CA2452212A1 - One-engine-inoperative training method and system - Google Patents

Abstract

A method and system of simulating one-engine-inoperative (OEI) conditions in a multi-engine single-output aircraft which involves the operation of the engines above non-zero power settings, and operating each relative to one another to simulate power loss experienced during an actual failure of pit least one engine.

Description

ONE-ENGINE-INOPERATIVE TRAINING METHOD AND
SYSTEM
FIELD OF THE INVENTION
[0001)The present invention relates to a method and system for training pilots in the operation of a helicopter under emergency operating conditions, and more specifically to a method for conducting one-engine-inoperative (OEI) flight procedures training in a twin-engine helicopter.
BACKGROUND OF THE INVENTION

[0002] Many of the helicopters being operated today embody a twin-engine power plant system which not only enhances the normal flight capabilities of a helicopter but also provides sufficient power to facilitate continued flight opez-ations in safety under emergency conditions, such as in the event of a one-engine-inoperative (OEI) condition, e.g.
a single engine failure.

[0003]The power plant in a modern helicopter is typically a gas turbine engine which usually operates within a normal rated power output range. Such engines are capable of producing power at a level significantly above the normal rated power range, however operation in this elevated power output greatly reduces the life expectancy of certain critical components such as the turbine blade, etc.
Operation of a twin-engine helicopter in a OEI event necessitates relaxing of normal engine control criteria and allows the helicopter operator to demand and receive power from the remaining operating engine at levels in excess of the normal operating range. The shift in control logic is justified in such emergency situations for obvious safety reasons.

[0004]The training of helicopter pilots for engine failure operation has long caused problems for instructors and helicopter operators. The objective of initial pilot certification and pilot referential training is to ensure that. pilots achieve and maintain a high degree of proficiency in all aspects of helicopter flight operations, including emergency procedures such as OEI flight operations. Such proficiency is typically achieved by repetitive training conducted under actual flight conditions, e.g. actual flight envelopes, actual gross weights (based on pressure altitude and ambient temperature), actual power settings, and actual cockpit instrument displays, Realistic training in OEI flight operations conventionally requires the pilot to temporarily disable the fuel control on one engine, reducing it to an idle condition effectively with a zero power output, and then operate the other engine within its elevated emergency rated power range. As noted above, such emergency power operation shortens the life expectancy of the engine, thereby increasing the frequency of extensive maintenance.

[0005] Helicopter gas turbine engines are rated by manufacturers and regulatory agencies for each permitted mode: of operation. The rating of an engine establishes allowable time limits for operation at various power levels. Such levels may range from continuous at a normal or part-throttle ~.evels, to the higher emergency power levels under certain time limits, such as 30 secondl2 minute and/or 2.5 minute ratings. One factor in determining a one-time emergency limited rating for an engine, is the frequency with which i~he engine is expected t.o deliver such elevated levels of power. The realistic flight training method discussed above requires repeated use of emergency power during training exercises, resulting in a lower power level than would be allowable for a one-time actual emergency use.

[0006)An alternative commonly used within the industry is to reduce the weight of the helicopter to a minimum, and to operate the one engine at a flight idle power level with the other engine being controlled within its normal operating range. The cockpit displays are however, biased to indicate simulated maximum emergency power ratings, based on the weight biasing factor, in order to simulate the dynamics of an aircraft in a fully loaded condition.
One example of this type of training method is disclosed in United States patent 5,873,546, issued to Evans et al.. on February 23, 1999.

[0007]One disadvantage of the prior art training methods results from operation of the helicopter with one engine in an idle condition. Should for any reason the power producing engine experience an unplanned failure, requiring the idling engine to be brought up to a full power state, the helicopter would experience a period of time in which the total available power is extremely low, thereby restricting maneuverability and possibly resulting in operating outside of safety margins.
[000$]Another conventional approach involves conducting OEI
flight procedures training, utilizing both engines operating at an intermediate power output rating. In this approach, each engine is operated at a reduced power rating so that both engines in combination provide a power output at the intermediate power output rating that is equivalent to the power output provided by a single operative engine operating under a maximum emergency power rating. One example of this approach is disclosed in United States patent 4,831,567, issued to Lea on May 16, 19$9 and assigned to the same assignee as this application.
[0009] Nevertheless, further an improved OEI training method is desirable to simulate an actual OEI situation.
S~JMr2ARY OF THE INVENTION
[0010] One object of. the present invention is to provide a method of simulating a one-engine-inoperative (OEI) condition in a twin-engine helicopter for pilot training procedures.
[0011]In accordance with one aspect of the present invention, there is provided a method of simulating a one-eng:ine-inoperative (OEI) condition in a multi-engine single-output helicopter having at least first and second engines, the method comprising the steps of operating the fir:~t arid second engines at a selected operational power level, commencing an OEI simulation by reducing the power levE~l of. the first and second engines to respective non-zero power levels, and then accelerating the first and second engines from their respective non-zero power levels in ;~ manner to simulate a output power transient occurring in an actual OEI situation.

