engine may be seen during the next flight. With the CF34, unlike most other engines, oil from the tank doesn’t normally migrate to the gearbox. You’ll never go wrong by motoring the engine for 30 seconds at 28% N2 and then checking the oil AT THE TANK.

Improper installation is the biggest reason for accessory gearbox Garloc Seal leaks. Packings being left off of the accessory shaft and cutting of the packing during installation, surprisingly, are the main reasons. If maintenance has just been done to any of the Garloc’s and fluctuating and/or low oil pressure are experienced during flight it is almost certain a packing has been left off the shaft, Garloc housing, or mating ring. This may not be seen during a ground run, especially if it’s the axis D, F, or L. When installing a Garloc Seal, lightly rotate the housing radially while you’re pushing forward on the seal housing and feel the lip of the housing as it falls into place. While holding the housing in that position, tighten the nuts to the proper torque. If you slip at any time during this process, start over. Don’t forget to use a feeler gauge to check the seating of the housing. The ears of the housing may not break initially, but they will bend. This is easily overlooked if a feeler gauge is not used. During the flight, this bent ear will break and then a small leak turns into a big one.

Improper functional checks are another common problem. Work done to the scavenge side of the oil system will require a high power engine run. While there will be scavenge flow at idle, scavenge pressure won’t build until the engine is at power. DO NOT hurry this process. Allow the engine oil to fully warm up. Put an observer on the ground during the run to watch for any oil leakage from the cowlings and the operator to monitor the oil pressure followed by an open cowling inspection after shutdown.

Although these topics are covered in the Standard Practices Manual, it is the simplest steps that get overlooked and then come back to hurt us. Complacency and rushing to make a flight are some of the reasons used. It is a good practice to have a second set of eyes look at every packing installed and at the finished job. If something is to be covered up, it is absolutely necessary to have that second set of eyes look in-process. If no one is available to check the work, have a checklist together before you start.

Your Duncan Contact

To discuss this topic or other issues with your CF34 engine, call Bill Walker at Duncan Aviation at 402.540.4152 or Gerry Riffle at 402.525.1187.

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