Data processing: measuring – calibrating – or testing – Measurement system – Performance or efficiency evaluation
Reexamination Certificate
1999-12-20
2002-06-18
Shah, Kamini (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system
Performance or efficiency evaluation
C701S029000, C701S030000
Reexamination Certificate
active
06408258
ABSTRACT:
TECHNICAL FIELD
The present invention relates to engine component trend monitoring and, in particular, to aircraft and helicopter engine component trend monitoring for maintenance management. The invention further relates to a an engine maintenance monitoring display.
BACKGROUND OF THE INVENTION
It is well known that aircraft turbine engines have to be regularly overhauled and inspected to prevent problems during engine operation. One particular type of inspection, known as Hot Section Inspection (HSI), is typically performed on a turbine engine after a predetermined period of time to assess the wear and tear on specific engine components. Hot section inspections are expensive in terms of the cost of manpower involved, since these inspections typically require that the engine be partially disassembled to view the particular parts under inspection. They are also expensive because they require the particular aircraft involved to be taken out of service. Another type of maintenance that may be required at any time during aircraft service is the replacement of critical components that have a declared life limit. Life limits are typically specified in terms of a maximum number of cycles or hours. Another type of engine maintenance which must be performed on turbine aircraft engines is what is known as Overhauls. Overhauls involve the aircraft and engine being taken out of service so as to permit the inspection, the repair or the replacement of all engine components. This type of maintenance is particularly expensive and can cost as much as 70% of the original cost of the engine, depending on the engine type and exactly what components need to be overhauled. For helicopter engines, most manufacturer maintenance concept requires that the basic time between overhaul (TBO) be performed at about the three-thousand hour service mark. With relevant supporting data and the help of the engine manufacturer, fleet operators can obtain extension from the published basic TBO or adhere to a “on-condition” engine overhaul program.
The problem that arises with most aircraft turbine engines is that the engines are exposed to different levels of wear during their operational service. For example, the helicopter engine may be exposed to higher levels of wear if there are a large number of take-offs and landings during a given mission. During each take-off, the engine must be spooled up to its lift-off rotational velocity and when the helicopter lands, the engine must be spooled back down to a low speed so that the helicopter can loiter on the ground, or the engine is spooled down to shut off. Each one of these take-offs and landings represents a single cycling of the engine, and for an in-service helicopter, there may be several take-offs and landings during a given mission. The greater the number of cycles per mission, the greater the wear on the engine components.
Another element which further adds wear to the engine components is the manner in which the engines are throttled-up and down during each one of these cycles. Pilots often have different styles of flying, due to different weather conditions or personal experience and may sometimes use the throttle controllers in a manner which places higher levels of stress on the engine components than what may be ordinarily expected. For example, a helicopter pilot who is flying on a tight mission schedule, may spool up the engine faster so as to get off the ground sooner. That same pilot may also spool down the engine faster so as to land more quickly, loiter on the ground at a high engine rotational velocity and then quickly spool the engine back up to become airborne again more quickly. Operational usage of the engine under these circumstances places even higher stresses on the engine components than would normally be expected. This reduces the amount of in-service time before the engine components require either a hot section inspection, a critical part replacement, or a complete overhaul.
Since different aircraft fleets are exposed to different levels of operational stress, the actual wear on engines from one fleet to another may vary considerably. Likewise, different aircraft within a fleet may be subjected to different levels of operational stress, and the actual wear on engines from one aircraft to another may vary considerably.
Aircraft engine maintenance is a significant cost in operating any aircraft-based service. Poor financial planning for the costs of inspections, part replacements, engine overhauls, etc., cannot be tolerated. Various maintenance plans have therefore evolved in the aircraft maintenance industry to provide aircraft-based service operators with a schedule of fixed costs for engine maintenance over a period of a number of years. Since engine maintenance plans, e.g. a guaranteed financial protection plan (GFPP), are standardized, some aircraft fleets with lesser degrees of actual wear may require maintenance too soon, while other fleets with greater degrees of wear may require maintenance sooner than anticipated.
The standardization of aircraft engine maintenance is based on a rough, although sometimes sophisticated, estimate of expected engine component and aircraft usage in a fleet for the period of time of the maintenance plan. In the case of an established operation, the plan can thus be based on a prediction of engine component wear and usage by analyzing the history of engine usage and/or aircraft usage as well as the particular maintenance requirements of the engines. Flight log books can be analyzed to determine factors such as altitudes reached, fuel consumption, the number of engine cycles (i.e. take-offs and landings, as well as engine spooling downs), and hours in flight. In the case of a new operation or a new engine, the standardization of the maintenance plan can even be more difficult and thus it may have a larger margin of error. As a result, it becomes a difficult task for an engine maintenance service provider to determine whether a rate for maintenance plan is being fairly applied to each of its customers. It also becomes a difficult task for maintenance managers of aircraft fleets to determine if the engines in the fleet are being flown in proper compliance with a maintenance plan. Furthermore, it becomes a difficult task for aircraft maintenance managers to accurately predict and optimize the dates for shop visits or predict the costs inherent with shop visits.
The net result of following such a maintenance plan according to the prior art is that aircraft-based service operators who use and operate their aircraft with care and under favorable conditions actually pay more than they should. Thus there is no incentive in the maintenance plan to manage the operation of an aircraft or fleet to reduce or control engine component usage.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a method for monitoring engine usage, and determine time remaining until hot section inspections, critical component replacements, and engine overhauls. According a first broad aspect of the invention, this object is provided by a display which allows for a comparative indication of engine component usage relative to maximum recommended usage.
It is another object of the invention to provide a method for monitoring engine usage to predict shop visit dates and maintenance plan costs.
It is another object of the present invention to provide a method for monitoring engine usage to determine a suggestion as to better use of an aircraft or particular aircraft within a fleet of aircraft to control engine wear on aircraft having higher levels of wear.
It is a further object of the present invention to provide a method for monitoring engine usage to determine compliance with an engine maintenance plan, and to produce reports pertaining to engine maintenance plan compliance.
According to a first aspect of the invention, there is provided a method of monitoring operation of at least one engine comprising establishing a time schedule of planned maintenance activities for the engine based on an expect
Bachman & LaPointe P.C.
Pratt & Whitney Canada Corp.
Shah Kamini
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