[0012]in accordance with another aspect of the present invf:ntion, there is provided a method of simulating a one-eng:ine-inoperative (OEI) condition in a mufti-engine helicopter, the method comprising the steps of: providing a OEI training program in control system such that the conl~rol system is adapted to control the engines in an engine operation mode and in an OEI training mode; and providing a selector for selection of mode to allow the cont:.rol system to control at least first and second engines at :Least in accordance with the following steps: reducing a powesr level of the each of the first and second engines from respective operational power settings to a non--zero powE~r settings, and then accelerating the first and second engines from their. respective non-zero power settings to simulate a power transient which would occur in an actual OEI situation.
[00'13] In accordance with a further aspect of the present invention, there is a method of simulating a one-engine-inoperative (OEI) condition in a twin-engine helicopter, the method comprising the steps of substantially simultaneously decelerating first and second engines from respective engine operation power settings, terminating the deceleration of the first engine at a first non-zero power setting, terminating the deceleration of the second engine at a second non-zero power setting which is lower than the fir:~t non-zero po~.aer setting, accelerating the first engine, immediately after the first engine reaches the fix~:~t non-zero power setting, until the first engine reaches a predetermined power setting, accelerating the second engine, immediately after the second engine reaches the second non-zero power setting, until the second engine reaches the predetermined power level, wherein the acceleration of at least one of the engines is adjusted in a manner adapted to simulate a power transient caused by a fai_Lure of one engine and an emergency acceleration of the other engine in an actual OEI situation.
[0014]In accordance with a further aspect of the present invention, there is a method of simulating a one-engine-inoperative (OEI) condition in a twin-engine helicopter incuding at least first and second engines, comprising steps of simulating an OEI condition by operating the first and second engines both in non-zero power settings, and biasing a cockpit indicator relating to at least a parameter of the first engine to show a combined indication of she parameter for both engines to thereby simulate the appearance of said display as if only the first engine is oilerating.
[0015]In accordance with a further aspect of the present ;~nvemtion, there is a method of simulating a one-engine-ino~>erative (OEI) condition in a mufti-engine helicopter, comprising a step of displaying an engine expiry flag in a cockpit indicator to simulate an expiry of time allowance for a maximum 0EI power when the twin--engine helicopter is operated in an OEI training mode.
[0016]The present invention advantageously provides a simulation of the power loss encountered during an actual engine operation transition from a normal engine operation situation in which all engines are operating (AEO), to a OEI situation. During an actual OEI occurrence, the power provided by the affected engine is assumed to be lost ws.t.l~~.in one second. In this rare event, the total power is instantly reduced, even though the remaining running engine has almost instantaneously started to accelerate and provide additional power to a maximum OEI setting in order to compensate for the power provided by the lost engine.
In the OEI training mode of the present invention, this transient total power lost is simulated by decelerating both engines because the maximum deceleration rate of one eng.i_ne is insufficient to simulate the transient power loss in t:he actual situation. The end result is that the pilots in training experience the same rotor droop characteristics as those experienced in an actual OEI situation.
[0017]The training method and system of the present nvention also permits the training of pilots with the maximum allowable helicopter weight, because the two engines in the OEI simulation provide the same power as a sine;le engine in an actual OEI situation, without the enga.ne deterioration incurred by an engine operating in a single engine mode at a higher emergency power setting.
mhi.<<~ also provides a more realistic experience to the pilot in training, because the acceleration capability of the engine varies with the power level, and thus by training at a higher power level, the pilots get a real feeling of how quickly the engine power comes on.
[0018]Other features and advantages of the present invention will. be better understood with reference to the preferred embc>diments described hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019]Having thus generally described the nature of the present invention, reference will now be made to the ___.... . . ;

