1. A method for real-time monitoring of aircraft performance and efficiency, comprising the following steps performed by one or more processors during an aircraft flight of interest: (a) deriving an efficiency baseline for the aircraft's intended trajectory based on at least baseline trajectory profile data, said efficiency baseline comprising respective baseline values for a plurality of efficiency parameters; (b) establishing updated trajectory profile data for said aircraft flight of interest; (c) deriving updated values for said efficiency parameters from said updated trajectory profile data; (d) for each efficiency parameter being monitored, determining the value difference between a baseline value and an updated value; and (e) determining whether any of said value differences exceed respective thresholds.