TBO Trade-Offs or

Tips From Fred

Airline deregulation has caused changes. Many aircraft powered by Lycoming reciprocating engines are being used in the commuter market. These aircraft operate under Part 135 of the Federal Air Regulations and generally have a regular schedule which must be maintained day after day. The engines of these aircraft, like those operated for individual or corporate transportation, are expected to reach the manufacturer’s recommended TBO when operated and maintained as specified in the Pilot’s Operating Handbook (POH) and appropriate maintenance publications.

Many commercial operators have requested assistance and advice on the subject of operating and maintaining their engines in a manner that will assist in meeting regular schedules and achieving recommended engine TBO. In response to these requests, a series of operating tips has been developed to emphasize that a slightly more conservative and cautious mode of operation will help to increase expected engine life. These tips are directed specifically at TI0-540-J series engines, but they may be applied to other Lycoming engines as well.

Individual or corporate operators may also find these tips beneficial for insuring long, reliable engine operational life. Considering this, it seems appropriate to print these suggested operating tips for the benefit of all Lycoming TIO-540-J series engine owners and operators. These tips are applicable where maximum engine service life rather than maximum aircraft performance is the primary consideration.

"Tips From Fred" were outlined in a memo which is reprinted below:

1. Introduction:

This memo was originally directed at Part 135 Commuter usage, but any operator of Lycoming turbocharged engines where long engine service life is a major consideration may benefit. Power settings and procedures within the normal range, but more conservative than the maximum allowable limits specified in the Pilot’s Operating Handbook (POH) may be helpful in achieving this extended engine life. The following suggestions deal with the engine areas that lead to the necessity of overhaul by attempting to minimize wear rates and potential cylinder problems, and to maximize turbo system and wastegate life through changes in operational procedures. Economic or performance considerations may require deviation from ideal recommendations with the possible attending loss of some of the maximum possible engine service life.

2. Ground operation:

(a) In extremely cold weather (20o F and colder) engine and/or oil preheating should be utilized to minimize accelerated cold wear rates during the engine warm-up period.

(b) Avoid rapid acceleration after any cold start-up and make every effort to maintain a constant speed of about 1000 RPM during the initial warm-up period for several minutes.

© Adhere to the lubricating oil recommendations for the average ambient air temperature, as listed in the latest revision of Lycoming Service Instruction No. 1014. Note that SAE 15W-50 or 20W-50 all temperature oil (MIL-L-22851 Spec) is approved for use in TI0-540 series engines.

(d) Oil temperature indications should register on the aircraft gage before takeoff is attempted so that problems associated with unusually high oil pressure will be minimized.

(e) All power settings must always be accomplished slowly and smoothly to minimize possible damage to the crankshaft dynamic counterweight system.

(f) Taxi at the minimum power setting required to get the job done.

3. Takeoff:

(a) Part throttle takeoffs should be avoided. The fuel injector metering jet is a two hole unit, which is interconnected with the throttle. The secondary jet is fully opened only at full throttle conditions. The richer fuel flow supplements engine cooling and deters engine damaging detonation. The turbocharger control system automatically seeks to maintain approximately a constant density air charge at the fuel injector entrance. The density controller setting should be checked routinely with a temperature probe in accordance with Lycoming Curve Number 13225-C, as described in detail in the latest revision of Lycoming Service Instruction No. 1187. It is normal for the takeoff manifold pressure level to vary significantly as daily ambient ground level temperature changes. Never attempt to set rated manifold pressure based upon ambient temperature comparison and interpolation with the various rated power levels shown on Lycoming Curve Number 3216-C. That curve is intended only as an explanatory curve and should not be used for setting manifold pressure at rated conditions below critical altitude. Items such as a dirty air filter, alternate air door not completely shut, loose rag or similar foreign object blocking the air filter will affect the rated manifold pressure level. The correct density setting can only be obtained by monitoring compressor discharge temperature and manifold pressure simultaneously.

(b) The RPM should be at 2575 RPM for takeoff and a full rich mixture must be utilized.

4. Climb:

Climb should be accomplished with engine cooling in mind. Cowl flaps should always be open for climb. A higher than normal climb speed of 140 MPH is recommended to aid cooling. Maximum normal operating power of 2400 RPM, 40" Hg manifold pressure with partial leaning, in accordance with the POH, is permissible where terrain or conditions permit. A conservative climb power setting of 2400 RPM, 35" Hg manifold pressure is also recommended while maintaining cylinder head temperature as cool as 400oF by manual leaning. For maximum engine service life, an exhaust gas temperature of 1400oF should not be exceeded.

5. Cruise:

Conservative cruise power settings will also increase engine service life. A power setting of 2200 RPM and 31" Hg manifold pressure is recommended for all cruise flight. A maximum 1450oF exhaust gas temperature and maximum cylinder head temperature of 420oF is recommended. Slight enrichment or cowl flap opening should be utilized if the cylinder head temperature level cannot be maintained. The preceding conditions correspond to a power setting of about 63 percent at standard conditions and approximately best power mixture strength. It may be necessary to increase the cruise manifold pressure setting on a hot day and to decrease the cruise manifold pressure on a cold day. As a rule of thumb, modify manifold pressure by 1% for each 10oF variation from standard altitude conditions. Note that this cruise power setting is not recommended for new engines or engines in service following cylinder replacement or top overhaul of one or more cylinders. Under those circumstances, to assure the proper ring seating, cruise should be at 65 percent to 75 percent power for the first 50 hours of operation, or until oil consumption has stabilized.

6. Descent:

Rapid cool down during initial descent can damage the engine. Gradual cool down is preferable. The descent power reduction should be accomplished in several steps. Ideally, the descent should begin by nosing the aircraft over slightly while engine power and mixture remain at the cruise setting. The added speed will initiate a gradual cool down. When the CHT has stabilized reduce the manifold pressure to 25" Hg and relean the mixture to maintain 1350o F exhaust gas temperature, which will prevent rapid cool down. After a period of at least one minute, a further reduction of manifold pressure to 20" Hg and 2000 RPM can be made, if necessary. Again, mixture should be leaned to maintain 1350o F exhaust gas temperature. Cowl flaps should not be used as an aid in slowing the aircraft during descent. Descent power settings at greater than 20" Hg manifold pressure should be utilized for the greatest possible time to avoid accelerated piston ring wear.

7. Landing:

(a) Following landing, the minimum necessary taxi power will aid in engine cool down. Extending the ground idle cooling period reduces turbocharger temperature and reduces the tendency of turbo-coking following hot engine shutdowm. Ideally, a five-minute minimum cooling period is desirable. Following landing, opting for the second turn off can aid the cool down.

(b) Higher than required power settings for ground operation increase the possibility of dirt ingestion into the engine.