_ g _ accompanying drawings, showing by way of illustration the prei_erred embodiments thereof, in which:
[0020]Fig 1 is a schematic illustration of a twin-engine single-output power plant system of a helicopter incorporating a one-engine-inoperative (OEI) operation mode according to the present invention;
[0021]Fig. 2 is a graphical representation illustrating a transient of a total power output of a twin-engine power plant system of a helicopter during an actual OEI
occurrence; and [0022]Fig. 3 is a graphical representation illustrating a total power output of a twin-engine power plant of a helicopter in the OEI training mode of the present invention, simulating an actual OEI occurrence.
DETAILED DESCRIPTTON OF TFIE PREFERRED EMBODIMENT
[0023]Fig. 1 illustrates a twin-engine single-output power plant system for a helicopter, generally indicated. at numeral 10. The twin-engine power plant system 10 includes f:Lr:;t and second turbo shaft gas turbine engines 12 and 14 which are mechanically linked by gearbox 16, to provide a si.ncrle output at the main shaft 18. Tt is to be understood that. the single combined power output is represented by a shai:t output means, including electrical, hydrau:Lic, mechanical, etc., all driven by the combined output of the mechanically linked engines. Likewise, for a helicopter having multiple engines, the gearbox may supply shaft power to both the main rotor and the tail rotor rather than to a _ g _ sine;le shaft the output of which is then divided among the components .
[0024] Engines 12 and 14 are preferably identical. Each engine preferably has a gearbox 36 to generate engine tort;ue output on an output shaft 38 of the gearbox 36 for transfer to gearbox 16.
[0025] The power output of a gas turbine engine is typically related to the flow of fuel to its combustor section, with t:he actual power being limited by the high temperature endurance of the engine components immediately downstream of the combustor. The fuel flow and hence the turbine inlet temperature, are restricted to a rate which will permit the pilot to receive normal rated "full" power output for an extended period of time during a normal flight operation. Those restrictions for each engine 22, 1.~ are controlled by an appropriate electronic engine controller (EEC) 40 (shown as EEC 40a and 4b, respectively) according to an engine operation program 42 installed therein. EECs 40 communicate 53 with each other in a known manr_er to thereby provide an overall control system far the twir_-engine system. The engine operation parameters are displayed by cockpit indicators 44 and 46 relating to the respective engines 12 and 14. The cockpit indicators 44, 46 display engine torque provided by the output shaft 38 of each. engine; rotational speed of the compressor impeller and the compressor turbine (sometimes referred to as NU or N1}; the rotational speed of the power turbine (sometimes referred to as NPT or N2}; the gas temperature between the compressor turbine and the power turbine (mean gas temperature, or MGT, or interturbine temperature, or ITT);
etc.
[0026]During one-engine-inoperative situations, it is frequently advantageous for the pilots to have the ability to :receive power output in excess of the normal rated fuel output power from the remaining operative engine(s).
Aviation regulatory authorities have therefore established general over design criteria for the power plant system of a t:win-engine he7.icopter in order to ensure that the helicopter can be safely operated utilizing a single operative engine during OEI flight operations. These criteria have resulted in the over design of the engines comprising the helicopter power plant system so that a single operative engine is capable of praviding at least a 30-second/2-minute OEI power rating, a 2.5-minute OEI power rat:_ng and a maximum continuous OEI power rating that ens:zre safe helicopter flight operations during OEI flight opei:ations. Operation of a gas turbine engine in excess of the normal rated power output as staged above does reduce the life expectancy of certain engine components and thus the time between engine overhauls. 'Therefore, a training method is developed according to the present invention to simulate an engine OEI situation while operating the eng:i.nes at normal rated power settings.
[0027] Referring now to Figs . 1 and 2 , during normal operation each of the engines 12, 14 provides 50 percent of the total power required to fly the helicopter at a se.lE:cted power setting, each of the engines 12, 14 being operated below but close to its maximum power level for continuous operation. When one engine, for example engine 14, fails, the power output level represented by solid line B in Fig. 2, almost instantly drops to zero. The communicating 53 EECs 40 detect the failure of the engine 14 and power demand signals are sent, according to the engine operation program 42, to engine 12, causing engine 12 to be substantially simultaneous7.y accelerated at OEI
settings, to eventually provide the same output power level (100 percent? represented by solid line A, or a total output power level less than 100 percent, whereby a safe flight operation of the helicopter can be maintained. The tot<i1 power output level of the twin-engine power plant system 10, represented by broken line C, includes a transient which results from a time lag between the instant power loss of engine 14 and the compensating power increase of engine 12. An actual curve shape of the transient in the total output power level, illustrated by representative broken line C, will depend on the make of helicopter, the engines, etc.
[0028] Referring to Figures 1 and 3 , the twin-engine power plant system 10 further includes an OEI training program 48 ins~_alyed in the EECs 40 and a mode selection switch 50 connected to EECs 40. Actuating the mode selection switch 5~ will enable the EECs 40 to switch the power plant system operation between a normal engine operation. mode including operation procedures during an actual OEI occurrence according to the engine operation program 42, and OEI
training mode according the OEI training program 48, in order to simulate an OEI situation while operating both engines 12, 14 under normal operation conditions. OEI
training program 48 is designed to enable the EECs 40 to control the respective engines 12, 14, in order to provide out~~ut power levels A1, B1 as illustrated, in a manner such tha!_ the sum of the output power levels A1 and Bl, ind=icated by C1, is equivalent to the total output power level C, of an actual OEI occurrence as illustrated in Fig.
'?, ~,~=bile both output power levels A1 and B1 are maintained at non-zero power settings, i.e., neither one of the engines 12, 14 is operating at an idle condition. It is understood that the mode selection switch 50 may not necessarily be a mechanical or electric "switch", per se, but rather may be suitable control logic. Preferably, an interface is provided allowing the pilot (or others) to man~.zally initiate the OEI training mode, or return to the engine operation mode, as the case may be.
[0029] During the course of a normal flight in which engines 1'? and 14 are operated at a selected operational power setting, the mode selection switch 50 can be actuated (e. g.
