1. A flight itinerary alerting system for monitoring a flight itinerary associated with an aircraft flight, the system comprising: a central monitoring system comprising a computer server adapted to receive and store flight itinerary data which includes: i) an expected arrival time of the aircraft flight, ii) pilot contact data associated with a primary contact person corresponding to a pilot of the aircraft flight, iii) first tier contact data associated with at least one first tier contact person, and iv) second tier contact data associated with at least one second tier contact person; at least one user computer device associated each of the contact persons respectively; a communication interface enabling the central monitoring system to communicate with said plurality of user computer devices over a communications network so as to be adapted to: i) communicate a deactivation message from any one of the user computer devices to the central monitoring system, and ii) communicate alert messages from the central monitoring system to designated ones of the plurality of user computer devices as determined by the central monitoring system; an alert processing routine executable on said central monitoring system so as to be adapted to: i) determine a first tier alert condition if no deactivation message has been received by the central monitoring system from the primary contact person upon expiry of a first duration following the expected arrival time and send an alert message to said at least one user computer device of said at least one first tier contact person using the first tier contact data upon determination of the first tier alert condition; and ii) determine a second tier alert condition if no deactivation message has been received by the central monitoring system from the primary contact person or said at least one first tier contact person upon expiry of a second duration following the expected arrival time and send an alert message to said at least one user computer device of said at least one first tier contact person and said at least one second tier contact person using the first and second tier contact data upon determination of the second tier alert condition.