Sir, – After viewing on my computer the coverage of the departure of Pope Francis from Dublin Airport, I switched to Flightradar24, the aircraft tracking site, and saw the Aer Lingus A321 flight, St Aidan, or "Shepherd One", take off. A short time later I saw another Aer Lingus A321, labelled "EIN2AKL, DUB to Destination N/A", take off and follow the pope's aircraft.
It continued to follow the papal aircraft’s flight path all the way to Italian airspace, turned 180 degrees and flew back to Dublin without landing anywhere else on the way.
One reason for this second flight springs to mind: it was a back-up plane (Shepherd Two?) lest a technical problem cause the pope’s plane to divert.
Perhaps your readers can suggest other possibilities. – Yours, etc,
ABBAN J MURPHY,
Hounslow,
Middlesex, United Kingdom.