by the pilot) to commence an OEI simulation. The simulation commences by a reduction o:~ the power levels A1 and B1 of the respective engines 12 and 14 to a non-zero power setting. It is preferable to reduce the power level A~! of the engine 12 to a first non-zero power setting to simulate an operative engine in an actual OEI situation, and instantly reduce the power level B1 of engine 14 to a second non-zero power setting to simulate a inoperative engine in the actual OEI situation. The first non-zero power setting of engine 12 is preferably higher than the second non-zero power setting of engine 14, as shown. in Fig. 3. Therefore, the deceleration rate of engine 14 is more rapid than the deceleration of engine 12. (The first nor.--zero power setting is indicated by D and the second non-zero power setting is indicated by E.) [0030]In accordance with the OEI training program 4$, the EEC: 40 accelerate the engine 12 from the first non-zero power setting D at a selected acceleration rate and accf~lerate the engine 14 from the second non-zero power set~~ing E at different selected acceleration rate such that the sum of the power levels Al and B1 results in the power transient included in the combined total power level. C1, which reflects a simulated major temporary power loss during a lag between a failure of one engine and an emergency acceleration of the other engine, as occurs in an actual OEI situation. In order to more realistically simulate the power transient of the total power output level C of Fig. 2 in which an inoperative erzgine instantaneously accelerates to an OEI power setting, the OEI training program 48 is designed to enable the EECs 40 to adjust the selected acceleration rate of the respective engines 12, 14 as illustrated in the rising section of the power level A1, which includes two sections representing different power acceleration rates. More specifically, OEI
training program 48 can be designed to enable the EECs 40 to operate engine 14 in a manner such that, from the second non-zero power setting E, engine 14 further decelerates at a deceleration rate much slower than the original deceleration rate, to a further non-zero power setting indicated by F, and then from there accelerates at a selected acceleration rate, as illustrated by the power levers B1. in Fig. 3. The deceleration and acceleration rates can be selected and adjusted in various ways such that the transient of the combined power output level C1 realistically simulates the transient of the total power output level C of Fig. 2. The illustrated power output levels A1 and B1 of the respective engines 12, 14 are one example of the QEI training procedures of the respective engine operations.
[OU31] In Fig . 3 , the respective power output levels A1, B1, restore the original power level (50 percent of the total pow~=_r) and thus maintain the total power at the 100 percent levf~l after the transient. Thus, neither ane of the engines 12, 14 is operated in excess of their normal operating settings during the OEI training course. OEI
tra:ir_ing program 48 can also be designed to enable the EEC 40 t.o control the respective engines 12, 14 to operate at a power output level lower than their continuous maximum power level, that is, less than 50 percent of the total powE~r output level of the twin-engine power plant system 10, in order to simulate an OEI situation in which the total power output of the twin-engine power plant system 10 during an actual OEI event is less than a normal 100 percent power level for the helicopter flight, as described in t:he prior art patent, United States 4,831,567.
[0032JIn one embodiment of the present invention, OEI
training program 48 is designed to enable the EECs 40 to sub:~tantially simultaneously decelerate the engine 14 at a minimum fuel flow rate for one second and reduce the torque output of engine 12 at a 5 percent per. second rate for the f.~rst second when the OEI training mode is commenced.
After the first second, the EEC 40b limits the deceleration of engine 14 to a predetermined rate, depending on whether or not the engine 12 is on a limiting loop, which can be displayed by the cockpit indicator 46, either as engine operation parameters NG and MGT or engine operation parameter torque. At the same time, engine 12 is controlled by the EEC 40a to accelerate freely. It should be noted that the accelerating of the respective engines 12, 14 are conducted in accordance with the equally reduced acceleration limiting maps of the both engines such that the total power increase of the two engines matches the power increase of one single engine. An acceleration map is ~~ schedule which determines when and how the engine will be accelerated under certain predetermined conditions.
Acceleration limiting maps are used for surge protection in normal operation, but also determine how quickly power is allowed to increase. In this embodiment the deceleration and acceleration rates and the resultant power drops of the entire twin-engine power plant system 10, are tailored on a modf~l to match engine failure in an OEI situation.
j0033)Furthermore, means 52 for biasing the display of the cockpit indicators 44, 46 are provided with the EEC 40.
Thu:~, when the OEI training mode is selected, the displays o.f the respective cockpit indicators 44, 4& are biased to simulate the displays of the cockpit indicators of a hel-.copter in an actual 0EI situation. In particular, the cockpit indicator 46 which relates to engine 14 simulating a failed engine, is biased such that the display thereof is blanked out. The display of cockpit indicator 44 which relates to engine 12 simulating an operative engine in an actual OEI situation, is biased to indicate one or morn= of the various engine parameters including torque, NG, MGT and NPT, according to the total power values of the entire twin--engine power plant system 10, rather than the aci~ual power level of engine 12. In particular, the biasing means 5~? :i.s adapted to add the amount of torque output of engine 14 to t:he amount of torque output of engine 12 such that the cockpit indicator 44 displays a total amount of torque output of the two engines. The biasing means 52 is also adapted to add an amount of the respective engine parameters NG and MGT equivalent to a power level provided by engine 14, to the amount of the corresponding engine parameters NG and MGT of engine 12 such that the cockpit indicator 44 is biased to display a total power level of the two engines.
[0034]As described above, aviation regulatory authorities and/or the engine manufactures, have established general cve:r design criteria for the power plant system of a twin-eng.ine helicopter such as the 30-second/2-minute maximum OEI power rating and the 2.5-minute maximum OEI power rating. Each set so-called OEI-limits on values of NG,. MGT
and torque, etc., up to which the engine can operate for a spe~:ified period of time before the engine deteriorates in performance below an acceptable level. Switching frorri one set of OEI limits to the other is completed by the pilot by selecting a switch. Engine expiry flags are used to pro~,ride indication that at least one OEI logic counter, used to count the occurrences of these events, has expired.
The EECs 40 are adapted to control the cockpit indicators 44, 46 to display engine expiry flags alerting the pilot when he has used up any time allowance on the engine parameters NG, MGT or torque, in an actual OEI situation.
In the engine operation mode the display of engine expiry fla<~s is recorded in the non-violate memory (NVM) (not shoran? installed in the EECs 40.

