Interesting thread with some positive feedback to it.pilot737.
To answer the original question I believe that the procedure is floored, in that potential would still exist for the melted frost to refreeze prior to take-off. While the uplifted fuel may raise the temperature of the upper wing skin to above the FP, other areas, e.g. where the L/G and engine(s) are attached to the wing, contain large amounts of metal which may have remained below 0 deg. C since the previous flight, or have dropped below that level due to the sub-zero conditions reported. Also if the frost was originally present on the L/E or T/E surfaces, it is unlikely to have been removed by the uplifted fuel. As suggested in the majority of posts, the only safe option would be to have the upper surface of the wings de-iced prior to take-off.
With regard to the Boeing ‘upper wing frost’ alleviation on their 737 NG aircraft, it is my understanding that this only comes into play under very closely defined conditions. For example, when ‘normal’ de-icing conditions exist at an Airport, i.e. when surfaces of all/the majority of departing aircraft have been contaminated by frost, ice slush and snow and require de-icing, standard procedures will apply and the upper wing surfaces of all aircraft, including the 737 NG, will receive a full de-ice.
However, due to the design of the 737 NG it is not uncommon for frost to be found on specific areas on the upper wing surface, even though the OAT may be above 0 deg. C and the majority of other aircraft types do not require de-icing. Don’t have any details but assume it’s associated with the design of the wing. I believe the alleviation allows for take-off with frost in these relatively small areas, provided it is within the painted lines. Must say that I have also seen similar small areas of frost on the wings of A320 series aircraft under the same conditions but presumably Airbus have not been pressurised by customer airlines into introducing a similar alleviation for these aircraft.
A significant number of the above posts quite rightly question the advisability of allowing take-off with frost patches, albeit small ones, on the upper surfaces of the wings. However, one aspect that hasn’t been discussed is the aerodynamic effect of the de-/anti-icing fluid residues that remain on the wings following treatment.
Following work they carried out during the late 80’s Boeing stated, “Flight tests show that both Type I and Type II (Type III and Type IV fluid did not exist at that time) de-icing/anti-icing fluids do flow off the wings of a treated aircraft in significant amounts during initial take-off ground run. However, the residual fluid is sufficient to cause a temporary decrease in lift and increase in drag during rotation and initial climbout....” They subsequently confirmed that sufficient performance margins were available on their aircraft to offset the effects of the fluids but there was still a detrimental effect on performance.
It’s possible that the aerodynamic effect of the small frost patches on 737 NG aircraft was found to be less than that of the de-/anti-icing fluid flowing off a fully de-iced wing, so there would appear to be some justification for introducing the alleviation.