In the case of active frost, which continually grows, mechanical means will not adequately remove the contamination. Rather, a de/anti-icing fluid application is required to prevent active frost from adhering to your aircraft.

If a Type I fluid is properly heated and professionally applied, you might have 45 minutes after the start of the fluid application to liftoff before the fluid fails. If the fluid is not as hot, you will have less time.

Verify that the frost has not reformed immediately prior to departure.