[0035]In order to realistically simulate OEI situations, the EECs 40 can display on the cockpit indicator 44 expiry flags to indicate expiry of the time allowance for the specified power limits, based on the combined total power of the two engines operated in the selected OEI training modf=, when such time allowance for the power limit is used up. In other words, in the OEI training mode, the display of engine expiry flags for maximum OEI time allowance is not: based on the true or actual value of engine parameters NG, MGT or torque of engine 12, but on the biased value of the corresponding parameters to better simulate an actual OEI situation. However, simulated engine expiry flags are preferably not recorded as if they were real engine expiry fla<~s incurred in actual OEI operation.
[0036~Modifications and improvements to the above-described embodiments of the present invention may become apparent to those skilled in the art. For example, though a dual-communicating-EEC system is described, any suitable com~~ination of controller or controllers and associated control logic may be used to achieve a system capable of performing the described simulation method. The skilled rea<~er will understand that the above description is somewhat schematic and descriptive in nature, and the function and operation of individual components of an actual system may vary from that described above. For example, features described as distinct above may be inr_orporated, and conversely, features described as integrated may instead be separate. Though described in respect of a twin-engine system, any multi-engine system may be present. The foregoing description is therefore intended to be exemplary rather than limiting. The scope of the present invention is therefore intended to be limited solely by the scope of the appended claims.

