This is a sorta stale subject in the safety community I work in but perhaps it is of interest to someone in this forum.
Why is there oil on the engine cowling?
Thank you for bringing this to our attention. The Flight Crew looks at this and all other parts of the airplane prior to each flight. Here is what makes this condition so common.
Pratt & Whitney’s JT8D engine has an oil tank that if installed in the "normal" (level) position holds 5 U.S. gallons. On the 737-200 aircraft, Boeing has installed an oil quantity transmitter in this tank at a location common to either left or right engine. The 737’s left engine is installed with a 6-degree angle that will allow for additional oil capacity. Also, the left engine’s tank filler and breather vent is on the outboard side, out of sight from inside the cabin. In contrast, the right engine also has a 6-degree angle but it’s tilted in a way that allows for less oil capacity. Oil leaking and/or breather venting is also much more obvious.
The oil system of this model of engine includes air seals, which introduce compressor air into various compartments for sealing purposes. This air system naturally causes breather pressure, which is vented in very close proximity to the oil tank filler described above. There is an air/oil separator (slinger), which removes almost all of the oil from the vapor, but this separator is over taxed whenever the oil level is too high in the tank.
With an equal amount of oil in each tank the right hand engine’s oil level is much closer to the tank’s filler limit. That is to say, the right engine’s oil level is usually kept as close to the top of the filler port as possible. In fact, due to some other design characteristics, the tank’s level does not stay constant when an engine is shut down. Consequently, servicing after long periods of parking can contribute to a higher then normal tank level. This overfilling condition is not usually considered a major concern because after all, the worst thing that can happen is it will blow out the breather vent and run off the cowling and the reverser.
On every flight that passes through Anchorage a mechanic checks the oil quantity gauges and records it in the maintenance logbook. Each engine’s oil tank quantity is also physically checked each night. All oil added at any time is recorded in the aircraft’s maintenance logbook. The Power plant Reliability Group tracks each engine’s oil utilization daily as part of the trend-monitoring program. An investigation is called for any engine that exceeds a limit of .25 quarts consumption per flight hour (leaking and/or burning). P&W’s maximum consumption limit is 2.0 quarts per hour.
Granted, because of the inherent nature of oil showing on the cowling it could give the appearance that we are ignoring a potential problem. However, we have a system in place to keep this well within the allowable limit.
Why is there oil on the engine cowling?
Thank you for bringing this to our attention. The Flight Crew looks at this and all other parts of the airplane prior to each flight. Here is what makes this condition so common.
Pratt & Whitney’s JT8D engine has an oil tank that if installed in the "normal" (level) position holds 5 U.S. gallons. On the 737-200 aircraft, Boeing has installed an oil quantity transmitter in this tank at a location common to either left or right engine. The 737’s left engine is installed with a 6-degree angle that will allow for additional oil capacity. Also, the left engine’s tank filler and breather vent is on the outboard side, out of sight from inside the cabin. In contrast, the right engine also has a 6-degree angle but it’s tilted in a way that allows for less oil capacity. Oil leaking and/or breather venting is also much more obvious.
The oil system of this model of engine includes air seals, which introduce compressor air into various compartments for sealing purposes. This air system naturally causes breather pressure, which is vented in very close proximity to the oil tank filler described above. There is an air/oil separator (slinger), which removes almost all of the oil from the vapor, but this separator is over taxed whenever the oil level is too high in the tank.
With an equal amount of oil in each tank the right hand engine’s oil level is much closer to the tank’s filler limit. That is to say, the right engine’s oil level is usually kept as close to the top of the filler port as possible. In fact, due to some other design characteristics, the tank’s level does not stay constant when an engine is shut down. Consequently, servicing after long periods of parking can contribute to a higher then normal tank level. This overfilling condition is not usually considered a major concern because after all, the worst thing that can happen is it will blow out the breather vent and run off the cowling and the reverser.
On every flight that passes through Anchorage a mechanic checks the oil quantity gauges and records it in the maintenance logbook. Each engine’s oil tank quantity is also physically checked each night. All oil added at any time is recorded in the aircraft’s maintenance logbook. The Power plant Reliability Group tracks each engine’s oil utilization daily as part of the trend-monitoring program. An investigation is called for any engine that exceeds a limit of .25 quarts consumption per flight hour (leaking and/or burning). P&W’s maximum consumption limit is 2.0 quarts per hour.
Granted, because of the inherent nature of oil showing on the cowling it could give the appearance that we are ignoring a potential problem. However, we have a system in place to keep this well within the allowable limit.
