Let us suppose it is a Green Flight, by which is meant conservation trumps speed, as described in a puzzle in this collection by that name. The flight is maximizing fuel economy and minimizing its 'carbon footprint' by flying slower than its normal cruise speed of 500 knots (575 MPH). 

Aptly named, the airbus has been throttled back to its 'minimum drag speed' of 228 knots (262 MPH), which is still faster than the fastest bullet trains in service.