Claims (33)

1. A method of simulating a one-engine-inoperative (OEI) condition in a mufti-engine single-output helicopter having at least first and second engines, the method comprising the steps of:
operating the first and second engines at a selected operational power level;
commencing an OEI simulation by reducing the power level of the first and second engines to respective non-zero power levels; and then accelerating the first and second engines from their respective non-zero power levels in a manner to simulate a output power transient occurring in an actual OEI situation.

2. The method as claimed in claim 1 further comprising a step of returning the engines to their respective said selected operational power levels after the transient is simulated.

3. The method as claimed in claim 1 wherein the step of reducing the respective power levels of the engines comprises reducing the power level of the first engine to a first non-zero power value to simulate an operative engine, and reducing the power level of the second engine to a second non-zero power value to simulate an inoperative engine, the first non-zero value being higher than the second non-zero value.

4. The method as claimed in claim 3 comprising adjusting the selected acceleration rate of at least one engine in. a manner adapted to simulate the power transient of the total power output, in which an inoperative engine instantaneously ceases and an operative engine instantaneously accelerates to a OEI power setting.

5. The method as claimed in claim 3 wherein the step of reducing the respective power levels of the engines further comprises substantially simultaneously decelerating the second engine at a minimum fuel flow rate for one second and reducing a torque of the first engine at a 5 percent/sec rate for one second.

6. The method as claimed in claim 5 wherein the step of reducing the respective power levels of the engines further comprises limiting the deceleration of the second engine to a predetermined rate immediately after the one second deceleration thereof, depending on whether ox not the first engine is on a limiting loop.

7. The method as claimed in claim 6 wherein the acceleration of the engines comprises accelerating the first engine immediately after the one second deceleration thereof.

8. The method as claimed in claim 1 wherein the acceleration of the engines comprises equally reducing acceleration limiting maps of the respective engines such that a combined total power increase of the first and second engines is similar to a power increase of a single engine experienced in the actual OEI situation.

9. The method as claimed in claim 1 further comprising a step of biasing at least one cockpit indicator relating to the first engine in a manner adapted to simulate an indication display of the operative engine in the actual OEI situation.

10. The method as claimed in claim 9 further comprising a step of biasing another cockpit indicator relating to the first engine to simulate an indication display of an inoperative engine in the actual OEI situation.

11. The method as claimed in claim 9 wherein the indicator biasing step comprises adding an amount of torque output of the second engine to an amount of torque output of the first engine such that the indicator relating to the first engine displays a combined total amount of torque output of the two engines.

12. The method as claimed in claim 9 wherein the indicator basing step comprises adding an amount of one of the engine parameters NG and MGT equivalent to a power level provided by the second engine, to an amount of a corresponding one of the engine parameters NG and MGT of the first engine such that the indicator relating to the first engine displays a combined total power level of the two engines.

13. The method as claimed in claim 9 wherein the indicator biasing step comprises displaying an expiry flag to indicate an expiry of a time allowance for a maximum OEI power limit, based on a combined total power of the two engines, when such an event occurs.

14. A method of simulating a one-engine-inoperative (OEI) condition in a multi-engine helicopter, the method comprising the steps of:
providing a OEI training program in control system such that the control system is adapted to control the engines in an engine operation mode and in an OEI training mode; and providing a selector for selection of mode to allow the control system to control at least first and second engines at least in accordance with the following steps:
reducing a power level of the each of the first and second engines from respective operational power settings to a non-zero power settings, and then accelerating the first and second engines from their respective non-zero power settings to simulate a power transient which wound occur in an actual OEI situation.

15. The method as claimed in claim 15 comprising:
biasing at least one display of cockpit indicators relating to the respective engines to cause the display appear as if only the first engine is operating when the OEI training mode is selected.

