We evaluate the impact of optical amplifier failure on the achievable information rate (AIR) of a transmission
link. We consider two scenarios to avoid link failure. First, we consider that after amplifier failure the optical
signals are switched to a redundant passive optical line card which surpasses the damage amplifier. Second, we
assume that the optical signals are switched to a redundant amplifier card. From the evolution of the AIR with
the position in the link where the failure occurs we demonstrate which are the critical amplifiers that demand
amplifier cards redundancy to avoid a link failure, and in which place a redundant passive optical line card is
admissible. We consider polarization multiplexing (PM) quadrature amplitude modulation (QAM) constellations.
To evaluate the AIR, we consider the optical amplified spontaneous emission noise and the nonlinear interference
optical noise coherent, as well as the receiver thermal and shot noise sources. Results show that for the
first scenario the maximum value attainable by the AIR is strongly dependent on the position of the amplifier
failure on the transmission link, being the first amplifiers more critical for the performance of the link. Findings
also show that a failure of the last amplifier tends to not affect the AIR. We also observe that it is possible to
partially compensate the AIR decrease after an amplifier failure in the first scenario, by optimizing the gain of
the remain available amplifiers on the transmission link and by optimizing the transmitter power.