If the climb speed schedule changes from 280/0.74 to 290/0.74, what happens to the crossover altitude?

When the climb speed schedule changes from 280 knots to 290 knots at a Mach of 0.74, it effectively alters the aircraft's performance profile during the climb phase. The crossover altitude is the point where the climb changes from a speed-based climb (in knots) to a Mach-based climb.

Increasing the climb speed to 290 knots means that the aircraft will be able to climb more efficiently at a higher indicated airspeed. This increase in speed allows the aircraft to reach its cruising altitude in a more energy-efficient manner. As a result, the point where the aircraft transitions from a speed-based climb to a Mach-based climb occurs at a lower altitude.

This is because as the aircraft climbs, the higher true airspeed (from increasing the indicated airspeed at the same Mach number) allows it to reach a condition where it will need to switch over to Mach-based climbing at a lower altitude, essentially lowering the crossover altitude.

Thus, the correct interpretation of how a change in climb speed affects the crossover altitude is that it will be lower with the revised speed settings.