16. The method as claimed in claim 15 further comprising a step of in the OEI training mode, the control system displaying on a cockpit indicator a simulated expiry flag indicating an expiry of a time allowance for a maximum OEI power Limit, wherein the simulated expiry flag is based on a combined total power of the two engines operated in the selected OEI training mode.

17. A method of simulating a one-engine-inoperative (OEI) condition in a twin-engine helicopter, the method comprising the steps of:
substantially simultaneously decelerating first and second engines from respective engine operation power settings;
terminating the deceleration of the first engine at a first non-zero power setting;
terminating the deceleration of the second engine at a second non-zero power setting which is lower than the first non-zero power setting;
accelerating the first engine, immediately after the first engine reaches the first non-zero power setting, until the first engine reaches a predetermined power setting; and accelerating the second engine, immediately after the second engine reaches the second non-zero power setting, until the second engine reaches the predetermined power level, wherein the acceleration of at least one of the engines is adjusted in a manner adapted to simulate a power transient caused by a failure of one engine and an emergency acceleration of the other engine in an actual OEI situation.

18. The method as claimed in claim 17 wherein the respective acceleration of the engines is achieved using acceleration limiting maps such that a combined total power increase of the two engines simulates a power increase of a single engine in a real OEI
event.

19. The method as claimed in claim 17 further comprising terminating the respective acceleration of the engines when the engines reach the predetermined power level, thereby providing a combined total power level of the two engines simulating a power level of one-engine in an actual OEI situation.

20. The method as claimed in claim 17 further comprising a step of manually actuating a switch to select a at least one of a normal mode and a OEI training mode.

21. A method of simulating a one-engine-inoperative (OEI) condition in a twin-engine helicopter including at least first and second engines, comprising steps of:

simulating an OEI condition by operating the first and second engines both in non-zero power settings; and biasing a cockpit indicator relating to at least a parameter of the first engine to show a combined indication of the parameter for both engines to thereby simulate the appearance of said display as if only the first engine is operating.

22. The method as claimed in claim 21 comprising biasing a second cockpit indicator relating to the second engine to simulate an appearance of the second indicatoras if the second engine is not in operation.

23. The method as claimed in claim 21 wherein the biasing step includes adding torque output parameter of the second engine to a torque output parameter of the first engine such that the indicator displays a combined torque output of the two engines.

24. The method a.s claimed in claim 21 wherein the biasing step includes adding an amount of one of the engine parameters NG and MGT equivalent to a power level provided by the second engine, to an amount of a corresponding one of the engine parameters NG and MGT
of the first engine such that the indicator relating to the first engine displays a combined total power level of the two engines.

25. The method as claimed in claim 21 comprising a step of actuating a switch for selecting a pilot training made of engine operation in which acontrol system controls the respective engines in accordance with a OEI training program installed in the control system, to be operated at the non-zero settings, and controls the biasing of the display of the cockpit indicator.

26. The method as claimed in claim 25 wherein the control system controls displaying in the cockpit indicator an expiry flag to indicate an expiry of a time allowance for a maximum OEI power limit, based on a combined total power of the two engines, when such an event occurs.

27. The method as claimed in claim 26 wherein the control system disables a recording system installed therein such that the expiry of the time allowance is not recorded.

28. The method as claimed in claim 25 wherein the control system controls the respective engines to be operated in a procedure including:
operating first and second engines each at a selected operational power setting;
commencing a OEI simulation by reducing the respective power settings of the first and second engines to respective non-zero power settings;
and accelerating the first and second engines from their respective non-zero power settings to simulate a power transient which reflects failure of one engine and an emergency acceleration of the other engine, occurring in an actual OEI situation.

29. A method of simulating a one-engine-inoperative (OEI) condition in a mufti-engine helicopter, comprising a step of displaying an engine expiry flag in a cockpit indicator to simulate an expiry of time allowance for a maximum OEI power when the twin-engine helicopter is operated in an OEI training mode.

30. The method as claimed in claim 29 comprising a step of actuating a control system to shift the engines from an engine operation mode to the OEI training mode.

31. The method as claimed in claim 30 wherein the control system controls the engines operated at non-zero settings, respectively, to simulate an actual OEI
situation, and biases a display of a cockpit indicator as if one engine is not operating.

32. The method as claimed in claim 31 wherein the display of the expiry flag is based on a combined total power level of the engines.

33. The method as claimed in claim 32 wherein the simulated expiry of the time allowance is not recorded.