I agree with 9818,
HQ has alot of excess NAC scanias, that's why they gave 90 an NAC
fleet on most of the days and borrow other buses like 8, 157 to 90
on Sundays/ Saturdays or RSAF open houses.
If you don't believe, go to TPY Int and take note of the rego and
the type during both peak and off peak.