No, it doesn't work like that. Operating the OEI Training switch will select the engine you want to keep 'alive'. In fact neither engine spools back, instead the PFD will show that the selected engine is working normally whilst the other indicates zero TQ. Meanwhile, the MFD will show the pilot what is really happening. Both engines are working normally but have an artificial TQ limit of 70% each. Thus a total of 140% TQ is available for the 'fly-away' - this is 20% below the normally available 160% in a real OEI situation. This is why it is critical for the IP to check that the mass of his aircraft is in line with the appropriate training section of Supplement in the RFM. One that didn't do that made a horrid mess of the exercise because he was apparently, allegedly, about 900 kg overweight.
Of course, there are protection systems that take the OEI training switch out of the circuit when needed, so, if the TQ LIM switch is deselected (it is required to allow access to the OEI Training System), or if an engine fails, if either EMS is moved or the NR droops below 87% then the normal performance level is returned - INSTANTLY. That is important to note for the resumption of the normal configuration will result in such a rush of power that an overswing of T5 may occur. It has in the past which is why some companies now limit OEI training to the sim.
Incidentally, the OEI Training Switch is a three position, spring loaded switch. It will remain in the central (OFF) position until No1 or No2 engine is selected. If the TQ LIM switch has been selected and both EMS are in the 'FLIGHT' position then the OEI switch will be retained in the selected position by a magnetic clutch. It is the circuit holding the switch in the ON position that is controlled by the various safety circuits. If one of these operates the mag clutch is released and the OEI switch is then de-selected and it returns to the central (OFF) position.
G
Last edited by Geoffersincornwall; 19th Apr 2018 at 04:48.
Reason: additional info